Intense intermittent radiation at the plasma frequency on EAST

Intense intermittent radiation has been observed regularly in EAST by using a Michelson interfer-ometer and a Q-band radiometer system. The radiation bursts are related to a fast process with characterization time of a few microseconds. An electron density window exists for the occurrence of the bursts, and the upper electron density threshold is dependent of the toroidal magnetic field. The frequency of the emission f is at the plasma frequency, and the frequency bandwidth Δ f is very narrow (∼1.5 MHz FWHM, Δ f / f ∼ 3 × 10−5 ). Fine structure of the spectrum with multi-peaks have been observed, and the frequency interval is around 3 MHz. Numerical simulation results of cavity modes indicate that the frequencies of these modes are close to the central plasma frequency, and the departure from the central plasma frequency becomes larger for higher order modes.