Visible imaging and spectroscopy of disruption runaway electrons in DIII-D

The first visible light images of synchrotron emission from disruption runaway electrons are presented. The forward-detected continuum radiation from runaways is identified as synchrotron emission by comparing two survey spectrometers and two visible fast cameras viewing in opposite toroidal directi...

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Bibliographic Details
Published in:Physics of plasmas 2013-04, Vol.20 (4)
Main Authors: Yu, J. H., Hollmann, E. M., Moyer, R. A., Commaux, N., Jernigan, T. C., Eidietis, N. W., Humphreys, D. A., James, A. N.
Format: Article
Language:English
Subjects:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
APPROXIMATIONS
BEAM-PLASMA SYSTEMS
CAMERAS
COMPARATIVE EVALUATIONS
ELECTRIC FIELDS
ELECTRON BEAMS
ELECTRON DETECTION
ELONGATION
MEV RANGE 10-100
PLASMA CONFINEMENT
PLASMA DIAGNOSTICS
RELATIVISTIC RANGE
RUNAWAY ELECTRONS
SPECTROMETERS
SPECTROSCOPY
SYNCHROTRON RADIATION
SYNCHROTRONS
TOKAMAK DEVICES
VISIBLE SPECTRA
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Summary:The first visible light images of synchrotron emission from disruption runaway electrons are presented. The forward-detected continuum radiation from runaways is identified as synchrotron emission by comparing two survey spectrometers and two visible fast cameras viewing in opposite toroidal directions. Analysis of the elongation of 2D synchrotron images of oval-shaped runaway beams indicates that the velocity pitch angle v{sub Up-Tack }/v{sub ||} ranges from 0.1 to 0.2 for the detected electrons, with energies above 25 MeV. Analysis of synchrotron intensity from a camera indicates that the tail of the runaway energy distribution reaches energies up to 60 MeV, which agrees with 0D modeling of electron acceleration in the toroidal electric field generated during the current quench. A visible spectrometer provides an independent estimate of the upper limit of runaway electron energy which is roughly consistent with energy determined from camera data. Synchrotron spectra reveal that approximately 1% of the total post-thermal quench plasma current is carried by the detected high-energy runaway population with energies in the range of 25-60 MeV; the bulk of the plasma current thus appears to be carried by relativistic electrons with energy less than 25 MeV. In addition to stable oval shapes, runaway beams with other shapes and internal structure are sometimes observed.
ISSN:1070-664X
1089-7674
DOI:10.1063/1.4801738