Breakdown of Argon and Nitrogen inside a Microgap Driven at High Frequency

The high-frequency oscillation of free electrons in a microgap (gap size< 1mm) leads to gas breakdown when the driving electric field exceeds a threshold, Ebd. In these experiments, with microwave signals introduced into a re-entrant microwave resonator, Ebd for argon and nitrogen was measured over a wide range of pressures and microgap sizes. As gas pressure is reduced below atmospheric, two distinct gap size dependent behavioral pressure regimes are observed where plasma transitions from uniform breakdown within the gap at higher pressure, to a glow discharge outside of the gap at lower pressure. The transition between these two regimes predictably occurs when the size of the microgap exceeds the dimension where microgap boundary loss of the oscillating electrons can be expected, resulting in a simple power law relationship between the transition pressure and the microgap size.