[BTeam] higher linac current capability

[Jay Benesch]

Colleagues,

It is proposed to test whether the C100s can support 800 uA so CEBAF can 
complete the approved physics program (sans SoLID) this decade.  MOLLER 
has requested 80 uA fifth pass, leaving little or no beam current for 
Hall C with 450 uA limit.  lem suggests that the linacs can _now_ 
support 800 uA at 1000 MeV/linac.  BBU instability is a concern because 
the HOM damping in the C100s is poor.  A test is warranted.  If BBU is 
not an issue, relatively inexpensive changes (H wall stub tuners) should 
be able to better match C100 and C75 cavities to klystrons at the higher 
current.  If BBU is an issue, linac optics changes might help.

CREX contingency runs Friday 3/27 to Saturday 4/4.  It is proposed that 
Ops "banks" beam studies time for most of February and March, totalling 
96 hours.  The test could then be scheduled Wednesday April 1 to 
Saturday April 4.  This would interrupt Halls B/C/D but has long term 
benefit to C.  a1n/d2n could schedule their last target change during 
CEBAF setup.  45 uA five pass to C (carbon target) and 115 uA fifth pass 
to A (carbon) would then put 800 uA in the linacs. Wien assumed left as 
is so little polarization to B and C during the run but easy restore.

Two energy options present:

990 MeV, 100 MeV below design, provides a stringent BBU test at an 
energy within expected range for high current experiments.

930 MeV setup is available in allsaves from December 2018.  Fifth pass 
to A, second pass to C, 40 uA max during allsave.  Perhaps too stringent 
a test, given BBU scaling inversely with energy.

I attach a spreadsheet which has beam property measurements made during 
the Nov. 2018 930 MeV setup.  These may be compared to the ones made a 
year later with improved procedures.

Comments?  Shall we discuss it Tuesday February 4?

Jay

DOE documents allowing 2000 kW beam in CEBAF

Environmental Assessment Determination (8 pages)
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

Environmental Assessment (395 pages)
https://jlabdoc.jlab.org/docushare/dsweb/Get/Document-15071/EA-1534!.pdf
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