Minutes Feb 17
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General Meeting Summary
Summary of APEX 2/17 meeting
1. All aspects of the physics and the experiment were discussed.
2. Two main aspects, which were discussed intensively, are:
a) Optics calibration plan: needs for the targets and the items in the run plan: Targets: Optics Up, Optics Down. Each with 15 and 10 cm spacing and 2.5 cm shift: OU15, OD15, OU10/2.5, OD10/2.5. It will take two 12(10)-cm vertical slots in the ladder. OU10/OD10 C-channel is shifted by 2.5 cm relatively OU15/OD15. Decouple Y and Z by using a beam with raster-OFF at several positions - an area of 10 x 10 mm as a 5x5 matrix.
b) Target ladder cooling is required. Target alignment is already available in the Meekins's system. SLAC will need to design and built a plate with the inlet/outlet for cooling. The design of that plate will need approval from Paul Brindza. Dave Meekins has the accurate drawings of the related parts of the PREX target. That plate will be attached to the Meekins's ladder. There is 20" vertical space which could be used for the APEX targets. Alignment could be as bad as +/-0.5 mm over 500 mm length after vacuum and cooling are completed.
3. The expert teams, which formulate the optimized proposals, will include the key members of the Hall A collaboration.
a) for the detector installation schedule/recommendations:
J.Segal, D.Higinbotham, A.Shahinyan
b) for the target design configuration:
SLAC Ken's group, D.Meekins, E.Folts, A.Gavalya
c) for the optics target configuration:
J.Huang, D.Higinbotham, J.LeRose, V.Sulkosky
d) for the septa fields, cycling and polarity changes:
J.LeRose, P.Brindza, E.Folts, J.Segal
e) for the VDC high rate analysis software modification, the test with available 0.5 MHz data:
O.Hansen, J.Huang, M.Paolone, G.Ron
Comments and Discussion: Target Designs (Ken Moffeit) and Installation (Dave Meekins)
The primary target for the test run should demonstrate
- demonstrate feasibility of a design where the beam sees 10% X0 and typical scattered electrons see only 0.3%.
- demonstrate that such a target can survive 80 uA beam current
- be used to demonstrate high-rate data-taking
- be used for physics data-taking
In the same target assembly, we need a single-wire target for absolute angle calibration and an optics calibration target consisting of carbon foils perpendicular to the beam.
Ken presented four concepts (strung tungsten wires, etched tungsten wires, angled molybdenum foils, and perpendicular tungsten foil strips) for the primary target. The wire targets are expected to reach temperatures of 2000K.
Ken: How to prevent overheating if raster mechanism fails? Increased beam size? Reduced current? Interlock system? (Doubling the size of the beam spot is sufficient -- it will double the momentum resolution, but this has negligible effect on mass resolution)
Ken: Raster distance seems conservative (+/- 0.5 mm vs. target spread of 2.5 mm). If raster does not cover whole target, is uneven heating a problem?
Specifications for optics calibration target (perpendicular carbon foils) need to be sharpened.
Dave: Temperature-dependence of tungsten wire strength?
Dieter: This has been accounted for, but above 2100 C, re-crystalizing of W may pose problem.
Dave: 50 um alignment of target is not realistic (1mm or 0.5 mm is standard).
Ken: Target mis-alignment of order few mrad is not a problem, if raster area can be adjusted depending on the target angle.
Dave: No active cooling right now. A cooling circuit for target is needed.
Comments and Discussion on Run Plan (Bogdan)
Organize: web page, detector preparation, calibration, run plan, analysis
Run plan must include detector calibration, target alignment, HRS optics calibration, production studies, study of production data quality vs. beam intensity.
(See slides for details)
May need to use HRS momentum calibration from PREX (opposite polarity) to obtain momentum calibration at 1.1 GeV, as we will only have 2.26 GeV beam energy available.
Given uncertainty in maximum momentum of PREX septa, should determine sensitivity in test run with lower central momentum than Ebeam/2.
Comment: Need more time for PREX target removal and APEX target survey.
Dave: Cooling requirements mean target must satisfy tighter engineering requirements for pressure system.
