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Gentle folk:</div>
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I fully expect that configuring SRF for higher circulating current is more restrictive an activity than is restoring the low-energy (for example, summer HPS run) configuration. The current and momentum scale linearly for a BBU test, and there is no reason
to believe that (for example again) the HPS setup will differ in any way more significant than the evening-up of the linac gradient profile. SRF power requirements drop as the product of momentum and current, which is quadratic in the scale factor for momentum
when seeking a BBU threshold.</div>
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If the goal is truly and principally a BBU test, I see no reason to keep the beam momentum unnecessarily high. At higher momentum we are more subject to S.R.-driven emittance growth, which will be a much smaller nuisance at 900 MeV per pass than more than
900 MeV/linac.<br>
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Respectfully submitted,</div>
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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 Jay Benesch <benesch@jlab.org><br>
<b>Sent:</b> Sunday, February 2, 2020 10:59<br>
<b>To:</b> Xiaochao Zheng <xiaochao@jlab.org>; BTeam <bteam@jlab.org><br>
<b>Cc:</b> Jian-Ping Chen <jpchen@jlab.org>; Paschke, Kent Dieter (kdp2c) <paschke@virginia.edu>; 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> Re: [BTeam] higher linac current capability</font>
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<div class="PlainText">Colleagues,<br>
<br>
After reviewing the draft 2021 schedule it seems to me that a test at <br>
the present energy April 3-4 is a more prudent first step. If we can <br>
send 45 uA five pass to C (carbon) and 75 uA five pass to A (carbon, <br>
setup required) without BBU issues this will provide a step towards <br>
higher luminosity. Since the 2021 schedule has 980 MeV/linac and 910 <br>
MeV/linac runs, subsequent BBU tests at higher linac currents could be <br>
run then.<br>
<br>
All three tests will require effort and agreement by JLab management to <br>
revise the 900 kW limit prescribed in many places.<br>
<br>
April 3-4 is the end of the CREX contingency period. CREX removal and <br>
SBS installation is to start April 6. Running the test at the present <br>
energy implies beam will always be in Hall C. a1n/d2n on He3 while five <br>
pass to A is set up, then carbon while current is ramped in both halls. <br>
I expect a day of RF stabilization as the current increases. With this <br>
plan, He3 target replacement will not be possible for the two days even <br>
if necessary.<br>
<br>
Again, if approved, beam studies time would be banked in the next two <br>
months so no scheduled beam delivery for Physics is taken.<br>
<br>
Jay<br>
<br>
On 2/2/20 10:37 AM, Xiaochao Zheng wrote:<br>
> Hi Jay:<br>
> <br>
> I just want to add that the date April 1-4 may not be when we schedule <br>
> to change our cells. The cell typically last a month, and changing it <br>
> too early or too late is not practical for the running of A1n/d2n. And <br>
> if we don't change the cell then we will lose 3 days of beam time.<br>
> <br>
> Is your proposed date Apr 1-4 flexible to some extent?<br>
> <br>
> Thanks,<br>
> <br>
> Xiaochao<br>
> ------------------------------------------------------------------------<br>
> *From:* Jay Benesch <benesch@jlab.org><br>
> *Sent:* Friday, January 31, 2020 4:55 PM<br>
> *To:* BTeam <bteam@jlab.org><br>
> *Cc:* Cynthia (Thia) Keppel <keppel@jlab.org>; Garth Huber <br>
> <Garth.Huber@uregina.ca>; Jian-Ping Chen <jpchen@jlab.org>; Gordon D. <br>
> Cates <cates@virginia.edu>; Brad Sawatzky <brads@jlab.org>; Xiaochao <br>
> Zheng <xiaochao@jlab.org>; Paschke, Kent Dieter (kdp2c) <br>
> <paschke@virginia.edu><br>
> *Subject:* higher linac current capability<br>
> 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>
<br>
<br>
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