Longitudinal and Transverse Measurement to Evaluate the Beam Impedance on a Ceramic Ring-Loaded Thin-Wall Vacuum Chamber in BRing at HIAF

Due to high ramping rates on the Booster Ring (BRing), which is the key part of the high-intensity heavy-ion accelerator facility (HIAF) complex at the Institute of Modern Physics (IMP), thin-wall vacuum chambers are required for all magnets to maintain the eddy currents at a tolerable level. A novel thin-wall vacuum chamber supported by ceramic rings was discussed and evaluated for the HIAF at the IMP to reduce the manufacturing cost, reduce the difficulty, shorten the production cycle, and improve the quality. Because the beam coupling impedance aspects are highly important for beam stability, several approaches were used to evaluate the impedance on the ceramics-loaded tube. In this article, we describe the results from the single- and two-wire bench measurements and the numerical simulations. The simulated and measured impedance results are consistent with each other. Several effective methods to mitigate the impedance were proposed and investigated in detail. According to the simulation and measurement results of the beam coupling impedance mitigation, this novel ceramic-ring copper-coated thin-wall vacuum chamber structure will be considered for application to the HIAF project with the highest priority.