Commissioning Plan 2017

2017 Hall C Commissioning Plan (draft)

Magnet Field Setting

HMS

• ALWAYS set DIPOLE by NMR coming DOWN from 900 A - still true?
• Set QUADS by initially setting to a current of 200 A above the set currents (or the maximum current of 1100 A for Q1 if set current + 200 > 1100), and then coming DOWN.

SHMS

• Set HB magnet to 1500 A and then go up or down setting HB by NMR
• Set QUADS … - need Q1 mapping data in form we can decide on this

Set DIPOLE by NMR (or with Hall Probe at highest momentum settings, not relevant for this commissioning plan) …

Beam Energy and Equipment Assumption

Hall C Pre-Ops presumably will start at beam energy above 6 GeV (3-pass or 4-pass) as first order one needs to prove the Key Performance Parameters are met. This means also the noble gas Cherenkov is in place. As soon as data is collected for this Cherenkov to validate the detector being operational (i.e., seeing signals fulfilling the Key Performance Parameters), we need to remove this detector and replace by the alternate SHMS vacuum extension, to reduce multiple scattering before the focal plane. This would require removal of some roof blocks and tech assistance. Beyond the >6 GeV checkout for most of the detector and spectrometer optics studies, we will also need about one day of one-pass beam energy, assumed to be in the 2.0-2.2 GeV range, to measure the dispersion matrix elements of the SHMS with a Carbon elastic scan.

Beam Energy > 6 GeV

Check Electronics and Detector Functionality

Set the spectrometer magnets to the initial settings as calculated with the FIELD_12GEV (has a start been made already?) program. This can be done before any optics fine-tuning of the quadrupoles/optics as the initial detector checkout can occur with a defocused run (in fact, it is preferred). Start at a spectrometer angle of 15 degrees and a central momentum of -3.0 GeV/c (assuming >6 GeV beam energy, if this would be one-pass beam energy choose -1.0 GeV/c). Use a current of about 10 μA, the central (Carbon) target of the optics target, and the fast raster with a size of 1 by 1 mm2. Use the large (pion or HMS-100 for HMS) collimators. Check that all electronics signals are well timed. Determine correct thresholds. Verify that all detector channels are counting. At this time checkoff the Initial Detector Checkout Plan (“near-final” for HMS, initial for SHMS to check off Key Performance Parameters) to make sure all detectors are operational. Check carefully that all wire chamber channels are cabled up correctly. Verify all scalers are incrementing. Check for double pulsing and time the wire chamber signals. Determine the scintillator plane efficiency for detecting electrons with the correct discriminator threshold, and make sure that the scintillator signals for detecting hadrons are on scale in the scintillator ADCs.

Beam Checkout with Superharps and Beam Position Monitors

Since the beam line has drastically changed with respect to the 6-GeV beam operations we need to establish the nominal settings for the beam position at the last BPMs before the target. This can be done before or after the initial HMS checkout but should be done before the optics tuning of the SHMS.

Superharp Scan

Make sure there is no target in the beam line, or the central carbon target that can also handle unrastered beam. Take a superharp scan with fast raster off (2 μA current) with superharps IHA3H07A and IHA3H07B. Verify that the beam size is as expected – this was <math>\sigma_x \approx 80 \mu m</math>, <math>\sigma_y \approx 150 \mu m</math> under 6-GeV conditions, as long as it is roughly <math>200 \mu m</math> or better in both directions it should be good enough to proceed.

Last Beam Line Girder Commissioning

At a stable beam condition, using the fast raster with a size of 1 by 1 mm2 and the central carbon target, monitor the values of the three BPM's of the last beam line girder (IPM3H07A-C, or “A, B and C”) and take a short run (~10K). Verify that we have all three BPM's (in Epics readout) of the last beam line girder in the data stream and that the values are consistent with those from the MEDM/TCL screen. Next, use unrastered beam (fast raster off) and the central Carbon target of the optics targets, and 10 μA current. Record superharp scans (they will give us the absolute scales) and check those versus the beam positions given by the BPM's both from the MEDM/TCL screen and from Epics readout. Ask MCC to move the beam horizontally by ±1 and ±2 mm with a far upstream magnet, and record at each setting both superharps and the three BPM's, both from MEDM/TCL and from the data stream after short runs. Have the beam moved back to the nominal central position (horizontally) and ask MCC to move the beam vertically by ±1 and ±2 mm, recording at each setting again the two superharps and all three BPM's. Change the current to 20 μA and repeat the whole sequence. Change the current to 60 μA and repeat. Go back to 10 μA current and take a short run (~10K) with a fast raster with varying size, say 2 by 2, 3 by 3, and 4 by 4 mm2, recording superharp scans after each run (this to calibrate the fast raster size).

Tuning Optics

Reestablish Standard HMS Tune

Use the HMS sieve slits in combination with the Carbon optics target (i.e. the central Carbon target on the optics target assembly hanging off the cryo target system). Use a current of less than 10 μA, and a fast raster size of 1 by 1 mm2, or with 0.5 mm radius. The exact raster shape does not matter: the raster can even be off in this configuration. Measure a short Carbon spectrum, about 250K events. Produce an ntuple, and do the following: select electrons with shower counter and/or Cherenkov cuts, and make a spectrum of x vs y at the nominal focal plane. What you should see is a ``spider" with 5 legs. The non-straightness of the central leg indicates there is an offset in the Z or Y direction. If you don't see a ``spider" or something resembling it one of the polarities of the HMS magnets is set wrong (or the magnet is off). If you see a ``spider" next thing to figure out is what the X, Y, and Z offsets are of your present beam-target interaction point, but at least your tune is fine for detailed electronics/detector checkout.