Design of the fast-imaging FIDA diagnostic system in the HL-2A tokamak

The study of the fast ion distribution and its transport behavior is important for magnetically confined fusion plasma physics. In this paper, a fast-imaging fast ion deuterium alpha emission diagnostic (FI-FIDA) system on the tangential window of the HL-2A device is designed with the aid of the open-source code FIDASIM. Since active FIDA (aFIDA) radiation viewed by tangential sightlines is heavily influenced by spectral lines such as neutral beam emission spectra (BES), direct charge exchange spectra (DCX) and halo spectra (Halo), and the passive FIDA (pFIDA) emission can reach detectable levels comparable to aFIDA radiation in the edge region, this FI-FIDA system design is based on the edge pFIDA radiation. The simulation results show that under the typical HL-2A discharge conditions, the FI-FIDA system can be used to achieve a time resolution of the order of (10–100) <i>μ</i>s and a spectral resolution of 1 nm with channle-channel view chords spacing of 0.5^○±0.1^○ which is about 2 cm radial separation in the plasma volume at the same time. Taking advantage of the existing BES diagnostic system in HL-2A experiments, the pFIDA signal was observed, verifying the feasibility of the design.