Sound emission from an arc cathode

Sound waves have been detected from an electrode acting as the cathode in a vacuum discharge. Results from arcing on carbon fibre reinforced carbon (CFC) and stainless steel (SST) an 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. Very few frequencies are present during the arc but no obvious dependence of their power on the arc current was found. To identify eigen-oscillations of the plate some experiments have been repeated using an electrode with reduced thickness. For comparison with a different material additional experiments on stainless steel have been carried out.