Second Harmonic Imaging Interferometry for Magnetic Fusion Devices

40459 Princeton Scientific Instruments, Inc. Interferometric arrays of 10 to 30 channels, used in measuring electron density profile and time history, are standard elements of most contemporary magnetic fusion devices. As fusion devices evolve toward large complex cross sections and shaped profiles there is a accompanying need for higher or 2D spatial resolution and systems which are insensitive to vibrations. This project will develop an imaging second harmonic interferometer which is extremely compact, vibration insensitive, and can resolve spatial variations of a few millimeters and temporal changes as fast as 20 ¿s. Second harmonic interferometry measurements have demonstrated that single chord resolution of nc1~1013 cm-3 could be obtained on a fusion plasma. This sensitivity is sufficient to allow accurate profile measurements on present and future magnetic confinement fusion devices. The evaluation of this diagnostic technique will include the following possibilities and limitations: resolution limit, field of view limitations in the doubling materials, the effects of cross talk among spatial elements, calibration techniques, fringe leveling techniques, and other sources of noise. Anticipated Results/Potential Commercial Applications as described by the awardee: Commercial applications include imaging electron density in plasmas found in lasers, arc welding, plasma torches, and arc furnaces and in other large scale imaging of dispersive phenomena such as humidity variations in atmospheric turbulence.