DEVA User Guide
Contents
1. Resetl Separat Q4 Q8 DEVA DEVA EMU Reset2 QIOA spare JQIOC Q2 Q6 Q9 Helm Septum Septum QUA QOIIB QILC Ql on off jon off on off holtz JA C PLC on off jon off Jon off Q3 5 Q7 B1 2 QI2A QIOB Q12C Spares spares spare SWXI SWY2 Resetl interlocks with reset buttons for Q1 Q9 B1 2 and the Separator supplies Reset2 interlock reset buttons for QIOA QI2C Septum Switchyard and instrument magnets DEVA Manual 27 on off panel with ON and OFF buttons for the power supplies spare Spare supplies not connected or powered up ISIS staff use only The PLC has status lights for the second group of magnets and for the shutters the upper row of modules show inputs from various sensors and switches and the lower row is the outputs to enable the supplies For interlocks the general rule is Lights ON good lights OFF tripped Farnell supplies press the interlock reset buttons then the green ON button next to the power supply It should not be necessary to touch the controls on the supply itself Check it returns to the setpoint and the green Output Enable light is on Danfysik supplies septum press the interlock reset buttons then on the supply itself press OFF Reset and then ON Check the setpoint and readback values The Separator electric field is provided by the Glassman unit in the rack next to the kicker The usual value is 90kV 9 1 4 Photomultipliers These are powered from the Lecroy HV supply in the2. 4 Magnetic Fields 4 1 Longitudinal Field This is provided by the large water cooled Helmholtz coils powered from a Danfysik supply located next to the beamline magnet supplies It is controlled from the computer in the cabin The maximum field is 2100 Gauss From MCS type LFO to select it then SET MAG SET x as required 4 2 Transverse Calibration Field This uses two small coils inside the main magnet powered by the Thurlby Thandar supply in the cabin also under computer control The maximum is 30 Gauss The field is Vertical Type TF20 to turn it on and set 20 Gauss and then SET MAG SET x if a different field is required 4 3 ZeroField setting This is automated using a triple axis fluxgate probe and three pairs of compensation coils Control is via a Labview program on the PC under the Zerofield tab in Ray of Light in turn controlled from MCS EMU zero field control Manual i OS eee Set zero Activity Update Interval stop Geo Hoo STOP MeasuredmG CorrectedmG Setpoint mG Currents Field from Others Ref Currents L oo oo 09 T 00 oo 0 9 v 6 1 0 1 0 9 L 50 0 Magnets Enabled 40 0 Field Now fa 30 0 Status 20 0 Field Log 30 0 L 40 0 50 0 ki 2772 Operating modes are e Auto Feedback the probe is read and used to control the currents to keep the field at the set point This is usually zero but can be any field up to the lim
3. 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 7 5 The Analysis Menu The Analysis menu is entered by selecting the option Analyse in the UDA Main menu Using the options outlined below it is possible to select a model function 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 Select a group and a bin range to work on PLOT Plot the data and the fit allows fit to be written to an ASCII file FIT Run fitting routine using the starting values displayed in right hand window HELP Enter the help system at the Analysis menu level VALUES 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 THEORY Select a theory function number of sub components and lineshape ALPHA Change value of alpha UNDO Undo fit and restore original parameters EXIT Exit this menu and return to the main UDA menu WRITE Write parameters out to a file RE
4. 6cm diameter and graticule can be seen Actual size DEVA Manual Profiles taken from the beam camera for a number of slit settings Horizontal profile a u Slits 4 8 16 edge of scintillator xl 1 in WA 0 2 4 6 8 10 Width cm The beam pictures can be fitted to a Gaussian profile Parameters are shown here Spot Size gaussian o in cm Intensity at centre a u 2 0 n m width kl O height Slits 5000 4500 4000 3500 3000 2500 2000 1500 1000 500 Slits DEVA Manual 6 With a mask of 20mm diameter a slit setting of 8 is found to give 75 of the muons on the sample To maximise the counts on a small flypast sample use a slit setting of around 20 The slits are adjusted from the rack in the kicker control area down the steps behind EMU Be careful to adjust only the DEVA slits 2 3 Frequency response due to pulse width At ISIS the muons are produced in large numbers in short pulses about 80ns 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 to 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 f
5. 2 3 RF pickup With high RF pulse power it can be picked up by the detector wiring This may change the sensitivity of th electronics when counting actual events or even make it count cycles of the RF waveform First try to improve the shielding of the coil or insulate it from the spectrometer s metal framework Changing frequency if possible often helps as the pickup is via resonances in the cables etc If the problem is not too severe just remove that histogram from the grouping when analysing the data If it has a huge count rate it may be necessary to disconnect that detector from the electronics in the cabin so that the total counts in the run correspond to usable events 9 3 Computer The PFI key locks unlocks the screen or the currently selected Decterm window This can give the appearance of a crash and can actually cause a crash if left locked for too long Many problems with MCS can be cleared by restarting it e first SAVE the current run If it refuses to do this you have to kill MCS itself from another Decterm window e type EXIT e Wait a few seconds for all the windows to disappear e If any remain type SHOW SYSTEM to get the list of processes Look for MTEMP MMAG MACQ MWSDISPLAY and MWSWINDOWS Kill them with STOP IDznnnnnnnn where nnnnnnnn is the number to the left of the process name e type MCS to restart No communication with the data acquisition hardware from MCS type SYS SHOW SYSTEM and look for the
6. 32 MCSCONF gt SET FREG DEV LTDC CRATE 20 STATION 1 MCSCONF gt SET SGATE DELETE Start MACQ if it was stopped set resolution histogram length readout interval as required DEVA Manual 25 8 2 5 Setting up To select the data acquisition mode e To enable Frame by Frame n Green frames for every 1 Red MCS gt SET MACQ RGMODE n eg SET MACQ RGMODE I gives 25 Hz SET MACQ RGMODE 4 gives 10 Hz etc e To collect data in blocks of red and green MCS gt SET MACQ RGMODE 0 e To turn off red green completely single set of histograms MCS gt SET MACQ NORGMODE Now collect data as usual 8 2 6 Timing notes In Frame by frame mode the Red Green output changes after each frame whether or not MCS wants the data Therefore the lamp RF pulse etc runs at a steady frequency and any sample heating should be constant The output usually changes at about 175 us after the Frame Start but can be later if the crate controller was busy receiving data from the Ethernet when the TDCs finished collecting data Do not use it as a time reference only as a veto or enable signal When driving slow equipment such as the flash lamp from the previous frame s Extract Trigger the usual method is to use a delay set to about 19ms which then drives an adjustable delay of about Ims For correct operation connect the Red Green signal to the Veto of the last delay stage or the lamp itself Vetoing the first 19 ms delay unit would get Red
