Bursts of electron cyclotron emission during disruptions of high beta discharges in the Tokamak Fusion Test Reactor tokamak

Journal Article · Wed Jan 01 04:00:00 EST 1997 · Review of Scientific Instruments

DOI:https://doi.org/10.1063/1.1147617· OSTI ID:453647

Janos, A; McGuire, K; Fredrickson, E; Parks, W; Zweben, S ^[1]; Hastie, J ^[2]

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1. Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)
2. UKAEA, Culham, Abingdon, Oxon OX14 3DB (United Kingdom)

Disruptions are sudden terminations of tokamak plasma discharges. During disruptions at high beta {beta} where {beta}{equivalent_to}plasma pressure/magnetic pressure, short (order of {mu}s) and intense bursts of electron cyclotron emission (ECE), an order magnitude above thermal levels, are observed in the second harmonic electron cyclotron frequency range, which corresponds to 100s of GHz in the Tokamak Fusion Test Reactor tokamak. A unique combination of two, fast, 500 kHz, 20-channel grating polychromator instruments, located at different toroidal positions, is used to measure the emission and characterize these bursts. New insights into the three-dimensional dynamics of these disruptions and the accompanying bursts of ECE have been obtained. Bursts of ECE occur at the beginning of the thermal quenches and exhibit strong toroidal asymmetries. Bursts are localized to the vicinity of the ballooning mode, a fast growing (few ms) medium toroidal mode number (n=10{endash}20) precursor, localized toroidally, poloidally, and radially, which triggers the disruptions. Fast-particle losses occur with the explosive growth of the ballooning mode, followed by plasma/wall interaction. Bursts of ECE occur shortly afterwards, within 10s of {mu}s of the fast particle losses. An explanation of the bursting is presented which is consistent both qualitatively and quantitatively, with observations predicting, for example, radiation enhancement factors of {approx}10. Bursting can be explained in terms of the reduction of absorption of thermal emission. Bursting is consistent with a modification to the electron distribution function f{sub e} due to a rapid energy or particle exchange between hot electrons and cold electrons from the edge, momentarily reducing the velocity gradient of f{sub c} in the thermal region. Large edge localized mode events also exhibit bursts of ECE due to a similar sequence of events. {copyright} {ital 1997 American Institute of Physics.}

• Research Organization: Princeton Plasma Physics Laboratory
• DOE Contract Number: AC02-76CH03073
• OSTI ID: 453647
• Report Number(s): CONF-960543--
• Journal Information: Review of Scientific Instruments, Journal Name: Review of Scientific Instruments Journal Issue: 1 Vol. 68; ISSN 0034-6748; ISSN RSINAK
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
BALLOONING INSTABILITY
BOUNDARY LAYERS
ELECTRON CYCLOTRON-RESONANCE
HIGH-BETA PLASMA
MICROWAVE EQUIPMENT
MICROWAVE RADIATION
PLASMA DENSITY
PLASMA DIAGNOSTICS
TFTR TOKAMAK
WALL EFFECTS
plasma-wall interactions
radiometry