Catalytic mechanism of divertor plasma recombination provided by hydrocarbon impurities

It is shown that the hydrocarbon molecules CxHy, when present in a divertor plasma, provide a powerful catalytic mechanism for volume plasma recombination at temperatures below 6–8 eV. The mechanism is based on the proton charge exchange with CxHy and the subsequent recombination of CxHy+ with plasma electrons, while its catalytic property derives from the simultaneous creation of new hydrocarbon molecules Cx′Hy′ in each charge exchange–dissociative recombination cycle. The plasma recombining efficiency of CH4, C2H6, and C3H8 molecules is for a factor of about 10, 30, and 40 higher than the efficiency of the similar ion conversion–dissociative recombination mechanism based on the molecule hydrogen. A 2.5% of C3H8 in the divertor molecular gas has the same effect on divertor plasma recombination as the entire content of molecular hydrogen in the divertor.