Implementation of a far-infrared interferometer on the Madison Symmetric Torus

A collaboration between IPFR (Institute for Plasma and Fusion Research) at UCLA and the University of Wisconsin at Madison has begun in order to study the physics of the reversed field pinch (RFP) and tokamak magnetic confinement configurations. The proposed collaboration initially involves the design, fabrication, and installation of a far-infrared (FIR) interferometer system on the Madison Symmetric Torus (MST). This beginning stage will be used to accurately determine the density profile of MST. The system will be capable of low-cost upgrades which will allow the measurement of internal magnetic fields via Faraday rotation and density fluctuation spectra via collective scattering. An RFP device does not allow the typical slotlike ports used in FIR scattering and interferometry as tokamak plasmas. The ports available on MST are <4 cm in diameter and are not all radially aligned. To provide enough spatial resolution, the ports are staggered toroidally, separated by 4°. The optical system must take into account this arrangement. The optical system comprises an optical tower which supports the optics and their associated mixers, a dielectric waveguide for propagation of the FIR beam from the laser, and a tunable CO₂ laser and dual FIR laser