Transport of Carbon Dust Particles in Tokamaks

Abstract

Summary form only given. Dust in fusion devices has been identified as having a potentially large impact on tokamak performance and operation safety. In this work transport of carbon dust particles in fusion devices is studied using the DUST transport (DUSTT) code. The code simulates 3D trajectories of dust particles in realistic geometry and plasma conditions of tokamaks taking into account dust heating, charging, acceleration and ablation in the plasma as well as dust-wall collisions. Recent developments of the DUSTT code are reported, which include: i) thermionic and secondary electron emission, ii) dust size correction for thermal radiation, iii) presence of impurities in the plasma. The effects of these processes on dust dynamics are discussed. In particular, it is shown that thermionic electron emission provides a feed back mechanism for enhanced dust heating in the plasma, and that dust can grow due to deposition of impurities in relatively cold contaminated plasma regions of tokamaks. A zone picture of tokamak plasmas is introduced to describe dust survivability conditions. Results of dust particle dynamics simulations for current tokamaks (NSTX, DIII-D, and Alcator C-Mod) are presented. The simulations demonstrate that dust particles are very mobile and can be accelerated by plasma flows to large velocities (a few 100 m/s). An important role of dust inertia and dust-wall collisions in the dust transport is shown. Spatial profiles of dust particle density, average radius, and other dust parameters in the tokamaks are obtained using statistical averaging over a large number of dust trajectories. It is predicted that dust particles can significantly enhance penetration of carbon impurities toward the plasma core.