Report from Working Group III on Accelerator Performance Limitations

1. Report from Working Group III on Accelerator Performance Limitations • Topics Discussed • Comparing Modeling and Experiment on CSR • LCLS experiments • Improving connection • So far, agreement is excellent,; time resolved measurement needed • Suppression of CSR with vertical blowup; requires real work • Skew quad method of measuring longitudinal effects • Question: can we use CSR as design element for shaping • Microbunching instability • Want to see laser heater experiment; watershed event • JLab experiments • Past: CSR in bends sensitive to bunch lengths; two lobes; not yet modeled • Future (or taking over Hall A) • “High charge,” high brightness injector in Jlab: CSR in arc; possibilities to compensate transverse effects; microbunching • Reducing undulator gaps • Wakefields; e.g., resistive wall • Jitter amplification (transients, cw??) • Collimating looks good for dealing with halo (agreement?) at least in pulsed machines • In vacuum makes cross polarization more attractive than APPLE II

2. Bunch Compression & CSR Measured after BC2 (0.25 nC) BC2 (4.3 GeV) TCAV (5.0 GeV) BSY (14 GeV) 550 m sz < 5 mm nominal sz 2 mm old screen used sz > 25 mm L2 4 wires

3. OTR12 OTR12 time With CSR With CSR Skew quad OFF Skew quad ON OTR12 OTR12 x vs. z x vs. z With CSR With CSR Skew quad OFF Skew quad ON

4. Report from Working Group III on Accelerator Performance Limitations • Topics Discussed • Charge and bunch length issues • Flat top for seeding may limit how low charge • Recirculation (without energy recovery) for cost savings • A recirculations could save $$$$ • More than one, less than five; broad minimum • Average current looks okay from power and bbu looks okay; also HOM losses, since rep rate low • Might add operational complexity • Might add operational flexibility: feedforward, several energies, footprint; maybe compression in Arc, but CSR??? • CSR is on the margin at 2.5 nC at 250 amps (BESSY FEL report); lower charge may solve • Emittance exchange • Encourage continuation of program • Beam conditioning • Could be game changing

5. Beam stability issues Peak current distribution 1000 random seeds seed laser pulse z, mm Useful part Sample errors: Charge: 1% RF phase: 0.1 degree RF amplitude: 0.01% Peak current

6. Report from Working Group III on Accelerator Performance Limitations • Actions, R&D Discussed • Workshop in Hawaii • Comparing Modeling and Experiment on CSR • Skew quad method of measuring longitudinal effects • Bunch length/charge jitter coupling to transverse jitter • Xband deflector to really see internal structure • More realistic, better modeling with vertical effects • Question: can we use CSR as design element for shaping • More experiments with “edgy” electron distributions to really test, e.g., elegant • Microbunching instability • Want to see laser heater experiment; watershed event • 4 D vlasov solvers • Call microbunch workshop • JLab experiments • “High charge,” high brightness injector in CEBAF at Jlab: CSR in arc; possibilities to compensate transverse effects; microbunching • JLab FEL linac experiments

7. Report from Working Group III on Accelerator Performance Limitations • Actions, R&D Discussed • Workshop in Hawaii • Reducing undulator gaps (most leverage of items here) • Spring 8 measurements • Measuring energy loss and spread as function of charge, bunch length • Collimating looks good for dealing with halo (agreement?) at least in pulsed machines • Call WG II thoughts • Charge and bunch length issues • Really setting specs; RF control development could buy lower charge • Recirculation (without energy recovery) for cost savings • JLab CEBAF experiments • Design studies • Emittance exchange • Encourage continuation of program • Beam conditioning • Could be game changing • Need to scope out experiment; scale awkward