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Optimal Linac Setup for S20 Performance: R56 Chicane Selection and Tuning Procedure

This document outlines the Linac setup based on S20 performance estimates, including selecting an R56 chicane setting, observable parameters, free parameters, linac setup procedure, emittance tuning, and simulation results. It also covers BBA, ballistic studies, response matrix scans, beta matching, beam tuning, and more.

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Optimal Linac Setup for S20 Performance: R56 Chicane Selection and Tuning Procedure

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  1. FACET MD Plans – 2014 Spring Run • Linac setup based on S20 performance estimates: • Choose an R56 chicane setting to use based on simulation performance estimates {0-10mm} • R56 config • Observables: sig_z fully compressed, 2-bunch parameters notched, sig_x, delta_E • Free parameters: stag_chirp, comp_V, R56 • Linac setup procedure: • comp_V on [ LI02 pyro / max(LI02 pyro) ] • stag_chirp on [LI18 pyro / max(LI18 pyro)] OR LI20 pyro • Discrete configs for fully compressed & notched setups • … then LINAC emittance tuning • S20 pencil-beam studies [0.5Q, uncompressed] IP beta = 0.5x5 m • BBA key QUAD BPMs • 2050, 2147, 2235, 2365, 2445 & [3011 – 3156] • Sextupole alignment check • parabolic orbit & dispersion methods • Achieve 100% transmission to S20 dump • ballistic studies with bends @ 20.35 GeV • check individual quads powered (that are not part of above BBA procedure, especially strings) to check for any coarse misalignments • 2-D response-matrix scans • J. Sheppard plan • Beta matching at WS1,2&3 • Sexts OFF high IP beta • Sexts ON, low IP beta • Get beta, emit-limited focus-point beam sizes • Re-check BBA before compressing to assess stability • 0.5Q, Compressed config • Check sig_z, 2-bunch notched params & delta_E against model predictions for chosen R56 config • Waist beam tuning & beta-match check • 1Q, compressed

  2. Choice of LI20 Chicane R56 • Simulation of particle transport LI02-LI20 with Lucretia: • Starting with standard DR extracted bunch assumed • 6mm sig_z, 2E10 charge and usual asymmetry parameters • If bunch length longer, will change setup parameters, this is probably worth studying with measured DR bunch length… • Use a “typical” klystron compliment • Load an LI20 R56 optics [0:10 mm], 10x100 cm IP beta @ MIP • For a given LI02 compressor voltage setting, scan staggered_chirp to minimize bunch length at IP: keep 9GeV @ LI10 and 20.35GeV @ LI20 using LI09 and LI18 energy feedbacks and adding/removing tubes as required

  3. Simulation Results • Bunch density is 1/(sig_x*sig_y*sig_z) based on gaussian fits to x/y/z projected profiles • “Chromatic sensitivity” is relative increase in sig_x when changing centroid bunch energy by 0.5% • In general terms: • Bunch density improves with increasing R56 • Chromatic sensitivity degrades with increasing R56 • Increases below 4mm because chicane betas become too small for sextupoles to sufficiently compensate chromaticity and second-order dispersion, could improve by re-matching with higher beta functions in chicane • Chicane beta-functions increase with increasing R56 • Energy spread does not vary very significantly • 2-bunch notch setup becomes qualitatively easier with higher R56 • For some chicane configurations, the bunch density performance is more sensitive to chirp configuration than others- doesn’t correlate with R56 magnitude • Based on the above observations, an optimal choice for LI20 chicane optics is chosen to be 7mm.

  4. 7mm Chicane Optics(10x100 cm IP Beta Option)

  5. Choice of Compressor Voltage for 7mm Optics

  6. Example 2-Bunch Longitudinal Config, Set – Change staggered_chirp by 0.5 degree (-ve z = head of bunch)

  7. Linac Setup • Set optimal config using LI02 and LI20 PYROs • 55% of max PYRO in LI02 assuming proportional to 1/sig_z using compV • MAX PYRO in LI20 unsignstaggered_chirp LI02 PYRO 55% of max (+ve V from peak) Compressor V = 40.408 MV Staggered_Chirp= -1.742 degrees (*[0 0 1 2 3 3 0 0 0 5] LI sector multipliers ) -> == max PYRO signal in LI20

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