PARTICLE SIMULATIONS OF COLLISIONAL TRANSPORT IN A HIGH RECYCLING, DIVERTED TOKAMAK SCRAPE-OFF LAYER

The transport of particles and energy through a high recycling divertor scrape-off layer (SOL) in a tokamak is studied via a kinetic transport model. This model combines particle-in-cell (PIC) methods with Monte Carlo algorithms which simulate Coulomb collisions and charged/neutral interactions (charge exchange and electron impact ionization). The resulting transport code provides a fully kinetic description of transport and potential formation in a single spatial dimension (along the open field lines of the SOL) and two velocity components (parallel and perpendicular to those field lines). Plasma transport in the SOL system is modelled as a function of neutral particle recycling. The level of neutral recycling is varied by changing the average ionization frequency 〈νion〉 relative to the average Coulomb collision frequency 〈νc〉 over the range 0 ≤ ν′ ≤ 0.25, with ν′ ≡ 〈νion〉/〈νc〉. This study indicates that the plasma flow velocity, temperature and total kinetic energy flux decrease as the level of neutral particle recycling is increased. The variation of other transport quantities with neutral recycling intensity is presented, and the results are compared with those from other SOL transport models. © 1990 IOP Publishing Ltd.