A seminar by Theresa Wilks
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Future fusion power plants are expected to operate with high pedestal density at low collisionality, conditions that create an opaque scrape-off layer and shallow neutral penetration. This regime supports parameters essential for both high fusion performance and robust exhaust solutions, namely flatter pedestal density profiles, higher temperature gradients, reduced impurity influx, and elevated pedestal pressures. Reaching and sustaining these conditions in present devices, however, remains a central challenge in closing the Integrated Tokamak Exhaust Performance (ITEP) gap, often referred to as Core-Edge Integration.
DIII-D implemented a major divertor upgrade—the “Shape and Volume Rise” (SVR) which enabled operation at high elongation (κ≈2.0) and triangularity (δ≈0.95) with plasma currents up to 2.2 MA. The SVR divertor removed the upper cryopump to allow pumping in strongly shaped configurations and added enhanced shaping control systems. This new geometry was designed to enable access to the “Super-H-mode” (SH) regime, where pedestal pressure increases continuously with density, unlocking a path toward more reactor-like pedestals at high opacity and low collisionality.
A 2.5 year long research thrust to utilize the SVR divertor pursued three complementary operational scenarios of ELMy H-mode, Resonant Magnetic Perturbation (RMP) H-mode, and Quiescent H-mode (QH). Together, these experiments provide the most comprehensive exploration to date of strongly shaped pedestals and their integration with divertor performance.
Key achievements from this activity include 1) Record Pedestal Pressures in ELMy H-mode, 2) QH-mode Access at High Current, High Density, and High Pedestal Pressure, 3) RMP ELM Suppression in Strongly Shaped Plasma, and 4) Detachment Physics in Reactor-Relevant Pedestals.
These results advance understanding of pedestal stability, fueling, and impurity transport in regimes directly applicable to ITER, SPARC, and prospective U.S. fusion pilot plants. While challenges remain, this research thrust establishes a roadmap for optimizing pedestal performance through shaping, fueling, and ELM control.
Dr. Theresa Wilks
MIT Plasma Science and Fusion Center
Research Scientist and Lead Scientific Coordinator for MIT Research at the DIII-D National Fusion Facility
Dr. Theresa Wilks is a research scientist in the field of fusion science and technology using magnetic confinement of plasmas with a focus towards energy production. As a researcher for the Massachusetts Institute of Technology, Theresa’s research concerns understanding and mitigating tokamak edge transient events, developing integrated tokamak scenarios viable to be projected to future power producing devices, and diagnostic development for vacuum ultraviolet spectroscopy. She collaborates with the experimental group working on the DIII-D fusion experiment, where she is a physics operator supporting a broad range of physics objectives. She is the chair of the US Transport Taskforce and actively participates in the APS Division of Plasma Physics in both scientific research and mentorship programs.
