Experimental study of a short low-current vacuum arc on the electrodes of refractory metal

Abstract

In this work the average current per cathode spot (CS) and the velocity of CS motion in a short low-current vacuum arc was investigated on electrodes of Molybdenum, subjected to a magnetic field. The study was performed on electrodes of 30 mm in diameter and 2mm gap at arc currents up to 300A. Two components of the external magnetic field were varied independently. The axial magnetic field (normal to the cathode plane) B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> was varied from 0 to 0.1T and the transverse magnetic field (tangential to cathode plane) B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> was varied from 0 to 0.3T. The dependence of the average current per CS on the magnetic field amplitude and its inclination to the cathode surface was found. The average current per CS was found to raise with B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> the slower the greater the B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> value. The CS velocity was found to be proportional to B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> in case the current per CS at certain magnetic field value doesn't exceed the arc current. At fixed arc current the CS velocity saturates with B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> . The Robson angle was found to be proportional to the magnetic field vector inclination to the cathode surface angle with a factor of ~0.5. The results obtained were compared with the data in references.