Plasma structure inside and outside a helicon thruster

Summary form only given. The HPH.COM project [Pavarin, D., et al., 2009] of the 7^th Framework Program is aimed at designing, building and testing a helicon thruster of 50-100W. In its simplest arrangement, a helicon thruster consists of a cylindrical helicon source, where the plasma is generated and heated, and a magnetic nozzle, where the plasma beam is accelerated supersonically [Ahedo, E., 2011]. Plasma heating is due to energy absorption of rf helicon waves emitted by a rf antenna surrounding the source. The no-wall magnetic nozzle, created exclusively by an applied longitudinal magnetic field, would channel the plasma beam ejected by the source. Supersonic acceleration is attributed to the expansion in the divergent topology as in a solid nozzle. Plasma must detach efficiently from the magnetic nozzle before or at the turning section. Two dimensional models of the plasma flow inside the source and in the external magnetic nozzle are presented, for a known amount of absorbed power from the rf waves (i.e. plasmawave processes are not described) [Ahedo, E., 2009; Ahedo, E., et al., 2010]. If the magnetic field in the source is large enough, fluxes and energy losses to the lateral walls become marginal. Conditions for high propellant utilization and high current efficiency are determined. In the magnetic nozzle, electrons remain within magnetic streamtubes. Azimuthal electron currents formed inside the source are responsible of a magnetic force with a double role: first, to impart thrust on the thruster magnetic circuit, and two, to confine radially the electrons. Typically (and conveniently) ions are weakly magnetized and detach inwards from the magnetic streamtubes but plasma quasineutrality is preserved with the appropriate ambipolar electric field. Other detachment mechanisms proposed in the literature do not apply here or are incorrect [Ahedo, E., et al., 2011].