SuperB and the ILC Damping Rings Andy Wolski University of Liverpool/Cockcroft Institute 27 April, 2006

2 Comparison of parameters SuperB*ILC DR e - (e + )PEP-II LERPEP-II HER Circumference3 km6.7 km2.2 km Beam energy5 GeV 3.1 GeV9 GeV Bunch charge2× × × ×10 10 N o bunches Average current1.6 A0.4 A (0.2 A)2.4 A1.5 A Bunch length4 mm6 mm11 mm Energy spread0.11%0.13%0.07% Horiz. emittance0.4 nm0.5 nm35 nm60 nm Vert. emittance0.002 nm 1.4 nm Damping time10 ms27 ms70 ms37 ms * P. Raimondi, 1 March 2006

3 Beam Dynamics Concerns for ILC Damping Rings Electron cloud Keeping cloud density at a level low enough to be able to maintain beam stability will be a challenge. Present baseline configuration specifies two positron damping rings to keep beam current low. Fast ion instability Ions accumulate during passage of a bunch train in the electron damping rings. Frequent clearing gaps (of length ~ 40 ns) are needed to maintain stability. Microwave instability Larger rings have smaller momentum compaction. This leads to very demanding specifications for the vacuum chamber impedance. Intrabeam scattering Expected to increase horizontal emittance by up to a factor of 2 at the nominal bunch charge. IBS effects are reduced by having a short damping time. Low emittance tuning Lowest vertical emittance achieved anywhere is ~ 4 pm. Is 2 pm realistic? Acceptance Major issue for injection efficiency in damping rings; lifetime issue in storage mode.

4 Technology Concerns for ILC Damping Rings Vacuum system Needs to handle extremely high radiation power in local areas (wigglers); will be worse in SuperB because of higher beam currents. Overall, very low pressure (< 1 ntorr) is needed to mitigate ion effects. Design and manufacture critical for achieving sufficiently low impedance to avoid single-bunch instabilities. Wiggler Superconducting wiggler (couple of hundred metres per ring) based on CESR-c wigglers. Expensive. Radiation tolerance is a potential concern, but probably ok in terms of other technology issues (aperture, field quality…) RF system BIG. Presently, 50 MV needed per ring; may be reduced by tuning for smaller momentum compaction, at the cost of reducing some instability thresholds. Damping rings also use unconventional frequency (650 MHz) for reasons specific to ILC. Fast feedback systems Will be critical for suppressing coupled-bunch instabilities. Instrumentation and diagnostics A range of advanced instruments will be needed for achieving and maintaining the necessary beam quality.

5 Synergy… The present B factories work with very high beam currents, but because the beams are relatively large, they are less sensitive than damping rings to beam instabilities. Nonetheless, some issues (such as electron cloud) have been a real problem. Studies for ILC damping rings are relevant to a storage ring SuperB. Some results of simulation studies (e.g. electron cloud and ion effects) may be directly applicable, or easily extended to, SuperB. For other effects (e.g. IBS) the operating regimes are close enough that we can etimate their impact relatively easily, based on tools developed for ILC damping rings. Engineering and cost studies for the ILC RDR and TDR may also be relevant. Many systems (vacuum, magnets, RF, tunnel) will be costed in such a way as to allow an overall parametric cost estimate to be produced. This may be helpful to give some broad idea of the cost regime of a storage ring SuperB. It should also be helpful to identify priority areas for beam dynamics, technology or engineering studies for a SuperB.