Application of millimeter-wave imaging system to LHD

Millimeter-wave imaging systems in the frequency range of 70-140 GHz have b een developed for diagnostics of magnetically confined plasmas. The 70 GHz imaging system successfully measures time evolutions of both radial and axi al profiles of line density and electron cyclotron emission (ECE) in a tand em mirror. The imaging system is being installed in Large Helical Device (L HD) at the National Institute for Fusion Science. In order to cover the fre quency range of the second harmonic ECE on LHD, a new detector using monoli thic microwave integrated circuit technology has been designed and fabricat ed. The detector consists of the integration of a receiving antenna, a down -converting mixer diode, and an intermediate frequency amplifier on a GaAs substrate chip. The heterodyne response up to 10 GHz was confirmed at 70-14 0 GHz. The optical system consisting of an ellipsoidal mirror and a flat mi rror was designed by using a ray-tracing code and evaluated experimentally at 140 GHz. (C) 2001 American Institute of Physics.