GEM Chamber Gain Calibration

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Introduction

Gain calibration of a detector is relatively straightforward measurement but it can be a challenge to setup and extract a good signal.

You will record the number of particles detected in a given time period along with the electric current that is induced on the readout strips. These measurements will be done at various values of current supplied to the HV divider until a sufficient number of data points are collected.

For an ideal detector a plot of the number of counts vs. HV divider current should behave as a sigmoid.

Experimental Setup & Procedure

Once your triple-GEM chamber has been assembled and grounded you are ready to begin setting up the nuclear instrumentation modules (NIM) that will be used in the experiment. The specific instrumentation you will use at your home institute will depend on what you have available. However, all setups will share the same key components; they are, given in order from the detector, as follows:

  1. Preamplifier
  2. Amplifier
  3. Discriminator
  4. Counter

Additionally a power supply cable of supplying the requisite potential to the chamber with sufficient safety controls to protect the GEM-foils from internal discharges is required. Programmable high voltage (HV) power supplies manufactured by CAEN are ideal for this purpose due to their programmable trip protection. This feature allows the power supply to cut power to the GEM chamber if the current and/or voltage go above their programmable limits for a given amount of time (also programmable). Other manufacturers supply similar HV power supplies, whose operation is similar, and may be suitable if a CAEN module is not available.

The NIM that you will use here at the school, excluding the preamplifier which is a standalone device, are shown below:

NIM_Module_Description.png

additionally you will be provided with an oscilloscope to check the pulse shape at various stages.

The linear FAN-IN/FAN-OUT module will allow you to split the signal to numerous other pieces of electronics.

Setup of NIM

Your instructor will show you where all the LEMO cables, T-splitters, adapters, and terminators can be found in the lab. Some of the electronics you will use have only BNC connections while in the lab we have only LEMO cables. If a BNC to LEMO adapter is not present on the connection you are attempting to use you will have to attach one.

Whenever possible try to use the shortest cable that can comfortably join two pieces of electronics together. This minimizes the attenuation of signal due to cable lengths and the induction of electromagnetic noise that may be induced along the cables. An example of how your final setup should look is presented at the end of this subsection.

The CAEN Mod. A422A charge senesitive preamplifier should already be connected to the bottom of the last GEM foil via the LEMO connection present on the chamber's HV circuit.

The CAEN Mod. N1470 HV programmable power supply should also be connected to the chamber's HV circuit via a red SHV cable. Do not turn on or enable the HV yet and leave all HV channels in the kill position for now.

In all steps below the labels of the connections on the electronics are given in bold. If there is any confusion on which connections to use look for these exact phrases when connecting cables or ask your instructor for help.

  1. The NIM should be void of any connections at this time; unhook any cables that are already present.
  2. GainCal_NIM_Logic_Setup_Step1.png

  3. Connect the ENERGY output of the preamplifier to the INPUT of the ORTEC 474 timing filter amplifier. Using a splitter send the OUTPUT from the amplifier to both CH1 of the oscilloscope and the SIGNAL of the Amptek multichannel analyzer (either MCA8000A or MCA8000D). The connection to the oscilloscope is described in Step 5. Setting up the oscilloscope configuration will be done for all channels during Oscilloscope Configuration below.
  4. GainCal_NIM_Logic_Setup_Step2.png

  5. Set both the INTEGRATE and DIFF times on the ORTEC amplifier to 500ns.
  6. GainCal_NIM_Logic_Setup_Step3.png

  7. The pulses from the GEM chamber will be negative unipolar pulses. However the multichannel analyzer, which you will use to investigate the output spectrum from the GEM chamber, accepts only positive unipolar or positive-leading bipolar pulses; therefore flip the switch on the amplifier down to the INV position.
  8. GainCal_NIM_Logic_Setup_Step4.png

  9. Using a splitter connect an output cable to CH1 of the oscilloscope. Connect this cable to the first IN of the first channel of the LRS Model 428A Linear FAN-IN/FAN-OUT. Note there should now be two LEMO cables connectd to CH1 of the oscilloscope. The connection to the FAN-IN/FAN-OUT is shown below in Step 6.
  10. GainCal_NIM_Logic_Setup_Step5.png

  11. Connect the OUT from the first channel on the LRS Model 428A Linear FAN-IN/FAN-OUT to the first IN on the next channel. This will allow you to tune the bias voltage on the signal to an acceptable level for the ORTEC 935 quad constant fraction discriminator (CFD) in Setting NIM Thresholds below.
  12. GainCal_NIM_Logic_Setup_Step6.png

  13. Connect the first OUT of the second channel on the FAN-IN/FAN-OUT to CH2 of the oscilloscope.
  14. GainCal_NIM_Logic_Setup_Step7.png

