Page 2 - Two-chord Interferometry using 3.39 µm He-Ne Laser on a Flux-Coil-Generated FRC

2
HTPD2010, Wildwood, NJ, 5/17/2010 Presenter: Hiroshi Gota Privileged and Confidential
A two-chord λ~3.39 μm He-Ne laser interferometer system was developed for a flux-coil-generated field-reversed configuration (FCG FRC) to measure the electron density (ne) and estimate the total temperature (Ttotal = Te + Ti) of the FRC plasma.
The two-chord heterodyne interferometer system consists of a single ~2 mW infrared He-Ne laser, a visible (λ~632.8 nm) He-Ne laser for the alignment, a 40 MHz acousto-optic modulator (AOM), IR photodetectors, and quadrature phase detectors (QPD).
Initial measurement was performed and the measured line- averaged electron densities were 1–10x1019 m-3 at two different radial positions (r=12, 20 cm) in the midplane. A time shift in density was observed as the FRC expands radially. The time evolution of the line-averaged density agrees with the density estimated from the in-situ internal magnetic probes, based on a rigid-rotor profile model.
Overview