SNS: an overview

1. SNS: an overview Robert McGreevy Deputy Director Neutron Sciences Directorate May 3rd 2012

2. Oak Ridge Neutron Sciences • Operate two world class neutron facilities • Carry out world class research • Enable an outstanding User Science Program • Develop signature science programs and partnerships • Stay at the leading edge of neutron science by developing new capabilities, instruments and tools

3. How do we produce neutrons? Fission • chain reaction • continuous flow • 1 neutron/fission • 180 MeV/neutron Spallation • no chain reaction • pulsed operation • 40 neutrons/proton • 30 MeV/neutron

4. Chopper system makes gaps 945 ns 700 ns mini-pulse Current Current 1 ms macropulse 1ms SNS Accelerator Complex Accumulator Ring: Compress 1 msec long pulse to 700 nsec Collimators Front-End: Produce a 1-msec long, chopped H- beam Injection Extraction RF 1 GeV LINAC ~1000 MeV RTBT 2.5 MeV HEBT LINAC Front-End Liquid Hg Target 1 ms macropulse 1 ms

5. H- Ion source

6. SNS Cryomodule Designed to operate at 2.1 K (superfluid helium) 11*Medium beta Return end can Helium vessels 12*High beta Space frame Supply end can Fundamental power couplers

7. High Beta Cryomodule

8. Stripper foils Now standard foil U-shaped corrugations, corner cut off This foil lasted an entire run cycle

9. SNS Design Parameters

10. SNS accelerator system performance continues to be outstanding – availability for FY12 so far is ~95%

11. Energy and power on target from October 2006

12. Liquid Hg target

13. Lifetime limited by cavitation damage

14. Target exceeds initial goal of 2500 MWhrs

15. Moderator-reflector

16. Neutron moderators BL-11 BL-2 Both hydrogen at 20 K BL-5 • coupled • moderator thickness - 5 cm • pre-moderator - light water • decoupled – 1.4 mm Cd poisoned - 0.8 mm Gd poison depth – 2.5 cm

17. Neutron moderators BL-14 BL-17 BL-8 • symmetric to the top downstream moderator • decoupled – 1.4 mm Cd poisoned - 1.2 mm Gd poison depth - 1.5 cm BL8 2.5 cm BL17

18. Neutron Guides

19. Neutron Detectors • 3He Multiwire proportional chambers • 3He Position sensitive proportional tubes • Commercially available tubes • Scintillation detectors with wavelength shifting fiber readout • New development • Anger cameras with position sensitive photomultiplier tubes • New development

20. Instruments

21. Sample environment

22. Software

23. Bio-Energy: Converting Bio-Mass to Bio-Fuel In-situ biomass degradation for cellulosic ethanol production Switchgrass. Photo Courtesy NREL. • Primary subunit swelled from ~8.5 Å (0 min)to ~19 Å(2 min). • In the initial state (0 min), cellulose fibrils form a random network (Q-2.5). • On treatment (2 min), large particles ~135 Å appear possibly Lignin lumps. • Micron-sized superstructures with smooth interfaces (roughness < 50 nm) persist even after 10 min pretreatment (Q-4).

24. Polymer Multilayers and Films: Charged and hydrogen-bonded polyelectrolyte films PMAA

25. Nanostructuring: High-zT Thermoelectrics La3-xTe4 and nano-crystalline Si. • La3-xTe4 is capable of zT ~ 1.2 near 1300 K, making it the highest performing, bulk n-type material above 1000 K. • La3-xTe4 adopts the Th3P4 structure (left), and accommodates up to 1/9 vacancies on the La site. • Nanostructuring is an effective method to decouple electrical and thermal transport parameters to achieve high efficiency (zT). • Dramatic reductions in the lattice thermal conductivity by nanostructuring bulk silicon with limited degradation in electron mobility can be achieved, leading to an unprecedented 3.5 times performance increase over that of the parent single crystal material. • Phonon measurements performed on the ARCS spectrometer reveal the large effect of the nanostructuring on phonons (above). • The disorder in the lattice induced by the vacancies is thought to enhance phonon scattering and contribute to the low lattice thermal conductivity (between 0.4 and 0.8 W/m/K). • The phonon DOS measured on ARCS reveals a systematic trend, associated with a change in bonding with increased vacancy concentration (below). S(Q,E) bulk Si, 300K (ARCS) S(Q,E) nano Si, 300K (ARCS) O. Delaire, M. Lucas, M. Stone, D. Abernathy (ORNL)