7. Peas AY Bele Anita 15 S33 Seriptsz isse AG SR es tha Re tee esis ee de 16 6 Computing and Data Analysis 0 ec eceeceesceeecesecesecesecsaecseecaeecseseaeseeeseeeeeeseesecssecsaeesaesseenaes 18 6l Computers o Gene teh ek Re AAS Re ione SA eA Bat 18 6 2 MUTOT and UDA iret Saone npe EE 18 6 3 7 WIMDA eom SCIES tehna fi eodeni ee RE Eid 18 6 4 Taking your data home ie e ara a eire NESE trennen teen neen rene enne enne en 19 GS lt ATCHIVING open eee IE ie eee teni ie RE 19 YEN vc EE E 20 T Jntroduction Rer fun Aw ene 20 12 Running UDA e seis iis Sele Ree eR UMP Bee u tad s 20 T3 The MaunDa t Me nu ieeesp eel Ba A ee hes g eh 20 TA The Grouping Men oem ree rei cine OaS ESON e r Eh Ee ies cers iz NS 20 Tz The Analysis Menu ie eee do ie o eh o te redd 21 TLO Gompu terhles ros iae mee Pte eda tee ino e nte d Maa eterna 21 7 Theory functions defined in UDA Lm ern ens n nn nn nsara nee rennen enne ens 21 EBs TIME ZOLO si E eas seks e E o ire bande edu te ere 22 8 RFand other special Setups isseire nn neen renim ee Ekr nn tne nts nsa netten enne 23 8 1 Timing and Acquisition osese A bii je sbie secescenssteve ee eee e E ENEE SE EE EEA 23 8 2 TheL croy TDCS n etae be ege ee a ire Fo 23 9 Jro bleshootimg ci eco ee EI D eI Ee E Itn ide e petite 26 9 1 No muons or far fewer than expected sess ener en nennen 26 92 Strange data ioco aeta tree Id cea e e e e hte ide
8. You can also scan fields on a log scale up or down Enter first last runs where runs is the number of runs required The ratio between successive fields will be printed as confirmation Normally fields in a script mean Longitudinal and you should be sure the longitudinal field is selected with LFO before starting a script which is to set fields If you execute a script when the Transverse supply is already in use any field setpoints will use it until a T20 entry is reached The script will update the field and temperature values in the label file header when it changes the actual field or temperature Before running a script that starts the first run itself check that the other entries sample name comments etc are correct Set them with the MCS command SET LABEL The script is saved in a file of the form name COM To run it type name in MCS To interrupt a script in progress press CTRL C This does not stop the current run although the run will stop when the pre set number of counts are reached You can stop and save the run manually To resume the script first read it into MKSCRIPT2 and edit it to remove the entries which have been run Also you may need to change the current run which will now be the first in the script to have KEEP for temperature and field Write it back to the file exit MKSCRIPT2 and restart with name Experienced users may want to edit their scripts with the VMS editor They contain a header wh
9. and Green the wrong way round as compared to block red green where this does not matter Once set up Frame by frame mode actually turns on or off on starting the next run when you type lt return gt or Y lt return gt to the Clear Devices prompt 8 2 7 Discriminators These are normally set up manually from the front panel with threshold levels of 50 or 75 mV and pulse width 10ns Users should not need to change anything However it is possible to use a program on the FEM to put these in Remote mode and then program the threshold levels Neither MACQ nor the downloaded program LTDCFF accesses them directly DEVA Manual 26 9 Troubleshooting If you have to reset any equipment as described below remember to tell your local contact as soon as possible it may indicate that something is about to fail completely or needs repairing 9 1 No muons or far fewer than expected First check e The Frame Start light on the DTU module in the DASH2 TDC rack is lit if not the beam is off or there is no start pulse from the Cerenkov detector Frame Start flashing means ISIS is at base rate 1 32 of 50Hz e If Frame Start is present is the computer reading back from the electronics Type SHOW RUN e Is there any beam going to the other muon instruments 9 1 1 Beam Off Check the proton beam current the big display in the hall or the ISIS PPP Monitor program on the PC The last hour graph on the ISIS web page only upda
10. of 2 non uniform below 2ns care 32 histograms of up to 8192 bins each for each of Red and Green Maximum time length of histogram 32us Either frame by frame or block at a time red green mode can be used In frame by frame mode you can select from n 1 to n 126 green frames for every red frame giving red frame rates between 25 Hz and 0 4 Hz Note that the header of the saved file indicates the number of frames in the red histograms but for n gt 1 the green histograms contain more frames worth of data Take care when analysing this data especially when applying dead time corrections 8 2 2 CAMAC Modules LP Hytec 1341 List Processor with 256k word data store Dis Lecroy 3412E discriminator TDC Lecroy 3377 time to digital converter PCR Nuclear Enterprises Harwell Preset Counting Register ECC Hytec 1365 Ethernet Crate Controller with 4M RAM DEVA Manual 24 8 2 3 Connections Frame start ECL to COM on TDC Ethernet to FEM second private ethernet port free slots for Via hub if another GPIB etc crate is in use CAMAC crate Optional terminal 9600 baud Inputs from Red Green outputs TTL photomultipliers A 0 Red 1 Green A 0 Green 1 Red Notes e The List Processor must be in station and the others adjacent to it as shown e No connections to the front panel of the List Processor e Short ribbon cables between the discriminators and the TDC as shown e The Discriminators are usually in Manual operat
11. process name ecc 1365 If missing it usually requires a reboot to get it going again Warning closing the DECterm window in which MCS is running using the close icon usually kills the ecc 1365 process No communication with Labview from MCS type SYS SHOW SYSTEM and look for the process name DCOMSRPCSS If missing it usually requires a reboot to get it going again If you find DCOM STARTUP instead this indicates it has failed to initialise correctly in this case contact Computer Support If all else fails there is a reset button on the Alpha workstation Log out first if possible then press this to reboot 9 4 Magnets 9 4 1 Main field If the Danfysik Longitudinal field supply trips MCS will print error messages every few seconds One or more red LEDs will light on the supply control panel Pressing the buttons next to them will indicate exactly what it thinks is the problem MAG Overtemperature can mean the Helmholtz Interlock key by the door e In MCS type GFO to stop the error messages e Clear the problem if it was the door interlock close the door and raise the blocker If a problem with water flow press the three reset buttons on the interlock PLC rack e Reset the power supply press LOCAL to make the Remote light go out then OFF RESET which should turn off any red lights then Remote e In MCS type LFO e Then type SET MAG SET xxx to go back to your setpoint 9 4 2 Zero field The Zero field pro
