Switching Modes

In the process of editing and updating this page. Please contact Juliette Mammei crowder@jlab.org with questions or suggestions.

PREX Main<< HOW TOs

This page details the checklists for switching between counting and integrating modes. For reference, here are the instructions from PREX I. It is critical to do these steps in the correct order, especially for switching from counting to integrating. The detectors which are used in counting mode can be damaged if they are on when the rate is as high as it will be in integrating mode.

Counting to Integrating

1. Turning OFF the HV
   • VDC HV
   • Scintillator HV
   • GEM HV
   • Adjust Quartz Detector HV for Integrating mode
2. Switching to High-Current Integrating Mode
   • Septum off
   • Take access.
   • Expert to do the switch of the detector signals to integrating mode
     • Cavities: take out amplifiers. Put in attenuator on BCM. This is important.
     • Set up cavities pre-gain and phase using established values.
   • Septum on
3. Set Up Beam
   • Do the Beam Recovery procedure
4. Take data ! Check all data including cavities.

Integrating to Counting

1. Preliminaries. to do long before switching
   • Make sure spectrometer DAQ works (might need reboots). Use the CODA guide if necessary.
   • Check cavities in integration mode and counting mode at high current. Run analysis macros. Do they work ?
   • Check with spot++ that rastered size is approx 4 x 3 mm (whatever is our present norm.)
   • Check the beam position ("centered" to within 0.3 mm, using the production criterea, see white board).
2. Switching to Low-Current Counting Mode
   • Septum off
   • Take access.
   • Expert to do the switch of the detector signals to counting mode
   • While inside the hall check gas flow into the GEM detectors. For small GEM flow should be greater than 30 cc/min and for large GEM flow should be greater than 100 cc/min.
   • Switch cavities to have amplifiers. Take out attenuator on BCM. Note: Cannot exceed 2 uA with amplifiers in place.
   • Set up cavities pre-gain and phase using established values.
   • Septum on
3. Set Up Beam
   • Do the beam recovery procedure.
   • Establish 50 nA on Pb target (or appropriate current on another target). Normally with laser attenuator = 65 and slit = 13, and then some adjustment to get rates low.
4. Setting HV
   • Do NOT turn on scint or VDC HV yet ! Must establish rates first.
   • Turn on the HV for upper scint and S0 (if S0 is in place).
   • Adjust Quartz Detector HV for Counting mode.
   • VDC HV on (3.5 kV) if the T1/T2/T6 rates are below 500 kHz. If above 500 kHz do not turn on HV.
5. Take CODA run and analyze it as usual.