  15. While the Amptek MCA can only accept positive unipolar or positive-leading bipolar pulses the ORTEC 935 quad CFD can only accept negative unipolar pulses. Flip the switch on the second channel of the FAN-IN/FAN-OUT down to the INV position.
  16. GainCal_NIM_Logic_Setup_Step8.png

  17. Connect the OUT from the second channel of the FAN-IN/FAN-OUT to IN 3 of the ORTEC 935 quad CFD.
  18. GainCal_NIM_Logic_Setup_Step9.png

  19. Connect the second OUT of channel 3 on the CFD to the NIM IN of CH1 on the CAEN Mod. N145 quad scaler and preset counter-timer. Connect the third OUT of channel 3 on the CFD to CH3 of the oscilloscope. Connect the first OUT of channel 3 on the CFD to START of channel 2 on the dual timer.
  20. GainCal_NIM_Logic_Setup_Step10.png

  21. Link both DLY connections on channel 3 of the ORTEC 935 quad CFD with an external LEMO cable. Since we are not interested in precise timing information for this measurement any cable length will be suitable; a length of 0.5-1.0ns is recommended to avoid cable clutter.
  22. GainCal_NIM_Logic_Setup_Step11.png

  23. Connect the monitor (M) output on channel 3 of the ORTEC 935 quad CFD to CH4 of the oscilloscope. This will let you observe the signal manipulation the CFD performs to make it's decision to send an output gate on.
  24. GainCal_NIM_Logic_Setup_Step12.png

  25. For some unknown reason during testing the CFD occassionally produces two gates per input signal pulse. This is a problem and causes double-counting of incident particles on the GEM chamber. If this behavior is observed after the HV is applied in Programming the High Voltage Supply and the chamber is exposed to a radioactive source in section Y connect the OUT of channel two on the dual timer to the VETO on the bottom of the CFD. You will setup this veto later in Setting NIM Thresholds below.
  26. GainCal_NIM_Logic_Setup_Step13.png

  27. Equip the additional OUT on channel 2 of the dual timer with a LEMO cable. You will connect this to CH4 of the oscilloscope instead of M from channel 3 of the ORTEC 935 quad CFD in Setting NIM Thresholds below to assist in tuning the veto gate.
  28. GainCal_NIM_Logic_Setup_Step14.png

  29. Connect the OUT of CH5 of the CAEN Mod. N145 quad scaler and preset counter-timer to the GATE of CH1 on the same module. This will supply a logic pulse with a programmable width to the input channel; any pulses arriving from the ORTEC quad 935 CFD to the counter will only be counted if they are within this logic pulse.
  30. GainCal_NIM_Logic_Setup_Step15.png

  31. Any connection linked by a solid white line on a NIM is electrically connected in some way. Unused connections need to be terminated with a 50ohm LEMO terminator to prevent reflections and other noise from impact the signal. Terminate the extra connections on the counter that are shown in the image below.
  32. GainCal_NIM_Logic_Setup_Step16.png

  33. Programm the counter by: 1) setting the clock to 10'000, 2) moving the single/repeat switch to the SGL position for single measurements, 3) moving the timer units switch to the 1ms position, and 4) flipping the COUNTER switch to the right so it is set to the timer function.
  34. GainCal_NIM_Logic_Setup_Step17.png

You have now properly connected all the electronics for measurements. Your setup should look similar to the image below if you have done everything correctly:

GainCal_NIM_Logic_Setup_Step18.png

Next you will setup the HV supply to the GEM chamber as described below in Programming the High Voltage Supply. Then before you begin to take data will need to tune the thresholds/settings on the FAN-IN/FAN-OUT, CFD, and dual timer as described below in Setting NIM Thresholds with the HV on.

Programming the High Voltage Supply

Each channel on the CAEN Mod. N1470 4CH HV programmable power supply has the following parameters:

  • ISET: the current limit given in micro-amps,
  • MAXV: the voltage limit given in volts,
  • RUP: the voltage ramp up rate given in volts per second,
  • RDWN: the voltage ramp down rate given in volts per second,
  • TRIP: time spent with the current (voltage) above ISET (MAXV) before the HV is killed,
  • and PDWN: action to perform when switching off the HV.

For safe triple-GEM chamber operation the ISET value should be set at or below 710 micro-amps with a TRIP time of 0 seconds. This ensures that if a spark or discharge from one foil to the next occurs power is immediately cut and the GEM-foils are not damaged.

The MAXV should be set to a value slightly higher than the highest voltage value planned for a gain calibration measurement to prevent the accidental application of to high of a voltage.

The RUP rate should be set to a low value (50-100 V/s). However the RDWN rate should be set to a high value (~250 V/s) and always be higher than the RUP rate.

