A MONTE-CARLO MODEL FOR VELOCITY SPACE EFFECTS IN LOW RECYCLING SCRAPE-OFF LAYER PLASMAS

A Monte Carlo model solving only in velocity space is proposed to inve stigate a low recycling scrape-off layer (SOL) plasma. In the model, t he effects of Coulomb collisions are accurately described by a non-lin ear Monte Carlo collision operator; a conductive heat flux into the SO L is effectively modelled via randomly exchanging the source particles and the SOL particles; secondary electrons are included. A steady sta te SOL plasma, which satisfies the particle and energy balances and th e neutrality constraint, is determined in terms of the total particle and heat fluxes across the separatrix, the edge plasma temperature, th e secondary electron emission coefficient and the SOL size. The model gives gross features of the SOL, such as plasma temperatures and densi ties, the total sheath potential drop and the sheath energy transmissi on factor. Simulations neglecting unlike collisions are performed. It is found that the potential drop and the electron energy transmission factor in collisional SOL plasmas are in close agreement with theoreti cal predictions. The present model primarily provides useful informati on about collisionless SOL plasmas that is difficult to obtain analyti cally.