Halo formation in high-power klystrons

Summary form only given. Beam losses and radio-frequency (RF) pulse shortening are important issues in the development of high-power microwave (HPM) sources such as high-power klystrons and relativistic magnetrons. In this paper, we explore the formation and characteristics of halos around intense relativistic electron beams in a periodic permanent magnet focusing klystron as well as in a uniform solenoidal focusing klystron. A self-consistent electrostatic model is used to investigate intense relativistic electron beam transport as an RF field induced mismatch between the electron beam and the focusing field develops, To model the effect of such mismatch in the PPM klystron experiment, we initialize the beam with an envelope mismatch. For zero canonical angular momentum and an initial mismatch of 100 percent, for example, our preliminary results show halo particles with a maximum radius extending up to several core radii at the RF output section. Transient effects and the influence of finite canonical angular momentum are being studied.