Superpermeable Membranes in Plasma Physics

Although the membranes used to extract hydrogen isotopes from plasmas meet the criterion for the definition of superpermeability, in that every atom of hydrogen incident upon the feed side surface of the membrane is transported through the dense membrane, it must be noted that superpermeability is achieved, in very large part, because of the relatively low flux of hydrogen incident upon the membranes. The plasma density in the quoted experiments was 5 x 10 cm-, and the total gas pressure was relatively low, 0.002-0.004 torr (0.3-0.6 Pa) [2]. 

In the plasma experiments, the sticking coefficient of hydrogen on niobium must be equal to one if the membrane is to be classified as truly superpermeable. For highly energetic and ionized plasma species, including H2+, H3+, D2+ and D3+, 

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