Space and time resolved Langmuir probe measurements in a 100 kHz pulsed rectangular magnetron system

Using a cylindrical Langmuir probe, the temporal evolution of the electron density ne, electron temperature Te and plasma potential Vp has been measured at positions along the centre line in a 100-kHz pulsed magnetron plasma. The duty cycle was fixed at 50% and the Ar gas pressure was 0.27 Pa. At the beginning of the ‘on’ phase, a population of hot electrons was observed (for approx. 1 μs), with Te and ne approximately 50% higher than their time-averaged values. During the remainder of the ‘on’ phase, the electrons heat and then cool, following the rise and dip in the target potential. At the beginning of the ‘off’ phase, ne is seen to fall rapidly by over 60% at all positions and Te rises, however, both parameters recover after 1 μs and then slowly decay with a time constant of ∼40 μs. During the transition from ‘on’ to ‘off’ phases, Vp, rises rapidly from its usual value, a few volts above ground potential, to a few volts above the cathode potential (e.g. Vp∼+25 V). Some simple explanations for the observations are given.