Features of plasma structure observed in high-current quasi-stationary magnetron discharge

• We investigate the plasma structures in a high-current impulse magnetron discharge.
• The plasma structure is strongly affected by the magnetic field magnitude.
• The behaviour of plasma spokes was studied both in the initial discharge stage and in the quasi-stationary phase.
• The build-up time of azimuthally symmetric structure of spokes at constant discharge parameters has an order of 10 μs.

The plasma structures in a high-current impulse magnetron discharge (HCIMD) were studied by means of a fast gated camera facing the cathode target, made from Cu, Ti, and Mo. The current–voltage characteristics of HCIMD were obtained for the range of transverse magnetic field on the cathode surface Bs = 40–65 mT and working gas (Ar) pressures pAr = 0.5–2 Pa. Fast camera images were recorded throughout the pulses for all experimental regimes, and the regions of plasma non-uniformity were found. The I-V curves studied in detail revealed from three to five distinct discharge regimes with quite different plasma appearance and behaviour, depending on the target material. Our observations of the initial stage of HCIMD indicate that in a certain discharge current range there is a characteristic time (~ tens μs) needed for the azimuthally symmetric structure of spokes to build up, even while the discharge current remains constant. During a quasi-stationary stage of HCIMD a well-defined spoke structure may rotate or remain stable depending on the discharge power.