Optics of a multiple color gas puff imaging diagnostic on the HL-2A tokamak

Abstract

The optics of a new Multiple Color Gas Puff Imaging (MC-GPI) diagnostic on the HL-2A tokamak is presented. MC-GPI utilizes the helium I (He I) line ratio technique to infer plasma density ne and electron temperature Te in edge plasma simultaneously. A compact four-channel beam splitter and dichroic mirrors enable the selection of the intensities of He I lines at specific wavelengths, i.e., λ=587.6 nm, λ=667.8 nm, λ=706.5 nm and λ=728.1 nm. The transmittance of these four specific He I lines after passing through the optical fiber bundle and the beam splitter is 34%, 33%, 33% and 30%, respectively. The temporal resolution of MC-GPI is 100μs and the spatial resolution is 2.5 mm × 2.5 mm. This diagnostic has been experimentally tested on an optical table as well as on a linear plasma device to verify its capability for ne and Te measurements. A newly designed light splitter with double-layer layout is under developing to absorb the stray light, aiming at improve the performance of the diagnostic.