26. Superconductivity: Iron arsenides Complementarity of SNS and HFIR: Spin waves – HB-1 @HFIR Zhao et al. PRL 101, 217002 (2008) Phonon DOS - ARCS @SNS Christianson et al., PRL 101, 157004 (2008) Spin waves – HB-3 @HFIR McQueeney et al. PRL 101, 227205 (2008)

27. Neutron powder diffraction to understand the synthesis and structure of novel battery materials • Lithium transition metal fluorophosphates with a tavorite structure have been recognized as promising electrode materials for lithium-ion batteries because of their good energy storage capacity combined with electrochemical and thermal stability. • The structure of the pure single phase end-member Li2FePO4F was synthesized by lithiation of LiFePO4F, and solved via Rietveldrefinement of the combined X-ray and neutron diffraction data, showing that Li+ occupies multiple sites in the tavoritelattice. • Neutron powder diffraction data were collected at the HFIR HB-2A diffractometer and in this study highlight the critical need for neutron diffraction to accurately and quantitatively “see” the light atoms such as Li, which is crucial to understanding the microscopic behavior of Li battery materials. Ellis, B.L., Ramesh, T.N.,Rowan-Weetaluktuk, W.N.,Ryan, D.H. Nazar, L.F., Solvothermalsynthesis of electroactive lithium iron tavorites and structure of Li2FePO4F. JournalofMaterialsChemistry, inpress.

28. Small angle neutron scattering to understand polyglutamine aggregation in Huntington’s Disease SANS on polyglutamine fibrils: Using time-resolved small-angle neutron scattering (SANS), we capture “snapshots” of the early protein aggregates: fibril-fibril interactions at lower Q TEM image of the fibrils With SANS, we are learning about the structural formation of the aggregates related to Huntington’s disease. This work will aid in determining the toxic mechanism and developing treatments for the disease. Stanley, C.; Perevozchikova, T.; Berthelier, V. Biophys. J.100, 2504–2512 (2011).

29. Using neutron diffraction to help solve ITER’s superconducting cable degradation • Performance of the cable had degraded much sooner than expected and ITER staff needed to determine the reason. • Testing at the SNS on VULCAN measured the strain state of the superconducting conductor and is assisting US ITER to assess the strain’s impact on conductor degradation. The cryostat was specially developed by the ITER Team for this experiment. • VULCAN is the only neutron scattering instrument capable of a study combining sample size with the ability to gather data in reasonable time scales.  • Initial studies show the cable has three phases: Cu, Nb3Sn, Nb. After magnetic cycling, Nb3Sn and Nb suffer a “tensile” stress. This is balanced by a “compressive” stress in Cu. Stainless steel jacket shows very little strain, consistent with mechanical measurements. • Results were reported at a February 2012 ITER meeting in Japan. • Studies will continue during the next SNS cycle at cryogenic temperature to assess the effect of cooling on the stress state. • Top: The 3 m long superconducting cable was mounted in a cryostat to be operated at superconducting temperatures. Each data point took about 30-60 minutes. The tubes have seen cycling under high magnetic field, and our goal is to determine the change in stress state and to assess the damage mechanism due to the magnetic cycling. Right : Cable stainless steel jacket is 50 mm on edge with superconducting bundles surrounding a center cooling channel.

30. SNS Second Target Station