Two dimensional spatial Argon metastable dynamics in HiPIMS discharges

The spatial and temporal dynamics of the Ar metastable (Ar-M) density and temperature is studied by an extended Tunable Diode Laser Absorption Spectroscopy set-up (TDLAS) within a High Power Impulse Magnetron Sputtering (HiPIMS) pulse. A beam expander in combination with a photo diode array is used to simultaneously measure the spatial and time resolved absorption profile of an Ar-M transition. HiPIMS discharges are known for their complex physics, e.g. drifting ionisation zones called spokes, that occur in a discharge with crossed magnetic and electric fields. By analysing the Doppler shift of the absorption line, we found evidence for a small azimuthal velocity of the Ar-M in ExB direction. However, this observed azimuthal velocity is three orders of magnitude slower than the reported ion drift velocities and four orders of magnitudes slower than the ExB drift velocity. This finding may be caused by the weak coupling between the plasma rotation driven by ExB drift and the background gas, providing an estimate of the coupling between the plasma drifting in ExB direction and the neutral background gas.