Sound emission from an arc cathode

Sound waves have been detected from an electrode acting as the cathode in a vacuum discharge during electrical breakdown and subsequent arcing. Results from arcing on graphite, carbon fiber reinforced carbon, and stainless steel are reported. Distinct frequencies could be reproducibly detected in the power spectrum belonging to different groups. Most of the modes show a strong damping demonstrating that the nonlinear disturbance associated with the breakdown excites a wide spectrum. To identify eigenoscillations of the cathode plate some experiments have been repeated using an electrode with modified geometry. Different disturbances during the lifetime of the moving arc are reflected in different selections of sound eigenmodes.