Electron Detector

Standard Running Procedure

with the previous beam activity ongoing (parasitically)

• take a quick CODA run to check DAQ functionality
• check analyzer functionality
• from any cdaq machine, from the directory ~/compton execute StripTool edetectorEpics.stp . This pulls up the strip chart of some relevant epics variables for e-detector. If you are unable to locate this file, the following epics variables should be explicitly opened.
  • 4 Hall-C Chicane BPMs
    • 3P01A (IPM3P01A.XPOS , IPM3PO1A.YPOS)
    • 3P02A (IPM3P02A.XPOS , IPM3PO2A.YPOS)
    • 3P02B (IPM3P02B.XPOS , IPM3PO2B.YPOS)
    • 3P03A (IPM3P03A.XPOS , IPM3PO3A.YPOS)
  • Normalized Compton Photon Rates (cComptPhotonRateNorm)

Request beam to be set through the chicane and verify the same

• Check Chicane view: on any cdaq machine type edmmonticello, from the Monticello screen
  • open Magnets -> Magnet Commander
    • 3C -> Compton Combo
    • In this Hall C Compton Control screen, the REQUESTED and ACTUAL current readbacks should be ~104 A
  • open BPM -> BPM Overview
    • open Absolute -> on the Hall C column from the left bottom of this screen
    • BPM 3P01A, 3P02A, 3P02B and 3P03A should have finite non-zero read back
• Check compton rates from the photon detector (typically 600 per uA per second)

Request beam to be taken off, for lowering the e-detector

• Lower the e-detector to a position in accordance with current run plan
  • Motion mechanism [[1]]
    • begin with the program Go Home
    • jog to the intended position
    • Request beam according to the intended run plan

Run Plan

Nov 17

• Form an external coincidence between strip #5 or 6 of all three planes.
  • count it on a visual scaler. look at each of the 3 plane signals on a scope to determine a good coincidence window.[this setup is ready]
  • record 1/3, 2/3 and 3/3 at 2.8, 2.0 and 1.2 cm from the beam, with and without beam. Collecting statistics for ~ 3-5 minutes
• Repeat above with the full DAQ. Again 1/3, 2/3 and 3/3 at same distances from the beam, with and without beam.
  • Try a couple of different trigger coincidence widths in the 100 - 250 ns range.
  • Take a few long runs with 2/3 and 3/3 trigger at 1.5 cm from the beam, with and without beam, with and without laser

Nov 22

Seek a beam time of 6.5 hrs. Following tasks to be accomplished:

• With laser turned off for this entire running period resolve the plane-4 HV ambiguity: (~ 1 hr)
  • look at output from all 3 planes on the scope, triggering on 2-plane coin while turning on HV of only one plane at a time
    • do this for plane-2 and plane-3 first
    • finally turn on p4 (repeat for a few neighboring strips if needed)
    • record scope shots triggered on coincidences

• with the DAQ, try to observe a shift in the strip pattern as the detector is lowered towards the beam. (~ 3.5 hrs)
  • If the plane-4 ambiguity is resolved then use all 3 active planes for trigger decision
  • If plane-4 is not resolved, turn off the HV input to "plane-1" as well as "plane-4", mask the plane-4 signals and use 2-plane triggers only with plane-2 & plane-3.
  • take quick runs to check if smaller or higher cut on minimum width helps
  • try to find a trade-off between unmasking the strips neighboring the closest active strip and noise rates
  • take 30 min runs with 5 uA, 3 uA and 1 uA beam with the detector at a reasonably close position (say 1.6 cm from beam)
  • Repeat in steps of 1 mm as the detector is moved closer to the beam (~ 3 steps should be sufficient)

• HV scan for plane 2 only (~2 hr)
  • With the detector at the closest position, and a 3 uA beam scan the HV from 300 - 700V in steps of 100 V taking 10 min runs at each voltage
    • use 2-plane trigger, check to see if the background is different with change in applied HV
    • use a 1-plane trigger, check to see if the background is different with change in applied HV
      • It might be useful to increase the cut on minimum width in order to look over the excessive noise in the case of single-plane trigger.

upcoming beam-time (slot-1)

• from last run-plan (~ 2 hr)
  • HV scan using a 1-plane trigger using "plane-2"
    • mask off the plane 3 & 4, on which the HV is not being changed(to help minimize noise rate)
    • at y = -8.5, i = 10 uA and laser On
    • masking off slave-2 & 3(as was on Nov 22) and increasing the minimum accepted width further might prove useful
    • take a run @ V = -250V, -350V & -450V, only if a difference is seen, proceed in this part with smaller steps
    • vary HV from 250-700 V in steps of 50 V
    • take 5 min runs
  • If above exercise shows the HV plateau, repeat the same with "plane 4"
  • If above does not work, proceed to HV scan using 2-planes trigger
    • take a run @ V = -250V, -350V & -450V, only if a difference is seen, proceed in this part with smaller steps
    • vary HV from 300-700 V in steps of 75 V on "plane-2" & "plane-4" simultaneously (HV on "plane-2" shows a current readback beyond -260V)
    • take 10 min runs

• Nailing down the possibility of HV on p2 and p3 being swapped. (~ 0.5 hr)
  • we need to take runs with 2-plane trigger with HV turned on at the same vertical position and same beam current for
    • "plane-1" & "plane-3"
    • "plane-1" & "plane-2"

(above two will establish if plane-2 and plane-3 are also swapped!)

• Looking for the Compton edge (~ 4 hr)
  • Using 3 plane trigger, 20 uA beam, starting from y = 8.7 cm, with laser ON, take 15 min runs
    • starting y ~ -8.7 cm, move away from beam in steps of 0.2 cm, until we see the counts/strip becoming equivalent to no-laser or until y ~ -7.5 cm
    • with laser off, beam On; take data at positions y ~ -8.6, -8.0 and y ~ -7.5

(it would be interesting to have runs with laser Off at all of above positions, particularly when detector is close to beam)

beam-time (slot-2)

• variation of min_width to see the variation in signal acceptance with 3-plane triggers
  • at two different vertical positions
  • vary min_width from 0-300 ns in steps of 25 ns

(these can be only 15 min runs)

(I expect to see a plateau, which will help us operate at that optimum value)

• vary the Hold-off time from 200 ns to 500 ns keeping the min_width at the nominal 50ns

• variation of PWTL from 25-100 ns in steps of 25 ns

(to see if the response of various planes and respective QWADs are different from the assumed (current used) 50 ns)

beam-time (slot-3)

• variation of PWDL (keeping it larger than PWTL)
• modify the firmware to accept (say)10 values neighbouring the given trigger

this will be a wild check to verify if we are losing anything at all due to miss-timing !

this will check the off-timing if it is anywhere within +/- 5 clock cycles

beam-time (slot-4)

• modify the firmware to record the width of the incoming signals.

use the existing counter which implements the min_width,

it will be an interesting quantity to look at as we vary position or beam

Backout Procedure

1. Turn OFF HV
2. Retract the detector to position defined as Go Home
3. Retract further to position defined as Garage
4. make hclog entry to inform completion of the intended studies, with any quick conclusion which are obvious

---

courtesy: Thanks to Dave Gaskell for the motivation to organize this information

---