Surface potential of a photoemitting plate

Earlier work [Guernsey and Fu, 1970] studied the potential distribution in the neighborhood of a photoemitting plate immersed in plasma. The result indicates that two steady state potential distributions can exist, namely one in which the potential decreases from its plate value to zero monotonically and one in which it decreases from its plate value to a negative minimum and then increases to zero (‘overshoot’ type). In the present work a Maxwellian distribution is assumed for the emitting photoelectrons instead of a Fermi shape distribution. Furthermore the difference of the surface potential for these two types of distributions is investigated in more detail. The result shows that this difference can exist only if 1<Te/Tν<nν/ne, where Te, Tν, ne, nν, are the temperatures and number densities of plasma electrons and photoelectrons.