Yoshikazu Miyahara

Soft X-ray Beamline Specialized for Actinides and Radioactive Materials Equipped with a Variably Polarizing Undulator

This report presents the design of an undulator beamline at SPring-8 to be used for soft X-ray spectroscopy focused on radioactive materials. Photoemission spectroscopy experiments are carried out in a radioisotope (RI)-controlled area where actinide compounds as well as unsealed radioactive materials are usable. Intrusion of the radioactive materials into the electron storage ring or to the outside of the evacuated beamline components can be avoided by a specially devised RI protection/inspection mechanism. The combination of a variably polarizing undulator and a varied-line-spacing plane-grating monochromator provides linearly or circularly polarized soft X-rays with a high resolving power in the energy range 0.28-1.5 keV. The beamline will become operational in December 1997.

Design of a new type of planar undulator for generating variably polarized radiation

Abstract A small prototype model of a new undulator is under construction for generating variably polarized radiation. This undulator consists of two pairs of planar permanent magnet arrays above and below the electron orbit plane in a storage ring. This device has no magnetic structures in the horizontal orbit plane in order to avoid the conflict with the aperture of the electron orbit. The on-axis magnetic field generated by shifting the relative position of pairs of magnet arrays in this device induces helical and sinusoidal electron orbit motions. It leads to the generation of circularly and linearly polarized undulator radiation. This new undulator will be installed in the JAERI storage ring (JSR) in order to examine the performance for generating variable polarization.

First operation of circular dichroism measurements with periodic photon-helicity switching by a variably polarizing undulator at BL23SU at SPring-8

This article presents the first operation of the magnetic circular dichroism (MCD) measurement system with periodic photon-helicity switching. The measurements were performed at the newly constructed soft x-ray beamline—BL23SU— at the third-generation synchrotron radiation facility, SPring-8. The monochromator control system was synchronized to the movement of the magnetic row (phase shift) of an APPLE-2 (Sasaki) type variably polarizing undulator. The periodic phase shift of the undulator provided the switching of helicity polarizing soft x rays up to 0.1 Hz. The closed-orbit distortion of the storage ring was controlled to avoid optical axis disturbances at this beamline as well as at other beamlines. The circular dichroism spectra with helicity switching by APPLE-2 show the possibility of high-sensitivity MCD measurements. This method promotes precise MCD measurements and can be a powerful technique to study magnetism as well as dichroism.

First observation of undulator radiation from APPLE-1

Abstract Various polarized radiation was observed in the visible region generated by the new type undulator APPLE-1 (Advanced Planar Polarized Light Emitted - 1). The undulator was installed in the low energy electron storage ring JSR and we have succeeded in observing linearly polarized radiation in both planes and circularly polarized radiation with the aid of a Wollaston prism. During the process of shifting the arrays and changing the undulator gap, no noticeable change of radiation axis was observed.

CONCEPTUAL DESIGN OF QUASIPERIODIC UNDULATOR

A new type of undulator which suppresses the rational harmonics is considered. This undulator consists of quasiperiodic arrays of magnet blocks and generates irrational harmonics which can be eliminated by the conventional crystal monochromators. The radiation power emitted from this undulator and the width of each radiation peak are comparable with that of the conventional periodic undulator of the same periods.

Design of a local bump feedback system for a variably polarizing undulator.

A local bump feedback system is under construction to correct the orbit distortion caused by the magnetic field errors of a double-array undulator used to generate linear and circular polarization of light for a soft X-ray beamline. The local bump orbit is created by steering coils several turns long and four sets of steering magnets. The kick angle of the long steering coils and the steering magnets is determined according to the motion of the undulator and by detecting the beam position.

Synchronous beam diagnostic system using cordless telephones at SPring-8

Abstract Recently, we have developed a synchronous SR beam position diagnostic system. In this system, more than one X-ray beam position monitor is used synchronously and an oscillation of the SR beam position all through the storage ring can be detected. For an example, during the high speed driving of the insertion device, beam oscillation and shift can be simultaneously observed at different beamlines. To start the measurements simultaneously at the different beamlines, a trigger signal was conveyed by a cordless telephone. This paper describes the system and performance tests of it.