Revealing spatiotemporal dynamics of electrons in planar magnetron plasmas

Partially-magnetized plasma devices such as planar magnetrons create fast localized azimuthal electron drifts. The electron confinement is key to the efficient ionization and acceleration in such devices, however, investigation of regions where such confinement occurs is challenging, and requires specialized non-invasive tools. In this work, direct time-resolved measurements of the electron global velocity are made using incoherent Thomson scattering and reveal the dynamic nature of the electron motion: (i) the azimuthal drift, perpendicular to the magnetic field, arising through the combination of crossed field (ExB) and diamagnetic drifts, and (ii) a radial drift along the magnetic field lines. A key consequence of the presence of such drifts is the development of small-scale instabilities which may affect particle transport and the overall discharge characteristics in such devices. Such instabilities are identified through the measurement of electron density fluctuations using complementary coherent Thomson scattering investigations. In this work, we show how localized measurements of the electron properties and drifts may be combined with direct measurement of such fluctuations to better understand the dynamic features of crossed-field plasmas.