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Author: Aaron Bader
Requested Type: Poster
Submitted: 2016-02-12 12:03:11

Co-authors: A. H. Boozer, C.C. Hegna, O. Schmitz

Contact Info:
University of Wisconsin-Madison
309 Eagle Heights Apt F
Madison, WI   53705

Abstract Text:
Divertors for quasi-symmetric stellarators neet to be robust to changes produced by the evolution of the plasma pressure and bootstrap current. The divertor must be capable of handling heat flux and exhausting particles from start-up to steady state, without resorting to fine-tune control of the plasma bootstrap current with external drives. We present results that show that HSX has these properties, as the location of strike points is
seen to always lie on helical stripes even if the shape of the last closed flux surface (LCFS) and the size of edge islands and stochastic regions change considerably. Additionally, the helical stripes are also relatively insensitive to additional plasma currents, and hence are insensitive to the value of the edge rotational transform. Full 3D calculations with EMC3-EIRENE also show that the heat flux patterns for these very different onfigurations are also similar. This behavior may indicate that HSX is an example of a ``non-resonant'' divertor[1], one where the edge behavior is determined by the topological ridges of the LCFS rather than rational iota values at the edge. Non-resonant divertors may provide an alternate path to resonant island divertors for solving the edge exhaust problem in stellarator reactors.

1: Boozer, A. Jour. Plas. Phys. (2015) 81, 515810606