对比研究了真空管道中环形电子束与位于束团中心的实心束在管道壁上产生的场分布，证明束流位置探测(BPM)技术可用于电流密度均匀分布的环形电子束位置测量。采用点密度不均匀性模型，分析了环形电子束角向不均匀性对测量精确度的影响。结果显示，当环形电子束电流密度不均匀性为 10%时，对位置分辨率精确度的影响为 0.1 mm。初步开展了 BPM系统设计，并对纽扣电极半径和输出端口半径进行了优化设计。

The electric field on the wall of a circular chamber produced by an annular beam is compared with that of a pencil beam located at the same axes. It is proved that Beam Position Monitor (BPM) system can be used for position measurement of annular beams. Taking a single-point non-uniform model, the influence of the azimuthally non-uniformity on measurement accuracy is analyzed. And it is revealed that 10% single-point non-uniformity caused a 0.1 mm measurement deviation. A BPM system is preliminarily designed, and the radius of the button electrode as well as the radius of the output port is optimized.