Multichannel millimeter wave interferometer for W7-AS

A newly designed ten channel microwave interferometer for Line integrated electron density measurements at the experiment W7-AS stellarator is described. The probing signals in the frequency range of 160-162 GHz are generated by Gunn oscillators with subsequent frequency doublers. Double conversion heterodyne receivers with 2 MHz bandwidth are used for detection. All oscillators involved are phase locked. Use of each Gunn oscillator is twofold: as a source for the probing signal and as a local oscillator for heterodyne detection. The dynamic range of the millimeter wave part is about 70 dB. The instrument operates up to a peak density of 7 x 10(19) m(-3) with a temporal resolution of 5 mu s. This article gives a detailed technical description of the system and demonstrates its usefulness by means of an experimental example. (C) 1997 American Institute of Physics.