1. ORNL is managed by UT-Battelle for the US Department of Energy High Power Targets for Accelerator Based Research Facilities Bernard Riemer Spallation Neutron Source / ORNL ICHEP 2014 37 th International Conference on High Energy Physics 2-9 July 2014 Valencia, Spain

2. 2 High Power Targets for Accelerators Targets in accelerator facilities are used for diverse science applications Spallation neutron sources –Neutron scattering science –Neutron physics Time-of-flight Ultra-cold neutrons Muon sources Materials irradiation Neutrino factories Radioactive ion beams –ISOL –Fragmentation Isotope production Accelerator driven systems Anti-matter

3. 3 High Power Targets for Accelerators What’s a “high-power” target, anyway? Dealing with energy deposited by accelerator beams Continuous beam Time-averaged power Time-averaged volume power density Pulsed beam Energy per pulse Volume energy density per pulse Large range within the high-power target community

4. 4 High Power Targets for Accelerators MW class spallation neutron sources SINQ at PSI –Continuous beam, 570 MeV H + SNS at the ORNL – 60 Hz, short-pulse, 1 GeV H + JSNS at MLF / JPARC – 25 Hz, short-pulse, 3 GeV H +

5. 5 High Power Targets for Accelerators MW class spallation neutron targets SINQ at PSI –Pb in Zr tubes, D 2 O cooled SNS at the ORNL – Circulating Hg in SS vessel JSNS at MLF / JPARC – Circulating Hg in SS vessel Pb / Zircaloy target Mercury

6. 6 High Power Targets for Accelerators Why use a liquid metal (LM) for high power spallation targets? Circulating metal serves as the spallation target material as well as its own coolant –About 60% of beam power is deposited as heat in the target High Z materials are best for neutron production via the spallation reaction –Neutron flux or brightness matters to science instruments Solid targets cooled by water require increasing volume fractions of water with increasing power –Effective density and neutron flux suffer One problem with short-pulse LM targets …

7. 7 High Power Targets for Accelerators Micro-second beam pulse generates pressure waves that lead to cavitation Disks are 60 mm dia. LM cavitation bubble collapse causes pitting damage on vessel surfaces SNS mercury vessel beam entrance inner wall (not a containment wall) Beam entrance window of SNS target after samples extracted

8. 8 High Power Targets for Accelerators kW class spallation neutron sources Water-cooled solid targets ISIS TS-1 at RAL –50 Hz, SP 800 MeV H + –160 kW –W plate target with Ta clad ISIS TS-2 at RAL –10 Hz, SP 800 MeV H + –32 kW –W rod target with Ta clad Lujan LANSCE at LANL –20 Hz, SP 800 MeV H + –100 kW –W disk target with Ta clad

9. 9 High Power Targets for Accelerators Tantalum cladding is needed to protect tungsten from aggressive corrosion Tungsten vulnerable to radiolytic assisted corrosion But tantalum decay heat is long-lived Lujan un-clad tungsten target Andrew Nelson, IWSMT-10, LANL

10. 10 High Power Targets for Accelerators 5 MW of 2.5 GeV protons 14 Hz, long-pulse (2.86 ms) Rotating target of tungsten blocks – cooled by helium – no cladding R. Linander, ESS (AccApp13) 2.5 m dia. target wheel ESS rotating solid tungsten target

11. 11 High Power Targets for Accelerators Günter S. Bauer (1941 – 2013)

12. 12 High Power Targets for Accelerators High power target design challenges High volume power or energy density –H–Heat removal –T–Thermal shock Physics & engineering interfaces Radiation damage effects on materials Required target duty cycle & lifetime Remote handling for required maintenance Corrosion, radiation assisted corrosion Safety – facility, personnel, environment Waste handling Ever-increasing demands for greater physics performance lead to greater challenges

13. 13 High Power Targets for Accelerators Target interfaces are critical to physics performance SNS has 3 liquid hydrogen moderators and 1 water moderator Embedded in beryllium reflector Interfaces to neutron beam guides, choppers …