12. 10 Contacts and further information Address ISIS Facility Rutherford Appleton Laboratory Chilton Didcot Oxon OX11 0QX U K Phone Main switchboard 01235 821900 Fax User Office 01235 445103 Fax ISIS Staff 01235 445720 Web page http www isis rl ac uk muons Ordinary phone extensions starting with 5 or 6 can usually be dialled from outside the lab with 01235 44 ext or 44 1235 44 ext from abroad Mobile short codes starting with 1 only work on the RAL exchange To make outgoing calls just dial the full number There is no need to add a leading 9 10 1 Muon Group Office phone Mobile short code E mail Dr Steve Cottrell 5352 1665 S P Cottrell rl ac uk Prof Steve Cox 5477 S Cox rl ac uk Dr Gordon Eaton 5464 G H Eaton rl ac uk Dr Adrian Hillier 6001 1476 A D Hillier rl ac uk Dr Clive Johnson 6259 C Johnson rl ac uk Dr Philip King 6117 1716 P J C King rl ac uk Dr James Lord 5674 1101 J S Lord rl ac uk Dr Francis Pratt 5135 1114 F Pratt rl ac uk 10 2 Useful Phone numbers RAL ISIS Main Control Room MCR 6789 Emergencies Fire Ambulance 2222 Occupational Health minor illness 6666 Security lodge main gate 5545 Health Physics sample checking 6696 DEVA Cabin 6851 MUSR Cabin 6135 EMU Cabin 6831 ARGUS RIKEN Cabin 6766 User Office 5592 Local taxi bookings to B amp B or station User
13. 235 833249 The Harrow West Ilsley 01635 281260 The Plough Sutton Courtenay 01235 848801 Red Lion Drayton 01235 531381 Rose and Crown Chilton 01235 834249 The Swan Inn Sutton Courtenay 01235 847446 The Wheatsheaf Inn East Hendred 01235 833229
14. A The value of t0 will be different between the Lecroy and DASH2 TDC systems and completely different if triggering via a RF pulse generator Cable lengths are significant adding about 3m of extra cable length moves the data by one 16ns bin The first good data bin is about 0 1 us after t0 when all the incoming muons have arrived Some of the detectors may also show a peak around time zero due to muons decaying in flight in the beamline and the positrons produced not being properly focused and striking the detector directly For transverse field runs the phase at time zero is actually about 3 degrees due to the rotation of the muon spin in the kicker in a horizontal plane actually the lack of matching rotation of the spin as the muons are deflected by the electric fields There is also a rotation of about 6 5 degrees in the vertical direction due to the separator The overall effect is that the muon spin points slightly up and to the left looking upstream ie towards detector 16 The combined spin rotation is visible as wiggles of amplitude about 2 5 if looking at individual detectors in longitudinal field runs 20 200 Gauss 26 Detector 1 24 22 D E 20 E 2 o 18 16 14 0 2 4 6 Time us Silver 100G LF run 35709 Asymmetry plot of one detector only 2 7 Dead Times If two muons decay within a short interval of time and their positrons both reach the same detector only one e
15. AD Read parameters in from a file DIST Distribute parameters to all groups necessary for transverse geometry 7 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 2 they will have been copied to the new area automatically SETUP 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 2 6 TRANS UDA default transversal grouping LONG UDA default longitudinal grouping PDF UDA parameter definition file UDAHELP HLP help library source UDA matters 7 7 Theory functions defined in UDA A number of theory functions are predefined in UDA DEVA Manual 22 7 7 1 Longitudinal and zero field Function Name Definition 1 Lorentzian a exp At 2 Gaussian a exp At 3 LX exp Stretched Exponential a exp At 4 Keren LF extended Abragam a exp I t t see note 1 below 5 Kubo Toyabe Gaussian a 4 A At exp At 2 6 Kubo Toyabe Lorentzian a 4 4 1 At exp At 8 Dynamic Kubo Toyabe see note 2 below Note 1 24 rot Ge lar v M a v x exp v cos 2v exp v sinot where UDA s sigma is equivalent to A UDA s ta
16. DEVA Manual DEVA User Guide J S Lord S P Cottrell A D Hillier P J C King F L Pratt Version 1 0 DEVA Manual 2 Contents be Getting Started seco ee tei t rae ne dae e eed bee ie rente eed 3 1 Layout of Muon Instruments eii perti rhe rne E rir Hp eee ted 3 1 2 InterloCKS eee e eee eet eta ee i etie t e ii e ep erede d 3 2 Th Be m z sehe pRUHD IP i REOR U RENE ta OE 4 2 STC STUB bse hei sec scien Sats ege ade tn AS 4 2 23 Slits and sample size A is b D Poeno o pp 4 2 3 Frequency response due to pulse width enennnnnnnennnananennnnnnnnnnnzn nn nn nnaza 6 DA Detectorssi i ee i poder RP ORE DOCU a HOD URURO P DUE 6 2 5 Asymmetry shift with field ose oot ahi e eee edge 7 2 6 TimezZzem e eoo pea OP PEDI DURER ERO RE 8 24 Dead Tnmes snenono A RUE Dam A A DER 8 2 8 Muon stopping range and sample thickness sse emmmnennnnnzznnnennznnenznzzznenznzzznnznnzzz 9 3 Sample Environment 51 2 orerar cust eem nee O Eo EEEo SE PEKEE To DER OE treten 10 31 Elow Cryostats onse a A ab Pd GSP DIE ERE 10 4 Magnetic Fields iiie tee t a a TUR FED DERI ERR e ep E gen EU 14 4 1 Longitudinal Field 2 preter a sara ed 14 4 2 Transverse Calibration Field sese nee nren nee 14 4 3 Zero Field set ng operi Bae an AS pit aw emen 14 5s Data Acquisition aee ee npe dne 15 Diels ElectroblCS ese eo esg reete p pepe edite ST 15 Die MES sense bee tis ina ka dl Pe
17. MODE set Red Green mode SET MACQ NORGMODE set normal acquisition SET MACQ RESOLUTION p set TDC bin width in ps usually 16000 or 8000 with the DASH2 system 500 1000 2000 16000 with the Lecroy SET HIST LEN SET HIST IGOOD END4 ALL to change histogram length in bins both required SET MACQ READ NFRAMES n read out data and change between red and green every n frames ISIS pulses typically use 500 to 5000 SET MACQ SAVE s write data to disk every s readouts typically 1 to 6 SET DISP FIRST f NUM n which histograms to display SET DISP LEFT Ill RIGHT rrr range of time bins to display SHOW TEMP temperature values SHOW TEMP PAR temperature control PIDs etc SHOW MAG field value SHOW RUN counts per histogram etc SHOW MACQ data acquisition parameters SET LABEL change the label header of the current run if unsaved or that to be used for the next run 5 3 Scripts The program MKSCRIPT2 is used to write scripts From MCS type SYS RUN MKSCRIPT or from another DECterm window type RUN MKSCRIPT2 DEVA Manual 17 Select from the menu using the initial letter of each command or the arrow keys then RETURN The mouse will not work Add add an entry to the script This can scan through several fields or temperatures taking a run at each Press RETURN to use the default KEEP if a value is the same as the previous entry rather than retyping the same
