Low-frequency sheath admittance of a sphere in a collisionless plasma


  • R. Godard,

  • J. G. Laframboise


A systematic theoretical study of the low-frequency sheath admittance of a spherical electrode immersed in a collisionless, nonflowing, Maxwellian plasma with no magnetic field is done for the following ranges of plasma parameters: nondimensional electrode dc bias potential −25 ≤ p/kTe ≤ 25, ion to electron temperature ratio 0 ≤ Ti/Te ≤ 1, electrode radius to Debye length ratio 0 ≤ rp/λD ≤ 200. A surprising feature of the results is the existence of double and triple peaks in the sheath capacitance as a function of dc bias potential at certain values of rp/λD. The same capacitance results also show discontinuous behavior at space potential. Various plasma-diagnostics applications are suggested.