The “Balder beamline” at MAX-IV represents a popular approach for X-ray
absorption spectroscopy beamlines [144]. The beam from a 38-pole 2.1 T wiggler
source is collimated using a water-cooled mirror with either a Si or Ir surface (for
different cutoff energies). This is followed by a liquid nitrogen-cooled monochromator with Si(1 1 1) or Si(3 1 1) crystals. The beam is refocused into a 100 Â 100 μ
2
spot in the hutch with a toroidal mirror, again with either a Si or Ir surface. A huge
amount of the ~1.2 kW power from the source is dissipated in the optics: ~700 W in
the collimating mirror and up to ~500 W in the first crystal. The net result is a
monochromatic beam with ~10
12
–10
13 photons s
À1 .
Beamline BL09XU at SPring-8 is an example of a very productive beamline for
nuclear spectroscopy experiments [145]. Since the very-high-resolution monochromators are heat sensitive, the source flux is first reduced with a liquid nitrogencooled high heat load Si (1 1 1) monochromator. The initial asymmetric Ge(3 3 1)
crystal (b ¼ 1/2) reduces the vertical divergence from 10 to 5 μrad while expanding
the beam height from 0.5 to 1 mm. (This crystal also serves to set the output beam
close to horizontal.) More collimation comes from reflection by the asymmetrically
cut Si(9 7 5) crystal (b ¼ 1/10.8), which narrows the angular divergence from 5 to
0.09 μrad, while expanding the vertical size of the beam from 1 to 11 mm. The
second asymmetric Si(9 7 5) crystal demagnifies the vertical beam size back to
~0.5 mm (b ¼ 18). The high-resolution monochromator is contained in its own
separate hutch which keeps the temperature stable to ~0.02 K. This beamline now
yields a 0.8 meV bandwidth beam at 14.4 keV with a flux of ~2.5 Â 10
9 photons s
À1 .
Beamline ID28 at ESRF uses a different approach for inelastic X-ray scattering
experiments [146]. In this case the collimating element is chosen from a set of Be
compound refractive lenses. The device with 24 holes reduces the vertical divergence to ~1μrad. As with SPring-8, a Si (1 1 1) high heat load monochromator
disposes of most of the unwanted flux. Then, a flat Si backscattering monochromator
operating at 89.98
is used for high resolution: the Si (13 13 13) reflection can yield
~1.5 Â 10
9 photons s
À1 with ~0.5 meV resolution. The monochromatic beam is then
refocused onto the sample with a 120 period Ru/B 4 C multilayer mirror. The
scattered radiation is analyzed with a set of spherically curved analyzers that each
contain ~12,000 silicon (13,13,13) pixels that provide <1 meV resolution at
25,704 eV!
4.7.2 Soft X-ray Beamlines
Soft X-ray beamlines generally use grating monochromators over the range from the
Li K-edge (~54 eV) to ~2000 eV. Although crystals such as YB 66 and beryl can
cover the 1–2 keV range, for example, at beamline BL2A at UVSOR [148], they are
not “perfect,” and the resulting linewidths are broadened by their mosaicity. The Si
K-edge (~1839 eV) is in an overlap region which can also be covered well by InSb
(1 1 1) crystal monochromators. Above this energy, crystal monochromators using
4.7 Putting It All Together: Typical Beamlines
101
absorption spectroscopy beamlines [144]. The beam from a 38-pole 2.1 T wiggler
source is collimated using a water-cooled mirror with either a Si or Ir surface (for
different cutoff energies). This is followed by a liquid nitrogen-cooled monochromator with Si(1 1 1) or Si(3 1 1) crystals. The beam is refocused into a 100 Â 100 μ
2
spot in the hutch with a toroidal mirror, again with either a Si or Ir surface. A huge
amount of the ~1.2 kW power from the source is dissipated in the optics: ~700 W in
the collimating mirror and up to ~500 W in the first crystal. The net result is a
monochromatic beam with ~10
12
–10
13 photons s
À1 .
Beamline BL09XU at SPring-8 is an example of a very productive beamline for
nuclear spectroscopy experiments [145]. Since the very-high-resolution monochromators are heat sensitive, the source flux is first reduced with a liquid nitrogencooled high heat load Si (1 1 1) monochromator. The initial asymmetric Ge(3 3 1)
crystal (b ¼ 1/2) reduces the vertical divergence from 10 to 5 μrad while expanding
the beam height from 0.5 to 1 mm. (This crystal also serves to set the output beam
close to horizontal.) More collimation comes from reflection by the asymmetrically
cut Si(9 7 5) crystal (b ¼ 1/10.8), which narrows the angular divergence from 5 to
0.09 μrad, while expanding the vertical size of the beam from 1 to 11 mm. The
second asymmetric Si(9 7 5) crystal demagnifies the vertical beam size back to
~0.5 mm (b ¼ 18). The high-resolution monochromator is contained in its own
separate hutch which keeps the temperature stable to ~0.02 K. This beamline now
yields a 0.8 meV bandwidth beam at 14.4 keV with a flux of ~2.5 Â 10
9 photons s
À1 .
Beamline ID28 at ESRF uses a different approach for inelastic X-ray scattering
experiments [146]. In this case the collimating element is chosen from a set of Be
compound refractive lenses. The device with 24 holes reduces the vertical divergence to ~1μrad. As with SPring-8, a Si (1 1 1) high heat load monochromator
disposes of most of the unwanted flux. Then, a flat Si backscattering monochromator
operating at 89.98
is used for high resolution: the Si (13 13 13) reflection can yield
~1.5 Â 10
9 photons s
À1 with ~0.5 meV resolution. The monochromatic beam is then
refocused onto the sample with a 120 period Ru/B 4 C multilayer mirror. The
scattered radiation is analyzed with a set of spherically curved analyzers that each
contain ~12,000 silicon (13,13,13) pixels that provide <1 meV resolution at
25,704 eV!
4.7.2 Soft X-ray Beamlines
Soft X-ray beamlines generally use grating monochromators over the range from the
Li K-edge (~54 eV) to ~2000 eV. Although crystals such as YB 66 and beryl can
cover the 1–2 keV range, for example, at beamline BL2A at UVSOR [148], they are
not “perfect,” and the resulting linewidths are broadened by their mosaicity. The Si
K-edge (~1839 eV) is in an overlap region which can also be covered well by InSb
(1 1 1) crystal monochromators. Above this energy, crystal monochromators using
4.7 Putting It All Together: Typical Beamlines
101