To program the HV channel the triple-GEM chamber is connected too execute the following steps:

  1. Using the glowing blue knob turn until the number in the upper left corner of the LCD screen, which corresponds to the channel number, shows the channel which is connected to the triple-GEM chamber.
  2. Push in on the glowing blue knob. The red box that was highlighting the channel number in the upper left corner of the screen should now be highlighting the lower right box which shows the parameter name and value.
  3. Set each parameter to the values shown in Table 1 below.
  4. Table 1: Parameter values for CAEN Mod. N1470 4CH high voltage progammable power supply to be used for triple-GEM chamber operation.
    Parameter Units Value
    ISET uA 710
    MAXV V 4000
    RUP V/s 50
    RDWN V/s 250
    TRIP s 0
    PDWN - KILL

  5. To set a given parameter turn the glowing blue knob until the parameter name appears in the lower right box.
  6. Push in on the glowing blue knob; the text will change from orange to blue.
  7. Move to the cursor to the numeric value of interest, push the knob when the correct digit position is selected. The digit will change from orange to blue.
  8. Rotate the knob until the parameter is at the right value and push the knob to lock in your choice.
  9. Once the value is set push the knob in again to finalize the parameter and move to the next one.
  10. Repeat steps 4 through 8 for each parameter.
  11. Once all parameters are set flip the switch for the corresponding channel up to the HV EN/ON position. The red LED will now turn on indicating high voltage is now being applied to the chamber.
  12. GainCal_Programming_HV_Step2.png

Quick note on safety. Now HV is applied to the chamber. Do not touch or move any metallic object near or in contact with the HV circuit as this could cause a discharge which could damage the chamber or injure a participant. The readout strips are not exposed to HV they can be accessed without concern.

Oscilloscope Configuration

Note this section may be skipped if you are familiar with oscilloscopes. In the interest of completeness it was included. However, the output monitor signal (M) from the ORTEC 935 quad CFD requires AC coupling, all other signals we will observe require DC coupling.

With the exception of CH1 all other channels need to be terminated with a 50ohm LEMO terminator. Add a splitter to channels two through four and attach a terminator at the end if you have not already done so.

Use the colored channel menu buttons on the oscilloscope to configure the first three channels to have DC coupling (signals coming from the amplifier, the linear FAN-IN/FAN-OUT, and the CFD). The output monitor signal (M) from the CFD requires AC coupling. Next use the Trig Menu to change the source to CH1 and set the trigger slope to Rising instead of Falling if it is not already set. Also change the trigger mode from Auto to Normal if it isn't already. These menu buttons are highlighted in the image below.

Oscope_Menu_Access.png

To change the values once inside a menu use the highlighted vertical buttons along the side of the screen shown in the image below.

Oscope_Menu_Options.png

Adjust the vertical Position and Scale knobs until the screen resembles what is depicted in the image below; this image also highlights the location of the Position and Scale knobs. Note you may not necessarily see similar waveforms.

Oscope_Vertical_Scale_and_Position.png

Also adjust the horizontal scale so that the grid lines represent several microseconds as seen in the image below.

Oscope_Horizontal_Scale_and_Position.png

Adjust the trigger level (using the Level knob shown in the image below) to a slightly positive value so that you can see the electronic noise triggering the scope. Being able to see the noise will help you to tune the NIM thresholds in the next subsection.

Oscope_Trigger_Level_Position.png

Setting NIM Thresholds

Unless otherwise specificed. The steps below assume that the HV is on, the oscilloscope is configured as described above, and that a radioactive source is not present.

Tuning Zeros

Tuning the zero position of a waveform on an oscilloscope means we are tuning the bias voltage that is being applied. The difference between the zero position and the waveform for a given channel can be seen on the y-axis of the oscilloscope's screen; the colored integer which denotes the channel number will be to the right of a colored arrow on the y-axis. This colored arrow denotes the zero position of the channel. If the mean position of the waveform is offset from this colored arrow it means a non-zero bias voltage is being applied to the channel.

This colored arrow is shown in the image below for channel four:

Oscope_Channel_Vertical_Zero_Position.png

here we see that the mean position of the waveform is not offeset from the colored arrow. This means that either a very small or zero bias voltage is being applied.

Nonzero bias voltages can cause problems when using devices that are not intelligent enough to act on the difference between the waveform and a pulse. e.g. if a waveform with a 40mV bias voltage is sent to a low-tech device that will trigger on absolte voltage values above 20mV then it will always send a trigger for both noise and signal because the input waveform is above it's threshold.

