Effect of an external magnetic field on plasma torch discharge fluctuation

The effect of an external magnetic field on the anodic arc root movement inside a dc plasma torch has been investigated. In this letter, a virtual instrument technology was used to measure the arc voltage of the plasma torch at atmospheric pressure, and the rotating frequency of the anodic arc root was estimated by high-speed photography. The arc voltage fluctuation which represents the degree of the arc instability was reduced. And a new peak, whose frequency is consistent with the rotating frequency of the anodic arc root, was found in the Fast Fourier Transform spectra of the arc voltage signal. From the results, the helical instability generated directly by anodic arc rotation is put forward, and only the appropriate external magnetic field could inhibit and reduce the instability of the plasma torch and prolong the life of the anodic electrode. Furthermore, the measured voltage waveforms indicated that the arc root attachment mode would be controllable by an external magnetic field. Copyright (C) EPLA, 2013