Initial Measurements of Electron Density Fluctations on LTX-$\beta$ Using Microwave/Millimeter-Wave Diagnostics

The mechanisms for fluctuation suppression due to low-recycling lithium walls and their impact on the confinement properties of the LTX-$\beta$ device are key research topics for exploring the potential of lithium as a surface coating for plasma facing components in future fusion devices. UCLA operates a suite of microwave/millimeter-wave diagnostics for electron density profile and fluctuation measurements on LTX-$\beta$. Upgrades to existing systems will increase the sensitivity of the 288 GHz interferometer and the repetition rate of the 13.5$-$33 GHz profile reflectometers (sweep time down to 4 $\mu$s). Measurements from both diagnostics will be presented, as well as first results from the new two-channel tunable-frequency quadrature reflectometer (13.5$-$20.5 and 27$-$40 GHz individually), specifically designed for measuring low-$k$ electron density fluctuations over a wide spectral bandwidth (up to 5 MHz). Quantitative results from the fluctuation measurements (e.g.\ spatial localization, amplitude, wavenumber spectra) will require synthetic diagnostics and analysis tools. This will include modeling far-forward scattering of the interferometer beam as well as backscattering from the profile reflectometers. Discussion of these tools will also be presented.