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The MuSR User Guide

1. T T T T T T HSM A 0 6 0 4 0 2 0 0 0 2 0 4 0 6 VSM A Figure 15 Steering curve examples The above curves were produced by observing the muon precession amplitude in a 20 G transverse field using a 20 mm diameter silver mask on a haematite sample with the beamline slits set to 8 The steering is therefore best at the asymmetry minimum 22 02 05 9 Beamline 6 Computing This is a short guide to the computing facilities available to MuSR users 6 1 General Information e The two cluster computers available for MuSR users are MUSR and ISISA e MUSR is the data acquisition computer located in the instrument cabin It can be used for analysis during an experiment but cannot be logged in to remotely due to ISIS wide computer security measures e ISISA can be logged into from the cabin PC from terminals in the DAC Data Analysis Centre the room by the users coffee area or remotely from your home institution and can be used for data analysis etc It is the only ISIS node that can be logged into from off site e The account MUSR01 is available to all users for data analysis e The PC in the MuSR cabin can be used for normal PC applications Microsoft Office Origin SigmaPlot Fortran and as a terminal on to one of the cluster computers using the eXceed application 6 2 Data acquisition e Logging onto NDXMUSR Using the right hand PC the one with 2 screens log in using the musr account The password is
2. and to print text files print que ansi lsr5 file txt 22 02 05 9 Beamline 7 Data acquisition SECI The sample environment and data collection on MuSR are controlled by a computer program SECI running on the computer NDXMUSR Starting a Run Type begin Ending a Run and saving the data Type end Ending arun without saving Type abort Pausing a run Type pause Then to continue the run Type resume Setting a temperature Type settemp lt value gt Setting a field Type setmag lt value gt Selecting T20 power supply and setting 20Gauss Type TF 20 Selecting Danfysik power supply Type If 0 Selecting auto zerofield 22 02 05 9 Beamline Type f0 Automatic running of MuSR Scripts are created on the mkscript3 panel and should be saved on the u drive To load a Script Type load u nameof script gt gcl To runa script Type Runscript To keep the current run going type keep in the custom column To end a script Type lt rtl gt C Should mkscript3 crash then the easily way to restart mkscript3 is torestart SECI Under Start bottom left press killseci cmd W ait a minute or so Then under Start press startstation cmd If this is not possible or desirable then the mkscript3 exe program can be found in directory c labview modules mkscript3 However SECI will not have control of the window Setting the label Type setlabel qualifier s for sample c for comment u for user ro for rb
3. 5 Beam size event rate and steering A set of collimation slits in the MuSR beamline just after the kicker can be used to control the size of the muon spot and the rate at which muons hit the sample The muon beam can also be steered by small amounts in the horizontal and vertical directions to allow it to be centred on a sample 5 1 The muon beam spot size The muon beam spot is elliptical Its size in the horizontal direction can be changed using a set of slits in the beampipe which are controlled from a panel located behind the EMU area under the mezzanine floor CARE SHOULD BE TAKEN TO CHANGE ONLY THE MuSR SLITS As a guide set the x slit equal to the x dimension of the sample then check the data collection rate The beam spot size in the vertical direction cannot be altered and is of the order of 8 mm FWHM The beam spot size in the MuSR CCR has been measured for various settings of the beam slits using a haematite sample with a 20 mm diameter silver mask on top Muons falling on the haematite are rapidly depolarised whereas those falling on the silver maintain their polarisation The amplitude of the muon precession signal in an applied transverse field 20 G is a measure of the fraction of muons falling on the silver and therefore of the muon spot size Full asymmetry of 25 9 was measured using a plain silver plate with no haematite The results are shown in the plot below It should be noted that these measurements were p
4. 11 4 Local information List of figures Figure 1 Layout of the ISIS muon beamlines Figure 2 Field and detector arrangements in the two MuSR geometries Figure 3 MuSR detector numbering Figure 4 The top of the Oxford Instruments cryostat Figure 5 The front panel of the ITC5 temperature controller Figure 6 The Orange cryostat Figure 7 The flow cryostat centre stick Figure 8 Furnace connections Figure 9 MuSR sample mounts Figure 10 Range curve in the MuSR EMU furnace Figure 11 Frequency response in transverse fields Figure 12 Effect of high longitudinal fields on asymmetry Figure 13 Measurement of the muon beam spot size Figure 14 Event rate as a function of slit setting 22 02 2005 1 Introduction Figure 15 Steering curve examples Figure 16 Beamline power supply layout Figure 17 Spin rotation by the separator seen in a single detector Figure 18 Grouped data with and without dead time correction Figure 19 Reference diagram for resetting the kicker DEVA a dipole ee ae kicker separator steering magnet SAEs Ci Y quadrupole MuSR gt mona tPA i f Te focusing magnet 4 om EMU F muon Loo e production target These components are unshielded g 4 to neutron and are visible from the platform production above the beamlines aaa l gt HE E proton a Figure 1 Layout of the ISIS muon beamlines 22 02 2005 1 Introduction 1 Introduction This User Guide is intended to be
5. ASCII button below the windows showing files is checked e Highlight the files you wish to transfer and click the appropriate arrow between the two file windows to copy the files e Further information can be found in the on line help within the program 22 02 05 9 Beamline 6 5 The MuSR PC The PC in the MuSR cabin is available for use as a terminal or to use one of the software packages installed the PC has Microsoft Office and Origin as well as normal applications If it becomes necessary to reboot the PC the login name and password are on the board in the cabin To start applications either click on the appropriate icon on the bar on the right hand side of the screen or use the START menu from the bottom bar Please ask your local contact for further information if you are unfamiliar with the Windows XP system 6 6 Printers The following printers are available for users Black and white laser printers LSRO R3 Computer Support Office LSR1 R3 2nd floor LSR2 R55 DAC LSR3 MARI cabin LSR4 CRISP cabin LSR5 MuSR cabin LSR7 PRISMA cabin LSR8 SXD cabin LSR10 outside EMU cabin LSR11 HET cabin Colour printers R3_COLOO R3 Computer Support Office R3_COL01 R3 2nd Floor POSTS INKO Deskjet 1200 in MARI POST INK2 Deskjet 1200 in DAC POSTS INK4 Deskjet 1200 in CRISP To print PostScript files on the MuSR cabin printer print que post lsr5 file ps 22 02 05 9 Beamline
6. If the heater does not work then check the Eurotherm trip 22 02 05 3 Sample Environment 3 7 Furnace The muon furnace is designed to allow uSR experiments to be carried out on the EMU and MuSR spectrometers with MuSR in either longitudinal or transverse orientation at temperatures from room temperature up to 1000 K It consists of an outer vacuum jacket with a thin 30 um titanium window to allow muon entry into which a centre stick is inserted which holds the sample and heating element The sample temperature is monitored by a thermocouple sensor mounted on the sample plate and controlled by a Eurotherm temperature controller this in turn is monitored and controlled from MCS The outer body of the furnace is cooled by water flowing through external pipes and around the muon entry window Two heat shields also 30 um Ti between the entry window and the sample position also reduce heating effects on the furnace window Zero field should be reset after the furnace support is mounted 3 7 1 Sample mounting The furnace centre stick allows samples up to 40 mm x 40 mm to be mounted and the Ti mounting plate is drilled to allow sample holders of the size and shape used on the EMU blue cryostat to be fixed M3 screw holes arranged in a square with 30 mm between their centres Titanium sample holders are available for use with powdered samples These consist of a Ti plate with a depression into which a powder can be packed and over which
7. The door can now by opened by removing the locking bolt If itis necessary to open the gate on the MuSR platform remove a second key from the key box and insert it into the gate lock turning it clockwise 22 02 2005 1 Introduction 22 02 2005 2 The MuSR Spectrometer 2 The MuSR spectrometer Positrons from the decay of muons implanted into the sample under investigation are detected using scintillation detectors MuSR contains 64 such detectors each consisting of a piece of plastic scintillator joined by an acrylic light guide to a photomultiplier tube The detectors are arranged in two arrays around the sample position on a cylinder concentric with the coils of the main Helmholtz magnet The detector arrays and Helmholtz coils can be rotated on their support platform about a vertical axis When the spectrometer is in longitudinal geometry the Helmholtz coils provide a field of up to 2500 G which is parallel to the initial muon polarisation direction Rotating the spectrometer through 90 in a clockwise direction looking from above puts in into transverse geometry in which the Helmholtz coils provide a field which is perpendicular to the initial muon polarisation direction In this case fields of up to about 600 G are useable limited by the frequency response caused by the finite width of the muon pulse see section 4 3 1 magnets and detectors oo a 7 NSS 7 magnet and detectors u amp sample
8. a practical manual to help users of MuSR set up and run an experiment on the instrument It contains details of all the main procedures but if there are things you are unsure about always check with your local contact or the instrument scientist 1 1 Setting up an experiment There are certain standard procedures common to most of the experiments run on MuSR Before beginning to take data the following must be considered e correct instrument geometry see section 2 e operation of sample environment see section 3 e correct magnetic field for a compensation of the Earth s field b calibrations c measurements see section 4 e appropriate beam size event rate and steering see section 5 e use of computing facilities for data acquisition and analysis see sections 6 8 Section 9 gives details of other elements of the muon beamline and spectrometer which the user should be aware of and section 10 is a brief guide to what to do when things don t seem to be working Further sources of information and details of how to contact people within the facility are given in section 11 1 2 The MuSR area interlocks 22 02 2005 1 Introduction 1 2 1 Closing the area The blocker which prevents muons entering the MuSR area can only be raised once the area interlocks are complete For this to happen Close the gate which allows access above the spectrometer on the top of the MuSR platform remove its key and insert into th