18. Office 5592 in working hours MCR 6789 out of hours Airport transport User Office 5592 give 24 hours notice Technical support see the list in the cabin Out of working hours phone the MCR who will contact someone on call Computer support 1763 working hours DEVA Manual 10 3 Transport 31 Trains National Rail 08457 484950 http www railtrack co uk It is usually possible to arrange a Enquiries taxi to either Didcot or Oxford station Buses Oxford Bus 01865 785410 http www oxfordbus co uk Local buses and coaches to London Company and the airports Stagecoach 01865 772250 http www stagecoach Local buses some serve the oxford co uk Harwell Business Centre bus park opposite the RAL main gate Air BAA http www baa co uk Flight arrival departure information for Heathrow and Gatwick airports 10 4 General Information Oxford Tourist Information Centre 01865 726871 Oxford Guide on the Web http www comlab ox ac uk archive ox 10 5 Eating and Drinking Didcot Tandoori 222 Broadway Didcot 01235 812206 Cherry Tree Inn Steventon 01235 831222 The Crown and Horns East Ilsley 01635 281205 Fleur de Lys East Hagbourne 01235 813247 The George and Dragon Sutton Courtenay 01235 848252 The Great Western Junction Hotel Didcot 01235 511091 The Hare Inn West Hendred 01
19. an helium gas through it use a piece of rubber tube over the cryostat end 3 1 7 Computer control Type FLOW_ITC502 to set up the computer then set temperatures with SET TEMP SET x The range is 4 to 400K for the low temperature cryostat or 4 to 600K for the cryofurnace Temperatures slightly below 4K can be obtained by careful adjustment of the needle valve in manual mode The computer uses two thermometers One is on the cryostat heat exchanger labelled Readback on the computer and plotted as a dotted red line on the graph The temperature controller uses this to control the heater and the computer uses it to decide when the temperature is stable at a new setpoint The second is on the sample stick This is labelled Sample on the computer plotted as a solid white line and recorded in the log file 3 1 8 Changing Samples Warm the cryostat to 25K or above Remove the KF50 clamp holding the sample stick in place Let the sample space up to 1 atm with helium Remove the sample stick Unless you have another sample stick ready put the blanking plate on the cryostat and pump out the sample space 3 1 9 Changing the Dewar Check the level regularly Full is about 550mm don t go below about 50mm A dewar may last from 2 days to a week depending on the temperature the cryostat is running at below 10K uses rather more helium The sample can be left in place during the changeover although the temperature may rise Tur
20. cabin Turn all channels on or off with the HV ON and HV OFF buttons The Cerenkov start counter is supplied from the HV supply next to the slit controls check the other instruments are counting data OK 9 1 5 Beamline Vacuum This is monitored on the rack on the platform above the target kicker control area Check that the vacuum in the beamlines is OK about 10 mbar or better and that all the valves are open except for those labelled vent and bypass The line valve in each branch of the beamline is linked to that instrument s shutter Do not attempt to open or close valves ask your local contact or the MCR for advice 9 1 6 RF triggering Is the data acquisition being triggered from the RF zero crossing if so is it working properly 9 1 7 Computer There may be muons but the computer is not reading back from the electronics See below 9 1 8 Blocker Closed The blue lights in the area will light if the blocker has been opened correctly 9 2 Strange data 9 2 1 Light leaks On an asymmetry vs time plot this gives asymmetry going to 100 or 100 at later times If a detector develops a light leak large background number of counts in the later time bins turn its voltage off to prevent damage 9 2 2 Beamline Magnets If a beamline magnet trips there may still be muons but the spot size could be huge and the asymmetry change to an implausible value Reset it as above DEVA Manual 28 9
21. cbe tet ees erred 27 9 3 JCOBIDUfGr eto t eR tote tton BA p 28 DA Magnets NU i A A N REA 28 9 5 Temperature CODLtOl s eet RU e etit eec een ete ERU ostrea 29 10 Contacts and further information ms sse an E E tan nennen eene enne ene 30 10 1 Mon GEOUD 5 ise t ipe OR RO Lot HO edt a bt debe eee 30 10 2 Useful Phone numbers RAL sese enne ener enne nennen enne nnne 30 10 3 Transport HEP EE 31 10 4 General Information tenete ten utei distet EN 31 10 5 E tin and Drinking seio e eee Uie eO Reboot iet risen 31 DEVA Manual 3 1 Getting Started This manual describes the DEVA instrument as used with the RF spectrometer for either normal muon spin relaxation or RF resonance experiments 1 1 Layout of Muon Instruments ELECTROSTATIC KICKER x ORS 1 2 Interlocks 1 2 1 Closing the area e Check no one is in the area and press the Search Button e Close and bolt the door e Remove the key DEVA S and put it in the blue interchange box Once all spaces are filled the master key is released e Remove the master key DEVA M from the blue box this locks the other keys in place e Put the master key in the green interlock box and turn clockwise 90 e Turn the Helmholtz Interlock key to the vertical position Do not turn the key until this stage or the magnet will trip off e Press and hold Raise until the green light goes out e Turn the Helmholtz Interlock key to the hori
22. cquisition software USRFILE Read a uSR file from the disk OLDFILE Read one of the old PDP run files WRITE Write grouped data to a uSR file INSPECT Inspect run and all histograms GROUP Enter the Grouping Menu CHANGE Change run file parameters PLOT Plot one or more groups on the terminal screen ANALYSE Enter the analysis menu SETUP Set program configuration parameters HELP Enter the VAX VMS help facility to read the UDA help library QUIT Exit UDA and return to VMS prompt 7 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 aB F AB is calculated 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 DEVA Manual 21 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 section 2 7 The options available for grouping and correcting data are shown below CHANGE Change histogram grouping
