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HiFi User Guide

1. END IMMEDIATE Ends and saves the run without waiting for the period cycle to complete Use only if in period mode and the beam has gone off and you want to take advantage of the break to change sample ABORT Ends the run and throws away the data Use with care ZFINE Selects the Z coil for small longitudinal fields after FO or small sweeps around the main field value after LFO and SETMAG to a starting point LF Re select the main coil after ZFINE Leaves main field on turns others off TEX Select transverse field in the X direction no setpoints sent TFY Select transverse field in the Y direction no setpoints sent TF20 Selects the Y transverse coil and sets 20 Gauss LT Put the cryostat in Low temperature mode manual flow control HT Return the cryostat to the default high temperature mode auto flow control 7 5 Temperature Control The temperature controllers such as Eurotherm or ITC5 use Proportional Integral Differential PID control parameters to adjust the heater power These are all set from the computer each time a new setpoint is sent with SETTEMP from the command line or by a script Values are read from a table which can be viewed in SECI under the Settings menu The first two columns on each line indicate the temperature range over which the parameters listed are applicable These should be in increasing temperature with no gap
2. L e 45mm from end spacer to sensitive point 46 Probe number Field min T Field max T 3 0 17 0 52 4 0 35 1 05 5 0 7 2 1 6 1 5 3 4 7 3 0 6 8 As the probe is not exactly at the field centre a correction of around 600 ppm may have to be made The plots below were measured with the magnet bore at atmospheric pressure and the probe tube free to slide into the field centre in the side port nearest MuSR Fields were in the sequence shown after having been to larger ve fields 200 400 600 800 Field Shift ppm 1000 1200 s Field centre and specified homogeneity m 0 4T Probe 4 m 0 4T Probe 4 8 1 0T Probe 5 m 1 5T Probe 5 Em 2 01 Probe 5 B 0 8T Probe 5 100 110 120 130 Probe tube position mm 140 167mm to clear CCR or Flow 150 172mm to clear Variox nm a K sometimes WA mh no lock at 172mm with probe 5 160 170 180 SECI will read the NMR field if available convert to Gauss display it on the dashboard and log it in the data file The value NaN not a number is displayed instead if the probe isn t locked onto the field or if the NMR unit is switched off or not present This is usually logged as 0 47 13 Troubleshooting If something appears to be wrong then users should contact their local contact for assistance Howeve
3. 2 plugs Thermocouple Services Panel Mount the sample in fly past geometry on the thermocouple in the centre between the two heater lamps oriented at 45 degrees to both the lamps and the incoming muon beam Transparent samples or loose powders may be wrapped in thin Ti foil Thin Ta wire may be used to hold it in position The thermocouple should be in contact with the sample and not in front where muons may hit it a hole drilled in the sample is ideal a pocket of Ti foil spot welded onto the Ti sample packet will also work For lower temperatures consider using copper loaded grease or heat sink compound to improve thermal contact The thermocouple position and angle may be adjusted by slackening the nut on its vacuum feedthrough Do not use aluminium it will melt or silver even well below its melting point it will sublime and silver plate everything The thermal shields each have 3 layers of Ti foil Bolt them around the sample position with the 4 screws between the two halves at each corner check the shields are centred Carefully insert the furnace into the magnet it slides in through the side port nearest MuSR opposite to the CCR The instrument vacuum must then be pumped 28 Connect the water hoses to the self sealing push fit connectors on the services panel with the flow meter in the return side Hoses and cables can be run between the quadrupole base and the upstream detector frame Turn the water su
4. 2015 03 05 15 44 33 Highest dae detector card crate number used 0 1 1 2015 03 05 15 44 33 Number of time regimes 1 2015 03 05 15 44 33 CRPT memory used for histograms 0 Mb 2015 03 05 15 44 33 Number of periods daq total 1 1 2015 03 05 15 44 33 Resetting DAE ignore veto counter values as not yet cleared 2015 03 05 15 44 33 FIFO Veto is ENABLED vetoed 0 frames 2015 03 05 15 44 33 SMP chopper Veto is DISABLED counted 0 frames 2015 03 05 15 44 33 Internal Veto is ENABLED vetoed 0 frames 44 33 Fermi ChopperO Veto is DISABLED counted 0 frames 33 TS D lata ie DISABLED fcountad D Fram 7 7 Monitoring your experiment If you are away from the experimental hall the ISIS beam current and MCR messages are available at nttp ww isis rl a There are also screens showing the beam current at other locations on site for example the R1 and R22 Coffee Lounges The dashboard showing the status of the instrument and run in progress is available on the web at Select HiFi from the list of instruments The instrument and beam status is also available via a WAP enabled mobile phone at older phones may need to use http wap isis rl ac uk index htm 8 Data Analysis Raw data is accessible on the internal network at 38 isis instS NDXHIFI Instrument Data cycle_yy_c HIFI12345678 nxs And also hifidata HIF112345678 nxs data from previous ISIS cycles will be archived to hifi data cycle vu c HIFI00000
5. a thin Mylar sheet or aluminium foil on a frame Powder samples can be ina packet of thin plastic or aluminium or silver foil The furnace always operates in flypast mode and the sample is attached to the end of the thermocouple using a titanium foil packet for powders or small pieces of sample and thin Tantalum wire to anchor it in place 6 2 Dilution Fridge Oxford Instruments photo of fridge cryostat photo of insert photo of pumping rack The Variox cryostat for the dilution fridge is first mounted on the magnet the vacuum pumped and it is filled with liquid nitrogen and helium The sample is mounted on the end of the dilution insert the IVC can with window is placed over it and the insert lowered into the cryostat and cooled This will normally be set up by one of the ISIS sample environment staff Users should be prepared to mount samples in advance to give time for preparation and cooling Thermal contact and radiation shielding of the sample will be critical Temperature control is in either of two modes dilution mode from base 25mK up to 6 5K using a weak thermal link between mixing chamber and sample stage or cryostat mode with the mixture recovered and helium exchange gas in the IVC can from 1 5K up to 300K There is a different SECI configuration for each mode There are two sample thermometers RuO reads from base to 6 5K and Cernox from 1 3K to 300K and both are logged in each mode At low temperatures eddy
6. access to the bolts e Unbolt the bellows from the magnet slacken the 6 clamps and turn through 90 degrees do not remove them completely e Slide out the CCR and lock it in the fully removed position e Slacken the 3 grub screws turn is sufficient do not remove them and slide off the radiation shield can e Detach the floating thermometer from the sample plate e Remove the sample plate e Ifyou are not ready to mount another sample immediately close off the magnet side port with the blanking plate and pump the vacuum 25 Blanking plate fitted to the magnet port e If you have finished using the CCR ensure the slide is locked in the fully withdrawn position Leave the can off in case there is any residual moisture inside the shield 6 5 Flow Cryostat Transfer line Thermometer connection on stick Additional ports for RF wiring etc Clamp for Cryostat sample thermometer stick and heater cable Sample Vacuum space valve valve not used on HiFi Top view of the Flow cryostat in situ in the instrument 26 The Flow Cryostat takes helium continuously from a storage dewar and evaporates it in a heat exchanger in contact with the sample pulling the gas through using a diaphragm pump on the outlet Temperature control uses an ITC controller a heater on the heat exchanger and a motorised needle valve on the transfer line The sample space contains static exchange gas usually 20mbar helium and i
7. get confused like this after large temperature changes in Auto flow mode Switch the controller s main power off and on again to make it reset the valve then check it is set back to auto operation and re send the setpoint with SETTEMP e The flow valve or capillary is blocked Ask for assistance to get it unblocked If the cryostat or CCR will not warm up on demand warms rather slowly or cools below its setpoint e The heater protection circuits have tripped For the ITC controller it may say Hot 1 or Hot 0 on the display Check that all the thermometer leads are plugged in then switch off and on again to reset For the Eurotherm controller CCR there is a small reset button to be pressed The CCR also has a thermal switch on the cold head check that the compressor is still running especially with setpoints above room temperature e The heater itself or a lamp in the furnace has burnt out Ask for assistance The CCR has to be warmed up and withdrawn in order to replace its heater e The helium flow valve is stuck open when the controller thinks it is shut There will be a large flow of gas and the pumping lines will be covered with ice Reset the controller to close the valve then re send the setpoint If the temperature does not stabilise e The P I D parameters or maximum power are incorrect for this sample Some adjustment may be necessary with large samples or special centre sticks or in th
8. muons still contribute to the statistical noise To obtain data of equal quality a sample covering only half the beam needs to be measured for 4 times as long as a large sample 19 In flypast mode a small sample is suspended in the beam and any muons not stopping in the sample ideally pass through the hole in the backward detector bank and out to the end of the flypast tank where their positrons are not detected not contributing to statistical noise or background Now the half sized sample only needs twice the counting time of the large one The background fraction is not quite so well defined in flypast mode since a few muons are scattered in the windows and might hit the cryostat tails or backward detector bank This is mainly a problem in lower fields where the scattered muons are not refocused by the field The background fraction varies as the muons are focused onto the sample by the field smallest spots at 2 6 and 4 3T Flypast operation is best used together with modulation RF or field switching when a distinctive relaxation behaviour is expected or for a level crossing resonance or similar sharp feature in a field scan rather than a gradual repolarisation Consider running a reference scan with a piece of silver or aluminium cut to the same shape size and thickness mass as the sample The sample is suspended on a thin silver rod cryostat centre sticks or frame CCR or if exchange gas is present it can be attached to
