Spring 2017 Commissioning Plan

Spring 2017 Commissioning Plan

• The plan will be a shorten version of the plan of the full SHMS commissioning.

Initial beam setup

• Take a superharp scan with fast raster off (2 μA current) and no target with superharps IHA3H07A and IHA3H07B. Beam size should be < 300um. This is part of the KPP commissioniing so should be standard.
• Bull-eyes scan.
• Carbon hole recheck ( should already be done by KPP commissioning)
• BCM calibration
• Take harp scans with raster to measure raster size.

Initial HMS detector checkout

• HMS set for electrons at 3 GeV/c at 15 degrees with single carbon target.
• Expect mostly pions
• Hodoscope timing calibration and check beta plot. Check 3/4 trigger efficiency.
• Gas Cerenkov calibrate number of photo electrons.
• Shower calibrate gain matching using pions.
• Drift chamber. HV and Threshold plateau. Determine drift time calibration.
• Need to have PID to be able to use the sieve effectively.

Initial SHMS detector checkout

• set for electrons at 3 GeV/c at 15 degrees with single carbon target.
• Expect mostly pions
• Much is done as part of KPP commissioning.
• First need to establish that the S2Y quartz plane is working and the number of photoelectrons.
• With first three Hodoscope planes do timing calibration and check beta plot.
• Once 2Y plane is working then add to trigger. Do timing calibration and check beta plot. Check 3/4 trigger efficiency.
• Heavy Gas Cerenkov calibrate number of photo electrons.
• Noble Gas Cerenkov calibrate number of photo electrons.
• PreShower/Shower calibrate gain matching using pions.
• Drift chamber. HV and Threshold plateau. Determine drift time calibration.

Reestablishing the HMS tune

• HMS at 15 degrees , electrons at 3 GeV/c . No raster and central carbon foil. HMS sieve.
• 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. 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.

Verification of Beam-Target Interaction Point

• HMS at 15 degrees , electrons at 3 GeV/c . No raster and central carbon foil. HMS sieve.
• Take a short run (100K). Analyze and make an ntuple. Make the following plots: x vs y at the focal plane, xp vs yp at the target (you may have to use some Particle Id. and reconstruction cuts here!), and y at the target. You want to check the following: is the central leg of the ``spider" in x vs y at the focal plane straight? is the reconstructed y position close to y = 0? Is the central sieve slit hole close to (yp,xp) = (0,0)? If the xp position of the central sieve hole is close to 0, you probably are a bit off in vertical beam position after all, fix this. If you are far off (larger than 2 mr), check all your results carefully, did something go wrong in the vertical beam assignment? If the central leg of the ``spider" is close to vertical, you are close to having mid-plane symmetry for the spectrometer. You can vary the horizontal beam position a bit to check this. Note that the present quad alignment is such that the quad system is about 1 mm to the right of the line through the nominal pivot and the spectrometer angle, so the y position at the target can be a little bit negative, and the central leg of the spider can be slightly tilted. If the yp position of the central sieve hole is within 1 or 2 mr of the nominal zero position you are probably fine. The big uncertainty will be whether the targets are actually located at the nominal pivot (z = 0) position. If the target survey says otherwise, you expect (i) the central leg of the ``spider" not to be straight, (ii) the y reconstruction not to be perfect, and (iii) an offset in yp for the central sieve hole. If the three pieces of information are pretty much consistent with the survey assume you are done (note: the HMS sieve is at a distance of 1.66 meter of the target). You can consider checking this by using a hole target, or by rotating the spectrometer to a larger angle, and verifying that indeed things are consistent.

