<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<style type="text/css" style="display:none;"> P {margin-top:0;margin-bottom:0;} </style>
</head>
<body dir="ltr">
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
"Too stringent" is a term I consider inapplicable to this. Lower energy makes it all easier to accomplish, and provides a better measure of headroom. One will never be able to touch all transfer function combinations, which are critical in BBU interactions.
We had to touch the linac focusing only very slightly to eliminate BBU when we encountered it long ago. We had every opportunity not to see it, given that it was driven by so few (a single?) cavities. It seems much wiser to make the lower energy test with
greater likelihood of driving marginally vulnerable modes.</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
Or so it seems to me. One issue still open: the previous low-energy experience was w/o C100s in use. This means they were far off-resonance. The BBU participant modes do not require any particular fundamental cavity mode frequency, but the test would seem
more representative of our accelerator were all cavity gradients scaled down proportionally from how we expect them to be driven for Moller and contemporary experiments.<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
Michael Tiefenback<br>
</div>
<div>
<div id="appendonsend"></div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
<br>
</div>
<hr tabindex="-1" style="display:inline-block; width:98%">
<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 Jay Benesch <benesch@jlab.org><br>
<b>Sent:</b> Friday, January 31, 2020 16:55<br>
<b>To:</b> BTeam <bteam@jlab.org><br>
<b>Cc:</b> Jian-Ping Chen <jpchen@jlab.org>; Paschke, Kent Dieter (kdp2c) <paschke@virginia.edu>; Xiaochao Zheng <xiaochao@jlab.org>; Brad Sawatzky <brads@jlab.org>; Gordon D. Cates <cates@virginia.edu>; Garth Huber <Garth.Huber@uregina.ca>; Cynthia (Thia)
Keppel <keppel@jlab.org><br>
<b>Subject:</b> [BTeam] higher linac current capability</font>
<div> </div>
</div>
<div class="BodyFragment"><font size="2"><span style="font-size:11pt">
<div class="PlainText">Colleagues,<br>
<br>
It is proposed to test whether the C100s can support 800 uA so CEBAF can <br>
complete the approved physics program (sans SoLID) this decade. MOLLER <br>
has requested 80 uA fifth pass, leaving little or no beam current for <br>
Hall C with 450 uA limit. lem suggests that the linacs can _now_ <br>
support 800 uA at 1000 MeV/linac. BBU instability is a concern because <br>
the HOM damping in the C100s is poor. A test is warranted. If BBU is <br>
not an issue, relatively inexpensive changes (H wall stub tuners) should <br>
be able to better match C100 and C75 cavities to klystrons at the higher <br>
current. If BBU is an issue, linac optics changes might help.<br>
<br>
CREX contingency runs Friday 3/27 to Saturday 4/4. It is proposed that <br>
Ops "banks" beam studies time for most of February and March, totalling <br>
96 hours. The test could then be scheduled Wednesday April 1 to <br>
Saturday April 4. This would interrupt Halls B/C/D but has long term <br>
benefit to C. a1n/d2n could schedule their last target change during <br>
CEBAF setup. 45 uA five pass to C (carbon target) and 115 uA fifth pass <br>
to A (carbon) would then put 800 uA in the linacs. Wien assumed left as <br>
is so little polarization to B and C during the run but easy restore.<br>
<br>
Two energy options present:<br>
<br>
990 MeV, 100 MeV below design, provides a stringent BBU test at an <br>
energy within expected range for high current experiments.<br>
<br>
930 MeV setup is available in allsaves from December 2018. Fifth pass <br>
to A, second pass to C, 40 uA max during allsave. Perhaps too stringent <br>
a test, given BBU scaling inversely with energy.<br>
<br>
I attach a spreadsheet which has beam property measurements made during <br>
the Nov. 2018 930 MeV setup. These may be compared to the ones made a <br>
year later with improved procedures.<br>
<br>
Comments? Shall we discuss it Tuesday February 4?<br>
<br>
Jay<br>
<br>
DOE documents allowing 2000 kW beam in CEBAF<br>
<br>
Environmental Assessment Determination (8 pages)<br>
<a href="https://jlabdoc.jlab.org/docushare/dsweb/Get/Document-50496/EA%20Determination%20-%20Proposed%20Upgrade%20&%20Operation%20of%20CEBAF%20&%20FEL%20Accelerators%202004%2010-Year%20Plan.pdf">https://jlabdoc.jlab.org/docushare/dsweb/Get/Document-50496/EA%20Determination%20-%20Proposed%20Upgrade%20&%20Operation%20of%20CEBAF%20&%20FEL%20Accelerators%202004%2010-Year%20Plan.pdf</a><br>
<br>
Environmental Assessment (395 pages)<br>
<a href="https://jlabdoc.jlab.org/docushare/dsweb/Get/Document-15071/EA-1534!.pdf">https://jlabdoc.jlab.org/docushare/dsweb/Get/Document-15071/EA-1534!.pdf</a><br>
</div>
</span></font></div>
</div>
</body>
</html>