School of Physics, Engineering and Technology
The magnetic fields of a tokamak provide a very high resistance to energy and particles crossing the field lines – such good confinement leads to the high densities and temperatures in the core plasma necessary for optimising the fusion reaction rate! However, we want opposite for the SOL – we want to encourage cross-field transport so as broaden the narrow heat flux channel for power being conducted to the divertor, thus lowering the high power density reaching the divertor target.
Our research on the SOL plasma region focuses on both characterising the cross-field transport and understanding the turbulence which is felt to drive that transport. The general belief is that cross-field transport of heat and particles is driven by turbulence which is in the form of filamentary objects extended along the magnetic field. Electric fields develop within each filament which, in interaction with the local magnetic field, propel the filament across the magnetic field, carrying ions in the filament and their energy.
The primary diagnostic we utilise for studying such filaments is to light up a filament with injected gas not typically present in such plasmas, and obtain camera images/movies of the filament characteristics including size and motion. That information, how the filament properties scale with changing SOL conditions, is used to compare to both analytic and computational models as well as seek correlations with changes in density profiles in the SOL and the heat channel width.