9. mutually perpendicular sensors either side of the sample position just behind the detectors The probes are positioned to detect the major component of remanent field which varies quadratically with position and correct for it see Appendix 1 Two additional probes are built into the magnet All of these are logged on the computer together with a best estimate of the actual central field which is also used to set zero field The possible operating modes are Main field alone Main field plus the auxiliary Z field to provide either modulation or a fine sweep range Zero field adjusted with the X Y and Z coils and the main field turned off preferably in persistent mode X or Y coils to provide a transverse field for calibration Zero field offsets are included Zcoils for low longitudinal fields with Zero field offsets included The auxiliary Z coil is wound to have zero coupling to the main longitudinal coil so the field change it produces is independent of whether the main coil is in persistent mode or not The zero field setting has to compensate for the remanent field of the magnet due to trapped flux this is dependent on the recent field history and is about 16G at the sample position after a field scan all the way to 5T and in the same direction as the recent high field The remanent field is larger away from the centre but fortunately it is aligned along z has axial symmetry and resu
10. not leave the system unattended for too long when V2 is open The turbo pump may never reach its full speed and the pump controller will eventually time out and will then vent the pump and instrument and you have to start again To vent e Close the gate valve V1 and bypass V2 if still open e Turn off the pumps right button on controller the green light will now flash occasionally The pump will vent itself automatically once the turbo has slowed down a bit e To vent with air acceptable with the CCR if the Defrost Heater has been used and the sample is not air sensitive simply open the vent valve e To vent with dry gas connect the gas line from the services panel photo below to the vent valve Use nitrogen to vent the CCR Helium gas should be used when removing a cold cryostat Set the regulator to only just above atmospheric pressure to avoid the risk of over pressure Open the valve on the flow meter and then the vent valve to vent the instrument Monitor the pressure on the dial gauge and close the valve once atmospheric pressure 1000mbar is reached Do not rely on the electronic gauges reading atmospheric pressure of 1 0E 3 mbar accurately especially with helium or argon Regulator and pressure gauge 6 Sample Environment The choice of sample environment equipment will be made in advance of the experiment either on the experimental proposal form or by discussion with the instrument scientists Changing between e
11. procedures for doing this are explained in section 3 1 The magnetic field is correct for a Compensation of the Earth s magnetic field b Calibrations c Measurements The procedure for setting the magnets is described in section 4 Sample environment is working as expected section 6 The beam slits and steering are chosen to match the size of the sample and the desired event rate This is described in section 3 The data acquisition and analysis software have been set up correctly These are described in section 7 This manual also includes the details of how to access and analyse the data recorded section 8 and information for ISIS users to be added also see the ISIS web pages http www isis stfc ac uk user office useroffice html At the end of the manual are the troubleshooting section and a brief guide to commonly used SECI commands 2 Instrument layout The principal components are shown in this cross section of the instrument Cryostat Scintillators with central hole Magnet coils not shown Photomultipliers Flypast tank Muon Beam In Vacuum pump Beam not shown window The instrument is built around the 5T superconducting split pair magnet which is a cryo free design using the two pulse tube coolers at the top to keep the coils below Tc The magnet has a room temperature bore along the beam axis which contains the detectors and four transverse ports sides top and bo
12. the orientation the bolts on the cryostat flange can be used as a guide but note that the sample pit cage is not quite aligned with the beam field axis Tighten the clamp e Pump the sample space with the scroll pump Flush with helium and pump again e Admit 20mbar helium exchange gas and then close the sample space valve on the cryostat More gas pressure may help with low temperature operation or to prevent electrical breakdown with RF measurements Turn off the scroll pump when finished It may be necessary to disconnect the pumping line in order to close the sample pit door or because other instruments users will need the pump e Reconnect the thermometer cable Check it is using the appropriate channel on the temperature controller and is reading approximately the same as the cryostat channel 1 or cooling towards that value for a warm stick inserted in a cold cryostat 27 e If using a different stick to before don t forget to change the configuration in SECI To change over a helium storage dewar you should ask your local contact or a member of the ISIS sample environment team for assistance A level meter is available a full dewar reads 500 mm 6 6 Furnace photo of furnace As for the CCR any work on the Furnace in the area must use only the non magnetic tools provided Connection diagram Serial cable Muon Optical Furnace Mains Temperature Controller Heater ON power switch and cable Gs Interlock
13. update the Run 0 file at all Is the count rate too high in some detectors causing pile up distortion To monitor the run in progress select the DAE page in SECI and the Run Diagnostics 2 tab in the DAE VI which appears Enter 64 in the Number of Spectra box on the right and scroll up and down to see all the channels Note that the rate can be much higher in fields of 2 4T than in zero field especially with fly past samples Close the slits to reduce the rate to around 6 events frame Is the Magnetic field set correctly Check the Hall probe readings The beam may be badly focused and missing the sample Check the beamline and steering magnets The Kicker may have tripped or is still running but at reduced voltage and failed to veto the data 13 3 Magnetic Fields If the field drops rapidly to zero as seen on the Hall probe reading the magnet may have quenched This may be almost silent and there is no plume of helium released as might happen ona liquid helium cooled magnet but the coils may heat up to 70K or more as the stored magnetic energy is dissipated A cryostat may also show a temperature increase due to eddy current heating Check the magnet power supplies one is likely to say Quench Trip at x xxx Tesla on its display Check that the compressors for the magnet are both still running and making the characteristic chirp noise if they had stopped the magnet would start to warm to T which could trigge
14. 123 nxs From outside ISIS data can be downloaded via the web page http data isis rl ac uk You will need a User ID and password This now uses your email address the same as for the online proposal submission experimental risk assessment and user registration People who were not on the experimental team may not be given access if you think you should be granted access ask the instrument scientist Calibration data is available to any logged in user 8 1 WiMDA This is installed on the analysis PC NDLHIFI and also available for download from the ISIS Muon web pages if you want to run it on your own laptop If WiMDA is connected to hifi data as above loading run 0 will load the run in progress this updates every 5000 frames See the WiIMDA manual for full instructions 8 2 Mantid This is installed on the analysis PC NDLHIFI and also available for download from http www mantidproject org Time domain data can be fitted using Muon Interface and algorithms for analysis of level crossing and RF resonance curves are available 9 Appendix 1 Zero Field operation 9 1 Estimating the central field After running the magnet to a high field and back to zero current it has a remanent field with an axially symmetrical profile approximated in the region of the sample as B B B 2z7 r B B 2zr where B and B are functions of the field history B4 is of order 5 15 Gauss In addition there may
15. HiFi User Guide James Lord Peter Baker et al Contents Re deele LBE 3 2 Instrument layte e tend EE cas ei bee ena gege a a 3 3 Beani and Kg EE 5 3 1 Shutter and Instrument Access 5 3 2 Muon rate steering and Iocusing eee eee inner 6 3 3 Dead times and Count rate limits siennes 8 3 4 MUON Fain Be a coe cece veces voces Ailes entrer Does tee menti de Reece vente nr annee een nee ue th AEA R EAER 9 3 5 Frequency Le EE 10 3 6 Full Asymmetry and Background AREE EE EERE E ES EANES Eai 11 Ai ET e EE 12 4 1 SE LOS E E RE ET RER TE PE SR PEU RE DE RE PE RE EUR PER SRE PE ES 12 4 2 RI 12 4 3 Eddy c rrent heating must dns vodee cos a vaa aa 14 CSL Tu sens rene mn ln men ni ba va bedava venice va en enr obese ya a echdeeyas 15 6 Sample Environment a ee geed e eegene EE ee 17 6 1 Sample ole ln le EE 18 6 1 1 PowWderhold rs sise tn AE te dire dan cannes Eed ectuecess 19 6 1 2 lte Del Eege ee Seege ee See 19 6 1 3 Backing plate MOUNTING geed ce HNR uastee austere 19 6 1 4 Be UE 19 6 1 5 Fly past SamMpleMOUNTIAR er nn TR YON een 19 6 2 Dilution Fridge Oxford Instruments ss 20 6 3 Variox d EE 20 6 4 COR TT 22 6 5 LA Le PA CryOStat TTT 26 6 6 FURNACE sot ne N A EST Eege KEE Eege SE 28 7 Data Acquisition and Computing inner 29 7 1 D T CIOrS rame Rte nt Re TA E T AT ein vanes 29 7 2 sl leng 30 7 3 Configurations astres attirent su eu Dae Sade as EES nes aa el ENEE einen 31 7 4 Commands EE 32 7 5 Temperature CO
