Author: Philip B Snyder
Requested Type: Consider for Invited
Submitted: 2022-03-11 09:34:13
Co-authors: John Canik, Jerry W. Hughes, Matthias Knolker, Orso Meneghini, Thomas Osborne, J.M. Park, Wayne Solomon, Theresa Wilks, Howard Wilson
Oak Ridge National Lab
1 Bethel Valley Rd
Oak Ridge, TN 37830
The pressure and temperature at the top of the pedestal play a key role in fusion performance, and complex physics within the narrow edge transport barrier regulates these. Combining insight from gyrokinetic/gyrofluid and MHD analysis, significant progress has been made toward a predictive understanding of the physics governing the pedestal structure, including the development of the EPED model. We employ and further develop the EPED model to predict the pedestal structure, and derive a set of metrics to evaluate pedestal contributions to fusion performance. We review comparisons of EPED predictions to observations on several tokamaks, including “predict-first” experiments where predictions were made prior to the experiment and used to aid experimental planning. We focus on high pedestal regimes, including the “Super H-Mode” regime, where EPED predicts a bifurcation of the predicted pedestal solution into 3 branches. Strong shaping and moderate aspect ratio facilitate operation with a high pressure pedestal limited by current-driven kink/peeling modes (“peeling limited”) even at relatively high density. In the peeling-limited regime, the pedestal is predicted not to be degraded by high separatrix density, facilitating compatibility with a dense radiative divertor plasma. Optimization of the pedestal facilitates not only high fusion power density but also very high (>80%) bootstrap current fraction, enabling relatively compact devices with low recirculating power and continuous operation. A regime is identified with intermediate R/a~2.3-2.7, and strong shaping, which holds promise for next-generation fusion devices such as a compact fusion pilot plant (CFPP) and an Exhaust and Confinement Integration Tokamak Experiment (EXCITE).