The spectroscopy of cathode spot of pulsed vacuum arc discharge in a wide range of current

摘要

The aim of the experiment was the dynamics of the emission spectra of single vacuum arc cathode spots with focus on the dependence on arc current. A thin capillary tube was used as cathode that was filled with gallium-indium alloy liquid at room temperature. Vacuum arc discharges with current amplitudes between 10 and 150 A were powered by a low voltage RC-circuit with ~3 μs time constant. The discharge was ignited by the impact of a short-duration focused laser beam at the cathode. Momentary light emission from laser ablation plasma was used as a time marker. The temporal evolution of spectra was recorded by combination of a spectrograph (Spectra Pro SP-2300) with a streak camera (Hamamatsu C10910). The spectral range 410-440 nm was analyzed containing a Ga I resonant atomic line at 417 nm as well as lines from single and double charged ions at 425-426 nm (Ga II) and 438 nm (Ga III). In agreement with earlier publications at first the light emission from double charged ionic lines appears and reaches the maximum, then consistently the single-charged ionic lines, and the neutral atomic line follow. An increase of the current amplitude causes an increase of the percentage of light emission from double-charged ion line, but a relative decrease of neutral atomic line intensity.