Arcing in ambient air triggered by pulsed x-ray radiation

The generation of arcs in air at atmospheric pressure induced by static voltage and triggered by x-ray pulses is analyzed. A static voltage is set between a cathode and an anode, and the arcing process is triggered by irradiating the air gap of a pin-to-plane switch with an x-ray photon pulse in the MeV range. This x-ray pulse produces a weakly ionized non-equilibrium air plasma (called the pre-plasma), which reduces the breakdown threshold. The influence of this pulsed x-ray on the arcing process is analyzed. The reduction of the breakdown voltage has been quantified, and for low static voltages, the creation of a sheath that is responsible for a delay in the arcing process is highlighted. Electrical measurements (currents and voltages) and optical emission spectroscopy have been performed to characterize the arcs in terms of electron density, temperature, and electric conductivity. A good agreement between measurements and 3D Maxwell calculations is achieved, which allows us to determine the electric conductivity of the arc in both self-triggered and x-ray-triggered regimes.