Spherical tokamak science on LTX- b utilizing millimeter wave diagnostics

Co-PI: Dr. William Peebles, UCLA and Professor Troy Carter, UCLA The Regents of the University of California, Los Angeles UCLA will continue its successful science collaboration on the LTX-β spherical tokamak located at Princeton Plasma Physics Laboratory, Princeton, NJ. UCLA currently operates two diagnostics on LTX-β: a mm-wave interferometer system and a fast electron density profile reflectometer system. UCLA will upgrade the interferometer to a low-k scattering system to measure density fluctuations in the frequency range 0-500 kHz (this is in addition to its base interferometry function). This scattering function will not affect the diagnostic's operation as an interferometer. In addition, a new tunable density fluctuation reflectometer system is near completion and is planned to be operational in late FY22. It should be noted that the low-k scattering system and the fluctuation reflectometer described here are the only internal measurements of turbulence and mode activity on LTX-β (magnetics and Langmuir probes are at the edge plasma or external). These diagnostics will therefore provide critical insight into these physics processes. For reference, a listing of the project objectives is shown below. Project Objectives (1) Lead and collaborate in state-of-the-art turbulence and transport experiments in support of both the US fusion energy research program and the LTX-β research program. (2) Continue to operate a density profile reflectometer and a mm-wave interferometer on LTX-β for high time resolution density profiles and chord averaged electron densities. These are essential diagnostics for LTX-β transport and confinement studies. (3) Install and operate a tunable density fluctuation reflectometer system. (4) Upgrade the current interferometer phase measurement to address unwanted phase jumps observed on LTX-β interferometer data. UCLA will examine several approaches to this upgrade including an improved phase comparator, a fully heterodyne upgrade, improved software analysis, or other enhancements. This will be followed by fabrication, testing, and installation. (5) The interferometer will also be configured as a low-k forward scattering system for density turbulence and coherent mode detection. This low-k scattering configuration does not interfere with the base interferometer operation. (6) This effort will support UCLA's education goals through the training and further education of an onsite post-doctoral scholar.