Simulation on suppression of virtual cathode effects in collector of L-band multibeams klystron

Virtual cathode in collector of multibeam klystron (MBK) is formed when the electron beam current exceeds the space charge limited current. Then the electron-beams return the drift tubes of output cavity causing device performance deterioration as stated in W. Jiang et al. (2005). A number of collector designs have been developed in this paper to eliminate this nuisance. Virtual cathode effects were simulated with PIC (Particle in Cell) software. The results show that setting bottleneck and thin slot structures at the port of a collector are beneficial to restrain the formation of virtual cathode.