Ion velocity distribution dependence on λ/ρ_i and ψ in a weakly magnetized plasma boundary

We report velocity distribution functions measured in the E × B direction and perpendicular to a plasma-facing surface in a boundary with a weak magnetic field. In these scenarios, the mean free path and the ion gyroradius are comparable (λ ∼ ρ_i) and the Debye sheath dimension is small (λ_D « ρ_i). Ion flows in the E × B direction, which are predicted to attain significant fractions of the sound speed, have recently been experimentally observed. We report measurements of ion velocity distributions in this direction for a range of collisionality λ/ρi and magnetic angles ψ. Experiments are conducted in the vicinity of a boundary region created in the HELIX helicon source, which produces plasma densities of 10¹⁶-10¹⁸ m^-3 and magnetic fields up to 1 kG. Electrostatic probe measurements of electron energy distributions and plasma potential are presented as well. Measurements are compared to distribution functions calculated using the fully-kinetic full-orbit Particle-in-Cell code hPIC including Monte-Carlo collisions.