Modelling of fast response surface thermocouples for fusion plasma facing components

Surface eroding thermocouples have been studied to measure temperatures and heat fluxes in the divertor of the DTT facility [1]. Thermal measurements are performed on plasma facing components of fusion machines especially on the divertor to provide local temperatures relevant to the material surface (sensors embedded in the component under the exposed surface [2]), bulk calorimetry (time variation of temperature observed at the same sensor [3]), or the power density deposited on castellated modules ( temperatures detected at the same time by sensors located at different distances from the heated surface [ 4, 5]). Signals of these temperature measurements will be used during pulse operation or first wall conditioning for parameters monitoring, component protection, and machine control. Surface eroding thermocouples ( or "self-renewing thermocouples") can be used to instrument plasma facing components in which the thermojunction is formed in a very thin layer at the surface of the sensor [6]. This construction leads to a fast thermal time response (10 ms), robust design against heat loads around 10 MW/m2, and is particularly useful to characterize the surface temperature evolution of the plasma facing component with the carrier body made of the same material as the component. Surface thermocouples also enable a simple computation of the power density applied to the component. Arrays of surface thermocouples proved to be a vital component of the overall diagnostic set and can be installed to measure pulsed heat fluxes in the divertor of tokamaks [ 6]. The study deals with modelling the signal response of surface eroding thermocouples, developing a sensor design, and integrating the concept in the castellations of the DTT device divertor [7].