Hight Brightness Neutron Compact Sources
What is a compact accelerator-based neutron source ?
An accelerator-based neutron source consists of the following components:
- a proton or deuteron source producing a beam of particles at energies of the order of 100 keV with a peak intensity of 100mA ;
- a RFQ (Radio-Frequency Quadrupole) stage whose role is to shape the continuous ion beam and to ensure an initial acceleration to an energy of a few MeV;
- additional acceleration stages to increase the energy of the ions to the desired energy (several 10 MeV);
- transport lines to the target;
- a target made of a material that generates neutrons during the interaction with protons;
- a moderator and a reflector whose role is to slow down the neutrons to the energy required by the end-users (typically from 2 to 100 meV);
- several neutron beam lines bringing the neutrons to the spectrometers.
While in a reactor, the number of neutrons produced is of the order of 1018 n/s, the neutron flux on a sample is of the order of 107 n/s. Only a fraction of the order of 10-10 of the neutrons produced is actually used. This leads to secondary effects in terms of shielding. In a CANS (Compact Accelerator based neutron Source), the term “Compact” refers to the Target-Moderator-Reflector (CMR) assembly which can be made very small (a few liters) compared to reactor moderators (D20) whose volume is in the m3 range. Therefore, while the gross number of neutrons produced on a CANS may be low, high source brightness can be achieved in the small volume of the RMC. The fraction of useful neutrons is much larger. The whole philosophy of a compact neutron source is “produce what you need”. The entire source is also physically compact (10-30 m long) compared to spallation facilities (600 m long) operating at very high proton energies (∼ 1 GeV).
Expected performances for neutron scattering on a compact high brightness source
In Europe, several institutes are considering high brightness CANS facilities using the latest available technologies. The CEA has considered a reference design (SONATE) with the following parameters: Ep = 20 MeV, Ipeak = 100 mA, duty cycle = 4%, P = 80 kW. These parameters were chosen in part because they correspond to the first 20 m of the ESS LINAC (out of 600 m). Therefore, the components (Source, RFQ and DTL) are available without R&D development. Monte-Carlo simulations (MCNP – GEAN4) suggest that a brightness of 1.2×1011 n/cm²/s/sr can be obtained at the moderator exit. This brightness value has been used as input in Monte-Carlo instrument simulations (using McSTAS). The table below compares the performance of different scattering techniques in terms of flux at the sample in terms of neutrons/cm²/s.) The calculations suggest that a high brightness CANS can provide performance equivalent to medium power reactors.
| Technique | Flux on sample | Reference spectrometers | Potential gains |
|---|---|---|---|
| Reflectivity | 0.8x107 n/s/cm2 |
HERMES@LLB 1x107 n/s/cm2 POLREF@ISIS~1x107 n/s/cm2 |
ESTIA@ESS concept x10 Advanced Deconvolution ×3 |
| SANS |
0.7x106 n/s/cm2 (low Q) 2.2x106 n/s/cm2 (med Q) 6.7x106 n/s/cm2 (high Q) |
PAXE@LLB (low Q) 0.7x106 N/s/cm2 SANS2D@ISIS 1x106 N/s/cm2 |
Slit setup × 10 Focusing optics for VSANS (small Q) x10 |
| Powder diffraction | 2x106 n/s/cm2 | G41@LLB 2x106 n/s/cm2 |
Large solid angle detector (7C2 type) x20 |
| Imaging (white beam) |
1.5x106 n/s/cm2 (or LD = 240) 1.3x107 n/s/cm2 (for LD = 80) |
ICON@PSI 1x107 n/s/cm2 CONRAD@PSI 1x107 n/s/cm2 (for L/D = 240) |
MCP detectors x5 Coded Source Imaging x10 |
| Imaging (time resolved) |
1x105 n/s/cm? (for L/D = 500) DI/I = 1% |
ANTARES@FRM2 5x105 n/s/cm2 | |
| Direct TOF |
3x104 n/s/cm2 (thermal) 1.8x105 n/s/cm2 (cold) |
IN5@ILL 6.8x105 n/cm2/s | MUSHROOM (LETx70 on single crystals) |
| Inverse TOF | 1x107 n/cm2/s | OSIRIS@ISIS 2.7x107 n/cm2/5 | |
| Spin-Echo | 2x106 n/cm2 | MUSES@LLB 2x107 n/s/em2 (et 5A*) | Multi-MUSES (×70) |
State of the art in France
In the framework of the CMR50 (Target-Moderator-Reflector 50 kW) project, the Systems Engineering Department, the DACM (Nuclear Physics Department), the SPR (Radiation Protection Service) and the Léon Brillouin Laboratory are working on a target-reflector assembly (and its shielding) that can support a 50 kW proton beam. The project runs from 2017 to 2019. Initial time-of-flight measurements were performed on the IPHI facility in 2016 to validate the Monte Carlo simulations. Further testing is planned to acquire reliable input data for the simulations. The goal is to be able to finance the construction of a “demonstration” instrument that would operate at Ep = 3 MeV on the IPHI facility in Saclay (SESAME project “IPHI-Neutrons”). In parallel, we are trying to create links with other European partners. A PRCI collaboration has been proposed to formalize a CEA / JCNS collaboration on TMR aspects and on cold sources in particular. An H2020 design study project (CAN4EU) has been submitted with a number of European partners (JCNS, INFN, CNR, ESS-B, KFKI, PSI, CEA, CNRS / LPSC). The objective of this project is to propose a coherent vision of a network of CANS sources in Europe in the medium term.
Usefull links
Existing CANS sources and projects
- LENS The Low Energy Neutron Source (Indiana University)
- RANS RIKEN Accelerator-driven compact Neutron Source
- JCANS Japan Collaboration on Accelerator-driven Neutron Sources
- UCANS Union for Compact Accelerator-driven Neutron Sources
- Le projet de source à haute brillance du Jülich Center for Neutron Scattering
High Brillance Neutron Source (website) - The Jülich HBS Project CDR
- Neutrons at ESS-Bilbao : From Production to Utilisation:
ARGITU compact accelerator neutron source: A unique infrastructure fostering R&D ecosystem in Euskadi - SARAF – Soreq Applied Research Accelerator Facility
- SONATE, an accelerator-driven neutron source
- LvB at Mirrotron
Technical documents and prospectives
- Page web du LLB
- Focus Point on Compact accelerator-driven neutron sources [ Eur. Phys. J. Plus ]
- Lavelle et al., 2008: https://doi.org/10.1016/j.nima.2007.12.044
https://www.sciencedirect.com/science/article/pii/S0168900208000028?via%3Dihub - Rucker et al., 2016, The Jülich high-brilliance neutron source project [ Eur. Phys. J. Plus ]
- Fabrèges et al., 2016, Performances of Neutron Scattering Spectrometers on a Compact Neutron Source [ arXiv ]
- Menelle et al., 2016, Neutrons production on the IPHI accelerator for the validation of the design of the compact neutron source SONATE [ arXiv ]
