Prisma Instrument Manual RAL-TR-1998-049
Contents
1. PRISMA has a number of detector modules that are used for different types of experiments These modules are frequently referred to locally as PRISMA n where n 2 3 or 4 They are detailed in Table 1 Detector module Local name Number of Range in Horizontal analyser energy collimation detector transfer after sample systems meV minutes General purpose PRISMA 2 0 100 60 diffraction inelastic High resolution PRISMA 3 0 40 30 or 60 inelastic Diffraction PRISMA 4 N A 10 or 30 Table 1 Characteristics of the three detector modules The sections that follow give a basic outline of the layout of the spectrometer on the ground and perhaps more importantly for the user the different functions of the various terminals and computers in the PRISMA cabin This is because unlike most ISIS instruments but more in common with a conventional triple axis spectrometer PRISMA has a significant number of independently moving parts and hence operation is a somewhat involved process which requires the use of a purpose written program called PRISMA as well as the usual commands to the DAE and CAMAC PRISMA User manual 1 1 The PRISMA cabin The PRISMA cabin contains a number of terminals and a PC that are used for different and specific jobs The layout is shown in the diagram below You have a choice of two terminals on which to run the instrument if you require hardcopy output during your experiment then2. PRS DR EF1 2 13 5 EF3 14 where arms 1 to 2 are driven to 13 5 meV and arm 3 is driven to 14 meV Note that the lowest possible analysing energy you can use is about 13 meV with the PRISMA 2 27 PRISMA User manual general purpose module and 3 meV with the PRISMA 3 double analyser module The scan is started by typing PRS gt BEGIN after the appropriate time channel boundaries and values of MNS and MNT have been set Also don t forget to read section 4 6 on theupdate and store commands The diagram below shows the scan trajectories for arms 1 to 8 as used in an experiment looking at very broad inelastic scattering in the hhl plane of a frustrated antiferromagnet The parameters for the scan are Q 69 53 and EF1 8 18 meV Each scan trajectory is a curve in the three dimensional Q F space and the diagram shows these trajectories projected onto the Q plane The E axis is thus out of the page The slanting straight lines are the projections of the scan trajectories and the curves that cut across these trajectories represent constant energy contours We only show contours between 10 and 10 meV in this diagram in steps of 5 meV OM 69 PHI1 53 EF1 8 18 meV 2 0 o o 4 1rFo o o 4 o o ES eque e Oo CJ ope Oo O 4 O 1 2 h h 0 28 PRISMA User manual 4 5 Using Command Files to Control PRISMA Command files may be written to control the instrument and are best
3. handed axes so that if you were looking at a cubic crystal with the usual scattering plane containing the 1 1 0 1 1 1 and 00 1 directions and the 1 1 0 vertical you would type 16 PRISMA User manual PRS gt SE PX 1 1 10001 iv Change the time channel boundaries by typing PRS gt SE START 1000 12000 10 PRS gt SE MNT 1 MNS 1000 v Drive the arcs to zero if they are not already zeroed by typing PRS DR GX 0 0 PRS DR GYz0 0 vi We now assume that the detector has been set up by your local contact in the standard way with detectors 13 to 16 used for diffraction Drive 5 to 90 by typing PRS DR PHI13 90 vii You are now ready to begin an alignment scan You should start with PRS SC OM13 16 46 5 0 1 NP 11 This command tells the spectrometer to measure the signal in detectors 13 to 16 while only Q is scanned where the crystal moves by 1 in total around Q 46 5 by an 11 point scan with a step size of 0 1 Since we are using 4 detectors the net Q angle covered is 4 in this one scan At each point in the scan a printout of the integrated counts in each detector is given in the control program When a large signal is seen in any of them typically over 1000 then a Bragg peak is going into that detector You can look at the intensity in each detector as a function of the sample d spacing by using the program PP in GENIE Follow these steps for using PP a Run GENIE in a window on the work
4. The raw data must first of all be processed in GENTE to produce the file CRITICAL OUT The macro VCRS is used for this purpose A step by step guide to processing diffraction data to produce a colour plot is given here i Create a rebin file which the VCRS macro uses to bin your data as it is processed This file should be in the GENIE command file format and should have a relatively short name such as BIN COM for instance The file consists of only one line which is a rebin command for workspace 4 so an example might be gt reb w4 0 5 0 01 1 5 The limits are the wavevector transfer in units of A and the binning should be chosen so that there are no more than 500 bins in the workspace In this example there are 100 ii Go into GENTE and type gt gt vers iii Enter the name of the rebin file iv Answer 1 to calibrate your data with a vanadium run v Type in the run number of the vanadium calibration and answer the usual questions about the sample parameters and the detectors to be analysed vi Answer the next question about smoothing the vanadium with a 1 vii When the vanadium run has been analysed the macro asks for the first run number of the data set to process The macro will then process this and come back asking for another The output is written to a file called CRITICAL OUT and subsequent runs will be appended to it When you have processed all of the runs required f
5. so that any subsequent operations of CC with other data sets will create anew CONTOUR OUT rather than appending to the old one ix An optional step is to create a normalisation file at this point It is not necessary to have one just for a rough look at data in PRSPLOT but since the detector efficiencies may vary quite markedly you will need one to produce good plots The normalisation file has the following format the first line is the run number and the following 16 lines contain three columns with the detector number a scale factor and background After that there may be another run number and 16 more rows etc if your CONTOUR OUT file contains data from more than one run The scale factors are obtained from the vanadium calibration that you should have performed at the start of your experiment PRSPLOT will alter data according to the following formula modified data scale factor original data background Here is an example normalisation file 2235 376 0 978 1 349 0 645 8 1 2 3 4 1 5 1 037 6 7 8 9 301 0 992 1 035 EI E C CX D C2 CO OO KA CD OOO OD CO CO Co CO Q C50 QC 0 0 0 Q 0 OC 0 Q c 5 200140 PFHn cGco OOOO N L3 py pes p ps poe OO rmt 2235 LST 971 N H C2 C C CO C Cc WwW C3 and so on x The next step is to start PRSPLOT simply by typing prsplot answering the questions about terminal type MX11 if you are usi
6. Angular range Resolution Notes N2 95 K Methane poisoned at 2 25 cm 9 035 m Horizontal 15 Vertical 23 Width 30 mm Height 50 mm Above sample table 0 635 m Above goniometer 0 246 m 3 250 meV 1 052 m 1 037 m 5 He 10 atm elliptical gas tubes at 90 Final flight path 1 056 m 0 573 m 0 170 m Width 45 mm Height 55 mm Width 10 mm Height 40 mm 16 12 5 mm He gas tubes Reuter Stokes 29 Horizontal 60 Vertical 5 12 meV E 30 meV 120 to 40 dEgE 0 04E 4 4 58 Germanium 1 The PRISMA 2 detector is normally operated with 12 inelastic detector arms and 4 diffraction detector arms ie analysers removed from inelastic arms 2 It is not possible to operate PRISMA 2 and PRISMA 3 simultaneously 44 PRISMA User manual PRISMA 3 Final flight paths Sample to front analyser LSF Front analyser to rear analyser LFR Rear analyser to detector LRD Analysers Pyrolytic graphite 0 0 2 Detectors Angular separation of detector arms Final collimation Final energy Resolution Notes 0 600 m 0 045 m 0 211 m Width 45 mm Height 55 mm 5 1 2 10 atm He gas tubes Reuter Stokes 10 Horizontal 30 nil 60 nil 30 60 Vertical 5 3 meV lt Er 12 meV 30 60 dE E 4 60 nil dE Er 2 3 0 5Es 1 Lengths marked are defined when LFR is at 90 to LSF 2 PRISMA 3 can be operated simultaneously with PRISMA 4 The
