Princeton University Astrophysical Sciences Special Seminar

Fusion, the process that powers the stars, offers the potential to provide plentiful clean energy here on earth. Magnetic confinement of high temperature plasmas in toroidal devices known as tokamaks is a promising approach to fusion, one that has successfully produced millions of watts of fusion power. High performance in tokamaks is achieved via the spontaneous formation of a transport barrier in the outer few percent of the confined plasma. This narrow insulating layer, referred to as a “pedestal,” typically results in a >30x increase in pressure across a 0.4-5cm layer. The overlap of drift orbit, turbulence, and equilibrium scales across this narrow layer leads to rich and complex physics, and challenges traditional analytic and computational approaches. Development of high resolution diagnostics, and coordinated experiments on several tokamaks, have validated understanding of important aspects of the physics, while highlighting open issues. A predictive model (EPED) has proven capable of predicting the pedestal height and width to ~20-25% accuracy in large statistical studies. This model was used to predict a new, high pedestal “Super H-Mode” regime, which was subsequently discovered on DIII-D, leading to high fusion performance, and motivated experiments on Alcator C-Mod which achieved world record, reactor relevant pedestal pressure. Coupling this new understanding of pedestal physics to models of the core plasma enables extensive optimization of global fusion performance, including development of attractive scenarios for a fusion pilot plant.