Run Plan (DVCS3)

For the 12 GeV DVCS experiment, go to [DVCS3 wiki ].

Assume:

• longitudinally polarized beam
• max 20 uA but for short times when it can go higher
• 7.3 GeV-4 pass and 5.5GeV-3Pass and possibly 9.10 GeV-5Pass later on

Commissioning/ Calibration

Beam instruments

BPM/Raster checks/Beam centering

1. Send unrastered beam to the four corners of a 2*2 mm square around assumed (0,0) position (as defined by RAD reading in beam dump). At each position compare harps against BPMs reading.
2. JR: How to decide on beam centering beyond the RAD readings in the beam dump? Do we need to even go further than that?
3. Check size raster using the spot++ tool. Pending target boiling studies result, we will use a 2*2 mm2 raster. (3*3??)
   

BCMs

Use the procedure that is under .....
Need: To insure that minimal beam lost in the machine can be measured, beam that would go up to about 100 uA. We also need to be the only hall receiving beam.
JR: Do we want to calibrate against the Unser monitor? Is the Unser operational? Do we know its calibration constant

Polarization measurement

Goal : ΔP/P~2%
We have to be mindful of the issue of the intrinsic polarization and the issue of its direction. JR: How often do we want to measure the polarization? For this fall: At this time, we are hoping to be able to use the Compton only as a beam quality monitor (pending there is actually a photon detector in place). We could use the Mott polarimeter as a monitor of the intrinsic polarization and something in the Hall as a quick check of the direction of the polarization.

Energy measurement

Goal: Δ E/E ~ 0.5 %

Luminosity

Target Boiling

Goal: hopefully less than 1% boiling at 20 uA. Check that the Carbon target doesn't boil. In similar conditions check if the hydrogen target does boil (just a little). Figure out the best combination between the fan speed

Deadtime check

The plan is to have multiple triggers that would let us check the deadtime. The cabling of these is yet to be defined.

Charge asymmetry

We want to maintain the charge asymmetry below 100 ppm per run. To be done preferably after BCM &BPM calibrations.

1. Check that the RHWP angle and PITA voltage and the charge asymmetry are recorded in the run-start and end-of-run logbook entries.
2. Check that we can measure a charge asymmetry using the BCM scalers. Check that a change in RHWP angle (~45deg) or PITA voltage (~1V) results in a change in measured charge asymmetry. About 15 min for each measurement. Request HWP out.
3. Set the PITA voltage in the middle of its range. Measure the charge asymmetry each 45deg of the RHWP from 0 to 180 deg. Estimate the best angle to null the charge asymmetry.
4. Measure the charge asymmetry for 4 or so voltage of the PITA. Estimate the best PITA voltage to further null the charge asymmetry.
5. Measure the charge asymmetry for the new nominal setting you determined. Repeat measurement with HWP in. Re-measure the charge asymmetry, hopefully it is about the same result that what you had with HWP out.

HRS

Measure efficiencies S2m, Cerenkov and wire chamber

The DVCS trigger module can be triggered on any-two combination of s0, s1, s2 and the cerenkov. We should use this capability to measure the efficiency of the s2 and the cerenkov. We should double the study with using the MLU from the HRS.

Optics

The resolution of the calorimeter (about 3.5% in energy and 2mrad in angles) dominates the resolution of our experiment. So our optics needs are quite limited. In a first attempt we believe that it will be sufficient for our purpose to check that the target foils are reconstructed with about sigma=1.2mm/sin(spectro angle). We might also want to measure an elastic point detecting electrons in the HRS and no detection in the calorimeter.

Calorimeter

ARS calibration

For this we need to switch the HRS polarity to positive to detect proton in the HRS and electrons in the calorimeter