Design of a one-stage bunch compressor for ILC PAL June Eun-San Kim

Introduction We present preliminary results on design of a one-stage bunch compressor. The one-stage bunch compressor system consists of a matching section, RF sections and a chicane. We show that bunch length of 6 mm rms can be compressed by a factor of 20 by the designed one-stage BC.

Status of present designed bunch compressors  Single stage bunch compressor 6 mm -> 300  m  Two stage bunch compressor 6 mm -> 300  m 6 mm -> 150  m  Three stage bunch compressor 6mm -> 300  m 6mm -> 150  m By Tor, PT and Andy in LET meeting ( 2th June ) at SLAC

Twiss parameters of designed one-stage BC

Twiss parameters of a matching section between DR and RF section

Twiss parameters of a chicane

Parameters of bunch compressor RF cavity : Length = 1.0 m Voltage = 35MeV/m rf phase = -50 deg Freq = 1.3GHz R56 = m Bending angle = 6.5 deg Length of a bending magnet = 2.03 m Length of the chicane : ~ 10 m

Performance of bunch compressor Initial Final bunch length 6 mm 300  m energy spread 0.15 % 7.9 % X-Emittance 8  m 9.1  m Y-Emittance 0.02  m 0.02  m

25 % -25% 0.0% 0.03mm-3mm Final longitudinal phase space distribution

Summary We showed preliminary results on a one- stage bunch compressor and the BC system satisfies basic parameters that are required for BC. We also need more discussions with LET groups for the further optimizations and for the choice of ultimate design goals. Two-stage BC for bunch length of 150  m will be presented in next meeting.

Work plan for fast-ion instability in ILC damping ring configuration selection Co-leaders D. Schulte (CERN) E.-S. Kim (POSTECH) F. Zimmermann (CERN) Draft: 22 June 2005

Evaluation of “Fast-Ion Effects” for ILC Damping Ring Configuration Selection ( 8th Task force item ) Aims A baseline configuration for the ILC will be selected by the end of The fast-ion instability is one of the criteria to be considered when choosing circumference, bunch charge and bunch spacing. Methodology 1) Pertinent parameters for three different rings (17 km, 6 km and 3 km circumference) will be compiled, including beam size in arcs, wiggler, and straights, bunch spacing, tunes, and average beta functions; 2) Trapping condition of ions inside the train is evaluated at injection and at extraction; 3) The rise times in the different sections will be computed analytically, again for injection and extraction, when ions are trapped, and a global rise time calculated for each ring, both for extraction and injection, assuming a vacuum pressure of 1 ntorr; the maximum acceptable train length can be determined for each ring; 4) Ion induced tune shifts will also be compared; 5) If time and resources are available, simulations at various degree of sophistication could be performed to verify the differences between rings or ring sections; If time and resources are available, experiments could be performed and/or analysed to benchmark the simulations and validate the analytical approach.

Expressions of interest and available tools S. Heifets (SLAC) has offered to look at ways to speed up the ion-instability simulations. T. Raubenheimer (SLAC) provided an example excel spreadsheet which could be used for points 2) and 3). N. Walker (DESY) is interested in simulating and understanding ion effects in wigglers and undulators. T. Raubenheimer has written a PIC simulation code for the fast beam-ion instability. Also, the HEADTAIL PIC code for electron-cloud instabilities, originally written by G. Rumolo and F. Zimmermann at CERN, could be modified for simulations of ion instabilities. Other contributions are highly welcome! Comparisons with existing machines Simulations and experimental growth rates were found to be in excellent agreement for PLS. A comparison with analytical formulae is planned.