Real Time Two Wavelength Interferometer System

摘要

A two wavelength interferometer system is used to measure the electron density in Double III. THe use of two separate wavelengths allows the resolution of phase shifts due to changes in plasma density and phase shifts due to mechanical vibrations. The initial system collected the measured phase shifts during a shot and then subsequent to the shot the electron density as a function of time was calculated in a minicomputer. A system is described which uses a combined analog and digital electronic circuit to produce the plasma density as a function of time during the progress of the shot, i.e., in real time. The phase shifts are obtained by an accurate instantaneous measurement of the intermediate frequency is obtained by mixing the light in the plasma path with the doppler shifted light in the reference path. Mathematical operations are performed on these measured phase shifts by the logic circuit resulting in a real time measurement of the plasma density.