9. a thin Ti window can be fixed using a clamping ring Ti screws and thin Ta wire are available for attaching a sample holder to the mounting plate Ti produces a negligible depolarisation of the muon signal at furnace temperatures and so is suitable for use as a mask material Thick windows in front of a sample should be avoided as the four Ti foils including the one on the sample mount reduce the muon penetration to less than 70 mg cm a range curve a taken in the furnace is given in figure 8 section 3 8 It should be noted that Al and Ag sample holders are NOT suitable for use in the furnace owing to the low melting point of Al similarly users should consider whether their sample has a melting or decomposition temperature within the reach of the furnace and take suitable precautions 22 02 05 3 Sample Environment 3 7 2 Mounting the furnace on the instrument MuS ft ereh i ehon MuSR in longitudinal using a the PMT frame on top of this is bolted a trolley which allows the furnace to be slid in and out of the spectrometer Th furnacefarngemustbebettedtethemside of the trolley flange for the sample to be in the correct position when the tfolley is pushed in MuSR in transverse The furnace is again mo F ed on its trolley to be slidjinto the spectrometer but now the trolley is supported but now the trolley is supported by larger frame which bolts to the rotatin e 7 1 a te stnsa pe s flowmeter lg irail tad ihe cent
10. act as a velocity selector The settings of the two fields are correlated so that muons of a particular velocity are transmitted with the E field at 100 kV the B field supply must be run at 43 A and with E at 90 kV the B field requires 39 A etc The power supply for the B field is located with the other beamline power supplies see section 9 1 the E field is controlled from a unit located below the mezzanine floor behind the EMU area The required voltage for the separator E field can only be achieved by conditioning that is slowly increasing the voltage until the field breaks down and leaving it at this setting for a period before increasing it further This process is done at the start of each cycle but is often required during the middle of a cycle if the separator voltage becomes unstable 22 02 05 9 Beamline 9 2 1 Spin rotation by the separator When the muon beam is deflected by a magnetic field the spin and momentum vectors remain collinear However the same is not true if the beam is passed through an electric field when the muon spin is rotated with respect to its momentum vector The effect of the electric field in the separator is to rotate the muon polarisation upwards slightly by about 6 so that there is a component transverse to the momentum direction This rotation is best observed by examining individual detectors for data taken in small longitudinal fields up to 400 G Under these circumstances there is a pre
11. aration dilution fridge sample plates Figure 9 MuSR sample mounts 22 02 05 3 Sample Environment 3 10 Range curve The muons in the beam hit the front surface of the sample at about 0 25c 3 0 MeV and are then slowed by interactions within the material before stopping The implantation energy of the muons results in them passing through several hundred microns of material before they come to rest The actual amount of material traversed and the width of the muon distribution depend upon the material s density as a rough guide the muon range is roughly 100 mg cm of material i e about 1 mm of water 500 um of silicon etc Figure 8 below shows the diamagnetic asymmetry in a 20 G transverse field as thin titanium foils thickness about 25um are added in front of a thick quartz plate mounted in the MuSR EMU furnace Initially a low asymmetry is recorded as all muons are stopped in the quartz where there is an appreciable muonium fraction Adding more than four titanium foils causes the asymmetry to rise as an increasing proportion of the muons are stopped in the metal in which all muons thermalise into a diamagnetic state Full asymmetry is obtained when at least ten foils have been added Range Curve Furnace 30 7 Ti foils 11 2mg cm2 in front of Quartz plate Asymmetry Number of foils Figure 10 Range curve in the MuSR EMU furnace It should be noted that in the dilution fridge additional windows in the cryo
12. controls the heater power range Occasionally it is necessary to alter the PID values that OpenGENIE is using This can be done by editing the appropriate muon_temperature tpar file use notpad and then re sending the temperature set point for Eurotherm ITC5 Information in the tpar files is arranged as a table with columns labelled as in the table above 22 02 05 3 Sample Environment 3 9 Sample mounts MuSR SAMPLE HOLDERS CCR 100 mm Blue Variox cryostat 46 mm TOP z 56 mm n ba cl a hole hole for g diameter Seron re 2 mm M2 N attachment clearance holes are 3 5 mm diameter AETS drawn ooking along the beam direction This shows the dimensions of the Variox sample stick blades Sample holders should not exceed 45 mm across Dilution refrigerator 4 40 mm Orange cryostat 32 5 mm 40 mm hole diameter 3 5 mm g hole diameter Avoid holders made of Al or other n 3 1 mm M3 materials which undergo a clearance superconducting transition at low temperatures Please remember to bring some thin 10 um thickness silver foil to use as a heat shield for This is the orange cryostat mounting plate the fridge samples sample plate to go on top mustn t exceed 49 mm width and can have four holes drilled to match Users should arrive at least one day any of the three sets shown above the mount before the start of their beamtime to will take EMU blue cryostat sample plates and allow time for fridge prep
13. following sample environment equipment is available on MuSR Equipment Temperature Range Dilution refrigerator TBT 40 mK 4 2K Dilution refrigerator Ol 40mK 300K Sorption cryostat 350 mK 50 K Oxford Instruments Variox cryostat 1 6 K 300K Orange cryostat 1 6 K 300K Flow Cryostat 4K 400K Cryofurance Cryostat 6K 600K Closed cycle refrigerator 12 K 400K Furnace 300 K 1000 K Generally the choice of sample environment will have been made several weeks before the start of the experiment and the equipment will have been prepared by the ISIS sample environment SE group Although the SE group will help in the preparation of cryostats they cannot be expected to provide support 24 hours a day and users should therefore be able to change samples and temperatures unaided The spot from the laser mounted on the MuSR area wall is close to the correct beam position and should be used as a guide for positioning samples in the CCR Cryostats should be inserted into the beamline with the laser spot as close to the cross on the back of the cryostat tail as possible and the spot should fall on the centre of the 12 pin Jaeger connector on the furnace stick when it is in the correct position 3 1 Dilution refrigerator Users of the dilution refrigerator DR are expected to arrive at ISIS at least 24 hours before the start of an experiment to work with the local contact mounting a 22 02 05 3 Sample Environment sample and starting
14. for many UK airports including Heathrow and Gatwick General Information Oxford Tourist Information Centre Oxford Guide on the Web Eating and Drinking Didcot Tandoori 222 Broadway Didcot Chhokar Tandoori 226a Broadway Didcot Cherry Tree Inn Steventon Fleur de Lis East Hagbourne The George and Dragon Sutton Courtenay The Great Western Junction Hotel Didcot The Hare Inn West Hendred The Harrow West Ilsley The Plough Sutton Courtenay Red Lion Drayton Rose and Crown Chilton The Swan Inn Sutton Courtenay The Wheatsheaf Inn East Hendred 22 02 05 0345 48 49 50 or http www railtrack co uk travel 01865 785400 http www oxfordbus co uk index html 01865 727000 http www heathrow co uk baainfo baainfht html 01865 726871 http www comlab ox ac uk archive ox 01235 812206 01235 813573 01235 831222 01235 813247 01235 848252 01235 511091 01235 833249 01635 281260 01235 848801 01235 531381 01235 834249 01235 847446 01235 833229
15. from the cryostat and dewar Warm both ends with the hot air gun Blow clean helium gas through it use a piece of rubber tube over the cryostat end 3 5 6 Removing 22 02 05 3 Sample Environment e Warm the cryostat to 25K or above e Ensure the needle valve on the transfer tube is open set the ITC5 to Local then press Gas Flow and Raise then shut the valve on the pumping box The pressure should rise rapidly to 1 atm If it doesn t check with your local contact e The transfer line can then be removed Be careful not to bend either of the legs If the cryostat will be used again during the experiment the transfer line may be left in the dewar with the needle valve closed Be sure to fit the protective tube over the free end of the transfer line e Unplug all the electrical leads from the cryostat Close the sample space tap and disconnect the sample space pumping line e Close the OVC value and switch off and disconnect the turbo pump e The cryostat and lift it out e Remove the frame 22 02 05 3 Sample Environment 3 6 Closed cycle refrigerator CCR The CCR is controlled using the Eurotherm TC820 controller in the rack in the MuSR area Check that both data switches in the MuSR area and in the back of the MuSR cabin are at the CCR position Users will need to know how to change the sample in the CCR In preparation for a sample change the temperature should be set to 300K and the compressor turned off Once
16. given by asymmetry x rate so that small changes in asymmetry can be significant 5 3 Steering the beam The muon beam can be steered by small amounts to centre it on the sample under investigation Particularly when small samples are being used it is important to ensure that the beam is steered correctly to maximise the fraction of muons hitting the sample Also in transverse geometry the applied transverse field shifts the muon beam spot slightly in the vertical direction and it is necessary to compensate for this On MuSR it is possible to steer the beam in the horizontal and vertical directions using dipole magnets in the beamline These are controlled from the two Kingshill power supplies at the bottom left of the rack in the back of the MuSR cabin the current is set on the front of each supply The horizontal steering is more sensitive than the vertical the horizontal steering magnet being located further upstream movement sensitivity is approximately 25 mm A horizontally and 5 mm A vertically Making the current for the vertical magnet more negative moves the beam downwards 22 02 05 5 Beam size event rate steering The two plots below are examples of steering curves produced in the MuSR CCR The best settings for the steering magnets shown here should not be used in general as they depend on the precise sample position However the curves can be used as guides to the steering magnet sensitivity Asymmetry Asymmetry
