ISSN:
1089-7666
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Measurements of electrostatic fluctuations on the edge of the Advanced Toroidal Facility (ATF) torsatron [Fusion Technol. 10, 179 (1986)] are used to study the role of the edge turbulence in the particle transport in this current-free magnetic configuration. Spatial profiles of the plasma electron density ne, temperature Te, and fluctuations in density (ñe) and in the plasma floating potential (φ˜f ) are measured at the edge in electron cyclotron heated plasmas using a Langmuir probe array. At the last closed flux surface (LCFS), r/a≈1, Te≈20–40 eV, and ne≈1012 cm−3 for a line-averaged electron density n¯e=(3–6)×1012 cm−3. The relative fluctuation levels decrease as the probe is moved into the core plasma. For Te(approximately-greater-than)20 eV, ñe/ne≈5%, and eφ˜f /Te≈2ñe/ne at r/a=0.95. The measured fluctuation spectra are broadband (40–300 kHz) with k¯ρs≈(0.05–0.1), where k¯ is the average wave number of the fluctuations and ρs is the ion Larmor radius at the sound speed. Near the LCFS, the density fluctuations can be approximated by ñe/ne ≈0.4/k¯Ln, where Ln is the gradient scale length of ne. The propagation direction of the fluctuations reverses to the electron diamagnetic direction at r/a〈1. The phase velocity of the fluctuations and the electron drift velocity are comparable. The particle flux estimated from the fluctuations is consistent with fluxes obtained from the particle balance using the Hα spectroscopic measurements. Many of the features seen in the ATF edge fluctuations resemble those of Ohmically heated plasmas in the Texas Experimental Tokamak (TEXT) [Phys. Rev. Lett. 62, 1844 (1989)].
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.859882
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