Recent Results and Future Plans for Interferometry & Far-Forward Scattering Measurements on LTX-β

The UCLA 288 GHz interferometer has provided routine line density measurements along a midplane chord on LTX-β. The combination of a narrow-band chirped-frequency source and direct-conversion detection is used to create a heterodyne IF signal. For electron density fluctuations, interferometry (k_⊥<1 cm^-1) and far-forward scattering (FFS, k_⊥~0.7-3 cm^-1) provide different wavenumber sensitivies for contrasting MHD and turbulence. The current hardware introduces distortions to the IF signal, which can couple the interferometry and FFS portions of the IF signal. Proper consideration of this issue has improved phase tracking (reduced fringe skips), as well as generated turbulence spectra (from FFS) with comtamination from MHD significantly reduced. Estimates of turbulence levels range from less than one percent to several tens of percent, where the assumption for the scattered field E_s~δn needs to be revisited. Future plans for the diagnostic include eliminating distortions by upgrading to heterodyne detection. A design at f~300 GHz involves using a hamonic mixer in a transceiver layout. Results from past experiments and progress with the interferometer upgrade will presented.