16. MAG value Sets the selected magnetic field to the specified value in Gauss FO Sets zero field using the Hall probes and X Y and Z coils This is a one off adjustment each time FO is typed not continuously monitored as on MuSR TFCAL Selects the transverse Y coil and sets it to 90G for calibration Other values can then be set if required SETTEMP value Sets the temperature on the cryostat CCR furnace usually in K SLITS value Sets the beam collimating slits The SETTEMP command also automatically sets the appropriate control parameters heater power P I D values and for scripts the required stability before a run begins The BEGIN command will ask for information for the file header These header details can also be changed at any time before the run ends using the SETLABEL command which will ask for the new value It s important to get the RB number correct if you want to be able to retrieve your data from the archive in the future SETLABEL S Sample name O Orientation T Temperature E Field RB RB number 32 U Users C Comments In addition to the header the measured values shown on the dashboard such as the sample temperature magnetic field and slits are logged in the run file The following additional commands may be needed in special cases
17. NGO TTT 33 7 6 Sieden 35 7 7 Monitoring your experiment sse ee ee ee ee ee ee ee ee ee ee ee ee ee eee 38 Be gt DatarANal ysis ere ance sts deed ed Ee ENEE EE 38 8 1 WIMDA EE 39 8 2 MAM e DEE 39 9 Appendix 1 Zero Field operation sise 39 9 1 Estimating the central field 39 9 2 S ttINS Z TO red E are dE RE de D Cie ee ee D et rm eee 40 10 Appendix 2 Period switching and Field modulation sss sese sese eee eee 41 10 1 Turning on field modulation in 41 10 2 Turning off field modulation 43 11 Appendix 3 Persistent and Driven modes 43 12 Appendix 4 NMR eee rat en dE deve the net da daim ed ne aan ee En ENEE 44 13 TERIO oE bert DE S Z RS E En ERA 48 13 1 No muons or very few MUONS iii 48 13 2 Counting but strange data ie 50 13 3 Magnetic ST unir Mi cessdecs ds ee dininasee d EEN ee 50 13 4 Temperatures E 51 14 QUICK Guide To SEC hessen E eege eege eege 53 1 Introduction This manual is designed to provide all the basic information needed to perform an experiment using HiFi If there is anything you remain unsure about you should check the details with your local contact or one of the instrument scientists Before starting to collect data it is worthwhile to check the following things are set up as desired The spectrometer area has been cleared of personnel tools and any other stray items the interlocks have been set correctly and the beam blocker has been raised to allow muons through to the sample The
18. The instrument vacuum provides the insulation for the cryostats and also the vacuum around the sample for the CCR and furnace It is pumped with a turbo pump located next to the fly past tank backed by a scroll pump The controller and pressure gauges are located in a rack to the left of the magnet by the quadrupoles The magnet s own insulating vacuum and that in the beamline upstream of the window are both independent To pump 16 Close the vent valve by the pump Check that the turbo is stopped 0 Hz on controller Open the gate valve V1 handle in lower position Open the bypass V2 This speeds up initial pumping since the exit port of the turbo would restrict the flow rate at higher pressures Turn on the pump right button on the controller the green light will come on continuously this activates both the backing pump and turbo pump The yellow Vacuum On warning lights will come on as soon the pressure starts to fall Monitor the pressure on the gauge by the controller sensor A2 which should switch to A1 at low pressure If the pressure stops decreasing for a while around 1 mbar this may be due to water vapour being pumped condensation in the magnet bore or on the CCR cold head Once the pressure reaches 3 10 mbar or if it is below 1mbar and not falling close the bypass valve V2 The pressure should immediately start to fall again indicating the turbo pump is now helping with the pumping Note do
19. any people tools or other stray items that have been left inside Press the two search buttons as you go round one either side of the magnet The buzzer will sound once both are pressed Close and lock the door and put the interlock key in the red box again using the lowest space This is not necessary if you have not opened or entered the ground floor area for example you have only done a sample change on the cryostat The red box should now be filled with 5 keys Check all are turned clockwise start at the bottom Press the red Open Blocker button and hold until the green closed light goes out The Beam On light and blue lighting in the area should turn on Anyone still in the area when the blue lights come on should press one of the Beam Off buttons To turn off the beam and gain access Unless necessary for your experiment ensure the magnetic field is set to zero Confirm that the Magnet On light is extinguished Press the green Close Blocker button The Beam On light should turn off and the white lights in the area turn on Remove keys from the red box starting at the top to open the ground floor or upper doors as required 3 2 Muon rate steering and focusing The muon beam is focused to some extent by the magnetic field and this focusing varies with field The background asymmetry for a small sample on a sample plate or the rate in flypast may vary with field Ze
20. applied by our data analysis software based on a dead time for each detector element the time within which the second muon is missed These values are calibrated each cycle For experiments such as RF resonance with a large sample and where you only need to integrate or fit the data after a pulse you may open the slits to improve the data rate This may also be appropriate for level crossing in those cases where the initial asymmetry is constant and the later time shows varying Gaussian relaxation such as nuclear quadrupole lines or weak Am 0 radical lines Check the form of the signal first and ensure there is no underlying relaxation Part of the increase of count rate in high fields is due to double counting where a spiralling positron passes diagonally through more than one detector element giving a signal in each The flat disc detector geometry is designed to reduce this but cannot eliminate it completely The fraction is found to vary linearly with field negligible in zero field and reaching about 25 at 5T The data quality is not affected since these are all good positrons though the x of a fit may be increased from the ideal 1 0 to around 1 4 in 5 Tesla 3 4 Muon range The surface muons reaching HiFi start with an energy of around 4MeV and can penetrate a limited distance in matter before they stop and interact with their surroundings There is a spread of ranges due to both random scattering in the
21. be relatively uniform stray fields from external sources or gradients from the quadrupoles for example If the magnet has been partially demagnetised by running to a low negative field after high positive fields additional field gradients may be present the temperature of the coils may not be exactly uniform during the sweep and some parts could demagnetise before others 39 The fixed magnetic field sensors clearly cannot be positioned at the sample position or anywhere in the beam they are actually located behind the detector banks where the field may be 10 20G different The values measured must be corrected The two three axis groups of Hall probes are located at positions 0 y z and 0 y z i e above the beam in forward and backward positions The X field in the y z plane is unaffected so obtained directly from the two sensors The Y component of the remanent field has equal and opposite values at the two positions so averaging the Y sensor readings gives the central Y field The difference of the two Y values gives the remanent field coefficient B2 The two Z readings should be the same but can then be corrected using the Y difference to get the central Z field The uniform component B behaves the same as a uniform stray field of external origin There are additional corrections to allow for a the inhomogeneity of the X Y and Z coils themselves b a known offset due to sensor zero offsets or stray field gradients presumed c
22. current heating of the sample will be seen if the field is varied at the normal ramp rates perhaps from base to 400mK for a field sweep 0 to 1T Beam heating is also noticeable for example 7mK at a count rate of 30 Mevents hour Also the heat capacity of the copper blade and maybe your sample will increase in high field with a corresponding increase of temperature response times 6 3 Variox cryostat Plain sample sticks are also available for the Variox cryostat as used for the dilution fridge insert for use from 1 5 to 300K Users can mount samples and change these over themselves The sample should be centred at 39 mm above the bottom of the sample plate As the stick is very long thermal 20 contraction is significant so you should let it reach equilibrium before starting measurements on a small sample even for sample temperatures close to room temperature The sticks are rather flexible so keep them vertical when possible and do not let them bend when lowering onto the bench for sample mounting To change a sample 21 Ensure the cryostat and sample temperatures are 50K or above Preferably set the field to zero Close the blocker and open the door on the platform giving access to the cryostat Connect a small scroll pump on trolley to the cryostat s sample space pumping port and pump out the line Connect the helium gas line from the panel to the pumping trolley valve closed for now Remove the clamp holding the cry
23. d in foil packet 5 8 Small sample suspended 0 0 10000 20000 30000 40000 50000 Field G The flattest backgrounds are obtained with thin samples ideally 2 muon stopping ranges thick mounted centrally in the instrument in flypast mode but large enough to intercept the whole beam Larger variations are seen with thick sample holders or cells or small samples where the ratio of muons incident on the sample vs background varies 4 Magnetic fields 4 1 Safety The magnetic field is strong enough to attract magnetic items such as tools with the possibility of injury or damage No magnetic tools are to be brought into the downstairs area especially scalpels or scissors A set of non magnetic tools are provided for use on HiFi only return these to the toolbox after use and do not remove them from the instrument Fields high enough to affect pacemakers may be present over most of the muon beamline and instrument areas from other magnets in addition to HiFi The magnetic field area is marked observe the warning notices 4 2 Details The superconducting magnet system has 4 sets of coils each with its own power supply All supplies can provide positive or negative fields and the polarity switching is automatic simply enter positive or negative values Main field in the Z direction up to 5T 50000 G This has a persistent mode switch Positive main field points downstream Xcalibration field up to 100G Positi
