Fast expansion of a plasma beam controlled by short-circuiting effects in a longitudinal magnetic field

The transverse expansion of a plasma beam with finite ion gyroradius injected along a magnetic field has been treated analytically and numerically in low β plasma. It has been demonstrated that the transverse expansion of a beam is much faster than predicted by standard ambipolar diffusion owing to the short-circuiting currents in the system. In the vicinity of an injector, plasma expands with the sound speed while at larger distances the transverse velocity tends to zero and a cylindrical shape of the beam is formed.