Study of intermittent small-scale turbulence in Wendelstein 7-AS plasmas during controlled confinement transitions
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)
Confinement transitions in the Wendelstein 7-AS stellarator [H. Renner et al., Plasma Phys. Controlled Fusion 31, 1579 (1989)] can be induced by varying either the internal plasma current or the external magnetic field. In this paper we report on experiments where closely matched confinement states (good and bad) were constructed using the latter method. Analysis using the former scheme has been reported upon previously [S. Zoletnik et al., Plasma Phys. Controlled Fusion 44, 1581 (2002)]. The electron temperature, along with the major spectral characteristics of magnetic and small-scale electron density fluctuations, changes dramatically at the transition from good to bad confinement. The fluctuation power is intermittent, and core bursts traveling in the electron diamagnetic drift (DD) direction are correlated between the bottom and top of the plasma, especially during degraded confinement. A corresponding top-bottom correlation for the edge ion DD direction turbulence feature was not found. Strong correlations are observed both between the two density fluctuation signals and between magnetic and density fluctuations in bad compared to good confinement. The correlation time of the bursts is of order 100 {mu}s, similar to the lifetime observed during edge localized modes.
- OSTI ID:
- 20657973
- Journal Information:
- Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 1 Vol. 12; ISSN PHPAEN; ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
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