1. SNS Experimental Facilities Oak Ridge X0000910/arb Neutron Sources for Materials Research T.E. Mason Experimental Facilities Division Spallation Neutron Source Acknowledgements: Jack Carpenter

2. SNS Experimental Facilities Oak Ridge X0000910/arb 2 The neutron was discovered in 1932 by Chadwick Coherent neutron diffraction (Bragg scattering by crystal lattice planes) was first demonstrated in 1936 by Mitchel & Powers and Halban & Preiswerk as an exercise in wave mechanics The possibility of using the scattering of neutrons as a probe of materials developed with the availability of copious quantities of slow neutrons from reactors after 1945. Fermi's group used Bragg scattering to measure nuclear cross-sections 98-6245 uc/vlb Neutrons and Neutron Sources

3. SNS Experimental Facilities Oak Ridge X0000910/arb 3 Neutrons and Neutron Sources A reactor moderates the neutrons produced in the fission chain reaction resulting in a Maxwellian energy distribution peaked at T (300K). 98-6243 uc/rfg

4. SNS Experimental Facilities Oak Ridge X0000910/arb 4 The application of slow neutron scattering to the study of condensed matter had its birth in the work of Wollan and Shull (1948) on neutron powder diffraction: The neutron is a weakly interacting, non-perturbing probe with simple, well-understood coupling to atoms and spins The scattering experiment tells you about the sample not the probe 98-6244 uc/rfg Neutrons and Neutron Sources

5. SNS Experimental Facilities Oak Ridge X0000910/arb 5 You can easily work in extreme sample environments H,T,P,...) e.g. 4 He cryostat (Shull & Wollan) and penetrate into dense samples The magnetic and nuclear cross-sections are comparable, nuclear cross-sections are similar across the periodic table Sensitivity to a wide a range of properties, both magnetic and structural 98-6242 uc/rfg Neutrons and Neutron Sources

6. SNS Experimental Facilities Oak Ridge X0000910/arb 6 Energies and wavelengths of thermal and cold neutrons are well matched to relevant energy scales in condensed matter (300K = 30 meV, 50K = 5 meV) – Inelastic experiments with good energy (1 meV) and momentum (0.01 Å-1) are possible Cross-section is proportional to static and dynamic correlation functions – Results are of direct relevance to modern mathematical descriptions of interacting systems - Superconductivity - Magnetism - Phase transitions - Electronic properties - Non-equilibrium phenomena - Structure and dynamics 98-6246 uc/vlb Neutrons and Neutron Sources

7. SNS Experimental Facilities Oak Ridge X0000910/arb 7 Work leading to the development of inelastic neutron scattering was carried out throughout the 50's The real breakthrough was the development of the “constant-Q” mode of operating the triple-axis spectrometer pioneered by Brockhouse and co-workers at Chalk River: – this permitted the systematic investigation of the dynamic response of the material – concentrating on the regions of interest 98-6241 uc/rra Neutrons and Neutron Sources

8. SNS Experimental Facilities Oak Ridge X0000910/arb 8 How Are Neutron Beams Produced? Neutrons are one of the fundamental building blocks of matter that can be released through: – The fission process by splitting atoms in a nuclear reactor – The spallation process by bombarding heavy metal atoms with energetic protons The moderated neutrons, once released, can be transmitted through beam guides into the laboratory and used for a wide variety of research and development projects 98-3807A uc/djr

9. SNS Experimental Facilities Oak Ridge X0000910/arb 9 Development of Neutron Science Facilities 97-3924E uc/djr

10. SNS Experimental Facilities Oak Ridge X0000910/arb 10 Neutrons: Where? Fission: n + 235 U = n + n + fragments moderated by available D 2 O (H 2 O) to E = T (Maxwellian) Sustain chain reaction200 MeV/n 98-6239 uc/vlb

11. SNS Experimental Facilities Oak Ridge X0000910/arb 11 Types of Neutron Sources Reactor e.g., ILL, France ~1.5x10 15 n/cm 2 /s (recently underwent major refurbishment) Advantages: – high time averaged flux – mature technology (source + instruments) – very good for cold neutrons Drawbacks: – licensing (cost/politics) – no time structure 98-6237 uc/rra

