Temporal evolution of double layers in pulsed helicon plasmas

Delays of the order of tens of milliseconds in the appearance of the fast argon ion population in the expansion region of a pulsed helicon plasma are observed in time-resolved, laser induced fluorescence measurements. The fast ion population is a proxy for the presence of a double layer. The magnitude of the time delay depends strongly on the length of the interval between plasma pulses; the shorter the time between pulses, the shorter the time delay. The time delay approaches zero for inter-pulse intervals smaller than 30 ms. The double layer strength is not affected by plasma source modulation frequency.