Beam Commissioning Adam Bartnik

Scope of the Talk 4-Pass ERL (UPP) Parameters Energy: 6 (injector), 42, 78, 114, 150 MeV Injection rate: 125 pC @ 325 MHz = 40 mA Commissioning the UPP is not the subject of this talk…

Scope of the Talk = KPP Single Pass (KPP) Parameters Energy: 6 (injector), 42 MeV Injection rate: 25 pC @ 41.9 MHz = 1 mA Here I will be talking about beam operation through the KPP only.

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

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 Q1 2018 Full Arc Energy Scan Q1-Q2 2019 Energy recovery 5. KPP: Single Pass Energy Recovery Q3-Q4 2019

Gun-ICM-Dump Recommissioning Partially DOE funded (separate project) Already completed (Q4 2016) Recover basic injector operation Gun: 350+ kV ICM: 1 MeV / cavity Laser: 5 W @ 50 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.)

Gun-ICM-Dump Recommissioning Summary of results Target, min. Achieved Cathode: 1% QE, offset 3% Gun: 350 kV 350 kV ICM: 1 MeV / cavity 1 MeV - CBETA needs further conditioning Laser: 5 W @ 50 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

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

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

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

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

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

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

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

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

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

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)

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

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