The effect of the electron-beam parameter spread on microwave generation   in a three-cavity axial vircator
  The behavior of the generation efficiency and radiation spectrum of a three-cavity axial vircator versus the radius of the injected electron beam, its impedance and energy homogeneity is studied. This paper establishes that for each geometry of a three-cavity resonator, there exist the optimal (maximizing the generation efficiency) values of these parameters and determines the range within which they may vary without losing the efficiency of generation. 
E.A. Gurnevich, P.V. Molchanov
physics.acc-ph nlin.CD physics.comp-ph physics.plasm-ph