Influence of SWS Size on Mode Purification in an Overmoded Ka-Band Cerenkov Oscillator

摘要

Overmoded slow-wave structure (SWS) plays an important role in developing the performance of Cerenkov oscillators at the millimeter-wave range. To investigate the effect of SWS size on power capacity as well as the problem of mode competition, the properties of the resonance modes in an overmoded SWS are focused on. Based on the mode selection method of enhancing the field of TM01 and keeping the field of TM02 mode steady, the output results for SWSs with various sizes are studied. Consequently, the size of SWS is reasonably determined, which can provide an effective beam-wave interaction process and the purified output mode. Moreover, the study on electron's movement in the diode area under the magnetic field of 0.8 T is conducted and then the value of the overmoded ratio alpha is finally confirmed as 2.5 to guarantee a lossless transportation of the electron beam. Verified by the particle-in-cell (PIC) simulations, the optimized structure shows a good capability of improving the output power and purifying the output mode.