Instrument reflections and scene amplitude modulation in a polychromatic microwave quadrature interferometer

Abstract

A polychromatic microwave quadrature interferometer has been characterized using several laboratory plasmas. Reflections between the transmitter and the receiver have been observed, and the effects of including reflection terms in the data reduction equation have been examined. An error analysis which includes the reflections, modulation of the scene beam amplitude by the plasma, and simultaneous measurements at two frequencies has been applied to the empirical database, and the results are summarized. For reflection amplitudes around 1096, the reflection terms were found to reduce the calculated error bars for electron density measurements by about a factor of 2. The impact of amplitude modulation is also quantified. In the complete analysis, the mean error bar for highdensity measurements is 7.596, and the mean phase shift error for low-density measurements is 1.2".. PACS no.'s/OCIS codes, etc analogue I. Introduction.

Plume detachment from a magnetic nozzle

“…A polychromatic quadrature interferometer is used that operates simultaneously at 70, 90, and 110 GHz. 18 This instrument is positioned near the nozzle entrance, 0.33 m downstream from the choke magnet. The spatial resolution for this interferometer is 0.015 m, with a minimum sensitivity of 10 16 m −3 over the 1 m path length.…”

“…Calibration of all interferometer systems was conducted daily, providing estimates of random and systematic error due to beam reflection and detector voltage drift. 18 Interferometer density measurements are performed in two ways. Independent density profiles are obtained by vertical translation of the polychromatic interferometer over several plasma shots.…”

Physics of Plasma Detachment in a Magnetic Nozzle

“…A polychromatic quadrature interferometer is used which operates simultaneously at 70 GHz, 90 GHz and 110 GHz. 9 This instrument is positioned near the nozzle entrance, about 0.5 m downstream from the plasma source. The spatial resolution for this interferometer is typically 0.015 m, with a minimum sensitivity of 10 16 m -3 over the 0.1 m pathlength.…”

Analysis of multifrequency interferometry in a cylindrical plasma

“…This interferometer has been used to measure the electron density in the VASIMR VX-20 device. 2,3 The VX-20 experiment employs a helicon discharge in helium which produces a flowing plasma with a high degree of ionization. We discuss measurements at a location where the plasma diameter of ϳ3 cm is comparable to the beam size.…”