PrimEx Beam Position Monitor

1

• PrimEx Beam Position Monitor
• By Liping Gan

The beam position monitor consists of two
identical modules. Each module is a linear
hodoscope of multi-channel fibers (X module has
61 channels and Y module has 62) forming a plane
perpendicular to the photon beam. This detector
is mounted on a remote controlled table with (X
and Y motion) located behind HYCAL.
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Structure of detector

• Each scintillating fiber has dimension of 2X2X13
  mm3. The scintillating light from the fibers
  transmit through the light guide and is detected
  by four 16-channel R5600-M16 Hamamatsu PMTs. A
  compact electronics module provides 64 channels
  of amplifier and discriminators for anode
  signals, then convert them to ECL readout through
  a time-over-threshold circuit. The ECL signals
  are sent over to SIS3801-256-flat scalars and
  read into epics systems

3
Voltage setting

• The R5600-M16 PMT has substantial gain variations
  among the different pixels, so a nominal initial
  HV setting for the PMTs was determined based on
  the average behavior. Then a gain map was
  calculated by normalization of the gain using
  cosmic ray data. As a result, the HV setting
  should not be changed during the run.

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Online monitoring

• During the run, the x and y beam positions are
  displayed through a GUI. There are three options
  that you can select
• Raw will display beam profile by using raw
  data
• accumulate will accumulate the counts from the
  raw data. We only use this option for the gain
  calibration
• Smooth will apply the gain normalization
  factors to the raw data and fit the profile
  distribution.
• Please make sure to select the mode smooth
  only during the run so that the gain
  normalization factors will be applied to the
  data!!!

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How to run BPM monitor online

• Login clon01 as clasrun user.
• Type medm x APP/primex_profiler/medm/pg_profile
  .adl to bring up the GUI
• Click the gp HV button to open HV GUI, make
  sure the HVs are turn on with the correct voltage
  values.
• Click the gp motor button to open motion
  control GUI to make sure the beam hitting the
  center area of the detector ( the area of channel
  25-45 for both x and y are recommended) .
• Select mode smooth on the PrimEx BPM GUI so
  that that the gain normalization factors will be
  applied to the display.

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EPICS variables
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Conversion factor

• Conversion factors from the fiber channel number
  to x and y position displayed on the GUI for
  LG_BPM are
• X position on GUI 2x fiber chan-61
• Y position on GUI 2y fiber chan-61

8
Marks on detector

• There are marks on the detectors for survey
  purpose. The mark positions on x module is at
  fiber channel