Measurements of edge-localized-mode induced electron cyclotron emission bursts in DIII-D

Intense bursts of nonthermal electron cyclotron emission (ECE) have been observed in H-mode (high confinement) discharges in the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)], measured with heterodyne radiometers and a broadband far infrared (FIR) detector. These bursts are triggered by edge-localized modes (ELMs) and consist of single or several spikes, most lasting 5-150 mus. Radiation temperatures reach up to several MeV. Observed spectral bandwidths are typically less than 4 GHz. Bandwidths as low as 500 MHz, which is the limit of the instrumental filter spacing, have been found. Statistical analysis shows a steady decrease of the number of spikes with rising spike energy. Burst frequencies seem to depend linearly on the magnetic field. It is speculated that the bursts are coherent second harmonic ECE. (C) 2001 American Institute of Physics.