Thomas H. Stix Award for Outstanding Early Career Contributions to Plasma Physics Research: Pathways to Transient Control in Tokamak Plasmas*

Though the tokamak concept for magnetic fusion energy production is technically rather mature, challenges remain in the control of transient events associated with high-performance operation. This presentation will highlight ongoing work at the DIII-D tokamak facility to advance alternate pathways to avoid or mitigate edge-localized mode (ELM) instabilities occurring during the stationary phase, as well as relativistic electron (RE) populations excited during fast shut-downs. For ELMs, the relatively unexplored pathway of negative triangularity shaping offers the promise of integrating a high-pressure core plasma with an ELM-stable edge. Appropriate shaping is found to inhibit the steep edge gradients that destabilize ELMs. Examination of DIII-D plasma performance without ELMs highlights the integration potential of this edge solution via its unique access to high power and high density, while also clarifying pathways to improve absolute fusion performance. For the REs, emerging work highlights the beneficial effects of large-scale non-axisymmetric fields – intrinsic or extrinsic – for control. Destabilization of intrinsic plasma instabilities yield prompt dispersal of the entire RE population over an area that is larger than otherwise found, and experimental recipes to access the instability are under development. While intrinsic properties require no special equipment, their robustness is yet to be proven – thus motivating the use of extrinsic fields delivered via purpose-built conducting structures to more reliably achieve the same effect. For both challenges, the DIII-D tokamak acts as a proof-of-principle test-bed for these alternate transient control approaches. Planned and potential upgrades to the facility promise to enable unique validation of the underlying control concepts and pave the way to more robust tokamak designs with reduced physics risk towards high fusion power operation.