CRISTAL

CRISTAL’s source is an in-vacuum U20 undulator (98 periods of 20 mm) offering to choose the X-ray energy between 5 keV and 30 keV with a minimum gap of 5.5 mm.

The monochromator is a Si(111)-Double Crystal Monochromator (DCM) with possible sagittal (horizontal) focusing (i.e. bending of the second crystal).
The first crystal is cooled down by a liquid nitrogen closed loop circuit (Cryotherm company). The tuning of the monochromator is ensured by a piezo-actuator, controlled by a feed-back loop on the intensity or the position of the beam measured downstream.

The mirror system consists of two horizontal 300 mm long Si mirrors (SESO), placed in a dedicated hutch. The first one is bendable. These mirrors are coated by Rh and Pt tracks (harmonic rejection in the whole energy range). Slope errors are about 0.40 µrad for both mirrors. The minimum beam FWHM has been measured to be 27 µm @ 8 keV at the sample position at 6-circle diffractometer center.

Most of the powder diffraction experiments are performed on the 2-circle diffractometer. This dedicated instrument was initially optimized to record high angular resolution diagrams for ab initio structure determination, microstructure analysis or to study phase transitions, thanks to its multi-analysers detector (21-Si(111) crystals). A complete powder diagram up to 100° 2θ can be measured in less than 1h.

The curve below gives the instrumental resolution determined from the full width at half maximum of the Bragg peaks extracted from the powder diagram of a LaB6 sample (NIST-SRM660, cubic Pm3m) at 25 keV.

Instrument Résolution Function (IRF) at 25.55 keV as a function of the 2theta diffraction angle.

Recently (2018), a curved pixel detector (9x Dectris Mythen II modules, positioned on a cylinder with a radius of 720 mm) was added to the detection circle, providing a 50° 2θ coverage with small gaps (0.5°) or a 25° coverage with no gaps when a non-symmetrically position with respect to the incident beam direction is adopted. A good angular resolution is kept (<0.02° 2θ) is kept. Due to its very short readout time (2ms), a complete powder diagram (up to 2θ = 50°) can be acquired within a few seconds if the detector movements are optimized.

For PDF experiments, to achieve high Q values (> 25Å-1), the highest energies available are used (28 to 30 keV), combined to a scan of the detector position to at least 120° 2θ. Using the Mythen detector, a complete diagram for pdf analysis purposes can be obtained within 1 hour (6 h with the multi-analysers).

View of the 4-circle diffractometer equipped with a gas streamer (CryoIndustries of America) to cool the sample. Insert: axes names.

The 4-circle diffractometer allows an easy, fast and precise data collection on single crystals in different sample environments. The instrument specially built for the beamline has resulted from the association of two companies each well known in their area: Newport (Microcontrol) for the goniometer part and Rigaku Oxford Diffraction) for the detector and data analysis software. 
The data are measured using the oscillation method: for each image acquisition, the diffraction signal is measured while the sample is rotated at constant speed over a small angular range (typically 1°).

The main characteristics of this instrument are: 

• a 2D CCD detector permanently mounted, which can be translated (80 mm < dtx < 340 mm) ,
• high accuracy of motions, 
• very small Sphere Of Confusion* to be able to study micro-crystals (Ø < 10 µm), 
• data acquisition/analysis software package standard and familiar to most users. 

*the Sphere of Confusion (SoC) is the largest dimension of the spherical volume described by the sample during the motion of all the axes.

Newport 6-circle diffractometer, in a vertical position.

The 6-circle diffractometer is the most versatile instrument of the beamline.

It consists of four rotation axes for the sample stage (Mu, Komega, Kappa and Kphi) and two rotation axis for the detector stage (Delta and Gamma). 3 additionnal translations are supported by the kphi rotation axis to accurately position the sample onto the center of the diffractometer.

The measured angular accuracy of all axes are better than 0.001°. The sphere of confusion is better than 60 µm.

An analyser (beam polarisation analysis) can be mounted on the detector arm (as shown on the picture).

This instrument accommodates the following experimental setups:

• Bragg Coherent Diffraction Imaging,
• Micro-Diffraction,
• High Pressure using Diamond Anvil Cells,
• Pump-probe Diffraction,
• “customized” setup to the specific needs of a user project: heavy sample environment (i.e. up to 15 kg), specific detector (up to 10 kg).

The 2-circle and 4-circle diffractometers have their own detection system (respectively a 21-analyzers system/Mythen detector and an Agilent 2D CCD detector). Below is a list of other detectors used at CRISTAL, either belonging to the beamline or to the detector pool. The possibility to use a particular detector on a given instrument is symbolized by the colored icons. 

Point detectors

 YAP, CeBr₃ scintillators                    CRISTAL : point detectors used for high resolution diffraction     

2D Detectors

	Pool: XPAD 3.1, XPAD3.2: Hyprid pixel detectors developed by SOLEIL, in collaboration with the ESRF CRG BM2 and CPPM.  Sensor: Si 500 µm/ 560x960 pixels (8 modules of 7 chips each of 80x120 pixels). Pixel size 130x130 µm2,  Total entrance window surface: 7.28 x 12.48 cm (with blind zones ≈7%).  XAPD3.2 is gatable for time resolved experiment  Used for:  • All diffraction experiments  • Time-resolved diffraction
	Pool: MAR345  Image plate detector. 100x100 µm2 pixel size  Used for :  • Low resolution powder diffraction experiments  • High Pressure diffraction
	Pool: Rayonix SX165    CCD camera, 165 mm diameter, 40 µm pixel size min.  4096x4096 pixels  Pixel size: 40x40 µm2 (min).  Used for:  • Crystallographic measurements,  • Powder diffraction
	CRISTAL/SIXS/GALAXIES beamlines: MAXIPIX 2    Purchased in common with SIXS and GALAXIES  Will be available in Novembre 2012.  Will be used:  • Coherent diffraction and ptychography.

Cryostats

	Powder diffraction top-loading He-cryostat with rotating capillary (max 2 rps) facing the 2-circle diffractometer (conception R. Steinman, ESRF).  Temperature range: 4-300 K.
	Closed cycle cryostat (Advanced Research System, ARS DE-302). This cooling system has been designed to fit the 6-circle diffractometer in order to allow many diffraction configurations. Beamline usage shows that the limitation mainly comes from the He-outlet. This cryostat is used for the diffraction experiments which are not sensitive to vibrations.  Tmin = 6 K.
	ARS HELITRAN liquid helium flow cryostat placed on the 6-circle diffractometer with the coherent diffraction settings. This cryostat, which has angstrom level vibrations, is well suited for such experiments. Contrarily to the previous displex system, this cryostat is not free to move in any orientation, and should work near the vertical position as shown on the picture.  Tmin = 4 K

Gas blowers

	Hot gas blower (Cyberstar) for powder and single crystals.  Temperature range 20-900 °C
	Gas streamer cooler (N2/He)  From Cryo Industries of America. Lowest temperature with N2 : 80 K and with He: 15 K. In order to avoid ice formation on the sample, a heated goniometer head is used.
	Gas streamer cooler (N2/He)  Powder diffraction at low tempertaure from 60K to 300K using a Cryo Industries of America gas streamer and a special enclosure to prevent icing.