1. HALLA APEL REPORT Yves Roblin Hall A colllaboration Meeting
January 25, 2018

2. OUTLINE
Hall A and CEBAF 12 GeV parameters
Current Status
Preparation for upcoming runs
Configuration for low energy spread
Raster versus intrinsic beam size
Conclusion

3. 6 GeV vs 12 GeV CEBAF Top Level Parameters
Energy to Halls A,B,C / D
11 GeV
Number of passes for Halls A,B,C / D 5
Duty Factor CW
Max. Current to Halls A+ C / B
200 A / 5 A
Max. Current to Halls A+C / B+D
85 A
Max. Beam Power
1 MW
Emittance at max. energy (unnormalized, rms): x, y
1 nm-rad, 1 nm-rad
10 nm-rad, 2 nm-rad
Energy spread at max. energy (rms)
2.5 x 10-5
5 x 10-4

4. Transverse Emittance* and Energy Spread†
Area
p/p
[x10-3] x
[nm] y
Chicane
0.5
4.00
Arc 1
0.05
0.41
Arc 2
0.03
0.26
0.23
Arc 3
0.035
0.22
0.21
Arc 4
0.044
0.24
Arc 5
0.060
0.33
0.25
Arc 6
0.090
0.58
0.31
Arc 7
0.104
0.79
0.44
Arc 8
0.133
1.21
0.57
Arc 9
0.167
2.09
0.64
Arc 10
0.194
2.97
0.95
Hall D
0.18
2.70
1.03
DBA option
Damping
Values are calculated at the end of each arc.
Normalized emittance is beta.gamma*egeometric
These calculations were checked with 3 different codes and also agree with a simpler analytical estimate (sand’s formula) which
Does not take into account synch rad. Loss in quadrupoles.
Sync. Rad.
* Emittances are geometric
† Quantities are rms

5. Ratio of non-Gaussian tail to Gaussian core.
12 GeV Beam Requirements
Hall
Emittance
Energy spread ()
Spot size (s)
Halo A
εx < 10 nm-rad,
εy < 5 nm-rad
12 GeV: 0.05%
2-4 GeV: 0.003% (with alt. Optics)
12 GeV: x<400μm, y< 200μm
2-4 GeV: y < 100 μm Can do x<200μm, y< 200μm
<0.01%(1)
These are the official specs as provided to the 12GeV project.
Ratio of non-Gaussian tail to Gaussian core.

6. Beam Delivery Constraints
Hall D is running:
Any other Hall at 5 pass will need to be at Mhz
Halls at lower passes can choose or 500 Mhz
Four Halls Running:
Two Halls will have to share the same slit at the chopper. They will be at Mhz.
Energy Reach:
Nominal is 1090 MeV gain per linac
It is possible to request less (lower limit is about half that)
A significant energy change requires a full setup, a small one (up to a few percents) should be manageable within a couple of shifts (we need to quantify this for future experiments)

7. Beam Delivery Constraints (cont)
Current Limitations: Several factors limit the maximum current available:
Klystron power in linac cavities limits it about 485 𝝁𝐀, so about 85 𝝁𝐀 at pass 5.
Dump are rated to 1kW in Hall A/C but administrative limit is 800 Kw.
Polarization constraints:
We have a double Wien filter allowing for a way to fully flip polarization 180 (like the half-wave plates do).
We can optimize for maximum polarization in the presence of synchrotron radiation. This process is done offline. A new tool allowing for this to be done ”on-the-fly” is being developed.

8. Current Status
Tritium experiments on the floor now . Hall A is operational at 5 pass (ran with 22 𝝁𝐀)
Recommissioned the vertical 5 pass extraction to prepare for three beams at five pass (this run period).
Matching process is robust, allows for spot sizes at target of 200 𝝁𝐦 𝐚𝐭 𝐭𝐚𝐫𝐠𝐞𝐭 𝐩𝐚𝐬𝐬 𝟓, 𝐬𝐦𝐚𝐥𝐥𝐞𝐫 𝐚𝐭 𝐥𝐨𝐰𝐞𝐫 𝐩𝐚𝐬𝐬𝐞𝐬
Beam positions stable with the slow lock system. We are planning to recommission the fast-feedback during beam studies this run period.
Target misalignment relative to the beamline can be an issue with the tight aperture requirements for Tritium.

9. Preparations for fall run
One experiment in particular E :
It will require low energy spread, good energy stability
We need to make sure the fast-feedback is functional (hardware was upgraded)
We need to make sure we can measure energy spread at 1C12 (new OTR system)
We need to revert to the 6GeV low energy optics
Beam studies during the winter run period (now) will be used to check that the fast-feedback system is operational and cross-calibrate the OTR 1C12 with the harp at 1C12.
Any other particular requests regarding this upcoming fall run ? Need to know now if it requires beam studies.

10. Low emittance growth, Low beta. We reached 800 kW with it.
12GeV HALL A optics
Low emittance growth, Low beta. We reached 800 kW with it.
We used these to do a full power CW run in Hall A.
Low emittance, easy tunability optics.
Very small beta’s in ARC which reduces HALO formation
Beam is divergent after target to spread it onto diffuser and dump, lowering density of energy deposition.

11. Low Energy Spread optics

12. HALL A beamline raster configuration
Fast raster
septum
The actual 3D of the septum and target area will be shown in a a separate talk.
Hall A raster is upstream of Moeller target. Four quadrupoles are between it and the experimental target
Adjusting these quadrupoles affect both intrinsic beam size and raster deflection. Also, one has a constraint on minimum spot size at diffuser in case of raster failure.

13. Raster checks with beam
8.843 GeV/c
In my model, I have a simple tv-raster uniform scan. The real one has triangular waves and a more complex pattern.
My model has infinite bandwidth. The BPMS are limited to 1000 Hz or so. They sample at 2Khz. Raster is 24 Khz.
Nevertheless, one can use that model to predict raster size. In practice, it is also adjusted by using spot++.
This is for a 2mmx2mm raster. Optics model can predict raster size.

14. Conclusions Hall A can deliver the requested 12 GeV beam parameters
It can be configured for the first 2 passes with an optic that is designed to monitor energy spread
The higher passes are configured with an optic which reduces emittance growth and allow control of spot size.
Fast-feedback system has not been yet commissioned for pass 5, planning to do so this winter.