Thursday 17 Sep 2015: Zonal flows, collisions, and energy confinement in fusion plasmas (GAFD seminar)
Greg Colyer - University of Oxford
Harrison 209 14:30-16:00
Nuclear fusion offers the future possibility of a long-term, carbon-free source of energy. One of the challenges remaining to be overcome in the pursuit of this goal is the understanding and control of plasma microturbulence (on the Larmor radius scale), which is beginning to be resolved both experimentally and computationally.
In the MAST experiment at Culham, in Oxfordshire, radial energy transport degrading the confinement of the plasma can be dominated by electron microturbulence, driven for example by the electron temperature gradient (ETG). We have been using the framework of gyrokinetics to study the dependence of ETG-driven energy transport on electron collisionality. We find that they decrease together; this favourable scaling is important because it points towards improved confinement in future, hotter devices. The scaling is in agreement with that found experimentally, but in simulations is only apparent after long times, because of the slow growth of zonal flows that eventually regulate the turbulence and are weakly damped by collisions.