Observation of coherent radiation at the electron plasma frequency from a tokamak

Abstract
High‐resolution spectral measurements have been made of the fluctuating electron plasma frequency (ωpe) radiation from Alcator C. Results of spectral measurements with a dispersive delay line indicate that one or more very narrow, irregularly spaced components are present in each ‘‘burst’’ of ωpe emission. A direct‐sampling technique with an instrumental resolution of 200 kHz has been used to resolve the individual features of a burst. Features as narrow as 350 kHz have been observed (Δf/f=6×106). This result suggests that a highly coherent process is responsible for the emission.