Electron cyclotron emission imaging on a large helical device

In this article, we describe the electron cyclotron emission (ECE) imaging system applied to the Large Helical Device (LHD) at the National Institute for Fusion Science. The imaging system consists of focusing optics installed inside the vacuum chamber of LHD and planer-type detectors fabricated by monolithic microwave integrated circuit technology. The detector consists of the integration of a bowtie antenna, a down-converting mixer using a Schottky barrier diode, and heterojunction bipolar transistors (HBTs) on a GaAs substrate. The HBTs work as an intermediate frequency (IF) amplifier with a 10 GHz bandwidth and a 10 dB voltage gain. The ECE signal and local oscillator beam are irradiated from both sides of the detector. The ECE signals are down-converted at the mixers and the IF signal is fed to a filter bank with center frequencies of 1–8 GHz. The time evolution and the intensity of the ECE signals agree with those obtained by a conventional ECE heterodyne receiver. The cross-correlation spectra of t...