Difference between revisions of "Optics and Commissioning"

Revision as of 22:28, 5 April 2024

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From Andrew Puckett lognentry

At GEN-RP kinematics for 2nd-pass running, the elastically scattered electron energy is about 2 GeV, so the BBCAL trigger sum threshold should generally not be higher than about 1.5 GeV (perhaps a bit lower for LD2 running). EXPECTED elastic ep rate on LH2 in GEN-RP kinematics is ~1.6 Hz/uA (I believe this is for the coincidence, but I would have to check the calculation I did 4 years ago).

The “standard” BigBite optics run plan with sieve slit, modified for the GEN-RP/KLL case would be (in no particular order):

GEM-Hall alignment for BigBite: Settings and procedure are:

• BigBite AND SBS magnets OFF.
• Target is single Carbon foil, preferably unrastered
• BigBite singles trigger, threshold ~1.0 GeV, adjust as needed for few kHz rate.
• Beam current ~10 uA (zero-field running produces a lot of background from low-energy charged particles that are absent when the magnet is on).
• Take short run to check rates, adjust beam current and/or trigger threshold to give ~few kHz trigger rate.
  • Higher current and higher threshold is better than lower current, lower threshold due to pi/e ratio.
  • As long as GEM and other detector rates and occupancies are acceptable (raw strip multiplicities <~ 1000 or so), and as long as trigger rate is comfortably under 5 kHz with a threshold not more than 1.5 GeV or so, you can increase beam current as high as ~20 uA or so, but if you do this with magnets off, you may want to turn off SBS GEMs (if they are on).
• Once you have a suitable beam current and trigger threshold, take a longer run(s), collect about 10 M triggers in this configuration. At 3 kHz that is about an hour run.

BigBite Optics calibration with sieve slit/multifoil (and SBS vertex reconstruction): Settings and procedure are:

• BigBite on at 750A
• SBS on at (nominal production field setting = ??).
• BigBite sieve is IN.
• Targets are multi-foil carbon optics (4-foils and 5-foils).
• Trigger is BigBite singles.
• SBS GEMs in the data stream so we can at least calibrate SBS vertex reconstruction.
• Start with trigger threshold ~1.0 GeV and beam current ~10 uA.
  • Again, take a short run to check rates and detector occupancies.
  • As long as trigger rates and detector rates/occupancies are acceptable, and as long as trigger rate is not more than ~3 kHz with a threshold not higher than ~1.5 GeV, you can increase the beam current.
• After determining optimal beam current and trigger threshold, take about 15M triggers each on the 4-foil and 5-foil optics targets (this may take 3-4 hours or about half a shift)

GEM-Hall alignment for SBS GEMs (preliminary, maybe optional): Settings and procedure are:

• BigBite and SBS magnets OFF
• BigBite sieve is (in or out? probably OUT to get higher trigger rates)
• (IF POSSIBLE without moving SBS GEMs, otherwise nominal configuration is okay): Steel analyzer is OUT so we can align the rear GEMs too. Probably not practical.
• Trigger is BigBite-HCAL coincidence. ~1 GeV threshold on BigBite, nominal threshold in HCAL.
  • NOTE: since we have no PID detectors in SBS, we will presumably need to rely on the vertex correlation with BigBite to cleanly select good tracks in SBS originating from the single C foil with sufficiently high energy. I don't even know if this plan will work in the GEN-RP context particularly with the analyzer since the tracking is basically unconstrained.
• Start at ~1-5 uA (since there will be no sieve slit in BigBite OR SBS and no magnetic field, the rates in BigBite and SBS GEMs may be quite high).
• Take a short run, check trigger rates and GEM occupancies. If GEM occupancies are sufficiently low (unlikely), you can increase current to get more trigger rate. Alternatively the threshold in BigBite and/or HCAL can be lowered to increase the rate. Target is a coincidence trigger rate of ~2-3 kHz.
• Take about ~10-20M? BigBite-HCAL coincidences. This might give us enough good electron (in BigBite) + some charged particle (in SBS) coincidences to get a good sample of straight-line tracks for the alignment of the SBS GEMs (front GEMs anyway).

LH2 elastic calibrations for BigBite momentum, all SBS optics, GEM tracking efficiency/luminosity study/analyzing power calibration (this doesn't all have to be taken at the same time as the multi-foil/sieve slit data!)

• BigBite and SBS magnets ON at nominal production settings (750 A BB, ?? SBS)
• Target is LH2
• Sieve slit is OUT
• Trigger is standard production coincidence trigger (BigBite ~1.5 GeV, HCAL at nominal threshold of ??)
• Steel analyzer is IN
• Luminosity study (take runs of ~15 minutes each at the following beam currents, a bit longer at low current):
• 3, 10, 20, 30, 45? 50? More? uA (as always, adjust trigger thresholds to keep DAQ rate manageable while maintaining high efficiency for elastic in both BBCAL and HCAL)
• LH2 optics runs: Take some longer runs (~2-3 hours worth) at, say, 15-20 uA (compromise between elastic rate and cleanliness of tracking) for BigBite momentum and SBS optics calibrations
• Analyzing power calibration: I had estimated we need 16 hours at 60 uA LH2 for this purpose. Since I assume we won’t be able to get 60 uA, and since we don’t yet know if the BigBite/SBS GEMs can even handle 60 uA LH2 in the GEN-RP kinematics anyway, this might need to be adjusted for somewhat longer time at lower beam current.

Other: HCAL neutron detection efficiency study (time and logistics permitting; I know this isn't part of GEN-RP/KLL!):

• Target is 15-cm LH2 with radiator
• BigBite is ON at 750 A with reverse polarity (positive, for positively charged particles upbending). SBS is ON at its standard production field setting.
• Trigger is coincidence, with a lower threshold of ~0.5-0.75 GeV in BigBite to get good efficiency for charged pions. Standard threshold for HCAL
• Steel analyzer is OUT (mandatory for this measurement)
• 3rd-pass beam.
• Time required is ??