[Table of Contents]

Plasma and Fusion Research

Volume 2, S1025 (2007)

Regular Articles

Plasma Turbulence Imaging via Beam Emission Spectroscopy in the Core of the DIII-D Tokamak
George R. McKEE, Raymond J. FONCK, Deepak K. GUPTA, David J. SCHLOSSBERG, Morgan W. SHAFER, Réjean L. BOIVIN1) and Wayne SOLOMON2)
University of Wisconsin-Madison, Madison, Wisconsin, 53706, USA
1)
General Atomics, San Diego, California, 92121, USA
2)
Princeton Plasma Physics Laboratory, Princeton, New Jersey, USA
(Received 2 December 2006 / Accepted 6 April 2007 / Published 20 November 2007)

Abstract

Beam Emission Spectroscopy (BES), a high-sensitivity, good spatial resolution imaging diagnostic system, has been deployed and recently upgraded and expanded at the DIII-D tokamak to better understand density fluctuations arising from plasma turbulence. The currently deployed system images density fluctuations over an approximately 5 × 7 cm region at the plasma mid-plane (radially scannable over 0.2 < r/a ≤ 1) with a 5 × 6 (radial × poloidal) grid of rectangular detection channels, with one microsecond time resolution. BES observes collisionally-induced, Doppler-shifted Dα fluorescence (λ = 652-655 nm) of injected deuterium neutral beam atoms. The diagnostic wavenumber sensitivity is approximately k⊥ < 2.5 cm-1, allowing measurement of longwavelength (k⊥ρI < 1) density fluctuations. The recent upgrade includes expanded fiber optics bundles, customdesigned high-transmission, sharp-edge interference filters, ultra fast collection optics, and enlarged photodiode detectors that together provide nearly an order of magnitude increase in sensitivity relative to an earlier generation BES system. The high sensitivity allows visualization of turbulence at normalized density fluctuation amplitudes of ‾n/n < 1%, typical of fluctuation levels in the core region. The imaging array allows for sampling over 2-3 turbulent eddy scale lengths, which captures the essential dynamics of eddy evolution, interaction and shearing.

Keywords

turbulence, plasma diagnostic, imaging, beam emission spectroscopy, density fluctuation, anomalous transport

DOI: 10.1585/pfr.2.S1025

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This paper may be cited as follows:

George R. McKEE, Raymond J. FONCK, Deepak K. GUPTA, David J. SCHLOSSBERG, Morgan W. SHAFER, Réjean L. BOIVIN and Wayne SOLOMON, Plasma Fusion Res. 2, S1025 (2007).