Observations on arcing on the metal plasma-facing components in EAST. (March 2023) - Wang, Baoguo
Highlights: Some arcs on the first mirrors can form patterned traces which affect more than 25% of grey values of the visible images. The arcs on the LHCD antenna surface can produce large numbers of impurity particles, which result in disruption. Abstract: Arcing on the plasma-facing components (PFCs) is one of the mechanisms of material erosion and impurity production in the magnetic-confinement fusion devices. EAST tokamak has been upgraded to almost full metal PFCs. The arcing phenomena in EAST has special features due to the lithium coating and the RF heating. Post-mortem analysis of arc traces is performed on both plasma-wetted components and PFCs in sub-limiter remote areas. The arcs in sub-limiter remote areas nearly have no influence on the normal discharges as most of them were produced during the glow discharge cleaning. But some arcs on the first mirrors of infrared and visible tangential wide-angle viewing systems in EAST can form patterned traces in the videos, which affects the precision of temperature measurements and visible imaging quality. The arcs on plasma-wetted components were mainly observed at two locations: the tungsten upper divertor and the lower hybrid current drive (LHCD) antennas. The random-walk arc traces on the surface of the upper tungsten divertor are limited to a very small area and most probably formed without magnetic field during glow discharge, unable to influence plasma discharges so far, and still need long-term tracking. The arcs on the LHCD antenna surface can be sustained for more than hundreds of milliseconds, and produce large numbers of impurity particles and molten droplets, which can result in plasma current quench and disruption, and the effects of arcing on LHCD heating mode and power should be further studied.