The Very High spatial Resolution (VHR) infrared thermography diagnostic developed by CEA-IRFM is installed in the WEST tokamak to measure surface temperature of the actively cooled W-monoblocks components as foreseen for the International Thermonuclear Experimental Reactor (ITER) Divertor. Purposes of such apparatus are to study the evolution of components introduced in the tokamak, the influence of the shaping of these components submitted to high heat load deposition, the behavior of the leading edges regarding the assembling tolerances between adjacent monoblocks and finally contribute to the specification assessment of the ITER divertor units. It is a major diagnostic to investigate the behavior of Plasma Facing Units (PFU) during experimentation thanks to its very high spatial resolution (0.1 mm / pixel), movable field of view (FoV) and wide-range temperature measurement. This diagnostic was operational during the 2019 WEST experimentation and its design has been enhanced for the 2020 WEST experimentation campaign.
In order to monitor 28x12mm monoblocks temperature, the VHR IR diagnostic is able to move its narrow FoV (64x51mm) to specific targets on the observable divertor (360×420mm). Position and focus steering is achieved through motor-controlled mirrors and lens operated by a dedicated Labview application on a remote unit. The distance separating the first mirror with the target area induces large ratio distance over angle that must be taken into account to avoid detrimental misplacements. Positioning mirror maneuver between pulses under a 10-6Pa vacuum, a 1T magnetic field, at 70°C, and can withstand thermal radiation and disruptions during pulses. Motors are outside of the VV, operate mirrors through stainless steel cables and pulleys inside the VV, inducing a hysteresis that has to be dealt with. Repeatability, hysteresis, mechanical components reliability are critical parameters to provide accurate positioning (<1mm).The tuning and calibration of these actuators in accordance with WEST environment is crucial to guarantee the best position and optical performances. It is calibrated on a test bench at CEA-IRFM and inside WEST tokamak to insure valid positioning throughout experimentations.
This paper gives the implementation details and FoV positioning performance comparison between the two mechanical designs and software implementations for the 2019 and 2020 campaign.