Directions in Neutron Source Development

1. Directions in NeutronSource Development Physics ColloquiumBrookhaven National Laboratory Thomas E. MasonLaboratory Director Upton, New YorkNovember 21, 2007

2. Neutron sources:How far have we come? SNS 1018 SNS ESS ILL HFIR NRU MTR ISIS 1015 LANSCE HFBR KENS NRX IPNS ZING-P SINQ-II SINQ Tohoku Linac X-10 1012 ZING-P 109 Thermal Neutron Flux (n/cm2-sec) CP-2 Berkeley37-inch cyclotron Next-generation sources CP-1 106 Fission reactors Particle driven (steady-state) Particle driven (pulsed) 0.35-mCi Ra-Be source trendline reactors 103 trendline pulsed sources Chadwick ORNL 97-3924f/djr 100 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020 (Updated from Neutron Scattering, K. Skold and D. L. Price: eds., Academic Press, 1986) Brookhaven_0711

3. We have consistently managedto squeeze more out of existing sources • By adding cold sources to existing reactors: • NIST, JRR-3M, HFIR, etc., and more coming • By improving target/moderator optimization: • SINQ target, Lujan coupled moderators • Accelerators also have the potential for increase in beam power • Well exploited by high-energy physicists (e.g., AGS) • Increases in current at ISIS, Lujan, PSI • Next-generation sources (J-PARC and SNS) have made provision for power increases in their design What are the prospects for iterative improvement on the current technology base? Brookhaven_0711

4. The 20-year plan for SNS • Evolve along path envisagedin Russell Panel specifications • In 20 years: • Operating ~45best-in-class instruments • Two differently optimizedtarget stations • Beam power of 3–4 MW • Long WavelengthTarget Station (LWTS)and Power Upgrade should followa sequence that mesheswith deployment of initial capabilityand national needs • Similar developments likely elsewhere:Japan, China, Europe, . . . Brookhaven_0711

5. Power upgrade • Increase energyby adding to SC linac • Allows storageof more current in accumulator ring • Relatively straightforward for ring and linac 3-MW linac at 6% duty factorscales to 50 MW CW(not ours) 5 Managed by UT-Battellefor the Department of Energy Brookhaven_0711

6. SNS external antenna H– source Heliconplasmagenerator Ions Meeting the H– needs of the SNS power upgrade:Helicon driver for the SNS ion source • Demanding requirements: • Beam current: 70–95 mA • Pulse length: 1 ms • Duty factor: 7.4% • Proof-of-principle experiment (LDRD funding) to combine • VASIMR helicon plasma generator, ORNL Fusion Energy Division • SNS H– ion source, ORNL-LBNL • Expected to increasemaximum source plasma density(by a factor of ≥3) at reducedrf power, resulting in: • Increased H– current • Reduced heat removal requirements Helicon test facility, Building 7625 Goulding et al., AIP Conf. Proc.933, 493–496 (2007) Brookhaven_0711

7. One potential bottleneck: Stripping H– Novel approach to laser stripping: Use a narrowband laser to convert H– to protonsfor high-power operations Laser beam High-fielddipole magnet High-fielddipole magnet H– H0 a H0* proton Lorentz stripping Laserexcitation Lorentzstripping H– H0 + e– H0(n = 1) + g H0*(n = 3) H0* p + e– V. Danilov et al., Phys. Rev. ST Accel. Beams 10, 053501 (2007) Brookhaven_0711

8. Proof-of-principle experiment at SNS Light invacuum chamber Magnetic insertions Laser and optics H– beamcurrent Stripped electrons by laser light Stripping efficiency> 90% 12 8 4 0 30 40 50 60 Brookhaven_0711

9. Another potential bottleneck: Target Pressure pulse mitigation • Bubble injection (shock absorbers) • Proton radiography bubble visualization experiment: • Analysis is progressing, with about 500 images processed • Quantification of bubble sizes, numbers, and void fractionover a wide range of test conditions pRad bubble visualizationexperiment, LANL • Test conditions • Mercury thickness: 22 mm • Mercury velocity = 0.4 m/s • Helium gas flow throughjet bubbler 1: 140 sccm Brookhaven_0711

10. Original SNS-LWTS concept (Developed without assumption of additional beam power) Brookhaven_0711

11. Optimizing the neutronic environment and increasing beam power Time-averaged neutron spectra • We have many knobsfor tuning moderator/ reflector designto maximizeuseful neutrons • Timing • Energy • We don’t have verygood ways to tailorneutron direction 1.E+15 1.E+14 1.E+13 Brightness (n/s/cm2/sr/eV/MW) Second target station 1.E+12 Russell Panel Long-Wavelength Target Station High Power Target Station, beamline 5 1.E+11 1.E–05 1.E–04 1.E–03 1.E–02 1.E–01 1.E–00 Energy (eV) Brookhaven_0711

12. Source development • No existing or under construction source takes advantageof spallation process efficiency to make more neutrons • We have taken advantage of spectra and time tailoring to make more “useful” neutrons Figure courtesy K.N. Clausen, PSI Brookhaven_0711

