Reduction of helium ash by selective helium pumping

The concept of the reduction of the helium ash concentration in a fusion plasma, based on selective pumping of helium ions, is discussed. Where this procedure is employed together with the pumping of a divertor, the helium ash concentration may be considerably reduced. Thus, this method might be helpful to sustain the burning plasma state or the ignition condition. The pumping condition required for the selective pumping metal is also discussed.