Collective effects near transition energy in the proton mode of HIAF/BRing

Abstract

The High Intensity heavy-ion Accelerator Facility (HIAF) is under construction. The lattice of HIAF/BRing is the same for both heavy ion beams and proton beam. Since the proton beam will cross the transition energy during acceleration, a γt jump scheme with maximum Δ γt of 2 is designed to reduce the growth of momentum spread and influence of collective effects near transition. The broadband impedance of the ceramic-lined rings in the vacuum chamber has been significantly reduced by a 2 μm-copper coating. Thus, the impedance model has been updated for analyzing collective effects in the BRing. The longitudinal collective effects can be compensated by the multi-harmonic feedforward system. The transition energy crossing point should be optimized to reduce the bunch oscillations after transitions. In both two transverse planes, the normalized emittance growth given by the Simulation Platform for Collective Instabilities (CISP) are stopped by the broadband impedance near transition and there is no obvious transverse collective instability, which is quite different from the Vlasov results. More researches will be performed to find out the reason.