1. Beam Commissioning
Adam Bartnik

2. Scope of the Talk 4-Pass ERL (UPP) Parameters
Energy: (injector), 42, 78, 114, 150 MeV
Injection rate: MHz = 40 mA
Commissioning the UPP is not the subject of this talk…

3. Scope of the Talk = KPP Single Pass (KPP) Parameters
Energy: (injector), 42 MeV
Injection rate: MHz = 1 mA
Here I will be talking about beam operation through the KPP only.

4. Three areas of commissioning
Low energy injector commissioning
0–6 MeV, space charge dominated
Goal: >1 mA beam current
Goal: <1 micron emittance, < 4 ps length, with optics match
Orbit through the FFAG
42+ MeV, limited by MLC available power
Space charge largely ignorable
Goal: Orbit into 2nd splitter, large FFAG energy acceptance
Energy recovery
42 MeV, energy recovered
Goal: 1 mA

5. Five operation periods
Low energy injector commissioning
Gun-ICM-Dump Recommissioning Q4 2016
MLC and Diagnostic Line Q2 2017
Orbit through the FFAG
Partial Arc Energy Scan Q
Full Arc Energy Scan Q1-Q
Energy recovery
5. KPP: Single Pass Energy Recovery Q3-Q

6. Gun-ICM-Dump Recommissioning
Partially DOE funded (separate project)
Already completed (Q4 2016)
Recover basic injector operation
Gun: kV
ICM: 1 MeV / cavity
Laser: MHz
Current: At least 1 mA (KPP), push for 50 mA (>UPP)
BNL BPM hardware prototyping with beam (see diagnostics talk)
Note: No detailed bunch diagnostics (emittance, bunch length, etc.)

7. Gun-ICM-Dump Recommissioning
Summary of results
Target, min. Achieved
Cathode: 1% QE, offset 3%
Gun: kV kV
ICM: 1 MeV / cavity 1 MeV - CBETA needs further conditioning
Laser: MHz 10 W
Current: 1 mA 4 mA Discussed in injector talk
Achieved all necessary goals for this phase, ran out of time for push to UPP current

8. MLC and Diagnostic Line
Layout changes
Remove beam stop. Add merger, MLC, diagnostic line
Two sets of goals
Beam through MLC (go/no-go 1)
Each cavity powered individually, beam phased on-crest (12 MeV)
Diagnostic Line
Low emittance, optics matching settings at 0.7, 3, 25 pC
Prototype BPM hardware test

9. Negligible beam size dependence on cavity phase
MLC and Diagnostic Line
Beam through MLC
Can we phase a cavity without dispersive line?
0.3o BPM phase stability with 100 nA beam
±60o cavity phase produces 3-10o BPM phase
Defocusing from cavity phase not significant
Challenges
No BPMs in MLC – long initial drift for 6 MeV beam
May require diagnostic line tests to fine-tune beam optics first
+60o 0o
Negligible beam size dependence on cavity phase
Beam size (mm)
Cavity 1

10. Previously measured longitudinal profile, with simulation
MLC and Diagnostic Line
Previously measured phase spaces
Diagnostic Line
Full bunch characterization
Emittance, twiss from EMS (slits / scanner magnets / Faraday cup)
Targeting 0.7, 3, 25 pC
Prototype BPM hardware test
Check nonlinearity correction
Challenges
Previous emittance measurements in merger had unexplained horz. growth
Never had optics (twiss) match requirement in past experience
Previously measured longitudinal profile, with simulation

11. Partial Arc Energy Scan
New for this phase
Layout changes
Everything before the MLC remains identical, except
All MLC cavities are powered (SSA installed), beam = 42+ MeV
After MLC
1st splitter line in single-pass configuration
1st FFAG girder
Dipole, BPM, viewscreen after FFAG girder

12. Partial Arc Energy Scan
Diagnostics layout
Two BPM designs: position-only, and Beam Arrival Monitor (BAM)
One BPM per splitter quad
BAM / Viewscreen / beam-stop combination

13. Partial Arc Energy Scan
Goals
Verify simulated orbit / arrival time dependence on magnet / cavity settings at 42 MeV
Adjust MLC energy gain, scale splitter magnets, check energy acceptance of 1st FFAG girder
Check path length adjustment range
Check radiation tolerance of test permanent magnet
~mC damage threshold? (1 mC = 25 pC * 1 KHz * 11 hours)
(Scientific Reports 6, 37937)
Challenges
New BPM hardware
MLC microphonics? Studied during MLC test

14. Full Arc Energy Scan Layout changes
FFAG arc / transitions / straights completed
1st line of splitter B completed
Diagnostics
Every other FFAG cell has position-only BPM
Between FFAG sections there is 1 BAM
1 Viewscreen per FFAG girder

15. Full Arc Energy Scan Goals
Verify simulated orbit / arrival time dependence on magnet / cavity settings at 42 MeV
Adjust MLC energy gain, scale splitter magnets, check energy acceptance of FFAG
Challenges
Transition section orbit
Neither periodic (as in arc), nor centered (as in straight)
Current limit from radiation damage threshold?
Will BPMs be usable before the beam can be safely stopped?
Systematic errors in magnet placement may require magnet moving

16. No layout or diagnostic changes
Single Pass Energy Recovery
No layout or diagnostic changes

17. Single Pass Energy Recovery
Goals
Energy recovery, beam steered into high power dump
Injector current > 1 mA
Challenges
Phase adjustment
More than a 20 degrees will require manual vacuum work
Halo
Permanent magnets reduce ability to tune away halo
Magnet damage threshold may limit acceptable halo below typical levels
How to ramp current?
Increase bunch charge (at fixed rate)
Increase bunch rate (at fixed charge)

18. Single Pass Energy Recovery
Fixed charge, increase rate
Laser with fully tunable duty factor, from single pulse to CW
“Rejected” charge is badly matched to lattice, potentially lost
Laser extinction ratio will be investigated before PAT
Rejected bunches
Time
Charge
Fixed rate, increase charge
Laser always at CW, turn up power
Potentially complicated to maintain injector optics with varying charge
Required settings determined during MLC test
Laser size increases with charge, but profile shape is maintained

19. Summary From the charge…
Lattices for all commissioning phases are determined and beam operation periods are scheduled
Commissioning plan exists at a level sufficient for accelerator engineering design
Diagnostics needed for commissioning have been determined