Development of a Real-Time Power/Polarization Monitor using FPGA for Electron Cyclotron Resonance Heating on LHD

For optimization of electron cyclotron resonance heating (ECRH), it is important to measure power and polarization states of injected millimeter-waves in real-time. Arbitrary polarization states of millimeter-waves are realized by two grating mirror polarizers set at miter-bends in the corrugated waveguide transmission system on the Large Helical Device (LHD). The polarization state of an injected millimeter-wave determines the mode excitation purity, and therefore the power absorption efficiency in plasmas. The real-time power/polarization monitor of the injected millimeter-wave is required for optimization and/or feedback control of ECRH. The real-time power/polarization monitor is under development to be installed on a miter-bend near the ECRH antenna on LHD. Amplitudes and phases of two orthogonal polarizations of injected millimeter-waves are measured to determine the power and polarization states of waves. In this paper, the design and performance test of the real-time power/polarization monitor are reported. Intensities and relative phase of two orthogonal polarizations are measured by a newly developed monitor with heterodyne interferometer and fast ADC (800 MHz) with FPGA. Hardware of the power/polarization monitor works as designed qualitatively