Abstract
A permeation measuring system with a nickel membrane of 30μm thickness was installed in a spherical tokamak QUEST. The membrane was located near the mid plane of the tokamak so that one side of the membrane was faced to the plasma. After the membrane was heated to 502K, hydrogen plasma was discharged using 2.45GHz RF system. The permeation flux through the membrane increased with a proper time-lag, that is, a significant plasma-driven permeation was observed. A numerical calculation of the diffusion equation under recombination boundary conditions was successfully conducted to simulate the transient permeation behavior. The recombination coefficients, estimated in a temperature range of 412–575K, can be explained by a model of thermally activated processes. Stable operation of the permeation system indicates the suitability of this system for the measurements of atomic flux with known diffusivity and recombination coefficients.
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