Large-Aperture Broadband Polarization Rotator for the KSTAR ECE Imaging System

Abstract

The electron cyclotron emission (ECE) imaging system installed in the KSTAR tokamak has been designed for 2D electron temperature measurement based on the X-mode 2nd harmonic ECE radiation at a magnetic field similar to 2 T. For operation at higher magnetic fields (similar to 3-3.5 T) in the future, the frequency of the X-mode 2nd harmonic ECE (> 170 GHz) exceeds the detectable range of the system. Instead of extending the detector frequency range, large-aperture half-wave plates for polarization rotation have been developed to utilize the O-mode fundamental ECE, which is within the detectable range (similar to 65-135 GHz) of the present system.