Development of an insertion device selectively operational as a helical/figure-8 undulator

An insertion device capable of switching the operation mode between helical and figure-8 undulators, and thus referred to as a helical-8 undulator, has been developed. It has the advantage that the on-axis heat load can be kept low regardless of the polarization state, even when a high K value is required to lower the fundamental photon energy. This is in contrast to conventional undulators in which the on-axis heat load tends to be significantly high to generate linearly polarized radiation with a high K value, and optical elements can be seriously damaged. The principle of operation, specification and light source performance of the developed helical-8 undulator are presented together with further options to enhance its capability.

Demonstration of high-performance pole pieces made of monocrystalline dysprosium for short-period undulators

Reported here are the results of experiments carried out to demonstrate the magnetic performance of dysprosium (Dy) to enhance the capability of undulators. Tiny pieces of monocrystalline Dy surrounded by permanent magnets (PMs) work as pole pieces (PPs) to concentrate the magnetic flux, when cooled down below the Curie temperature of 85 K. A PP made of Dy is much more attractive than one made of a conventional material, because its saturation magnetization is much higher. Furthermore, it also allows for a more flexible selection of PM material, potentially leading to further enhancement of the performance of short-period undulators. Besides these advantages, practical issues related to using Dy PPs and countermeasures against them are discussed.

Lightweight-compact variable-gap undulator with force cancellation system based on multipole monolithic magnets

A lightweight-compact variable-gap undulator (LCVGU) having the force-cancellation system based on the multipole monolithic magnets (MMMs) has been developed. The LCVGU is free from the heavy mechanical frames, which is a fundamental element specific to conventional variable-gap undulators (VGUs) because of a strong attractive force, and thus the cost and time for construction and installation are expected to be significantly reduced; the MMMs counteract the strong attractive force in a cost-effective manner. Results of mechanical tests and magnetic-field measurements of two prototype LCVGUs equipped with the proposed force cancellation system have revealed the comparable performance with the conventional VGUs.