Ensure the bias voltage on CH2 of the oscilloscope is as low as possible by using a small flat headed screwdriver to turn the ZERO screws of channel one and two of the linear FAN-IN/FAN-OUT. The blue CH2 arrow on the y-axis should be at the mean position of the waveform as shown in the image below:

GainCal_Setting_NIM_Thresholds_Step1.png

CFD Thresholds

We will need to tune the CFD such that only signal pulses, and not electrical noise, will generate a logic pulse to be sent to the counter. We will tune the CFD threshold at the highest value of the noise. This will slighly impact our ability to detect low amplitude signal pulses but in this measurement we are interested in the detector's performance plateau and not its efficiency. The procedure for tuning the CFD threshold is given below:

  1. Using the CAEN N1470 4CH HV Programmable Power Supply increase the current being supplied to the HV divider to approximately 700 micro amps. To do this increase VSET value slowly until the IMON value reaches 700 micro amps
  2. Adjust the SCALE knob for CH1 so that the electrical noise is clearly visible. You may see either a harmnonic or random pattern on the oscilloscope; you may need to go as low as 20mV.
  3. Adjust the trigger Level so that only electrical noise is being acquired on the oscilloscope screen; the rate should be O(kHz).
  4. Using a small flat-head screwdriver slowly turn the threshold T screw until a logic gate is no longer generated for the electrical noise. This may take some more "playing" later to ensure that signal pulses are not removed.
  5. GainCal_Setting_NIM_Thresholds_Step2.png

  6. Using the multimeter determine the value of the threshold. This will help you later in determining if an input signal pulse will generate a logic gate. Is the value you read on the multimeter really the correct value of the threshold? Do a google search to find the manual of the ORTEC 935 Quad CFD and investigate for yourself.
  7. GainCal_Setting_NIM_Thresholds_Step3.png

  8. The length of the CFD logic pulse is not of much concern for this measurement since we are not using it to generate precise timing information. Still it is convenient to tune the pulse width to something we can see by eye. Use the same screwdriver to increase the logic pulse width to some sufficient value by adjusting the W screw.
  9. GainCal_Setting_NIM_Thresholds_Step4.png

Checking CFD Thresholds

In this stage you will be placing a radioactive source on the detector to investigate if your threshold is sufficient; ask your instructor for a radioactive source.

Move the trigger Level to various values to observe pulses of different heights. Try to determine the amplitude of the lowest pulses. Do you expect this pulse to generate a logic pulse from the CFD?

If the signal pulses are not generating logic pulses then you may need to retune the CFD threshold. This is a balancing act; you need to tune the threshold so that signal pulses (noise) do (not) generate logic pulses. Note that during this procedure you cannot change any of the settings on the electronics upstream of the CFD as this will affect the input pulses being sent to the CFD and invalidate your tuning efforts. Also any changes to any of the electronics after data taking for the gain calibration measurement has begun will invalidate your previous data.

CFD Veto Setup

We have observed with this setup that ORTEC 935 Quad CFD will occassionally generate two logic pulses for one signal pulse:

OscopeScreenCap_Need4Veto.JPG

this is most likely due to the fact that we had to invert the signal using the linear FAN-IN/FAN-OUT and this NIM will saturate and send out flat topped pulses (see CH2 on the oscilloscope). If this is not addressed the counter will double count the number of signal pulses. Frustratingly, not every signal pulse will generate two output logic pulses from the CFD; so we cannot simply divide the number on the counter by two. To solve this issue we have decided to use the Dual Timer to veto any secondary logic pulses for a given input pulse.

The CFD logic pulse is sent to both the counter and the dual timer. For each input pulse from the CFD the dual timer will generate an output logic pulse with a tuneable width. We will tune this width to encapsulate the signal pulse as shown below:

OscopeScreenCap_TimerVetoShort.JPGOscopeScreenCap_TimerVetoIntermediate.JPGOscopeScreenCap_TimerVeto.JPG

notice in the first two images the logic pulse from the dual timer is not long enough to encapsulate the signal pulse and secondary CFD logic pulses are not vetoed. It is only when the timer logic pulse encapsulates the signal pulse that secondary CFD logic pulses are vetoed as shown in the third image. In this arrangement we have solved our sporadic double counting issue.

Note we cannot make the timer logic pulse to long or else it will veto CFD logic pulses from the next signal pulse.

The procedure for setting up the CFD veto is given below:

  1. Temporarily disconnect the CFD's monitor M channel from CH4 of the oscilloscope and connect the additional OUT from the dual timer this channel.
  2. GainCal_Setting_NIM_Thresholds_Step5.png

  3. Change the coupling of CH4 on the oscilloscope from AC to DC as the dual timer requires DC coupling.
  4. Encapsulate the signal pulses by tuning the large and FINE WIDTH knobs on the dual timer.
  5. GainCal_Setting_NIM_Thresholds_Step6.png

  6. Disconnect the additional OUT from the dual timer from CH4 of the oscilloscope and reconnect the CFD's monitor M channel.

    GainCal_Setting_NIM_Thresholds_Step7.png

You are now ready to check the quality of your signal by attempting to measure the energh spectrum of the radioactive source.

