1. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 1 EURISOL DS PROJECT Task#2: MULTI-MW TARGET DESIGN STUDIES Adonai Herrera-Martínez & Yacine Kadi on behalf of T2 European Organization for Nuclear Research, CERN CH-1211 Geneva 23, SWITZERLAND Adonai.herrera.martinez@cern.ch

2. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 2 Overview 1.Sensitivity Studies –Particle Escapes / Neutron Yields / Power Densities –Conclusions: Baseline Parameters 2.Comparison of the BLD vs. Hg Jet (Hg-J) –Primary Particle Flux  Damage and Shielding –Neutron Flux and Energy Spectra –Fission Densities  Isotopic Yields –Energy Deposition  Temperature Increase 3.Intermediate Solution (IS)  Reference Design 4.Conclusions

3. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 3 Sensitivity Study http://eurisol-hg-target.web.cern.ch/eurisol-hg-target/ Or just Google: eurisol hg cern

4. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 4 Sensitivity Study Projectile Particle: Proton vs. Deuteron Beam Shape: Gaussian (1  35 mm  ) vs. Parabolic Beam Energy Range: 1 – 2 – 3 GeV Liquid Target Material: Hg vs. LBE Target Length: 40 – 60 – 80 – 100 cm Target Radius: 20 – 30 – 40 cm Spatial and Energy Particle Distribution Fission Target Composition: Natural vs. Depleted Uranium

5. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 5 Results of the Sensitivity Study The use of a 1 or perhaps 2 GeV proton beam on a compact (~15 cm radius ~50 cm long) Hg target would bring about important neutron yields with a reasonable charged particle confinement, therefore avoiding the need of a beam dump. The increase in the proton energy up to 2 GeV and use of a wide Gaussian beam profile, or even better, an equivalent parabolic beam, significantly reduces the maximum power densities in the target, improving the conditions for a proper heat removal, since this issue may be the bottleneck in the design. With respect to the use of deuterons as projectile, the neutron yield is increased by ~15% but the maximum power density is increased by ~30%. This fact and the increasing cost of a deuteron machine may justify the choice of protons. Lead-Bismuth Eutectic (LBE) was contemplated to avoid the low boiling point of Hg and to improve the neutron economy. However, the need of a heating system for LBE (melting point ~125  C) and the production of Po and other radiotoxic volatiles question this alternative. The use of natural U (0.7 % 235 U) combined with a BeO neutron reflector produces ~5 more fissions compared to pure 238 U (with or without reflector). These low-energy fissions produce neutron-rich asymmetric fission fragments. Considering these facts, a baseline design was proposed, where a 15 cm radius 60 cm long Hg target with a conical void and a cylindrical flow guide was designed, surrounded by a cooling helium tank. Around this converter block, a 3 cm thick nat UCx fission target was foreseen, together with a beryllium oxide reflector to recuperate the escaping neutrons.

6. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 6 Baseline Parameters of the MMW Hg Target ParameterSymbolUnitsNvalRange Converter Target materialZ conv -Hg (liquid)LBE Secondary Target materialZ targ -UC x, BeO Beam particlesZ beam -ProtonDeuteron Beam particle energyE beam GeV1  2 Beam currentI beam mA42 – 5 Beam time structure--CWPulsed 50Hz 1ms pulse Gaussian beam geometrys beam mm15  25, parabolic Beam powerP beam MW4  5 Converter lengthl conv cm45  85 Converter radius (cylinder)r conv cm158 – 20 Hg temperatureT conv ºC150 (tbc)< 357 Hg flow rateQ conv kg/s200 (tbc)< 3000 Hg speedV conv m/s2 (tbc)< 30 Hg pressure drop P1P1 bartbc<< 100 Hg overpressure  P 2 bartbc<< 100 UC x temperatureT targ ºC2000500 – 2500

7. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 7 Baseline Design BLD: Shape of Hg target optimised for neutron production (neutron balance) 15 mm sigma proton beam, fully contained in the Hg target U nat C 3 (3 g/cm 3 ) fission target, to also induce fission with neutrons below 1 MeV. Higher yields if high-density carbide is used Use of a BeO reflector to improve neutron economy, to shield HE particles and, possibly, to produce 6 He for the beta-beam, through (n,α) reactions in 9 Be Hg Target Reflector UCx/BeO Target Protons 73 cm 30 cm

8. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 8 Comparative Study BLD: Integration problems due to the large weight of the assembly and large volume of fission target Possibility of further reduction in Hg target dimensions → Intermediate solution (IS) Hg Target Reflector Target container UCx/BeO Target Protons 73 cm 30 cm Protons Reflector Hg Jet UCx/BeO Target 40 cm 4 cm Hg-J: designed for high-energy neutron fluxes in the fission target 4 mm sigma proton beam, mostly contained in the 4 cm diameter Hg Jet Fission targets closer to the Hg-J and the proton beam Hg Target Reflector Target container UCx/BeO Target Protons 68 cm 16 cm

9. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 9 Primary Proton Flux Distribution Primary flux (prim/cm 2 /s/MW of beam) 1GeV proton range ~ 46 cm BLD: Beam fully contained inside Hg-J: Important HE primary escapes (~10 13 prim/cm 2 /s/MW of beam), mostly at small polar angles → Beam dump IS: Some primary escapes through the endcap, mostly contained by the reflector BLD and IS: Beam window suffering ~100 μA/cm 2 /MW (radiation damage limit)

10. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 10 Neutron Flux Distribution Neutron flux (n/cm 2 /s/MW of beam) Neutron fluxes in the fission target ~10 14 n/cm 2 /s/MW of beam BDL and IS: Partial containment by the reflector of the escaping neutron flux Hg-J: Higher neutron flux in the fission target (~2×10 14 n/cm 2 /s/MW of beam)

11. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 11 Significantly harder spectrum for the Hg-J, with a peak neutron energy between 1 − 2 MeV, compared to 300 keV for BLD and 700 keV for IS Very low fission cross-section in 238 U below 2 MeV (~10 -4 barns). Optimum energy: 35 MeV Use of natural uranium:  f in 235 U (0.7% wt.): at least 2 barns Further gain if neutron flux is reflected (e.g. BeO) Neutron Energy Spectrum vs Fission Cross-Section in Uranium

12. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 12 High-Energy Neutron Flux Distribution HE Neutron flux (n[>20 MeV]/cm 2 /s/MW of beam) BLD: ~10 12 HE n/cm 2 /s/MW of beam reaching the fission target and ~3×10 11 n/cm 2 /s/MW of beam escaping the reflector BDL and IS: Containment of the HE neutrons (escapes 3 orders of magnitude lower than the initial flux) → Relevant for shielding and structural damage. Little back scattering into the beam line Hg-J: One order of magnitude larger HE neutron flux in the fission target (~2×10 13 HE n/cm 2 /s/MW of beam) and in HE neutron escapes

13. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 13 p or n fast vs. n th Induced Fissions Plot by: Jacques Lettry (CERN)

14. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 14 Fission Density Distribution in U nat C 3 Fission density (fissions/cm 3 /s/MW of beam) High-energy fissions in Hg → Radioactive isotopes in Hg BLD: 10 11 fiss/cm 3 /s/MW, homogenously distributed Hg-J: High and anisotropic fission density (~4×10 11 fiss/cm 3 /s/MW) IS: 2×10 11 fiss/cm 3 /s/MW, homogenously distributed → ~10 15 fissions/s for 4 MW of beam and a 1 litre U nat C 3 (3 g/cm 3 ) fission target

15. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 15 HE Fission Density Distribution in U nat C 3 Non-homogenous HE fissions in all cases BLD: ~10% of the fissions are HE (>20 MeV), compared to ~20% in IS and ~40% in Hg-J (although the HE neutron fraction only represents10% of the total) HE fission density (fissions[>20 MeV]/cm 3 /s/MW of beam)

16. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 16 Maximum energy deposition in the first 10 cm beyond the interaction point, in Hg BLD and IS, maximum power density in Hg: ~2 kW/cm 3 /MW of beam Hg-J, maximum power density in Hg: ~22 kW/cm 3 /MW of beam! Power density in the U nat C 3 target: ~3 W/cm 3 /MW of beam in the BLD and ~5 W/cm 3 /MW the IS, homogenously distributed in both ~20 W/cm 3 /MW of beam U nat C 3 target for the Hg-J, following the fission density distribution → Strongly anisotropic Power Densities (1) Power density (W/cm 3 /MW of beam)

17. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 17 Power Densities (2) Hg Beam Window More than one order of magnitude difference between the free surface Hg-J (~22 kW/cm 3 /MW) and the confined Hg targets (BLD, ~2 kW/cm 3 /MW) BDL and IS: Beam window suffering important power densities (~1 kW/cm 3 /MW → extra cooling plus radiation resistant material needed) Peak power densities similar to ESS and SNS

18. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 18 Radioisotope Yields in U nat C 3 Target (1) Harder neutron spectrum for the Hg Jet → more high-energy neutron induced fissions → large increase in the symmetrical fission products Small differences in terms of asymmetrical (low energy) fission fragments

19. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 19 Radioisotope Yields in the U nat C 3 Target (2) Isotopic yields (Ions/cm 3 /s/MW of beam) and ratio over BLD (statistical errors below 5%) (Z) Element-ABLDISHg-J (31) Ga-811.4E+072.3E+071.67.7E+075.5 (36) Kr-903.2E+094.7E+091.54.7E+091.5 (38) Sr-891.4E+072.5E+071.81.2E+088.6 (42) Mo-993.4E+076.2E+071.82.6E+087.6 (50) Sn-1326.4E+081.1E+091.71.9E+093.0 (62) Sm-1533.6E+058.4E+052.34.6E+0612.7 Fission yields increase between BLD and IS: 1.5  2.3 Fission yields increase between IS and Hg-Jet: 1.0  5.5

20. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 20 Conceptual Design of the MMW Hg Target Conclusions The Intermediate Solution brings us closer to the ideal performance of a Hg Jet in terms of fission density and relevant isotopic yields, additionally reducing the particle escapes and power densities in Hg The Hg Jet presents important technical issues regarding Hg cooling, radiation damage to the nearby structures and radiation shielding Need to clearly establish the beam requirements (i.e. CW vs. pulsed, beam frequency and beam shape), fission target configuration and specific isotopes, and yields to be produced

21. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 21 Thank you for your attention!

22. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 22 Radioisotope yields in BeO target  aim for 2x10 13 6 He at/s

23. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 23 3 times more fissions with U nat C compared to U nat C 3 (proportional to density) With 238 UC less isotropic distribution and fission yield reduced by factor 3 Fission Density Distribution: U nat C vs 238 UC U nat C 238 UC

24. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 24 Equal amount of high-energy neutron induced fissions (sym. distribution) 5 times less fissions with U238 overall BLD Radioisotope yields in UC x targets

25. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 25  At high masses it is characterized by the presence of activation products (Pu239 !!) ==> dominates over fission !!  Three very narrow peaks corresponding to the evaporation of light nuclei such as (deuterons, tritons, 3 He and  ) ==> very few ïAn intermediate zone represented double humped distribution corresponding to nuclei produced by low- energy fissions ï twice as much fission in radial position Radioisotope yields in UC x targets

26. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 26 Radioisotope yields in UC x targets (3)  harder neutron spectrum along the beam axis with 2 GeV protons ==> more high-energy neutron induced fissions and few evaporations  no differences radially

27. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 27  At high masses it is characterized by the presence of three peaks corresponding to (i) the initial target nuclei, (ii) those obtained after evaporation below and (iii) those obtained after activation above (A+1)  Three very narrow peaks corresponding to the evaporation of light nuclei such as (deuterons, tritons, 3 He and a) ïAn intermediate zone corresponding to nuclei produced by high-energy fissions (symmetric distr.) ï At higher proton energy nuclei from evaporation and multi-fragmentation (light nuclei) are more abundant Residual Nuclei Distributions in Hg

28. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 28 LE Fission Density Distribution in U nat C 3 LE fission density (fissions[<20 MeV]/cm 3 /s/MW of beam) BLD: LE fissions account for 90% of the radial fissions BDL and IS: Important effect of the reflector ← More LE fissions in the outside surface of the fission target Hg-J: Stronger anisotropy in the LE fissions and lack of containment for LE neutrons

29. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 29 Power Densities (3) Increasing  beam from 15 to 25 mm or taking parabolic beam of at least 45 mm radius → reduce  T in Hg by a factor 2 - 2.5 Doubling the flow rate (~2 m/s) will reduce  T by factor 2 →  T ~ 130 - 150 ºC

30. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 30 deuterons and protons have similar distribution (yield increases with energy) Above 500 MeV Deuterons more effective in producing neutrons +15% higher at 1 GeV Protons vs Deuterons: Neutron Yields Neutron yield in Hg for different types of projectile

31. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 31 With deuterons, neutrons are produced in larger quantities over shorter length Distribution is more peaked and flattens out with increasing kinetic energy ==> shorter target to make use of higher neutron fluxes > 600 MeV deuterons more effective Protons vs Deuterons: Neutron Distribution Neutron distribution along the central axis of the Hg target

32. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 32 deuterons & protons present a very similar neutron energy distribution, both, in the middle of the target (in spite of the ~20 MeV flux bump for deuterons) and through the end cap at low energies, the use of deuterons may bring about a higher and harder neutron spectrum, in particular through along the beam axis at high energies, such as the ones proposed for the Multi-MW target, namely 1000 MeV, the differences are rather small, not evidencing clearly the advantage of using deuterons as projectile instead of protons. Protons vs Deuterons: Neutron Spectra Neutron energy spectra for deuterons and protons at different target positions

33. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 33 The analysis of the power densities shows the difficulties of cooling a Multi-MW target driven by low energy deuterons since, for a  ~1.7 mm Gaussian beam at 100 MeV, the power densities exceed 1 MW/cm 3 /MW of beam Protons present lower power densities for all the energies analysed, from 35% lower at 400 MeV to 27% lower at 1 GeV The choice of a short target driven by a low energy (few hundred MeV) high-intensity deuteron beam would present important difficulties in terms of heat removal Protons vs Deuterons: Energy Deposition Energy deposition along the central axis of the Hg target

34. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 34 A beam size of  ~15 mm seems appropriate to reduce the maximum power density from ~27 kW/cm 3 /MW of beam to ~1.8 kW/cm 3 /MW of beam power (15 times less). A further increase in the beam size, for example going from  ~15 mm to 25 mm, reduces the maximum energy deposition by another factor of 2.4. For smaller , i.e., 2 mm and 5 mm, most of the energy is deposited along the axis or at small radii, whereas for larger , i.e. 20 mm or 30 mm, most of the energy is diluted on a larger volume at increasing radii (e.g. for  =30 mm, the maximum value is reached at 3.5 cm from the axis), therefore, reducing the maximum power densities Impact of the Beam Profile (1) Energy deposition as a function of the beam 

35. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 35 ~75% of the beam energy is contained inside the target and that  only has an impact on which radius contains ~50% of the energy (for  = 2 mm, this occurs at 3 cm, whereas for  = 30 mm, it happens at 6 cm). using a parabolic beam of at least 4.5 cm radius, would reduce by 40% the energy density in the Hg target Impact of the Beam Profile (2) Energy deposition as a function of the beam 

36. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 36 LBE Alternative

37. EURISOL Town Meeting, GANIL – Caen, France 28 – 29 November, 2005 37 Results of the Sensitivity Study 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 stop charged particles. No beam dump 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 escapes)  Use of natural uranium to take advantage of the high fission cross-section of 235 U in the resonance region  Improvement through use of neutron reflector Very localised energy deposition, 20 cm from the impact point along the beam axis ~30 kW/cm 3 /MW of beam power, reduced with the increasing proton energy ADD beam profile + Deuteron Possibility of using LBE eutectic to improve neutron economy and reduce maximum energy deposition, but increasing the technical difficulty (LBE melting point ~125  C)