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

Intense bursts of nonthermal electron cyclotron emission (ECE) have been ob served 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 heter odyne radiometers and a broadband far infrared (FIR) detector. These bursts are triggered by edge-localized modes (ELMs) and consist of single or seve ral spikes, most lasting 5-150 mus. Radiation temperatures reach up to seve ral MeV. Observed spectral bandwidths are typically less than 4 GHz. Bandwi dths as low as 500 MHz, which is the limit of the instrumental filter spaci ng, have been found. Statistical analysis shows a steady decrease of the nu mber of spikes with rising spike energy. Burst frequencies seem to depend l inearly on the magnetic field. It is speculated that the bursts are coheren t second harmonic ECE. (C) 2001 American Institute of Physics.