Cooling effect of secondary electrons in high temperature divertor operation

The scrape-off layer (SOL) plasma is studied over a wide range of Coulomb collisionality via particle Monte Carlo simulation with focus on the cooling effect of secondary electrons in the high temperature divertor operation. The electron distribution function in the collisionless regime shows a large departure from a Maxwellian distribution. In the presence of strong secondary electron emission the electron sheath energy transmission factor in the collisionless regime is found to be significantly smaller than that in the collisional regime, which indicates that a higher temperature is obtainable in collisionless SOL plasmas. In both collisional and collisionless SOL plasmas, the change in the conductive energy flux from the core region into the SOL has little influence on the normalized potential drop and electron energy transmission factor, while the electron temperature is raised as the conductive energy flux increases