Plasma heat load in the toroidal gaps of the ITER-like plasma facing units in WEST tokamak

Abstract

The heat load deposited in the toroidal gaps between two tungsten monoblocks remains an open problem to prepare safe and powerful experiments in ITER. An experiment has been carried out on the WEST tokamak aiming to study the power deposition on the toroidal surfaces with various monoblock and heat loading configurations. The very high spatial resolution (0.1 mm/px) infrared camera of WEST has been used to monitor the temperature distribution on the blocks. Few actively cooled ITER-like plasma facing units have been misaligned in the vertical and poloidal direction to maximize the heat loading and temperature on specific block areas. This paper shows the experimental results obtained during high power plasma experiment (4.5 MW injected power) performed with the outer strike line located precisely in the toroidal gap. The experimental IR images exhibit complex pattern with strong signal into the gap (greater than measured on the top surface) and shifted hot spot on the poloidal chamfer of the downstream component featuring poloidal misalignment (where optical hot spot are expected). Thermal and photonic modelling have been used to mimic the infrared thermal scene an try to provide a better understanding of the heat loading on the toroidal edge and on the optical hot spots. The importance of specular reflection is highlighted in the two cases because the reflective facets of the block facing each other.