  Theory for a gridded inertial electrostatic confinement (IEC) fusion system
is presented that shows a net energy gain is possible if the grid is
magnetically shielded from ion impact. A simplified grid geometry is studied,
consisting of two negatively-biased coaxial current-carrying rings, oriented
such that their opposing magnetic fields produce a spindle cusp. Our analysis
indicates that better than break-even performance is possible even in a
deuterium-deuterium system at bench-top scales. The proposed device has the
unusual property that it can avoid both the cusp losses of traditional magnetic
fusion systems and the grid losses of traditional IEC configurations.