24. e Control Listening Mode Ramp Rate Table LOW Amps HIGH Amps al Idir POSITIVE MAX A MID 4 0 0 Rad lt Then find SMS High level control vi and click Z Switching mode 42 Set the Z supply to Local control mode press the Remote button the light will go out Now you can set the main field with SETMAG or in a script and start taking data The Z field only switches while a run is in progress The Field_Z log value does not update while switching but you can monitor it using the Hall probes 10 2 Turning off field modulation End the last run Set the Z power supply back to Remote control mode light on button lit Disconnect the control cables from the supply On SMS High level control vi click High field mode Open the DAE VI go to Experiment Setup and Periods as before change the period type to Software and number of software periods 1 then click Save Experiment Setup 11 Appendix 3 Persistent and Driven modes The magnet s main coils have a persistent mode switch consisting of a length of superconducting wire with a heater attached This is connected in parallel with the coils When setting a field in persistent mode the heater is first turned on so that the switch changes to its normal or resistive state The power supply then ramps up the current which flows through the superconducti
25. e crystals solid lumps or pressed pellets Powders may also be mixed with diluted GE varnish if the background from this will not affect the measurement The sample is then held in position with yellow tape or with foil formed around the sample and wrapped round the plate edges Foil will act as a radiation shield with poorly thermal conducting samples Use silver foil in the dilution fridge Powders can be packed in an aluminium or silver foil envelope or a thin plastic packet we have a bag sealer to make these which can be used in inert atmosphere inside a glove bag if necessary 6 1 4 Liquid cells These have a welded metal window and a filling tube with either a valve or simply a compression fitting and stopper Check that there is space for the valve on the sample stick before filling On the CCR use an adaptor plate Many liquids must be de oxygenated before use and the cell may need to be filled in an inert atmosphere Use a syringe to inject the liquid through the fill tube and into the bottom of the cell and avoid bubbles Ensure the cell is sealed well otherwise liquid samples or their solvents may evaporate into the instrument vacuum over the course of the measurement 6 1 5 Flypast sample mounting For the normal sample mounts above all the muons will stop either in the sample or mask and their positrons will be counted For a small sample the change of asymmetry possible from the sample is reduced but all the
26. e fitted when the cryostat is mounted The Metrolab PT2025 control box should normally be set to automatic search operation and can track the field within the range of the probe It will track small field steps but for larger changes may temporarily lose the signal and then re acquire it The field must be approximately normal to the larger faces of the probe and the field polarity setting is important while NMR only measures a field magnitude the phase of the modulation coil would be wrong and the feedback loop won t lock for example with the probe installed with its label facing downstream and a positive main field set the polarity must be button in 44 45 Length between flanges 117mm to clear CCR Use adaptor plate when in top position Remove these 3 bolts to withdraw NMR probe Length between flanges 172mm to clear Variox Lit when de Choose field polarity field Button normally out Tesla Button in Auto Press to light up REM SEARCH to left Set FINE to 5 0 Slacken these 4 bolts to slide out probe a Ne an re gt ef A x N lt i N JA AA Select the appropriate probe for the field range of interest Probes can be changed at any time by removing the carrier insert Switch off the Metrolab control box before unplugging the probe from it Take care if the field is on When reinserting the probe you should just feel it touch the end of the tube
27. e furnace 51 52 The wrong calibrations are being used or the sample and control thermometers are swapped Is the stick connected to the correct channel on the temperature controller The helium flow rate is much larger or smaller than intended for this temperature Check the flow valve Sometimes the auto flow algorithm does not stabilise and it helps to set the valve to Manual operation this is OK for operation at a single temperature or small changes One of the thermometers is faulty or not in thermal contact with the sample stage Ask for assistance Similarly the heater may be in poor thermal contact with the sample The thermal cutout switch on the CCR is operating Is the setpoint too high Is the compressor on 14 Quick Guide to SECI Set temperatures SETTEMP value Set magnetic field SETMAG gauss Select longitudinal field starting at zero LFO Select transverse field 90G TFCAL Select zero field FO Start run BEGIN Finish run END 53
28. ed Cycle Refrigerator CCR is mounted on a slide at the side of the magnet It will operate from a base temperature of about 3K to 700K using the Hot Stage It uses the same sample holders as the EMU CCR There are two temperature measurement ranges and an option to reach the lowest temperatures ask your local contact to set up the appropriate one for you High temperature 50 to 700K The sample and hot stage temperatures are measured with Platinum resistance thermometers The fixed thermometer on the hot stage is used for control The two channels of the Eurotherm controller are used The Pt thermometers become inaccurate below 50K but the CCR will still reach base temperature if the heater is turned off note that a setpoint of T 1K may not be sufficient since the Pt thermometers may read 20K or 20K when actually at 5K Low temperature 5 to 300K The sample is measured with a Cernox thermometer and the Lakeshore controller which is also used for feedback and control The Pt thermometer on the hot stage is still available The Cernox sensor must not be taken above 325K or it will be damaged To go to base temperature set 1K not zero For the lowest base temperatures connect up the three copper braid links which bypass the weak thermal link on the hot stage Do not attempt to warm above 300K in this configuration For operation at and just above room temperature 295 300K for example with liquid samples it is possible to stab
29. erent thermometer calibrations From the menu bar at the top select File Open and select the appropriate one from the box which appears SECI will then automatically restart with the new settings A list of commonly used configurations is given below 31 Configuration name Sample Environment CCR_LowT CCR with Cernox thermometer 5 300K CCR_HighT CCR with Pt thermometer 50 700K Flow_ITC502 Flow cryostat stick 2 Flow_ITC503 Flow cryostat stick 3 Variox_ITC502 Variox cryostat stick 2 Variox_ITC503 Variox cryostat stick 3 OXDF_Low Dilution fridge when operating 0 03 6K OXDF_High Dilution fridge with mixture out or cooling 2 300K Furnace Optical Furnace 7 4 Commands Experiments are normally controlled by typing commands into the command line window on the Open Genie page in SECI Click in the window to make sure it has keyboard focus showing the underline cursor Commands are not case sensitive BEGIN Starts a run Asks for a sample name and other details The temperature and field entered here are used only for the file header and do not set anything END Finishes and saves a run waiting for the end of a period cycle if in period mode There is a last chance to change the header details PAUSE Pauses data acquisition RESUME Resumes data acquisition LFO Selects the main magnetic field initially set to zero SET
30. fective alpha varies or with fixed alpha the asymmetry varies assuming complete depolarisation The relaxing asymmetry difference between fully polarised and depolarised muons varies rather less with field and is always positive but is still not constant Both of these functions may be required to fully correct a repolarisation or level crossing spectrum where the lines are broad or to correctly fit slow relaxation rates in high fields where the baseline cannot be determined from the data Fortunately a simultaneous calibration of both curves can be done using a sample showing a Lorentzian relaxation with measurable lambda e g 0 2 1 us at all fields involving all muons for example a simple paramagnet or as here a semiconductor undergoing rapid charge exchange Ge at T gt 400K All these examples are in the Flow Cryostat Base InitAsym 55 m On AI sample blade 50 Ip e Suspended in foil packet oe ee ee m Small sample suspended e e 45 oe 8 40 L J r Wi a ee Dag s amp 304 ef e Bas D e z e ETA d eo eee 0 2 ESS wee aoe a 204 FEES SN Ba gt e Be 8 u 4 154 8 Ba a 10 Ba a 5 ef 7 a D A ol mage eee ep EB 5 0 10000 20000 30000 40000 50000 Field G 11 30 4 i d BS a ele g Z lt z L e BR e SCH 20 a 8 T AL B R we E 15 4 mu gt S a E 4 10 E m On Al sample blade C m Suspende
31. gnet Danfysik e Custom Command Insert At Delete Enty Clear m Script Run Tine Into a Current Count Rate 120 MeV hr Total Mevents in script 15 Est length of script 10 hrs 120 mins M Script Table Read only Unsaved Clear Script deletes a previous script table Read re loads a previous script for editing and re use To add an entry type in the required temperature field selecting main longitudinal field or calibration and number of Mevents and click Add If no change is required leave the temperature and or field values blank instead of re entering the same value this avoids having to wait to confirm the value is still stable The first entry can take control of and finish off a run that was in progress when the script starts in this case you would usually leave both temperature and field blank showing KEEP in the table For a linear scan of either temperature or field but not both enter the start end and step values Use only the Start value for a single run Scans can go up or down When setting fields you can select Danfysik which sets the longitudinal field main coils or Calibration which selects the Y transverse field these names are left over from MuSR and EMU You can highlight an entry in the table then Insert At instead of Add puts the new entry just before it or Delete removes this one T
