Direct decomposition of methane using helium RF plasma

In the fuel cycle system of a fusion reactor, tritium is extracted from exhaust gas and reused. When graphite materials are used in a part of plasma facing components, tritiated methane is contained in exhaust gas. Plasma decomposition is one of the techniques for extracting hydrogen from hydrocarbon. In order to evaluate direct decomposition of methane using helium RF plasma, a flow-type plasma reactor utilizing capacitively coupled plasma was developed and direct decomposition of methane was demonstrated. The decomposition rate of methane by helium plasma was proportional to the supplied RF power. However, it became small when total pressure of gas was high. A part of hydrogen generated from methane was retained in carbon deposits on the electrode. However, the accumulated hydrogen and carbon were effectively removed by the discharge-cleaning with oxygen plasma.