Interferometry and Far-Forward Scattering Analysis of Electron Density Fluctuations in LTX-β

Investigating the mechanisms for fluctuation suppression due to low-recycling Li walls and their impact on the confinement properties are key research topics for exploring the potential of Li as a surface coating for plasma facing components. With increased B_T and I_p, and the addition of NBI, LTX-β extends the investigation of low-recycling regimes to high performance plasmas.  Target discharges with longer duration and higher electron densities (with correspondingly larger fluctuation amplitudes) create both opportunities and difficulties for the f=288 GHz radial-chord interferometer.  Increased fluctuation levels enhance the far-forward scattering (FFS) component of the probe beam, which can severely degrade the interferometry signal.  Interferometry is sensitive to k_⊥<0.67 cm^-1 while the FFS response has a range of 0.4<k_⊥<1.7 cm^-1.  Fluctuations are characterized by using a physical optics model to synthesize the FFS contribution to the interferometer signal.  A correction is then generated to recover the electron line density.  Fluctuation analysis from recent discharges using this method will be presented.  Additional measurements from the profile and fluctuation reflectometers (13.5-33 GHz) are expected to provide better localization for further characterization of internal electron density fluctuations.