采用混合模型研究了周期永磁聚焦行波管中的离子噪声，编写了一维粒子模拟程序，并对行波管的离子噪声特性进行了分析；计算表明相同气压下，周期永磁聚焦离子噪声的频率比均匀聚焦要低，且频谱有所展宽；提出改善电子束匹配条件是降低离子噪声的有效方法。关 键 词 离子噪声; 行波管; 静电势阱; 粒子模拟Abstract Characteristics of ion noise in a traveling wave tube (TWT) focused by periodic permanent magnets (PPM) have been discussed by means of a hybrid model. One dimension Particle-in-Cell method (PIC) simulation code is developed. Compare to uniform magnetic field focus system the noise frequency is lower and the spectrum is wider by the PPM focus system. From the analysis results we find decreasing the axial electrostatic potential well would reduce this noise.Key words ion noise; traveling wave tube; electrostatic potential well; particle-in-cell