Abstract
Bursts of microwave emission are observed during ELM events on the Mega Ampere Spherical Tokamak. In agreement with observations on other machines, these bursts are up to 3 orders of magnitude more intense than the thermal background, but are electron cyclotron in nature. The peak in microwave emission is ~20µs before the peak in midplane Dα emission. Using the Synthetic Aperture Microwave Imaging radiometer, we are able to demonstrate that these bursts are often highly spatially localised and preferentially occur at the tokamak midplane. It is hypothesised that the localisation is a result of Doppler resonance broadening for electron Bernstein waves and the high perpendicular electron energies could be the result of pitch angle scattering in high collisionality regions of the plasma.
Highlights
The Edge Localised Mode (ELM) is a ubiquitous instability for tokamaks in H mode confinement regimes and is capable of delivering damaging heat loads to the divertors of future machines
On the Mega Ampere Spherical Tokamak (MAST), ELMs are almost always accompanied by intense bursts of microwave emission
ELMs on MAST are nearly always accompanied by several intense bursts of microwave radiation of duration 1-2μs
Summary
The Edge Localised Mode (ELM) is a ubiquitous instability for tokamaks in H mode confinement regimes and is capable of delivering damaging heat loads to the divertors of future machines. Understanding the trigger and heat transport mechanisms for this instability is a critical issue for future fusion machines. On the Mega Ampere Spherical Tokamak (MAST), ELMs are almost always accompanied by intense bursts of microwave emission. These bursts can be 10-1000 times more intense than the thermal background. Using the Synthetic Aperture Microwave Imaging (SAMI) radiometer, we show that the intense bursts appear spatially localised and originate preferentially from the midplane region of the tokamak. Details of the system can be found in our instrument paper [6]
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