1. Grigory Eremeev, Joe Grames, Reza Kazimi, Yves Roblin
CEBAF 18.5 MeV w/ 4K Demo
Grigory Eremeev, Joe Grames, Reza Kazimi, Yves Roblin
On March 28, 2017 we setup the injector with 4K to produce 50mA cw beam with energy of 18.5 MeV to the 4D spectrometer.
The goal of the test was to determine if the beam quality is sufficient to perform the proposed radio-isotope test.

2. 6.3 MeV Setup w/ SRF 0L02 @ 4K (beam to FC#2)
We have operated the injector cryounit (0L02) w/ SRF at 4K a few times over the past 2-3 years.
Our SRF setup steps have been essentially the same:
Maintain JT flow greater than 70%
Maintain LL greater than 90%
Tune cavities (resonance different at 4K vs. 2K)
Last year we compared standard injector setup of 6.3 MeV beam (beam to FC#2) with 4K vs. 2K, and found similar beam quality.
The momentum spread was determined to be somewhat larger at 4K, but still relatively small.
28th Linear Accelerator Conference, LINAC 16, East Lansing, Michigan, September 2016

3. 18.5 MV Setup w/ SRF 0L02 + 0L03 @ 4K (full injector available)
We begin testing assuming standard operation of 0L02, to provide 6.3 4K
Zones 0L03 and 0L04 were tested on two previous occasions, with our standard protocol
0L03 (C50) => Produced total envelope of about 27 MV/m => 13.5 MeV
0L04 (R100) => Produce only a few MV/m => not viable

4. 18.5 MV Stability w/ SRF 0L02 + 0L03 @ 4K (full injector available)
Total energy set to 18.5 MeV
PSS
Issue
Only period of
Instability one cavity
PSS
Issue
0L03
0L02
Liquid Levels
JT Levels

5. Beam Setup of 18.5 MeV w/ SRF 0L02 + 0L03 @ 4K (full injector available)
18.5 MeV Beam setup steps:
The beam was setup at 6.3 MeV to FC#2, with high transmission of 50uA cw.
The beam was found in the 4D spectrometer at the starting gradients and the energy measured.
The transport quads were scaled down which rounded up the beam spot.
The spectrometer was set for “18.52”, not sure if this calculation is precisely momentum or energy.
The RF gradient in last cavity was lowered to set the beam energy precisely.
Need uncertainty in the beam momentum (dp) due to the systematics of the 4D spectrometer.

6. Beam demo of 18.5 MeV w/ SRF 0L02 + 0L03 @ 4K (full injector available)
Beam demo of uA cw:
The beam was setup at 6.3 MeV to FC#2, with high transmission of 50uA cw.
50uA beam was delivered to 4D OTR foil (IOR4D00) and parked for about 15 min
the 4D harp (IHA4D00) was not reporting a signal, so we could not precisely measure the beam size (50uA tune)
we did however, measure emittance/Twiss at MQJ0L02 for later calculation of relative momentum spread (dp/p) and beam size

7. Beam demo of 18.5 MeV w/ SRF 0L02 + 0L03 @ 4K (full injector available)
Instead, we calibrated an image of the OTR fork to a best known drawing to estimate OTR beam size…
beam sigma-x = 3.8mm => FWHM = 8.5mm beam sigma-y = 3.5mm => FWHM = 7.9mm
This is very likely an overestimate of minimum accessible beam size…
Optimized quad settings w/ measured energy spread not loaded
No optimization to energy spread
OTR image from foil possibly overestimates beam size
Finally, we ran out of time (and PSS) and ended beam measurements.

8. Beam demo of 18.5 MeV w/ SRF 0L02 + 0L03 @ 4K (full injector available)
“Worst Case” might be what we measured:
beam size from OTR
momentum spread ~ 3 x 10-3
hand-tuning quads
“Best Case” might be what we measured:
beam size from 4D harp
mnimize momentum spread 1-2 x 10-3
optimized quads using Elegant model

9. Comments on energy and energy spread of 18
Comments on energy and energy spread of 18.5 MeV w/ SRF 0L02 + 4K
We observed a horizontal fluctuation (0.15mm) at the 4D bpm (IPM4D00), but not elsewhere, that suggests a 15 sec modulation of beam energy of about 5E-5 (10keV); assumes dispersion of 3m.

10. Summary/Outlook toward Test
We can produce 50uA 18.5 MeV w/ 4K to 4D spectrometer.
We need uncertainty of 4D spectrometer momentum to precisely set/measure the beam momentum (and energy).
We need 4D harp for more precise profile measurement (and optimization) of energy spread.
Elegant model can be used to predict and set beam size, provided we can measure dp/p well enough
Beam energy modulation at 15 sec is about 5E-4, and looks to be the temperature regulation of capture LCW.
New proposed harp/bpm for radio-isotope run would be calibrated to surveyed 4D harp; is this good enough?

11. Backup Slide

12. plots for dpp/p=1e-3, 2e-3 and 3e-3 with hand tuning quads