17. line 3 Vent the helium storage dewar by opening the red valve Open the top valve on the dewar then close both red and green valves 4 Slowly lower the longer end of the transfer line into the helium storage dewar The other end of the transfer line will require support The fitting on top of the storage dewar should be tightened to prevent gas escaping 5 Helium gas should immediately begin exhausting from the transfer line After approximately one minute cold gas will be felt and a short while later a plume will form 6 Once a plume is observed quickly insert the transfer line into the helium fill port on the cryostat normally closed by a brass plug Note that if refilling with helium the transfer line should only be pushed approximately halfway into the cryostat dewar 7 Helium transfer should now take place the process taking a few minutes for a refill 8 During the transfer an over pressure must be maintained in the helium storage dewar using a He gas line or bladder attached to the red port 9 When the helium level gauge measures 100 stop the transfer by releasing the pressure in the storage dewar typically by removing the gas line bladder and opening the red valve Remove the transfer line from the cryostat and replace the brass plug ensuring it has been fully tightened the fitting may require heating Remove the transfer line from the dewar and open the green valve 10 Leave the helium storage dewar with both the top
18. the CCR has reached a reasonably high temperature gt 270 K the following procedure can be carried out to remove the sample e Close the large isolation valve on the top of the pump e Switch off the pump e Open the vent valves to vent the pump and CCR e Swing the CCR out from between the magnet faces e Remove the CCR tails and unscrew the sample plate from the copper block TAKE CARE NOT TO BEND THE RhFe THERMOMETER LEADS After mounting a new sample close and restart the CCR in the following way e Dry the CCR heat shield and outer tail use a heat gun but be careful not to heat the thermal fuse Replace the tails checking that the windows are aligned and facing the muon beam pipe window e Swing the CCR back into place taking care not to knock the calibration coils e Check the vent valves are closed e Start the vacuum pump and switch on the Pirani gauge e Slowly open the large pump isolation valve e When the Pirani gauge reads lt 10 Torr the Penning gauge automatically switches on e Below 5x10 3 Torr the compressor may be switched on by turning the switch on the front the central compressor outside the area from 0 to 1 The compressor must be left on for all sample temperatures including those above room temperature There is a thermal fuse on the heater lead inside the CCR to prevent excessive heating Users can check that the heater is working by heating to slightly above room temperature before starting to cool
19. the precooling process This takes place out of the beam during the previous users beam time Once the DR is prepared it has to be lowered into the beam by a licensed crane driver 3 2 Sorption cryostat Users of the sorption cryostat are expected to arrive at ISIS at 24 hours before the start of an experiment to work with the local contact mounting a sample and starting the precooling process to 4K This takes place out of the beam during the previous users beam time Once the sorption cryostat is prepared it has to be lowered into the beam by a licensed crane driver There is a separate manual describing the operation of the He sorption cryostat 3 3 The Oxford Instruments Variox cryostat The Oxford Instruments Variox cryostat is a replacement for the MuSR Orange cryostat with faster cool down time and lower He consumption rate Its principles of operation are very similar with the exception that the Variox requires continuous pumping to promote He flow through its capillary whereas the orange cryostat used the pressure inside the He bath to achieve this above 4 2K The cryostat will have been prepared off beam by a member of the ISIS sample environment team It must be craned into place on the beam line only by a licensed crane operator Three spacers fit over each of the cryostat resting points on the platform above the beamline to position the cryostat at the correct height 22 02 05 3 Sample Environment alternat
20. u gt sample magnet and detectors Transverse Field Longitudinal Field Figure 2 Field and detector arrangements in the two MuSR geometries 22 02 2005 2 The MuSR Spectrometer In the longitudinal case one detector array is forward of the initial polarisation direction and one is backward Looking upstream i e anti parallel to the muon momentum parallel to the initial polarisation direction the detectors are numbered as below Beam In Figure 3 MuSR detector numbering In order to form a longitudinal forward backward grouping detectors 33 64 are summed to form the forward set and detectors 1 32 summed for the backward set In the transverse case the two detector arrays are perpendicular to the initial polarisation direction A suitable way of grouping the detectors in this case is in four groups of eight top 17 24 49 56 bottom 1 8 33 40 forward 9 16 57 64 and backward 25 32 41 48 These sets can be analysed separately or further arranged into forward backward sets top bottom forward backward MuSR can be rotated between transverse and longitudinal geometry in about 30 minutes However it is important that an instrument scientist be present when the rotation is carried out careless actions during the rotation can damage the photomultiplier tubes or puncture the windows in the beam line or dilution refrigerator 22 02 2005 2 The MuSR Spectrometer 3 Sample environment The
21. valve and the red valve shut and the green valve open 11 Switch the helium level gauge to low readout rate 12 When the He recovery flow has returned to less than 10 l min close the He recovery by pass valve 3 3 6 The Oxford ITC503 Temperature Controller 22 02 05 3 Sample Environment DISPLAY SWEEP HEATER PID CNTRL ADJUST POWER HOLD a LOCK SWEEP REM RAISE LOCAL e e SENSOR PROP INT DERIV SET RUN PROG SENSOR AUTO MAN AUTO AUTO LOC REM LOWER POWER EUR e a eee ee ee ea ne T aes Figure 5 The front panel of the ITC5 temperature controller A diagram of the front panel of the ITC503 is shown below Two types of interaction with the controller are possible inspecting the present settings while running the controller in automatic mode and switching to manual control to adjust parameters Inspecting the controller automatic operation To guard against inadvertently altering settings the user should ensure the controller is in remote mode i e the remote light is on before inspecting any parameter Pressing the LOC REM button toggles the controller between local and remote modes of operation View temperature of sensor Press the SENSOR button until the LED 1 20r3 corresponding to the particular sensor is alight View current set temperature Press the SET button View current heater voltage Press the AUTO button under Heater After checking the paramete
22. version numbers are displayed by typing the complete file ending e g 00123 TLOG 1 Will plot R00123 TLOG 1 The hard copy option produces a postscript file PGPLOT PS and this may then be sent to the MuSR laser printer using the command pRINT QUEUE POSTSLSR5 PGPLOT PS 6 4 3 ISISNEWS the status of ISIS Typing ISISNEws cuRRENT at the DEC prompt gives news on the status of ISIS Information may also be obtained from looking at the messages in Bulletin type BULLETIN at the prompt 6 4 4 Archiving data on to a PC floppy disk Data may be archived on to an IBM PC format floppy disk as follows e Convert all data files to ASCII format using CONVERT_ASCII e Ona PC launch the FTP application by double clicking the left mouse button on the WS_ftp32 icon on the left of the desktop e The program automatically comes up with a window requesting details of the connection to be made The host name should be set to isisa rl ac uk Enter a user name eg MUSRO01 and password and click on OK e When the connection is made and WS_ftp32 has read in the remote directory set the appropriate PC directory using the ChgDir box on the left hand side of the WS ftp32 window set this to a for transfer to a floppy and the mainframe directory on the right hand side for the MUSRO1 account files will be in scratch disk musr01 users userx where you should replace userx with your own area name e For ASCII data ensure that the
23. 338 ARGUS RIKEN wwavcdonviescvorcnmvases 6766 Health Physics Sample checking 6696 Computer SUPPOTt eeeeeeeeeeees 1763 7770858090 from outside the lab University Liaison Office 5592 Cosener s HOUSE eeeeceeeereeees 3007 or 01235 523198 Local taXxi S eeeceeeeeeeeteeeeteeteeeees 5592 during the night ring the MCR Airport transportation 24hrs notice required 5592 Gas bottles He N etc 6166 11 2 Contacting an instrument scientist Stephen Cottrell 5352 or 1665 Email s p cottrell rl ac uk Adrian Hillier 6001 or 1476 Email a d hillier rl ac uk Philip King 96117 or 1716 Email p j c king rl ac uk James Lord 5674 or 1101 Email j S lord rl ac uk Francis Pratt 5135 Email f l pratt rl ac uk 22 02 05 11 Contact Points From outside the laboratory certain extensions may be direct dialled the number being formed in the following manner 01235 44xxxx where xxxx is the required extension No prefix is needed to dial offsite 11 3 Further information on the ISIS muon beamlines For further information on the ISIS muon beamlines see Commissioning of the Rutherford Appleton Laboratory pulsed muon facility GH Eaton et al Nucl Inst Meth A269 483 491 1988 The ISIS pulsed muon facility past present and future A Carne et al Hyperfine Interactions 65 1175 1182 1990 UPPSET a pulsed electrostatic kicker to improve the uSR frequency response in th
24. ETUP UDA UDA reads some variables from the file SETUP UDA In particular the directory address of the data is set up in this way Of particular interest are the FORTRAN format strings used to convert a run number to a full file name BASETIME UDA contains the value which UDA will use for time zero see section 8 8 TRANS UDA default transversal grouping LONG UDA default longitudinal grouping PDF UDA parameter definition file UDAHELP HLP help library source UDA matters 8 7 Theory functions defined in UDA A number of theory functions are predefined in UDA 8 7 1 Longitudinal and zero field Function Name Definition 1 Lorentzian a exp At 2 Gaussian a exp At 3 LX exp Stretched a exp Ar Exponential 4 Keren LF extended Abragam amp XP I t see note 1 below 5 Kubo Toyabe Gaussian a 4 1 At exp At 2 6 Kubo Toyabe Lorentzian a A 1 2 exp Ar 22 02 05 9 Beamline 8 Dynamic Kubo Toyabe see note 2 below Note 1 2N T t Cae fo v M o v x exp vt cos f 2va expt sin t V l l i l i where UDA s sigma is equivalent to A UDA s tau is equivalent to 1 v and W 1Bo Note 2 Function 8 the dynamic Kubo Toyabe uses numerical integration to produce the fitting function and so requires more time than the other functions Only fit up to channel 1000 when using this option 8 7 2 Transverse field Function Name Def
