多重电子超越现象对高功率注入大间隙速调管中束流群聚特性的影响

Influences of the multiple electron overtaking on the bunching process of the wide-gap klystron amplifier under high power injection condition

当注入功率较高时,大间隙速调管输入腔的基频电流分布中,除常规意义上的最佳群聚电流峰值(第一峰值电流)外,出现了与第一峰值电流幅值相当的第二峰值电流.结合群聚理论和粒子模拟结果,研究和讨论了第二峰值电流产生的机理.研究结果表明,第二峰值电流的出现由高电压调制系数下出现的多重电子超越效应造成.当二极管电压600kV,束流5kA,工作频率3.6GHz时,利用多重超越效应可在保持最佳群聚距离基本不变的前提下,把大间隙速调管的束流群聚深度由80%提高到92%,群聚束流的基频功率也从2.2GW提高到2.8GW,增幅约27%.

Under the high power injection condition of the wide-gap klystron amplifier （WKA）, a second peak current appears besides the conventional optimally bunching current （or the first peak current） in the distribution of the fundamental integral current. Considering the electron bunching theory and the Particle-in-cell （PIC） simulation results together, the formation mechanism of the second peak current is discussed. The results indicate that the second peak current has a close relation with the electron multiple-overtaking phenomenon in the case of high voltage modulation coefficient. When the diode voltage is 600 kV, beam current is 5 kA and working frequency is 3.6 GHz, the beam modulation depth of the WKA is enhanced to 92% from 80% according to the multiple-overtaking mechanism. Simultaneously, the bunching current power is improved from 2.2 GW to 2.8 GW, and a 27 percent increment is obtained.