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Conventional magnetron discharge with a graphite target is a technology used worldwide to deposit thin films for a large range of applications. In the last decade, the high current density sputtering regime stands out as a very interesting alternative allowing the tailoring of coating properties. The peak power density normalized to the target area can exceed 107 W m−2, leading to an important ionization of the sputtered atoms. In this paper we focused on the electrical characterization of a magnetized plasma operated at average gas pressure (5 Pa; Ar and He) with a graphite target. A cross-correlation with a high-speed gated camera and optical emission spectroscopy measurements of the plasma evolution is also given. The analysis of the plasma–surface interaction zone on the target unveiled the physical mechanisms associated with the high current density range (1.8–32.5 A cm−2), corresponding to several regimes of discharge. For graphite, it will be demonstrated that the gas rarefaction induced by the vapor wind is negligible due to its low sputtering yield. Thus, the gas recycling is the dominant mechanism sustaining the discharge, even for the higher discharge current regime when a spot is present. Spokes and other instabilities were also identified and are discussed.

A classical two temperature magnetohydrodynamic modelling approach is used to study the influence of a large contact gap (up to 40 mm) on the behaviour of a diffuse vacuum arc controlled by a 5 mT/kA uniform external axial magnetic field between two copper electrodes with a 20 mm radius. The current constriction and energy flux density at the anode surface are more particularly analyzed, considering both supersonic and subsonic flow conditions. In the case of a supersonic arc, simulations show that the constriction of the current develops in the whole interelectrode region, but the constriction level at the anode surface does not evolve monotonically with the contact gap. The constriction is partly correlated to the radial compression of the plasma. In the case of a subsonic arc, the current constriction is related to the presence of the anode sheath. It occurs only close to the anode (from a constant distance from the anode of around 15 mm). Whereas the current constriction at the anode surface increases when the gap length goes from 10 mm to 20 mm, it no longer evolves when increasing the gap length from 20 mm to 40 mm. For both flow conditions, the evolution with the gap length of the radial profile of the energy flux density transferred by the plasma to the anode is similar as that followed by the current constriction at the anode.

The rational insulation design of a resistive superconducting fault current limiter (r-SCFCL) requires data gathered from experimental setups representative of the final apparatus. Therefore, an experimental study was performed to characterize the electrical breakdown (BD) of liquid nitrogen (LN2) in the particular conditions of a quenching superconducting device. To reproduce the electrical stress occurring within a real r-SCFCL winding, BD voltages with a grounded tape electrode were investigated with different polarities and pressures, with and without transient heating on the tape electrode. Pictures obtained with a high-speed camera and breakdown delay measurements allow to further characterize breakdown mechanisms.