ILC damping ring options and their critical issues 12th July th ACFA MDI/POL/ACC Pohang Accelerator Lab. Eun-San Kim

circumference cell shape Laboratory 3 km TME racetrack KEK 3 km PI racetrack SLAC 6 km TME circular FNAL/ANL 6 km FODO dogbone LBNL 16 km FODO dogbone LBNL 17 km TME dogbone DESY 17 km PI dogbone SLAC 17 km 2.5 PI dogbone KEK Proposed damping rings for ILC

ParametersDESYSALCLBNL Energy (GeV)555 Circumference (km) Emittance (nm) Tunes (x/y/s)76.31,41.18, ,83.65, ,76.41,0.025 Momentum compaction1.22x x x10 -4 Bunch length (mm) Energy spread1.29x x x10 -3 Chromaticity-125, , , RF frequency (MHz) RF voltage (MV) Damping time (ms)2827 Energy loss / turn (MeV) Main parameters of dogbone damping rings

ParametersKEKLBNLFNAL/ANL Energy (GeV)555 Circumference (km) Emittance (nm) Tunes (x/y/s)45.36,24.55, ,31.59, ,40.92,0.043 Momentum compaction3.62x x x10 -4 Bunch length (mm) Energy spread1.36x x x10 -3 Chromaticity-125, , , RF frequency RF voltage (MV) Damping time (ms) Energy loss / turn (MeV) Main parameters of small damping rings

Task Task leaders 1 Determine dynamic aperture (frequency map Analysis) ;Determine acceptance using realistic e+ distribution, including physical apertures, tuning errors etc. Determine impact of wiggler nonlinearities Y. Cai(SLAC), Y. Ohnishi (KEK) 2 Estimate sensitivity of vertical emittance to alignment, and develop coupling-correction algorithm. Estimate of impact of stray field J. Jones (Darebury), K. Kubo (KEK) 3 Estimate thresholds and/or growth rates from classical instabilities (microwave, coupled bunch, IBS) A. Wolski (LBNL) 4 Characterize space-charge effects.M. Venturini (LBNL), K. Oide(KEK) 5 KickersM. Ross (SLAC), T. Naito (KEK) 6 Specify SEY limits to prevent electron cloud F. Zimmerman(CERN) K.Ohmi(KEK) M. Pivi (SLAC) ILC damping ring assessment tasks(I)

Task Task leaders 7Specify vacuum requirements to prevent fast-ion effects Eun-San Kim ( PAL ) D. Schulte (CERN) F. Zimmerman (CERN) 8Make cost estimates. J. Noonan (ANL) S. Guiducci (INFN) J. Urakawa (KEK) 9Determine tolerable level of beam losses for the ring S. Guiducci (INFN) 10Estimate de-polarization D. Barber (DESY) 11Pre-damping ring evaluations M. Kuriki (KEK) 12Experimental demonstration of 2 pm ILC damping ring assessment tasks(II)

 Lattice design with acceptance of about 10 sigma  Design of pre-damping ring  DR in main linac tunnel or separate tunnel  Dynamic aperture and nonlinear wiggler effects  Development of fast kickers  Single particle dynamics for 2 pm vertical emittance  Collective beam instabilities - threshold of electron-cloud instability and fast-ion instability and so on….. DR items issued at 1 st ILC workshop

Study of dynamic aperture with wiggler in dogbone ring (by J. Urban) Linear ModelNon-Linear Model 3σ e+inj Dynamic aperture of dogbone lattice shows about 3  when multipole fields are included in the simulation.

Study of dynamic aperture with wiggler in 6km FNAL ring (by A. Wolsky) On-momentum wiggler nonlinearities cause noticeable but modest DA reduction Nonlinear wigglers Linear wigglers Frequency maps measure diffusion in tune; allow identification of resonances that may be affecting the DA. Bluer orbits have more regular motion. Reddish orbits are chaotic. chaotic motion regular motion (M. Venturini) - Short term tracking done with MaryLie3.0 - Error-free lattice

Performance in ILC may be limited by an electron cloud and collective beam instabilities in damping rings. Collective effects in damping rings

 Microwave instability Keil-Schnell-Boussard criterion for longitudinal threshold shows  || /n = 191 m  km  163  m  km   100  m  km    Space-charge tune shift shows incoherent tune shift of ~ 0.05.

Methodology 1)Pertinent parameters for three different rings (17 km, 6 km and 3 km circumference) [: “For some studies (e.g. electron-cloud build-up) it probably is not necessary to study every lattice in detail, but pick one in each circumference.”] 2)Electron cloud build up is simulated for the different regions (arcs, wigglers, straights) considering different secondary emission yields. 3)For the wigglers simulations the field can be modeled at various levels of sophistication, and the importance of refined models has to be explored; 4)Single-bunch wake fields and the thresholds of the fast single-bunch TMCI-like instability are estimated; 5)Multi-bunch wake fields and growth rates are inferred from e-cloud build up simulations; 6)Electron induced tune shifts will be calculated and compared; 7)Predictions of electron build up from different simulation codes are compared; Collective effects in damping rings Working plans for Electron-Cloud Effects Co-ordinators : Kazuhito Ohmi (KEK) M. Pivi (SLAC) Frank Zimmermann (CERN)

Collective effects in damping rings Working plans for Fast-Ion Effects 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 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 analyzed to benchmark the simulations and validate the analytical approach. Co-ordinators : E.-S. Kim ( PAL ), D. Schulte (CERN), F. Zimmerman (CERN)

Exponential growth time of fast-ion instability at LBNL 3 km damping ring Preliminary simulation results show necessity of bunch by bunch feedback system to suppress the beam instability in the vacuum pressure of 0.1 nT.

Accelerator Test Facility for ILC at KEK International test facility for low-emittance studies, precise beam diagnostics and final focus beam test

Summary  Preparation of the baseline configuration design for DR –Items of the tasks were identified. –Responsible peoples were identified.  2nd ILC workshop at Snowmass - 1 st week will identify the decisions needed to reach a baseline configuration - 2 nd week will prepare documents for the baseline configurations decided in the 1 st week.  A baseline configuration for the damping ring will be selected by the end of 2005 and CDR will be completed by end of 2006.

Acknowledgments 1 st ILC Workshop at KEK, WG3, J. Urakawa, F. Zimmerman, S. Guiducci and so on ILC-Europe workshop and ILC-BDIR, SLAC ILC DR Homepage, A. Wolski, Y. Cai, M. Pivi and so on