Development of a magnetic circuit for a short period undulator for the production of quasi-monochromatic hard x-rays

在1998财政年度，我们为圆偏振同步辐射短周期波荡器研制了一种新的磁路。用于圆形同步辐射的波动器具有沿波动器的轴线螺旋变化的磁场。为了开发这种类型的磁场，我们采用了纯型磁体配置。由于波荡器的周期很短(10-20 mm)，为了实现足够强的磁场，磁体阵列之间需要很短的间隙(约5 mm)，因此需要将整个磁体阵列引入加速器的真空系统中，以便直接向电子束施加波动器磁场。我们利用在高能加速器研究机构KEK的PF-AR中建造40 mm周期的真空型X射线波荡器所获得的知识和技术诀窍，研制出了20 mm周期的圆极化磁路，在4 mm间隙产生3500高斯。为了准确、高效地测量波荡器磁场，我们开发了一种使用小有源区霍尔传感器的磁测量系统。我们还研制了一个翻转线圈式的磁测量系统，用于快速测量波动器场的第一积分。1999财年，我们开发了测量和调谐短周期波动器场的方法。在这一过程中，我们需要注意磁体阵列表面的清洁度，并开发出适用于短周期在真空波动器的方法。在波动器场的排列过程中，我们调整了每个极点的电子踢出量，使它们的方差减小到0.2%以下。研究表明，在周期长度为10-20 mm的范围内，可以实现短周期的波荡器磁路。

In the fiscal year 1998, we developed a new magnetic circuit for the short period undulator for circularly polarized synchrotron radiation. The undulator for the circularly synchrotron radiation has a magnetic field which varies helically along the axis of the undulator. We adopted a pure-type magnet configuration in order to develop this type of magnetic field. Since the very short periods (10-20mm) of the undulator require very short gaps (around 5mm) between magnet arrays between which an electron beam pass through for realizing adequately strong magnetic fields, the entire magnet arrays need to be introduced into the vacuum system of an accelerator, for direct application of undulator magnetic field to the electron beam. We were able to develop the circularly polarizing magnetic circuit with the 20mm period to produce 3500Gauss at 4mm gap by utilizing knowledge and technical know-hows which we obtained when we constructed the in-vacuum type x-ray undulator with the 40mm period which was installed in the PF-AR at KEK, High Energy Accelerator Research Organization.For an accurate and efficient measurements of the undulator magnetic field, we developed a magnetic measurement system which used Hall sensors with a small active areas. We also fabricated a flipping-coil type magnetic measurement system for quick measurement of the first integrals of the undulator field.In the fiscal year 1999, we developed methods for measuring and tuning the undulator magnetic field having short periods. In this process we need to pay attention to cleanness of the surface of the magnet arrays, and developed the methods which were applicable to the short period in-vacuum undulator. In the arrangement process of the undulator field, we adjusted kick amount given to the electron at each pole and reduced their variance less than 0.2%. By the present study, we showed that short-period undulator magnetic circuit can be realized in the region of 10-20mm period length.