Date: August
5, 1999
From: Leigh Harwood
To: K. DeJager
B. Mecking
R. Carlini
E. Smith
Re: Beam emittance and energy spread for “12
GeV CEBAF”
I believe you are all aware the synchronton
radiation in the upgraded accelerator will significantly degrade the emittance
of the beam. I need your participation in deciding which direction to go from
here.
There were criteria set at Director’s Council for
the upgrade (12 GeV Upgrade Parameter List) which included specifications for
the emittances; we will be significantly above them with the baseline
optics. With a modest additional cost
increase of ~$150k we should be able to improve the horizontal emittance, but
at the expense of the vertical. (It would be done by interchanging the x and y
phase spaces after the beam goes the north linac on 5th pass but
before it enters the 9th arc.)
Improvements beyond this would require
reconfiguration of the arcs to add a bunch of quads, cost on the scale of
several M$ and required an additional 6-month shutdown for the installation.
I have included graphs of the emittances vs energy
for both options so you can see how things vary if you run at a lower
pass. Also, I include a graph of the
energy spread. I also include how the
emittance increase translates into how the spot size would increase relative to
the size at 4 GeV; divergence would
change comparably; some trade-off between the two could be done, of
course.
There
needs to be a change request done to address the fact that we won’t meet the
spec’s in the DC’s parameter list. I
need feedback from y’all to know which way to jump with the change
request. So…..how do these projections affect your anticipated programs?
I’d
like to close this issue by the end of the month. Is this possible?
Parameter |
DC parameter list |
Value in baseline |
Value with x/y exchange |
|
5-pass |
|
|
|
|
x-emittance (m) |
1x10-10 |
7x10-9 |
5x10-9 |
|
y-emittance (m) |
1x10-10 |
1x10-9 |
4x10-9 |
|
Energy spread |
0.01% |
0.023% |
0.023% |
|
5.5-pass |
|
|
|
|
x-emittance (m) |
1x10-9 |
10x10-9 |
7x10-9 |
|
y-emittance (m) |
1x10-9 |
2x10-9 |
4x10-9 |
|
Energy spread |
0.1% |
0.026% |
0.026% |
Baseline 12 GeV optics
12 GeV optics with x/y interchange before arc 9
Energy spread
for both sets of optics
