Harmonic Rejection Mirrors

A double-mirror harmonic rejection system is installed in the experimental hutch to overcome harmonic contamination from the monochromator. This contamination is also amplified by preferential absorption of the Si (111) reflection in the beryllium windows compared to the (333) and (444) reflections. The Pyrex® mirrors are currently being replaced by silicon mirrors. An picture of the old mirror system is shown below.

Phase-Plates

The synchrotron incident linear polarised radiation can be converted into circular polarisation Pc by using a quarter-phase-plate. Circular polarisation can also be obtained from x-rays emitted above or below the electron orbit. The former technique is the only way to look at highly anisotropic magnetic materials for which the direction of the sample magnetisation cannot be reversed. The phase retarder assembly is situated about 3 m upstream of the diffractometer. The phase-plate crystals are mounted on a Huber goniometer and are driven to their quarter-wave-plate conditions, for maximum Pc, with a theta and a chi circle. The former rotation stage, which moves the crystal off the Bragg condition, has an accuracy of 0.0001° (0.36 arcseconds). It is orthogonally mounted on the chi circle. The chi rotation sets the optical axis of the phase-plate at 45° to the incident and plane polarisation, with an accuracy of ±10 arcseconds. A counter-balance is also mounted onto the arm of the chi circle. These two rotations are positioned upon two translation stages giving horizontal and vertical adjustment within 10 µm. All the motors are controlled from the SPEC software, which is also used elsewhere on the beamline. The theta circle has an encoder installed. A full description of the operation of phase-plates on XMaS can be found hereLink opens in a new windowLink opens in a new window.

Diffractometer

The 11-axis HuberLink opens in a new window diffractometer was installed in 1997. The vertical z-translation exists to permit alignment of the sample to the three possible beam positions: white unfocussed (z = 0 mm); monochromatic unfocussed (z = -14 mm); monochromatic focussed (z = 105 mm). Since the mirror deflects the monochromatic beam upward by 5 mrad, the possibility to tilt (±1°) is provided in order to maintain perpendicularity between the focused beam and all horizontal circle axes. A horizontal x-translation is present to centre the diffractometer in the beam. With the use of the SPEC software, orientation matrices may be defined in psic 6-circle (eta, delta, chi, phi, mu, nu) scattering geometry. Equivalence with 4-circle horizontal and vertical geometries are provided. For surface diffraction or to control the incidence angle and/or the exit angle between the x-ray beam and the sample surface, it is possible to use all six circles to define orientation matrices.

The physical layout of the diffractometer is shown above. Two multi-position plates at the front and rear of the base can be used to mount user equipment. All metallic parts around the sample circles are of non-magnetic material. The Huber 512 Eulerian cradle carries a 1003 sample goniometer head on the phi circle. There is a 10 mm diameter hole in the head and the distance from the base of the hole to the centre of rotation is 43.5 mm. The new detector arm is equipped with two support offset by 25°. This two different detection schemes to be permanently mounted.

Polarisation Analyser

The three-axis XMaS polarisation analyser, shown below, has been designed to facilitate the study of changes in the polarisation of the x-ray beam after diffraction from the sample. The in-vacuum design allows the device to be used at low energies (~3 keV) which is particularly useful, for example, in experiments performed at uranium M-edges. The theta axis allows alignment of the analyser crystal to a diffracting condition, with theta Bragg at, or close to, 45°. The second rotation axis allows rotation of the diffracting plane of the analyser crystal about the scattered beam. Any component of the incident polarisation lying in the diffracting plane will go to zero on charge scattering for theta Bragg = 45°. The third linear axis allows translation of the detector in a 2-theta geometry in order to track the diffracted beam. Conventionally, for vertical scattering experiments, the incident polarisation is referred to as σ polarised and any component orthogonal to it (i.e. vertically polarised) as π polarised. Thus, by positioning the rotation about the beam such that the diffracting plane of the analyser crystal is vertical, one is sensitive only to the σ polarised component and conversely a horizontal analyser crystal diffraction plane measures the π component. The choice of analyser crystal depends on energy.

Full technical details of the polarisation analyser can be found here.

0D Detectors

Avalanche Photodiodes

Avalanche PhotoDiode (APD) detectors are available and offer a very high dynamic range and linearity. They consist of PerkinElmer® silicon avalanche photodiode chips with an integrated preamplifier. Two types of APD are available on the beamline: one with a chip of 10 mm x 10 mm active area shielded by a kapton window and another one with a 5 mm x 5 mm active area protected by a 80 µm thick Be window which is mounted onto a KF-16 vacuum flange. Each APD is controlled by an ACE unit through SPEC. This module includes a user interface in local and remote control mode. SPEC communicates to the module through a RS232 serial line port.

