Design of APD Detector Circuit for Thomson Scattering System on J-TEXT Tokamak

Thomson scattering (TS) diagnostic is one of the most powerful methods to measure electron temperature and density. A signal measurement circuit has been designed and tested in the laboratory for readout of avalanche photodiode (APD) detector on J-TEXT TS diagnostic. In this circuit, an APD with required signal-amplifying module is used for detecting the scattered photons. A novel temperature control circuit based on thermoelectric cooler is developed for maintaining APD at a constant temperature with short response time (~600 ms), and it enhances the signal to noise ratio of the detection circuit up to 18. These features are expected to improve the accuracy of TS light measurement. The detailed design processes and test results of the APD detector circuit are presented.