Scattering in backward wave oscillators from turbulent electric fields

Abstract

Relativistic electrons resonating in microwave-emitting slow-wave structures can scatter from background turbulence. We calculate the expected scattering rate from strong fields characterized by a single mean correlation length. Comparison with recent data from a backward wave oscillator, using the measured magnitude of E-fields, shows agreement with the magnitude of outward scattering. The implied correlation lengths then explain why gas ionization in the same oscillator does not proceed exponentially, as earlier work showed was expected but not observed. Plasma electrons scattered over the correlation length cannot gain the necessary energy to ionize many gas atoms. These results suggest that inadvertently produced plasmas may have a quick, decisive effect on beam geometry, ending microwave emission prematurely.