Publication details

Study of spoke rotation, merging and splitting in HiPIMS plasma

Authors

KLEIN Peter LOCKWOOD ESTRIN Francis HNILICA Jaroslav VAŠINA Petr W. BRADLEY James

Year of publication 2017
Type Conference abstract
MU Faculty or unit

Faculty of Science

Citation
Description Study of self-organized structures called spokes was performed in the HiPIMS plasma using simultaneous broadband optical screening via ICCD camera (200 ns time scale) and the embedded probes measuring the local current delivered by the spoke to the target. As a spoke passed over a set of embedded probes in the niobium cathode target, a distinct local current modulation is observed. Typically the current modulation was up to twice the average value, matching well with the radially integrated optical emission intensities obtained by the ICCD. The dual diagnostic system enabled the observation of a set of spokes as they rotated and the events of the spoke merging and splitting were recorded. The two spokes with similar sizes and intensities were observed to merge into one larger spoke, while the retaining the velocity of the trailing spoke. In the merged spoke both the plasma emission intensity and current collected by the embedded probes was redistributed to have their maximum at a trailing edge. The reverse process, in which spokes split was also observed. The total charge collected by the embedded probes during the spoke splitting was conserved. After the spoke merging or splitting events occurred, the new spoke configuration was not always stable in time. Often the large spoke split into two smaller spokes only to reform a short time later. However for a given experimental conditions only a slight variation from the average mode number m was observed (typically a change of m = 1). In addition a simple phenomenological model was developed to relate the spoke mode number m with the spoke dimensions, spoke velocity and gas atom velocity.
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