Flow damping in stellarators close to quasisymmetry

Iván Calvo, Felix I. Parra, José Luis Velasco, J. Arturo Alonso

Research output: Contribution to journalReview articlepeer-review

7 Scopus citations

Abstract

Quasisymmetric stellarators are a type of optimized stellarators for which flows are undamped to lowest order in an expansion in the normalized Larmor radius. However, perfect quasisymmetry is impossible. Since large flows may be desirable as a means to reduce turbulent transport, it is important to know when a stellarator can be considered to be sufficiently close to quasisymmetry. The answer to this question depends strongly on the size of the spatial gradients of the deviation from quasisymmetry and on the collisionality regime. Recently, criteria for closeness to quasisymmetry have been derived in a variety of situations. In particular, the case of deviations with large gradients was solved in the 1/ν regime. Denoting by α a parameter that gives the size of the deviation from quasisymmetry, it was proven that particle fluxes do not scale with α3/2, as typically claimed, but with α. It was also shown that ripple wells are not the main cause of transport. This paper reviews those works and presents a new result in another collisionality regime, in which particles trapped in ripple wells are collisional and the rest are collisionless.

Original languageEnglish (US)
Article number014014
JournalPlasma Physics and Controlled Fusion
Volume57
Issue number1
DOIs
StatePublished - Jan 1 2015
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Nuclear Energy and Engineering
  • Condensed Matter Physics

Keywords

  • Flow damping
  • Quasisymmetry
  • Stellarator

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