Neutron delivery guides and infrastructure

Our expertise lies in the comprehensive design of the neutron guide systems, vacuum housings, alignment systems and all supporting infrastructure. From the H1-H2 beamtube insert in the reactor to the neutron instruments, our designs address the unique challenges of neutron transport, incorporating precision engineering to optimise neutron delivery to each instrument.

The mechanical design, installation and alignment of these systems are carried out by ILL’s in-house mechanical services, making these some of the most ambitious and intricate neutron guide projects in the neutron scattering community.
As part of the Endurance programme five major guide projects have been successfully completed resulting in nearly a kilometre of new high-performance neutron guides:

H1-H2 thermal- and cold-neutron in-pile neutron guides (280 m)
H15 cold-neutron multiple-branch guide (330 m)
H24 thermal-neutron double-branch guide (210 m)
H16 elliptical focusing guide (45 m)
H112 variable focusing guide (11 m)

Contact

Jérôme Beaucour
Head of Service
beaucour@ill.fr
Tel. +33 4 76 20 79 77

Neutron technology brochure

Neutron_technologies-brochure.pdf

H1-H2 neutron guide in the pool of ILL 5C

H1-H2: IN-PILE NEUTRON GUIDES

Approximately every 15 years, the H1-H2 beamtube must be replaced due to irradiation damage and to ensure the structural integrity of this critical reactor component. At the same time, we take the opportunity to replace the in-pile neutron guides, mounted on the so-called plateau inside the beamtube. These guides degrade over time due to radiation exposure, and their replacement allows us to install higher-performance optics and optimise their geometries for improved neutron extraction.

To further enhance reactor safety, an additional 48 metres of neutron guides were installed on the 11 guide feedthroughs between the reactor building and ILL7 guide hall, reinforcing the system against seismic events and improving overall robustness.

H16 (IN5): FOCUSING ELLIPTICAL GUIDE

Converging neutron guides, although not a new concept, have seen growing applications with the development of high critical angle supermirrors, which enable better control and optimisation of neutron transport. These focusing guides enhance performance by progressively narrowing the guide cross-section—either horizontally, vertically, or both—resulting in an increased divergence of neutrons within the guide. This process transforms a larger, less divergent neutron beam into a highly divergent one over a smaller spatial area, producing a more intense beam at the guide’s exit.

H24: DOUBLE-BRANCH THERMAL-NEUTRON GUIDE

The H24 guide has been replaced with a 110-metre-long double-branch guide featuring supermirror coatings, significantly improving neutron transport to the downstream instruments. The new guide utilises higher critical angle coatings up to m = 3 and introduces an elegant common-curved-trumpet design.

This approach exploits the differing radii of curvature of the H241 (R = 14,000 m) and H242 (R = 8,000 m) downstream sub-branches, allowing the guide to gradually expand over 22 metres with m = 2 divergence. As the guide curves, it naturally splits into two distinct branches before further subdividing into five end-of-guide positions. This configuration supplies neutrons to multiple instruments: XtremeD, CT2, and FIPPS access the lower, middle, and upper sections of H241, while D10+ and IN13 utilise the lower and upper sections of H242. The installation of the new guide, along with its associated civil engineering work, was carried out during the long H1-H2 shutdown in 2022.

Top: H24 guide and instruments sighting | Bottom: H24 simulated guide geometry

The new H24 guide delivers approximately three times more neutrons than the previous m = 1 guide, primarily due to the increased critical angle coatings of the new m = 2 guide (with a theoretical gain factor of four when transitioning from m = 1 to m = 2 divergence). This enhanced flux and divergence can be fully exploited by the modernised instruments, with total performance gains exceeding an order of magnitude for instruments such as the D10+ single-crystal diffractometer.

H15: MULTIPLE-BRANCH COLD-NEUTRON GUIDE

The new H15 cold-neutron guide replaces one of the last remaining original guides installed alongside the first suite of ILL instruments in 1972. Cold-neutron instruments typically benefit most from dedicated end-of-guide positions. Historically, this was not always possible, and performance was limited by upstream monochromators and the need to share a single guide cross-section between multiple instruments.

In addition to the more usual curved neutron guides, the H15 guide incorporates various neutron optical devices to efficiently separate individual guide branches. These include non-polarising and polarising deflectors for D11 and D007, as well as converging guides (D007) and elliptically focusing guides (SHARPER), ensuring optimised neutron delivery tailored to each instrument’s specific requirements.