Abstract
This paper describes a tunable X-ray focusing apparatus, referred to as a transfocator, based on compound refractive lenses. By varying the number of lenses in the beam, the X-ray energy focused and the focal length can be varied continuously throughout a large range of energies and distances. The instrument can be used in both white and monochromatic beams to focus, pre-focus or collimate the beam. The transfocator can be used with other monochromators and/or other focusing elements, leading to significant increases in flux. Furthermore, the chromatic nature of the focusing means the transfocator suppresses harmonics and can also be used as an extremely high flux broad-band-pass monochromator. These devices have been installed in the first optics and second experimental hutches at the ID11 beamline at the ESRF.
Highlights
A large variety of X-ray focusing elements are available, such as single and double Kirkpatrick–Baez (KB) geometry (Kirkpatrick & Baez, 1948; Liu et al, 2005; Hignette et al, 2007; Mimura et al, 2009) normal and multilayer mirrors, bent crystals (Lienert et al, 1998; Suortti & Schulze, 1995; Suortti et al, 2001) and zone plates (Baez, 1961)
The mechanical design of the transfocator is based on that of the in-air prototype described earlier (Snigirev et al, 2009a), which has been in use at ID11 for microfocusing applications for two years
In the present case the design has been upgraded in order to function in high vacuum near the front of the beamline, and cooled to accept white beam. Both transfocators are based on a system of pneumatically actuated cartridges containing a geometric progression of numbers of lenses, allowing, in the case of the in-air transfocator (IAT), between two and 254 Al lenses and between one and 63 Be lenses and 32 to 96 Al lenses for the in-vacuum transfocator (IVT)
Summary
A large variety of X-ray focusing elements are available, such as single and double Kirkpatrick–Baez (KB) geometry (Kirkpatrick & Baez, 1948; Liu et al, 2005; Hignette et al, 2007; Mimura et al, 2009) normal and multilayer mirrors, bent crystals (Lienert et al, 1998; Suortti & Schulze, 1995; Suortti et al, 2001) and zone plates (Baez, 1961). Zone plates are in-line optics and can be used to produce extremely small beams, but are compromised with respect to background and are inefficient at high energy, it is possible to stack them to partially overcome the poor efficiency (Shastri et al, 2001; Maser et al, 2002; Kamijo et al, 2003; Snigireva et al, 2007a,b) Since their development a little over 12 years ago (Snigirev et al, 1996), the use of X-ray refractive lenses has rapidly expanded (Lengeler et al, 1999a,b; Kohn et al, 2003; Snigirev & Snigireva, 2008) and they are in common use on synchrotron beamlines. The band pass of this monochromator is well matched to exploit the spectrum of the harmonic peaks of an undulator insertion device at a thirdgeneration storage ring
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