Beam–magnetic-field interaction and return-current topology

Determine the structure and dynamics of the return current associated with a long-range relativistic electron beam propagating through the interplanetary plasma, and ascertain whether the beam–return-current configuration remains magnetically neutralized or is bent by the interplanetary magnetic field; resolve this by modeling the interaction between the beam’s magnetic self-field and the frozen-in background field (e.g., via particle-in-cell simulation) to assess feasibility of sustained propagation over hundreds to thousands of astronomical units.

Background

To deliver energy over distances of 100–1000 AU, the paper proposes using relativistic electron beams that either self-confine relativistically or propagate in a pinched mode through the space plasma. Because a net charge cannot be exported from the solar system, a large-scale return current must form in the background plasma.

If the return current forms a cylindrical sheath around the beam, the system may be magnetically neutralized and largely immune to large-scale interplanetary magnetic fields. However, by analogy with the heliospheric current sheet, the return current might instead spread and close along diffuse polar paths, potentially allowing the interplanetary magnetic field to bend the beam substantially (with an estimated radius of curvature ~10^-3 AU at γ ≈ 100). Clarifying this behavior requires detailed kinetic modeling.