7. Calculates the average temperature of a run Other useful macros gt gt FF Fits a workspace with Gaussian Lorentzian or Kropf or Reverse Kropf functions gt gt TT Transforms a workspace from time of flight to wavelength incident energy d spacing or wavevector gt gt ERR Rescales error bars which are too small 5 2 Inelastic Data Inelastic spectra from individual detectors may be transformed into energy transfer using the MRX macro in GENTE and then displayed After typing 33 PRISMA User manual gt gt mrx and giving the run number etc the macro asks whether any of the parameters such as lattice parameter analysing energy etc should be changed from what they were stored as when the data were saved For instance you might have decided that the lattice parameters that you typed into the PRISMA control program when you aligned the crystal were wrong and so you can easily change them again at the data analysis stage After that it asks for which detectors are to be analysed and the energy transfer required The useful range is 20 to 100 meV for the general purpose inelastic module For the inelastic double analyser module the range of accessible energy transfers varies considerably depending on the analysing energy used However it is usually more satisfying to create a colour contour plot of the data using PRSPLOT Before this the raw data must be processed using the CC macro in GENIE The follo
8. Dat 4015 nf rte een Or Reine po cit en dual oeste S a eee 23 4 1 Setting Up the Time Channel Boundaries seen 23 42 Vanadium Calibration onere cues ERROR D Pg EE EE Eiei iaeaea 23 4 3 Diffraction Scans hee eus eue e ce dete ep tes 24 4 4 Inelastic Scans eee E E vetet ede 26 Z4 1 The CD Commahd 5 earn RR rt 26 4 4 2 More General Inelastic Scans eese eene nennen nennen enn 27 4 5 Using Command Files to Control PRISMA esee 29 4 6 Ending Pausing or Aborting a Run esee 30 5 Data Analysis and Visualisation eene nennen ener ent ennnneene 31 SLi GENIE Lia sccssssesesaisegevsascascsiaueateostesaveveavsatevvavcaveviausatevsadaevigudatavvan saved vavdaseviaedavevapnsasavvansaveny 31 5 1 1 PRISMA GENIE Data Analysis Programs eese 32 5 2 Inelastic Data PRISMA 2 and PRISMA 3 ccccccccscceseceescecsseeeeseecsseeeeseecnseeeeeeeees 33 5 3 Diffraction Data PRISMA 2 and PRISMA 4 sese 37 6 Summaries ei ln eo te med eee eed ead idee eR eod epa ieu tede 39 6 1 Instrument Control zeit ian lie ee ans 39 6 1 I PRISMA Control eee tee eee e edes 39 6 1 2 PRISMA Supervisor Window eese nne nren nennen enne 39 6 2 Data Analysis and Visualisation sse 40 6 2 1 GENIE iicet ee e e ee ple eret 40 6 2 2 Inelastic Dads iiie RR EPOR ERREUR EU
9. and start the scan with PRS gt BEGIN 4 3 Diffraction Scans When performing a diffraction scan you should consider how much of reciprocal space you need to cover in terms of the Q angle For a single setting of the spectrometer each detector measures a radial scan in reciprocal space so that a set of detectors covers a fan shaped area Since the detectors are 1 apart in for the PRISMA 4 module the separation corresponds to 0 5 in Q In the diagram below we show a schematic view of reciprocal space for a crystal with the fan corresponding to radial scans from 4 detectors 0 0 0 0 1 0 0 5 This corresponds to a single setting of the instrument By rocking Q it is possible to build up a succession of the fans and cover a much larger portion of reciprocal space However the first question to ask is what sort of energy integration do you require in the part of reciprocal space in which you are interested For instance if you wanted to look at diffuse scattering at the zone boundary point 2 5 2 5 0 where there is a soft acoustic mode with an energy 8 meV then you would require that the neutron energy for elastic scattering at 2 5 2 5 0 to be at least several times larger than 8 meV This will ensure a sufficient integration over the soft mode so that the quasi static approximation is fulfilled You can control this by changing the angle Go into PRSCAL on the workstation and use the BR command For our example using the defau
10. peak spot on 3 3 PRISMA 4 Diffraction detector module The PRISMA 4 detector module has 16 detector tubes separated by 1 in so if 0 90 then 15 75 The operation of aligning a single crystal using PRISMA 4 is almost identical to that of PRISMA 2 except that all 16 tubes can now be used For instance you might begin with the following type of scan 20 PRISMA User manual PRS gt SC OM1 16 45 0 1 NP 5 3 4 A Note of Caution The procedure outlined in the previous section regarding single crystal alignment is really for the rare case of a completely trouble free and easy alignment In practice numerous iterations around several of the steps may be necessary Difficult alignments are usually a result of a poor prior alignment of the sample in its mount particularly if the scattering plane of the crystal is tilted significantly from the horizontal in the mount The arcs on the PRISMA goniometer can only be tilted by 15 in any direction and less if you are using a cryostat which means that you may find that such a sample cannot be aligned during the first attempt on PRISMA If this is the case it must be removed from the beam and the excess tilt corrected on the mount itself This can turn into an extremely time consuming and tedious process and it cannot be emphasised too strongly that you should align your sample as well as possible in its mount using x rays before the start of the experiment This should hopefully el
11. peaks then this is probably what has happened and you should try scanning around the c position instead which may not be so badly misaligned in tilt In this case try PRS SC OM13 16 43 5 0 1 NP 11 and then around Q 39 5 47 5 and so on The following steps assume that you have found a but will work just as well if you have found c instead by substituting the appropriate 2 values Remember that for a detector at d 90 the a position should be Q 45 while the c position should be Q 45 ix When you have found the rough position of the a direction by using the multidetector array it is easiest to then complete the alignment by bringing around the a reflections into detector 13 at 90 First we need to work out the value of Q to bring a into the new value of 4 90 If in the multidetector scan you had found the strongest signal for a in detector 15 at Q 37 4 say then the following formula gives the value of Q that you need as 1 Q 90 Qet 7 90 9 where in our case Q9 37 4 However you need to know the value of the angle for detector 15 This may be obtained by the command PRS gt PR ANGL 18 PRISMA User manual and a complete list of all of the current spectrometer angles will be printed For our example we find that PHI15 86 which means that our new value of Q is 35 4 using the above formula x You should now perform a fine scan around the new Q value as a check PRS
12. prisma abort a prisma update a prisma store a prisma cset temp log Scan in omega angle centred on Q and collecting the data in detectors dj d2 with a step size of AQ Sets temperature TEMP logging on Sets temperature TEMP logging off Changes the setpoint of TEMP to T Pauses the current run so that no data are collected Resumes data collection after a PAUSE Ends the current run Aborts the current run Stores the current data in the CRPT Stores the CRPT ina sav file Turns the temperature logging on 39 PRISMA User manual prisma prisma cset max power lt P gt prisma prisma cset temp lt t gt 6 2 Data Analysis and Visualisation Sets the maximum power to be used to P as a percentage of the highest power available Sets TEMP to temperature t LLLLLLLLLLLLLLLDLLDLLLLLLLDLLLDLLLLLLDLLDLDLLLLLLDLLDLDLLLLLLDLLLDLLLLLLLLLDLDLLLILILLLD Note if you are about to run GEN E or PRSPLOT in your own account on a window on the PRISMA workstation type set disp create node prisma before you start This will ensure that the correct graphics windows are created LLLLLLLLLLLLLLDLLLDLLLLLLDLLLDLLLLLLLDLLDLDLLLLLLDLLLDLLLLLLDLLLDLLLLLLLLLDLDLLLILILLLD 6 2 1 GENIE gt gt tm Toggles between point plotting and histogram plotting mode gt gt d m w lt workspace gt xmin xmax lt ymin gt lt ymax gt Displays the given workspace with markers in point mode gt gt d h w lt w
13. the number To page somebody dial 70 choose option 1 enter the pager number followed by an 11 digit message usually the extension number you are calling from followed by sufficient zeros to fill the message Wait for the tone before replacing the receiver Other numbers RAL extension ISIS Main Control Room 6789 EMERGENCY 2222 ISIS Health Physics 6696 ISIS User Liaison Office 5592 5103 fax Main Gate 5545 42 PRISMA User manual 8 Eating and Drinking 8 1 On site R22 Restaurant Mon Fri Breakfast 0730 0830 Lunch 1145 1345 Dinner 1715 1915 R1 coffee lounge hot drinks snacks Sat Sun 0800 0900 1200 1300 1800 1900 0930 1130 1200 1530 1200 1345 R22 coffee lounge 8 2 Pubs Blewbury The Red Lion Chilton Rose amp Crown East Hendred The Plough Wheatsheaf East Isley The Crown and Horns The Swan Steventon The Cherry Tree Wantage The Lamb The Swan West Hendred The Hare West Ilsley The Harrow Monday Friday 43 PRISMA User manual Appendix A PRISMA Instrument Parameters Beamline Moderator Incident flight path Incident collimation effective Beam size Beam height Incident energy Monitor 1 position Monitor 2 position Line up detectors PRISMA 2 Final flight paths Sample to analyser Analyser to detector Analysers Pyrolytic graphite 0 O 2 Germanium Mica Detectors Angular separation of detector arms Final collimation Final energy
