Simulations of plasma filament dynamics in toroidal geometry

Abstract

Interchange driven propagation of so-called "blobs" arises in basic laboratory plasmas, in the scrape-off layer of fusion plasmas and as Equatorial Spread-F (ESF) phenomena. The propagation of such blobs has been demonstrated in the VTF experiment at MIT and in earlier simulations. Experimental results show that the velocity of these blobs is inverse proportional to the neutral gas pressure. These blobs have also shown the tendency to form mushroom-like shapes.

We here develop a two-field model for the interchange mechanism in magnetised plasma in toroidal chambers. This model is then used to simulate the dynamics of propagating blobs using a two dimensional advection-diffusion solver. Studying the effects of ion-neutral collisions and blob amplitudes, we observe the separation between an inertia dominated and one collisionally dominated regime. We also observe that this separation persists for all simulated amplitudes.

We further perform simulations with parameters set to closely resemble the VTF experiments. These simulations show that the experimental result of the velocity being inversely proportional to the neutral gas pressure is in a qualitative match with the simulated results for the collisionally dominant regime.