Radial theory of the ion current onto a probe in a low-pressure plasma with allowance for volume ionization and collisions with neutrals

The ion current onto a spherical or cylindrical probe is analyzed in the cold-ion approximation with allowance for ionization and collisions with neutrals. An expression for the ion density that takes into account both ionization and collision in the finite-size perturbed region is derived. The current-voltage characteristics for the dimensionless parameters r p / λ D = 0.0001−10, λ i / λ D = 0.01 − ∞, and zλ D /( kT e / M ) 1/2 = 0−5 are determined by numerically solving Poisson’s equation, and the corresponding approximate expressions are obtained.