Relative Calibration between the ECEI Channels using the MHD instability

Abstract

A calibration method using MHD instabilities such as sawtooth and tearing mode is developed for the KSTAR electron cyclotron emission imaging (ECEI) diagnostic. The typical ECEI data has been represented as the normalized electron temperature (Te) fluctuation against the time averaged value due to difficulties in the absolute calibration. Although the normalized ECE images are useful detecting small variations, it is often very difficult to figure out the spatial structure of an instability when its spatial scale length is small or when it is coupled with other instabilities. For more intuitive understanding and direct comparison with the theory or simulation, the calibration method using a priori Te profile obtained from sawtooth or tearing mode oscillations has been devised and applied to the KSTAR ECEI measurements. The relatively scaled Te contours are well reconstructed in the sawtooth and tearing mode instabilities. *Work supported by NRF Korea under grant no. NRF-2014M1A7A1A03029865 and NRF-2014M1A7A1A03029881.