Influence of Axial Magnetic Field and Surrounding Gas on Dynamics of Cathode Spot Spectra in Pulsed Vacuum Arc

The dynamics of the emission spectra of single vacuum arc cathode spots with focus on the dependence on external axial magnetic field and residual gas pressure was investigated. The cathode was a gallium-indium alloy that is liquid at room temperature, which causes high spatial stability from pulse to pulse for a long operation time. The discharge was fed by an RC circuit with current amplitude below 70 A and pulse duration of ~ 3 microseconds. The external axial magnetic field up to 140 mT practically did not affect on the spectral composition of the radiation of the cathode spot. However, the width of the ionic spectral lines decreased with the magnetic field, and the duration of relaxation of these lines increased, which agrees qualitatively with the effect of compression of the cathode plasma by the magnetic field. The presence of the surrounding gas (argon) begins to affect the discharge at a gas pressure of ~ 0.1 Pa, reducing the commutation time of the discharge gap and resulting in corresponding changes in the dynamics of the spectral lines of the cathode material. With all this, there are practically no argon lines in the spectrum of the cathode spot.