Improvements to Interferometry and Far-Forward Scattering Measurements on LTX-β

The 288 GHz interferometer on LTX-β provides line density measurements along a single radial chord at the midplane. This diagnostic uses a single narrow-band chirped-frequency source and direct-converstion detection, and is highly sensitive to fluctuations from coherent modes as well as turbulence spanning several tens of kHz. When utilized as a far-forward scattering (FFS) diagnostic, the k_⟂ response reaches up to ~3 cm^-1. Recent changes to the demodulation algorithm have improved the phase tracking routine and significantly reduced distortions to the FFS signal. Estimates of the chord-averaged turbulence fluctuation level range from 2% to 6%. Modeling of the FFS diagnostic using a beam propagation code, as well as comparisons with separate analyses using the profile and fluctuation reflectometer data, are intended to corroborate the results from both sytems. Correlations between fluctuation levels and discharge characteristics will be examined. More recently the interferometer beamline was upgraded for better coupling with the viewing port and retro-reflector. Evidence showing improved beam coupling as well as changes to the k_⟂ sensitivity will be presented.