Axial and radial development of the hot electron distribution in a helicon plasma source, measured by a retarding field energy analyzer (RFEA)

Abstract The information about the electron population of a helicon source plasma that expands along magnetic nozzle is important for understanding acceleration across potential drop forms in nozzle. electrons need an energy higher than to escape from source. At these energies signal Langmuir probe less accurate. An inverted RFEA measures high-energy tail electrons. To reach probe, they must have above V P , which can vary over region measurement. By constructing full distribution by applying temperature T e obtained IV-curve and ion collecting or emissive density measure hot independent be obtained. variation EEDF both radial axial directions, two different cases 1) purely expanding field nozzle, 2) more constricted one current third, downstream coil was investigated. densities temperatures are then compared analytic models development density. first model considers pure Boltzmann while second takes additional expansion into account. A good match between measured found configurations. also allows directional measurement probe. This property used compare upstream showing much lower contribution comparison confined configuration.