Radial current distribution at a planar magnetron cathode

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Abstract
Experiments and theory are used to investigate the radial distribution of current at the cathode of a cylindrically symmetric, planar magnetron discharge. We have developed a simple model of the distribution of incident ions at the cathode, in the form of an integral equation. Energetic electrons, produced by secondary electron emission when ions strike the cathode, are accelerated into the discharge through a thin sheath. The Hamiltonian motion of the energetic electrons in the magnetic field determines the birthplace of discharge ions, and thus, the distribution of ion current density at the cathode. The radial current distribution has been measured for various magnetic fields using a radially staggered array of sixteen 1-mm-diam current probes imbedded in a 9-in.-diam cathode. In agreement with the model, the current distribution is peaked at the radius at which the magnetic field is tangent to the cathode plate, and the width of the distribution scales as the square root of the energetic electron Larmor radius.

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