Mass changes in NSTX Surface Layers with Li Conditioning as Measured by Quartz Microbalances
Authors: C.H. Skinner, H.W. Kugel, A. L. Roquemore, PS. Krstic and A. Beste
Abstract:
Dynamic retention, lithium deposition, and the stability of thick deposited layers were measured by three quartz crystal microbalances (QMB) deployed in plasma shadowed areas at the upper and lower divertor and outboard midplane in the National Spherical Torus Experiment (NSTX). Deposition of 185 μg/cm2 over 3 months in 2007 was measured by a QMB at the lower divertor while a QMB on the upper divertor, that was shadowed from the evaporator, received an order of magnitude less deposition. During helium glow discharge conditioning both neutral gas collisions and the ionization and subsequent drift of Li+ interrupted the lithium deposition on the lower divertor. We present calculations of the relevant mean free paths. Occasionally strong variations in the QMB frequency were observed of thick lithium films suggesting relaxation of mechanical stress and/or flaking or peeling of the deposited layers.
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Presented at: 18th Int. Conference on Plasma Surface Interactions in Controlled Fusion Devices,
May 26-30, 2008 Toledo, Spain
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Download PPPL-4319 (pdf 216KB 14pp)
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