Speakers
Description
Velocity-space tomography provides a way of diagnosing fast ions in a fusion plasma by combining measurement from multiple instruments. We use a tangentially viewing and a perpendicularly viewing fast-ion D-alpha (FIDA) diagnostic installed on the spherical tokamak MAST (before the upgrade) to do velocity space tomography of the fast-ion distribution function. To make up for the scarce amount of data, prior information is included in the inversions. We impose a non-negativity constraint, exclude the velocity space associated with null-measurements, and we encode the belief that the distribution function does not extend to higher energies than neoclassically expected. This allows us to study the fast-ion velocity distributions and the derived fast-ion densities before and after a sawtooth crash.
