Characteristics
| Characteristics | |||||
|---|---|---|---|---|---|
| Guide hall 1, thermal guide H242MonochromatorsVariable horizontal and vertical focussing | |||||
| HOPG (002) | 2.36 < λ < 2.5, 3.8 Å | ||||
| Si (115) | 1 < λ < 3.5 Å | ||||
| take-off angle | 38 < qM< 130° | ||||
| 3He trench multi-wire proportional 2D detector | |||||
|---|---|---|---|---|---|
| Angular coverage | horizontally 130°, vertically 24° | ||||
| Angular resolution | horizontally 0.15°, vertically 0.2° | ||||
| Height | 32 cm | ||||
| Radius of curvature | 76 cm | ||||
| Efficiency | 75% at λ=2.5 Å | ||||
| Local counting rate | 50 kHz | ||||
| Global counting rate | 2 MHz | ||||
| Sample environment | |||||
|---|---|---|---|---|---|
| Orange cryostat | 1.5 K to 300 K | ||||
| Cryofurnace | 1.5 K to 550 K | ||||
| Cryomagnet | 1.5 K to 300 K, up to 10 T | ||||
| Furnace | 300 K to 1200 K | ||||
| Paris-Edinburgh cell | 5 K to 300 K, up to 20 GPa | ||||
| Clamp cell | 1.5 K to 300 K, up to 1 GPa | ||||
Instrument Description
Monochromators
The variable focussing HOPG (002) monochromator is made up of 81 individual crystals arranged on a rectangular 9x9 grid. The monochromator mechanics allows adjusting the vertical and horizontal focussing independently. The HOPG monochromator is most useful at low take-off angles where relatively long wavelength ( »2.5-3.8Å) can be produced providing the incident flux on the sample »2´107 n´s-1´cm-2. Higher λ/2 harmonics are filtered out by a graphite filter. The variable focussing Si monochromator produces shorter wavelengths and better resolution at higher take-off angles. The secondary spectrometer is mounted on air cushions freely moving around the experimental area marble floor (“Tanzboden”), which permits a continuous change of wavelength.
Beam conditioning
A set of diaphragms and vacuum collimation tubes is available in order to adjust the shape and divergence of the beam incident on the sample. Depending on the sample size and instrument operation mode (powder, single crystal), the illuminated sample volume can be varied from a few cm3 to a few mm3. The signal-to-background ration is significantly improved placing a Radial Oscillating Collimator in the way of the diffracted beam, so that the contribution of bulky sample environments (such as cryomagnets, Paris-Edinburgh cells, etc.) is suppressed.
Detector
A curved Trench Multiwire Proportional Chamber 3He Detector covers an angular area of 130 ´ 24 degrees2 around the sample allowing for the collection of complete 2D diffraction patterns in a few seconds’ time. This brand new technology recently developed at ILL [1] ensures high neutron detection efficiency and signal stability, high angular resolution and excellent gamma event rejection. The detector design permits facile and quick data collection both from powders and single crystals.
Sample environment
XtremeD can host most of the ILL pool sample environment equipment with particular focus on extreme conditions of temperatures (both high and low), pressure and magnetic field. The sample environment is typically placed on a motorized sample stage permitting relatively quick and easy sample alignment in the beam. The whole of the secondary spectrometer is made of non-magnetic materials meaning steady magnetic field up to 10T used routinely on the instrument. Data collection and sample conditioning is automatically controlled via Nomad software.
References:
D. Barkats, J.C. Buffet, S. Cuccaro, B. Guerard, F. Lafont, J. Marchal, J. Pentenero, N. Sartor, "Trench-MWPC 3He Detector for XtremeD Neutron Diffraction Instrument," 2021 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), Piscataway, NJ, USA, 2021, pp. 1-8, doi: 10.1109/NSS/MIC44867.2021.9875652