Phenomenology of intense electron cyclotron emission bursts during high power neutral beam heating on TFTR (abstract)

Abstract

A 20-channel grating polychromator has been used to study intense bursts of electron cyclotron emission (ECE) from TFTR deuterium plasmas predominantly heated by 90–110-keV neutral beams (Pinj/Poh≳30). The ECE bursts have a duration of 20–150 μs and are usually seen 300–500 ms after the start of neutral beam injection, when the stored energy and neutron production are collapsing or rolling over. In most cases the ECE bursts have Δf/f∼0.2–0.5, if this frequency spread is due entirely to relativistic broadening it implies an electron energy of 10–100 keV (Core electron temperatures in these plasmas are typically 7–12 keV). The ECE bursts are often correlated with ELM activity during limiter H modes and appear to occur at the beginning of the rise in the Dα signal. In some instances the spectral width of the ECE burst is narrow enough (Δf/f∼0.1) to allow identification of the origin of the emission, in these cases the source appears to be within 0.2 m of the plasma edge and the ECE burst exhibits a delay characteristic of an outwardly directed velocity of 2–3×103 m/s. This work is supported by U.S. Department of Energy Contract No. DE-AC02-76-CHO-3073.