13. Neutron production • For power density limit,the ANS reactor designprobably representsa practical extreme(~5 ILL) • CW spallation sourcenot likely to have more than 20 ILLwithout going to large target volume(lower flux) Brookhaven_0711

14. Father of all spallation sources:Lawrence’s Materials Testing Accelerator • Deuteron acceleratorfor production of plutonium and tritium • NaK-cooledBe target • 500 MeV • 320 mA • 160 MW Brookhaven_0711

15. The neutrons themselvesare becoming a problem! 15 Managed by UT-Battellefor the Department of Energy Brookhaven_0711

16. What about the instruments? • We are bumping upagainst the limitin terms of steradians(and space) • We still have lotsof room to improve: • Optics • Sample environment • Detector speed, resolution, efficiency, background 16 Managed by UT-Battellefor the Department of Energy Brookhaven_0711

17. We shouldn’t ignore non-neutronic improvements: ZEEMANS beamline Ze Extreme MagneticNeutron Spectrometer SNS Target Building Choppers Neutron guide Existing buildings Magnet Detectors Spacefor future second magnet Preliminary concept: High magnetic field (≥30 T) instrument on SNS beamline 14 Johns Hopkins, SNS, National High Magnetic Field Laboratory, others Brookhaven_0711

18. Limits to growth • Intrinsic difficulties of dealing with extremely high neutron flux (radiation/activation, detectors) will ultimately limit useven if we solve the energy density problems through ingenuityor even more efficient production (fusion) • Solvable to some extent with money: Remote handlingof accelerator/significant parts of instruments,target + higher speed detectors with correspondinglysegmented electronics • Current “limit” on regional-scale scientific facilityis $1–2B (or Euros, Oku Yen, etc.) • Global model (ILC/ITER) might provide another orderof magnitude, but doesn’t work so well when capacityis as much an issue as performance • Current (3rd-generation?) spallation source technologywill scale to 3–5 MW with reasonable progressin ongoing R&D • Likely another order of magnitude in a 4th-generation(short pulse, long pulse, or CW: TBD) 18 Managed by UT-Battellefor the Department of Energy Brookhaven_0711

19. Overcoming the limits • Beyond a 4th generation of spallation sources(plus continued use of reactors when there is synergywith nuclear energy or isotope interests),things get harder • We may be hitting the “neutron limit” with either 100 SNS spallation or a fusion source, unless the economicsof science policy undergoes a fundamental shift • This highlights the importance of continuing to developways to make more useful neutrons • The x-ray community’s log plot world only applies to useful x-rays • Our success in arranging our neutronsmore usefully in time begs a question:What is the optimal time structure for scattering? • Current debate is constrained by the accelerators • Also: What can we do about spatial distribution? Brookhaven_0711

20. Update on SNS:Exceeding early power ramp-up goals 160 Actual 120 Commitment Integrated Beam Power (MW-hours) 80 40 0 Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct FY 2007 Brookhaven_0711

21. SNS is now the world’s most powerfulpulsed neutron source Brookhaven_0711

22. We are on schedulefor commissioning instruments Brookhaven_0711

23. Backscattering spectrometer Brookhaven_0711

24. Backscattering spectrometer:Measurement of a “spin ice” • Holmium titanate spin icedoped with nonmagnetic(La) voids: Ho1.6La0.4Ti2O7 • SNS at 150 kW, 30 Hz • Spectra: 10 h • 0 < Q < 1.8 Å–1(Q-independentspin dynamics) Are the spin dynamics thermally activated or defect assisted? Georg Ehlers, SNS Brookhaven_0711

25. Backscattering spectrometer:Hydration-water-induceddynamic transitions in lysozymes 1013 TL = 223 K 1012 Bulk water Reversible 1011 Water-lysozyme h = 0.3 1/D (sec/m2) VFT fit Cpmax Arrhenius fit Irreversible denatured 1010 VFT fit TD Strong-to-fragiledynamic crossoverin protein hydration water is conjecturedto initiate reversible protein denaturation 109 Native 108 2.6 3.0 3.4 3.8 4.2 4.6 5.0 1,000/T (K-1) Sow-Hsin Chen, MIT Brookhaven_0711

26. Backscattering spectrometer:Hydration-water-induceddynamic transitions in lysozymes (continued) Brookhaven_0711

27. Reflectometers 27 Managed by UT-Battellefor the Department of Energy Brookhaven_0711

28. Liquids reflectometer:pH-responsive weak poly-electrolyte multilayers • Sample • Multilayer consisting of • Poly(methacrylic acid) [PMAA]water-soluble acid • Quaternized poly(vinylpyrolidone)[PVP] salt (ionic) • Deuterated d-PMAA markersevery fifth bilayer • Goals • Determine how film reacts to changes in pH • First step to controlling release in vivo Kharlampieva and Sukhishvili (Stevens Institute of Technology) and Tao, Halbert, and Ankner (SNS), submitted to Phys. Rev. Lett. Brookhaven_0711

29. Si3N4 Mn  10 Si3N4 Si Magnetism reflectometer:Where does the ferromagnetism reside? H. Ambaye, R. Goyette, A. Parizzi, F. Klose, and G. Felcher Brookhaven_0711

30. 31 Managed by UT-Battellefor the Department of Energy Brookhaven_0711