Reduction of helium ash in fusion plasma by selective helium pumping

The concept for reduction of helium ash concentration in a fusion plasma, based on the selective pumping for helium ions, is described. In a case that this scheme is employed together with the pumping of divertor, the helium ash concentration can be considerably reduced. Thus, this method is helpful to sustain the burning plasma state or the ignition condition. The pumping condition required for the selective helium pumping metal is also discussed. (author)