Honors College Thesis


Using Divertor Strike Point Splitting to Understand Plasma Response and its Sensitivity Equilibrium Uncertainty Public Deposited

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  • Soon the largest fusion project in the world, ITER, will attempt to produce more fusion power than required to sustain the fusion reaction, this is known as ignition. The tokamak (a toroidal fusion device) being built in France will be running at such high temperatures that heat distribution is a problem. To prevent future calamity a tokamak run by General Atomics, DIII-D, is running experiments to modify the heat distribution in the divertor region; a narrow area on the floor of the tokamak. The resonant magnetic perturbations (RMPs) from 3D coils are varied to modify the splitting of the divertor strike points in DIII-D. This splitting is imaged in filtered visible and infrared emission to determine the particle and heat flux patterns on the target plates. The observed splitting is compared to vacuum modeling in discharges where a subset of the RMP coils were ramped to shift the divertor footprints from dominantly n = 3 to n = 2 pattern. The measured splitting has a very similar pattern to the modeled splitting, but is on a scale that is 5 times larger. These results could later be used to determine if the plasma response model can be validated with the measured splitting seen in the camera data. The sensitivity of the modeled splitting depend on details of the 2D equilibrium. The sequence of kinetic equilibria reproduce the time dependence of the measured splitting better than with magnetics only EFITs, indicating that the splitting is sensitive to aspects of the equilibria, such as the bootstrap current and q profile, that vary slowing during the discharge and aren’t modeled in a magnetics only EFIT reconstruction. This RMP ramp technique could be used in ITER to spread out the heat flux while avoiding excessive forces on the RMP coils. Key Words: Divertor, Splitting, Footprint, RMP
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