23. eater The standard temperature flow cryostat in its storage trolley shown with the muon entry window facing when in the instrument it will be rotated through 180 MUSR2002 MUSR2002 ransfer tube port Lifting eyebolts bars removable if required Sample stick access Sample space 4 pumping valve Heater thermometer connections OVC pumping valve Muon windows The sample sticks are interchangeable but only those designed for high temperatures with glass fibre wrapping around the central rod are suitable for use above 400K Also ensure that your sample and its coil or holder will cope with the expected temperature range 3 1 1 Samples The cryostat has helium exchange gas around the sample DEVA Manual 11 This cryostat can use the same sample holders as the EMU Blue cryostat 37mm square with mounting hole spacing 30mm or a flypast holder made of a thin strip of silver sheet The internal diameter of the cryostat is 43mm For RF experiments the sample size depends on the coil used but a typical size is 25mm square and up to 4mm thick Powders must be enclosed in a non conducting containter such as a Mylar envelope 3 1 2 Installing The cryostat fits into the top of the magnet frame bolted to the support plate using 4 of the bolts on its flange Check the alignment with the laser and adjust the bolts holding the support plate to the frame if necessary Use the appropriate ITC5 tempe
24. endicular to this You can rotate the sample relative to the beam if required by your experiment either now or when in the cryostat al Steering curve in the Flow Cryostat on EMU d xw Slits 8 VSM 0 1A Fe O with 20mm mask 164 144 J 8 124 X 4 x 105 E 4 E 84 D eb ed 1 A 44 B J gok 24 Oooo oto 5 10 15 20 25 30 Height of sample mm 3 1 5 Inserting the stick The sample can be changed when the cryostat is cold but heat it up to gt 25K first e Letthe sample space up to 1 atm with helium e Remove the blanking plate e Insert the stick the pin on the stick flange should locate into the hole in the flange on the cryostat e Ifthe cryostat is cold the stick may not go all the way into the cryostat the copper cylinder on the stick is designed to fit tightly into the heat exchanger and thermal expansion can prevent it fitting Either leave the stick partially inserted and wait a minute or warm the cryostat e Pump the sample space purge two or three times with helium and set the exchange gas pressure to 15 mbar 3 1 6 Inserting the transfer line and cooling This requires two people and you may also need a stool to be able to lift the transfer line high enough e Lifta Helium dewar onto the platform inside the area requires someone with a crane licence e Remove the dewar neck insert yellow valve by undoing the KF50 clamp and fit the one with the level meter probe Do this carefully but quickly t
25. gram on the PC will give a status message of Current Overload if it is unable to reach zero or its setpoint This may be due to DEVA Manual 29 e Set point too large the maximum available from the coils is about 1 Gauss 1000 mG as shown on the PC in each Transverse direction and 3G in Longitudinal The magnetometer range is 5G e The main LF or T20 magnet is on this should not happen if controlled from MCS e There is a fault with the coils or magnetometer 9 5 Temperature control 9 5 1 Needle Valve Sometimes the ITC temperature controllers can lose the zero position on the motorised valve leading to excessive helium use and high heater power with the valve reading 0 or the temperature drifting up with the valve apparently at 99 The latter could also be due to an empty dewar To reset e Switch the ITC off and on again e Wait for it to initialise the valve light flashing e Re send the setpoint with SET TEMP SET rtt 9 5 2 Empty Dewar Don t let the dewar run dry if possible If this happens Turn off the diaphragm pump immediately Check the pressure gauges on the dewar and the pump control box If below atmospheric you have to admit clean helium from the supply on the panel via the red valve on the dewar Gas will come out of the green non return valve once you are back at atmospheric pressure It may take several minutes Now remove the transfer line as usual and change to a new dewar DEVA Manual 30
26. ich MKSCRIPT uses when reading a script in but is ignored by MCS each line starts with This is followed by the actual commands executed by MCS DEVA Manual 18 6 Computing and Data Analysis 6 1 Computers e MUT Alpha VMS workstation the instrument data acquisition computer Can also be used to access ISISA e ISISA Alpha VMS central server available for data analysis with UDA etc e User PC Windows available for data analysis Has WiMDA Origin Microsoft Office Internet Explorer etc and eXceed to connect to the VMS machines e Labview PC Windows controls the zero field and other sample environment Not for general use e A Unix Linux service is available contact Computer Support Access is via Telnet or eXceed from the PC 6 2 MUTO1 and UDA The account MUTO is available for VMS data analysis Alternatively you can use your own account Log in to the account MUTOI using Exceed on the PC using SET HOST ISISA in a spare DECterm window on MUT or Telnet to isisa nd rl ac uk from off site Ask your local contact for the password Select one of the user areas offered by typing the name or ask your local contact to set up a new one Next type SETUP Now you can use UDA etc as on EMU or MUSR For instructions on using UDA see the next chapter The nearest printer is SYS LSR10 just outside the EMU cabin Others are SYS LSR5 in MUSR or SYS LSR2 in the DAC 6 2 1 Convert ASCII This converts the bina
27. ields At low fields the frequency is small and the polarisation precesses with full asymmetry As the field increases there is an appreciable phase difference developed between muons from the beginning and end of the pulse and the observed asymmetry falls This frequency response has been measured by observing the precession of muonium in quartz in small transverse fields the results are shown below m Quartz data Theory Transverse Asymmetry 0 2 4 6 8 10 12 14 16 18 20 Frequency MHz With RF precession measurements where the muons are implanted in longitudinal field and then rotated through 90 by an RF pulse the pulse width does not matter In this case the only limiting factors on the frequency response are the precision of the detectors and electronics and the bin width of the histogram 2 4 Detectors The positrons produced when the muons decay are detected with scintillators linked to photomultipliers DEVA Manual 7 ele CESS Diagram looking upstream Detectors 1 16 are forward 17 32 are backward Angles around the beam axis from vertically upwards are 24 41 58 75 92 109 126 143 degrees Looking from the side or top the detectors are at approximately 45 degrees away from the beam axis The photomultipliers are powered from the Lecroy HV supply in the cabin Users should not normally have to change anything Channels 0 31 correspond to MCS histograms 1 32 Voltages may be anywhere in
