Development of Beam Position Monitor Using HOM Coupler

用连接在JAEA ERL-FEL超导直线加速器上的HOM耦合器研制了束流位置监测器。设计并制作了一个移位磁铁来控制电子束的位置。利用三维电磁场分析软件MAFIA计算束流轨迹。移位磁铁安装在第一个主加速器的上游。通过改变移位器磁铁电流来测量HOM功率，发现HOM功率由束流位置的平方(初始束流位置和束流漂移与移位磁流成正比)和束流位置起伏的平方之和表示。用解析公式对测量的HOM功率和移位器磁流进行了拟合，估计了束流位置和束流位置的起伏。据估计，JAEA ERL-FEL在水平和垂直方向上的光束偏移量分别为0.23 mm和-0.31 mm，位置波动分别为0.21 mm和0.60 mm。当光束位置波动时，即使光束通过轴线，霍姆功率也不为零。扫描波束位置可以精确估计波束位置和波束位置起伏。

Abeam position monitor was developed using HOM coupler attached to JAEA ERL-FEL, superconducting linac. A shifter magnet was designed and made to control the electron beam position. Analysis of electro-magnetic field with 3D code MAFIA was used to calculate the beam trajectory. The shifter magnet was installed at the upstream of the first main accelerator. HOM power was measured by changing the shifter magnet current The HOM power was found to be represented by the sum of the square of beam position (sum of the initial beam position and beam shift proportional to shifter magnet current) and the square of the beam position fluctuation. The measured HOM powers and shifter magnet currents were fitted with the analytic formula to estimate the beam position and beam position fluctuation. JAEA ERL-FEL was estimated to have the beam offset of 0.23 mm and -0.31mm and the beam position fluctuation of 0.21 mm and 0.60 mm in horizontal and vertical reprehensively. When the beam position fluctuates, HOM power is not zero even if the beam passes through the axis. Scanning the beam position enable to estimate the beam position and the beam position fluctuation precisely.