Waves in Electron Streams and Circuits

Waves in Electron Streams and Circuits Of recent years, a good deal of work has appeared concerning small linear perturbations of uniform clouds of electrons and ions.* A number of questions can be raised concerning the physical interpretations of such mathematical labors. First of all, for there to be a very direct physical interpretation, the unperturbed state must exist at some time or place and then be modified in the manner described by the perturbation. This condition is satisfied, for instance, in the case of an electron stream of moderate current shot into a long metal tube and confined by a longitudinal magnetic field. However, if the current is made large enough, the uniform flow becomes unstable and the method of perturbations can be used only to establish such instability and not to determine what form the flow will assume. I feel some misgivings about drawing physical interpretations from perturbations of uniform d-c. plasmas and infinitely extending clouds of charge unless these unperturbed states can be shown to exist physically, or unless the results can be shown 1-4 5,6