Development of a two-dimensional hard X-Ray imaging system on the HL-3 Tokamak

Abstract Fast electrons are generated during radio frequency (RF) wave heating and current drive processes in tokamak plasmas. RF waves transfer energy to bulk electrons through resonant absorption to accelerate them into fast electrons that propagate along the toroidal field, and the propagation and power deposition characteristics of RF waves directly determine the spatial distribution and energy spectrum of fast electrons. Thus, diagnosing these fast electrons enables the acquisition of the propagation trajectory and power deposition location of RF waves. Meanwhile, plasma instabilities such as sawtooth activities and electron fishbone modes are associated with the behavior of fast electrons. For this purpose, a two-dimensional (2D) hard X-ray (HXR) imaging system has been developed on the HL-3 tokamak. This system measures X-rays produced by the bremsstrahlung of fast electrons to obtain the plasma radiation profile, thereby capturing the behavior of fast electrons and supporting research on RF wave heating and plasma instabilities. The system consists of an observation window, a shielding and collimating body, a detector, an electronic system, and a support structure. Among them, the 64-channel area array detector is formed by coupling Lutetium Yttrium Oxyorthosilicate (LYSO) with Silicon Photomultiplier (SiPM), and the electronic system adopts the front-end readout system DT5202 manufactured by CAEN. The system has a temporal resolution of up to 1 ms. Laboratory tests of the detector were conducted using radioactive sources, with an energy resolution of approximately 22 keV@122 keV, yielding stable energy spectra and enabling the acquisition of the 2D radiation intensity distribution of the sources. In the future, this 2D HXR imaging system will be used to carry out physical experiments related to high-energy electrons on the HL-3 tokamak, providing data support for improving the efficiency of RF wave current drive and enhancing plasma confinement.