| A computer code has been developed to model an isotropic inhomogeneous Vlasov plasma surrounding a DC biased spherical or infinite cylindrical electrode to which a radio-frequency potential is applied. The initial Maxwellian velocity distribution of the plasma is approximated by a multiple water bag distribution. The instantaneous response of the plasma to a sinusoidal potential applied to the electrode is calculated in the electrostatic approximation. Transient and nonlinear effects can be modeled in this way. Ions are usually treated as fixed, but some runs include ion dynamics with an ion/electron mass ratio of 16. Data produced by the code include the instantaneous particle flux and electric field at the electrode surface, from which the rf admittance is calculated. Results are presented for runs in the frequency range 0.1 (omega)(,pe) to 2 (omega)(,pe), rf amplitudes of 1 to 9 kT/e, and antenna radii of 1 to 10 (lamda)(,D). Here (omega)(,pe) is the electron plasma frequency and (lamda)(,D) is the Debye shielding distance. The code reproduces the admittance behaviour expected near the antenna-plasma series resonance. For some cases well above this resonance, negative rf conductance is seen. Some evidence for rf modification of the sheath is seen in the negative conductance cases. |