28. ion set the thresholds and widths on the front panel Widths should be 10ns e The discriminators have 2 sets of outputs the second can be used for other purposes eg fed to a DASHZ2 to check thresholds or timing etc e Noconnection to the counter inputs of the PCR Use the A outputs only e The TDC does NOT like a double start pulse as obtained directly from the Cerenkov counter Use a first discriminator set to a very large pulse width which then drives a second one set to 10ns Alternatively use one discriminator with a second output triggering a timer set to lus which is fed back to the Veto input of the discriminator 8 2 4 Initialising This should only be required if the crate has been switched off The script LECROY will do this with some help from the user otherwise e Stop MACQ if MCS is already running e Disconnect the Frame Start pulse from the TDC or disable it elsewhere e Reset the ECC push the switch to Reset and back to Norm Wait for it to initialise 10 seconds message appears on the terminal if attached ECCOP SETLAM 3 20 assuming crate address is 20 ECCOP SETLAMES 20 ECCOP COMMAND LOAD somesdisk some dirILTDCFF S ID 4 20 ECCOP BOOK 1 20 this runs the downloaded code more messages appear on the terminal Reconnect or re enable Frame Start May give more messages on terminal Now start MCS if it was not already running MCSCONF gt SET MACQ DEV LTDC CRATE 20 FIRST 1 NDEV 1 NHIS
29. it of the probe 5 Gauss and in any direction This mode is activated by F0 in MCS e Manual the probe is read but its value is not used The currents are left at the last set values or you can type in new values This is activated when one of the other magnets is selected in MCS e Dead Reckoning the probe value is read but not used The currents are adjusted as the main magnets on the other instruments vary to keep the field in DEVA steady You can adjust the field setpoint Either Hold Current or Dead Reckoning must be used if you are applying a field with the main longitudinal or transverse coils otherwise the zero field system will try to cancel it out DEVA Manual 15 5 Data Acquisition 5 1 Electronics Either the DASH2 system as used on EMU or MUSR or the Lecroy TDC can be used The Lecroy offers bin sizes down to 0 5ns for RF free induction decay runs but it is best to select 2ns or above if the high frequency response is not needed as the bin sizes are non uniform at faster settings 5 2 MCS MCS is the control program used to collect data It is the same as used on EMU and MUSR For historical reasons the computer is called MUT not DEVA together with related things like the account names and disks 5 2 1 Running MCS Log into the Alpha workstation MUT as user MUT Ask your local contact for the password You should get a DECterm window Type MCS to start the data acquisition program which wi
30. ively use the FTP command on VMS or WS FTP on the PC to PUT files to your own FTP server Data recently collected is in MUT DISKO DATA MUT Rannnn RAL and temperature logs in MUTS DISKO DATA MUT TLOG Rannnn TLOG Data restored from the archive is in SCRATCH DISK MUTMGR RESTORE Files created by UDA CONVERT_ASCII etc are in SCRATCH DISK MUT01 USERS areaname Raw data files must be transferred as Binary TLOGs as ASCII There is no FTP access into the PC network or off site access to shared PC drives 6 4 2 CD ROM The PC in the cabin has a CD writer Files should be copied to the local disk first Ask your local contact for a blank disk If you are taking raw data files you should also take a copy of the dead time calibration file 6 5 Archiving All data is written to the ISIS data archive as soon as it is saved from MCS The original files are kept on the local disk as long as space permits usually a year or so To restore data for runs run to run2 inclusive type in VMS RESTISIS mut run run2 and for temperature logs RESTISIS 1 mut run run2 Data is put into SCRATCH DISK MUTMGR RESTORE where our standard programs know to look for it Use RSTATUS to show the progress Some files are on tape and must be manually loaded during the next working day More recent files may take only a few minutes to return DEVA Manual 20 7 UDA 7 1 Introduction UDA is the simplified USR data analysis program There are three menu
31. ll open some more windows DEVA Manual 5 2 2 Commands NEW begin a run Asks for details for the file header does NOT actually set the temperature etc STOP RUN pause data collection STOP RUN AFTER ee arranges to pause the run when ee million positrons MEvents have been counted then you get a message and beep START RUN resume data collection CLEAR throw away data collected so far this run SAVE save the run and last chance to change the label SET TEMP SET t set the temperature of the cryostat to t K SET TEMP GASZMAN sets the helium valve to manual operation leaving it at the same setting SET TEMP GAS MAN m set the valve to position m 0 to 99 9 SET TEMP GAS AUTO sets the valve to automatic when the next setpoint is sent SET MAG SET m set the field to m Gauss EXIT end MCS RECOVER read in saved temporary data after a crash then use SAVE Q filename execute the script filename COM containing MCS commands SYS cmd line execute DCL command cmd line FO select zero field and enable auto zero feedback all main magnet supplies off LFO set up Longitudinal supply ready for use set to zero TF20 set 20G transverse field for calibration FLOW_ITC502 set up for the low temperature flow cryostat HTFLOW_ITC502 set up for the cryofurnace LECROY set up the Lecroy TDCs DASH2 set up the DASH2 TDCs SET MACQ RG
32. n off the diaphragm pump Open the needle valve to 99 9 Wait for the pressure on the pumping box to reach atmospheric Remove the transfer line being careful not to bend its legs and put it in the support tray Exchange the dewar put the insert with the level meter into the new one Warm the transfer line with the hot air blower and dry it with paper tissues Blow helium gas through the transfer line for a minute or two put the red gas line on the cryostat end with a piece of rubber tube e Re insert the transfer line as above If the cryostat was cold the temperature will rise initially until liquid reaches it 3 1 10 Removing the cryostat 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 Fit the protective cover over the cryostat end of the transfer line and put the stopper into the cryostat e Unplug all the electrical leads from the cryostat Close the sample space valve and disconnect the sample space pumping line e Close the vacuum valve and switch off the turbo pump Remove the vacuum line e Unbolt the cryostat and lift it out e Remove the level meter probe and replace the normal dewar neck insert DEVA Manual 14