14. the specified workspace d m w lt workspace gt xmin xmax ymin ymax Displays the given workspace with markers in point mode s Writes the plot to a postscript file called POST DAT 6 3 A Final Checklist Before you leave the experiment running for the night quickly go through the following checklist e Interlocks complete e Shutter open e Heater on if necessary e PRISMA IS RUNNING is shown at the top of the dashboard and the Counts section under Monitor of the dashboard is updating at about 16 000 counts every time If the monitor is updating at a much lower or higher rate then there are three possibilities the first is that the proton beam current is low the second is that the methane moderator is not working you can find out about its status by phoning the MCR Otherwise the chopper has stopped which is a job for the local contact 41 PRISMA User manual 7 Useful Phone Numbers In the event of any problems with the instrument computing or sample environment your first point of contact is your local contact failing that any member of the PRISMA team The names and phone numbers of the PRISMA team are RAL extension Home Mark Harris 6397 9 01865 724612 Martyn Bull 5805 9 01865 515520 Uschi Steigenberger 5145 9 813284 To dial a RAL extension from outside dial 01235 44 followed by the extension number To make an external call from a RAL phone dial 9 before
15. upd com In the supervisor window type time_upd lt n gt where lt n gt is the number of hours between saves The command file can be interrupted by typing lt CTRL gt Y Here is a summary of all the commands you need to know from this section All of the commands may be abbreviated to their first three letters update Stores the data collected so far in the current run parameter table crpt store Stores the data collected up to the last update in the file prismaS disk0 prsmgr data prs lt runno gt sav The store command should always be preceded by an update pause Pauses data collection resume Resumes data collection abort Aborts the current run without saving any data end Ends the current run and stores the data in prismaSdisk0 prsmgr data prs lt runno gt raw 30 PRISMA User manual 5 Data Analysis and Visualisation Several programs and utilities exist to help you analyse your data all of which are explained more fully in the other manuals in the PRISMA cabin The first stage of data analysis is always performed inside GENTE and a brief introduction is given here More detail may be obtained from the PUNCH Manual To use the PRISMA data analysis routines from your own account you should add the following line to the login com file in your top level directory Qprisma diskO0 prsmgr login com Note that if you are about to run GENIE or PRSPLOT in your own account on a window on the PRISM
16. A 3 respectively You can find out their current values with the command PRS PR ANAL If the parameters are not correct type PRS SE IANAL 1 DMIN 1 DMAX 12 and you answer NO i e N to the question about whether detectors 13 to 16 should be driven to their maximum angles 4 4 1 The CD Command This command enables an inelastic scan to be performed along a general direction in reciprocal space It takes the form CD h k l Ah Ak Al E These parameters are defined with reference to the analyser detector arm given by IANAL This arm measures a parabolic Q E trajectory about the h k I reciprocal lattice point along the Ah Ak Al reciprocal lattice direction E is the energy transfer where the trajectory crosses the h kl point For instance to perform a scan along the 1 1 0 direction around the 3 2 0 point you might type the following PRS gt CD 3 2 0110 1 5 You should always test out potential CD scans in PRSCAL since there is a possibility that clashes of the analysers and detectors may occur meaning that some configurations are physically impossible for the instrument PRSCAL will tell you if your scan is possible or not as well as giving you a plot of the trajectories in Q E space in order to visualise the coverage Note because of the spectrometer geometry it is never possible to perform a CD scan with a pure transverse or longitudinal polarisation As an example the diagram below show
17. A workstation type set disp create node prisma before you start This will ensure that the correct graphics windows are created 5 1 GENIE GENTE is the ISIS graphics software To run GENIE from any ISIS computer with VMS simply type genie Note unless you wish to look at data in the DAE itself e g during a crystal alignment when the macros DD and PP are used then you should run GENIE in your own account either on the workstation or HORUS or any other DEC Alpha machine If you wish to look at the data currently stored in the DAE you will only be able to do it while logged onto the instrument account with the userid PRISMA Individual x y e datasets are held inside workspaces in GENIE and it is possible to manipulate the y values of each workspace by using the usual mathematical symbols for add subtract multiply or divide For example if you wanted to subtract the y values in workspace 2 from those in 1 and then multiply the answer by 100000 you would type the following gt gt w3 w2 wl gt gt w3 w3 1 0e5 where the result is stored in workspace 3 Note that for this to work the x values for the two workspaces need to be the same If this is not so then you will need to rebin the two workspaces first see the GENIE section of the PUNCH manual To perform more sophisticated manipulations of workspaces the function and transform commands should be used which are also explained in the PUNCH man
18. DERIRUERIEU TS 40 6 2 3 Diffr ction DAA incendie ete itte aee etae pet ere ee evectus 41 0 2 4 PRSPEOP er aui Ui red 41 6 3 A Final Checklist coeno ree ee gree eerte Do etes 41 7 Useful Phone Numbers nite eet Le eem ect en eet tque RR Hv s ee tithe 42 8 Eating and Drinking he Sasi eee ELI Bad ite tec o P Re Ebr de ae e eles 43 8 1 Orissite rene actore to In OD eO ree o ae arbe eub 43 AMD 43 Appendix A PRISMA Instrument Parameters eese nre nennen 44 Appendix B Useful Conversion Factors cceescsesscesesecesecseesecueeseenaeeccsaeceeesecaeeseenaseeceaeeneeneeaees 46 Appendix C Geometrical Relationships For Simple Crystal Systems sss 46 PRISMA User manual Preface to the First Edition This manual is intended as an easy reference guide to help you perform an experiment on PRISMA and analyse the results In this sense it does not attempt to be an exhaustive guide and more detailed information may be found in the various publications and reports listed in the Introduction and in the more specific manuals which describe the operation and analysis programs Copies of all of these are in the PRISMA cabin The additional manuals are The PRISMA Operating Program Manual The PRSCAL Manual The PRISMA GENIE Data Analysis Manual The PRSPLOT Manual The PUNCH Manual Various RAL reports describing cryostat operation Preface to the Second Edit
19. PRISMA User manua l PRISMA Single Crystal Cold Neutron Spectrometer amp Diffractometer User Manual SECOND EDITION M J Harris and M J Bull July 1998 ISIS PRISMA User manual CONTENTS Prefaces to the first and second editions essere eren 3 Beginning an Experiment at TSIS oriens e ae enne nennen e eren nenne 4 T Introduction is S roe Idea ed ee coa pep ei ede tesi duit ee reins 5 1 1 The PRISMA cabin iezeons one pea enti e ODER 8 1 2 The PRISMA Dashboard 5 m ohne eet bete redes 9 1 3 The Layout of the Spectrometer sese 11 2 Installing a Sample on PRISMA sese nennen nennen nennen trennen enne nnen rennen 12 2 1 Room Temperature Experiments sss 12 2 2 Low Temperature Experiments Using the CCR eee 12 2 3 Orange Cryostat Experiments eese ener nren etre 13 2 4 Furnace Experiments 22 000 noia uo VOD D ee UR mi 14 3 Setting Up an Experiment 2 npn re HE EPOR RP THER Pr RR de ebeta 15 3 1 PRISMA 2 Single analyser detector module sss 15 3 2 PRISMA 3 Double analyser detector module sse 20 3 3 PRISMA 4 Diffraction detector module 20 JAA Not o Caution oo eto aO debui pe Ut e o REDE beers 21 3 5 Temperature Control o naues e ee ete E eet eL prete edite 21 4 Collecting