General Comments on the Setup

In Step 8 of Setup of NIM we inverted the signal so that it could be properly analyzed by the ORTEC Quad CFD. One may be interested in why we didn't simply send the normal negative unipolar pulse from the amplifier to the FAN-IN/FAN-OUT split it to the appropriate locations and then invert it to positive unipolar for the MCA. The reason for this is that the FAN-IN/FAN-OUT will saturate at high signal amplitudes. The output pulses will be distorted and have a flat top instead of the standard behavior. Since the area of the pulse is proportional to the energy this will cause a significant negative impact on the spectrum observed with the MCA and must be avoided at all costs.

However, discriminators are less sensitive to saturation and pulse shapes as they compare an input signal to a preset threshold. As long as the input signal, even with the distortion, is above the discriminator threshold an output gate signal will be sent.

Simplier ways to setup the electronics definitely exist. However, it is sometimes useful to be able to measure/observe signals from multiple steps/instruments at once. The experimental setup described above accomplishes this goal. Time permitting the participants will be encouraged to setup the electronics without the MCA to see cleaner pulse shapes.

Energy Spectrum Measurement

The sharpness of the turn-on curve of a gain calibration experiment is directly impacted on the level of noise in the system. One of the best ways to measure the signal quality (aka signal-to-noise ratio) is to investigate the energy spectrum of the energy spectrum.

The best source to do this with is Fe55. However we only have access to Cd109 in the TIF. The Cd109 source emits a 22 keV photon which is higher than the Fe55 source. Photons from both sources will be captured by the copper layer on the drift electrode causing the copper atoms to become excited and give off photons. These photons will then being to interact in the gase volume. We expect a spectrum with two peaks; the highest peak is the copper excitation peak and will be at approximately 8 keV; this corresponds to photons whose energy is totally converted inside the gas volume. The second peak, at approximately 5 keV, is known as the escape peak; this corresponds to photons whose energy is only partially converted in the gas volume and then escape the detector.

We will use an Amptek MCA8000D to measure the energy spectrum. You should already be supplying HV to the detector and have the radioactive source present from the previous steps. If this is not the case turn the HV on as you have done before and ask your instructor for the radioactive source.

The MCA should already be on and connected to both the amplifier and the computer; if it is not connected and powered on do so now. The procedure to acquire a spectrum is given below:

Note the following steps assume you are using the MCA8000D; operating the MCA8000A is very similar but the software is slightly older and will look slightly different than the images in this section. Also the MCA8000A shuts off when not in use and you will have to power it on and re-establish communication with the PC often.

  1. If you are using the Amptek MCA8000D (MCA8000A) open the DppMCA - Shortcut (ADMCA - Shortcut) on the desktop.
  2. The program should start with the popup window shown in the image below. If text box under the Find Device button does not display a ghosted FOUND then the MCA is not properly connected to the computer or powered on. Some trouble shooting may be required; otherwise press Connect.
  3. GainCal_MCASetup_Step1.png

  4. Familiarize yourself with the layout of the MCA software as you may have to take multiple spectrum. The first image shows the buttons of interest for taking measurements and the second image highlights the layout of the information panels.
  5. GainCal_MCASetup_Step2.png

    GainCal_MCASetup_Step3.png

  6. Click the Acquisition Setup button. Navigate to the MCA tab in the popup window that appears (see image below).
  7. GainCal_MCASetup_Step4.png

  8. Determine the range of signal pulse amplitudes in volts; you will need this for setting up the MCA parameters. The MCA has two operating ranges. The first accepts signals with amplitudes 0-1V. The second accepts signals with amplitudes of 0-10V. You could potentially damage the instrument if you have the wrong mode selected or you send a pulse with an amplitude that exceeds 10V to the MCA.
  9. We will now determine at what ADC channel the pedestal (noise) stops; to do this, close the source apperature, remove it from the detector, and set it aside in a safe location.
  10. In the DppMCA program make sure the settings in the MCA tab are configured as in the image below. Note the numbered boxes 1, 2, and 3 which respectively represent the Preset Real Time, Low Level Discriminator (LLD), and the Input Range.
  11. GainCal_MCASetup_Step5.png

  12. Change the parameters given in Table 2 below to the values given in the Pedestal column then click OK.

    Table 2: AmpTek MCA8000D Settings for taking signal and pedestal values.
    Parameter Signal Pedestal
    Preset Real Time (s) 60 5
    Low Level Discriminator (LLD) (V) See Step 9 0
    Input Range (V) See Step 5 See Step 5

  13. Press the Start/Stop button to acquire pedestal only data. Place the cursor in the region where the pedestal data stops as shown in the image below and record this channel.

