ASTROPHYSICAL SCIENCES PROGRAM IN PLASMA PHYSICS

The Lithium Tokamak Experiment (LTX) is a spherical tokamak designed to study the low-recycling regime through the use of lithium-coated shells conformal to the last closed flux surface (LCFS). A lowered recycling rate is expected to flatten core Te profiles, raise edge Te, strongly affect ne profiles, and enhance confinement. To study these unique plasmas, a Thomson scattering diagnostic uses a ≤ 20 J, 30 ns FWHM pulsed ruby laser to measure Te and ne at 11 radial points on the horizontal midplane, spaced from the magnetic axis to the outer edge at a single temporal point for each discharge. Scattered light is imaged through a spectrometer onto an intensified CCD. The diagnostic is absolutely calibrated using a precision light source and Raman scattering. Measurements of ne are compared with line integrated density measurements from a microwave interferometer. Adequate signal to noise is obtained with ne ≥ 2 × 1018 m−3. Thomson profiles of plasmas following evaporation of lithium onto room-temperature plasma-facing components (PFCs) are used in conjunction with magnetic equilibria as input for TRANSP modeling runs. Neoclassical calculations are used to determine Ti profiles, which have levels that agree with passive charge exchange recombination spectroscopy (CHERS) measurements. TRANSP results for confinement times and stored energies agree with diamagnetic loop measure-ments. Results of χe result in values as low as 7 m2/s near the core, which rise to around 100 m2/s near the edge. These are the first measurements of χe in LTX, or its predecessor, the Current Drive Experiment-Upgrade (CDX-U), with lithium PFCs. ii