32. ilise the temperature with the CCR compressor off This will save a lot of time 22 during sample changes as there is no need to defrost the CCR It will not be necessary to pump the vacuum Either temperature configuration may be used but High T Pt is probably easier to use Do not heat above 310K with the compressor off as this could overheat and damage the cold head of the CCR itself fine seme me rn ZE e Zi ES om B akeShore fee e Tuning Alarm Zei v naine a 10 3401 12679 5 Is em en e trot x a K 58 ver bope 16 2480 K L 159 0 pout im L eat eua d 0 0 a TU H 14 34 D GE Se ue Leap 340 Temperature Controller i I Lakeshore temperature controller used with the CCR CCR cold head showing the floating Cernox thermometer attached to a sample plate back view As the CCR is close to the magnet you must only use the non magnetic tools provided when working on it Do not bring scissors scalpels etc into the area Even if the field is off for sample mounting a scalpel left lying around nearby might go flying when the field is turned on again To mount a sample e Mount the sample on a standard sample plate fly past holder or similar this is done in the preparation lab well away from the magnetic fields As the sample is in vacuum thermal contact must be provided with vacuum grease or GE varnish for example e Fix the sample plate or fly past holder to the copper flange o
33. it under certain conditions type licence eK KK for details Configuration CCR conf se Te IE T e a fel FFE BS SECI icon e uidionserint icon Data collection scripting and control of sample environment equipment is run by ISIS Sample Environment Control Interface or SECI for short This should normally be running on the control PC If not you can re start it with the SECI entry under the Windows Start menu but let your local contact know it stopped The blue menu at the left allows various pages of windows to be chosen Selecting Labview VIs gives a row of tabs along the top and each of these contains some of the sample environment control programs as required ISIS News and Beam Status will show if the beam is off and why Usually you will select Open Genie Scripting and a temperature graph and command line window will be visible as above The dashboard along the top with run number counts temperature field etc is always present but can be minimised or restored using the arrow to the right of the run number if more screen space is needed for graphs or Labview VIs 7 3 Configurations SECI must be informed which sample environment equipment is in use so it can load the appropriate control programs and parameter files The current selection is shown in the bottom border of the window In some cases you must change over if you merely change sample sticks with diff
34. lar sample plates are available for the CCR 50mm wide the same size as EMU and MuSR s new CCR not the larger ones used on the old MuSR CCR The depression in the holder plate should be filled with powder sample then covered with a thin Mylar sheet fixed with epoxy resin The extension at the top allows for the powder to settle slightly while still keeping the main circular area filled Tap the holder on the bench to check it is full Aluminium powder holders should be used with an appropriate sized silver mask Silver holders should not need a mask 6 1 2 Clamped holders These all have a basic design of a cell body thin window bezel and screws One version has a metal o ring in a groove this is suitable for very air sensitive samples and can be filled in the glove box Gold seals will work up to high temperature while indium may be more reliable for work at room temperature and below Another type uses a knife edge seal and either a mylar window which will seal or a titanium window for higher temperature use Many of the cells are made from titanium with titanium screws and should not need a mask Some larger aluminium cells are also available and these will need a silver mask 6 1 3 Backing plate mounting A large silver plate is fitted on the sample stick or cold head and the sample attached to it using vacuum grease or GE varnish for thermal contact if in vacuum CCR or dilution fridge This is suitable for singl
35. lts in inhomogeneity over a 25mm diameter sample of less than 0 1G Alternatively a good zero field condition can be obtained by either a demagnetisation cycle of the main field or a soft quench heating the coils above Tc Both of these will be slow After the soft quench the magnet will take about 2 hours to re cool below Tc before any fields can be set even 20G transverse or any small field to compensate the Earth s field Ask your local contact if you think either of these will help your experiment 13 A transverse field of about 80 100G is recommended to obtain alpha as it will be affected less by any uncorrected remanent field in the longitudinal direction and is also easier to fit if there is strong relaxation If you need a calibration of diamagnetic asymmetry a 20G run may be better as this is affected much less by the finite muon pulse length The Magnet On light will show if the field is turned on above some minimum value about 500 gauss 0 05T In persistent mode the field will remain on if power to the supplies fails so the warning light is independently controlled and battery backed The magnet includes reverse wound self shielding coils to reduce the stray field outside the area or acting on the other instruments but there is still a field of up to 0 2T at the magnet casing Be careful if it is necessary to enter the area or approach the magnet if it is on especially if carrying any magnetic items Only no
36. n magnetic tools are to be used near the magnet 4 3 Eddy current heating As the field varies eddy currents may also be induced in the cryostat sample plate or your sample itself causing a temperature rise This is particularly noticeable in the dilution fridge where a field ramp at the default rate from 0 to 1T may cause the sample temperature to rise from base to around 400mK If it is important to stay below some transition having zero field cooled the sample for example the field ramp rate can be slowed down ask your local contact You may find it useful to set the sample temperature to some value above base so that the controller has power in reserve reducing heater power as eddy current heating starts and keeping the temperature constant during the ramp If the thermal history is not important and measurements are required close to base temperature a scripted field scan may need extra delays to be inserted to allow the temperature to recover before starting data taking A slow ramp rate will take longer but then require less recovery time good for small steps while for large field changes it may be quicker to use the full speed ramp and then a longer waiting time 14 5 Vacuum Vent valve Dial gauge Vent gas inlet 9 Gate valve Vi Bypass A valve MS V2 fe HL Hi a fi Z N TE iil f The Vacuum pump and associated valves 15 Pump On Off button ON light Select sensor to display
37. n the cold head with brass screws e Attach the floating sample thermometer to the back of the sample plate with a copper clip and brass screw and nut and copper loaded grease if necessary Handle the sensor with care the wires are easily broken s Slide the radiation shield can over the sample until it touches the fibreglass spacer Check the window orientation black line at the top Fix in position with the 3 small grub screws using a 2mm Allen key The orientation of the spacer ring does not matter 23 e Remove the locking pins to release the slide press the button in the centre of the handle then pull Slide the CCR into the magnet side port Locking pin one each side Side port open ready for CCR e Guide the bellows onto the flange and bolt the bellows to the magnet port using the six clamps which should be tightened fully leaving no gap between flanges Use the 13mm non magnetic spanner e Push the slide to the end stop compressing the bellows slightly and fix it there with both locking pins e Pump the instrument vacuum chapter 5 e If using the Lakeshore temperature controller Low T turn the heater on press Heater Range then A or Y until SOW is displayed on the bottom line then Enter e Once the pressure is below 10 mbar the compressor may be started the left one of the 3 compressors connected to the panel by the MuSR beam stop Press the ON button there may be a shor
38. ng coil windings instead of the switch Once the required field is reached the switch heater is turned off and the switch returns to its superconducting state The supply current may then be turned off leaving the current circulating through the switch instead The benefit is a much more stable field useful for RF resonance experiments The disadvantage is a small extra delay on changing the field as the switch is opened by heating it above Tc and closed When subsequently changing the field the power supply current must first be returned to the same value as the circulating current in the coils before the switch is opened again The software does this automatically if required The power supply current may be left turned on in persistent mode which will largely compensate for any small resistances or losses in the switch which are found to give a larger field drift This also avoids the delay while the current leads are ramped back to the persistent current setting before a change This is our preferred persistent mode operation Users performing a large number of short runs at closely spaced fields level crossing scans may wish to work in driven mode instead In this case the switch heater is left on all the time and the power supply is always running and its stability defines the field stability and drift rate To change modes for the next and subsequent setpoints set or unset the Auto PM indicator on the MagnetsControl VI
39. o estimate the counting time taken by a script enter the count rate in the box at the bottom left and MuonScript will calculate the total counts in the script and the estimated time This does not include time for temperature or field changes which may be significant Add another entry or click somewhere in the table to update the time after changing the rate Finally save the script with Write and choose a filename for it Put it in the default directory offered U To run a script return to the Open Genie window in SECI and type 36 load yourscriptname gcl using the filename you chose As a reminder the name is shown in the bottom border of the MuonScript window and you can also use Tab to auto complete the name Note that the script will not set or prompt for the sample name or any header entries other than the temperatures and fields it actually sets If you are about to start measurements on a new sample using a script use the SETLABEL command to ensure the sample name etc are correct If you have just set a temperature or field the script will not put this in the header either again use SETLABEL Finally type runscript to actually start the script When a script changes temperature the TPAR parameters Accuracy Wait and Timeout for the new setpoint are used The control temperature readback must be within Tset Accuracy continuously for the Wait time in minutes before the next r