    GainCal_MCASetup_Step6.png

  14. Change the Low Level Discriminator value in the MCA tab of the Acquisition Setup menu to the channel you determined in the previous step. Change the Present Real Time value to what is shown in the Signal column of Table 2 above.
  15. Place the radioactive source back on the detector and reopen the apperature. Note the kapton window on the detector acts like a mirror and can help you locate the apperature and safely place it on the detector.
  16. Record the HV being supplied to the HV divider and the current flowing through it (i.e. the VMON and IMON values on the CAEN HV Supply); press the Start/Stop button to acquire a quick spectrum. You should see something similar to the image below where the key features are remainin pedestal counts, the smaller escape peak, and the main peak.
  17. GainCal_MCASetup_Step7.png

  18. Change the Low Level Discriminator value in the MCA tab of the Acquisition Setup menu to remove these remaining pedestal counts. Change the Preset Real Time value so that the MCA will acquire data for 5-10 minutes. Press the Start/Stop button to acquire a long spectrum.

If your long spectrum looks similar to the image below than your noise levels are sufficiently small for the gain calibration measurement. Proceed to the next section.

GainCal_MCASetup_Step8.png

If your spectrum is not similiar to the one presented above some troubleshooting may be required. Discuss with your instructor on possible troubleshooting strategies.

Keithley Picoammeter Setup

You will need to measure the current collected on the readout strips for the gain calibration measurement. To do this we have joined all connectors together using LEMO cables and sent the combined output to a Keithley 6487 Picoammeter/Voltage Source. The procedure for configuring this device is given below:

  1. Power on the Keithley 6487 Picoammeter/Voltage Source. Watch the LED screen closely and record the SCPI ADDR value that displays on the screen as in the image below:
  2. GainCal_KeithleySetup_Step1.png

  3. Press the ZCHK button to perform the zero check as in the image below:
  4. GainCal_KeithleySetup_Step2.png

  5. The instrument is now running. Make sure the instrument is set to an appropriate measurement range based on the incoming current; i.e. you do not want to exceed the current range while you are performing the gain calibration measurement. Navigate to the 20nA or 200nA range using the RANGE buttons:
  6. GainCal_KeithleySetup_Step3.png

If current is being read out on the instruments display screen you have correctly configured the instrument and can proceed to the data taking!

Gain Calibration Experimental Procedure

It is assumed that a radioactive source is irradiating the detector at this time; if this is not the case expose the detector to a source and then continue with this section.

For the gain calibration measurement you will be recording the number of detected particles in a given time period. You will also be measuring the current from the readout using the picoammeter. You will take these measurements for a given value of current being supplied to the HV divider on the detector.

A plot of the number of counts vs HV divider current should behave similiarly to a sigmoid. In the data analysis section you will use these measurements to determine the rate of particles and the gain.

You will take data until a the number of particles detected goes to approximately zero. You are interested in the location of the plateau and the turn-on curve. The experimental procedure is given below:

  1. Change VSET on the CAEN HV Power Supply shown below until the current running through the HV divider (i.e. the IMON value) is approximately 700 micro amps.

    GainCal_ExpProcedure_Step1.png

  2. Record the VMON and IMON values.
  3. Press the LOAD button on the CAEN counter to start the clock as in the image below:
  4. GainCal_ExpProcedure_Step2.png

  5. Record the value shown in the LED display of CH1 after the LED display of CH5, i.e. the clock, goes to zero. Once you have recorded this value press the CH1 RESET button. This procedure is outlined in the image below:
  6. GainCal_ExpProcedure_Step3.png

  7. Using the Keithley 6487-Readout.vi shortcut on the desktop to start the LabVIEW VI to readout the current data if the program is not already running.
  8. Change the GPIB address to GPIB0::XX::INSTR where XX corresponds to the value you recorded in Step 1 from Keithley Picoammeter Setuo. Change the TemporaryFile and file path fields to the paths given in the links below. Then click the Run button in the top left corner of the VI to start the program. These steps are illustrated graphically in the image below:
  9. "C:\Users\Administrator\Desktop\Keithley Data\CMSGEMSchool_Summer2014\SchoolGEMxx_yyyyV_zzzuA-temp.dat"

    Where xx is the detector number (either 01 or 02), yyyy is the VMON value, and zzz is the IMON value.

    "C:\Users\Administrator\Desktop\Keithley Data\CMSGEMSchool_Summer2014\SchoolGEMxx_yyyyV_zzzuA.dat"

    Where xx is the detector number (either 01 or 02), yyyy is the VMON value, and zzz is the IMON value.

