138 / 2024-04-14 19:39:46

Investigation of Volt-Ampere Characteristics of Dark Current in Vacuum Pre-breakdown Phase

Vacuum Breakdowns,Field Emission,Dark Current

During the vacuum pre-breakdown phase, field emission serves as the primary physical process preceding the formation of plasma. This phenomenon, which cannot be observed optically, is referred to as dark current. Vacuum breakdowns are irreversibly triggered in the dark current stage, highlighting its pivotal role in the development of breakdowns.

However, a comprehensive understanding of dark current remains elusive. The objective of this paper is to elucidate the electrical characteristics of dark current, and thus identify the influence of field emitter parameters on electron emission. An experimental platform was established to characterize dark current in the pre-breakdown phase, facilitating the measurement of volt-ampere curves under various cathode structures. After that, physical parameters of field emitters, including the field enhancement factor β and effective emission area A_f, were determined through the Fowler-Nordheim theory.

The results reveal a significant impact of dark current on β, with a 4-10 times increase in β resulting in a dark current increase of at least three orders of magnitude. Furthermore, β is influenced by factors including the macroscopic shape of the cathode, the roughness of the cathode surface, and the presence of dielectric films. Moreover, there exists a positive correlation between A_f and the intensity of emission electron. Notably, increasing A_f can offset the reduction in emission caused by a decrease in β. In addition, the intensity of the dark current is limited by space charge effects, which weaken the electric field near the cathode surface, consequently reducing electron emission efficiency. As a result, dark current does not entirely conform to the exponential growth trend predicted by field emission theory.