Microwave Scattering System Design for ρe-Scale Turbulence Measurements on NSTX
Authors: D.R. Smith, E. Mazzucato, T. Munsat, H. Park, D. Johnson, L. Lin, C.W. Domier, M. Johnson, and N.C. Luhmann, Jr.
Date of PPPL Report: May 2004
Presented at: the 15th Topical Conference on High-temperature Plasma Diagnostics, 19-22 April 2004, San Diego, CA; proceedings to be published in the Review of Scientific Instruments.
Despite suppression of ρe-scale turbulent fluctuations, electron thermal transport remains anomalous in the National Spherical Torus Experiment (NSTX). For this reason, a microwave scattering system will be deployed to directly observe the ω and k spectra of ρe-scale turbulent fluctuations and characterize the effect on electron thermal transport. The scattering system will employ a Gaussian probe beam produced by a high-power 280-GHz microwave source. A five-channel heterodyne detection system will measure radial turbulent spectra in the range |kr| = 0-20 cm-1. Inboard and outboard launch configurations cover most of the normalized minor radius. Improved spatial localization of measurements is achieved with low aspect ratio and high magnetic shear configurations. This paper will address the global design of the scattering system, such as choice of frequency, size, launching system, and detection system.