25. Exit UDA and return to VMS prompt 8 4 The Grouping Menu The grouping menu is accessed through the option Group from the Main menu and defines the grouping and correction of raw histogram data There are currently two ways of grouping the histograms a the Simple grouping where histograms are simply added together b the Forward Backward F B grouping where the asymmetry ratio F oB F oB is calculated 22 02 05 9 Beamline Deadtime correction of data is turned on off using the DeadT option To compensate for deadtime UDA uses the same file of deadtime values as the RUMDA analysis program generated at the start of each cycle from a long silver run Please ask your local contact if you are analysing data from a previous cycle and so require UDA to use deadtime values from that cycle rather than the current deadtime file The effects of deadtime correction are shown in figure 16 of section 9 3 The options available for grouping and correcting data are shown below CHANGE Change histogram grouping READ Read grouping table from disk WRITE Write grouping table to disk DEADT Switch deadtime correction on off ALPHA Select F B scaling factor GUESS Estimate alpha for a T20 run BUNCH Setting the bunching to n adds n bins together HELP Display help text Don t panic EXIT Return to UDA Data main menu 8 5 The Analysis Menu The Analysis menu is entered by selecting the option Analyse in the
26. T20 coils nor the main Helmholtz coils are on The zero field calibration is different for longitudinal vs transverse setups change over by using Go To Longitudinal or Go To Transverse buttons 4 2 Calibration field When working in longitudinal geometry it is necessary to start each section of runs after a sample change or change from CCR to cryostat for example with a calibration measurement in a transverse field of approximately 20 gauss These measurements are usually quite short lt 5 Mevents and are often referred to as T20 runs Two small coils which hang either side of the sample are used to provide a small transverse field They are powered by a Gossen power supply and controlled by the computer through OpenGENIE with the command tr 20 4 3 Applied fields Magnetic fields are provided using the large Helmholtz coils powered by the Danfysik PSU This is controlled by MCS via a GPIB interface The maximum field available on MuSR is 2500 G The Danfysik is operated as follows e Type ifo in OpenGENIE this sets the magnet device to the Danfysik PSU Set fields using the command setmag x A read out of the field is given on the computer screen in the MAGNET window If this is not successful then check interlocks on front panel of magnet power supply Whenever the beam blocker is lowered the field generated by the Danfysik is automatically set to zero It is possible to over ride this process by carrying out the f
27. The MuSR User Guide AD Hillier PJC King SP Cottrell and JS Lord ISIS Facility CCLRC Rutherford Appleton Laboratory February 05 1 Introduction Contents CONTENTS 1 INTRODUCTION 1 1 Setting up an experiment 1 2 The MuSR area interlocks 1 2 1 Closing the area 1 2 2 Entering the area 2 THE MUSR SPECTROMETER 3 SAMPLE ENVIRONMENT 3 1 Dilution refrigerator 3 2 Sorption cryostat 3 3 The Oxford Instruments Variox cryostat 3 3 1 Removing a sample 3 3 2 Loading a sample 3 3 3 Operation above 4 2 K 3 3 4 Operation below 4 2 K 3 3 5 Filling with Helium 3 3 6 The Oxford ITC503 Temperature Controller 3 4 Orange cryostat 3 4 1 Removing a sample 3 4 2 Loading a sample 3 4 3 Cooling the cryostat to 4 2 K 3 4 4 Cooling the cryostat below 4 2K 3 4 5 Filling with Helium 3 4 6 Care of the cryostat when not in use 3 4 7 Additional notes 3 5 Flow Cryostat 3 5 1 Sample holder 22 02 2005 3 5 2 Installation 3 5 3 Connections 3 5 4 Inserting the stick 3 5 5 Cooling 3 5 6 Removing 3 6 Closed cycle refrigerator CCR 3 7 Furnace 3 7 1 Sample mounting 3 7 2 Mounting the furnace on the instrument 3 7 3 Connections 3 7 4 Eurotherm set up 3 7 5 Controlling the furnace 3 7 6 Typical data collection parameters 3 8 Temperature control files 3 9 Sample mounts MAGNETIC FIELDS 4 1 Zero field compensation 4 2 Calibration field 4 3 Applied fields 4 3 1 Effects of the finite muon pulse width on useable t
28. UDA Main menu Using the options outlined below it is possible to select a model function 22 02 05 9 Beamline and make a least squares fit of the model parameters The results of the fit can also be plotted and output to an ASCII file SELECT PLOT FIT HELP VALUES THEORY ALPHA UNDO EXIT WRITE READ DIST 22 02 05 Select a group and a bin range to work on Plot the data and the fit allows fit to be written to an ASCII file Run fitting routine using the starting values displayed in right hand window Enter the help system at the Analysis menu level Enter the parameter display to change parameter values status To move in the parameter display use UP or DOWN cursor keys To change a value use the ENTER key Status codes are changed by typing vary parameter fix parameter tie parameters together Return to the menu by the left or right cursor keys Select a theory function number of sub components and lineshape Change value of alpha Undo fit and restore original parameters Exit this menu and return to the main UDA menu Write parameters out to a file Read parameters in from a file Distribute parameters to all groups necessary for transverse geometry 9 Beamline 8 6 Computer files These files must be copied into the area you are working in If the area has been selected by SETUP as described in section 6 3 they will have been copied to the new area automatically S
29. after the kicker The power supplies for all the beamline magnets are located on the raised platform on the far East side of the experimental hall the steps up to this are opposite the steps taking you over the proton beam to the other side of the hall On the left at the top of the steps on the platform and working towards the far wall are the following units Figure 16 Beamline power supply layout Reset buttons for beamline magnet klixons flow and earth leakage trips Q1 supply Separator B field supply Q2 supply Q3 5 supply Q4 supply Q6 supply Q7 supply Q8 supply O ON OAR O N 22 02 05 9 Beamline 10 Q9 supply 11 B1 2 supply 12 DEVA Helmholtz supply 13 DEVA septum supply 14 EMU septum supply 15 Reset buttons for quads coils on individual beamlines 16 Panels showing on off status of klixons etc for quad coil supplies 17 Q10A supply DEVA 18 Q11A supply DEVA 19 Q12A supply DEVA 20 Q10B supply MuSR 21 Q11B supply MuSR 22 switchyard magnet supply 23 Q10C supply EMU 24 Q11C supply EMU 25 Q12C supply EMU 26 switchyard magnet supply The normal working currents for these supplies are shown by them but call your local contact if you think there is a fault 9 2 The separator The separator is located in the muon beamline before the kicker and acts to remove contaminant particles primarily positrons from the muon beam It consists of mutually perpendicular E and B fields which
30. cession of the muon spin in the field and an oscillating signal can usually be seen Shown below is the signal from detector 1 for a silver sample in an applied longitudinal field of 50 G The oscillations shown have an asymmetry of 2 2 asymmetry Figure 17 Spin rotation by the separator seen in a single detector By grouping the detectors however the effect is removed The graph below shows the data from this run arranged into a forward backward grouping This plot also shows the effects of deadtime the grouped data is displayed with crosses and without line deadtime corrections 22 02 05 9 Beamline asymmetry Figure 18 Grouped data with and without dead time correction 9 3 The kicker The kicker is responsible for supplying muons to the DEVA and EMU areas Muons are generated at the production target with the same time structure as the main proton beam i e two 80 ns wide pulses separated by 300 ns 50 times per second The first of these pulses is split in two in the kicker by a central electrode at high voltage This kicks half the pulse to the left and half to the right feeding the two side beamlines In the time between the two muon pulses the voltage on the electrode is reduced to zero and the second pulse travels undeflected to MuSR The kicker power supply is located under the mezzanine floor behind the EMU area and consists of a high voltage supply together with timing electronics to ensure that the kick oc
31. curs at the correct point with respect to the muon pulses The timing signal is taken from a lead glass Cerenkov counter located near the muon production target and fed to a delay unit Instructions on how to reset the kicker are given in section 10 5 but this should only be done by an instrument scientist 9 4 The photomultiplier tubes The photomultiplier tubes on the spectrometer are powered from one of the LeCroy crates in the back of the EMU cabin The crates are labelled MuSR and EMU make sure you switch the correct one on or off if you have to Slots 2 and 3 of the MuSR crate are used to power the MuSR PMTs with 16 outputs from 22 02 05 9 Beamline each slot addressed 0 15 not 1 16 Once the LeCroy crate is powered up it can be controlled from the terminal in the back of the MuSR cabin It should only be necessary to modify the PMT voltages in two circumstances e when rotating the instrument all tubes should be turned OFF don t forget to turn them back on again afterwards e if a scintillator develops a light leak please turn off the volts to its PMT The most commonly used commands for controlling the PMTs from the terminal are shown in the table below Command Action SS ON OFF switch the voltage on all tubes on or off RE 2 3 0 15 displays the voltage on all MuSR PMT tubes RE slot channel displays the voltage on one tube WR slot channel 0 sets the voltage on a single tube to zero WR slot channel
32. d as the RUMDA analysis program In the Analysis menu you can select a model function and make a least squares fitting of the model parameters The fitting result can also be plotted from this menu 8 2 Running UDA To access UDA from account MUSRO1 type setup followed by UDA as described in section 6 3 This will run the most recent version of UDA The display will be redrawn as a dashboard and the cursor will automatically select the option MCSFILE in the Main menu To select any other item from the menu use the cursor arrow keys or simply type the first letter of that item e g P for PLOT 8 3 The Main Data Menu 22 02 05 9 Beamline The Main Data menu allows you to read write and modify experimental data The options available from this menu are listed below Plotting of error bars on data points can be turned off on using the SETUP option MCSFILE USRFILE NEXUS WRITE INSPECT GROUP CHANGE PLOT ANALYSE SETUP HELP QUIT Read a MCS run file in the format used by the data acquisition software Read a uSR file from the disk Read a Nexus File the new and only data format on MusR Write grouped data to a uSR file Inspect run and all histograms Enter the Grouping Menu Change run file parameters Plot one or more groups on the terminal screen Enter the analysis menu Set program configuration parameters Enter the VAX VMS help facility to read the UDA help library
33. d periodically contact an instrument scientist to obtain the current one Once access has been obtained a list of users known to the account is displayed Select the most appropriate or alternatively use USERX and type the name at the prompt The cursor should change to reflect the current user For example USERX would proceed as follows Users known SCRATCH RAL RUNI BIRMINGHAM SUSSEX SHEFFIELD STUTTGART SOTON PARMA UPPSALA OXFORD LEICESTER BS LPOOL CNRS ILL USERX BRAUNSCHWEIG STANDREWS CSIC PARIS LYON 22 02 05 9 Beamline MUSRO1 gt USERX KKEKKKK KKK KK KK KKK KKK KKK KK KK KK KK KKK KKK KKK KKKKE KKK KKKKKKK KKK KKK YOU ARE NOW WORKING ON THE SCRATCH DISK FILES IN THIS AREA WILL BE DELETED AFTER 7 DAYS USE SETUP to access UDA kkkkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkkxkxkxkxkxkxkxkxkxkxkkxkxkxxkxx k USERX gt 3 Now type setup A list of the analysis software currently available will be displayed Any of these may be used by typing the program name For example to run UDA USERX would proceed as follows USERX gt SETUP Commands available TLOGGER a plot temperature logs HISTO look at the raw histograms CONVERT_ASCII turn the binary run data into ASCII format HEADERS make a list of MuSR data file header i
