Tungsten blow-off in response to the ignition of arcing: Revival of arcing issue in future fusion devices

Behaviors of an arc spot ignited on a tungsten electrode in response to a transient heat load are investigated in the linear divertor simulator NAGDIS-II using a pulsed laser as a transient heat source. Tungsten neutral emission from the arc spot is observed with an image intensified fast framing camera. When arcing is initiated, the tungsten emission continues much longer than the laser pulse width of ∼0.6 ms. The ignition of arcing becomes much easier compared to clean surface when the tungsten surface is exposed to the helium plasma and morphology is slightly changed.