    Note the "temp" is no longer present

    GainCal_ExpProcedure_Step4.png

  10. Allow the program to collect O(100) data points in the graph. This data will be shown in the Waveform Graph.
  11. Then use the Do Average feature to average the current and compute the standard deviation. Set the Points To Be Average value to 100 points. Then click the OFF button and record the value. Alternatively you do this offline since the data is stored in the *.dat file. Click the STOP button above the GPIB address field to end the program. Note if you click the red stop sign in the upper left corner of the screen a file will not be created (this is actually the improper way to stop a VI). These buttons are shown in the image below:
  12. GainCal_ExpProcedure_Step5.png

  13. Reduce the current running through the HV divider (i.e. IMON) by approximately 10 micro amps and repeat steps 2 through 8. Continue this until the number of counts detected goes to zero.
  14. Make a plot of counts vs. current supplied to the HV divider (i.e. IMON). If you do not have enough data granularity along the turn on curve take a few more points so that you can see the rise to the plateau.

Congratulations you have successfully taken data with a 10x10 triple-GEM detector.

Labview Programs

When not working in CERN, but in your own lab or in an external School, you need to install Labview on your Windows PC and need to install the right Labiview VI's to interface with the Keithley PicoAmperometer. You can find the Labview VI's on EOS. For this login to lxplus and list and copy the programs stored over there:
eos ls -l /eos/cms/store/group/upgrade/muon/GEMHardware/GainCalibrationTest
xrdcp -r root://eoscms//eos/cms/store/group/upgrade/muon/GEMHardware/GainCalibrationTest/Keithley_6487-Readout_Folder Keithley_6487-Readout_Folder
xrdcp root://eoscms//eos/cms/store/group/upgrade/muon/GEMHardware/GainCalibrationTest/NI4882_140.exe NI4882_140.exe
xrdcp root://eoscms//eos/cms/store/group/upgrade/muon/GEMHardware/GainCalibrationTest/admca_mca.zip admca_mca.zip

