Research And Development Of High-gain Amplifier For Soft X-ray Diagnostic System

Soft X-ray diagnostic system is one of the most basic means of diagnosis in the diagnostic systems of tokamak. It uses the plasma distribution of soft X-ray radiation measured to study the macroscopic MHD instabilities. Amplifier is a core part of the soft X-ray diagnostic system, and its role is transforming microampere level current signal into voltage signal. According to the physical requirements of the experiment it is not less than 15 kHz bandwidth. Several sets of large current sources running on tokamak simultaneously. These devices will generate strong electromagnetic radiation interference. This will seriously degrade the signal to noise ratio of the amplifier output signal. Hence we need to design a weak photocurrent signal amplifier for soft X-ray diagnostic system.In this paper, the basic noise model was established for amplifier circuit. Paper analyzed source of noise,noise gain and the effect of noise on the signal. Paper proposed a new amplifier circuit program which optimize the noise gain peak. Amplifier used a low dropout linear voltage regulator module to reduce the power supply ripple interference on op amp circuit. Article created a grounding model for shielding. It analyzed the importance of grounding for improving the system?s noise performance. The test result confirmed that the reasonable ground will suppress low-frequency noise of the system to a certain extent. Paper completed weak photocurrent signal amplifier?s design, simulation and Manufacture. Amplifier?s gain is 106V/A and its bandwidth is 22 KHz. Amplifier has a good noise characteristics in the complex electromagnetic environment. The designed amplifier run stable at discharge experiments on J-TEXT tokamak. Soft X-ray diagnostic system obtained multi-channel soft X-ray radiation signal and it provided a wealth of experimental data for the study of the physical properties of plasma.