Injection and propagation of a nonrelativistic electron beam and spacecraft charging

Two‐dimensional numerical simulations have been carried out in order to study the injection and propagation of a nonrelativistic electron beam from a spacecraft into a fully ionized plasma in a magnetic field. Contrary to the earlier results in one dimension, a high‐density electron beam whose density is comparable to the ambient density can propagate into a plasma. A strong radial electric field resulting from the net charges in the beam causes the beam electrons to spread radially, reducing the beam density. When the injection current exceeds the return current, significant charging of the spacecraft is observed along with the acceleration of the ambient electrons back to the spacecraft. As a result, a beam current much larger than the thermal return current can be injected into space. Recent data on the electron beam injection from the Spacelab 1 (SEPAC) are discussed.