Influence of vapor bubbles initiated by steady heating on the breakdown of liquid nitrogen

This paper presents an experimental study of the influence of vapor bubbles on breakdown in liquid nitrogen. Vapor bubbles are initiated by creating a small hot spot at the surface of an electrode. The behavior of vapor bubbles is first investigated by visualization, versus power dissipated by the heater, pressure and electric field. When breakdown occurs in the presence of bubbles, it is due to formation of either a vapor bridge between the electrodes (at low pressure), or a vapor layer on the hot spot (at high pressure). The results are discussed in comparison with gas breakdown fields obtained from the Paschen´s law.