34. d sample mount differs from 70mm adjust the top scale by the same amount For the standard blade set the angle to 0 degrees The muon arrival direction is in line with the locating pin on the top flange and the sample plate should normally be perpendicular to this You can rotate the sample relative to the beam if required by your experiment either now or when in the cryostat 3 5 2 Installation The cryostat fits into a support cage This cage should be mounted above dizital and the cryostat lowered into the support cage use of the crane requires a crane drivers license Install it with the transfer tube connection in the downstream direction The locating pin on the top flange will be towards the beam Use the appropriate ITC5 temperature controller for the cryostat and connect through the patch panel Start pumping the OVC using a turbo pump 3 5 3 Connections e Cryostat sample space port should be connected to a T connector which is connected to He gas gauge and rotarty pump e Cryostat heater thermometer to ITC channel 1 the stick thermometer to ITC channel 2 stick A or 3 stick B and the transfer tube needle valve to ITC Aux Out through the patch panel e Transfer tube gas outlet at the top of the dewar leg to the pumping box via a long plastic tube e Connect using the switch box 22 02 05 3 Sample Environment 3 5 4 Inserting the stick The sample can be changed when the cryostat is cold but heat it up
35. e ISIS pulsed muon beam A Borden et al Nucl Inst Meth A292 21 29 1990 The ISIS pulsed muon facility GH Eaton Z Phys C 56 S232 239 1992 The muon beamline at ISIS GH Eaton et al RAL Report RAL 94 077 The development of the pulsed muon facility at ISIS GH Eaton et al Hyperfine Interactions 87 1099 1104 1994 Fast E field switching of a pulsed surface muon beam the commissioning of the European muon facility at ISIS GH Eaton et al Nucl Inst Meth A342 319 331 1994 The ISIS muon group Web pages also contain additional information on the muon facility as well as the current instrument schedules etc the address is http www isis rl ac uk muons 22 02 05 11 Contact Points The main ISIS web pages contain details of all ISIS facility activities together with information on applying for beamtime electronic versions of proposal forms and A3 report forms latest beam information etc They can be found at http Awww isis rl ac uk 11 4 Local information 22 02 05 11 Contact Points Transport National Rail Enquiries It is usually possible to arrange a taxi to either Didcot Parkway or Oxford stations The Oxford Bus Company Oxford city local buses and coaches to London X90 Heathrow X70 and Gatwick X80 Stagecoach Bus Company formerly Thames Transit Oxford city and rural bus services including routes to from Harwell bus station near main gate BAA Flight Information Arrival information
36. e key box to the right of the lower area door Turn the key clockwise Check that no one is inside the MuSR area Press the search button situated on the far side of the spectrometer and close the area door and remove the key from the lock turning anticlockwise Insert this key into the key box to the right of the door turning it clockwise The key box should now be full Remove the bottom right hand key and insert it into the green box to the right of the key box turning it clockwise Check that the Helmholtz magnet interlock key below the blocker raise lower buttons is in the vertical position see section 4 3 The blocker can now be raised press the red raise button and keep it pressed until the blue area lights come on and the blocker has stopped moving 1 2 2 Entering the area To enter the MuSR area 1 If you require the main Helmholtz coil field to not be set to zero check that the key below the blocker raise lower buttons is in the override horizontal position see section 4 3 Lower the blocker by pressing and holding the green button The area lights come on once the blocker is down Remove the key from the green box by turning it anticlockwise insert it into the bottom right position on the key box and turn it clockwise Remove one of the keys the two left most keys on the top row are often the easiest from the key box and insert it into the door lock Turn it anticlockwise
37. eeii a A TA He fir We ie Flan 4 ves e P ta S LE ual za Copi E Leal re ae Eer f a ee P ae Sar fe Camber J r 5 S Lfe hur tapi NM Peak Hast oe Cange OS Mi Figure 6 The Orange cryostat Operation of the orange cryostat is very similar to that described above for the Oxford Instruments Variox The OC is controlled by the ITC5 temperature controller labelled MuSR orange on the platform above the spectrometer 22 02 05 3 Sample Environment 3 4 1 Removing a sample Instructions are as for the Variox the black three way valve on the top of the Variox has the same operation as the blue 3 way Hoke valve on the top of the orange cryostat 3 4 2 Loading a sample Again the procedure is the same as for the Variox cryostat 3 4 3 Cooling the cryostat to 4 2 K Operation is similar to the Variox in principle however the gas flow through the cryostat is controlled manually using the cold valve valve 4 in the orange cryostat diagram and the warm valve valve 6 The cold valve controls a needle valve which allows liquid helium from the main reservoir into the annular space via a capillary and heat exchanger To close the cold valve it should be turned clockwise Be careful not to over tighten it otherwise the needle may be damaged 1 Open the cold valve rotate it between half and one turn anti clockwise from when it first bites 2 Open the warm valve
38. enting the lowest energy positrons from being counted This has the effect of reducing the count rate requiring the beam slits to be opened more widely than normal and increasing the maximum asymmetry to close to 27 on MuSR Alpha values close to 1 5 are common owing to the shielding of the backward detectors by the sample mounting plate and heating element Check with your local contact for correct steering magnet values 3 8 Temperature control files Whenever a temperature set point is sent by OpenGENIE to a temperature controller various other parameters are also passed to enable the temperature to be controlled These include the appropriate Proportional Integral and Derivative PID values and the maximum heater power OpenGENIE reads these values from files which sit in the directory c labview modules mkscript3 muon_temperature tpar This file is changed when changing configurations aii ee TLOW and THIGH or specify a temperature range for given PID values MINTEMP MAXTEMP PROP proportional value 22 02 05 3 Sample Environment ACCUR the temperature range around the set point within which MCS will consider the temperature to be stable WAIT or TWAIT the length of time mins that the temperature must be within the accuracy band before MCS will start a run TMOUT or TIMEOUT the time after which even if the temperature has not stabilised within the accuracy band MCS will start a run anyway MAXI fridge only
39. erformed in the MuSR CCR with its heat shield and tails in place The window in the CCR tails 80um thick Mylar introduces some scattering of the beam increasing the beam spot size slightly with the CCR tails removed an asymmetry of 3 7 was obtained equivalent to 16 of the muons falling on the mask The spot size is larger still in 22 02 05 5 Beam size event rate steering the orange cryostat dilution fridge and furnace which all have additional windows typically 30 of the muons fall outside a 20 mm diameter area inside the orange cryostat with the slits set to 8 Asymmetry Slit width Figure 13 Measurement of the muon beam spot size The table below gives similar results expressed as fraction of beam falling on to the mask as a function of mask size for two slit settings again in the MuSR CCR The measurement errors are 1 60 7 20 1 12 4 63 7 25 6 15 6 Please note that the above figures are guides only The actual size of the muon spot at a particular time is dependent on factors such as the tuning of the extracted proton beam and can vary slightly from cycle to cycle 22 02 05 5 Beam size event rate steering 5 2 The event rate In addition to controlling the muon spot size the slits can be used to regulate the event rate and thereby control the distortion at the start of histograms due to detector dead time effects Because various parts of the detector have limitations on the speed wit
40. eturn panel or that a non return valve is fitted to the He outlet 7 4 Fill the sample space with He by turning the black 3 way valve 8 downwards Wait until the flow meter on the He return line registers flow again 5 Remove the blanking flange and introduce the sample stick quickly but smoothly 3 6 Pump the sample space via the 3 way valve 8 turned to its upwards position to 1 mbar the gauge on the top of the cryostat 10 reads the sample space pressure using the rotary pump 7 Turn the 3way valve 8 to its downwards position to add He to the sample space and pump again to about 1 mbar 8 Add He to the sample space again and pump until the sample space gauge 10 reads 20 mbar This is the correct exchange gas pressure 3 3 3 Operation above 4 2 K 22 02 05 3 Sample Environment Operation above 4 2 K is fully automatic once the 25 m hr pump has been set to pump He gas through the capillary Set points can be entered using the settemp command in OpenGENIE and the ITC503 controls the heater and needle valve settings 3 3 4 Operation below 4 2 K A different procedure is necessary for operation below 4 2K as the ITC503 temperature controller is unable to set the gas flow through the cryostat automatically for these temperatures To get to base temperature about 1 6K use the following procedure 1 Issue the command biue_it in the OpenGENIE window 2 Manually check that the set point in the ITC503 is zer
41. f opening the warm valve a small amount doesn t increase the flow rate open the cold valve until the rate increases and then close the warm valve to achieve the required rate e When the cryostat is at the required temperature the He flow rate should be reduced to about 4 5 I min But this rate should be monitored for the first hour or so after cooling as it will be affected by any liquid helium which has entered the annular space The flow rate may change as this liquid boils off and may become too low when the annular space no longer contains liquid e At very low temperatures an offset between the sample and cryostat thermometers can be expected owing to condensation of the exchange gas in the sample space 3 5 Flow Cryostat The Flow crystats are controlled using an ITC5 The temperature range is 4 to 400K for the normal flow cryostat and 6K 600K for the cryofurnace flow cryostat 3 5 1 Sample holder This cryostat can use the same sample holders as the EMu Blue cryostat 37mm square with hole spacing 30mm The internal diameter of the cryostat is 43mm Locating pin on top flange Length scale 19mm 70 mm Angular Locking screws Side view End view scale 0 deg Figure 7 The flow cryostat centre stick 22 02 05 3 Sample Environment With the standard blade and sample holder the length from the bottom of the copper block to the sample centre is 70mm and the top adjustment should be set to 19mm If a non standar
