Suppression of the coherent synchrotron radiation induced emittance growth in a double-bend achromat with bunch compression

Abstract

Multibend magnetic bunch compressors are commonly used to produce beams with high peak current in modern accelerators that call for high-brightness beams. If not well controlled, the coherent synchrotron radiation (CSR) in the dipoles of magnetic bunch compressors can severely affect the produced beam qualities, e.g., leading to emittance dilution. In contrast to the case without bunch compression, suppression of the CSR-induced emittance growth with bunch compression can be more challenging mainly due to the difficulties of analyzing the net CSR effect that involves a varying bunch length. In this paper, with the aid of the CSR point-kick model, theoretical CSR cancelation conditions of a double-bend achromat (DBA) with bunch compression are obtained. Such conditions point to an asymmetric DBA design, having dipoles of different bending angles or different radii or both and satisfying a certain transfer matrix relation. Taking a DBA with dipoles of different bending angles as an example, it is demonstrated that the CSR-induced emittance growth can be significantly suppressed if the proposed conditions are satisfied. As a numerical demonstration of application, we implement multiple DBA cells basically satisfying the proposed conditions in a 180° arc compressor, showing promising performance in suppressing the CSR-induced emittance growth. This study suggests a new appealing way to design practical arc compressors and is promising to serve as a starting point for the design and optimization of CSR-immune arc transfer lines in energy recovery linacs and other modern recirculation accelerators.