Microwave imaging reflectometry for KSTAR

A microwave imaging reflectometry (MIR) system with two probing frequencies is being developed for 2D measurement of electron density fluctuations for KSTAR plasmas. The two-frequency probe beam enables simultaneous measurement of density fluctuations at two cutoff layers. Laboratory test of two approaches (reflective and refractive optics) has suggested an extreme care is needed in designing the optics considering problems such as aberration issues and standing waves. Currently, an optics based on refractive element is being designed with the minimum number of lens. The detector system consists of array detectors and electronics for the fluctuation phase reconstruction. The two-frequency MIR system will be installed for the 2012 KSTAR campaign and will be expanded to five frequencies by 2014.