42. h which they can respond there is a dead time T4 after each event during which further positron decays are missed The effect of this dead time can be modelled and the reduced rate observed in the experiment Ta is found to be related to the true rate r by the expression 7 Although the effect is particularly evident at high event rates some distortion is always present Users should therefore always consider using the facilities provided by both UDA and RUMDA to correct for this effect when analysing data The effects of deadtime on data are shown in figure 16 of section 9 3 Rate must be kept below 55MeV hr as this will give DAE2 more hits per frame than it can cope with The graph below shows the event rate as a function of slit width for a large silver plate mounted on the MuSR CCR with the 10 mm muon production target in use and with ISIS running at about 170 uA The main curve was taken without the CCR tails in place addition of the tails reduces the event rate slightly point shown as a cross and also slightly increases the maximum asymmetry this effect is greatest in the furnace where the event rate is two thirds of that in the CCR and the asymmetry is typically a couple of percent higher 22 02 05 5 Beam size event rate steering Rate MeV hr 0 5 10 15 20 25 30 35 40 Slit width Figure 14 Event rate as a function of slit setting It should be noted that the figure of merit for an experiment is
43. he EMU User Guide 6 4 Utility programs 6 4 1 CONVERT _ASCIl converting data files to ASCII format The binary files written by MCS can be converted into ASCII files in one of three formats firstly in the same format as read by UDA s USRFILE option secondly as a column of raw counts for each histogram this is ideal for loading into PC spreadsheet applications thirdly as asymmetry data this format can be directly imported into PC analysis programs such as Origin The conversion program is run from account MUSRO1 using the command convert_ascii The program prompts for first and last files to be converted and the format of the output ASCII data Depending on the output ASCII file format required additional information may be requested When using format options two or three it is very important that correct values are entered for both the b and a Check also that the grouping used in option three corresponds to the current detector arrangement 22 02 05 9 Beamline 6 4 2 TLOGGER plotting TLOG files A plot of the temperature log for a data run may be produced using the command TLOGGER The program will request the beamline select option 2 for MuSR a run number and the type of graphics device you are using to view the plot enter xw when using DECwindows The file number need not have preceding zeros The TLOG file with highest version number is plotted for the given run files with lower
44. inition 11 Lorentzian with freq a cos t o exp Ar 12 Gaussian with freq a cos t exp Ar 13 LX exp Stretched a cost exp Ar Exponential with freq 14 Abragam with freq a cos t gt exp AT exp t t 1 1t 7 8 8 Time zero Time zero is usually taken to be the arrival time of the centre of the muon pulse On MuSR which receives the second of the two muon pulses produced by the proton beam this is found to be 0 645 us after the timing start signal produced by the Cerenkov counter near the muon production target This corresponds to slightly after the start of bin 40 in the detector histograms for a bin size of 16 ns UDA uses this value to set its time zero position it is written in the file basetime uda However useful data is not produced until after the complete arrival of the muon pulse so that bins 46 and above can be used for function fitting etc 22 02 05 9 Beamline 9 Other components of the muon beamlines 9 1 Beamline power supplies Located at intervals along the muon beamline between the production target and the spectrometer are dipole and quadrupole magnets which respectively act to steer and focus the muon beam see figure 1 at the foot of the Contents pages Most of the beamline magnets are located before the kicker and therefore any faults will affect all three muon beamlines however there are also two quadrupoles specifically for MuSR located
45. ive sample ere ene PKs N es ammm Me return line 7 _ three way valve 8 He level gauge connection 9 E LM i space pressure gauge 10 N fill port 5 2 VS He fill port 11 cryostat sensor connection 12 cryostat outer 2 ANY vacuum jacket A capillary pumping line 13 pumping 6 Figure 4 The top of the Oxford Instruments cryostat The cryostat is controlled from the Oxford Instruments ITC503 temperature controller labelled MuSR Variox Once in place above the instrument the cable from channel 1 of the patch panel should be connected to the sensor port on the cryostat 12 and that from either channel 2 or channel 3 can be connected to the sample stick check the number on the stick to know which channel is appropriate The needle valve motor drive lead on the cryostat 4 is also connected to the appropriate cable from the patch panel V1 The He return port on the cryostat 7 is connected to one of the return panels on the cage wall and the 25 n hr rotary pump is connected to the port marked capillary pumping 13 The He 9 and N 2 level meters are connected to the Oxford level metre gauge Below is a brief guide to operation of the blue cryostat More detailed information about filling with helium and changing a sample can be found in the following RAL reports e Use of cryogenic liquids on ISIS instruments J Chauhan A V Belushkin and J Tomkinson RAL 92 041 e Cha
46. n before filling and to turn it off afterwards You need to open the depressurising valve on the He return line on the cryostat valve 8 before filling remember to close it again afterwards 3 4 6 Care of the cryostat when not in use The cryostat can be left in its support frame either on the MuSR platform or at ground level when not immediately required In this case users should leave the cold and warm valves open a very slight amount to allow a small flow through the cryostat this reduces the chance of the cryostat blocking but does not use large amounts of helium Users should still remember to check the cryogen levels once every twelve hours and refill as required 3 4 7 Additional notes e At low temperatures the exchange gas in the sample volume may have condensed leading to poor thermal contact to the annular space The exchange gas pressure can be monitored using the meter on the small rotary pump with the pump valve closed and the blue Hoke valve turned upwards If the pressure has dropped add more gas by turning the Hoke valve to its downwards position for an instant and then pumping the sample space to the required pressure e f oscillations in the temperature of the cryostat are observed the exchange gas pressure may be too high Try pumping the exchange gas to 5 10 mbar 22 02 05 3 Sample Environment e When cooling the He flow rate through the return line should be controlled by the warm valve setting I
47. nformation ASYM analyse levelcrossing data UDA standard muon data analysis RESTMUSR restor datafile s from archive PRINT_MAN print the MuSR manual on LSR5S MuSR Cabin SUPERPLO general plotting program SUPERPLOTC for plotting in colour If access to RUMDA is required type RUMDA If access to MESA or TDSA is required type MESA_SETUP USERX gt UDA If access to RUMDA and GENIE is required type rumpa Again a list of the available commands will be displayed which give access to the RUMDA programs TDSA an alternative analysis program and MESA a maximum entropy analysis program for transverse field data are available ESA_S TUP 22 02 05 9 Beamline 6 3 3 Using your own account for data analysis 1 Login to ISISA or MUSR with your own user name and password 2 Type musrSdisk mumgr musr_users musr_setup to gain access to the data analysis software 3 You may want to edit your LOGIN COM file found in your top level directory to add the line preferably at the end of the file setup musrSdisk mumgr musr_users musr_setup 4 Typing SETUP when you next login will work as described above for the MUSRO1 account B If you use both MuSR and EMU instruments you may wish to add two lines to your LOGIN COM file one for MUSR_SETUP and one for EMU_SETUP as the SETUP files for the two instruments are different The EMU_SETUP command can be found in t
48. nging a sample on ISIS instruments J Chauhan A V Belushkin and J Tomkinson RAL 93 006 There is also an ISIS video on cryostat operation this can be viewed in the users coffee area near the Data Analysis Centre 22 02 05 3 Sample Environment 3 3 1 Removing a sample 1 Ensure the cryostat temperature is greater than 25 K too low a temperature and any liquid helium that s been pulled through the capillary could boil rapidly too high a temperature could cause He gas to diffuse through the Mylar window into the outer vacuum space 2 Ensure the cryostat is connected to the He return panel or that a non return valve is fitted to the He outlet 7 3 Close the valve to the pump on the capillary line 13 4 Fill the sample space with He by turning black 3 way valve 8 downwards Wait until the flow meter on the He return line registers flow again 5 Remove the sample stick quickly but smoothly by undoing the Klein flange Cover the sample space with the blanking flange Return the 3 way valve 8 to its horizontal position 6 If the cryostat is to be left for a time without a sample present pump the sample volume via the 3 way valve 8 turned to upwards position using the rotary pump connected to the port above the valve 3 3 2 Loading a sample 1 Ensure the sample stick is completely dry before inserting it into the cryostat 2 Ensure the cryostat is at about 25 K 3 Ensure the cryostat is connected to the He r
49. number t for temperature f for field g for geometry o for orientation You will be prompted for inf ormation 22 02 05 9 Beamline Changing configurations Select Configurations fromthe ISIS SECI window Select Open Configuration Select Correct configuration please do not save configurations SECI should start the correct vi s which are currently not running and close any that are not needed Type getblocks in the Opengenie window Blue Cryostat For operation below 5K Type blue_It For operation above 5K Type blue ht The temperature parameter files For all configurations the tpar files are in C labview modules mkscript3 directory and are called muon_temperature t par Displaying all control blocks Type cshow all 22 02 05 9 Beamline 8 Data analysis UDA 8 1 Introduction UDA is the simplified uSR data analysis program There are three menus in UDA the Main Data menu the UDA data Grouping menu and the UDA data Analysis menu On start up the program will always enter the Main menu At this menu you can read and write data files plot spectra and make changes to the data loaded In the data Grouping menu you can select how to map your raw histograms into the groups hat are used when plotting or analysing Two different grouping schemes can be used the Simple straight TF grouping or the F B LF ZF grouping Deadtime correction of data is available using the same correction metho
