一.引言稀土合金(特别是钐钴)用于大功率行波管的周期性磁聚焦得到了两个重大改进。首先,由于这类磁性材料能获得高矫顽力和高磁能积,在固定的电子注电压和输出功率情况下,所要求的磁性材料体积小得多。其次,在给定 I. INTRODUCTION Two major improvements have been made in the periodic magnetic focusing of rare-earth alloys (especially samarium-cobalt) for high-power traveling wave tubes. First, due to the high coercivity and high energy product of such magnetic materials, the required magnetic material is much smaller in volume with a fixed electron injection voltage and output power. Second, given