Harmonic Fast Kicker Development Update SRFCASA team with

Harmonic Fast Kicker Development Update SRF/CASA team with Summer Students Report by Haipeng Wang July 27, 2017

Outline and Contributions • Numerology and frequency recipe Andrew Hutton, Andrew Dotson, Jiquan Guo, Haipeng Wang • Old prototype cavity measurement, mode summation of 5 modes, wirestretching and scanning for e-center Sarah Overstreet, Haipeng Wang • ¼ lambda length stub summarizer on Yulu’s half-scale to generate 6 th harmonic mode and e-center of the mode, simulation and measurement Bob Rimmer, Sarah Overstreet, Haipeng Wang, Jim Henry, Bill Clemens, … • Scaling calculation for odd harmonic cavity with larger aperture and OD Haipeng Wang, Jiquan Guo for new Pos. Doc (to be on-board Sep. 16)

Harmonic Kicker Frequencies and UITF/LERF Test CEBAF/UITF/ LERF RF PEP-II or JLEIC e-ring RF JLEIC i-ring/ERL RF frequency Baseline JLEIC ERL gun laser reprate CCR turns harmonic kicker base RF photo cathode laser reprate in UITF/LERF test kicked beam reprate in UITF/LERF test 5 • 6 Odd harmonic frequencies of RF kicker: 86. 6 MHz x 1, x 3, x 5, x 7, x 9, x 11 (or +DC) =86. 6 MHz, 259. 8 MHz, 433. 0 MHz, 606. 2 MHz, 779. 4 MHz, 952. 6 MHz /DC • CCR harmonic number can NOT be multiple of 11 • More even harmonics help the kick pulse flatness and reduction of slopes of zero crossing

Old/New CCR/ERL Beam Dynamic Parameters Comparison Old: from Yulu Huang’s Ph. D thesis, Dec. 2016 Parameter New: From Steve Benson’s Status Report, July 2017 Old Value New Value Unit Electron energy 55 20 -55 Me. V Charge per bunch 3. 2 2. 0 (3. 2) n. C bunch length at CCR 3 (rms) 2 (tophat) cm Gaussian beer can 476. 3 MHz Normalized transverse emittance at cooling channel 1. 074 (non-mag) 36 (mag, drift) mm mrad Normalized vertical emittance at cooling channel 1. 074 (non-mag) 36 (mag, drift) mm mrad 3 E-4 Recirculation turns 10 11 -13? No. Kick angle 1 2. 5 mrad Total kick voltage 55 137. 5 k. V Beam-stay-clear aperture on kicker cavity (dia. ) 70 >70? mm Bunch distribution Bunch frequency Energy spread (uncorr)

Old/New CCR Turns and Harmonic Numbers Comparison Old: Dec. 2016 CCR turns: 10 Cavity harmonics: 10 (5 odd, 5 even) Cavity base frequency: 47. 63 MHz Cavity number per side: 4

Old Setup of Harmonic Summation with New Measurement Technique Old: Yulu, PRAB 19, 122001 (2016) New: Sarah, 2017, Summer Intern Report 5 -harmonic spectrum Time-domain waveform stub tuning • • • Also Yulu Huang Ph. D Thesis, JLAB-ACC-16 -2444 Or DOE/OR/23177 -4174 • Sample sum voltage on stretched wire than pickup probe HP/LP filters built for noise reduction of the wire-stretching measurement from motor and RF source Retune the cavity without stub but with the wire Wire-scanning for ecenter and multiple analysis wire x-scan New technique

New ¼ l 11 Length Stub Symmetrizer to Minimize Beam Loading Slice & Mirror Boolean Standing wave of Er on inner conductor surface New, July 2017 • • Old 2016 Both simulation (CST) and measurement studies for this modification 5 -Stub tuners could not turn higher harmonics back to targets Fixed stub length can only symmetrize e-center on the 6 th harmonic but not lower and higher ones Only 952. 6 MHz mode (and 476. 3 MHz) needs zero beam loading Symmetrizer optimization by Yulu in her thesis Dec. 2016 Ex & Ez vs z Ex Ez z

CST Simulation Result with New Stub on Old Cavity (TE 11 s in stub plane Z) 2 (TE 11 s in plane Y) 3

CST Simulation Result with New Stub on Old Cavity (TE 11 s in stub tuner plane Z) (TE 11 s in plane Y) (starts degenerate to TE 11 s) (TE 11 s in plane Y) (TE 11 s in stub tuner plane Z) (TE 11 s in plane Y) • Increase the stub length by 16. 1 mm will see the e-center of 857. 6 MHz (HM 5) instead of 1047. 9 MHz (HM 6) • Need fine tune both stub and cavity lengths for new cavity design • Need to suppress TE 11 s higher than HM 6, Freqcutoff clight/[ (a+b)], more difficult for larger (a+b)

CST Simulation Result Parameters with New ¼ l 11 Stub on Old Cavity TE 11 s • E-center has been found on HM 6 by wirescanning technique (Sarah’s summer interm report due next week) • HM 6 (HM 7 and HM 8) is among the HOMs (TE 11 s modes, TE 11 cutoff frequency is lowered by the stubs) • New design needs to suppress them to higher frequencies

Analytical Model of Harmonic Kicker Cavity Design from Text Book Disk capacitance + capacitance due to the fringe field enforcement factor, new! not in exact format yet Normalized transverse shunt impedance

Analytical Model of Harmonic Kicker Cavity Design from Text Book • Cavity length is sensitive to all odd harmonics • Stub tuning will fine tune each mode on resonance • Gap distance has less effect on the harmonic tuning

Scaling Calculation of Odd Harmonic Kicker Cavity Design Optimum =a/b=0. 35 In ref. 2

Scaling Calculation of 6 -Odd Harmonic Kicker Cavity Design Preliminary

Scaling Calculation of 5 -Odd 5 -Even Harmonic Kicker Cavity Design for 952. 6 MHz Preliminary

Scaling Calculation of New 5 -Odd Harmonic Kicker Cavity Design for 779. 4 MHz Preliminary Prelimina

5 -Odd Harmonic Cavity Design Dimensions for Stay-Clear Cavity Long Side Length (down): ~810 mm Cavity Short Side Length (up): ~83 mm (with symmetrizer) ~50 mm (without Symmetrizer) Cavity OD: ~332 mm Cavity inner conductor OD: ~117 mm Cavity Beam-Stay-Clear Aperture (dia. ): (70 mm, 1. 25 k. W); (120 mm, 6. 9 k. W) Less thermal problem to handle 7 k. W; More problems to bring 6 th Odd in. i. e. on the HOM (TE 11 s) suppression and a less efficiency of 6 th mode on its beam voltage to RF power. Earlier CAD model: needs also Inner conductor cooling tubes Preliminary James and Fredrik’s vacuum stress analysis