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Chris,</div>
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Such things are of interest to everyone, whether they really know it deep in their hearts or not.</div>
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Our BPMs are not perfectly reliable, and we do not handle the offsets terribly well, either. Our measure of the relative sensitivity of the wires changes with each "autocal," and also with the beam current due to saturation effects we may handle properly or
may not.</div>
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When we started doing "rayTrace" data sets, we found that the scale factors for the BPMs (what an indicated mm really means in real space) varied by +/- 10% or more and had a systematic dependence upon the electronics type. We still find random BPMs giving
random signals occasionally (I try to OPS-PR all that I see; but perhaps not all are reported, depending upon the level of expectation of the observer).</div>
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Ryan's data sets were interesting to view through an SVD filter. The collective modes are visible from varying early steering errors and orbit locks, and power supply ripple shows up in in modes matching the dispersion pattern. Single BPMs also show up as
isolated modes uncorrelated with other beam motion, and can readily be noticed.</div>
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The early injector may not be as ugly as it seems, as the energy is low and it is easier to deflect the beam. The variation that is seen is subject to acceleration damping, just like the emittance damps and for the same reason. So the beam appears to get
more stable as the energy rises. This does not mean that all is well, but rather that some of what is seen is consistent with expectation. Noisy BPMs? Not the sole problem, but also not something to tolerate lightly.<br>
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I hope these comments and opinions have been somewhat entertaining, somewhat illuminating, and tolerable to read. We are far too tolerant of such things, but that is a learned behavior borne of (among other things) lack of development budget.<br>
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Michael Tiefenback<br>
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<div id="divRplyFwdMsg" dir="ltr"><font style="font-size:11pt" face="Calibri, sans-serif" color="#000000"><b>From:</b> BTeam <bteam-bounces@jlab.org> on behalf of Christopher Tennant <tennant@jlab.org><br>
<b>Sent:</b> Tuesday, September 14, 2021 15:46<br>
<b>To:</b> bteam@jlab.org <bteam@jlab.org><br>
<b>Subject:</b> [BTeam] Injector BPMs (an observation)</font>
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Hi all,
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<div>Not sure if this is of interest to anyone, but just wanted to throw it out there...</div>
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<div>For a recent SBIR project we (Brian, Daniel, Reza and I) collected and analyzed data from the injector. Specifically, last fall we varied beamline components (solenoids, correctors, RF gradients) and recorded the downstream response (BPMs, BCMs, BLMs,
vacuum). I'm sharing the results of analyzing the BPM data which is in the attached slides.</div>
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<div><b style="">slide 1</b>: For this portion of the beam studies correctors were varied and the downstream response recorded. What is plotted here is the horizontal (top) and vertical (bottom) BPM readings after the corrector being varied has been returned
to its default value. That is, each marker in these plots represents the injector with the exact same corrector settings. (Note, the BPMs were allowed to settle, and an average reading was taken). The extent of the vertical smear at each BPM displays the system
reproducibility (or lack thereof).</div>
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<div><b>slide 2</b>: This represents an alternate way to view the information from slide 1. Here the standard deviation of the measurements at each BPM are plotted.</div>
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<div>I was rather surprised by these results, though perhaps for those more familiar with operations, this is expected (?).</div>
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--chris<br>
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