20. PRS gt DR OM 45 PRS gt SC GY13 0 0 1 0 NP 9 After you have optimised GY the crystal is aligned and you are ready to begin collecting data which is described in section 4 3 2 PRISMA 3 Double analyser detector module The PRISMA 3 detector module has 5 detector tubes and is always configured so that each tube is behind a set of double analysers The detectors are separated by 10 in so if Q 90 then s 50 The operation of aligning a single crystal using PRISMA 3 is almost identical to that of PRISMA 2 The principal difference is that a rough alignment us usually performed using some diffraction tubes fixed to the side wall of the instrument A strong reflection is then brought round into the double analyser module for a careful alignment Begin by scanning for Bragg peaks in the fixed detectors These will be set up to be detectors 6 10 while the PRISMA 3 detectors will be 1 5 For example PRS gt SC OM6 10 45 1 NP 11 When you have found a strong Bragg peak maximise the intensity using the arcs and then bring the peak into one of the PRISMA 3 detectors First of all you need to know the appropriate angle Let s say that one double analyser arm has been set up with an analysing energy of 5 meV and we want to look at the 1 0 4 peak Go into PRSCAL and type the following CAL bre 104 500 The program will respond with the appropriate Q and angle you need to see the peak You should do a small scan to get the
21. RISMA GENIE Data Analysis Manual The first three macros in the following list the alignment macros may be used to look at the current run simply by typing DAE when the run number is requested In this case you must be running GENIE on the PRISMA workstation For the other data analysis macros you must be running GENIE on a computer other than PRISMA and if you wish to look 32 PRISMA User manual at the current run you must first have done an update and store see section 4 6 and within GENTE have typed gt gt set ext sav Also when the particular macro asks the following question Enter file extension default is RAW reply with sav Macros useful during alignment may be used for analysing the DAE gt gt DD Displays diffraction data for a single detector scan gt gt PP Displays diffraction data for a multi detector scan gt gt AA Integrates an Q GX or GY scan so that a counts vs angle plot can be made Macros for analysing inelastic data gt gt MRX Transforms time of flight inelastic spectra to energy transfer spectra gt gt cc Transforms raw data to PRSPLOT format for contour plots Macros for analysing diffraction data gt gt VCRS Transforms raw data to PRSPLOT format for contour plots Macros for analysing temperature during a run gt gt TP Creates a temperature plot from a log file gt gt TPC Creates a temperature plot from the DAE gt gt AT
22. ask your local contact to set up the hardcopy LA120 terminal If not then you will be using a window on the PRISMA workstation A word of warning is appropriate the PC to the left of the LA120 hard copy terminal should NEVER be touched and you should NEVER exit from the PRISMA control program whether it is running on the LA120 or a window on the PRISMA workstation These two devices control the whole instrument and should not be tampered with Occasionally it may be necessary to restart the control program if the workstation has crashed This is simply achieved by logging the workstation back on using the account name PRISMA the password is obtainable from your local contact and then running the control program by typing PRISMA in a DECterm However this will hopefully not be necessary during the course of your experiment and unless a scan or job file is running the control window will always show the prompt PRS gt indicating that PRISMA is idle and is waiting for a command PC LA120 f PRISMA workstation K printer SYS LSR7 PRISMA cabin temperature controller SOPHIA Fig 3 The PRISMA cabin PRISMA User manual 1 2 The PRISMA Dashboard Before going on to describe the hardware of the spectrometer itself there is one more feature of the control operations which should be mentioned and that is the instrument dashboard This usually runs in the top left hand window of the PRISMA workstation and displ
23. ays most of the current instrument and sample environment parameters We shall refer to this as the supervisor window from now on Note that while the dashboard is running in this window it should only be used for certain commands The dashboard may be turned off by typing prisma prisma stat off and turned on again by typing prisma prisma stat on in the window We shall now describe the most important parameters displayed in the dashboard which are indicated in this diagram PRISMA is RUNNIN RUN XXXX Monitor Current run time Current XXX XXX Counts xxx Fig 4 The PRISMA dashboard always displayed in a window on the PRISMA workstation in the Control area of the desktop In the top left hand box of the dashboard are shown e the title of the current or most recent run e the users initials e useful telephone numbers PRISMA User manual The run title and user information may be changed with the change command which is described at the start of Section 3 In the lower left hand box of the dashboard are shown e the duration of the current run in days hours minutes and seconds e the ISIS proton current in uA and the total number of protons since the run started in LA hours The box to the right of this shows e the total counts measured in Monitor 1 before the sample position In the right hand most box are shown the following CAMAC parameters e the value of the set block TEMP usually th
24. cilities exist at your home institute you should use these To illustrate the alignment procedure we will describe a single crystal alignment for a crystal of trigonal NaNO3 where the scattering plane contains the two orthogonal symmetry directions a and c This procedure may easily be adapted for any other crystal by following the steps given here 15 PRISMA User manual First of all place your sample in the goniometer so that the c direction is along the GY arc as shown in the next diagram incident beam detector c goniometer Fig 6 A schematic view of PRISMA from above showing the goniometer with the GX and GY arcs and the sample orientation discussed in the text You are now ready to align the crystal on the instrument Follow these steps typing all of the relevant commands into the PRISMA control program running either on the workstation or the LA 120 1 Open the shutter ii Change the title on the dashboard by typing something like this PRS TI ALIGNMENT OF NANO3 CRYSTAL AT RT iii Type in the lattice parameters like so PRS SE A 5 07 5 07 16 82 120 90 90 These are the lattice parameters in the order a b c y amp D The scattering plane is set like this PRS SE PX 1 210 00 0 1 which tells the spectrometer that the 1 0 0 reciprocal lattice vector i e a is along the GX arc and that O O 1 i e c is along GY The convention is of course to use right
25. ct to this arm Also each analyser detector arm may be considered to have its own individual value of and since the separation of each arm from its neighbours in this module is 2 in then if 90 then 0 6 60 for instance background chopper sample moderator analyser1 Diffraction arm detector n Inelastic arm detector1 Fig 1 A schematic plot of PRISMA showing the setup for simultaneous inelastic and diffraction runs In inelastic mode the neutron counts are measured as a function of the time of flight so that the signal in each detector corresponds to a scan along a parabolic Q E path through S Q E the dynamic structure factor Since there may be a total of 16 analyser detector systems in all each of which measures along a parabolic path PRISMA allows for a two dimensional slice through Q E space for each ISIS pulse in a single setting of the instrument and sample In the case of a diffraction measurement each detector integrates over all energies of the scattered neutrons so that the result is a radial elastic scan in reciprocal space The vector diagram Fig 2 shows this for a single detector PRISMA User manual Fig 2 A diagram showing the scattering vectors for two times of flight t and t in a diffraction experiment using a single detector Q is the wavevector transfer k and ky are the incident and final wavevectors respectively and is the scattering angle i e 20
26. e controlling sensor e the value of TEMP 1 usually the temperature closest to the sample e the value of LAKES if a Lakeshore temperature controller is being used 10 PRISMA User manual 1 3 The Layout of the Spectrometer The schematic diagram below shows how the detector modules and sample environment equipment are located in the PRISMA sample area with respect to the incident beam N imonic chopper Incident beam e Detector module To beam stop M odule rotation table PRISMA Double analysers 11 PRISMA User manual 2 Installing a Sample on PRISMA The vast majority of experiments performed on PRISMA use single crystal samples but since crystals never come in standard sizes or shapes an individual mount must always be made up for each sample This can be a time consuming process and it is always best to do this well before the start of the experiment to minimise time spent in setting up It is also recommended that the sample be well aligned in advance on its mount usually with x rays because it can sometimes be a difficult job to do entirely from scratch on the spectrometer If the experiment is to be performed at room temperature or in a furnace the mount should end in a screw with an M8 thread This is standard for all ISIS instruments The sample should be supported by the mount on this thread and the whole mount should not be more than about 10 cm long in total i
