Improved Design And Construction Of The Ionization Chamber For Beam Loss Monitor System And Trial-Manufacture

China Spallation Neutron Source (CSNS) is composed of a 80MeV H Linac, a 1.6GeV fast cycle proton synchrotron, two beam transportation lines, a target station, five spectrometers and corresponding necessary service facilities. The power of the proton beam is designed as 100kW and the pulse frequency of the beam as 25Hz.154 ionization chambers(IC) are placed in different parts of the CSNS. During commissioning and the long-term running of the CSNS, number of the lost particles from beam and their position will be measured by the IC. The protection system of CSNS will be triggered once large dose of beam loss is found.Ionization chamber is one of the most important sub-detectors of the beam loss monitor (BLM) system. To meet the requirement on monitoring beam loss in the CSNS, the ionization chamber must have fast response time and good detecting sensitivity. To achieve this goal, a relative high working voltage is needed and a proper working gas should be chosen for the chamber. The IC prototype is needed to be improved.The performances of improved ionization chamber were tested and small mass production of 10 ICs was made. The good plateau(>2000V) and the measurement range up to 3.6×105 rad·h-1 are obtained in the improved ionization chamber. The highest detection sensitivity is 21.3 pA·rad-1·h, it can still work stably when the High-voltage added to 3500V. The test results show that the performance of the modified ionization chamber already reach the requirement of the BLM system for the CSNS.