Intense electron cyclotron emission bursts during high power neutral beam heating on TFTR

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/Pob>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 approximately 0.2-0.5. 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 near the beginning of the rise in the Dalpha signal. In some instances the spectral width of the ECE burst is narrow (Δ f/f << 0.1). In these cases the ECE burst exhibits a delay which could be interpreted as an outwardly directed motion of the source with a velocity of (2-3) × 103 m/s