BIOXAS Spectroscopy

Overview

The 07ID-2 sector, served by one insertion device (wiggler), comprises two beamlines, (1) a central beamline (07ID-2M) on the wiggler axis and (2) a side beamline (07ID-2S) with a 5 mrad separation from the central line. The source of X-rays on 07ID-2 is a "flat-top" permanent magnet wiggler inserted into the storage ring. As its name suggests, the wiggler produces a periodic magnetic field that causes the path of the orbiting electrons to wiggle, resulting in an emitted X-ray beam of higher spectral brilliance than could be produced by the simpler path taken by the electrons through a bending magnet. The "flat-top" design ensures that the maximum critical energy in the side beamline will be more than 90% of the maximum critical energy in the central beamline.

Technical Specifications

In a rush? These are the beamline specifications. More detailed information can be found in the next sections.

Side-bl

Main-bl

Status

Open

Supported Techniques

X-ray Absorption Spectroscopy (XANES, XRF, EXAFS)

Common Scientific Disciplines

Bioscience
Material Science
Environmental Science
Geology

Source

22-poles (11-periods), 2.1 Tesla, Flat-top Wiggler

Energy Range	Resolution DE/E	Spot Size	Flux-Main BL	Flux-Side BL
5-32 keV	1 x 10^-4	3 mm x 0.5 mm (W x H) @ 12 keV	1 x 10¹² @ 12 keV	1 x 10¹¹ @ 12 keV

Optics

M1 mirror: Toroidal, 1 m, Si, Rh-coated, Sagittal radius: 33 mm. Water-cooled.

Monochromator: LN₂ cooled, Si(220), ϕ = 0^o & 90^o, double-crystal, non-fixed exit slit (see mono gitch database)

M2 mirror: Flat Bent, vertically focusing, 1.1 m. Si, Rh-coated

For energies below 10 keV, double-bounce harmonics-rejection mirrors (C-coated Si)

M1 mirror: Toroidal, 1 m, Si, Rh-coated, Sagittal radius: 70 mm. Water-cooled.

Monochromator: LN₂ cooled, Si(220), ϕ = 0^o & 90^o, double-crystal, non-fixed exit slit (see mono glitch database)

M2 mirror: Toroidal, focussing, 1.1 m. Si, Rh-coated. Sagittal radius: 35 mm.

For energies below 10 keV, double-bounce harmonics-rejection mirrors (C-coated Si)

Instrumentation

Detectors: Ionization chambers, PIPS, Canberra 2 x 32-element HPGe solid-state (Main BL) and 32-element HPGe (Side BL).

Cryostat: Oxford Helium cryostat, cooled by liquid He Dewar (min. temp 10 K), or liquid Nitrogen Dewar (min. temp 80 k).

Other: Shutter and beam-attenuation filters to alleviate beam damage. Soller slits and fluorescence filters to limit scatter radiation in fluorescence mode.

Sample environment

Single and up to 4 sample holders for room temperature measurements. Single and up to 3 sample holders for low-temperature measurements. (see Available Sample Environments and Holders)

Cryostat temperatures listed under Instrumentation.

Typical sample dimensions, anything bigger than 5 x 1 mm will work, ideally 7 x 3 mm at least, but not too much bigger. Maximum size for samples to be placed in the cryostat 15 x 5 mm. See

Data Acquisition and Analysis

GUI based Data Acquisition Manager Software (AcquaMan) and Python Based Automation Package (cls_bxs_control).

Automatic scan queuing available for multiple samples and/or multiple spots on the same sample.

Athena, Viper, and Larch for data analysis.

In what remains, given their similarity, we'll only explain one of the beamlines, mentioning the differences when required.

Optical Design Overview

The image below shows the optical design and ray-tracing simulation of the Side Beamline aligned for 10 keV (the figure doesn't show the Ion chamber, nor the other radiation detectors, but they are detailed in later sections).

The figure was generated with XRT, which already includes a model for BioXAS-Main in the examples. More details about the figure can be found at https://aip.scitation.org/doi/abs/10.1063/1.5084640.

From left to right, both beamlines have:

A wiggler as the source of x-ray.
A fixed mask to let a fraction of the wiggler output reach the beamline optics.
A first collimating toroidal mirror M1. It collimates the beam vertically and focuses it horizontally.
A double crystal monochromator with Si 220 crystals.
A second, focusing, mirror M2.
A set of Double-Bounce Harmonic Rejection Mirrors (used for some energies, and not shown in the figure).
A set of vertical and horizontal slits in front of the sample.
The sample plane, where the sample is illuminated by the beam.

The detectors, which are not shown in the picture, are detailed in a later section

Installations overview

The images below show the most important areas of both beamlines (click any image to enlarge it). Details on the different areas will be shown in more detailed sections or pages when necessary.

Location	Main Beamline	Side Beamline
Primary Optical Enclosure (it contains optical elements from the three BioXAS beamlines)
Hutch
Endstation
User Area

Detectors

Both beamlines use a set of three ion chambers, and one (Side) or two (Main) fluorescence detectors, to measure the absorption spectrum in transmission and fluorescence yield, respectively. The setup is similar to the one shown in Fundamentals of X-ray absorption spectroscopy.

More details about the individual detectors can be found in the table below, and the links provided in the last column.

Element	Function	Available types	Detailed Information
Ion chambers	Measure beam flux	Filled with single gas: N2, He, Ar, depending on the energy range. The image shows the location of the fluoresce detector too. Notice the beam, represented by a green arrow, comes from the right.	Ion Chambers
Fluorescence detectors	Measure fluorescence and scatter radiation intensity	Solid State Ge detector, LN2 cooled, with 32 (8x4) Channels (left). Thre is 1 on Side and 2 on Main. PIPS detector Round, 7 cm in diameter (right).	Fluorescence Detectors

Endstation Details

The Spectroscopy Beamline Endstations have the detectors and sample stage on top of an optical table that can be aligned with the beam. In the middle of the table is the space to set the sample. The measurements can be performed at room temperatures or low temperatures using a cryostat (see Available Sample Environments and Holders). The table below shows some of the end-station details.

Standards Wheel	LN2 cooled Ge32 Fluorescence detectors (there are two on Main, one each side of the sample)	Cryostat for low-temperature measurements

Motorized stage and room-temperature sample holder	Double Bounce Harmonics Rejection Mirror	Soller Slits