Measurement of fluctuation induced particle flux by microwave imaging reflectometry in KSTAR plasma

This paper presents a spectral analysis technique [1, 2] to measure the frequency spectrum of particle flux induced by fluctuations across confining magnetic fields using microwave imaging reflectometry (MIR) diagnostic [3, 4] in toroidal devices. In this method density fluctuations measured by two correlated MIR radial channels are used to calculate radial particle flux spectrum over a finite frequency range. Analysis shows that during n=2 (with 0 phasing) non-axisymmetric magnetic perturbation (MP) the particle flux in the outward direction enhances and energy confinement degrades in a neutral beam heated Lmode discharge. Degradation of particle confinement is confirmed by reduction in line averaged density and stored energy signals during MP field application. Confinement regains its value due to decrease in the outward particle flux after the MP field is switched off

Relative Calibration between the ECEI Channels using the MHD instability

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

Turbulence induced particle flux measurements by microwave imaging reflectometry

In this paper we present a spectral analysis method [1] to measure the frequency spectrum of particle flux induced by fluctuations across confining magnetic fields using microwave imaging reflectometry (MIR) diagnostic [2, 3] in toroidal devices. In this technique density fluctuations measured by two correlated MIR radial channels are used to calculate radial particle flux spectrum over a finite frequency range. Analysis shows that during n=2 (with 0 phasing) non-axisymmetric magnetic perturbation (MP) the particle flux in the outward direction enhances and energy confinement degrades in a neutral beam heated discharge. Degradation of particle confinement is confirmed by reduction in line averaged density and stored energy signals. Confinement regains its value due to decrease in the outward particle flux after the MP field is switched off