When a small alternating potential V sin co t is superposed on the Langmuir probe, increase of the rectified direct current is given by
Δ
je=
jL{I
O(eδV/
kT)-1}
provided that electrons in a plasma have the Maxwellian distribution.
jL is the electron current density measured by the Langmuir probe. T is. the electron temperature. I
O(X) is the modified Bessel function of the first kind and of O-th order. Experimental studies have shown that, besides the resonance increase of the direct current at the electron plasma frequency, the rectified increase of the direct current diminishes quite rapidly in the high frequency region. In this paper, the diminishing of the rectified direct current increase is explained theoretically in terms of the finite transit time effect of electrons which traverse through the sheath region.
View full abstract