Characteristics
| Guide hall n°1, vertical cold source V1, in-pile H1 insert, cold guide H15, channel H153 (deflector) |
|---|
| Monochromator | |
|---|---|
| velocity selector | |
| Eleanore/ Felicia (ASTRIUM standard selectors) | variable, typically Δλ/λ = 9 % (FWHM) |
| incident wavelength | variable, 0.46 ≤ λ [nm] ≤ 4 |
| max. wavelength at max. detector dist. (39 m) | λ = 2.2 nm |
| selector rotation normal to n-beam possibleminimum wavelength at rotation -7° | -7° to + 7°λ = 0.32 nm |
| Collimation | |
|---|---|
| 17 guide sectionsstraight glass guides, m=1 (SwissNeutronics)elliptical focussing guides, m=1.5 (SwissNeutronics) | side of square cross section14 straight guides 45 mm over 28.8 m45 mm -> 47.65 mm from 5.6 to 4.1 m47.65 mm -> 46.10 mm from 4.1 to 3.1 m46.10 mm -> 38.0 mm from 3.1 to 1.6 m |
| guide-to-sample distances | 1.6, 3.1, 4.1, 5.6, 6.7, 7.7, 10.2, 12.7, 15.2, 16.5, 17.8, 20.3, 22.8, 24.8, 26.9, 29.4, 31.9, 35.2 m(18 discrete distances) |
| 4 variable-aperture slits (10B4C) | at 34.63, 27.85, 6.74 and 1.65 m from sample |
| 5 multiposition (8) aperture changer (10B4C) | at 26.92, 20.38, 15.31, 10.28 and 5.70 m from sample |
| Attenuators |
|---|
| choice between 3 slitted cadmium sheets of different transmissions that can be combined to achieve 7 attenuation factors fa:fa=4.63 (att 1), fa=16.9 (att 2), fa=72.7 (att 3)fa=77.7 (att 1 + 2), fa=348 (att 1 + 3), fa=1165 (att 2 + 3)fa≈8200(att 1 + 2 + 3) |
| Sample area | |
|---|---|
| flux at specimen at lowest resolution | 1.2 · 108n·cm-2·s-1at λ = 0.6 nm at 55 MW (as measured on the detector) |
| typical sample size | 7 × 10 mm2 |
| Detector | |
|---|---|
| sample-to-detector distancesL | continuously variable between 1.35 m and 38.9 m |
| typical momentum transfer range | 3·10-3≤ q [nm-1] ≤ 6 |
| detector type (since January 2021) | 3He gas detector (256 1-m long, 8 mm outer diameter stacked tubes from Reuter-Stokes, installed in 3 panels, shaped as a cross of 1.5×1.5 m2: 192 horizontal tubes + 2 side panels of 32 tubes each.3He at 10 bars. Stop-gas: Ar/CO2mix at 1.5 bars. Stainless steel 304 of 0.4 mm wall thickness. Operated at HV=1500 V. |
| efficiency | 90, 95 and 99.5 % at λ = 0.45, 0.6 and 1 nm within the tubes. Due to the geometry of tubes assembly, 12 % of neutrons avoid the detection area. |
| area | 2 m2 |
| pixel size | 8 mm across (rectangular psf), 3 mm FWHM along tubes (Gaussian psf) |
| background | 1.2 Hz on whole detector |
| detector deadtime | 1.5 µs per tube (~1/10 event loss at 66 kHz per tube, at 225 kHz) |
Technical description
The polychromatic beam from the cold source is monochromated by a helical slot (ASTRIUM) velocity selector which selects neutrons of ±9 % about a mean wavelength determined by the rotation speed of the drum. The neutrons are then collimated by a series of moveable glass guides. Guide sections are inserted into or removed from the beam depending on the incident beam divergence required.
The sample zone, situated 35 m down-stream from the velocity selector, may be equipped with various sample environments such as an automatic temperature controlled sample changer, cryostat, magnet, shearing cell, Bohlin rheometer, dilution refrigerator, horizontal sample-changer under vacuum, etc.
Neutrons scattered from the sample are detected on a 1.5 x 1.5 m2 multi-PSD 3He detector mounted on a moveable trolley within the evacuated detector tube. The detector may be placed at any distance between 1.35 and 38.9 metres from the sample position, giving a typical momentum transfer range of 3 10-3 to 6 nm-1 that can be a bit extended for specific cases.
The D11 collimation system has been completely renovated between 2021 and 2025 (Endurance 2 renewal project).
Collimation renewal project (2001-2004)
With 3 new collimation distances (1.5m, 28m and 34m), 6 new diaphragm changers, new mechanics including a complete re-alignment and the modifications at the selector area, the instrument has considerably gained in:
- performance
- resolution
- flexibility
- reliability
For instance, a flux gain of ≈ 10 is obtained for certain experimental conditions.
New detector and tank project (2005-2008)
The future scientific requirements are calling for an innovative evolution of the instrument with a “best possible” specification, in order to strengthen ILL’s leading position in small angle scattering and maintain D11 as one of the world-wide most powerful and versatile SANS instruments. Consequently, the project of developing a faster and larger SANS detector has started in 2005, in the framework of the ILL’s Millennium Programme.
The present 3He detector will be replaced by the 3He - MWPC 128x128-7.5 (the former CERCA 3He detector of D22). This detector has a considerably larger counting area thus a much better dynamic range, a better efficiency and a better spatial resolution. After some modifications of the detector electronics, the maximum possible countrate can be increased to about 300 kHz, i.e. a factor of 6 higher than the present D11 detector. The detector shall be installed in a new tank with an extended length and larger diameter. In conjunction with the enhanced counting area, the tank elongation will considerably increase the totally available Q-range of the instrument and allow for measurements at significantly lower Q-values than possible at present. Furthermore, it is planned to implement in the future a multi-hole imaging USANS option, thus challenging new frontiers in space and time resolution.
Guide replacement (2006-2008)
Following the review and analysis of the D11 guide system by McStas simulations in late 2005/ early 2006, an innovative guide design change had been decided in spring 2006. Significant flux gains can be predicted for a large range of collimation distances with a new widened glass guide with an opening 6.5m trumpet (30mm->45mm width) at the collimation entrance and a focusing trumpet at the collimation exit, near to the sample position
(see Lieutenant K., Lindner P., Gähler R. (2007) J. Appl. Cryst. 40, 1056 - 1063).
In June 2006 the guide replacement project has been approved and coupled with the "new detector & tank" projcet to result in the extended Millennium project “D11 Revised”.