neutron guides - from standards to the "finest art"
The fabrication of the neutron guides is performed according to the high standards of SwissNeutronics. The cross-section of the guides is defined by means of precisely ground substrates using a trottoir-ruler construction originally introduced by SwissNeutronics. This concept guarantees the mechanical stability of the neutron guides over many decades of years because irradiation effects on the glue do not affect the geometry of the guides. The supermirror coatings are prepared by DC magnetron sputtering with a sophisticated deposition process enabling for excellent reflectivity while internal stress is well controlled and minimized to guarantee long term stability regarding delamination. The quality of the guides is controlled by an extensive quality control management system that has been well established including complete inspections of all guide units with full traceability of every substrate.
Typical specifications of neutron guides by SwissNeutronics are:
- length of guide units: | 1.5 - 3 m |
- cross-section: | few mm to 400 mm x 500 mm |
- accuracy of cross-section: | ±0.02 mm, ≈0.01 mm (RMS) |
- waviness: | typically <1.0 x 10-4 rad |
- materials: | float glass, Borofloat 33©, N-BK7, S-BSL7, silicon, aluminium, copper |
- vacuum tight:
| Testpressure: < 5 x 10-2 mbar max. leakrate: 1 x 10-7 mbar*l/s |
SwissNeutronics produced many hundred meters of neutron guides for all major laboratories for neutron research. Among those are very special guide assemblies for dedicated applications exhibiting the “finest art” of neutron guide fabrication. In the following some highlights are depicted.
regular supermirror guide – SuperHRPD @ JPARC (2007)
The SuperHRPD @ JPARC utilizes a long supermirror guide to achieve a high resolution for the experiments. In 2007 SwissNeutronics produced 80 m neutron guides for this beamline including mechanical equipment (vacuum casings, alignment provisions). The guide is completely coated with supermirror of m = 3. The reflectivity of every deposition run was tested showing an average of about 88% at the critical edge. The installation was successfully performed early 2008.
Type: regular neutron guide Path/profile: curved horizontal (polygonal appros.) / straight Cross-section: 25 mm x 75 mm Length: 80 m Coating: Ni/Ti, m=3 Substrates: Float glass, Borofloat 33©
Monolith – NIST (2009)
SwissNeutronics was awarded the contract from NIST to fabricate three demanding, complex guide assemblies for the initial sections of their new guide system. First, the proper design was elaborated, in particular to link rigidly and precisely the individual guide units to the monoliths. Then the Borkron glass was processed and finished with a superior super-polishing of the surface, enabling for very high reflectivity for the high-m supermirrors. After grinding the substrates to their proper dimensions, they were coated with supermirror of excellent reflectivity, e.g. R = 0.84 for m = 3.6. Then a careful alignment with dedicated equipment and assistance by the laser tracker enabled a highly accurate positioning of the guide units with respect to each other. The typical accuracy was ±0.02 mm. In the end, three monoliths with supermirror coating of high reflectivity and high geometrical precision were fabricated and delivered to NIST in due time. In conclusion, NIST has obtained high-end neutron guide assemblies for the initial section of the new guide system from SwissNeutronics, which can be installed conveniently with high accuracy into the designated locations.
Type: neutron guide splitter (multi-units) Path/profile:
- H3 top
- H3 bottom
- H3C
- H3D
curved vertical / parallel
curved vertical / parallel
curved vertical / linear tapered
curved vertical / linear tapered
Cross-section:
- H3 top
- H3 bottom
- H3C
- H3D
50 mm x 50 mm
50 mm x 50 mm
115 mm x 60 mm
110 mm x 196.04 mm -> 211.29 mm
Length: 1500 mm Coating: Ni/Ti, m=1 / 1.5 / 1.65 / 2.4 / 2.7 / 2.8 / 3.6 Substrates: N-ZK7 (Borkron)
Neutron guide splitter – H14 @ ILL (2011)
Within their Millennium program the ILL refurbished major parts of the guide system. The most complex part was the Quad-guide, which branches an initial large cross-section into four sub-beams to increase the number of instrument positions. In order to separate the instruments and tailor the neutron beams to the desired phase space the various guides have individual characteristics comprising horizontal and vertical curvatures. Naturally, the individual guides are very close to each other at the beginning. In order to solve issues of the design of vacuum casings, installation and alignment it was suggested to build multi-units, finally called “Quad-guides”.
Type: neutron guide splitter (multi-units) Path/profile:
- H141
- H142
- H143
- H144
curved vertical & horizontal / parallel
straight / parallel
curved vertical / parallel
curved horizontal / parallel
Cross-section:
- H141
- H142
- H143
- H144
35 mm x 45 mm
35 mm x 45 mm
30 mm x 45 mm
105 mm x 45 mm
Length: 20 m Coating: Ni/Ti, m=1 / 1.4 / 2 / 2.4 Substrates: N-ZK7 (Borkron)
triple guide – H5 @ ILL (2013)
Within the millennium program the ILL refurbished the neutron guide H5. The initial common large cross-section (120 mm (w) × 240 mm (h)) branches into three individual guides, which supply neutrons to various instruments. The guide switch required complex assemblies because of vertical and horizontal curvatures of the guide axis in combination with divergent guide profiles. SwissNeutronics fabricated the triple guide switch for the entire length of 15 m.
Type: neutron guide splitter (multi-units) Path/profile:
- H521
- H522
- H523
curved vertical / linear tapered
curved vertical / parallel
curved vertical & horizontal / parallel
Cross-section:
- H521
- H522
- H523
117 mm x 120 mm -> 72.3 mm x 143.24 mm
115 mm x 60 mm
115 mm x 55 mm
Length: 15.5 m Coating: Ni/Ti, m=1.2 / 1.5 / 2 / 2.5 Substrates: N-ZK7 (Borkron)
Neutron guides - ILL
The ILL operates the largest neutron guide system worldwide. SwissNeutronics provided a major part of the guides for the refurbishment and the extension of the guide systems.
Total length: ≈ 460 m Coating: Ni/Ti, m=1 -> m=4 Substrates: Float glass / Borofloat 33© / N-ZK7 (Borkron) / N-BK7 (Borkron) / S-SBL7 (Borkron)
Neutron guides - NIST
When NIST refurbished and extended its neutron guides systems, starting in 2008, SwissNeutronics provided a significant number of neutron guide units according to their specifications. All the glass guides were made of Borkron glass super-polished by SwissNeutronics.
Total length: ≈ 136 m Coating: Ni/Ti, m=1 -> m=3.6 Substrates: N-BK7 (Borkron)
