Influence of negative bias pulse parameters on accumulation of macroparticles on the substrate immersed in titanium vacuum arc plasma

The paper presents the results of an experimental study of the influence of a substrate negative bias with various pulse lengths and pulse repetition rates ranging from several pulses per second to 105 pulses per second on the macroparticle accumulation on the substrate immersed in DC titanium vacuum arc plasma. It was found that the increase of the bias pulse frequency from 10 up to 105 pulses per second at pulse length 7 μs, as well as bias pulse lengths from 5 μs to 25 μs at fixed frequency of 30 pulses per second at bias pulse amplitude ˗2 kV and ion-plasma substrate treatment time 30 s led to gradual almost linear up to 3-fold decrease of the surface number density of MPs on the substrate immersed in titanium vacuum arc plasma at plasma ion saturation current density of 10 mA/cm2. The decrease of ion current density down to 3.5 mA/cm2 leads to the reduction of the macroparticle suppression efficiency. The influence of multiple recharging of the macroparticles in plasma and the sheath on the reflection of these macroparticles in the sheath electric field is discussed. It was experimentally found that the shape of MPs and their adhesion to the substrate surface strongly depends on bias pulse, plasma and substrate parameters. It was shown that cooled vacuum arc MPs can be melted in high-voltage plasma sheath.