Fast infrared thermography on the COMPASS tokamak

Abstract

A new fast infrared camera was purchased on the COMPASS tokamak recently. It is equipped with a medium wavelength infrared (3–5mm) InSb detector and is capable of reaching framerate up to 1.9kHz in full frame acquisition mode (320×256px.) and up to 90kHz in sub-windowed mode (64×4px.).First experimental measurements of plasma heat flux to inner and outer wall limiters of the COMPASS tokamak using the new camera are presented. Time evolution of parallel heat flux during sawtooth instability is studied showing strong modulation of the heat flux absolute value whilst keeping constant its radial decay length. Fast modulation of outboard midplane limiter heat loading due to runaway electrons is also presented.The camera will be part of a new fast divertor thermographic system with exceptional spatial resolution (∼0.6–1.3mm/px. on the target plane, 0.04–0.14mm/px. mapped to the outer midplane) with a possibility of measurements of radial profiles on the divertor with 320×4px. with temporal resolution better than 20μs. A design of the foreseen optical divertor system is described together with a design of a special divertor graphite tile used for the IR thermography, that will allow in-situ surface emissivity calibration.