14. 14 High Power Targets for Accelerators Neutron Economy at SNS 1.4 MW SNS produces:2×10 17 n/s Thermal neutrons at beamline start:2×10 12 n/s Neutrons at sample position (white):2×10 11 n/s Neutrons at sample (chopped):2×10 10 n/s Neutrons scattered:2×10 8 n/s Neutrons counted:5×10 7 n/s Neutron counted/Neutrons produced:3×10 -10 Is there a more cost effective path to higher performance than more power on target? Franz Gallmeier 5 th High Power Targetry Workshop, May 2014

15. 15 High Power Targets for Accelerators Interfaces: NuMI neutrino target @ Fermilab Pulsed target and magnetic horn are closely coupled to each other and to a small incident beam (~ 1mm) –Critical alignments High energy density/pulse Carbon fin target, water-cooled Remote beamline installation –Radiation area restrictions J. Hylen et al., FNAL

16. 16 High Power Targets for Accelerators Key parameters for some example targets P. Hurh et al.

17. 17 High Power Targets for Accelerators CERN Antiproton Decelerator  26 GeV/c primary beam  0.5x1mm 1   1.5*10 13 p/pulse  430 ns pulse length  Rep rate ~60 s  Iridium core  Requirements for physics:  Compact target  High-Z material  Very focused primary beam  Challenges:  Thermal shocks - extremely high energy density coupled with short pulse  7.5 kJ/cm 3 /pulse  ~17 GJ/cm 3 /s (instantaneous power) Marco Calviani 5 th High Power Targetry Workshop, May 2014

18. 18 High Power Targets for Accelerators CNGS neutrino targets @ CERN Carbon rods, radiative cooling T2K neutrino target and horn @ JPARC Carbon target, helium cooled Other examples: neutrino targets Target rod support structure Sealed cooling finned tube (Al 5083 H111) Target support tube (C-C composite) M. Calviani 5 th HPTW

19. 19 High Power Targets for Accelerators Ottone Caretta 5 th High Power Targetry Workshop, May 2014

20. 20 High Power Targets for Accelerators Some interesting target developments Demand for more intensity  greater thermal shock –Beyond solid target limits Liquid mercury jets – stabilized by magnetic field MERIT Collaboration Muon Collider/Neutrino Factory Fluidized tungsten metal powder targets O. Caretta, RAL N. Charitonidis, CERN CERN HiRadMat Experiment

21. 21 High Power Targets for Accelerators Chinese ADS: High power & volume power density Lei Yang 5 th High Power Targetry Workshop, May 2014

22. 22 High Power Targets for Accelerators High Power Targetry Workshop series This workshop series brings together interested scientists and engineers from the international community, in particular those operating or designing high power targets –Priority given to working discussions 5 th HPTW recently held at Fermilab, 97 participants –T–Target Design Challenges –R–Radiation Damage and Material Limits –T–Target Simulations –Beam monitoring / instrumentation –Facility challenges Remote handling

23. 23 High Power Targets for Accelerators IWSMT - International Workshop on Spallation Materials Technology A premier forum for exchanging the latest information on –spallation source related materials studies –operation and development of high power spallation targets –establishing new international collaborations on relevant materials The 12 th meeting will held in October 2014 Bregenz, Austria Emphasis will be on: –Results obtained from the post-irradiation examination (PIE) programs of the MEGAPIE, JSNS, SNS and SINQ targets, –Progress in materials R&D programs of ESS, MYRRHA and C-ADS projects –Progress in the fundamental understanding of the synergistic effect of displacement damage, helium, hydrogen and transmutation elements in various structural and target materials http://indico.psi.ch/conferenceDisplay.py?confId=3052

24. 24 High Power Targets for Accelerators RaDIATE Collaboration Radiation Damage In Accelerator Target Environments Born out of need to better understand and predict the radiation response of structural window and target materials The broad aims are threefold: –to generate new and useful materials data for application within the accelerator and fission/fusion communities; –to recruit and develop new scientific and engineering experts who can cross the boundaries between these communities; –to initiate and coordinate a continuing synergy between research in these currently disparate communities, benefitting both proton accelerator applications in science and industry and carbon-free energy technologies. http://www-radiate.fnal.gov/index.html

25. 25 High Power Targets for Accelerators Summary High powered targets for accelerators is a field diverse in applications and rich in technical challenges A modest size community with common interests is working to advance science by meeting increasing performance demands on targets