Demonstration of Tokamak Discharge Shutdown with Shell Pellet Payload Impurity Dispersal.

The first rapid tokamak discharge shutdown using dispersive core payload deposition with shell pellets has been achieved in the DIII-D tokamak. Shell pellets are being investigated as a possible new path toward achieving tokamak disruption mitigation with both low conducted wall heat loads and slow current quench. Conventional disruption mitigation injects radiating impurities into the outer edge of the tokamak plasma, which tends to result in poor impurity assimilation and creates a strong edge cooling and outward heat flow, thus requiring undesirable high-Z impurities to achieve low conducted heat loads.

Reduction of edge-localized mode intensity using high-repetition-rate pellet injection in tokamak H-mode plasmas.

High repetition rate injection of deuterium pellets from the low-field side (LFS) of the DIII-D tokamak is shown to trigger high-frequency edge-localized modes (ELMs) at up to 12× the low natural ELM frequency in H-mode deuterium plasmas designed to match the ITER baseline configuration in shape, normalized beta, and input power just above the H-mode threshold. The pellet size, velocity, and injection location were chosen to limit penetration to the outer 10% of the plasma. The resulting perturbations to the plasma density and energy confinement time are thus minimal (<10%).

Effect of parallel flows and toroidicity on cross-field transport of pellet ablation matter in tokamak plasmas.

The first complete set of time-dependent equations describing the cross-field drift of ionized pellet ablation matter in tokamak plasma caused by polarization in the nonuniform magnetic field has been developed and solved numerically. Important new features impacting the drift dynamics have been identified, including the effect of pressure profile variations in the tokamak plasma, curvature drive by near-sonic field-aligned (parallel) flows, and the rotational transform of the magnetic field lines, and are considered from the viewpoint of the parallel vorticity equation. These new features are necessary to obtain favorable quantitative agreement between theory and experimental fuel deposition profiles for both inner and outer wall launched pellet injection cases on the DIII-D tokamak.

Mitigation of tokamak disruptions using high-pressure gas injection.

High-pressure gas-jet injection of neon and argon is shown to be a simple and robust method to mitigate the deleterious effects of disruptions on the DIII-D tokamak. The gas jet penetrates to the central plasma at its sonic velocity. The deposited species dissipates >95% of the plasma by radiation and substantially reduces mechanical stresses on the vessel caused by poloidal halo currents.