The LTX-β Research Programme and First Results

Full text: The research programme for LTX-β, the upgrade to the Lithium Tokamak Experiment, combines lithium walls to produce gradient-free temperature profiles and stabilize ion and electron temperature gradient-driven modes, with approaches to stabilization of density gradient-driven modes, such as the trapped electron mode (TEM). Candidate stabilization mechanisms for the TEM include sheared flow stabilization, which will be tested on LTX-β using neutral beam induced rotation. The goal is to reduce anomalous transport in a low aspect ratio tokamak. The upgrade will approximately double the toroidal field of LTX- (to 3.4 kG) and plasma current (to 150-175 kA), compared to LTX. Upgrades to the diagnostic set are in the areas of equilibrium, core transport, scrape-off layer (SOL) physics, and plasma-material interactions. Neutral beam injection at 20 kV, 30 A will be added in spring 2018, using a neutral beam system provided by Tri-Alpha Energy. A 9.3 GHz, 50 kW, short-pulse (5-10 ms) magnetron will be available later in 2018 for electron heat pulse propagation experiments. New lithium evaporation sources allow between-shot recoating of the walls. LTX-β is a collaborative effort, with major participation from both Oak Ridge and Lawrence Livermore National Laboratories (ORNL and LLNL), as well as the University of California at Los Angeles (UCLA). ORNL and the University of Tennessee will focus on spectroscopic improvements, and edge plasma/plasma-material interaction (PMI) analysis. LLNL plans research in the areas of SOL transport and plasma-surface interactions with lithium and tin. UCLA is upgrading the LTX profile reflectometer for high radial wavenumber backscattering. The 1 mm UCLA interferometer system will also be upgraded to probe low perpendicular wavenumber density fluctuations. The LTX-β research programme will be discussed, and initial operation of the upgraded device will be described. Work supported by the U.S. Department of Energy, contracts DE-AC02-09CH11466, DEAC05- 00OR22725, and DE-AC52-07NA27344. (author)