50. o by pressing the SET button 3 Connect the 0 1000 cm min flow gauge to the Rootes pump exhaust 4 Manually adjust the gas flow on the ITC503 until the pump exhaust flow rate is about 450 cm min you need to be in LOCAL mode on the ITC503 to do this 5 The temperature should rapidly drop to below 2K 6 Enter set points as normal up to about 5K To return to automatic operation above 4 2K 1 Issue the command biue_ht in OpenGENIE window 2 Disconnect the flow meter from the Rootes pump exhaust 3 Set the desired temperature within MCS The ITC503 should go back to automatic control of the gas flow 3 3 5 Filling with Helium The time for which a helium fill will last is greatly dependant upon the type of experiment being carried out Sustained running at high temperatures or repeatedly cycling between high and low temperatures can require a fill every twelve hours At the other extreme a helium fill can last for well over twenty four hours if running at a near constant low temperature As a general guide the helium level should be checked at least once every twelve hours don t forget to fill with nitrogen too 22 02 05 3 Sample Environment The following procedure should be followed to fill the cryostat Users should note that two people are required Use the flexible transfer tube on the side of the MuSR platform 1 Set the He level gauge for high readout rate 2 Open the by pass valve on the He return
51. ollowing procedure 22 02 05 4 Magnetic Fields e Turn the key on the panel by the entrance to the experimental area to over ride before lowering the blocker e Open and close up the area as usual but return the over ride key to its original position before raising the blocker e Check there are no red lights illuminated on the Danfysik power supply If the power supply trips at any time it can usually be restored by reseting the interlocks on the front panel If this is not successful check the trip switches see section 9 1 After selecting a new magnet device always check that the field set via OpenGENlE has been accepted by the power supply 4 3 1 Effects of the finite muon pulse width on useable transverse fields At ISIS the muons are produced in short pulses about 80 ns wide at half height and the approximation is usually made that an average arrival time near the centre of the muon pulse can be used as time zero This is adequate if the time scale of the evolution of the muon polarisation is long compared with the width of the muon pulse but leads to difficulties in cases where the evolution is rapid The effect is seen clearly by considering a transverse field experiment performed at a succession of magnetic fields At low precession frequencies the polarisation is seen with full asymmetry As the frequency increases there is an appreciable phase difference developed between muons from the beginning and end of the pulse and
52. on the whiteboard Then select the remote terminal connection to NDXMUSR on the desktop This should automatically log you in and SECI will either start or already be running 6 3 Data analysis 22 02 05 9 Beamline 6 3 1 Logging on Logging in through an Xterminal These terminals are available for users in the Data Analysis Centre DAC Click on the CREATE option at the top of the terminal manager window and select DECterm followed by the machine you wish to connect to Then log in as normal using either the MUSRO0O1 account or your own account Logging in through a PC The PC in the MuSR cabin and other public access PCs can be used as terminals to log on to ISISA using the eXeed application On the MuSR PC click on one of the terminal icons on the desktop If you choose one of the MUSRO01 icons you will just be asked for the current password otherwise enter a username and password A terminal window will appear after a few seconds In order to allow graphics displays from UDA and other software to appear on the PC screen it is necessary to type SET DISPLAY CREATE NODE lt node gt TRANSPORT TCPIP where lt node gt is the IP number of the PC you are using the node name and IP number of the MuSR PC This can be found by typing ipconfig in a DOS command prompt 6 3 2 Using the MUSRO1 account for data analysis Log on to SISA or MUSR with the username MUSRO1 The password is change
53. onds e Turn key switch A through 90 back to ON position e Observe LED display on front panel Only the 120I A and 1201I B and the large DELAYED POWER ON should be unlit at this stage e After 120s the 120I A and 1201 B LEDs will light e After a further 180s the DELAYED POWER ON will light and the high voltage power supply will be powered up 22 02 05 10 Troubleshooting e Dedicated trigger should light e While pressing the READ SET VOLTS push button turn helipot B slowly clockwise to obtain a set volts readout of 32 5kV The current read out will be 2 02mA when the push button is released 22 02 05 10 Troubleshooting RUN Se VOW eal o ANON SET VOLTS READOUT HIGH VOLTAGE MAINS ON SWITCH i a A E sie SET CURRENT LIMIT pee i SET VOLTAGE B 2 SET CURRENT HELIPOT TRIGGER TIMING UNIT 120 A INTERLOCK 120 I B UNIT o INTERLOCK LED ON OFF KEY A THYRATRON POWER SUPPLY FILTER FAN FAN FILTER Figure 19 Reference diagram for resetting the kicker 22 02 05 11 Contact Points 11 Contact Points and further information 11 1 Laboratory contact points Rutherford Appleton Laboratory Chilton Didcot Oxfordshire OX11 0QX 01235 821900 national 44 1235 821900 international Main control room MCR 2 726789 EMU cabin R55 eseececeeeeees 6831 MuSR cabin R55 eeeeeeeeee 26135 DEVA cabin R55 26851 Experimental Areas 6
54. ooling water hoses are connected to the two tubes on the furnace body it doesn t matter which way round The hose with the flow sensor must then be connected to the water return socket on the area wall and the other hose connected to the water output socket Don t forget to turn the cooling water on there are two taps one on the feed line and one on the return line 7 The furnace pumping port on the centre stick is connected to the rotary turbo pump set in the area via a 4 way cross piece which also allows connection of a pressure gauge and a valve to admit He exchange gas It is useful to ensure that there is a valve capable of isolating the furnace in place between the furnace and the cross piece The pump set used should be one reserved for a furnace to avoid contaminating a clean set The flow sensor on the water return line is designed to cut off the heater power to the furnace if the flow falls to too low a level The LED on the heater box by the flow input goes out if the heater has been tripped in this way 22 02 05 3 Sample Environment 3 7 4 Eurotherm set up Normally a dedicated Eurotherm is provided which will be already set up for furnace use However in the event of a CCR Eurotherm having to be used to control the furnace please ask your local contact to configure it for use with thermocouple sensors For full details of operating a Eurotherm see The Users Guide to the Temperature Controllers by H M Shah co
55. pies are in the filing cabinet in the EMU cabin 3 7 5 Controlling the furnace Exchange gas within the furnace vacuum jacket is necessary to allow control over the low temperature part of the furnace range up to about 200 C The rotary turbo pump set connected to the furnace pumping port can be valved off once a good vacuum has been reached and 20 mbar or so of He gas introduced into the furnace body This can then be pumped out for high temperature operation There are six different heater power settings and an off 0 setting on the heater box The table below shows the heater settings PID and exchange gas values required at different temperatures Max Eurotherm Heater box working Heater voltage Temperature setting These settings have been optimised to achieve the best possible stability Users wishing to scan a temperature range on a script may be able to find a compromise in the settings that will still achieve reasonable stability but will allow unattended operation over an extended temperature range However please 22 02 05 3 Sample Environment note the maximum temperature that can be reached for each heater box voltage setting Eurotherm heater power set at 100 Heater box voltage setting 1 2 3 4 5 6 Max working temperature C 190 380 510 640 700 700 3 7 6 Typical data collection parameters The wall of the furnace vacuum jacket acts as a degrader in front of the scintillation detectors prev
56. probe can be fixed at the sample position and used to check the zero setting read this on the display with the unit in the rack The Instrument PC runs the Labview control program zerofield v5 vi which should automatically load and run when SECI starts Select the magnets tab to see it Normally you will not need to do anything here EMU zero field control Set zero Activity Update Interval stop Geo Foa ke Set MeasuredmG Corrected mG pointmG Currents A Field from Others Ref Currents Manual Mode EMAZAF Lf oof oof oof o612 oof 0 612 T oo oo ool 5 230 oo 5 239 vV 0 1 0 1 0 0 1 529 0 0 1 529 Magnets 50 0 Enabled 40 0 Field Now o 30 0 Status Ped 10 0 0 0 10 0 20 04 Field Log 30 0 X 40 04 aol v 2772 3795 FO tells Labview to use the auto zero field controller TF20 selects the TF20 or main magnet returns the currents to manual control of the currents Once the field is set to zero remove the probe from the sample position 22 02 05 4 Magnetic Fields If varying the current on the vi does not change the field at the sample position or the message current overload appears on the PC check that the coils have been reconnected to the box on the fence between MuSR and EMU If the field readings remain fixed at about 5000 mG their maximum check that neither the
57. r ensure that the controller is still in the required mode of operation usually with the heater in automatic mode Manually adjusting parameters Switch the controller to the local mode of operation by pressing the LOC REM button Note that SECI will periodically return the controller to the remote mode 22 02 05 3 Sample Environment Adjusting the set temperature Press the SET button with either the RAISE or LOWER buttons under ADJUST Adjusting the heater voltage Press the MAN button under Heater simultaneously with either the RAISE or LOWER buttons under ADJUST The voltage can be read Note that the heater sensor is always number one Adjusting Gas Flow Press the AUTO GAS button simultaneously with either the RAISE or LOWER buttons under ADJUST Adjusting PID s Press either P T or D button simultaneously with either the RAISE or LOWER buttons under ADJUST 22 02 05 3 Sample Environment 3 4 Orange cryostat Centre Stick s A 5 Posi lren 4yasi OSS ULE CEN as Vake 4 W Fle harm Va pou Pe Pas cempin i LX gt lt ee y P Waren Kire 4 3 De y27essesvi sin Se s K ala KA Helu m7 lt lt 1 E ee Kecovery N Kocurm lake A Ezd V PZZZZA ZIIZITA VZ Fessur SLL i Vake Pe i eae ee Cal Veka Lavi Mio Z P 77K E CA Ctr ber
