Direct measurements of ion dynamics in magnetic presheaths*

Ion velocities and temperatures are measured in the presheath of a grounded plate downstream from a helicon plasma source using laser-induced fluorescence. The plate is held 16 to 60 degrees relative to the 1 kG background magnetic field. Velocity profiles are compared to a 1D ion fluid model and are shown to agree well. Implications for ion flow to tokamak and Hall thruster walls are discussed.