Theoretical multiple beam overlap from channel transport of intense particle beams

The overlap of intense particle beams transported in current-carrying plasma channels for inertial confinement fusion has been studied. Basic geometric considerations suggest an upper bound on the current density gain of N/4 due to the overlap of N uniform beams that are transported to the overlap region in channels. For ’’hot’’ electron beams this limit is seldom approached. For ’’cold’’ ions beams with radial distributions peaked on channel axes, this limit can be attained and even exceeded. From the standpoint of channel energetics, it is desirable to minimize the transverse energy of the ions in the channel which is quantified by the average ion angle ϑ. In order to optimize the ion overlap it is necessary to satisfy ϑ<2N−1/2. A spherical multi-’’disk’’ model of converging plasma channels is developed with the constraint that the geometrical overlap radius (where the incoming channels touch each other) remain as small as possible in order to avoid excessive beam expansion in the overlap region. Details of electron transport and escape are explained using adiabatic drift theory.