During plasma disruptions in tokamaks, the fast current quench generates substantial electromagnetic forces on the vacuum vessel and can also produce a significant current of runaway electrons (REs). The REs are accelerated in the high electric field associated with the current quench and resemble an electron beam with velocities close to that of light. Model predictions indicate that in ITER a runaway electron current of up 70% of the initial plasma current could be generated due to a "secondary avalanche" process. REs are eventually lost to the first wall and this can result in significant local energy deposition, which can potentially cause damage such as localized melting of the first wall surface. Assessment of the severity of such events requires an accurate quantitative specification of the characteristics of the energy deposition of REs, e.g., probable locations of deposition, time duration of loss process and incident angle of electrons, is of primary importance.
Figure shows the penetration of gas injected from top left corner in TEXTOR (Julich, Germany). The plasma is cooled (seen by bright light due to radiation from the injected impurity gas) up to the surface with safety factor q=2 before the collapse occurs