Influence of an a-C:H layer on the gas and plasma driven permeation of hydrogen through iron
The dynamics of hydrogen recycling in carbonized tokamaks (surface covered with a-C:H) and of isotope exchange measurements in the laboratory suggest hydrogen bulk recombination and H(2)- molecule diffusion to be important mechanisms. The transport of hydrogen through a-C:H films using the permeation technique is studied. A UHV vessel in which a rf-assisted dc glow discharge (RG discharge) can be initiated, is separated from a second UHV chamber by a 0.125 mm thick pure iron membrane. An a-C:H film was deposited in situ onto the wall and membrane surface in the main vessel from 80% H(2)-20% CH(4) mixtures. The permeation from H(2) molecules and of the species from rf- and RG- discharges has been measured for various thicknesses of the film. Initially a strong increase of the permeation flux from rf and RG plasma species results from the suppression of the molecular recombination on the front surface. The permeation from H(2) molecules is unaffected by the a-C:H film up to the largest thickness investigated ( 55nm). The permeation from the low energy atomic or ionic species of the rf plasma is suppressed already for thicknesses less than 2nm whereas the more energetic particles from the RG plasma still cause enhanced permeation. Their effect starts to disappear when the thickness exceeds 5nm, indicating a correlation with the implantation range of the H-ions.
Bibliographic Reference: Paper presented: Amorphous Hydrogenated Carbon Films, Strasbourg (FR), June 2-5, 1987
Availability: Available from (1) as Paper EN 34448 ORA
Record Number: 198910162 / Last updated on: 1994-12-01
Original language: en
Available languages: en