Forward Modeling for Bolometry and Disruption Mitigation in Tokamaks or How to Kill Your Plasma With Confidence, Style, and Pizzazz

Abstract

The tokamak is a promising approach to magnetic confinement fusion. Tokamak functionality is threatened by plasma disruption events, which can damage critical machine components. Disruption damage can be mitigated by high-Z impurities, delivered by Massive Gas Injection (MGI) or Shattered Pellet Injection (SPI). Impurities radiate energy out of the plasma and onto the first wall. Evenly distributed radiation causes less damage than unmitigated disruption pathways, which deliver concentrated heat loads. In order to successfully develop and deploy mitigation systems, it is important to accurately measure and characterize disruption radiation. Accurate measurement is challenged by fast disruption timescales and highly asymmetric radiation patterns, which push the time and spatial resolution limits of radiant heat sensors. Previous radiation analysis approaches are typically limited to two dimensions or less by the highly under-determined nature of tomographic reconstruction and limited spatial resolution of sensors. Two dimensional analysis is often inaccurate for disruption radiation, which can be highly three dimensional as a result of localized impurity sources and fast 3D MHD events. In this thesis, I present a new algorithm for 3D radiation analysis in tokamak disruptions, called Emis3D. When Emis3D is applied to mitigated disruptions on the JET tokamak, a significant injection plume radiation effect in mitigated disruptions is revealed. When this effect is included in radiated energy calculations, the mitigated radiation fraction of plasmas with high thermal energy content is significantly improved, indicating that thermal mitigation is more effective than previously thought. Emis3D can also be used as a design tool to evaluate potential radiant heat sensor layouts. When applied to the SPARC tokamak, Emis3D demonstrates that toroidally skewed sensor sightlines improve spatial resolution and reduce blind spots, allowing more accurate measurement.