Top view of the DIII-D tokamak showing the Ar pellet trajectory. The shaded regions show the FOV for the two opposite viewing cameras, and the dashed lines show the spectrometer views. The runaway motion and magnetic field are in the clockwise direction.
(a) Time traces of plasma current (blue), a soft x-ray channel (red), and the spatially integrated camera signal (green). (b) Synchrotron emission from REs detected in broad-band visible light (no filter) from the forward viewing camera, with reconstructed flux surfaces overlaid. The thick red curve shows the last closed flux surface.
Synchrotron spectral curves for three chosen RE energies of 15 MeV (blue), 30 MeV (red), and 45 MeV (orange). At each energy, the synchrotron spectrum is shown for electron velocity pitch angle (solid) and 0.15 (dashed). The unfiltered camera system response is shown as the black solid line.
(a) Backward and (b) forward detected survey spectra during the runaway plateau at in shot 145524. (b) Solid curves show thecalculated synchrotron brightness for RE energies of 35 MeV (blue), 45MeV (red), and 55 MeV (orange), with detected REs carrying 1% of the total measured current. The dashed green curve shows the synchrotron spectrum with detected REs carrying 100% of the measured current and with energy of 30 MeV. The red curve gives the best fit to the shape and magnitude of the measured continuum spectrum.
The evolution of (a) plasma current, (b) toroidal electric field, and (c) RE energy obtained from a 0D model with synchrotron loss (solid) and no synchrotron loss (dashed) for shot 137611. The energy data points (black dots) are obtained from the synchrotron emission detected by the forward viewing camera with no filter.
Crescent-shaped RE beam observed in shot 146704 at with a 747 nm filter. Inner wall radius is located at .
A pair of small RE beams detected by the forward viewing camera in shot 142729 at using a filter that passes long wavelengths (>700 nm). The color scale has been adjusted to maximize visibility, with black corresponding to finite radiance rather than zero radiance.
Backward (a)–(c) and forward (d)–(f) viewing camera images during the RE current plateau in shot 142725. The backward viewing camera detects broadband light and the forward detected camera has a narrowband filter with central wavelength at 912 nm and bandwidth of 10 nm. A fragmented deuterium pellet was injected into the runaway beam at time , just before the time corresponding to images (b) and (e).
Top-view schematic showing the horizontal extension of detected radiation from a relativistic electron with angle of emission . The electron guiding center moves in a circular orbit with major radius . For a circular beam, the horizontal dimension of detected radiation exceeds the vertical dimension by the amount . Adapted from Ref. 30 .
Forward detected camera image from shot 142726 at using a narrowband filter with central wavelength 912 nm. The black dashed oval is the result of fitting an ellipse to the 50% intensity contour; the major and minor axes of the ellipse-fit are used to determine the runaway pitch angle.
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