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The structure of collisionless scrape-off-layer (SOL) plasma in tokamak reactors is being studied to define the electron distribution function and the corresponding sheath potential between the divertor plate and the edge plasma. One feature of the collisionless SOL plasma is that the edge plasma acts as an electrostatic trap for electrons because electrons that originally have parallel energy lower than the wall potential will be trapped between the inner and outer divertor plates. Trapped electrons are very important in collisionless SOL plasma and are mainly responsible for charge neutralization of ions. Therefore, a full solution of the kinetic equation of particle transport to determine various electron fluxes is required. In this study, the dynamics of the SOL plasma during disruption was investigated with a 2-D numerical model that solves the kinetic Fokker–Planck equation for electron distribution. The main component of the electric potential exists within a region where the SOL ions are absorbed, i.e., at the front of the expanding vapor cloud. |
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