Design of a millimeter-wave polarimeter for NSTX-Upgrade and initial test on DIII-D

作者：Zhang J^*; Peebles W A; Carter T A; Crocker N A; Doyle E J; Kubota S; Nguyen X; Rhodes T L; Wannberg C; Zeng L

来源：Review of Scientific Instruments, 2012, 83(10): 10E321.

DOI：10.1063/1.4733735

Polarimetry is a powerful diagnostic technique to probe plasma equilibria and magnetic fluctuations in fusion plasmas. In a high beta plasma such as the National Spherical Torus eXperiment (NSTX), these measurements are important to understand plasma stability and anomalous transport. A 288 GHz polarimeter operating along a major radial chord in retroreflection geometry has been developed and is being tested on the DIII-D tokamak to prepare for future implementation on NSTX-Upgrade. The system launches a rotating linearly polarized beam and detects the phase shift directly related to the polarization change caused by the plasma. To accomplish this, a pair of orthogonal linearly polarized beams with a stable difference frequency is generated using a single sideband modulation technique, then combined and transformed to be counter-rotating circularly polarized. To improve phase resolution, quasi-optical isolation, using Faraday rotators and polarizers, is utilized to eliminate a multi-path feedback effect, which is found to be the primary source of phase error. The bench tests in the laboratory and DIII-D power supply test discharges indicate <= 1 degrees phase resolution.

• 出版日期2012-10