Potential formation and ion distribution function in expanding magnetic field to divertor region

The stable electrostatic potential formation in quasi-neutral plasma with an expanding magnetic field to a divertor plate was studied by a one-dimensional analysis. The requirement for flow velocity of ions at an injection point is obtained. In case of no ion source in the quasi-neutral plasma region, the flow velocity of injected ions should be greater than the ion sound velocity, i.e. Bohm’s criteria. The ion source inside the quasi-neutral plasma, such as electron impact ionization, considerably mitigates this requirement.