Spot and diffuse mode of cathode attachments in a magnetically rotating arc plasma generator at atmospheric pressure

摘要

Adjusting the strength of an axial magnetic field is an effective method to control the cathode attachment. In this paper, a magnetically rotating arc plasma generator is constructed to study the cathode attachment modes under different magnetic fields. Two cathode attachment modes are observed: a spot mode and a diffuse mode. Images of cathode attachments, temperature distribution of the cathode surface, and arc voltage characteristics correlating to different cathode attachment modes are investigated. Results show that the spot mode is favored by the low magnetic field. With an increase in the magnetic field, the cathode attachment region expands gradually, until the spot mode evolutes to the diffuse mode. The diffuse mode is associated with a significantly increased arc voltage, indicating that the transition is an abrupt process rather than a gradual process. For the diffuse mode, the cathode end has a higher average and lower peak temperature, but there exists varying temperature distribution on the cathode end, such as the ring-shaped high temperature region. Additionally, a two-dimensional coupled model is applied to qualitatively discuss the effect of magnetic field on the cathode attachment modes. Simulation results reveal that energy flux to the cathode surface increases with the increase of the magnetic field, and the major increment is thermal conduction heating from the arc column to the cathode surface, which possibly arises from the axial compression of arc plasma. Thus, the diffuse mode tends to always operate in the large magnetic field. Published under license by AIP Publishing.