Speaker
Description
Understanding the evolution of transverse beam profiles is critical for stable high power operation of intense proton synchrotrons. A residual-gas ionization profile monitor (IPM) has been developed and commissioned in the 1.6 GeV Rapid Cycling Synchrotron (RCS) of the China Spallation Neutron Source (CSNS) to enable non-invasive, bunch-by-bunch horizontal beam profile measurements. Beam induced electromagnetic interference, insufficient microchannel plate (MCP) gain, and elevated vacuum pressure were successfully mitigated through RF shielding with an enhanced Faraday cage, the addition of a pull-down resistor in the MCP bias circuit, and additional vacuum pumping. The IPM employs a 25 kV field cage (~110 kV/m), a two-stage MCP with 32 anode strips (2.5 mm pitch), and operates in both ion and electron collection modes. Individual bunch profiles are reconstructed using a peak finding algorithm combined with RF-synchronized windowing. Residual gas species were identified as primarily $\mathrm{H_2}$, $\mathrm{H_2O}$, and $\mathrm{N_2}$, while electron-mode measurements confirmed a temporal resolution approaching 80 ns. Bunch by bunch profiles recorded during multi turn injection painting clearly capture the evolution of beam position and rms horizontal size. However, MCP saturation currently restricts operation of IPM at higher beam power. To overcome this limitation and enable full cycle beam profile measurement at CSNS 500 kW power upgrade, a gated IPM is under development. By controlling charge collection of secondary particles, the gated IPM will mitigate the MCP saturation and extend the lifetime.