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，我们开发了一种新的磁路短周期波荡器的圆偏振同步辐射。用于圆形同步辐射的波荡器具有沿波荡器的轴沿着螺旋变化的磁场。我们采用了纯型磁铁配置，以开发这种类型的磁场。由于波荡器的非常短的周期（10- 20 mm）需要在磁体阵列之间的非常短的间隙（大约5 mm），电子束在磁体阵列之间穿过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，以将波荡器磁场直接施加到电子束。利用我们在KEK高能加速器研究所PF-AR上建造40 mm周期的真空型X射线波荡器时获得的知识和技术诀窍，我们能够开发出20 mm周期的圆偏振磁路，在4 mm间隙产生3500高斯。为了准确有效地测量波荡器磁场，我们研制了一种使用霍尔传感器的磁测量系统。此外，为了快速测定波荡器磁场的一阶积分，制作了翻转线圈型的磁场测定装置。1999年度，开发了短周期波荡器磁场的测定和调谐方法。在此过程中需要注意磁体阵列表面的清洁度，并发展了适用于短周期真空波荡器的方法。在波荡器场的排列过程中，我们调整了对各极电子的反冲量，使它们的方差小于0.2%。通过本研究，我们发现短周期波荡器磁路可以在10- 20 mm的周期长度范围内实现。

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.