58. ransverse fields 4 3 2 Effects of high longitudinal fields on asymmetry BEAM SIZE EVENT RATE AND STEERING 5 1 The muon beam spot size 5 2 The event rate 5 3 Steering the beam COMPUTING 6 1 General Information 1 Introduction 22 02 2005 1 Introduction 6 2 Data acquisition 6 3 Data analysis 6 3 1 Logging on 6 3 2 Using the MUSRO1 account for data analysis 6 3 3 Using your own account for data analysis 6 4 Utility programs 6 4 1 CONVERT_ASCII converting data files to ASCII format 6 4 2 TLOGGER plotting TLOG files 6 4 3 ISISNEWS the status of ISIS 6 4 4 Archiving data on to a PC floppy disk 6 5 The MuSR PC 6 6 Printers 7 DATA ACQUISITION SECI 8 DATA ANALYSIS UDA 8 1 Introduction 8 2 Running UDA 8 3 The Main Data Menu 8 4 The Grouping Menu 8 5 The Analysis Menu 8 6 Computer files 8 7 Theory functions defined in UDA 8 7 1 Longitudinal and zero field 8 7 2 Transverse field 8 8 Time zero 9 OTHER COMPONENTS OF THE MUON BEAMLINES 9 1 Beamline power supplies 22 02 2005 1 Introduction 9 2 The separator 9 2 1 Spin rotation by the separator 9 3 The kicker 9 4 The photomultiplier tubes 10 TROUBLESHOOTING 10 1 No muons 10 2 Computer Problems Restarting SECI 10 3 Resetting the kicker 11 CONTACT POINTS AND FURTHER INFORMATION 11 1 Laboratory contact points 11 2 Contacting an instrument scientist 11 3 Further information on the ISIS muon beamlines
59. refAE 1 2 furnace tH cases the spot from the alignment lasg ae return iine thermo 2 pin yellow couple out water match yellow connector to yellow box inputs red 2 way split thermocouple box mains required mains required Eurotherm to acquisition computer temperature P controller sensor Lemo connectors 22 02 05 3 Sample Environment Figure 8 Furnace connections 3 7 3 Connections Once the furnace body with centre stick in place has been mounted on the instrument connections as shown in the diagram below are made 1 The lead from the sample thermocouple thermocouple B is connected via a red lead to the yellow terminal of the red thermocouple box A two way splitter is connected to the white output terminal of the box to feed two leads which attach to the sensor inputs on the Eurotherm controller via Lemo connectors 22 02 05 3 Sample Environment 2 The 12 pin Jaeger connector on the centre stick is connected to the 4pin output on the heater power box 3 The 9V DC output of the Eurotherm is connected to the 9V input on the heater box via Lemo connectors 4 The flowmeter signal wire is connected to the flow input on the heater box via a Lemo connector 5 The RS232 link on the Eurotherm is connected to the RS232 cable in the area use the one normally devoted to the CCR Eurotherm Check that the two sample environment data switches are in the CCR position 6 The two c
60. stat tails reduce the muons energy significantly before they reach the sample Any material placed over samples for the fridge should be very thin indeed 10 um thick silver is used for heat shields otherwise the muons may not reach the sample 22 02 05 3 Sample Environment Samples for uSR experiments should be appreciably thicker than the average muon stopping distance When thin samples are used sheets of metal or plastic should be added in front of the sample to maximise the signal from the sample and to prevent the muons from passing all the way through The decision to use either metal or plastic as the degrader will generally depend upon the nature of the sample being studied and the need to create a contrast between the sample and degrader For samples having a missing fraction metal is the most appropriate choice pre cut 30 um thick titanium sheets are available for this purpose while conversely a plastic degrader is ideal for metallic samples 22 02 05 3 Sample Environment 4 Magnetic fields 4 1 Zero field compensation Three pairs of orthogonal coils mounted around the sample position are used to cancel the earth s magnetic field They are powered from the three Iso tect power supply units labelled L V and T in the electronics rack inside the MuSR area The field is measured using a triple axis fluxgate magnetometer mounted just below the beamline window and is used to control the currents in the coils A second
61. the observed asymmetry falls This is seen in the plot below produced from the precession of muonium in quartz in low transverse fields data taken on EMU although the MuSR response is the same Even though MuSR will allow fields of up to 2000 G to be applied when in transverse orientation the low asymmetry limits the useable field to about 600 G 8 MHz 22 02 05 4 Magnetic Fields Frequency response of the USR signal Asymmetry w A nn vn Nl w N Frequency MHz Figure 11 Frequency response in transverse fields 4 3 2 Effects of high longitudinal fields on asymmetry The asymmetry measured for a large silver plate mounted in the MuSR CCR in longitudinal magnetic fields up to 0 25 T is shown below As the field is increased there is a small but gradual fall off in the measured asymmetry with roughly a 3 reduction at 0 25 T This change is an artefact that is probably a result of a shift in the value of amp caused by the interaction of the magnetic field with both the decay positrons and the photomultipler tubes Experimental data can be corrected for the effect however the precise form of the curve seems to depend on the initial value of and you are advised to perform your own calibration and not rely on the curve below asymmetry 0 500 1000 1500 2000 field G Figure 12 Effect of high longitudinal fields on asymmetry 22 02 05 4 Magnetic Fields 22 02 05 5 Beam size event rate steering
62. to gt 25K first Let the sample space up to 1 atm with helium Insert the stick the pin on the stick flange should locate into the hole in the flange on the cryostat Pump the sample space purge two or three times with helium and set the exchange gas pressure to 15 mbar 3 5 5 Cooling Check that the PTFE sealing washer is present on the cryostat end of the transfer tube Connect the needle valve cable Turn the ITC5 on This initialises the valve Open the needle valve fully press and hold Gas Auto and then press Raise Check it stays in Manual light off Check with your local contact that the dewar has the helium level probe installed Insert the leg of the transfer tube in the dewar Be very careful not to bend the transfer tube In practice the tube will need to be almost fully inserted into the dewar before the transfer tube can be inserted into the cryostat Reduce pressure in the dewar as required with the red valve Put the transfer tube into the cryostat and tighten the locking nut Turn on the diaphragm pump Open the valve on the pumping box There should be a very small flow After about 5 minutes the flow should increase as liquid reaches the cryostat and the temperature will start to fall The Green valve on the dewar should be open and the Red valve closed during operation If the cryostat is still not cooling after 20 minutes the tube may be blocked with ice or solid air Remove the transfer tube
63. until the He flow rate is at maximum on the He return line meter 10 l min 3 Wait for the cryostat to cool to the desired temperature 4 Close the warm valve until the He flow rate is 4 5 l min 3 4 4 Cooling the cryostat below 4 2K This requires the He brought through the needle valve to be pumped using the large Roots pump The cryostat temperature must be below K before pumping starts 1 Connect the Roots pump to the He pumping valve valve 3 of the cryostat 2 Close the cryostat cold and warm valves fully 22 02 05 3 Sample Environment 3 Make sure the cryostat valve 3 is closed Disconnect the flow meter from the Roots pump outlet if one is attached Turn the Roots pump on press both green buttons and open the big isolation valve on the pump to evacuate the line up to the cryostat Wait until the gauges on the pump read zero 4 Slowly open valve 3 of the cryostat Wait for a few minutes then reconnect the flow meter to the Roots pump outlet line Open the fine control of the cold valve very slightly until the pump flow meter is reading maximum 5 When the cryostat has reached the required temperature close the cold valve until the pump flow meter is reading lt 4 l min this may mean winding the valve control until it is fully closed 3 4 5 Filling with Helium Again this is very similar to the Variox cryostat A different He level gauge is used for the orange cryostat you ll need to switch this o
64. v sets the voltage on a single tube to v Ctrl C stops screen scrolling 22 02 05 10 Troubleshooting 10 Troubleshooting 10 1 No muons e Check the machine is running at a reasonable rate In the MuSR cabin there is a proton per pulse PPP monitor displaying the pulse intensity in LA If this reads 00 there are no protons and if it is flashing any number then ISIS is not running at 50 Hz and therefore the count rate will be lower than usual e f ISIS is not running check the facility status by typing IsIsnews current ina decterm not mcs control window or http Awww isis rl ac uk status index htm e Check the beam blocker is open the gate must be closed and locked to allow this The blue interlock light will be lit if this has been done correctly e Check that the high voltage to the photomultiplier tubes is on this is particularly likely to be the problem immediately after the instrument has been rotated The red lights on the photomultiplier tube bases should be on If not type on on the terminal controlling the high voltage power supply in the back of the MuSR cabin see section 9 4 for further details of the photomultiplier tube high voltage commands e Check the BEAM OFF button on the fence in the zone is not pressed If itis release it then restart the bending magnet power supply B1 2 above the cryostat store using only the START button see section 9 1 e Check that all the magnets are working b
65. y checking their power supplies see section 9 1 the current they should be set at is written on each If necessary reset or restart using the value given e Check that the kicker is working Instructions for resetting it if it has tripped are at the end of this chapter but please consult your local contact before doing this e Check that the separator is at its correct voltage typically 90 kV 22 02 05 10 Troubleshooting 10 2 Computer Problems Restarting SECI Goto the Start Menu and select killISECI After SECI has stopped goto the start menu again and select startstation If this does not resolve the problem then rebooting NDXMUSR might be necessary this can be done by type ctrl alt end together and then select shutdown Please select restart or NDXMUSR will not restart 10 3 Resetting the kicker If the spectra from the individual detectors displayed on the MuSR data acquisition screen shows the effects of a double pulse the electrostatic kicker has failed and all the muons are passing undeflected through to MuSR Before resetting the kicker check with the EMU and DEVA users that they have lost all beam In most cases EMU and DEVA users will notice a kicker failure before MuSR users The instructions for resetting the kicker are given below and are also attached to the kicker power supply unit e Turn key switch A through 90 to OFF position e Turn helipot B fully anticlockwise to 0 0 volts e Wait a few sec

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