MULTI-MW TARGET DEVELOPMENT FOR EURISOL & EUROTRANS

1. MULTI-MW TARGET DEVELOPMENT FOREURISOL & EUROTRANS Y. Kadi & A. Herrera-Martinez (AB/ATB) European Organization for Nuclear Research, CERN CH-1211 Geneva 23, SWITZERLAND yacine.kadi@cern.ch

2. Multi-MW Target Challenges • High-Power issues • Thermal management • Target melting • Target vaporization • Radiation • Radiation protection • Radioactivity inventory • Remote handling • Thermal shock • Beam-induced pressure waves • Material properties

3. Thermal Management: Liquid Target with window The SNS Mercury Target Harold G. Kirk et al. (BNL)

4. Thermal Management: Liquid Target with window • MEGAPIE Project at PSI • 0.59 GeV proton beam • 1 MW beam power • Goals: • Demonstrate feasablility • One year service life • Irradiation in 2005 F. Groeschel et al. (PSI) Proton Beam

5. Thermal Management: Liquid Target with window F. Groeschel et al. (PSI)

6. Thermal Management: Liquid Target with free surface DG16.5 Hg Experiments nominal volume flow 10 l/s BEAM Close to desired configuration • intermediate lowering of level • some pitting • axial asymmetry High-speed flow (2.5 m/s)permits effective heat removal

7. Thermal Management: Target Pitting Issue Before ESS team has been pursuing the Bubble injection solution. SNS team has focused on Kolsterizing (nitriding) of the surface solution. SNS team feels that the Kolsterized surface mitigates the pitting to a level to make it marginally acceptable. Further R&D is being pursued. After 100 pulses at 2.5 MW equivalent intensity Harold G. Kirk et al. (BNL)

8. Worldwide Programs

9. Thermal Management: radiation cooled rotating toroidal target • Distribute the energy deposition over a larger volume • Similar a rotating anode of a X-ray tube rotating toroid toroid magnetically levitated and driven by linear motors R.Bennett, B.King et al. solenoid magnet toroid at 2300 K radiates heat to water-cooled surroundings proton beam

10. Thermal Management: JET J.Lettry et al. (CERN) TT2A

11. Target Module with jumpers Outer Reflector Plug Target Inflatable seal Core Vessel water cooled shielding Core Vessel Multi-channel neutron guide flange Moderators Radiation Management The SNS Target Station

12. Radiation Management

13. Radiation Management The JPARC Kaon Target ~18m Concrete shield block ~10m Service space: 2m(W)1m(H) Water pump Iron shield 2m T1 container Concrete shield Beam

14. EURISOL – Multi-MW Target Objectives The objective is to perform the technical preparative work and demonstration of principle for a high power target station for production of beams of fission fragments using the mercury proton to neutron converter-target and cooling technology similar to those under development by the spallation neutron sources, accelerator driven systems and the neutrino factories. This high power target that will make use of innovative concepts of advanced design can only be done in a common effort of several European Laboratories within the three communities and their proposed design studies. In this study emphasis is put on the most EURISOL specific part a compact window or windowless liquid-metal converter-target itself while the high power design of a number of other more conventional aspects are taken from the studies in the other EURISOL tasks or even in other networks like ADVICES, IP-EUROTRANS.

15. EURISOL Target Stations • 3x100 kW direct irradiation • Fissile target surrounding a spallation n-source • >100 kW Solid converters (PSI-SINQ 740 kW on Pb, 570 MeV 1.3 mA / RAL-ISIS 160 kW on Ta, 800 MeV 0.2 mA / LANL-LANSCE 800 kW on SS cladded W, 800 MeV 1.0 mA ) • 4 MW Liquid Hg (windowless or jet)

16. EURISOL Hg-converter and 238UC2 target 60 kV 60 kV > 2000º Grounded < 200º

17. EURISOL – Multi-MW Target Participants Contributor P4 – CERN P18 – PSI Switzerland P19 – IPUL Latvia C5 – ORNL USA

18. EURISOL – Multi-MW Target

19. EURISOL – Multi-MW Target

20. EURISOL – Multi-MW Target

21. Breakdown of work (per sub-task)

22. Preliminary Studies • Projectile Particle: Proton • Beam Shape: Gaussian,  ~1.7 mm • Energy Range: 1–2–3 GeV • Target Material: Hg / PbBi • Target Length: 40–60–80–100 cm • Target Radius: 10–20–30–40 cm • Spatial and energy particle distribution

23. 1 GeV Primary Proton Flux 1 GeV Proton range ~46 cm • The beam opens up to ~20 degrees, with some primary back-scattering • Primaries contained in ~50 cm length and ~30 cm radius

24. Energy Deposition for 1 GeV protons • Maximum energy deposition in the first ~14 cm in the beam axis beyond the interaction point, ~30 kW/cm3/MW of beam dT/dt ~14 K/s (Hg boiling point at 357 ºC) • Energy deposition drops one order of magnitude at the proton range (~46 cm) • Large radial gradients (dE/dr ~200) in the interaction region

25. Neutron Flux Distribution for 1 GeV Protons Radial Front Cap End Cap • Neutron flux centered radially around ~10 cm from the impact point • Isotropic flux after ~15 cm from the center, decreasing with r2 • Escaping neutron flux peaking at ~300 keV (evaporation neutrons), with a 100 MeV component in the forward direction (direct knock-out neutrons)

26. Neutron Energy Spectrum vs Fission Cross-Section in Uranium • Very low fission cross-section in 238U below 2 MeV (~10-4 barns). Optimum neutron energy: 35 MeV • Alternatively, use of natural uranium: fission cross-section in 235U (0.7% wt.) for 300 keV neutrons: ~2 barns • Further gain if neutron flux is moderated

27. Alternative Target Configurations Standard Configuration Alternative Configurations Reflector? UCx Target Reflector / UCx Target Protons Protons Hg Target Hg Target Deuterons UCx Target Reflector / UCx Target UCx Target Reflector? Low-Z Filter (?)

