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，我们开发了一种用于圆极化同步辐射短周期波动器的新型磁路。环形同步辐射的波动器具有沿波动器轴线螺旋变化的磁场。为了产生这种类型的磁场，我们采用了纯磁体结构。由于波动器的周期很短（10-20mm），因此电子束通过的磁体阵列之间的间隙很短（约5mm），以实现足够强的磁场，因此需要将整个磁体阵列引入加速器的真空系统中，以便直接将波动器磁场应用于电子束。我们能够开发周期为20mm的圆极化磁路，在4mm间隙产生3500高斯，利用我们在建造40mm周期的真空型x射线波动器时获得的知识和技术知识，该x射线波动器安装在KEK，高能加速器研究组织的PF-AR中。为了准确有效地测量波动磁场，我们开发了一种采用小有效面积霍尔传感器的磁测量系统。我们还制作了一个翻转线圈式的磁测量系统，用于快速测量波动场的第一积分。在1999财年，我们开发了测量和调整短周期波动磁场的方法。在此过程中需要注意磁体阵列表面的清洁，并开发了适用于短周期真空波动器的方法。在波动场的布置过程中，我们调整了各极电子的踢脚量，使其方差减小到0.2%以内。通过本研究，我们发现在10-20mm的周期长度范围内可以实现短周期波动磁路。

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.