|approved||anderson_review_talk_post.pdf||2016-04-13 08:09:41||David Anderson|
|approved||the_role_of_theory_and_computation_in_advancement_of_the_stellarator_concept_v2.pdf||2016-04-07 14:30:48||David Anderson|
Author: David T. Anderson
Requested Type: Pre-Selected Invited
Submitted: 2016-03-03 18:45:05
University of Wisconsin-Madison
1415 Engineering Dr
Madison, WI 53706
Theory and computation have played a pivotal role in the resurgence of the stellarator as a candidate for fusion energy. With inherent steady-state operation, no disruptions in low-current manifestations, flexibility in plasma density, and no need for current drive, stellarators avoid many of the complications required of tokamak reactors. Theory and computation showed the concept of quasisymmetry, and its relative quasi-omnigeneity, provided a crucial solution to the challenge of low collisionality neoclassical transport. Stellarators needed optimization to succeed. Quasisymmetry was experimentally tested successfully in HSX, which showed greatly improved low-collisionality electron transport; quasi-omnigeneity formed the basis for the W7-X design and its resulting construction.
Theory and computation need to lead the way for the next advancements in the stellarator concept. Further improvements of stellarator design require a broad understanding of 3D plasma physic. One particularly intriguing question is can we optimize turbulent transport? Gyrokinetic tools are now in place to address this question. Impurity accumulation is perhaps the most critical issue for stellarators as the ion root suggests impurity accumulation in a reactor. Experiments show, however, that under certain conditions, impurities are expelled from the core. There is no theoretical understanding of these results. Another critical issue for stellarators is improved alpha particle confinement. Optimization for neoclassical thermal confinement does not necessarily ensure good confinement of energetic ions. Divertors in 3D also need attention, with scaling of existing divertor concepts to reactors being an open issue. Equilibrium tools need improvement to be able to deal with magnetic islands and plasma flow.
There are tremendous opportunities and needs for theory and computation within the stellarator arena, and a chance to make game changing impacts to the future of fusion.