Research on the compact design of bunching cavities for high modulation depth of intense-current relativistic electron beams

In order to overcome the bottleneck of improving the bunching depth of intense-current electron beams in klystron, this study proposes a design scheme of high bunching depth based on the staggered distribution of resonant cavity frequencies. By optimizing the high-frequency parameters and spatial configuration of the resonant cavities, the defects of limited modulation depth (typical value less than 120%) and long drift section in the traditional relativistic klystron bunching structure are solved. Under the condition of electron beam voltage of 420 kV, beam current of 8.5 kA, guiding magnetic field of 0.4 T, and 1.5% pre-modulation ratio, the scheme achieves 164.2% electron beams modulation depth over only three wavelength drift distances, which successfully verifies the feasibility of compact beam dynamics design. The compact bunching structure of the innovative frequency combination not only provides an effective way to break through the size limitation of the X-band GW-level high power devices but also has important technical support significance for the modular integrated development of the spatial power coherent combining system.