40. on the NDXHIFI_CRYOMAG PC The main field must be selected LFO in order to change the setting 43 El MagnetsControl vi l loj xl Operate Help Path to Configuration File fi C Cryogenic Software 2566 Initialisation ini OUTPUT UNITS x STATUS READY X Output 0 000000 4 Y Output SN MAIN Output rt MAIN PM Operation Mode Z SWEEP VALUES i pel x Target LOW VALUE HIGH VALUE 0 000000 G SET X FIELD YoY Z koa ZERO POINT HIGH FIELD MODE LOW FIELD MODE Z SWITCHING MODE _ a Target 3 0 000000 es SET Z FIELD aT ae MAIN Target r AUTO PM OFF Ton a l SET MAIN FIELD START HARDWARE SwWITCHING Keep Leads at B Note because the switch still has a finite resistance when open instead of open circuit the field will not follow the supply current exactly but will lag behind and take a short while typically 20 seconds to stabilise when the power supply current reaches the setpoint Users performing dynamic measurements taking short runs while the field is changing should refer to the fields measured by the Hall or NMR probes in addition to the power supply readback both are logged in the run files 12 Appendix 4 NMR For very accurate field calibration a NMR reference may be required A Metrolab NMR probe can be inserted into a tube which fits into the magnet side or top ports allowing the probe in air to be close to the field centre The tube must b
41. onstant and c any slight alignment errors between the Hall sensors and their intended axes The calculations are performed continuously by the Hall probe readout VI and the corrected values displayed in the Dashboard and logged in the run files The offsets b and other operation of the system can be checked by putting a fluxgate probe at the sample position 9 2 Setting zero The zero field setting procedure FO uses the magnet s X Y and Z coils to compensate the remanent field and any stray fields The operation is Set the main coils to zero if necessary Set the last used zero compensation values of X Y and Z fields and wait for them to stabilise Read the corrected central field Adjust the X Y and Z values and re send them Also store for future use The FO script only exits when this process is complete then data collection may start Setting fields with the X Y or Z coils in low field mode main coils off will add the stored offsets so for example a TF20 run will give a good 20 Gauss accurately transverse field provided the field history is the same as the last time FO was run For the best zero or low field measurements set the main field to persistent mode so its power supply cannot fluctuate and vary the field Merely setting all coils to zero as with LFO or SETMAG 0 will leave the remanent field The high field mode does not include an offset using either the Z or main coils because it is likely tha
42. ostat centre stick Unplug the thermometer Admit helium to the sample space to bring it to 1 atmosphere either from the gas panel via the pump trolley or use the 3 way valve to take helium from the cryostat recovery line but ONLY if there is a non return valve fitted Withdraw the stick Be careful not to lose the rubber seal If the next sample is not ready on the other stick put the short blank stick in the cryostat and pump it while waiting Insert the new stick checking the orientation of the sample as it goes in it should be facing towards the doorway the bolts on the cryostat top plate give an exact alignment The copper block with spring contacts part way up the stick engages with the heat exchanger so you have to push it into place do not twist Fit the clamp Connect the thermometer cable its socket is labelled with a sensor number and check it is reading a sensible value on the controller Pump out the sample space Refill with helium and pump out 3 times to flush out any residual air Set the exchange gas pressure to 200 300 mbar use the helium gas line and the gauge on the pump More exchange gas may help when running close to base temperature Close all sample space valves stop the pump and remove the pumping line Close the area If using a different stick to before check the calibration this may require re loading the SECI configuration on the computer The CCR in its operating position The Clos
43. ponts TI S On Off Autotune 400 AS 00 13 00 7 a 14 00 A d GT Be o E 2 00 We Derivative 10 00 ae Dino Mo TE 100 43 00 80 COS Max Output Power Derivative S L dan Oooo 7 00 o 40 nfOff AutoTune ES Wei 2 1 30 00 1 D _ Sensor calibration info sl Config file name FIXED_NOCONV1 CFG T Sensor Data File 4 On F 0 00 D T 1 1 14 58 15 00 15 02 15 04 15 06 If you have found improved PIDs you can edit the PID table and save it so that your new values will be used on subsequent temperature changes Note that the table is reloaded with our standard settings as appropriate for the equipment selected when SECI restarts You should make a note of the changes you have made and if you think your improved parameters would be of general use then discuss them with your local contact 7 6 Scripting We use a program MuonScript to generate a script from a table of fields temperatures and run lengths A new script can be edited while a previous run or script is still in progress MuonScript is started along with SECI but is not part of it at present Select it from the Windows task bar at the bottom 35 m MuonScript Script Details Read Write Clear Script Calibrat EI Print Help T T T Danfysik E Details f il i T T 0 Danfysik E General Entries B Events MeV 5 5 Temperature Start End T End Step Ma
44. pply on at the valves in both Flow and Return sides on the panel The two red lights on the flow meter indicate the flow is correct typically 3 litres minute Connect the sample thermocouple and lamp power cable as shown note there is a second thermocouple not normally used Check on the Eurotherm unit that the setpoint lower small number is at 0 the readback upper larger number is reasonable around 15 25C and the OP output indicator is not lit before turning on the heater power switch Setpoints are sent and temperatures logged in C Some adjustment of PID values may be necessary if the sample has a very large or small heat capacity Be sure to set the temperature back to 0 turn off the heater power switch and allow the furnace to cool before venting the instrument and removing it To speed cooling of a large sample you may close off the pumping valve and admit a few mbar of Argon through the vent valve You can leave the water connected and flowing and rest the furnace on the steps by the magnet to change samples It may be necessary to disconnect the heater and thermocouple cables if they are not long enough 7 Data Acquisition and Computing 7 1 Detectors HiFi has 64 detector elements each consisting of a scintillator light guide and photomultiplier tube These are divided into forward and backward banks each forming a circular disc with a central hole for the beam Detector positions are as shown looking ups
45. quipment may be time consuming since the cryostats must be cooled in situ or the liquid helium and nitrogen boiled off on removal 17 6 1 Sample mounting A variety of options are available for sample mounting Some of the standard ones are listed here Special setups such as gas handling or RF would be requested as part of your proposal Mount Sample size Dilution Variox Flow CCR Furnace fridge cryostat cryostat Square Al Various 20 No SC Yes Yes below Yes with No Powder to 35mm below 2K 350K adaptor holder diameter Rectangular Various 20 No No No Yes No Al powder to 40 mm holder plate diameter Square 20mm Yes Yes Yes below Yes with No silver diameter 350K adaptor powder 1mm thick holder Titanium 25mm Yes but SC Yes Yes Yes with Yes cell with diameter below 0 4K adaptor gold seal Titanium 25mm Yes but SC Yes Yes 350K Yes 350K No cell with diameter below 0 4K max max with mylar adaptor window Silver Up to Yes Yes Yes Yes No backing 40 40mm plate square Sealed Up to Yes but Yes Yes but Yes No liquid 40mm check size check size holders diameter or and fill 5ml tube Flypast cold From Yes Yes Yes Yes Yes finger 4 4mm Flypast From No No No Yes No frame 4 4mm 18 6 1 1 Powder holders There are square holders for cryostats 37mm square will fit in any cryostat and 45mm square will only fit in the Variox cryostat and CCR Rectangu
46. r ones during the period they are accumulating in the sample The result of this is that the asymmetry of precession signals decreases as a function of the frequency as can be seen in the figure below This applies equally to applied transverse fields internal magnetic fields or oscillations when close to a level crossing resonance in applied longitudinal field but not precession after an RF pulse Muonium triplet amplitude 0 2 4 6 8 10 Frequency MHz 10 The time zero defined in the data file is the average position of the muon pulse defined so that the initial phase remains constant as the applied transverse field is varied The initial phase angle is not zero because of the separator which rotates the muon spins in the vertical plane by about 6 as seen with X transverse field and the kicker about 4 horizontal spin rotation seen with Y field Experiments involving detailed analysis of phase shifts or strong relaxation should also take into account that the pulse is not quite symmetrical 3 6 Full Asymmetry and Background At low fields the full asymmetry for example in silver is about 22 As the field is increased the positrons emitted at high angles spiral into the detectors and those at lower angles and low momentum go through the holes in the centre The degrading effect of a thick sample means that forward and backward positrons of the same original momentum have different radii The ef
47. r the quench If all is otherwise OK the magnet will re cool though this may take 17 hours if quenched 50 from maximum field Inform your local contact who will be able to re start the system when ready meanwhile there is nothing to do which can speed up the cooling During a ramp up or down the field may pause at an intermediate value The magnet coils warm up slightly as the field is changed due to eddy currents and remanent field re distribution and there is a check built into the magnet system which will pause the sweep if the temperature is approaching T This limit is only likely to be reached after successive up down sweeps or sweeping through zero between large positive and negative fields Wait for the magnet to cool and the sweep should automatically resume The temperature log can be viewed on the PC NDXHIFI CRYOMAG 13 4 Temperatures If the cryostat will not cool when requested or starts to warm when it should be at a steady temperature e The cryostat has run out of helium In the case of the flow cryostat this means that the attached storage dewar is empty Was this due to repeated heating cooling cycles or because the flow valve was stuck open e The CCR compressor may have stopped There is a reset button If it happens again ask for assistance it may need refilling with more helium gas e The flow valve is actually closed when the controller thinks it is fully open the ITC5 temperature controllers can sometimes