Verify Quadrupole Settings SHMS

• SHMS at 15 degrees , electrons at 3 GeV/c . No raster and central carbon foil. SHMS collimator.
• Now that we know the beam-interaction point, we start looking at the SHMS. Use the Carbon optics target and beam raster pattern as before, and the collimator (no sieve slit needed yet). For SHMS, the point-to-point optics at the focal plane will look skewed as the horizontal bend magnet will ruin the regular symmetry of the spectrometer optics, so x and y will be coupled. Thus, for the SHMS you may have to compare simulated focal plane patterns with measurements to be able to judge if quadrupole fields differ from expected although you can do much with just looking at the focal plane pattern. First verify that we have obtained a point-to-point focus with the extrapolated quadrupole settings, by looking at plots of hsxfp vs. hsyfp. The SHMS should have a “tilted” hour glass pattern for a point target source, with the waist of the hourglass at (0,0). If not, vary the quadrupole settings in small steps (try 0.2, 0.5 or 1% steps. Q2 is most sensitive and 0.2% steps should be sufficient for Q2 – the gradient of motion of the hourglass waist is roughly 2 cm per % Q2 change. For Q1 it is about -0.4 cm per % Q1 change), until the golden tune (this is defined as the SHMS quadrupole settings that most closely reproduces the simulated sieve slit patterns at the focal plane) is obtained. Measure a spectrum with high statistics (>>100K) to use for later off-line checks and to continue the second phase of detector checkout – this is needed before starting the sieve slit runs. Check the time-to-distance maps, align the wire chamber positions in software and enable linked stub fitting, check the detector positions, check the timing and calibration constants (shower counter gains, pedestals, timing offsets, pulse height corrections, attenuation lengths, efficiencies, position dependencies). Optimize tracking properties. Make sure that Θ and Φ spectra are wide as expected. Construct x, y, Θ, and Φ spectra at the nominal focal plane. Does everything look reasonable? Check tracking with one wire chamber set against tracking with two wire chamber sets. Reconstruct target quantities.
• You can also use these plots to help guide the setting of the quadrupoles.

Establish Initial SHMS Tune

• SHMS at 15 degrees , electrons at 3 GeV/c . No raster and central carbon foil. SHMS collimator.
• Use the SHMS sieve slit with the middle vertical column centered in combination with the Carbon optics target. Use a current of less than 20 μA. Preferentially, the fast raster should be off for this series of measurements. However, a small fast raster size of 1 by 1 mm2 should also work. Measure a short Carbon spectrum of perhaps 100K events. Produce an ntuple, and do the following: make a spectrum of x vs y at the nominal focal plane. What you should see is a tilted ``spider" with 9 legs. The center of the spider/hourglass should be at (x,y) = 0 if everything went right. If not, check the beam interaction point and check the quadrupole magnet settings. Because the HB magnet destroys the mid-plane symmetry of the SHMS, you likely will need to compare simulated focal plane patterns with measurements to be able to judge if quadrupole fields are o.k. If you do see a difference you can try to change the quadrupole settings by say 0.1% and measure a new run and produce an ntuple to compare. If the patterns look similar we are done with establishing the Standard SHMS tune beyond the dispersion.

Establish Standard SHMS Tune and Test Linearity

• It is assumed that the previos initial SHMS Tune was at a SHMS angle of 15° and a central momentum of -3.5 GeV/c. We will now verify the chosen SHMS tune for linearity at the >6 GeV beam energy. Hopefully, we will be in luck and the dispersion check later on will show we picked the quadrupole settings roughly correct. To check the linearity, we will take further sieve slit data with the SHMS at a central momentum of -2.0 and -1.0 GeV/c, respectively. The multiple scattering with the noble-gas Cherenkov still in place will make his not useful for detailed sieve slit calibrations, but likely sufficient to check the linearity and obtain sufficient quality data to compare with the optics simulations.
• Start with the SHMS central momentum at -2.0 GeV/c. Use the SHMS sieve slit with the middle vertical column centered in combination with the Carbon optics target. Use a current of less than 20 μA. Preferentially, the fast raster should be off for this series of measurements. However, a small fast raster size of 1 by 1 mm2 should also work. Measure a short Carbon spectrum of perhaps 100K events. Produce an ntuple, and do the following: make a spectrum of x vs y at the nominal focal plane. What you should see is a tilted ``spider" with 9 legs. The center of the spider/hourglass should be at (x,y) = 0 if everything went right. If not, check the beam interaction point and check the quadrupole magnet settings. Because the HB magnet destroys the mid-plane symmetry of the SHMS, you likely will need to compare simulated focal plane patterns with measurements to be able to judge if quadrupole fields are o.k. If you do see a difference you can try to change the quadrupole settings by say 0.1% and measure a new run and produce an ntuple to compare. Now, repeat this whole procedure with SHMS at a central momentum at -1.0 GeV/c. In the end, one may consider returning to a SHMS central momentum of -3.5 Gev/c and repeat the procedure one more time. The goal is to establish a tune for the aberrative matrix elements that is linear over a swing in momentum from -1.0 to -3.5 GeV/c.