An antenna has been designed and fabricated for the Large Helical Device (Nagoya, Japan) which collects electron cyclotron emission (ECE) from the plasma and matches it to low loss corrugated circular waveguide. This antenna uses large aperture off-axis reflecting elements to efficiently collect and transmit radiation from 75 to 600 GHz to various diagnostic instruments for analysis. A spatial resolution in the plasma of 6 cm combined with the plasma-antenna separation of 300 cm required f:7 optics at the longest wavelength. The large collection optics are mounted inside the vacuum vessel due to the limited diameter of available windows. Plasma radiation at shorter wavelengths requires active cooling of the first mirror and plasma facing elements. To absolutely calibrate the antenna in situ, the primary mirror can be rotated 180 degrees away from the plasma to view a calibration source. The antenna itself consists of two aspheric elements, primary ellipsoidal and secondary paraboloidal mirrors, which fold the optical path and transmit the radiation through a 9.9 cm aperture Z-cut crystal quartz window to the waveguide. This paper describes the design, fabrication, and testing of the antenna which has been delivered as part of a contract and collaboration between the Princeton Plasma Physics Laboratory and the National Institute or Fusion Studies.

*Work supported by U.S. DOE Contract # DE-AC02-76-CHO3073.