Spherical tokamak science on LTX- b utilizing millimeter wave diagnostics
PI: Dr. Terry Rhodes, Research Scientist, UCLA
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.