Investigation of the surface temperature in contact with plasma by two-color pyrometry

A high-speed two-color pyrometer has been developed that allows measuring the intensity of thermal radiation in temperature range of 100–3500$^\circ$C with 2 $\mu$s time resolution. The analysis of main factors affecting the measurement of surface temperature in the conditions of its interaction with plasma is carried out. It is shown that at plasma temperature of more than 10 eV and moderate particles density, the wall plasma can be considered transparent to thermal radiation. Experimental studies on non-contact measurement of temperature of surface interacting with plasma on Globus-M2 tokamak and plasma gun test bench have been carried out. Sawtooth temperature oscillations were detected on the wall of tokamak chamber near the exit of outer separatrix branch. The period of these flashes was 3–4 ms, and duration was 2 ms. The maximum wall temperature measured by a high-speed pyrometer exceeded temperature measured by infrared camera. Front surface temperature measurements of W-Li sample were carried out at plasma gun test bench under conditions of deuterium plasma jet cyclic action under loads simulating regimes of plasma current disruption in tokamak. The sample temperature reached more than 3000$^\circ$C during $\sim$1 ms. The thermal conductivity of the sample degraded with an increase in number of plasma exposure cycles, which was expressed in progressive decrease in target cooling rate after the pulse. Using a high-speed pyrometer, it is proposed to control the formation of heat-insulating foils on surface interacting with plasma.