Mini-Conference on the First Microns of the First Wall

Abstract

Interactions between plasmas and their surrounding materials (plasma facing components) are with the survivability of these materials, as well as the impact of these interactions back on the plasma. These interactions begin on the surface, but can have consequences a few microns into the material.This mini-conference on these "first microns" was designed to bring to the Division of Plasma Physics Meeting experts on these topics who would otherwise not attend. At the same time, the mini-conference was intended to expose the broader fusion community to these issues.The mini-conference covered in three, half-day sessions the topics of lithium coatings and surfaces, mixed materials characteristics, and issues associated with graphite.

Simulation of Diffusive Lithium Evaporation Onto the NSTX Vessel Walls

“…The angular distribution of lithium atoms emitted by the LITERs measured in the laboratory [2] agrees well with a molecular flow calculation [7] made using the Cbebm code. A spline fit to the latter forms the basis for the angular distribution of the lithium source in DEGAS 2; the atoms have a thermal energy distribution with a temperature of 900 K. The LITERs are operated at a computer controlled temperature [2], and the corresponding evaporation rates are determined from the lithium vapor pressure and a molecular flow conductance calculation.…”

Physical erosion studies of plain and lithiated graphite

“…The evaporative flux of lithium under high temperature is not clear when in combination as a Li/C mixed surface, and would be dependent on surface oxidation rates, among other variables. Lithium peroxide existing on the surface, as suggested by XPS measurements [19], would not evaporate at this temperature, which would imply a minimal evaporative flux of Li and possibly a larger true sputtering yield at 200°C.…”

“…A Li/graphite surface was found by in situ XPS to contain predominantly lithium peroxide (Li 2 O 2 ) [19]. A higher surface binding energy of Li in this compound compared to that of pure lithium could explain the reduced Li yield.…”