An Audit of Occurrence of Dust in Tokamak and Stability of Fusion Plasma

Abstract

Proliferation of dusty layers inside the Tokamak prompts deleterious effect in Tokamak operation. The stability of the fusion plasma is adversely affected by building-up of dusty layers inside the tokamak which actuate disruptions in tokamak's performance. The current study is based on probing the mechanisms of dust accumulation inside the Tokamak device by simulating the process with the support of pulsed plasma accelerator. Experimentally it was observed that upon interacting with the pulsed power plasma stream, the materials used for designing the in-vessel elements of Tokamak such as graphite, lost its crystalline structure which in turn affects its inherent properties like ductility, malleability, rust resistance etc., thus emanation of dust paricles take place as a result of collisions between plasma species such as electrons, ions and neutrals with molecules of graphite as the tokamak material, ergo causing erosion in the tokamak material. The concatenated dusty layers formed due to accumulation of dust particles inside the Tokamak can cause probable instability in fusion plasma that would mar the function of the Tokamak device, besides the generated dust would become chemically reactive, radioactive or toxic. The dynamics of dust grains can be realised by Coulomb force, ion drag force, frictional forces on ions, ion pre-sheath drifts etc. and can also be interpreted from the kinetic theory of dusty plasma, to account this the numerical studies have been carried out with DUSTT and UEDGE codes to understand the dust dynamics and transport mechanisms.