12. SNS Experimental Facilities Oak Ridge X0000910/arb 12 The Institut Laue-Langevin, Grenoble 2000-05269 uc/arb

13. SNS Experimental Facilities Oak Ridge X0000910/arb 13 Types of Neutron Sources Pulsed reactor – only tried in Russia - IBR II Dubna – 2Hz 1500 MW when on Advantages: – high peak flux Drawbacks: – time structure not optimal (low average) – unlicenseable in the west 98-6238 uc/rra

14. SNS Experimental Facilities Oak Ridge X0000910/arb 14 Schematic View of the IBR-2, Dubna 2000-05274 uc/arb

15. SNS Experimental Facilities Oak Ridge X0000910/arb 15 The Principal Characteristics of the IBR-2 Reactor 2000-05276 uc/arb

16. SNS Experimental Facilities Oak Ridge X0000910/arb 16 Schematic Layout of the IBR-2 Experimental Hall 1-DIFRAN 2-DIN-2PI 3-RR 4-YuMO 5-HRFD 6a-DN-2 6b-SNIM-2 7a-NSVR 7b-NERA-PR 8-SPN 9-REFLEX 10-KDSOG-M 11-ISOMER 12-DN-12 13, 14-test channels 2000-05275 uc/arb

17. SNS Experimental Facilities Oak Ridge X0000910/arb 17 Neutrons: Where? Spallation: p + heavy nucleus = 20 n + fragments 1GeV e.g. W, Pb, U flux DR3Risø~2 x 10 14 n/cm 2 /s ILLGrenoble~1.5 x 10 15 n/cm 2 /s ISISaverage2 x 10 13 n/cm 2 /s 8 x 10 15 n/cm 2 /s 23 MeV/n 98-6240 uc/vlb

18. SNS Experimental Facilities Oak Ridge X0000910/arb 18 Spallation-Evaporation Production of Neutrons ‘ ‘ ‘ ‘ ‘ ‘ ‘ ‘ ‘ ‘ ‘ Original Nucleus Proton Recoiling particles remaining in nucleus EpEp Emerging “Cascade” Particles (high energy, E < E p ) ~ (n, p. π, …) (These may collide with other nuclei with effects similar to that of the original proton collision.) Excited Nucleus ~10 –20 sec Evaporating Particles (Low energy, E ~ 1–10 MeV); (n, p, d, t, … (mostly n) and  rays and electrons.)   e Residual Radioactive Nucleus Electrons (usually e + ) and gamma rays due to radioactive decay. e  > 1 sec ~

19. SNS Experimental Facilities Oak Ridge X0000910/arb 19 Types of Neutron Sources Pulsed spallation source e.g., ISIS, LANSCE 200 µA, 0.8 GeV, 160 kW 2x10 13 n/cm 2 /s average flux 8x10 15 n/cm 2 /s peak flux Advantages: – high peak flux – advantageous time structure for many applications – accelerator based – politics simpler than reactors – technology rapidly evolving Disadvantages: – low time averaged flux – not all applications exploit time structure – rapidly evolving technology 98-6235 uc/rra

20. SNS Experimental Facilities Oak Ridge X0000910/arb 20 IPNS Facilities Map 2000-05272 uc/arb

21. SNS Experimental Facilities Oak Ridge X0000910/arb 21 ISIS Instruments 2000-05273 uc/arb

22. SNS Experimental Facilities Oak Ridge X0000910/arb 22 Types of Neutron Sources CW spallation source e.g., PSI 0.85 mA, 590 MeV, 0.9 MW 1x10 14 n/cm 2 /s average flux Advantages: – high time averaged flux – uses reactor type instrumentation (mature technology) Disadvantages: – no time structure – high background 98-6236 uc/rra

23. SNS Experimental Facilities Oak Ridge X0000910/arb 23 PSI Proton Accelerators and Experimental Facilities 2000-05270 uc/arb

24. SNS Experimental Facilities Oak Ridge X0000910/arb 24 Principle of the Spallation Neutron Source SINQ 2000-05271 uc/arb

25. SNS Experimental Facilities Oak Ridge X0000910/arb 25 The Materials Testing Accelerator E. O. Lawrence conceived this project in the late 1940s as a means to produce Pu-239 and tritium, and later, U-233. Despite its name, MTA was never intended for materials research. Work went on at the site of the present Lawrence Livermore Laboratory, where scientists accomplished substantial high power accelerator developments. Efforts continued until 1955 when an intense exploration effort revealed large Uranium ore reserves in the U.S. and the project terminated. By that time the pre-accelerator had delivered CW proton currents of 100 mA and 30 mA of deuterons. The work was declassified in 1957. 2000-05265 uc/arb

