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epr_talk.pdf2014-08-08 13:01:18Craig Jacobson

Electron Transport in Plasmas with Lithium-Coated Plasma-Facing Components

Author: Craig M. Jacobson
Requested Type: Poster Only
Submitted: 2014-05-30 13:14:24

Co-authors: D.P. Boyle, E.M. Granstedt, R. Kaita, B.P. LeBlanc, D.P. Lundberg, R. Majeski, J.C. Schmitt

Contact Info:
University of Wisconsin-Madison
1150 University Ave
Madison, WI   53706
USA

Abstract Text:
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. A lowered recycling rate is expected to flatten core Te, raise edge Te, strongly affect electron density 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 electron temperatures and densities 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. Measurements of electron density are compared with line integrated density measurements from a microwave interferometer. Adequate signal to noise is obtained with electron density larger than 2x10^18/m^3. Kinetic profiles measured in plasmas with helium-dispersed solid lithium coatings 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 measurements. TRANSP results for confinement times and stored energies agree with diamagnetic loop measurements. Analysis of electron thermal diffusivity results in values as low as 7 m^2/s near the core, which rise to around 100 m^2/s near the edge. These are the first measurements of local transport coefficients in LTX, or its predecessor, the Current Drive Experiment-Upgrade (CDX-U), with lithium plasma-facing components. Supported by US DOE contract #DE-AC02-09CH11466.

Characterization: 1.4

Comments:
Please group with other LTX posters per R. Majeski's instructions.

Workshop on Exploratory Topics in Plasma and Fusion Research (EPR) and US-Japan Compact Torus (CT) Workshop
August 5-8, 2014
Madison, Wisconsin

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