Self-organization in planar magnetron microdischarge plasmas

Evidence is presented of rotating azimuthal wave structures in a planar magnetron microdischarge operating at 150 mTorr in argon. Plasma emission captured using a high frame rate camera reveals waves of azimuthal modes m = 3–5 propagating in the −E→×B→ direction. The dominant stable mode structure depends on discharge voltage. The negative drift direction is attributed to a local field reversal arising from strong density gradients that drive excess ions towards the anode. The transition between modes is shown to be consistent with models of gradient drift-wave dispersion in the presence of such a field reversal when the fluid representation includes ambipolar diffusion along the direction parallel to the magnetic field.