Simultaneous two-dimensional measurement of plasma density and electron temperature evolution via multi-color gas puff imaging on the HL-3 tokamak.

Abstract

A Multi-Color Gas Puff Imaging (MC-GPI) diagnostic system has been implemented on the HL-3 tokamak, employing a helium line intensity ratio methodology for simultaneous two-dimensional (2D) measurements of plasma density and electron temperature. The system utilizes four distinct helium emission lines at 587.6, 667.8, 706.6, and 728.1 nm, with an optimized high-transmissivity short-wave-pass dichroic mirror array designed to address the weaker intensity of the 728.1 nm spectral line. Compared to conventional MC-GPI configurations, the redesigned optical path demonstrates a 15.3% enhancement in 728.1 nm line intensity under identical plasma conditions and other optical components. The diagnostic achieves temporal synchronization through simultaneous image acquisition using a single high-speed camera, ensuring precise time alignment across all spectral channels. Absolute calibration was performed through cross-validation with Langmuir probe measurements in linear plasma configurations. Its spatiotemporal resolution is 0.36 mm and 44 μs. This optimized system not only demonstrates superior measurement capabilities for edge plasma characterization in large tokamaks but also shows significant potential for diagnostic applications in various helium plasma environments.