[BTeam] Fw: Configuration Cleanup A/B/C/D 2025-05-13

[Michael Tiefenback]

Since Jay mentioned this on the list, I thought it might be good for me to provide the setting.  Background halo counts in Hall B triggered this concern, and there are some presently confusing details which may be interesting to some of you.  It's not particularly sophisticated, nor guaranteed to home in on a solution.

Michael Tiefenback

________________________________
From: Michael Tiefenback <tiefen at jlab.org>
Sent: Tuesday, May 13, 2025 10:02
To: Eduard Pozdeyev <pozdeyev at jlab.org>; Michael Merz <mmerz at jlab.org>; Daniel Moser <moser at jlab.org>; Jacob Blackshaw <bjacob at jlab.org>; Brian Freeman <bfreeman at jlab.org>; Jay Benesch <benesch at jlab.org>; Yves Roblin <roblin at jlab.org>; Dennis Turner <dturner at jlab.org>
Cc: Douglas Higinbotham <doug at jlab.org>; Mike Spata <spata at jlab.org>
Subject: Configuration Cleanup A/B/C/D 2025-05-13

To all concerned:

This message outlines the actions to be engaged today, tentatively starting at 10:00 EDT, targeted at cleaning up beam transport to Hall B with horizontal RF extraction in the AE region (consistent with Hall D operation) while also delivering Hall A/C beams.  The background is that recent concurrent A/B/C beam delivery has been "clean" for Hall B in not lighting up their upstream halo counters only when magnetically extracted in the AE region.  This is inconsistent with concurrent delivery to Hall D.  We have noted unusual beam steering in the forest of extraction and recirculation septa downstream from the AS region, and this reasonably will result in impaired clearance of beam to material surfaces.  Hall B upstream halo counters respond quickly to scattered particles from any resultant scraping, flagging what Hall B deems to be elevated background signals inconsistent with the intended data collection.

As background, recent tests have established that elevated halo counter rates occur with RF extraction in the AE region (horizontal RF separation at ~750 MHz), but not with magnetic extraction.  Testing yesterday with no Hall D beam but beam to all of Halls A/B/C indicated that turning off #4 of the four separator cavities resulted in "clean" halo counters, but this may be misleading.  No RF diagnostic presently referenced indicates that cavity #4 has problems.  To avoid responding to an apparent problem due to otherwise normal operation in the presence of impaired beam clearance in the septum regions, a plan has been crafted to revise the beam steering through the busy extraction region and restore intended beam clearances.  If halo problems persist for Hall B, then the prospect of separator cavity faults will be pursued.

Outline of Test


  1.
Document current setup via various viewer images and harp traces for A/B/C beams.  The list is in the control room white board.
  2.
Restore BPM Survey offsets (SOF) values for the AS/AE/AA/AT line to historic values, excepting the recently re-determined AE02 XSOF.  The AT line values are the historic values.  Mostly these are 0.5 mm deviated, or less, but two vertical offsets deviated up to 2 mm exist.
  3.
Revise dipole region steering in AS/AE/AT regions per procedure.
  4.
Establish magnetic extraction in the AE region (no HallD support) with 3-way vertical separation in the AT region, and verify "clean" Hall B beam delivery (low halo count rate).
  5.
After success for 3-way split without HallD extraction, establish standard RF separation in the AE region, verifying Hall D extraction using the AE02 and AA01 viewers.
     *
This should include verifying that the four cavity phases are properly set, avoiding the prospect that phase drift diminished the overall separation provided by these cavities.
  6.
Verify that A/B/C separation remains acceptable with acceptable Hall B halo counts in the presence of (prospectively) improved beam clearance margins from step 3 above.
  7.
If halo background in B is acceptable, then we are done.  If not, then we must follow up with separator examination.  The first option (after 6a above) is that cavity 4 is the problem source, so its gradient should be halved and the gradients of cavities 1-3 increased to provide the proper total Hall D separation, then checking transport quality to Hall B again.

Michael Tiefenback
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