453 / 2017-05-03 17:10:32

The Imaging Observation of the Initial Development Process of the Vacuum Breakdown

Vacuum ,breakdown,ICCD

Vacuum breakdowns, which are in most cases harmful, occur in many field, such as particle accelerators, satellite systems and vacuum interrupters. Understanding how breakdowns initiate in vacuum is of great importance for the improvement of vacuum devices. However, the initial stage of vacuum breakdown is still lack of direct experimental evidence because it is difficult to observe and measure. The objective of this study is to observe the light emission in the initial stage by optical diagnosis. We adopted a ICCD camera to catch a series of images in a breakdown and two optical filters to distinguish the light from copper atom (Cu I ) or singly charged copper ion (Cu II). A tip-to-plane gap was installed in a vacuum chamber; the gap varies from 0.5 mm to 5 mm; the voltage was provided with an impulse source with a peak value of 50kV; the current was measured by a Pearson sensor with a bandwidth of 200MHz. From the results, a vacuum breakdown was initiated by the electron emission from the cathode surface, leading to a strong evaporation of copper atoms. The electrons from the cathode will travel to and heat the anode. After a short delay, the anode region became much more luminous than the cathode, and the plasma formed in front of anode spread from the anode to cathode.