According to the document:
The “Electro-ring” concept of using electron rings in space for energy storage originated with the author during Rand studies of radiation (laser, particle beam) weapon systems in space. The requirement for large energy sources in space to support military radiation systems is evident from this work, as reported in R-1802-ARPA, Electron Rings in space for Energy Storage (U), and other Rand studies on space-based weapon systems.
The space systems considered here have been examined on an exploratory basis only. The research has focused on applications, under the tacit assumption that the formulated electron beam (e-beam) concepts will be feasible. The author identifies various concepts and discusses their potential mechanization on a broad basis. The level of effort was not sufficient for a rigorous pursuit of the physics and engineering of the systems.
Known physical effects have been factored in as performance constraints: however, many unknowns exist, particularly in the area of electron beam stability. Additional effort is required to resolve technical questions more precisely; project support to date has not permitted such in-depth resolution. Both theoretical investigations and in-orbit experimentation will be needed to determine the future prospects of electron beam weapons and Electro-ring energy storage devices.
Electron Beam Systems in Space, June 1977 [70 Pages, 9.9MB]