27. e development of the PRISMA spectrometer at ISIS Steigenberger et al 1991 Nuclear Instruments and Methods in Physics Research B53 87 96 The PRISMA Spectrometer at ISIS Steigenberger et al 1990 Rutherford Report RAL 90 004 A novel double crystal analyser system for the PRISMA spectrometer at ISIS Bull et al 1997 Physica B234 236 1061 1063 The resolution characteristics of PRISMA are discussed in New considerations on a multi analyser spectrometer resolution function Hagen and Steigenberger 1992 Nuclear Instruments and Methods in Physics Research B72 239 254 In addition there is a great deal of information about the instrument and HTML versions of the manuals on the World Wide Web at PRISMA has a dual role as both a neutron diffractometer and spectrometer In diffraction mode it is identical in principle to the other single crystal diffractometer at ISIS SXD This principle is described on the following page When operated as a spectrometer it is perhaps understood best by comparison with a conventional triple axis spectrometer Both machines use Bragg reflection from analyser crystals to select the neutrons scattered by the sample that will ultimately be detected However unlike a triple axis spectrometer PRISMA has an array of independent analyser detector arms instead of just one Also instead of having a monochromator crystal to define the incident neutron energy PRISMA utilises the time of flight tech
28. edited on the workstation The correct directory to use is prisma disk0 prisma run and the command file should end with the extension JOB An example command file called EXAMPLE JOB follows illustrating a sequence of most of the commands you might need Note these commands may typed into the file directly without starting each line with a as you would in a usual VMS command file It is very important to note that the command to change temperature has a slightly different format to the usual CAMAC command you would use on the workstation se start 15 19995 1 sets the time channel boundaries for a run se mns 900000 mnt 1 sets the duration of the scan to be 900000 frames cset temp log sets TEMP logging on cset templ log sets TEMP 1 logging on ti example cd 0 6 4 Q 0 1 3 5 change the title of the scan to example cd cd 0 6 4 0 0 1 3 5 runs the scan for 900000 frames vx c cset temp 250 sets TEMP to 250 K vx c cset templ 250 sets TEMP 1 to 250 K dr phi9 2 50 drives the angle for detector 9 to 50 se mns 3000 sets the duration of each time period to be 3000 frames i e one minute per point sc om9 16 30 0 1 np 11 omega scan using detectors 9 to 16 se mnt 0 sets the duration of the scan to last until operator intervention i e END or ABORT is typed in the supervisor window ti example at 250 K inelastic scan change the title of the scan begin runs the scan until opera
29. ere is a choice of two furnaces for PRISMA experiments the dedicated PRISMA furnace or a RAL furnace The disadvantage of the PRISMA furnace is that it cannot be used for temperatures above about 800 K but it can hold a relatively large sample up to about 60 mm in diameter On the other hand a RAL furnace will go up to about 1300 K but is more restrictive so that the sample must be 35 mm or smaller in diameter The sample mount is screwed directly into the centre stick of the furnace both PRISMA and RAL types The sample sensor should then be bent so that it is as close as possible to the sample without being directly at the beam height As with the CCR and orange cryostat it is assumed that the furnace has already been installed and set up by the local contact 14 PRISMA User manual 3 Setting Up an Experiment First of all the information displayed on the dashboard should be changed for your experiment and initials since this is stored with the data you will collect The change command allows you to edit the dashboard information and to modify the icp instrument control parameters In the supervisor window on the workstation the one with the dashboard type the command prisma prisma change can be abbreviated to cha which initiates the dashboard editor Move between areas using the cursor keys and over type or toggle as instructed The first page contains title and user information and only this should be changed To
30. exit press the PF1 GOLD key then an e The PF1 key is on the keypad to the right of the keyboard Note that if you only want to change the run title in the dashboard you can do this from the PRISMA control program by typing PRS gt TI lt your title gt It is a good idea to include all details about temperature type of scan etc in the title For example PRS gt TI CsNiCrF6 at 9 K phil 53 om 10 ef1 8 18 d9 16 0 0 If you intend to set a command file running to change scans or temperature automatically the experimental run title can be written directly to the dashboard by using the TI command in the command file This is detailed in section 4 3 3 1 PRISMA 2 Single analyser detector module The PRISMA 2 detector module has 16 detector tubes and is usually configured so that the first 12 have analyser crystals in front of them for inelastic scattering while the last 4 have no analyser crystals and so are used for diffraction The 16 tubes cover a range in the p angle of 30 so if 0 90 then 0 6 60 The operation of aligning a single crystal using PRISMA 2 is now described Alignment of the sample is usually the most demanding part of a PRISMA experiment which is why it is always best to have a prior alignment of your crystal in its mount before starting the experiment Currently an x ray Laue camera and the ALF neutron alignment facility are periodically available in the Laboratory for this purpose but if x ray fa
31. gt SC OM13 29 4 0 2 NP 5 You can see the data measured by the scan as a function of d spacing by using DD in GENTE which is similar to PP but is for a single detector scan xi Drive the Q angle to the maximum of this scan and scan around the tilt angle Gx by typing PRS gt SC GX13 0 0 1 0 NP 9 You may wish to do a finer scan after this to define the maximum in GX more precisely You should then drive the GX angle to the peak by typing PRS gt DR GX lt peak in GX xii Now we are ready to set the zero of the Q angle Usually we define Q 45 when the a direction bisects the angle between the incoming beam and the detector at 90 This is the situation shown in the previous diagram and is the alignment that we have just obtained Print out the zero angles by typing PRS PR ZERO We want to adjust the value of the parameter ZOM so that the Q setting becomes 45 We use the following equation ZOMnew ZOMolg t 22445 Where ZOMga is given on the printout and Q is the current angle Reset ZOM by typing PRS SE ZOM lt new value The computer should reply by typing the value of ZOM and that OM 45 00 ora number very close to it Note in the general case when you want to reset the Q value from O4 to O4 the formula you should use is ZOM new ZOMold Qold Qnew 19 PRISMA User manual xiii We are now ready to align the c arc Drive Q to 45 and do a GY scan by typing the following
32. iminate the possibility of one or more late nights at the start of your experiment 3 5 Temperature Control The temperature can be controlled either from the dashboard or using the PRISMA control program It is conventional to turn the logging on so that you can follow the temperature on the dashboard the TEMP TEMP1 or LAKES blocks within the control program using the following commands PRS gt CSET TEMP LOG PRS gt CSET TEMP1 LOG PRS gt CSET LAKES LOG Now change the temperature on the supervisor window of the workstation prisma prisma cset temp lt your desired temperature gt prisma prisma cset templ lt your desired temperature If the change involves heating you may need to alter the power limits Try prisma prisma cset max power lt P gt prisma prisma cset max powerl lt P gt where P is a percentage of the total available try 10 to start with You may also need to change the operating voltage of the heater This is controlled by a dial at the back of the Eurotherm crate which sits in the rack in the side room of the PRISMA cabin 21 PRISMA User manual The only other thing you may need to change are the PID parameters The usual PID parameters for the PRISMA CCR are 1 0 60 0 and 1 0 respectively Values for other pieces of sample environment equipment are available in HELP by typing prisma prisma help temperature You can then change these parameters prop propl int intl deriv de
