Radial behaviour of the electron energy distribution function in the cylindrical magnetron discharge in argon

The cylindrical magnetron consists of a coaxial inner cathode and an outer anode. The magnetic field is applied in the axial direction and is almost homogeneous in the whole magnetron volume. The electric field has radial direction and therefore the charged particles in the cylindrical magnetron discharge move under the influence of the × field. Due to its comparatively simple geometry, the cylindrical magnetron represents a suitable experimental tool that can be used to confirm theoretical results of modelling and theoretical studies of magnetrons in general. We studied experimentally the radial behaviour of the electron velocity distribution function (EVDF) in a cylindrical magnetron discharge in argon. We checked experimentally the anisotropy of the EVDF due to the influence of the magnetic field. For the assessment of the anisotropy of the EVDF we used a planar probe, whose collecting surface was adjustable at different angles to the direction of the magnetic field in the plane perpendicular to the electric field, as well as being movable in the radial direction. We found that in the measurable range of electron energies (energies greater than approximately 2 eV) and at magnetic fields up to 40 mT the anisotropy of the EVDF is not detectable within the experimental error limits. Therefore, for the study of the radial behaviour of the EVDF we used the thin (42 µm in diameter) tungsten cylindrical probe that was movable in the radial direction by a precise screw. For the theoretical determination of the EVDF in the cylindrical magnetron discharge we solved numerically the Boltzmann equation in a crossed × field, assuming the usual simplifications. The results of the calculation and the experiment in argon are compared and discussed.