Design of the wall current monitor system at CSNS rapid cycling synchrotron

Wall current monitors (WCMs) were designed and built for the rapid cycling synchrotron (RCS) of China Spallation Neutron Source (CSNS).The WCMs are used to measure longitudinal bunch shapes in the macro and micro view, calculate longitudinal emittance, and diagnose beam instabilities.The key parameters (e.g., size of the ceramic gap, selection of the resistor and the magnetic materials) of designing a WCM are discussed in this article.The bandwidth of the RCS-WCM can be up to 500 MHz during the lab test, while 30 MHz is required for online operation.The WCM system performed quite well during the beam commissioning and the normal operation of the RCS, beam injection, macro envelope of the accelerating period, and the shape of a single bunch can be observed clearly and accurately.