Excitation temperature features of monovalent Cu ion under diffuse mode in vacuum arc

Since vacuum arc is usually considered as non-LTE plasma, it is reasonable to believe that the temperature of ions is different from the temperature of other particles whereas it still remains unknown. To achieve a better understanding of the vacuum arc, we measure the excitation temperature of Cu II (monovalent Cu ions or Cu
⁺
) by spectroscopic measurement and multiple-image optical measurements. As a result, the Cu II ions follow the Boltzmann distribution, and its excitation temperature has a negative linear relation with the gap length under diffuse mode at the peak of alternating current about -500 K/mm. In addition, the temporal evolution of excitation temperature does not follow the current’s sinusoidal wave strictly and it can be divided into 5 phases: (1) rapidly rising phase, (2) slight drop phase, (3) steady phase, (4) slow drop phase, (5) rapid drop phase, which could be simulated by square wave roughly. Besides, the 2-D distribution of excitation temperature shows that the cathode and anode have a higher temperature than inter-electrode space, as for the inter-electrode space, the excitation temperature increases from the vicinity of the cathode to the anode gradually.