Mainz 2022 – scientific programme

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P: Fachverband Plasmaphysik

P 1: Invited talks I

P 1.2: Invited Talk

Monday, March 28, 2022, 11:30–12:00, P-H11

Optical emission spectroscopy of spokes in magnetron sputtering discharges — •Julian Held, Philipp A Maaß, Volker Schulz-von der Gathen, and Achim von Keudell — Experimental Physics II, Ruhr University Bochum, Germany

Spokes are patterns of increased light emission, observed to rotate in front of the cathode of magnetron sputtering discharges. They move through the plasma at velocities of several km/s in or against the ExB direction of the discharge. The often distinctly triangular shape of these features has captivated many scientists. Nevertheless, the reason for this curious shape is still not fully understood. This is because the high velocity of spokes and their initial creation at arbitrary positions render measurements challenging. Thus, more demanding plasma diagnostic techniques that require data acquisition over multiple discharge pulses require synchronization between measurement and spoke movement. In this contribution, we present optical emission spectroscopy of spokes in both high power impulse magnetron sputtering (HiPIMS), as well as direct current magnetron sputtering (DCMS). A gated camera is combined with optical filters, isolating emission lines of metal and working gas neutrals and ions. The camera is then triggered on the spoke movement, allowing us to accumulate light from several acquisitions without averaging out the spoke signal. These measurements reveal the dynamic of electrons drifting through spokes in both DCMS and HiPIMS and explain how the distinct spoke shape is formed.