Exploratory Study on High-Efficiency High-Power W-Band Klystron Based on Kladistron Technology

To achieve tens of kilowatt (kW) output power, ${W}$ -band klystron usually employs a large beam tunnel to accommodate high current. The deteriorated effective impedance of the cavity could be reenhanced by adopting extended interaction (EI) cavities. In this article, a new approach utilizing simple fundamental modes in cascaded single-gap cavities for ${W}$ -band klystron is proposed and discussed. Although the effective impedance of each cavity is far lower than its EI klystron (EIK) counterpart, this disadvantage could be efficiently compensated by densely populating those single-gap cavities using the kladistron technology previously conceived for the ${C}$ - or ${X}$ -band high-efficiency (HE) klystrons. However, kladistron is rarely reported and normally regarded as less a promising HE bunching technique overwhelmed by the self-excitation issues caused by adjacent mode coupling. Fortunately, such instability could be naturally suppressed in a higher frequency regime, so further exploration of kladistron technology is intriguing. In this article, an exemplary 30-kW ${W}$ -band klystron equipped with big circular beam tunnel is designed using the kladistron technology, which finally shows no instability issues in 3-D particle-in-cell (PIC) simulation. This novel device delivers up to 37% electronic efficiency and 24% RF efficiency, validating that the kladistron concept is well suited for this millimeter-wave amplifier, which indicates possible HE substitutes for existing EIK technology.