28. Alternative Target Configurations Alternative Configurations Reflector / UCx Target Protons Hg Target Deuterons Reflector / UCx Target UCx Target Low-Z Filter (?) • Increasing HE neutron flux through the End-Cap with decreasing Hg target length • Increasing charged-particle and photon escapes with decreasing Hg target length • Possible use of a low-Z filter to “tune” the average neutron energy to 35 MeV (maximise fission probability in 238U)

29. Neutron Balance Density for 1 GeV Protons Neutral balance boundary Neutron absorbing region Neutron producing region • Neutron absorbing region ~6 cm behind the interaction region, following the primary particle distribution • Neutron producing region extending to the end of the target • Small contributions from regions beyond the proton range • Neutron producing region not extending beyond r =10–13 cm

30. 2 GeV Primary Proton Flux 2 GeV Proton range ~110 cm • Forward peaked primary distribution at ~10 degrees • No back-scattering and rare radial escapes • Few end-cap escapes: • 210-3 escapes/primary with an average energy of 1 GeV for 80 cm • 2 10-5 escapes/primary with an average energy of 0.7 GeV for 100 cm

31. Energy Deposition for 2 GeV protons • Largest energy deposition in the first ~18 cm beyond the interaction point, ~16 kW/cm3/MW of beam dT/dt ~8 K/s (40% lower compared to the use of 1 GeV primary protons) • Identically, smaller radial gradient in the interaction region (dE/dr ~100)

32. Neutron Flux Distribution for 2 GeV Protons Neutron Yield (2 GeV proton) : 57 – 77 n/p • Neutron flux centered radially around ~15 cm from the impact point, presenting a forward-peaked component • Escaping neutron flux peaking at ~300 keV, with a 100 MeV component in the forward and radial directions and few 1 GeV neutrons escaping through the end-cap • Harder neutron energy spectrum and higher flux and in the target compared to the 1 GeV case

33. Neutron Balance Density for 2 GeV Protons • Increase in the relevance of the axial region in the neutron production • Neutron producing region still not extending beyond r =10 – 13 cm • The neutron capturing region gains relevance (–610-4 bal/cm3/prim) compared to 1 GeV (–610-5 bal/cm3/prim) • Significant reduction in neutron captures (one order of magnitude) by reducing the radius to 20 cm Neutral balance boundary Neutron absorbing region Neutron producing region

34. 3 GeV Primary Proton Flux 3 GeV Proton range ~175 cm • The beam opens up to ~8 degrees, no back-scattering and few radial escapes (even for 20 cm radius) • Some primaries escapes through the end-cap (~ 5 10-5 escapes/primary) • Average energy of the escaping protons ~750 MeV

35. Energy Deposition for 3 GeV protons • Largest energy deposition in the first ~22 cm beyond the interaction point, ~12 kW/cm3/MW of beam dT/dt ~6 K/s (60% lower compared to the use of 1 GeV primary protons) • Smaller radial gradient in the interaction region (dE/dr ~50) compared to the 1 GeV case

36. Neutron Flux Distribution for 3 GeV Protons Neutron Yield (3 GeV proton) : 82 – 113 n/p • Neutron flux centered radially around ~20 cm from the impact point, with a larger forward-peaked component • Escaping neutron flux peaking at ~300 keV, with a 100 MeV component in the forward and radial directions and some 1.5 GeV neutrons escaping through the end-cap • Slightly higher neutron flux in the target compared to the 2 GeV case

37. PbBi Alternative – 1 GeV Primary Particles 1 GeV proton range in Hg: ~46 cm Hg 1 GeV proton range in PbBi: ~60 cm PbBi

38. PbBi Alternative – Energy Deposition Maximum energy deposition ~30 kW/cm3/MW of beam Hg Maximum energy deposition ~21 kW/cm3/MW of beam PbBi

39. PbBi Alternative – Neutron Flux Hg PbBi

40. PbBi Alternative – Neutron Balance Hg Neutron absorbing region Neutral balance boundary Neutron producing region PbBi Neutron producing region

41. PbBi Alternative – Neutron Spectrum

42. Summary of the Results • Optimised for neutron production: • Radius: 10 – 15 cm target radius from neutron balance point of view is enough • Length: Extend to the proton range to maximise neutron production and avoid charged particles in the UCx • Energy Spectrum of the neutrons: • Dominated by the intermediate neutron energy range ( 20 keV - 2 MeV) • Harden neutron spectrum by reducing the target size (but reduce yield and increase HE charged particle contamination) • Use of natural uranium to take advantage of the high fission cross-section of 235U in the resonance region  Improvement thorough neutron energy moderation • Alternatively, axial converter-UCx target configuration for depleted uranium target • Very localised energy deposition, 20 cm from the impact point along the beam axis ~30 kW/cm3/MW of beam power, reduced with the increasing proton energy • Possibility of using PbBi eutectic to improve neutron economy and reduce maximum energy deposition

43. Future Work • Optimise the energy deposition once the size is fixed • Study the effect of the shape of the beam (parabolic, annular, variations in the sigma of the Gaussian distribution) • Activation of the target (calculate the spallation product distribution) • Model the fission target (including moderator/reflector) and optimise the fission yields • Analyse alternative target disposition to improve the fission yields • Study the use of deuterons as projectile particle