The area of the sheath around a thin, disk-shaped electrode that is biased
below the plasma potential has been computed using a hybrid simulation with
cold, collisionless ions and Boltzmann electrons. That is, the "collecting
area" of a double-sided, planar Langmuir probe has been determined for the
ion saturation current regime. Sheath areas are calculated for probe radii
from 10 to 45 electron Debye lengths and for probe biases from -5 to -30 t
imes the electron temperature. The dependence of the sheath area on probe r
adius and bias is parameterized using simple empirical formulas. (C) 2000 A
merican Institute of Physics. [S1070-664X(00)04807-2].