Net current generation and beam transport efficiency of grad-B-drift transported relativistic electron beams

Numerical simulations of grad-B drifting, high-current, relativistic electr on beams are presented. The simulations use a hybrid fluid/particle-in-cell code to study the net-current and conductivity evolution for 200 to 900 kA , 1.3 MeV annular electron beams in a background gas of nitrogen (N-2) at p ressures of 1-60 Torr. Optimum guide-wire current and gas pressure for effi cient beam transport are found from the simulations to be similar to 40 kA and similar to5-15 Torr of N-2, respectively, with energy transport efficie ncies as high as 80% for transport distances up to 200 cm. For beam current s and/or gas pressures near the high end of the ranges considered, large ne t currents significantly alter the magnetic-field profile and result in dec reased transport efficiency. Transport efficiencies up to 90% are also foun d for a self-pinched transport mode in the 1-15 Torr N-2 range with no wire current. (C) 2001 American Institute of Physics.