Optical studies of plasma inhomogeneities in a high-current pulsed magnetron discharge

Drifting localization of ionization runaway: Unraveling the nature of anomalous transport in high power impulse magnetron sputtering

“…We observed an intensification of the plasma zones in terms of brightness and related density as the discharge current increases. We do not find that the number of structures is proportional to the current, as stated by Kozyrev et al 33 Future research will need to address this issue. We note that the ad-hoc assumption of a sin-modulated density profile, assumed by Kozyrev et al, 33 is not consistent with the shape of the ionization zone observed.…”

“…32 Finally, as pointed out by a reviewer of this manuscript and unbeknownst to us at the time of this research, such structures have also been reported in a recent publication by Kozyrev and co-workers. 33 We will later compare our results with those by Kozyrev and others.…”

“…19 With the exception of the recent paper by Kozyrev et al, 33 the literature on HiPIMS generally does not specify anything about the localization of ionization processes other than that ionization processes are concentrated in the neartarget zone, i.e., the magnetic pre-sheath, which is determined by the arched magnetic field. Although Kozyrev et al 33 used quite different HiPIMS conditions in terms of current, voltage, target material, and so on, high speed photographs showed more-or-less periodic structures along the racetrack, which are similar to those shown here in Fig. 3.…”

Self-organization and self-limitation in high power impulse magnetron sputtering

“…[9][10][11] The dense plasma zones move in the E× B direction with typically 10 4 m/s which is only a fraction of the electrons' drift velocity (~ 10 5 m/s). It was suggested that the moving dense plasma zones are better described as moving ionization zones since it is not the plasma itself that is moving but the location of most intense ionization.…”

“…This implies a drift of the ionization location in the E× B direction, in agreement with observation. [9][10][11] The speed of the ionization zone is determined by how fast the ions are evacuated by the electric field.…”