Presheath environment in weakly ionized multi-species plasmas

Summary form only given. The presheath located near boundaries in weakly ionized multi-species plasmas is a rich environment in which charge exchange, ionization and ion-ion streaming instabilities compete to establish the electric fields that accelerate ions to close to the Bohm velocity at the sheath/presheath boundary. In weakly collisional plasmas, charge exchange and ionization set the presheath scale length and are essential to the creation of the presheath. Measurements in argon-helium multi-dipole plasmas of plasma potential with emissive probes, wave propagation with Langmuir probes, drift velocities with Mach probes and IEDfs with LIF are presented. These data show that ions are heated both perpendicular and parallel to the boundary, the argon ions are speeded up, and the ion-ion instability grows and saturates. The transition of mobility limited ion flow near the bulk plasma to free fall motion close to the plate for single species plasmas and the role of instabilities in multi-species plasmas in altering ion velocities near the presheath/sheath boundary are explored.