Research On The High Performance Multi-channel Photoelectric Detection System On The J-TEXT Tokamak

The physical parameters of high-temperature plasma cannot be measured directly,so we must use some indirect methods to obtain. Many important parameters and operating status of the plasma can be inferred by measuring a variety of spectral signals during discharge. The optical signals can be converted into weak current signals by photoelectric detectors, which are mostly in the form of array-type. In order to be acquired and analyzed easily, the output signals of detectors should be amplified by suitable circuits. Because of the complex electromagnetic environment during Tokamak discharge, the EMC of entire system should be given full consideration.Taking the AXUV thermal radiation diagnostic system for example, we made a detailed discussion of the multi-channel photoelectric detection system design process.Based on the full investigation of the three photoelectric detectors working principle, we have done a comparative analysis of many amplifying circuits. Then we chose the suitable trans-impedance amplifier(TIA) circuit and made a detailed analysis of the circuit on its stability, bandwidth and noise. Finally, we proposed an optimized circuit using frequency compensation technique to enhance the system bandwidth. The EMC solutions have been improved by using rational distribution circuit boards and appropriate grounding and shielding. Through experimental tests, the photoelectric detection system can achieve the high performance of 500 kHz bandwidth and 660 uV noise voltage RMS value with stably working. The engineering prototype has been successfully applied in the J-TEXT radiation diagnostic system, and the AXUV signals have been observed during Tokamak discharge.On the basis of AXUV detection system, we have analyzed on the characteristics of other photoelectric detection systems on J-TEXT and presented some design ideas and reference solutions for those systems.