Implementation of a far-infrared interferometer on the madison symmetric torus

A collaboration between IPFR at UCLA and the University of Wisconsin at Madison has begun in order to study the physics of the Reversed Field Pinch 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. A Reversed Field Pinch device does not allow the typical slot-like ports used in FIR scattering and interferometry as tokamak plasmas. The ports available on MST are small < 4 cm diameter and are not all radially aligned. In order to provide enough spatial resolution, the ports are staggered toroidally, separated by 4 degrees. The optical system must take into account this arrangement. The optical system comprises an optical tower which supports the optics and their associated mixers, dielectric waveguide for propagation of the FIR beam from the laser and a tunable C02 laser and dual FIR laser. The FIR laser will provide enough wavelength range, 118 to 1222 microns, to cover a variety of operating conditions. The mixers are of corner cube type design and utilize a GaAs Schottky diode for mixing. The reference and probe beam are mixed quasi-optically and by use of a lens are focused onto the mixer. The design of the optical towfer and reaction mass required for the laser are being designed jointly with fabrication performed by the MST team. At 743 microns the optical tower has been designed so that vibration will not cause a phase change greater than 1/25 of a wavelength in either leg of the interferometer.