33. ion PRISMA has undergone a complete rebuild since the First Edition of this manual resulting in a rather different instrument to that of January 1995 Now that the development of the instrument has reached a quiescent stage this new edition of the manual describes the operation of PRISMA for the foreseeable future PRISMA User manual Beginning an Experiment at ISIS Before starting your experiment you must report to the Main Control Room MCR You will be issued with a swipe card which will let you in and out of the Experimental Hall R55 pick up a film badge from the Health Physics Office opposite the MCR watch the safety video either in the coffee room adjacent to the DAC or in the coffee room on the top floor of R3 sign a card to register that you have done so get the sample record sheet from the DAC and make sure that you understand the sample handling instructions acquaint yourself with the operation of the safety interlock system Your local contact will explain this to you PRISMA User manual 1 Introduction PRISMA PRogetto dell Istituto di Strutura della MAteria del CNR is the result of a collaboration between the Italian Consiglio Nazionale delle Ricerche CNR and the British Engineering and Physical Sciences Research Council EPSRC A brief introduction to how PRISMA works is given here but detailed accounts may be found in the following publications which are available from your local contact Th
34. lt lattice parameters in PRSCAL if you try CAL br 2 5 2 5 0 90 0 0 where the fourth number is 90 PRSCAL gives the incident neutron energy for elastic scattering at 2 5 2 5 0 as E 31 96 meV This is sufficient to integrate over the soft 24 PRISMA User manual mode but it may be better to try an even higher energy to satisfy the quasi static approximation more completely In this case a value of d 50 gives the much more satisfactory energy of E 89 46 meV Since we are using 16 detectors one of the detectors in the middle should be driven to this value of To drive the scattering arm to the correct angle type PRS gt DR PHI8 50 Note it may be necessary at a later stage to change the value of slightly to eliminate problems with multiple scattering since this is often highly dependent on the incident energy Now that you know the angles of the detectors you will work with you can calculate the range in for the area of reciprocal space you want to look at To take yet another example suppose you wanted to perform a fine scan around the 2 2 0 Bragg peak using the angle that we have just determined You could use two offset but interleaving scans with detectors 13 to 16 Since this makes four detectors in total each setting covers a fan of 1 5 in Q Hence by stepping the Q angle you can easily get a wide coverage of the area around 2 2 0 You could try two interleaving scans each comprising five
35. manual Reflection Conditions all reflections allowed Simple Cubic sc Face Centred Cubic fcc h k must be all even or all odd Body Centred Cubic bcc h k 1 must be even allowed reflections must satisfy 2n or h k 1 3n or h k 2 3n where n is an integer Hexagonal Close Packed hcp 47
36. minimum detector separation is 60 3 Pyrolytic graphite filters are available to remove second order contamination 4 Beryllium filters are available for use with E 5 meV PRISMA 4 Final flight path Detectors Angular separation of detector arms Final collimation Notes 0 825 m 16 14 He gas tubes Reuter Stokes 1 Horizontal 30 60 Vertical 1 3 1 PRISMA 4 can be operated simultaneously with PRISMA 3 Minimum detector spacing is 60 45 PRISMA User manual Appendix B Useful Conversion Factors Density p gcm A amu x p atoms x 1 66057 where A is atomic mass and p is density Neutron Energy hk be i t _ hv k T A 395541 2m 2mA 2t L 1787 L OTe 4 13540 5 2276 x 10 7 0 086165T Xo E 2 0717k E meV A v Thz k A L m t usec T K Appendix C Geometrical Relationships For Simple Crystal Structures Interplanar spacings Orthorhombic 1 Wh k amp P Tetragonal a b ae ae ER o Cubic a b c Hexagonal 1 4 W4 kK4P P d 3 EUM a c Rhombohedral 4 h k 1 sin 2 hk kl hl cos 0 cosa do a 1 3cos a 2cos 0 Monoclinic 1 1 h k sin B 1 2hlcosp 27 13 zt 2z tT d sin Bla b c ac Volumes of Unit Cells Orthorhombic V abc Tetragonal a b Cubic a b c Hexagonal 3 V Ba 0 866a c Rhombohedral V a Jl e Acos a 2cos a Monoclinic V abcsinp 46 PRISMA User
37. ncluding the thread 2 1 Room Temperature Experiments If the sample is not to be heated then the best material to use for making a mount is aluminium It is preferable to use a small strap of aluminium around the crystal which is attached to an M8 screw thread You should use as little aluminium as possible in the strap to avoid spurious scattering and the rest of the mount should be shielded from the beam by wrapping cadmium sheet around it The M8 thread on the mount is screwed into a PRISMA candlestick which is then attached to the large goniometer inside the instrument This procedure must be carried out by your local contact do not attempt to change samples yourself To ensure that the sample will be fully in the beam the height should be adjusted so that it is about 13 cm from the top surface of the candlestick 2 2 Low Temperature Experiments Using the CCR The majority of PRISMA experiments use the CCR since it should allow for temperatures between 10 and 300 K and hence there are a number of aluminium sample cans available which fit directly onto the cold head of the PRISMA CCR The sample is actually mounted inside the can on an aluminium rod which should be cut so that the distance from the base of the sample can to the centre of the crystal is 48 mm as shown in the diagram just overleaf This ensures that the crystal sits at the correct height for the centre of the beam The sample end of the rod should be filed to shape to e
38. ng a workstation or a PC running an X Windows emulator hardcopy device usually Colour postscript and font on simp comp or cenb are three possibilities xi Type 35 PRISMA User manual gt 1 wl contour out or whatever the title is if you have renamed it xii Choose option 5 for the FILE TYPE and then either 1 or 2 for CD or CEF data i e a general inelastic scan xiii The data are then read in and you must choose the x axis variable For instance if your data were collected with the command CD 0 6 6 O O 1 2 5 the x axis variable would be L and you would reply with a 3 xiv Type in the name of your normalisation file if you have one or give a carriage return if you don t xv Type in the titles of the axes for the plot xvi You are now ready to plot your data by typing gt d s w1 for the whole data set or gt d s wl lt xmin gt lt xmax gt lt ymin gt lt ymax gt for a section of it You can also change the contour levels by typing gt a h i xvii To make a hardcopy of your plot type gt s and then leave PRSPLOT by typing gt j P and print the POST DAT file that has been created You can print it on the colour printer in the coffee room in R3 with the command print queue colour Sphaser0 notify post dat 36 PRISMA User manual 5 3 Diffraction Data The procedure for visualising diffraction data is similar to that for inelastic data
39. nique This is the natural way of defining neutron energies at a spallation source such as ISIS since it produces a pulse of polychromatic neutrons every 20 milliseconds which is roughly 30 microseconds wide The spallation technique produces very high energy neutrons and these must first of all be moderated to thermal energies before they can be of any use This is accomplished by forcing the neutrons to pass through a dense hydrogenous material usually liquid methane at a PRISMA User manual temperature of about 100 K for PRISMA before reaching the instrument Since thermal neutrons travel at relatively slow velocities for instance a thermal neutron with an energy of 10 meV has a speed of about 1400 ms their energies may be realistically measured from their flight times between the moderator and instrument As mentioned above PRISMA can also be configured as a high resolution low background diffractometer This is achieved simply by removing the analyser crystals In fact by using the single analyser detector module known locally as PRISMA 2 it is possible to perform inelastic and diffraction runs simultaneously A schematic view of the operation of this module is shown in Fig 1 with one detector in the module set up for inelastic scattering and the other for diffraction The left most analyser detector arm in the array is always referred to with the index 1 and the scattering angle of the whole array 0 is measured with respe