Data Analysis

-- BrianDorney - 17 Jun 2014

Topic attachments
I Attachment History Action Size Date Who Comment
PNGpng GainCal_ExpProcedure_Step1.png r1 manage 493.8 K 2014-06-19 - 17:50 BrianDorney  
PNGpng GainCal_ExpProcedure_Step2.png r1 manage 486.1 K 2014-06-19 - 17:50 BrianDorney  
PNGpng GainCal_ExpProcedure_Step3.png r1 manage 504.9 K 2014-06-19 - 17:50 BrianDorney  
PNGpng GainCal_ExpProcedure_Step4.png r1 manage 526.9 K 2014-06-19 - 17:50 BrianDorney  
PNGpng GainCal_ExpProcedure_Step5.png r1 manage 442.8 K 2014-06-19 - 17:50 BrianDorney  
PNGpng GainCal_KeithleySetup_Step1.png r1 manage 611.3 K 2014-06-19 - 17:50 BrianDorney  
PNGpng GainCal_KeithleySetup_Step2.png r1 manage 607.3 K 2014-06-19 - 17:50 BrianDorney  
PNGpng GainCal_KeithleySetup_Step3.png r1 manage 623.0 K 2014-06-19 - 17:50 BrianDorney  
PNGpng GainCal_MCASetup_Step1.png r1 manage 346.4 K 2014-06-18 - 16:41 BrianDorney  
PNGpng GainCal_MCASetup_Step2.png r1 manage 250.9 K 2014-06-18 - 16:41 BrianDorney  
PNGpng GainCal_MCASetup_Step3.png r1 manage 246.0 K 2014-06-18 - 16:41 BrianDorney  
PNGpng GainCal_MCASetup_Step4.png r1 manage 283.5 K 2014-06-18 - 16:41 BrianDorney  
PNGpng GainCal_MCASetup_Step5.png r1 manage 338.3 K 2014-06-18 - 16:41 BrianDorney  
PNGpng GainCal_MCASetup_Step6.png r1 manage 260.3 K 2014-06-18 - 16:41 BrianDorney  
PNGpng GainCal_MCASetup_Step7.png r1 manage 281.8 K 2014-06-18 - 16:41 BrianDorney  
PNGpng GainCal_MCASetup_Step8.png r1 manage 280.6 K 2014-06-18 - 16:41 BrianDorney  
PNGpng GainCal_NIM_Logic_Setup_Step1.png r1 manage 1126.8 K 2014-06-09 - 14:43 BrianDorney  
PNGpng GainCal_NIM_Logic_Setup_Step10.png r1 manage 1142.1 K 2014-06-09 - 14:48 BrianDorney  
PNGpng GainCal_NIM_Logic_Setup_Step11.png r1 manage 1127.6 K 2014-06-09 - 14:48 BrianDorney  
PNGpng GainCal_NIM_Logic_Setup_Step12.png r1 manage 1129.1 K 2014-06-09 - 14:48 BrianDorney  
PNGpng GainCal_NIM_Logic_Setup_Step13.png r1 manage 1127.7 K 2014-06-09 - 14:48 BrianDorney  
PNGpng GainCal_NIM_Logic_Setup_Step14.png r1 manage 1141.3 K 2014-06-09 - 14:48 BrianDorney  
PNGpng GainCal_NIM_Logic_Setup_Step15.png r1 manage 1128.9 K 2014-06-09 - 14:48 BrianDorney  
PNGpng GainCal_NIM_Logic_Setup_Step16.png r1 manage 1125.0 K 2014-06-09 - 14:48 BrianDorney  
PNGpng GainCal_NIM_Logic_Setup_Step17.png r1 manage 1126.4 K 2014-06-09 - 14:48 BrianDorney  
PNGpng GainCal_NIM_Logic_Setup_Step18.png r1 manage 1150.9 K 2014-06-09 - 14:48 BrianDorney  
PNGpng GainCal_NIM_Logic_Setup_Step2.png r1 manage 1206.3 K 2014-06-09 - 14:43 BrianDorney  
PNGpng GainCal_NIM_Logic_Setup_Step3.png r1 manage 1144.5 K 2014-06-09 - 14:43 BrianDorney  
PNGpng GainCal_NIM_Logic_Setup_Step4.png r1 manage 1126.0 K 2014-06-09 - 14:43 BrianDorney  
PNGpng GainCal_NIM_Logic_Setup_Step5.png r1 manage 995.6 K 2014-06-09 - 14:43 BrianDorney  
PNGpng GainCal_NIM_Logic_Setup_Step6.png r1 manage 1131.9 K 2014-06-09 - 14:43 BrianDorney  
PNGpng GainCal_NIM_Logic_Setup_Step7.png r1 manage 1130.1 K 2014-06-09 - 14:43 BrianDorney  
PNGpng GainCal_NIM_Logic_Setup_Step8.png r1 manage 1126.4 K 2014-06-09 - 14:43 BrianDorney  
PNGpng GainCal_NIM_Logic_Setup_Step9.png r1 manage 1127.0 K 2014-06-09 - 14:43 BrianDorney  
PNGpng GainCal_Programming_HV_Step2.png r1 manage 204.2 K 2014-06-09 - 16:18 BrianDorney  
PNGpng GainCal_Setting_NIM_Thresholds_Step1.png r1 manage 684.3 K 2014-06-17 - 17:33 BrianDorney  
PNGpng GainCal_Setting_NIM_Thresholds_Step2.png r1 manage 907.6 K 2014-06-17 - 17:33 BrianDorney  
PNGpng GainCal_Setting_NIM_Thresholds_Step3.png r1 manage 662.6 K 2014-06-17 - 17:33 BrianDorney  
PNGpng GainCal_Setting_NIM_Thresholds_Step4.png r1 manage 824.5 K 2014-06-17 - 17:33 BrianDorney  
PNGpng GainCal_Setting_NIM_Thresholds_Step5.png r1 manage 648.4 K 2014-06-17 - 17:33 BrianDorney  
PNGpng GainCal_Setting_NIM_Thresholds_Step6.png r1 manage 884.5 K 2014-06-17 - 17:33 BrianDorney  
PNGpng GainCal_Setting_NIM_Thresholds_Step7.png r1 manage 643.0 K 2014-06-17 - 17:33 BrianDorney  
PNGpng NIM_Module_Description.png r1 manage 1113.7 K 2014-06-09 - 14:43 BrianDorney  
JPEGjpg OscopeScreenCap_Need4Veto.JPG r1 manage 134.2 K 2014-06-17 - 17:41 BrianDorney  
JPEGjpg OscopeScreenCap_TimerVeto.JPG r1 manage 142.9 K 2014-06-17 - 17:33 BrianDorney  
JPEGjpg OscopeScreenCap_TimerVetoIntermediate.JPG r1 manage 146.4 K 2014-06-17 - 17:33 BrianDorney  
JPEGjpg OscopeScreenCap_TimerVetoShort.JPG r1 manage 144.4 K 2014-06-17 - 17:33 BrianDorney  
PNGpng Oscope_Channel_Vertical_Zero_Position.png r1 manage 1022.5 K 2014-06-09 - 20:18 BrianDorney  
PNGpng Oscope_Horizontal_Scale_and_Position.png r1 manage 1021.6 K 2014-06-09 - 20:18 BrianDorney  
PNGpng Oscope_Menu_Access.png r1 manage 948.2 K 2014-06-09 - 20:18 BrianDorney  
PNGpng Oscope_Menu_Options.png r1 manage 950.4 K 2014-06-09 - 20:18 BrianDorney  
PNGpng Oscope_Trigger_Level_Position.png r1 manage 1008.6 K 2014-06-09 - 20:18 BrianDorney  
PNGpng Oscope_Vertical_Scale_and_Position.png r1 manage 1030.7 K 2014-06-09 - 20:18 BrianDorney  
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