Readout Electronics for Fast Neutron Flux Measurement with High Time Resolution on HL-2M Tokamak

Neutron flux measurement provides essential data for the diagnostic tools that control plasma combustion, equipment maintenance, and radiation safety and reveals key information on plasma physics, machine protection, and control issues. To obtain rapid change of the neutron emission rate by magnetohydrodynamic instabilities, a fast neutron flux measurement system with high time resolution (~10 ) was developed on the HL-2M tokamak (located at Southwestern Institute of Physics, China). The system includes four EJ-410 detectors and four digitizers that we developed ourselves with dedicated field-programmable gate array firmware, including a waveform recording function, real-time count rate measurement, and real-time integration measurement. The simulation results show that the throughput rate of the readout electronics is 96.7% when the input counting rate is 1 mega count per second (Mcps) and the throughput rate could achieve 63.8% when the input counting rate is 6 Mcps. Moreover, when the input counting rate increases further to 10 Mcps, the integration model may be used. Given that this measurement system is highly portable and has a high time resolution, it is suitable for the fast neutron flux diagnostic on the HL-2A tokamak.