Upgrade of 2D Mircrowave Imaging Reflectometry (MIR) in KSTAR

Abstract

Microwave reflectometry is one of the most commonly used diagnostics for the measurement of electron density profiles and its fluctuating behaviors in tokamak plasmas [1]. However, in the case of multidimensional, large amplitude and short wavelength fluctuations, the interpretation of reflectometry data is still a remaining issue due to diffraction and complex interferences patterns of the reflected waves [2-4]. An advanced diagnostic concept for the electron density fluctuation measurement, microwave imaging reflectometry (MIR), has been developed to overcome the shortcomings of conventional microwave reflectometry. MIR system adopts a large-aperture probing and imaging optics in order to launch the probing beam properly and collect the majority of the reflected beam while minimizing the interference problem [2-4]. Measurement of semi-2D (radial and poloidal) electron density fluctuations can be realized in MIR system through the combination of the large-aperture optical system and the array of detectors (and one another for 2D measurement). From the 2014 KSTAR campaign, KSTAR MIR system has been upgraded to have doubled radial channels for investigating the radial structures of the plasma turbulence. In order to expand the detection channels, most components of the KSTAR MIR system such as I/Q electronics, optics, probing source and also DAQ system have been modified or replaced. In this work, laboratory test results of the upgraded KSTAR MIR system will be addressed and discussed. *Work supported by NRF Korea under grant no. NRF-2014M1A7A03029865.