26. SNS Experimental Facilities Oak Ridge X0000910/arb 26 The Materials Testing Accelerator: Machine Parameters There was already by that time some information on the production of spallation neutrons by 190-MeV deuteron-induced spallation on Uranium, about 30% more than by protons of the same energy. This guided the choice of accelerated particle type and beam energy. With the anticipated required production rate, the parameters of the accelerator were set: – Deuterons – Particle energy – 500 MeV – CW operation – 320 mA (beam power 160 MW) 2000-05266 uc/arb

27. SNS Experimental Facilities Oak Ridge X0000910/arb 27 The Materials Testing Accelerator: Target Original ideas concerned a Uranium target Subsequent development led to target systems alternatives including moderated subcritical lattices (k < 0.9) Finally the chosen target system consisted of a NaK-cooled Beryllium primary target, and depleted Uranium secondary target for neutron multiplication, within a water-cooled depleted Uranium lattice for breeding Plutonium 2000-05267 uc/arb

28. SNS Experimental Facilities Oak Ridge X0000910/arb 28 Sketch of Cutaway View of Linear Accelerator – Looking East – Injector End 2000-05268 uc/arb

29. SNS Experimental Facilities Oak Ridge X0000910/arb 29 The ING Project The Chalk River Laboratory of Atomic Energy of Canada Limited launched the Intense Neutron Generator (ING) Project in 1964. The goal was a “versatile machine” providing a high neutron flux for isotope production and neutron beam experiments. Work continued until late 1968 when the project was cancelled due to the perceived high costs and insufficient political support in the Canadian scientific community. ING was estimated to cost about $150 M to build and about $20 M/yr to operate. Technical developments that resulted from the ING project were significant, even seminal 2000-05257 uc/arb

30. SNS Experimental Facilities Oak Ridge X0000910/arb 30 The ING Project: Machine Specifications Proton linac Length: – Alvarez section – 110 m – Waveguide section – 1430 m Total RF power – 90 MW Energy – 1 GeV Current – 65 mA (CW) Proton beam power – 65 MW 2000-05258 uc/arb

31. SNS Experimental Facilities Oak Ridge X0000910/arb 31 Perspective View of ING (artist’s conception) 2000-05259 uc/arb

32. SNS Experimental Facilities Oak Ridge X0000910/arb 32 The ING Project: Target System Flowing Pb-Bi eutectic, 20 cm ø, 60 cm long Vertical (downward) incident proton beam Beryllium “Multiplier” thickness 20 cm D 2 O moderator – 100 cm radius Global neutron production rate 10 19 n/sec Max thermal neutron flux 10 16 n Th /cm 2 -sec Beam tubes, 5 tangential (10 cm ø), one radial (10 cm ø), one through-tube (20 cm ø) 2000-05260 uc/arb

33. SNS Experimental Facilities Oak Ridge X0000910/arb 33 Cutaway View of the Target Building 2000-05261 uc/arb

34. SNS Experimental Facilities Oak Ridge X0000910/arb 34 Lead-bismuth Eutectic Flow in Target Zone 2000-05262 uc/arb

35. SNS Experimental Facilities Oak Ridge X0000910/arb 35 Intense Neutron Generator 1952 W.B. Lewis promotes spallation and accelerators for neutron production 1960s at CRNL – 65 mA CW protons to 1 GeV – Accelerator development – Pb-Bi loops – Experimental facilities and design – Cockcroft-Walton limitation – 35 mA CW at 750 keV Led to Accelerator Breeder program in 1970s – ZEBRA in 1980s 2000-05263 uc/arb

36. SNS Experimental Facilities Oak Ridge X0000910/arb 36 Measured Neutron Yield vs. Proton Energy for Various Targets 2000-05264 uc/arb From Fraser et al., measurements at Brookhaven Cosmotron

37. SNS Experimental Facilities Oak Ridge X0000910/arb 37 Pulsed Spallation Neutron Sources (primary source pulse widths of all are less than 0.5 µsec) 2000-05277 uc/arb

