BL13U (Beamline Group)

Several endstations are ready for users at BL13U, depending on the target measurements.

μ-XMCD station

This station is designed for microscopic X-ray Magnetic Circular Dichroism (XMCD) and Linear Dichroism (XMLD) measurements under ultra high vacuum. Focused bean smaller than 3 μm is available at this station. Several probes (electron, photon, etc.) can be used to measure x-ray absorption. Operando measurement to apply voltage to the sample is also feasible.

Typical data taken at this endstation.

Right) Magnetic domains of a SmCo5 magnet (dark and white area).

※ Sample is provided by S. Li, S. Sakai and T. Ueno (QST)

Left) XAS difference measured with circularly polarized beams at each domain (XMCD)

Flag-style sample plate.

Typically 10×10 mm² (thickness < 2 mm) sample can be mounted.

Free ports

BL13U has free ports without any endstations. These ports are available for users who are planning to bring their own experimental setup. At the free ports, both the focused beam down to ~30 μm and unfocused beam whose footprint is ~ 3 mm are available.
Some instrumentations designed to use this free port are available for general users. Please find details here (in Japanese).

An user-brought instrument to measure X-ray ferromagnetic resonance (XFMR)

(A photo courtesy of T. Ueno, QST)

Nano XAS station (under construction)

This station is dedicated to ultimate spatial resolution for XAS measurements. Fresnel zone plates are used to achieve the spatial resolution better than 10 nm. This endstation is under construction and hopefully open for users in few years.

This unique insertion device consists of a series of 4 short undulator segments and 3 electromagnetic phase shifters between each segment. Each undulator segment has the APPLE-II type magnet configuration, providing the beam with linear horizontal (LH), linear vertical (LV), and circular (C) polarizations. The phase shifters tune the interfere condition of photons from each undulator segment and thus control the polarization of the exit beam [3, 4].

The segmented undulator provides wide range of energy with a variety of polarizations. The mixture of the left- and right-handed circular polarization results in the linear polarization with its electric field vector tunable to any orientations perpendicular to the beam axis, not limited to the horizontal and vertical directions. The interference between LH and LV is circular polarization. Since one can use the 3^rd harmonics of the synchrotron radiation from each segment, wider energy range of circularly polarized beam is available at BL13U, comparing to the ordinal (non-segmented) APPLE-II-type undulators.

Practical performance of the segmented undulator is in commissioning [6]. This photon source becomes available for general users, hopefully soon.

(left) A picture of the segmented undulator at BL13U

(right) A schematic drawing of the segmented undulator

(left) Simulated spatial distributions of flux density and polarization of the synchrotron radiation beam from the segmented undulator. The 1st and 3rd (2nd and 4th) undulators are set to provide LH (LV) polarized beams.

(right) Simulated energy spectrum and circular polarization integrated in the dashed square in the left.

This simulation is performed by SPECTRA [5] and the figures above are from ref. [2].

References:
[3] T. Tanaka, Phys. Rev. Accel. Beams 17, 060702 (2014).
[4] I. Matsuda et al., e-JSSNT 17, 41 (2019).
[5] T. Tanaka, J. Synchrotron Rad. 28, 1267 (2021).
[6] K. Inaba, Y. Ohtsubo et al., in preparation

The beamline optics is schematically depicted below. The varied-line-spacing plage grating (600 lines/mm) together with the pre-focus cylindrical mirror optics focuses the monochromatized beam on the exit slit (S2).

Detailed explanation and performance is shown in the references [1, 2].

Figure: Schematic diagram of the optical path and beam envelope of BL13U, reproduced from ref. [2].

* The data above is from ref. [1]