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 i njected along a magnetic field has been treated analytically and numer ically in low beta plasma. It has been demonstrated that the transvers e expansion of a beam is much faster than predicted by standard ambipo lar diffusion owing to the short-circuiting currents in the system. In the vicinity of an injector, plasma expands with the sound speed whil e at larger distances the transverse velocity tends to zero and a cyli ndrical shape of the beam is formed.