38. SNS Experimental Facilities Oak Ridge X0000910/arb 38 Pulsed Spallation Neutron Source Construction, Proposals and Studies 2000-05278 uc/arb

39. SNS Experimental Facilities Oak Ridge X0000910/arb 39 97-3792B uc/djr Anatomy of a Pulsed Spallation Source

40. SNS Experimental Facilities Oak Ridge X0000910/arb 40 The Spallation Neutron Source The SNS will begin operation in 2006 At 2 MW it will be ~12x ISIS with a time averaged flux ~NIST The peak thermal neutron flux will be ~125x NIST SNS will be the world’s leading facility for neutron scattering It will be a short drive from HFIR, a reactor source with a flux comparable to the ILL (~3x NIST)

41. SNS Experimental Facilities Oak Ridge X0000910/arb 41 Summary Parameters for the SNS Proton beam power on target2.0 MW Average proton beam current on target2.0 mA Pulse repetition rate60 Hz Peak linac H- current52 mA Chopper beam-on duty factor68 % Linac length, with 5 empty cryomodule slots331 m DTL output energy87 MeV Number of DTL 402.5-MHz 2.5-MW klystrons7 CCL output energy 185 MeV Number of CCL 805-MHz 2.5-MW klystrons8 SRF linac output beam energy~1.0 GeV Number of SRF cavities97 Number of linac 805-MHz 0.5-MW klystrons97 2000P-03544/jhb

42. SNS Experimental Facilities Oak Ridge X0000910/arb 42 Summary Parameters for the SNS (cont.) Linac beam duty factor6.0 % HEBT length170 m Accumulator ring circumference248.0 m Ring orbit rotation time945 ns Number of injected turns1060 Ring fill time1.0 ms Ring beam extraction gap250 ns RTBT length151 m Protons per pulse on target2.08E+14 Proton pulse width on target695 ns Target materialHg Number of ambient/composite/cold mod.1/1/2 Number of neutron beam shutters18 Initial number of instruments10 2000P-03545/jhb

43. SNS Experimental Facilities Oak Ridge X0000910/arb 43 Function – Create 65-mA H - ion beamIon Source/LEBT – Accelerate beam to 2.5 MeVRFQ – Chop beam into mini-pulsesLEBT/MEBT – Match 52-mA beam into Drift-Tube LinacMEBT Ion Source LEBT RFQ MEBT 2000P-03547/jhb

44. SNS Experimental Facilities Oak Ridge X0000910/arb 44 SNS High Beta Cryomodule

45. SNS Experimental Facilities Oak Ridge X0000910/arb 45 Ring Lattice 2000P-03550/jhb

46. SNS Experimental Facilities Oak Ridge X0000910/arb 46 SNS High Power Target Station 2000-03440/arb

47. SNS Experimental Facilities Oak Ridge X0000910/arb 47 Target Systems Summary 2-MW mercury target, shielding, remote handling, neutron beam transport 3 beam dumps Associated R&D: target test facility, materials compatibility, thermal shock TEC 85.9 M$ R&D 17.3 M$ 2000-03443/arb

48. SNS Experimental Facilities Oak Ridge X0000910/arb 48 Multistory building 202 feet wide by 325 feet long Instrument floor houses neutron instruments, instrument/target shops to support experimenters and target mock up activities RTBT shielded area brings beam to target Target Shield Stack and Hot Cell are bulk of category 2 nuclear facility housing Target and Target Maintenance Facilities Basement area includes services for the entire building, a portion is included in the nuclear facility The high bay area houses the cryogenic system for the moderators and allows access for maintenance of target system components The west yard contain service areas bringing in building utilities including helium and nitrogen Target Building - Scope of Target Building

49. SNS Experimental Facilities Oak Ridge X0000910/arb 49 Target Building - Current Layout

50. SNS Experimental Facilities Oak Ridge X0000910/arb 50 Target Building - Current

51. SNS Experimental Facilities Oak Ridge X0000910/arb 51 A full, 24 instrument, experimental hall layout has been developed to provide constraints on target/conventional interfaces and facilitate instrument planning Includes instrument under study plus realistic “placeholders” Instrument Planning 2000-03453/arb

52. SNS Experimental Facilities Oak Ridge X0000910/arb 52 The Spallation Neutron Source (SNS) is designed from the outset to allow operation with two target stations Long Wavelength Target Station 2000-03457/arb