Spherical Langmuir Probe in ``Drifting'' and ``Accelerated'' Maxwellian Distribution

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Abstract
The treatment in a preceding paper of the ``accelerated half‐Maxwellian'' (AM), essentially according to Langmuir's probe theory for spherical probes, is supplemented by that of the Maxwellian with superimposed drift (DM). The differences between the two cases can be characterized in the following way. (a) Energy spectra: In the DM at least an infinitesimal number of carriers which happen to fly exactly against the drift have zero energy, whereas in the AM there are no carriers with energies smaller than corresponding to acceleration voltage. The energy spectrum in the AM, therefore, is zero between zero and acceleration energy, with an abrupt rise at the latter energy. The energy spectrum in the DM is zero only at zero energy, with a smooth rise to a maximum. (b) Ions: In the AM, carriers of opposite sign are accelerated in opposite direction and the acceleration energies are proportional to the charges of the carriers, whereas the drift energy in the DM is proportional to the masses of the carriers, which all drift in the same direction. Therefore the ion probe current in the DM at large enough drift velocities is as significant as the electron probe current, whereas in the AM the ion probe current retains its secondary role which is essentially determined by (me/mi)½, me=electron mass, mi=ion mass. The second derivatives of the probe currents with respect to the probe voltage show most clearly the significant differences between the two cases. Typical examples are plotted.

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