First evidence of optical hot spots on ITER-like plasma facing units in the WEST tokamak

摘要

The lower divertor of the WEST tokamak has been partially equipped with actively cooled plasma facing unit (PFU) prototypes with the aim of testing ITER tungsten monoblock technology in a real tokamak environment. The relative alignment of these ITER-like PFUs and their exposure to the heat flux is of particular interest as the risk of monoblock edge melting was previously predicted in numerical studies. After the 2018 experimental campaign, the monoblock surface evolution was investigated by optical microscopy. The monoblock surfaces exhibit the presence of optical hot spots at the magnetic projection of the toroidal gaps of the upstream monoblocks, confirming for the first time in a tokamak environment the recent modelling predictions. Surface cracking over the full height of the optical hot spots and some localized melting is observed.