An X-ray Transfocator – a tunable X-ray focusing apparatus 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 device 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.
X-ray Transfocators based on compound refractive lenses are very flexible and powerful focusing/collimating devices. In terms of the conditions of use of the Transfocators, there are two constructive solutions: In-air and In-vacuum. The In-vacuum Transfocators benefit from being closer to the X-ray source where it captures a larger proportion of the diverging X-ray beam.
In terms of lenses switching type, there are two main approaches: discrete-type lenses switching and binary-type lenses switching. The discrete-type lenses switching, referred to as the single-lens approach, allows the implementation of moving lenses one by one independently providing a smooth variation of foci and predictable focal positions. In the case of binary type lens switching, the lenses are inserted into the beam by means of pneumatically driven cartridges containing a geometric progression of numbers of lenses between two and 254 lenses (in steps of powers of two).
There are three main options for the mechanical design of X-ray Transfocators:
- Ultra-Compact Transfocator (UCTF) with discrete-type lenses switching
- In-vacuum Transfocator (IVTF) with binary-type lenses switching
- In-vacuum Transfocator with water cooling system (IVTF+)
All basic parameters of the devices can be changed depending on the specific task of their use. For example, Ultra-Compact Transfocator can be manufactured in the In-vacuum version and equipped with a water cooling system to ensure stable operation when the device is used under vacuum conditions. The number of lenses can be changed at the customer’s request.
The UCTF is a brand new instrument capable of automatically changing the focal length by changing the number of refractive lenses along the optical axis. The standard version of the UCTF is equipped with 50 parabolic refractive lenses. The main distinguishing features of the device are the compactness, low weight, and a single-lens approach – the number of inserted individual parabolic lenses are moving one by one independently.
Providing permanent energy and focal length tunability, the CTF can be adjusted depending on the task: it can be a beam collimation system, a short-focal magnifying objective and can be also used for precise measurements of source sizes, thus being suitable for a wide range of applications even at non-specialized imaging beam-lines.
The UCTF has a control unit based on the single-board RaspberryPi computer with Raspbian 4.9 OS. Special Python-based software was designed to provide high-level access to device-control functions with the possibility to create custom commands. The software can be integrated into most modern synchrotron beamline controlling systems such as SPEC or ACTL.
|Dimensions [mm]||150 x 90 x 100|
|Number of lenses||50|
|Energy range [keV]||1-200|
|Focus position accuracy [𝜇m]||0,4|
|Materials||Al, Be, Ni|
|Lens switching time [sec]||10|
|Radius of curvature [𝜇m]||50, 100, 200|
|Number of lenses||can be changed according to the specific task|
|Software||custom set of user commands|
Use under vacuum conditions
In terms of the conditions of use of the Transfocators, there are two constructive solutions: In-air and In-vacuum execution options. The In-vacuum Transfocators benefit from being closer to the X-ray source where it captures a larger proportion of the diverging X-ray beam. Both versions of the devices can be equipped with water cooling to ensure stable operation when the CTF and IVTF are used under vacuum conditions.