Drift-wave-like density fluctuations in the Advanced Toroidal Facility (ATF) torsatron

Journal Article · Wed Feb 01 00:00:00 EST 1995 · Physics of Plasmas; (United States)

DOI:https://doi.org/10.1063/1.870966· OSTI ID:6635705

Shats, M G ^[1]; Harris, J H; Likin, K M; Wilgen, J B; Baylor, L R; Bell, J D; Ma, C H; Murakami, M; Sarksyan, K A; Aceto, S C; Bigelow, T S; Bell, G L; Colchin, R J; Dory, R A; Dunlap, J L; Dyer, G R; England, A C; Goldfinger, R C; Hanson, G R; Hutchinson, D P ; Isler, R C; Jernigan, T C; Langley, R A; Lee, D K; Lyon, J F; Qualls, A L; Rasmussen, D A; Richards, R K; Saltmarsh, M J; Simpkins, J E; Vander Sluis, K L; Zielinski, J J ^[2]

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1. Australian National University, Canberra (Australia)
2. Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-8072 (United States)

Density fluctuations in low-collisionality, low-beta ([beta][similar to]0.1%), currentless plasmas produced with electron cyclotron heating (ECH) in the Advanced Toroidal Facility (ATF) torsatron [Fusion Technol. [bold 10], 179 (1986)] have been studied using a 2 mm microwave scattering diagnostic. Pulsed gas puffing is used to produce transient steepening of the density profile from its typically flat shape; this leads to growth in the density fluctuations when the temperature and density gradients both point in the same direction in the confinement region. The wave number spectra of the fluctuations that appear during this perturbation have a maximum at higher [ital k][sub [perpendicular]][rho][sub [ital s]] ([similar to]1) than is typically seen in tokamaks. The in--out asymmetry of the fluctuations along the major radius correlates with the distribution of confined trapped particles expected for the ATF magnetic field geometry. During the perturbation, the relative level of the density fluctuations in the confinement region (integrated over normalized minor radii [rho] from 0.5 to 0.85) increases from [ital [tilde n]]/[ital n][similar to]1% when the density profile is flat to [ital [tilde n]]/[ital n][similar to]3% when the density profile is steepened. These observations are in qualitative agreement with theoretical expectations for helical dissipative trapped-electron modes (DTEMs), which are drift-wave instabilities associated with particle trapping in the helical stellarator field; they suggest that trapped-electron instabilities may play a role in constraining the shape of the density profile in ATF, but have little effect on global energy confinement.

• DOE Contract Number: AC05-84OR21400
• OSTI ID: 6635705
• Journal Information: Physics of Plasmas; (United States), Vol. 2:2; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
STELLARATORS
DRIFT INSTABILITY
FLUCTUATIONS
ECR HEATING
LOW-BETA PLASMA
MAGNETIC CONFINEMENT
MICROWAVE RADIATION
PLASMA DENSITY
PLASMA DIAGNOSTICS
TRAPPED-PARTICLE INSTABILITY
TURBULENCE
CLOSED PLASMA DEVICES
CONFINEMENT
ELECTROMAGNETIC RADIATION
HEATING
HIGH-FREQUENCY HEATING
INSTABILITY
PLASMA
PLASMA CONFINEMENT
PLASMA HEATING
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
PLASMA MICROINSTABILITIES
RADIATIONS
THERMONUCLEAR DEVICES
VARIATIONS
700340* - Plasma Waves
Oscillations
& Instabilities- (1992-)