48. r there are a few things that could be checked first 13 1 No muons or very few muons Is the proton beam on Check the beam current display in the hall and in SECI check MCR News and Beam Status The beam displays take a few seconds to update and the MCR might not send a message until they have some idea what went wrong Base rate used to set up the accelerator causes a corresponding reduction in muon count rate by a factor 32 Did you open the shutter The Beam On light over the area door the red shutter open light by the shutter control buttons and the blue lights inside the area should be lit The Kicker may have tripped This vetoes data taking in all instruments to avoid accumulating double pulse data or just background turns on a flashing yellow light in the MuSR cabin and sends an alarm to the MCR who should reset it Resetting takes 5 minutes if the beam has not returned after this time phone the MCR Has a muon Beam Off button been pressed This turns off the muon beams and the white lights come on in all the muon areas Check if someone is locked in an instrument area or has used the emergency release break glass bolt on the door Anyone who is in any instrument area or blockhouse when blue lights come on should contact the MCR after pressing the beam off button There are a few other things which can be checked but you should ask for assistance to fix the problem Some may res
49. ro field usually gives the largest spot size The plots below are taken from beam camera pictures fitting a Gaussian ellipse which is a fair approximation I x y l exp ax bxy cy dx ey f The width and height plotted are the maximum extent of the ellipse ax bxy cy dx ey f 1 0 where the flux is 1 e of the central value projected on each axis and are suitable for square or rectangular samples The major axis measurement is more appropriate for a circular sample or mask The ellipse axes rotate linearly as the field varies with one complete revolution in about 3 3 Tesla S ri Ki Kal G G G up 911010 uelssney syypm Jjey yods up ajyoid uerssnes sjybieu yey yods a S 2 5 Spot ellipse major half axis an a Ln o Ln Field T In special cases over limited field ranges it may be beneficial to adjust the beam focusing with the quadrupoles please discuss with your local contact The slits are located at an intermediate focus in the beam and open in the horizontal x direction They can be used to adjust the rate and approximate spot size though due to spiralling this may be either the width or height or has little effect on size above 1T Too high a rate can cause detector overload and distortion see the next section The slits are controlled from the instrument computer The value set is the opening in mm Usual values will be between 8 and 30 and beyond about 60 the whole of the beam goes through
50. ruary 2011 a Field_X 0 000 G Steer_HSM 0 313 A Temp_Sample 284 116 K User s JSL Field_Y 0 000 G Steer_VSM2 0 891 A Temp_Power 0 000 long titie Field_Z 0 000 G Steer_Septum 0 000 Temp_P 750 000 Current Run Time 17 50 26 Total MeV 0 Field_Hall_X 0 184 G Temp_I 20 000 Good Raw Frames 0 3210823 Count Rate 0 Field_Hall_Y 0 357 G Temp_D 0 000 Current Period lofi Kicker Status OFF Field_Hall_Z 5 643 G Temp_MaxPower 100 000 Experiment Details Temp_SP Setpoint Temp_Cryostat Temp_Sample LabVIEW VIs 285 852 aa x System Messages er eae R Beam Status 5 284 6832 ISIS News 284 2936 Report a Problem 283 904 Hep o 10 36 00 10 38 00 10 40 00 10 42 00 10 44 00 Time 34 lines scanned compiled Open GENIE successfully started at 21 Feb 2011 10 24 51 091090 39 lines scanned compiled oading Smalltalk image from C Program Files lt x862 CCLRC ISIS Facility Open GE TE genie in oading TCL commands if needed from C Program Files x86 CCLRC ISIS Facilit Open GENIE sre tc 1lNinterface tcl pen GENIE U2 3 BUILD 5776 2010 02 24 15 57 01 Linked Feb 24 2010 19 43 44 library version 1 2 Running on x86 Windows_NT 6 1 built with MS Visual C U5 or greater Copyright lt C gt 1996 2682 CCLRC Rutherford Appleton Lab Open GENIE comes with ABSOLUTELY NO WARRANTY for details type warranty This is free software and you are welcome to redistribute
51. s if no line matches a new setpoint this is an error and it will not be set Then follows the maximum power and the P I D parameters Negative numbers here will not be set Finally the required stability stabilisation time and timeout limit when running under control of a script For experimentation with new PID values you can change the numbers on the temperature controller s VI in one of the tabs under LabVIEW VIs For the ITC5 Flow and Variox cryostats you only need to enter new values and check that the PID Source is set to its usual value of Labview Pane 33 oI TC503 1 vi S 1 Cryostat Temp 320 1000 2 Stick 2 320 1000 3 Stick 3 448 1000 For the Lakeshore CCR enter the values in the column to the right and click Set PID to send them Lakeshore 340 S Front Panel 1 vi IIe IT For the Eurotherm controller CCR with Hot stage or Furnace set the values in the right column Controls 1 Temperature T EurothermController vi File Edit Yiew Project Operate Tools Window Help 1 30 Warning Changes may take a few seconds to come into effect Logtofile 10 sec Main Page Multiplot Activity Ai Graph Buffer Size zJ 1000 Fixed Sample Default Default Default Default Indicators1 Controls1 Setpont Se Temperature PSN Temperature K L s i 100 ape fo Bast srar P 2 P 14 00 lun
52. s purged with an additional scroll pump when mounting a sample The operating range is 5 to 300K Helium consumption is highest when operating at low temperature but a small flow is used even around room temperature Samples should be mounted with their centre at 39mm above the bottom of the aluminium sample plate or 45mm below the copper block if you are using a flypast or other special holder To change a sample you will need to enter the area downstairs and use the steps next to the magnet to reach the top of the cryostat A second person should open the sample pit above operate the sample space pump and lift out the sample stick e Ensure the cryostat is at 50K or higher to prevent frozen air on the windows e Connect the scroll pump to the sample space valve Connect a helium gas line to the small valve on the pump but do not open it yet Turn on the scroll pump pump out the line and then close off the pump Open the sample space valve on the cryostat e Remove the clamp holding the stick into the cryostat the stick will still be held in place by vacuum Disconnect the thermometer cable from the stick e Admit helium gas to the sample space to bring it to 1 atmosphere use the pressure gauges and small valve on the pump set e Withdraw the sample stick Leave the O ring on the cryostat flange e Ifthe new sample is not ready yet put the blank plate on the cryostat and pump the sample space e Insert the new sample stick Check
53. t delay before it starts up Cooling from room temperature whole CCR warm to base should take about 110 minutes If the compressor has been running a while and the sample temperature held at 300K subsequent cooling 24 will take only 60 minutes The compressor should be run at all times especially if working above room temperature Warming from base to 300K with the compressor on will take about 90 minutes To remove the sample e Stop the CCR compressor Set the temperature to 300K e Turn on the mains supply to the Defrost Box Press the large square button on the Defrost Box the orange light will come on Press the left two buttons under the display simultaneously to reset and turn on the second heater The display in deg C will flash if below 200 e Wait for it to warm typically 30 minutes from base temperature While waiting you may wish to set the field to zero Once the orange light on the Defrost box has gone off and the temperature display reaches 10 and then flashes IFSH it is ready to open e Turn off the mains supply to the Defrost Box e Ifin Low temperature configuration Cernox thermometer press Heater Off on the Lakeshore temperature controller e Vent the instrument vacuum chapter 5 Use inert gas if the sample is air sensitive but then disconnect the gas hose and re open the vent valve to fully equalise the pressure e Unlock the slide and pull the CCR back a few centimetres to allow easier
54. t the Periods tab rs l CH 2000 fioo rem rem 10000000 Set the period type to Hardware Internal DAE and in the table set the first 4 rows to 41 Period Type Frames Binary Output Label 1 DWELL 80 0001 Ramp Up 2 DAQ 1000 0000 Field On 3 DWELL 80 0010 Ramp Down 4 DAQ 1000 0000 Field Off All remaining lines should start UNUSED The labels are optional for your convenience The numbers shown here will give 80 frames or 2 seconds for the field to change and stabilise then 1000 frames or 25 seconds of counting time before switching again Longer change times may be necessary with very large modulation fields Once finished click Save Experiment Setup Make sure the main field is selected in SECI command LFO Connect the cables from the DAE to the magnet power supply via the NIM to TTL level converter module in the cabin and the patch panels They are usually left disconnected at the power supply end Period output 1 goes via patch cable HE1 to Mid and 2 via HE2 to Zero Next set the magnetic field which will be switched On NDXHIFI_CRYOMAG find Shim Z vi Switch to the Listening Mode tab and enter the current corresponding to the required field B1 into the top row of the table as Low The relationship is 1 Amp 6 3 Gauss Put a slightly larger current in High E Shim Z vi Operate Help Activ
