Evolution of ion and electron energy distributions in pulsed helicon plasma discharges

The temporal evolutions of the ion and electron energy distributions of pulsed helicon diffusion plasmas are measured. High power (<1 kW) moderate length (10 ms pulses, 10% duty cycle) 13.56 MHz RF discharges show three distinct pulse phases: (a) breakdown (the first 250 μs), characterized by high electron temperatures (>8 eV) and high ion energies (>40 eV); (b) a mid-pulse phase, which is identical to CW operation, and (c) the termination and afterglow which displays a collapsing plasma potential, splitting in ion energy peaks and a transient hot electron component (>11 eV). The hot electrons in the breakdown and termination phases are characteristic of a capacitive antenna coupling mode, while high densities and low plasma potentials of the steady-state mid-pulse phase are characteristic of an inductive/helicon wave coupling mode.