Shigemi Sasaki

Design and performance of the APPLE-Knot undulator

The design and performance of the Apple-Knot undulator which can generate photons with arbitrary polarization and low on-axis heat load are presented.

HiSOR-II, Compact light source with a torus-knot type accumulator ring

We are designing a new ring based on the shape of a (11, 3) torus knot for our future plan HiSOR-II. This ring has eleven 3.6-m-long straight sections though the ring diameter is as compact as 15 m. The emittance reaches down to 20 nmrad with the lattice having bending magnets with combined function. This level of emittance is as low as the conventional compact 3rd generation light source. On the other hand, there are a few potential problems. One of them is that the orbit radius varies in a bending magnet and hence the focusing force are not constant. However, precise calculations by dividing a bending into several sections show that it does not make serious influence to the stored beam. Detailed parameters survey of this ring and estimation of performance confirmed that this new scheme may plausible as a synchrotron light source ring.

Generation of vector beam with tandem helical undulators

We propose a scheme to produce structured light in synchrotron light sources. In this scheme, light beams from two undulators are superposed by using a technique akin to the “cross undulator.” We demonstrate that a vector beam, in which the polarization direction varies with the azimuthal angle about the beam axis, is produced by superposing harmonic radiation from two helical undulators in tandem. Although this scheme is demonstrated in the ultraviolet range at the low-energy synchrotron UVSOR-III, it can be applied to high-energy synchrotrons to produce vector x-ray beams, which would open a new field in the application of synchrotron radiation.We propose a scheme to produce structured light in synchrotron light sources. In this scheme, light beams from two undulators are superposed by using a technique akin to the “cross undulator.” We demonstrate that a vector beam, in which the polarization direction varies with the azimuthal angle about the beam axis, is produced by superposing harmonic radiation from two helical undulators in tandem. Although this scheme is demonstrated in the ultraviolet range at the low-energy synchrotron UVSOR-III, it can be applied to high-energy synchrotrons to produce vector x-ray beams, which would open a new field in the application of synchrotron radiation.

Quasi-Periodic Variably Polarizing Undulator at HiSOR

A 1.8-m-long 78-mm-period quasi-periodic APLPE-II undulator was installed in the 700-MeV HiSOR storage ring of Hiroshima Synchrotron Radiation Center. At the minimum gap, achievable lowest photon energies are 3.1 eV, 6.5 eV, and 4.8 eV for horizontal linear, vertical linear, and circular polarization, respectively. Observed photon energies of fundamental and higher harmonic radiations are in good agreement with those of model calculations using measured magnetic field of undulator and the HiSOR beam parameters. Also, observed flux through a slit and a grating monochromator was more than twice larger than that from previously installed 100-mm-period helical undulator for the whole range of radiation spectra. The feedforward COD correction was done to avoid the intensity fluctuation of photon beam in other beamlines due to the gap and phase motion of undulator. No fatal effect on the stored electron beam by installing the undulator was observed though a slight beam size change was observed at the minimum gap.