Temporal Evolution of Bimodal Argon-Ion Velocity Distribution in an Expanding Helicon Plasma

Laser-induced-fluorescence (LIF) measurements, with 1-ms resolution, of the temporal evolution of the argon-ion velocity distribution function in the expansion region of a pulsed helicon plasma show two ion populations 19 cm downstream of the helicon source: a slow population that forms as soon as the 200-ms-long discharge is created and persists for few milliseconds after the RF pulse terminates and a fast population whose LIF signature appears ~28 ms after the RF pulse begins.