55. t the remanent offset will change once the main field is varied For accurate low longitudinal fields below 400G use FO and then ZFINE to activate the Z coils with the offset added 40 10 Appendix 2 Period switching and Field modulation The 7 coil power supply has a set of digital inputs which can turn it on or off or switch between two or more values These can be driven from the data acquisition electronics to allow data collection into two sets of histograms or periods at two fields alternating every 10 100 seconds to cancel out any gradual drift in the beam or instrument This is usually used in conjunction with a slow scan of the main field via a script Subsequent data analysis could give a differential line shape 10 1 Turning on field modulation This example will switch the Z field between 0 and B1 since the Z and main fields oppose each other the total field will be BO B1 in period 1 and BO in period 2 Other options are possible discuss with your local contact Switching can be either at a fixed frequency or as here by counting good frames so equal numbers of muon pulses are collected in both states If not already in use select the main magnet supply with the command LF The switching interval is set in the data acquisition system Select the DAE page on the blue menu and click Experiment Setup on the DAE VI this button is only available when there is no run in progress Then selec
56. the slits The beam is steered by three steering magnets and also varying the septum magnet allowing control of both the position and approach angle of the muon beam in the horizontal and vertical planes These are controlled from the computer Normally these will be set to default values so that the beam spot is at the field centre and does not then move around as the field is varied With a small sample and operation over a limited field range it may be beneficial to steer the beam more accurately onto the sample The HSM and VSM2 are the best to use for this in zero field where the HSM has a sensitivity of 21 6 mm per Amp with positive currents moving the beam to the right towards the CCR cold head away from MuSR The VSM2 has sensitivity 7 3 mm per Amp with positive currents moving the beam up 3 3 Dead times and Count rate limits For any non zero count rate it is possible that two muons decay nearly simultaneously with their positrons hitting the same detector so the scintillator pulses overlap and only register as one event in the histogram The probability is proportional to the instantaneous rate so more likely for high count rates at the earlier part of the muon decay curve and for the forward detectors given asymmetry gt 0 and equal solid angles ie alpha 1 The resulting distortion usually looks like a Lorentzian relaxing component with lambda 1 t 0 455 us and a negative amplitude Fortunately the correction is easily
57. tream Forward Backward For longitudinal measurements the usual grouping is simply Forward 1 32 Backward 33 64 For transverse measurements RF precession 4 groups can be defined Left 5 13 52 60 Right 21 29 36 44 Top 13 21 44 52 Bottom 1 5 29 36 60 64 At high frequencies RF the small variations in time zero between individual detectors will have to be allowed for perhaps by fitting the individual spectra 7 2 Computers Computer NDXHIFI is in control of taking the data and most sample environment equipment It is accessed by a remote desktop link from the PC at the right of the desk HEI this remote desktop session is normally left open This screen is mirrored on the platform next to the sample access pit The other PC on the desk NDLHIFI is available for data analysis The magnet is controlled by another PC NDXHIFI_CRYOMAG which users will not normally need to access directly as setpoints are sent from the main control PC It is located next to the magnet power supplies and has its own monitor and keyboard if it is more convenient to access it from the cabin a remote desktop or VNC connection can be used 30 EX Sample Environment Control Interface ersion 1 0 9 27216 Lei File Manager Next Run 15471 E Magnetic Field Field_Mode High Field Mode Steering Temperature Field_Main 0 000 G a_selected_magnet Steer_VSM1 0 814 A Temp_Cryostat 285 728 K 10 45 21 Feb
58. ttom through the split for introducing sample environment equipment These ports form a cruciform which is usually pumped and provides the insulating vacuum for cryostats independent of the magnet s own insulating vacuum or that of the beamline The detectors are in two banks of 32 in the form of flat plates segmented radially Each bank has a central hole allowing incoming muons and exiting muons in fly past mode Light from the scintillators is brought out to the photomultipliers situated next to the end plates of the magnet A tank attached to the downstream end of the magnet bore ensures the fly past muons stop well away from the detectors Other equipment in and around the experimental area is shown in the plan below plan of muon areas 3 Beam and Steering 3 1 Shutter and Instrument Access Status lights Shutter control buttons Red interlock key box all keys are the same M N BEAM OFF ei Search button Typical lock on area and sample position doors Beam Off button The HiFi area shutter is controlled from by the area door on the ground floor To turn on the beam Close the gate giving access to the upper sample position If the door won t close check the pin on the door frame is aligned it is easily adjustable Remove the interlock key and insert it in the lowest available space in the red interlock box by the ground floor door Turn clockwise Search the ground floor area for
59. ult in a lower or unsteady count rate instead of a complete loss The Separator should be on and at a steady 90kV Its control unit is found in the rack next to the kicker and should look like this There is also a spare unit in the rack Low current Steady 90kV This light reading ON This light OFF 48 The beamline magnets should be on Their power supplies should show a current reading most look like this There may be one or two spares in the racks too not plugged in Label may be provided Steady current Output ON with magnet name and reading and CURRENT normal setting lights lit Two magnet supplies are like this The On button at the top left should be lit The Septum magnet power supplies full rack sized units should be on Their control panels should look like this with the Main Power On light lit and a readback current lout matching the setpoint 49 13 2 Counting but strange data Is your data analysis correct the right grouping and alpha Try with another program if in doubt Be sure you are looking at the correct run Run 0 for the run in progress is only available after a new run has accumulated 5000 frames about 2 minutes if the beam is on at full current before then you get the previous one When a run ends the Run 0 file is not updated with the final data so for final analysis re load the data using its run number instead A sequence of very short runs might not
60. un starts No check is made on the sample log temperature the Wait must be long enough to allow it to come to equilibrium For very large samples Wait may have to be increased If the temperature is not stable after Timeout minutes even if it had just reached the setpoint and the Wait interval is now counting down the run starts anyway To stop a Script Ensure the OpenGenie window is active underline cursor visible and press Ctrl C There may be a message about wait cancelled then the prompt returns If a run was in progress it will still be running and will not stop at the number of events specified in the script use END to stop it when appropriate Alternatively you might write a new script or edit the old one to complete this run and continue To pause a script during a run for example while closing the blocker and entering the area go to the DAE page in SECI on the DAE VI open the Run Summary tab and click the Pause Run button near the top right Use the Resume Run button when the blocker is open again This will avoid accumulating empty frames which will upset the dead time calculations If the ISIS beam is off no frames are counted anyway The same method works if running from the command line although here the equivalent Pause and Resume commands are also available 37 2015 03 05 15 44 33 BEGIN run 76985 2015 03 05 15 44 33 Run started in software period 1 2015 03 05 15 44 33 Setting up DAE
61. ve X is towards MuSR Y calibration field up to 100G Positive Y is upwards Zauxiliary field up to 400G Positive Z field is upstream in the opposite direction to positive main field 12 As with most superconducting magnets the main field is slow to change compared to the copper electromagnets on the other ISIS muon instruments Users should consider the order of measurements for example alternate upward and downward field scans at successive temperatures or even temperature scans at a number of fixed fields However for the most repeatable field scans you should use the same scan range and direction each time You may also want to take a series of short runs while the field is ramping up or down Because the persistent switch still has a finite resistance when open at the end of a ramp although the power supply current is steady the main field takes a short time to stabilise This time constant Lmagnet Reswitch is about 25 seconds for small field steps For larger changes 50 Gauss and above the switch heats up further and the time constant reduces to about 7 seconds When running with scripts there is a delay included to allow for this When the main field is changing the magnet coils heat slightly For large field changes in practice maximum to zero and then reversing polarity and ramping up again the ramp automatically pauses to allow the magnet to cool when necessary There are six Hall probes in two sets of three
62. windows and sample and the spread of incoming energy It is important that the muons stop in the sample and not in either the cryostat windows or the back of the sample cell The range curve can be measured for each sample environment by adding degrader foils in front of a standard sample and is shown below For very thin samples it may be necessary to add such foils to optimise the fraction of muons in the sample The choice of degrader material metal foil or plastic film are usual choices may depend on the measurement to be performed also take care what material is present behind the sample If optimising the degrader for your sample note that pumping the exchange gas in a cryostat or the vacuum in the CCR will make a small but possibly significant difference to the range In the CCR the air vacuum in the beam path is equivalent to about one Ti foil HiFi Range Curve in the CCR Ti foils over a quartz plate on an aluminium plate 16 Radiation shield on 18um Al foil windows Sample space pumped 18 14 m Muonium Quartz a 12 e Diamagnetic mostly Ti L E 12 foils i E 8 E 6 H a ee H H 4 B 16 foils 2 23 March 2015 S 0 20 40 60 80 100 120 140 160 180 200 Density mg cm2 Figures for various other SE 3 5 Frequency response Because the muons in one bunch do not arrive at the sample at the same instant any transverse fields within the sample cause the early muons to precess relative to the late

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