Appearance of Vacuum Arcs in Axial Magnetic Field and Butt Contacts at Intermediate Frequencies

Intermediate-frequency power technology is widely used in aircraft power-supply systems. This paper studies the appearance and motion of vacuum plasmas in an axial magnetic field (AMF) and butt contacts at 360-800 Hz. Under the influence of an AMF, electrons travel in a cylindrical spiral, which is advantageous for maintaining arc diffusion. The experimental results show that when the contact separation was 3 mm, the vacuum arcs were uniformly distributed and diffused in the AMF contacts. We found that the maximum magnetic pinch pressure in the arc column was approximately 10^{4} Pa. However, in butt contacts, the arc was intense and was clearly constricted. The order of magnitudes of the magnetic pinch pressure in the center reached 10^{5} Pa at the minimum radius of the arc column around the current peak, which formed a higher pressure gradient that caused the plasma and metal vapor to flow to the lower pressure region and form a plasma jet.