速调管离子噪声特性的模拟分析

Simulation of ion noise character in klystron

离子噪声已成为影响现代微波管性能的一个重要因素,采用一维混合模型研究了速调管的离子噪声,用自编的1维粒子模拟程序对速调管的离子噪声特性进行了分析。采用小信号近似,从理论上推导出了速调管离子噪声与相位畸变关系的表达式,表明微波管相位噪声直接来源于管内离子量的变化。模拟了有离子噪声时速调管的相位特性,对模拟过程做了离子诊断并与实验结果进行比较,证明了模拟过程的正确性。探讨了电子束电流、电压以及聚焦磁场对离子噪声的影响规律,束电流与束电压改变后,离子噪声的周期与大小相应改变,增大束电流,离子噪声幅度会下降,并趋于稳定,而在束电流不变的情况下,离子噪声存在一个最小值。束电流与束电压确定,存在最佳的磁场使离子噪声幅度最小。

Characteristics of ion noise in a klystron was discussed by using a hybrid model. One-dimensional particle-in-Cell method (PIC) simulation code is developed and the relation between ion noise and phase distortion was obtained. The characteristics of the ion noise in a klystron are treated as an example to be analyzed by this PIC code and the diagnosis of ion current on cathode was made. The numerical simulation results accord with measured values very well. When the beam current increases, the ion noise amplitude will decrease and become stable. There exists on optimal value of magnetic focusing field and beam voltage, which can minimize the ion noise amplitude.