Impedance benchmarking of resistive wall and tapered transitions for the PF-HLS

The PF Hybrid Light Source (PF-HLS) has been proposed in the High Energy Accelerator Research Organization (KEK), capable of utilizing both high-quality beams from a superconducting linac and beams from a low-emittance storage ring. The coupling impedance will cause beam instability, which must be carefully handled. It is essential to benchmark impedance models using analytical methods and different simulation codes. This paper focuses on the impedance benchmarking of resistive wall and tapered transitions in PF-HLS. The regular round chamber (radius of 12 mm), insertion device (ID) chamber (half-height of 4 mm), and the corresponding tapered transitions are studied. Simulation codes, including ImpedanceWake2D (IW2D), CST, and Azimuthal Beam Cavity Interaction (ABCI), are used. For resistive wall calculations, some analytical formulae describing the round chamber impedance and the Yokoya form factors of the ID chamber are applied. For tapered transitions, some formulae calculating the impedance at low-frequency regions (inductive regime) are chosen to compare with results from CST. In high-frequency regions, the impedance result comparison between CST and ABCI is carried out.