40. nsure a good contact with the crystal The crystal is then glued in place using Kwikfill but it is important to reduce spurious scattering from the glue and the aluminium rod with a cadmium or gadolinium shield inside the can To ensure a good thermal contact from the sample to the cold head a sample can should always be filled with helium exchange gas and sealed with a fresh piece of indium wire Your local contact will show you how to prepare a sample in this way Once the can is ready it can simply be screwed directly onto the cold head of the CCR and the CCR 12 PRISMA User manual loaded into the instrument This requires the Pelloby crane on the beamline and must normally be done by the local contact unless you have a valid crane driver s licence Crystal 48 mm 12mm Fig 5 A side view of a crystal mounted for a CCR experiment 2 3 Orange Cryostat Experiments PRISMA has its own orange cryostat with an internal bore of 50 mm This means that samples larger than 50 mm in diameter will not fit inside it The sample is mounted on the end of the cryostat centre stick using a mounting arrangement similar to room temperature experiments i e an aluminium strap attached to an M8 thread Brief information is given below concerning the valve settings and flow rates It is important to remember that both the warm and cold valves should only be finger tight Over tightening them will cause damage Much more detailed inf
41. or one data set rename CRITICAL OUT so that any subsequent operations of VCRS with other data sets will create anew CRITICAL OUT rather than appending to the old one viii The next step is to start PRSPLOT simply by typing PRSPLOT answering the questions about terminal type MX11 if you are using a workstation or a PC running an X Windows emulator hardcopy device usually Colour postscript and font on simp comp or cenb are three possibilities ix Type gt 1 wl critical out or whatever you have renamed your file to 37 PRISMA User manual x Choose option 6 for the FILE TYPE question xi The data are then read in and you must choose the variables along the x and y axes and the angle between the two axes xii The next prompt is for the name of your normalisation file If when you processed your data using VCRS you included the vanadium run at the start then the normalisation is automatically included in the data and you can simply give a carriage return here Otherwise you may use a normalisation file as for the inelastic data xiii Type in the titles of the axes for the plot xiv You are now ready to plot your data by typing gt d s w1 for the whole data set or gt d s wl lt xmin gt xmax lt ymin gt lt ymax gt for a section of it You can also change the contour levels by typing gt a h i xv To make a hardcopy of your plo
42. orkspace gt lt xmin gt xmax lt ymin gt lt ymax gt gt gt a b lt bin gt gt gt p e w lt workspace gt gt gt p l w lt workspace gt gt gt k h gt gt j plaser7 dec_postscript dat gt gt j p gt gt exit 6 2 2 Inelastic Data gt gt mrx gt gt cc Displays the given workspace as a histogram in histogram mode Bins the data into groups of bin Plots error bars Plots the workspace as a line over the top Creates a hardcopy file Prints on the PRISMA laser printer Leaves GENIE temporarily type log to get back in Leaves GENTE GENIE macro to transform raw data to energy transfer for quick visualisation GENIE macro to process raw data into full PRSPLOT format Data written to CONTOUR OUT 40 PRISMA User manual 6 2 3 Diffraction Data gt gt vers GENIE macro to process raw data into full PRSPLOT format Data written to CRITICAL OUT 6 2 4 PRSPLOT V 1 wl file name gt Loads data into PRSPLOT a h i Alters contour levels d s w workspace lt xmin gt xmax ymin lt ymax gt Displays the given workspace as a colour contour plot t wl Allows you to change the axis titles for a contour plot a n i Alters normalisation only use in the absence of a vanadium normalisation x p w a free workspace xmin xmax lt ymin gt lt ymax gt Cuts through the contour data set between the given limits and puts the result in
43. ormation is given in the RAL reports 93 006 and 92 041 copies of which are kept in the PRISMA cabin Cooling to gt 4K Constant temperature gt 4K Cooling to lt 4K Open the cold valve 1 2 turn Open the warm valve until the flow observed on the gas recovery flow meter is 10L min Once the required temperature has been reached reduce the flow to 4L min using the warm valve and the temperature will be controlled by the Eurotherm and the cryostat heater or if you want the temperature to remain stable at 4K switch the heater off Close the warm valve and open the cold valve 1 2 turn Slowly open the Roots pump valve never letting the pressure rise to above 10 torr When the pump valve is fully open use the cold valve to set the flow to 0 5 to 1 L min 13 PRISMA User manual 2 4 Furnace Experiments When the sample is to be heated above room temperature but not above about 700 K then aluminium may still be used to make the sample mount For temperatures above about 700 K tantalum foil is generally suitable It is still important to use as little material as possible around the crystal so as to eliminate spurious scattering and the rest of the mount should be shielded from the beam as in a room temperature experiment However UNDER NO CIRCUMSTANCES should cadmium be used for shielding the mount when heating above room temperature since it may melt or oxidise Gadolinium foil is available for this purpose instead Th
44. riv1 by typing for instance prisma prisma cset derivl 2 0 At any time you may display a parameter by typing cshow enq For instance if you type prisma prisma cshow enq powerl the current power will be returned If you wish to perform an alignment scan it is easiest to turn the temperature logging off for the duration of the scan This is because the logging slows the scan up Type PRS CSET TEMP NOLOG PRS CSET TEMP1 NOLOG PRS CSET LAKES NOLOG These commands simply mean that the dashboard no longer displays the current temperature it does not mean that the temperature control itself is turned off In any case you should have the temperature logging on while you are actually collecting data You can change the set point from within the PRISMA control program by typing PRS VX C CSET TEMP lt your desired temperature PRS gt VX C CSET TEMP1 lt your desired temperature The VX command is used in command files for changing the temperature This is explained in Section 4 5 22 PRISMA User manual 4 Collecting Data 4 1 Setting Up the Time Channel Boundaries For both diffraction and inelastic scans the time channel boundaries should be set up by typing the following PRS gt SE START 15 19995 1 If you want to perform a scan usually an inelastic scan for a single setting of the instrument that will count indefinitely i e until end is input to the supervisor window type PRS gt SE MNT 0 O
45. s typical scan trajectories using PRSCAL obtained with the command CD 0 6 6 0 O 1 2 5 fora crystal of KNO The scattering plane was the b c plane so that the following commands were issued to the control program to set the sample parameters PRS SE A 5 425 9 120 6 228 90 90 90 26 PRISMA User manual PRS gt SE PX 1 010001 The scan was performed simply by typing PRS gt CD 0 6 6001 2 5 after the time channel boundaries had been set up and values of MNS and MNT given Also don t forget to read section 4 6 on theupdate and store commands Q 0 000 6 000 6 000 DQ 0 000 0 000 1 000 E0O 2 5 50 45 b 40 Oe 4 Energy transfer meV A272 M M A o a 6 L 341 L c3 C1 eo Oo T l on j l oS SS 4 45 S5 5X5 6 GS 7 7 5 8 Oo Wavevector QL rlu 4 4 2 More General Inelastic Scans It is possible to perform more general purpose inelastic scans than are possible with the CD command Here you would drive each analyser detector arm to a fixed analysing energy and then position and Q so that the scan trajectories cover the region of interest PRSCAL is invaluable in considering this type of scan because it will plot out the scan trajectories for you and enable you to fine tune all of the instrument parameters The plots are made using the zc command in PRSCAL and choosing the CF path option The arms are driven to the desired analysing energies as in this example
46. station and type gt gt pp b Respond to the first question with the number of detectors being scanned in our case it is 4 c Type in the absolute value for the first detector in the array i e 90 d Put in the limits for display in Angstroms as something like 0 5 and 3 5 e Input the bin size usually 0 005 f For the next question about the run number answer dae if you want to look at a scan which is still running or else type in the run number 17 PRISMA User manual g Now the program asks for the detector spectrum and the point in the scan to be displayed After this it will plot the spectrum of your choice viii If you cannot see any signal in the scan from the peaks corresponding to the a direction you should scan more widely in Q with one of the following scans PRS SC OM13 16 50 5 0 1 NP 11 or PRS gt SC OM13 16 42 5 0 1 NP 11 In this way you can cover a range of 4 in Q with each scan It may well be that you have to perform several of these scans before you find a Bragg peak that you can identify For each successive scan you should increment or decrement the 2 value that you type in by 4 since each scan covers a 4 range in Q However sometimes the tilt of the crystal is misaligned by a few degrees out of the scattering plane such that the required fundamental Bragg peaks cannot be seen at all If you have performed several scans and still cannot see any recognisable Bragg