33. o avoid getting air into the dewar e Connect the helium level meter cable e Remove the protective cover from the cryostat end of the transfer line Check that the PTFE sealing washer is present on the cryostat end of the transfer tube e Connect the needle valve cable Turn the ITC5 on This initialises the valve e Open the needle valve fully press and hold Gas Auto and then press Raise Check it stays in Manual light off e Insert the long leg of the transfer tube in the dewar Be very careful not to bend the transfer tube the second person should support the cryostat end Reduce pressure in the dewar as required with the red valve The tube should end up standing on the bottom of the dewar with about 10cm length still visible e The second person should put the transfer tube into the cryostat once it will reach without bending the dewar leg and tighten the locking nut Turn on the diaphragm pump Open the valve on the pumping box There should be a small but non zero flow e After about 5 minutes the flow should increase as liquid reaches the cryostat and the temperature will start to fall e The Green valve on the dewar should be open and the Red valve closed during operation DEVA Manual 13 If the cryostat is still not cooling after 20 minutes the tube may be blocked with ice or solid air e Remove the transfer tube from the cryostat and dewar e Warm both ends with a hot air blower Dry with paper tissues e Blow cle
34. pping in Ti foil 4 6 Number of 30um Ti foils This measurement was taken in the high temperature flow cryostat It uses a 2mm thick quartz sample with a number of 30um Ti foils in front and a small applied transverse field Signals from paramagnetic muonium in the quartz and diamagnetic muons some in quartz full asymmetry in Ti are measured For a thin sample a degrader of about 70mg cm equivalent to 5 Ti foils can be used including any window on a sample cell The sample itself should ideally have minimum thickness of 40 mg cm It is best to choose a degrader whose own muon signal is easily distinguished from that of your sample and add or remove foils to find the optimum thickness The degrader must be as close to the sample as possible as it will scatter the muons and could increase the muon spot size DEVA Manual 10 3 Sample Environment 3 1 Flow Cryostats There are two flow cryostats e The standard one with temperature range 3 5 to 400K with an exit window e The high temperature cryostat with temperature range 4 to 600K Liquid helium is taken from a storage dewar via a needle valve and passes through the inner tube of a concentric flexible transfer line It flows through a heat exchanger near the sample before returning as gas along the transfer line and to the pump The sample is in a separate static exchange gas at typically 10 15mbar An ITCS temperature controller controls the valve and h
35. rature controller for the cryostat DEVA Flow 1 for the lower temperature cryostat To minimise stress on the sample space windows ensure the cryostat vacuum space OVC is at vacuum before pumping the sample space Pump the OVC lower of the two small taps using a portable turbo pump set 3 1 3 Connections e Cryostat sample space port to a T piece One branch goes to a rotary pump with pressure gauge and valve the other has a valve and adaptor for the red helium line Cryostat heater thermometer to ITC channel 1 Stick thermometer to ITC channel 2 stick A or 3 stick B Transfer tube needle valve to ITC Aux Out Transfer tube gas outlet at the top of the dewar leg to the pumping box via a long plastic tube Serial cable from the optical fibre modem to this ITCS serial port 3 1 4 Mounting the sample Length scale 19mm Side view 70 mm 615 mm Angular Locking screws scale 0 deg Locating pin on top flange End view Sample 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 standard sample mount differs from 70mm adjust the top scale by the same amount The overall length from flange to sample centre is 615 mm DEVA Manual 12 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 perp
36. ry data files produced by MCS into ASCII suitable for reading into general purpose data analysis programs or spreadsheets Type CONVERT ASCII The output formats are e Histograms listed individually USR format e Histograms as columns with a time column at the left easier to read in e Asymmetry and its error bars There is an option to apply dead time correction to the data Depending on the format you can also specify alpha the detector grouping and time zero A batch of files can be converted at once 6 2 2 TLOGGER Type TLOGGER to run the program to plot out the temperature log files Printouts are left in files named PGPLOT PS in the current directory with one file version per run plotted Print them with PRINT QUEUE SYSS LSR10 PGPLOT PS 6 2 3 RUMDA This is available on VMS See the separate manual 6 3 WiMDA This is set up on the PC in the cabin See the separate WiMDA Manual for instructions You should make your own subdirectory under D users and store temporary files there The PC disks are NOT backed up and old files may be deleted to free up disk space so take a copy of anything valuable when you leave The data is accessed via the shared drive NDAVMS MUTDATA From other PCs on site you may need to connect to it before WiMDA can load data DEVA Manual 19 6 4 Taking your data home 6 4 1 FTP From outside ISIS connect to isisa nd rl ac uk and log in either under your own account or MUTOI Alternat
37. s 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 that 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 method 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 7 2 Running UDA To access UDA from account MUSROI 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 7 3 The Main Data Menu 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 Read a MCS run file in the format used by the data a
38. temperature or field this also makes the script run faster as it doesn t have to wait for stabilisation each time T20 add a T20 measurement run selects Transverse field and sets it to 20 Gauss collects data then selects the Longitudinal supply again Delete remove an entry Undo reverse the last change Read read in a previously saved script for editing Write write the script to disk so that MCS can run it Print print a summary of the script if you do this after Write it puts the script name on the printout Help simple online instructions Quit return to MCS or the DCL command line Use the PAGE UP PREV and PAGE DOWN NEXT keys to scroll through the script if it is too long to fit the screen Putting KEEP for both the field and temperature of the first entry means it assumes you will have already set the temperature field and started the run and the script only waits for the required counts Putting a count limit of 0 for the last run means it leaves the run counting when the script finishes and you have to stop and save it manually To scan temperature or field type first last step at the Temperature or Field prompt instead of a single number The ast value wil be rounded if required to give a whole number of steps of the size specified The number of steps calculated is printed as confirmation You can scan up or down enter a positive value of step in both cases You cannot scan temperature and field at the same time
