Micro-plasma formation during opening of a low current electrical contact

The opening of a low current electrical contact using a piezoelectric actuator controlling the separation distance within the nanometre range is investigated. During the contact opening, formation of several short duration micro-plasmas is observed, followed by a contact re-closing. The arc duration was observed to increase from event to event, finally leading to the contact opening at a typical distance of about 5-6 μm. During the contact opening a liquid metal bridge is formed undergoing transition to a very dense plasma. Emission spectroscopy of the micro-plasma indicates that the arcing event consists of a dense metal plasma produced from the contact materials. In view of the small geometrical dimensions of the micro-discharge and estimates of the electrical conductivity of the plasma from electrical measurements, it is argued that a strongly coupled plasma must be present at the very beginning of the arcing event