Zocco A, Podavini L, Garcìa-Regaña JM, Barnes M, Parra FI, Mishchenko A, Helander P. Gyrokinetic electrostatic turbulence close to marginality in the Wendelstein 7-X stellarator.
Phys Rev E 2022;
106:L013202. [PMID:
35974606 DOI:
10.1103/physreve.106.l013202]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2022] [Accepted: 07/07/2022] [Indexed: 06/15/2023]
Abstract
The transition from strong (fluidlike) to nearly marginal (Floquet-type) regimes of ion-temperature-gradient (ITG) driven turbulence is studied in the stellarator Wendelstein 7-X by means of numerical simulations. Close to marginality, extended (along magnetic field lines) linearly unstable modes are dominant, even in the presence of kinetic electrons, and provide a drive that results in finite turbulent transport. A total suppression of turbulence above the linear stability threshold of the ITG modes, commonly present in tokamaks and known as the "Dimits shift," is not observed. We show that this is mostly due to the peculiar radial structure of marginal turbulence, which is more localized than in the fluid case and therefore less likely to be stabilized by shearing flows.
Collapse