BL25SU

◆Outline of beamline

The BL25SU has two branched beamlines, called the micro-beam branch (branch A) and the nano-beam branch (branch B), respectively. The nano-beam branch is mainly dedicated for the Elements Strategy Initiative project of Ministry of Education, Culture, Sports, Science and Technology, but is partly used for other experiments.
The BL25SU beamline is designed for research elucidating electronic and magnetic states, and the surface structure of solids. The light source is twin-helical undulators composed of a pair of helical undulators (1.5 m-length for each) which selectively produce right- or left-hand circularly polarized soft X-ray beams. The helicity of the circular polarization can be switched periodically (0.1, 1 and 10 Hz modes are available now), using a kicker magnet system. Either branch A or branch B is used at any one time by switching pre-focusing mirrors. In the A-branch, Retarding field analyzer (RFA) and a photoemission electron spectroscopy (PES) device are located at the end-station, and high energy resolution (E/ΔE > 10000@1 keV) soft X-rays in the range 0.12～2 keV can be used. In B-branch, on the other hand, high flux beams (0.2 ~ 2 keV, 1012photons/s, E/ΔE > 3000@1 keV) are utilized for the X-ray magnetic circular dichroism (XMCD) measurements. The nano-beam XMCD apparatus is newly installed at the end-station of B-branch, where the Elements Strategy Initiative Center for Magnetic Materials (ESICMM) project is conducted. At the nano-beam XMCD apparatus, the soft X-ray beam is focused to < φ100 nm using a Fresnel Zone Plate lens. All the experiments are performed under ultra-high vacuum (10^-8 ~ 10^-7 Pa) conditions. Radioisotope (RI) elements and reactive gases cannot be used in this beamline.

IMPORTANT

Due to a trouble in the twin helical undulators, either of the undulators is temporally operated until the repairment is completed. Ask the beamline scientist for details.

◆Research field

A-branch
・Research on electronic states and band structures by photoemission spectroscopy (PES) and angle-resolved photoemission spectroscopy (ARPES)
・Analysis of atomic arrangements by photoelectron diffraction (PED)
B-branch
・Research on element-specific magnetic states by X-ray magnetic circular dichroism (XMCD), analysis of magnetic states using soft X-ray nano-beam

◆Light source and optical system

・Light Source
The light source “twin helical undulators (THU)” is designed for helicity switching of circularly polarized X-rays. THU consists of two helical undulators and five kicker magnets. The kicker magnets are used to generate bumped electron orbits at the undulators. For
example, when a bump orbit is formed at the first undulator (ID1, ID: insertion device), the synchrotron radiation (SR) generated at ID1 is deflected out of axis and that at ID2 is exclusively introduced to the beamline. The helicity of the circular polarization can promptly be switched by changing the generating position of the bump orbit between ID1 and 2. Three periodical switching modes, 0.1 Hz (trapezoidal waves), 1 Hz (trapezoidal waves) and 10 Hz (sine waves), are available in this beamline. This helicity switching system is often utilized in PED and XMCD.

・Beamline
The synchrotron light is exclusively introduced to either A- or B-branch at the uppermost stream in a shielded optics hutch, by moving a mirror stage equipped with vertical focusing mirrors (M0a, M0b).
The synchrotron light is horizontally focused by a mechanical bent mirror (M1*) and then monochromatized by a spherical mirror (M21 or M22) and a varied-line-spacing plane grating (G). According to the experimental purpose, the available energy range can be selected by choosing the particular combination of M2 and G. The entire optics is designed to obtain high energy resolution (E/ΔE> 10000@1 keV) in the A-branch and high photon flux (〜1012 photons/sec) in the B-branch. The synchrotron light beam is kept horizontal (A-branch: ~1532 mm-height, B-branch: ~1344 mm) after being extracted from a planation mirror (MFa, A-branch) or the grating (Gb, B-branch). The beam is refocused by post-focusing mirrors (M31~33 and M41~43) installed just in front of each apparatus. In the A-branch, RFA and PES apparatuses are installed. The B-branch is aimed at the research using XMCD and pulse-magnet XMCD, electro-magnet XMCD and nano-XMCD. Typical beam sizes on the experimental samples are ten 〜 one-hundred microns in the A-branch, several-ten 〜 -hundred microns in the B-branch (except for the nano-XMCD station). In the nano-XMCD station, the beam is focused down to <φ100 nm, using a Fresnel zone plate. (Note that the beam sizes may vary depending on settings of the optical components).

* In the figure below, an index “a” or “b” is added for the names of optical components to show the belonging beam branch.

◆Contact

*For e-mail addresses, add "@spring8.or.jp." after the accounts.

Yoshinori KOTANI
SPring-8 / JASRI
1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198
Phone : +81-(0)791-58-0833
Fax : +81-(0)791-58-0830
e-mail : ykotani

Takayuki MURO
SPring-8 / JASRI
1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198
Phone : +81-(0)791-58-0833
Fax : +81-(0)791-58-0830
e-mail : muro

Takuo OHKOCHI
SPring-8 / JASRI
1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198
Phone : +81-(0)791-58-0833
Fax : +81-(0)791-58-0830
e-mail : o-taku

Hitoshi OSAWA
SPring-8 / JASRI
1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198
Phone : +81-(0)791-58-0833
Fax : +81-(0)791-58-0830
e-mail : hitoshio