Density Fluctuation and Edge Profile Measurements at the TAE Field Reversed Configuration Machine

Microwave reflectometry/Doppler Backscattering (DBS) is used for the first time to probe density fluctuations in a FRC plasma. A six channel tunable heterodyne system coupled to monostatic beam optics and a steerable parabolic mirror launches~ X/O-mode waves (26-90 GHz) towards the C-2 FRC plasma [1]. At oblique incidence, DBS is used to measure density turbulence with k$_{\theta }\rho _{i} \quad <$ 4. Turbulence levels increase with radius and are correlated with the density gradient: they are large in the SOL, and small near the field null. Recently, a dedicated, fast swept profile reflectometer was developed for measurement of the edge density profile in the 0.3-2.2x10$^{13}$ cm$^{-3}$ range, with 2.5 $\mu $s maximum time resolution. The challenging requirements were solved with a bistatic two-band design, a specialized fast varactor-tuned source, and very fast data acquisition using a 1 Gs/s LeCroy oscilloscope. Sample edge density profiles, their comparison with the wings of CO2 interferometer profiles, and some physics implications will be discussed. \\[4pt] [1] M. W. Binderbauer \textit{et al}, Phys.Rev.Lett. \textbf{105,} 045003 (2010).