Averaging of Spontaneous Radiation in Relativistic Strophotron
  The main resonance frequency is shown to depend on the initial conditions of the electron, and in particular on its initial transversal coordinate xo. This dependence is shown to give rise to a very strong inhomogeneous broadening of the spectral lines. The broadening can become large enough for the spectral lines to overlap with each other. The spectral intensity of a spontaneous emission is averaged over xo. The averaged spectral intensity is shown to have only a very weakly expressed resonance structure. 
I.V. Dovgan
physics.acc-ph