47. steps of 0 1 To do this you first need to find out the Q angle corresponding to one of the middle detectors In our example 44 50 and 04 5 49 so we could try CAL br 20 0 500 0 which gives the angle you need as 65 with the default lattice parameters By using these two interleaving scans PRS sc om13 16 64 8 0 1 np 5 PRS gt sc om13 16 65 3 0 1 np 5 you can cover a range of nearly 4 in Q in steps of 0 1 very rapidly To cover a large portion of reciprocal space interleaving scans are often unnecessary So the scan PRS gt sc omi 16 65 16 np 23 covers a much wider range by a fan with 14 spokes separated by 0 5 The rc command in PRSCAL enables a plot of the scan trajectories in reciprocal space to be made See the PRSCAL manual for full details In all cases a diffraction run will be some sort of Q scan like those above To set the number of frames that each point in the scan will be counted for use the MNS parameter after ensuring that MNT 1 See section 4 1 25 PRISMA User manual 4 4 Inelastic Scans Both the CD and the BEGIN commands described in the following two sections use a specified analyser detector arm as their reference This is the arm given by the parameter IANAL and the default is IANAL 1 It also requires the parameters DMIN and DMAX to be set to the numbers of the arms being used for inelastic work Usually these values are 1 and 12 for PRISMA 2 and 1 and 5 for PRISM
48. t type gt s and then leave PRSPLOT by typing gt j p and print the POST DAT file that has been created You can print it on the colour printer in the coffee room in R3 with the command print queue colour Sphaser0 notify post dat 38 PRISMA User manual 6 SUMMARIES 6 1 Instrument Control 6 1 1 PRISMA Control PRS gt PRS gt PRS gt PRS gt PRS gt PRS gt PRS gt PRS gt PRS gt PRS gt PRS gt PRS gt SE START 1000 10000 10 SE START 15 19995 1 TI SE lt character string gt MNS 1000 MNT 1 SE MNT 0 DR EF lt n gt lt n7 gt lt E gt BEGIN Sets time channel boundaries for crystal alignment Sets time channel boundaries for full data collection Sets title Sets number of frames to be counted in each period to be a 1000 this is usual for sample alignment Sets run to end only by operator intervention i e an END or ABORT in the Supervisor window Drives analysers detectors n m to the analysing energy E Starts collecting data in current configuration CD lt h gt lt k gt lt l gt lt u gt v lt w gt Ey Inelastic run through h k l along the u v w direction SC OM d d5 2 O0 AOQO NP no of steps CSET TEMP LOG CSET TEMP NOLOG VX C CSET TEMP lt i gt 6 1 2 PRISMA Supervisor Window prism prism prism prism prism prism prism a prisma pause a prisma resume a prisma end a
49. therwise type PRS gt SE MNT 1 which means that the DAE will count on ISIS frames If you want to count for say 900000 frames which is 5 hours type PRS gt SE MNS 900000 Remember that 50 frames 1 second 4 2 Vanadium Calibration It is usual to perform a calibration to account for the detector efficiencies before starting a diffraction or inelastic experiment Do this by placing the vanadium rod in the beam on a candlestick and then run a scan that is effectively the same as the one that you will eventually use to collect data from your crystal A calibration scan only requires about 40 minutes of beam so you should type PRS gt SE START 15 19995 1 MNT 1 MNS 120000 before starting the scan For calibrating diffraction scans which use detectors 13 to 16 you would type something like the following after having driven 013 to the appropriate value where you will collect data PRS gt SC OM13 16 45 0 0 NP 1 Obviously the 2 angle has no relevance for a vanadium calibration and in the above command it was set to a nominal value and left there for the duration of the scan 23 PRISMA User manual For calibrating an inelastic scan you have two choices depending on the type of inelastic scan you will eventually use see section 4 4 For a CD calibration simply type the appropriate CD command on the LA120 For the more general type of inelastic scan drive the angle and the analysing energies to their correct values
50. tor intervention When you have finished editing the file turn the dashboard on again by typing prisma prisma stat on The command file may then be run by typing PRS DO EXAMPLE JOB in the control program Execution of the whole command file may be stopped only when the dashboard shows that PRISMA is actually running and this is done simply by typing end or abort in the supervisor window on the workstation 29 PRISMA User manual 4 6 Ending Pausing or Aborting a Run The commands to end pause or abort a run should all be typed in the supervisor window while the dashboard shows that PRISMA is RUNNING These commands are simply end pause or abort end stops a run and stores the data in the DAE in the file prisma disk0 prsmgr data prs run no gt raw pause stops the DAE from counting neutrons until resume is typed in the supervisor window and abort ends a run without saving the data In addition it is possible to save the DAE data to a file without ending the run This means that you can look at a run periodically to see how it is getting on The commands you need are update and store typed in this order in the supervisor window These store the current data in the DAE in the file prismaSdisk0 prsmgr data prs lt run no gt sav If you leave PRISMA running for long periods of time say more than 12 hours you should do this sort of backup anyway in case something goes wrong by running the command file time
51. ual Now we will briefly describe the commands for viewing the data in a workspace First you must decide whether you wish to plot your data as points or histograms Toggle between the two modes by typing the following gt gt tm 31 PRISMA User manual The workspaces may be displayed with the command d The plot command p allows you to plot the data as markers with error bars or to plot one workspace on top of another For example gt gt d m wl 10 90 O 10 plots intensity of workspace 1 as markers from 0 to 10 against energy transfer from 10 meV to 90 meV gt gt p e wl adds error bars gt gt p l w2 overplots w2 as a series of lines joining up its points You may alter the binning of your data by gt gt abs5 bins the data into groups of 5 To get a hardcopy of a plot use the following two commands gt gt k h gt gt j plaser lt n gt dec postscript dat where the laser printer number n identifies the location of the printer according to the table below laser printer location number 0 Computer support office R3 1 Coffee room R3 2 DAC R55 7 PRISMA cabin To leave GENIE type gt gt exit 5 1 1 PRISMA GENTE Data Analysis Programs Various GENIE macros and FORTRAN programs exist for analysing PRISMA data The PP facility has already been introduced in section 3 1 and here we give a list of all of the macros you might need to use More detailed information is given in the P
52. wing list of operations is a step by step guide to processing an inelastic data set using CC and then plotting it with PRSPLOT 1 Create a rebin file outside of GENIE which the macro uses to bin your data as it is processed This file should be in the GENIE command file format and should have a relatively short name such as BIN COM for instance The file consists of only one line which is a rebin command for workspace 3 so an example might be gt reb w3 10 0 5 20 1 40 2 60 and the data will be binned with the variable steps in the range 10 to 60 meV ii Start GENTE and type gt gt dd iii Answer the next question about monitor efficiency with a 1 iv Enter the name of the rebin file v Type in the run number and answer the usual questions about which directory the data file is in and whether it is a RAW or SAV file vi Answer the question about whether the sample parameters i e lattice parameters analysing energies etc need to be altered vii Type in the first and last detectors to be analysed and then answer the prompts for individual detectors with a O or 1 viii When the run has been analysed the macro asks whether another run should be processed The output from all runs is written to a file called CONTOUR OUT and subsequent runs will be appended to it When you have processed all of the runs required 34 PRISMA User manual for one data set rename CONTOUR OUT
Download Pdf Manuals
Related Search