[BTeam] Fw: 5th pass horiz separator(s)

[Michael Tiefenback]

________________________________
From: Michael Tiefenback <tiefen at jlab.org>
Sent: Thursday, September 9, 2021 16:18
To: Mike Spata <spata at jlab.org>; Edith Nissen <nissen at jlab.org>; Tomasz Plawski <plawski at jlab.org>; Camille Ginsburg <ginsburg at jlab.org>; Curt Hovater <hovater at jlab.org>; Mark Wissmann <wissmann at jlab.org>
Subject: 5th pass horiz separator(s)

Gentle folk:

Tomasz mentioned questioning the 4th of the separator cavities possibly having less effective strength than the others.  This question may be better to answer than not.

The sequence of hookup of the four separators is a way of handling mutual reflections and power coupling through a splitter.  However, one potential reason for the single fourth cavity not adding in the expected way to the other three might involve power reflections inside the multi-cavity network somehow altering the relative phases of the four cavities.  No, I can't think of a mathematical statement of this, but Tomasz's observation worries me.  I have overlooked things before.  To put resistive loads on ports 1-3 and connect 4 alone to observe its deflection effectiveness seems a straightforward way to test this.  The deflections ought to add sensibly linearly, and Tomasz' observation is that this was not so for cavity 4.

On optics, the standard optics in AE/AA has a 55-ish meter peak dispersion at MQNAE02, closely followed by the MYA extraction septum magnet.  There is on the recirculation line another pair of M12 extreme values of approximately +/- 58 meters at IPMAA09 and IPMAA25.  These provide reasonable M12 already within the standard optics.

Running the AA03[AB] quads at +25% and the AA19[AB] quads at -20% leaves the betas mostly untouched in the latter half of AA, doubling betax (and M12) at IPMAA09.  This appears to double the resolution for the BPM and may be accessible for single-cavity operation.  This could be quite useful for single cavity setup with others replaced by loads, but not so accessible for stacking the separator cavities up one by one to go to full deflection.  I had initially imagined that the cavities would be excited in this way, loading the other ports resistively in sequence, then connecting all cavities and expecting to sum the deflections.  This may be too naive.

But doubling the M12 at IPMAA09 (where, by the way, also lies a viewer) may be a useful thing.  It is a magnification effect, and might well be practical to triple the BPM signal there with accompanying tripling of beam size if scraping is not already limiting the span.

Michael Tiefenback

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