Simulation Studies of the Beam Monitor for the CSR External-Target Experiment

A beam monitor system is being developed for the cool storage ring (CSR) external-target experiment (CEE) at the Heavy Ion Research Facility in Lanzhou (HIRFL). The beam monitor is required to measure the lateral position of each beam particle with spatial resolution less than 50 mu m andwith beam rates up to 1 MHz. As the beam intensity increases, the build-up of slow-moving positive ions created from the ionization of the detector gas by the beam leads to a significant distortion of the nominal electric field in the drift region. In this work, simulation studies of the beam monitor are performed, in particular the space charge effect and the correction strategy. It shows that the space charge at the nominal drift electric field of 700 V/cm modifies the electric field in the sensitive volume by roughly 5% in both the drift and transverse directions. The distortion on the measured position is up to 0.35 mm in the 5s region of the beam profile. The expected spatial resolution of 500 MeV/u U ion is 34.5 mu m considering the pixel noise of 400 e(-) and the 100 mu m x 1 mm pixel size of the charge sensor chip in the selected gas mixture.