APD with KF-16 vacuum flange (5 mm x 5 mm PerkinElmer® chip)	Standard APD (10 mm x 10 mm PerkinElmer® chip)	ACE unit

Vortex Si Drift Diode

Vortex® multi-cathode X-ray detectors feature the largest active area single element detector (~50 mm2, 8 mm diameter) available of its kind. Vortex® detectors are produced from high purity silicon using state-of-the-art CMOS production technology. They feature excellent energy resolution (<136 eV FWHM at Mn Kα is typical) and a high count rate capability (input rate >1 Mcps). At a very short peaking time of 0.25 µs, an output count rate of 600 kcps is achieved. A unique feature of these detectors is their ability to process high count rates with virtually zero loss in energy resolution and no peak shift with count rate. The detector at XMaS features a 25 µm thick Be window mounted onto a KF-40 vacuum flange, reducing air absorption (old FET pream, no Cube-ASIC technology yet).

PILATUS3 S 1M

The Dectris Pilatus3 S 1M has a 450 μm silicon sensor. The detector has dimensions of (WxHxD) of 265 × 286 × 455 mm and weighs 25 kg. The frame rate is 500 Hz with a 2.03 ms readout time. The pixel size is 172 µm x 172 µm. The active area has 981 x 1043 pixels and 168.7 × 179.4 mm2 size. The detector has 10 modules (2x 5) with 17 pixels in the intermodule gap. The detector has a 20-bit dynamic range (counter overflow state 1048573) and a ~107 ph/s maximum counting rate per pixel. It can operate in the ~3-36 keV energy range.

This detector is mounted on the XMaS SAXS rail for SAXS and WAXS experiments (its 25 kg prevents it from being mounted on the diffractometer 2theta arm).

MAR165 CCD Camera

The MAR165 CCD Link opens in a new windowcamera is a 2D detector with a round, 165 mm diameter active area. It has overall dimensions of (WxHxD): 220 x 220 x 340 and has a weight of ~20 kg. It uses one 4k x 4k chip, permanently bonded to a single fiber-optic taper. The camera reads the chip from four channels (quadrants) simultaneously, resulting in a 2048 x 2048 pixel image. The readout time is ~5 seconds. The pixel size is 80 µm x 80 µm.

The MAR camera is controlled from SPEC, by specific macros, through a Linux device server running on xmas6 holding the camera controller card. The full MAR165 technical sheet is available here.

PILATUS3 300K

The Dectris Pilatus3 300K is based on the newly developed CMOS hybrid-pixel technology and operates in single-photon counting mode with a point spread function of 1 pixel only (FWHM). The detector has dimensions of (WxHxD) of 160 x 194 x 262 mm and weighs approximately 7.5 kg. It reaches a framing rate up to 500 Hz with a 0.95 ms readout time in fast mode. The pixel size is 172 µm x 172 µm. The active area has 487 x 619=301453 pixels and 83.8 x 106.5 mm2 size. The detector has three modules with 17 pixels in the intermodule gap. The detector has a 20-bit dynamic range (counter overflow state 1048573) and a ~107 ph/s maximum counting rate per pixel. It can operate in the ~3-36 keV energy range. An external 5V TTL signal can be used to trigger the detector.

PILATUS 300K-W

Only available on request !!! This detector has dimensions of (W x H x D) of 384 x 100 x 458 mm and weighs approximately 12 kg. It reaches a framing rate up to 200 Hz with a 2.7 ms readout time in fast mode (100 Hz and 3.6 ms in standard operation) and has a pixel size of 172 µm x 172 µm. The detector features 1475 x 195 pixels (3 x 1 chips).

The Pilatus 300K-W consists of a detector head connected to a Linux acquisition workstation by a fiberoptic link. The detector head includes the detector module, the interface board with connection to the acquisition workstation, and power supplies. The acquisition workstation device server is based on the "LIMA" software library developed by the ESRF for 2D detectors control and 2D data acquisition.

The Pilatus 300K-W technical sheet is available hereLink opens in a new windowLink opens in a new window.

MAXIPIX

The MAXIPIX is a fast readout, photon-counting pixel detector system developed by the ESRF and based on the Medipix2 readout chip developed by CERN and the Medipix2 collaboration. It has dimensions of 145 x 140 x 222 mm and weighs about 4.7 kg. The system achieves up to 1.4 kHz frame rate with 0.29 ms readout dead time and has a pixel size of 55 µm x 55 µm. The available detector features 512 x 512 pixels (2 x 2 chips).

--- A 1280 x 256 pixels (5 x 1 chips) detector is also available only on request!! ---

MAXIPIX consists of a detector head connected to a Linux acquisition workstation by a fiberoptic link. The detector head includes the detector module, the interface board with connection to the acquisition workstation, and power supplies. The interface board can drive detector modules implementing up to five Medipix2 or Timepix chips with simultaneous readout of each chip. The acquisition workstation device server is based on the "LIMA" software library developed by the ESRF for 2D detectors control and 2D data acquisition.

The Maxipix technical sheet is available hereLink opens in a new window.