Abstract
This paper describes a theory for plane collisionless sheaths separating plasmas ionized by thermal electrons from emitting electrodes affected by sheath fields. Examples for cesium plasmas and thermionic-diode configurations show sheath effects over ranges of conditions: temperatures from 1400° to 2400°K for electrodes, from 1600° to 2400°K for plasma atoms and ions, and from 1700° to 2700°K for plasma electrons; plasma-electron number densities from 1012 to 1015 cm−3; and work functions from 1.5 to 5 V. Sheath drops from 0 to 2.1.V and net currents from 0 to over 100 A cm−2 result. Over-all sheath characteristics correlate with work function minus plasma potential, plasma-electron concentration (Nep), electrode temperature (TE), and an emission Debye length λDE≈6.9(TE/Nep)1/2. Effective sheath widths range from 1.7 to 2.6 emission Debye lengths.
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