39. tes every 10 minutes 9 1 2 Kicker The racks in the kicker control area down the steps behind EMU are Momentum slit do not Kicker HV supply Kicker monitor scope Old UPPSET unit touch not in use Kicker main control panel Beam slits for each Thyratron Separator HV supply instrument HV for Cerenkov start pulse detectors If the kicker trips off DEVA and EMU have no beam and MUSR will have a double pulse with twice the usual rate Some lights will be lit on the control panel but the HV supply will be off Instructions for resetting it are attached Check with the other users before doing anything The kicker status is indicated in the MCR someone from the crew may reset it 9 1 3 Beamline Magnets When one of these trips the beam may be lost completely or just reduce in rate and have a huge spot size Magnets Q1 Q9 B1 2 and the Separator are common to all three beamlines B1 2 goes off if any of the Muon Beam Off buttons are pressed and the white lights will come on in all the areas Warning it is possible to press a button gently accidentally without it latching in yet trip the beam Septum A and Q10A Q12A are for the DEVA branch only B is MUSR C is EMU The Switchyard magnets are normally off The magnet supplies are located on the platform at the far end of the hall Each position is labelled with the required current for that magnet
40. the range 1000 to 2000 volts depending on the individual tube s properties Select the channel to display by pressing CHANNEL and UP or DOWN Change the setpoint by pressing VOLTAGE and UP or DOWN Turn all channels on or off with the HV ON and HV OFF buttons If a detector develops a light leak large background number of counts in the later time bins turn its voltage off to prevent damage 2 5 Asymmetry shift with field The high magnetic fields affect both the trajectory of the positrons and the sensitivity of the photomultiplier tubes and can cause small changes of asymmetry 23 0 22 8 m normal mounting a 0 79 k O stick reversed a 0 91 N N D 22 4 asymmetry bv 22 0 21 8 0 500 1000 1500 2000 Field G The above graph is for a silver plate in two positions in the flow cryostat If this matters for your experiment you should perform a similar measurement with a setup as close to your actual experiment as possible DEVA Manual 8 2 6 Time zero This is the average arrival time of the muons in the pulse measured from the start of the histogram It is calibrated by measuring muon precession in a series of different transverse fields and extrapolating back to the point when all the phases are equal The latest value is saved in the file basetime uda kept in MUTSDISK MUTMGR MUT USERS UDAJ and copied to the current directory when setting up the data analysis program UD
41. u is equivalent to 1 v and y Bo 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 7 7 2 Transverse field Function Name Definition 11 Lorentzian with freq a cos t exp At 12 Gaussian with freq a cos ax exp At 13 LX exp Stretched Exponential with a cos t f exp At freq E 14 Abragam with freq a cos t 4 exp A7 exp t T 1 t T 7 8 Time zero UDA reads the file basetime uda to get the value of time zero used in the fits See section 2 6 for the definition DEVA Manual 23 8 RF and other special setups There are cables between the area and the cabin labelled X1 X2 X3 In the cabin these cables come to the patch panel at the bottom of the rack together with the Cerenkov signal cable C3 and the Extract Trigger cable EX3 8 1 Timing and Acquisition Normal setup the Cerenkov goes via a discriminator to the Frame Start on the TDCs Red Green from the TDC can be connected via one of the cables to the RF rack Usually the Extract trigger will be used to time the RF pulse Special setups the Cerenkov or ISIS Extract Trigger signals can be used to trigger the RF which in turn triggers the data acquisition 8 2 The Lecroy TDCs 8 2 1 Specifications Bin width selectable 0 5 to 16ns in powers
42. vent may be counted The minimum time to resolve two events is the dead time for that detector This effect causes distortion mainly at the start of the histograms when the muon count rate is highest Asymmetry plots tend to hide the distortion as both forward and backward counts are reduced The data can be corrected for this effect our data analysis programs do this However at very high count rates the correction becomes inaccurate A count rate of 20 30 Mevents hour is a reasonable compromise between high distortion and inefficient use of the beam The most recent calibrated dead time values are kept in the file DTMPAR DAT in MUTS DISK MUTMGR MUT_USERS RUMDA Another copy of this file is in the data directory MUTS DISKO0 DATA MUT or NDAVMS MUTDATA as seen on the PC If you are analysing older data old dead time files are preserved with names DTMPAR date DAT DEVA Manual 9 2 8 Muon stopping range and sample thickness The muons are produced with energy 4 MeV but slow down by interaction with matter Their range is dependent mainly on the mass per unit area Some of this range is taken up by the beamline and cryostat windows Ideally all the muons should stop in your sample not the window or the back of the sample cell Range mg cm 0 20 40 60 80 100 120 paramagnetic fraction O diamagnetic fraction some muons in each e Asymmetry 96 all muons reaching quartz all muons sto
43. zontal position e The blue lights in the area come on to indicate that the beam is on 1 2 2 Opening the area If you want to leave the field on first turn the Helmholtz Interlock key to the horizontal position and leave it there Otherwise it may be necessary to reset the magnet supply next time it is used e Press Lower e Once the blocker has closed and the blue lights have gone out you can remove the master key from the interlock box e Put the master key in the interchange box and remove one of the other keys e Unlock the area door DEVA Manual 4 2 The Beam 2 1 Steering The alignment laser mounted on the beam stop indicates the beam centre The cryostat should be lined up with it X on tail or centre of exit window by adjusting the nuts on the mounting plate There is a vertical steering magnet controllable from the Farnell supply in the cabin normally left at zero switched off It will give 4 mm Amp with ve current moving the beam UP A limited amount of horizontal steering can be obtained by adjusting the septum magnet ask your local contact about this Both reduce the beam intensity if steered too far 2 2 Slits and sample size The slits adjust the horizontal spot size and also the intensity of the beam count rate although the spot size reaches a minimum below slits 10 The vertical size remains the same Pictures from the beam camera for slits 8 and slits 60 the outline of the camera s scintillator
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