: The Impact of transient Mitigation on the MAST edge plasma

The impact of transient mitigation schemes on the MAST edge plasma Andrew Thornton Thesis submitted for the award of Doctor of Philosophy University of York Department of Physics January 2011 Supervised by; Dr. K.J. Gibson Department of Physics, University of York, Heslington, York, YO10 5DD Dr. A. Kirk Culham Centre for Fusion Energy (CCFE), Culham Science Centre, Abingdon, Oxon, OX14 3DB Abstract Adisruptionisthesuddenanduncontrolledlossofplasmaconfinementinatokamak. Disruptions on the Mega Amp Spherical Tokamak (MAST) are characterised in terms of thermal quench timescales, energy balance and pre disruption energy loss. Analysis of the energy balance during disruptions on MAST has shown that approximately 10% of the stored energy is radiated during a disruption and 80% is deposited onto the divertor. The energy loss prior to the thermal quench is found to be 50% of the maximum energy in the plasma, which is half the value assumed for the ITER design. Disruptions occur when operational boundaries, in terms of current, pressure and density, are exceeded. An analysis of the operational boundaries in MAST shows that the frequency of disruptive events increases as the density is raised to 1.5 times the Greenwald density limit and that the pressure limit is consistent with empiricalscalings. ThecurrentlimitonMASTistriggeredbeforetheexpectedvalue ofq is reached.