Development of the gas puffing imaging diagnostic on J-TEXT tokamak

Edge turbulence is important for plasma confinement, so the gas puffing imaging (GPI) diagnostic was proposed on the J-TEXT tokamak for the two-dimensional measurement of turbulence in the edge region. GPI is a diagnostic of plasma turbulence that uses a puff of neutral gas at the plasma edge to increase the local visible light emission for improved space–time resolution of plasma fluctuations. Considering the conditions of J-TEXT, the observation area is 21° away from the position of the optical system in the toroidal direction, and the observation area is 10 cm × 10 cm inside and outside the last closed flux surface. To have a lower divergence of the gas flow, the gas puff nozzle is specially designed. An interface has been developed for operation. To photograph the line radiation generated by the neutral gas cloud along the magnetic field lines, the optical system is designed. It is composed of a quartz glass, mirrors, commercial lenses, filters, and high-speed cameras. The high-speed camera can capture the line radiation with a speed up to 180 000 frames/s with 256 pixels × 256 pixels and an exposure time of 5 µs. In a recent experiment, the new GPI diagnostic has obtained some preliminary pictures.