Variable control of neutron albedo in toroidal fusion devices

This patent describes a toroidal fusion plasma device, including a vacuum vessel for confining a plasma which contains fusion neutrons. The vacuum vessel has inboard and outboard walls, a arrangement for varying, between steady state operating modes, one of the flux and the energy spectrum of the fusion neutrons which are incident on the outboard wall. The arrangement comprises: neutron reflective material exclusively disposed immediately adjacent the inboard wall so as to reflect ones of the fusion neutrons having a predetermined flux and energy spectrum onto a predetermined portion of the outboard wall; and means for positioning the neutron reflective material into and out of communication with the fusion neutrons, whereby at least one of the flux and the energy spectrum of the fusion neutrons which are incident on the outboard wall is varied when the albedo material is in communication with the fusion neutrons