Plasma Seminar: The Negative Triangularity Tokamak: Ensuring Robust Access to a High-Performance, ELM-Free Fusion Power Plant

A. O. Nelson
Columbia University
Tuesday, January 23, 2024
11:00 am
FRH 4135

Zoom Link:

Abstract: The pursuit of commercial fusion energy, which could provide a clean and effectively limitless power source for humanity, is often heralded as one of the most important and difficult scientific endeavors of our time. One of the leading approaches for fusion, the tokamak, uses magnetic fields to confine a hot and dense plasma inside a toroidal vacuum vessel. Typically, this configuration can access plasma conditions capable of sustained fusion reactions, but in the process of doing so creates periodic edge instabilities called “ELMs” that release tremendous heat fluxes onto the machine walls. Avoidance of ELMs is essential to power plant operation, but existing techniques to do so are often extremely sensitive to plasma conditions and come with a measurable decrease in plasma performance. Enter negative triangularity (NT). Simply by changing the shape of the plasma cross-section, NT scenarios can provide a robust solution to the power-handling problem in tokamaks by eliminating the triggering of ELMs via direct regulation of the pressure gradients in the plasma edge. On the DIII-D and TCV experimental tokamak facilities, inherently ELM-free NT regimes are found to be fully compatible both with high core performance and with divertor detachment, both of which are essential for operation in future devices. Since this behavior is linked directly to geometry-induced changes in the magnetic shear, NT fusion power plants are predicted to maintain advantageous ELM-free edge conditions even in burning plasma regimes. Further, the natural tendency for NT plasmas to avoid plasma state bifurcations at high heating power could simplify impurity regulation and auxiliary power control in a reactor setting, and the NT geometry could facilitate larger divertor surfaces for exhaust mitigation. Together, these characteristics suggest that negative triangularity may be able to provide something that no other tokamak scenario can: a robust and rapid path to a commercial fusion energy system.

Laszlo Bardoczi