Target studies for LBNE at 0.7 MW – 2 MW operation

1. RAL High Power Targets Group: Chris Densham, Tristan Davenne, Mike Fitton, Peter Loveridge, Matt Rooney, Otto Caretta In collaboration with Fermilab: Patrick Hurh, Bob Zwaska, James Hylen, Sam Childress, Vaia Papadimitriou Target studies for LBNE at 0.7 MW – 2 MW operation

2. NOvA 700kW 15kt Liquid Scintillator iron mine at Soudan MINOS (Far Det.) NSF’s proposed Underground Lab. DUSEL 735 km 2.5 msec 810 km MiniBooNE SciBooNE MINOS NOvA MINERvA MicroBooNE 1300 km ~300 kton Water Cerenkov ~100 kton Liquid Ar TPC Project X: ~2 MW Combination of WC and LAr Matter – Antimatter Asymmetry with Neutrinos Proton Decay Supernovae Neutrinos US Superbeam Strategy: Young-Kee Kim, Oct. 1-3, 2009

3. Beam Parameters used in study

4. Assumptions for target technology options • Target length 2λ, material within bore of horn for maximum neutrino flux • Low z target material • lower heat load per pion produced • lower production of neutrons and other secondary particles • less secondary heating and radiation damage to horn and target station components • Candidate materials • Baseline: graphite, water cooled (IHEP study) • Alternatives for this study: Be and alloys • Geometry options: • Target integral with horn inner conductor (water spray cooled) • Separate target and horn inner conductor cooled by: • Water • 2-phase water • Helium • Air

5. Physics Optimisation Target and Beam Dimensions • For neutrino flux – the smaller the better? • Target performance evaluated using FLUKA to generate a simple ‘Figure of Merit’ by convoluting selected pion energy histogram by a weighting function: • W(E)=E2.5 for • 1.5 GeV < E < 12 GeV • pT <0.4 GeV/c

6. Physics vs Engineering Optimisation ?Target and Beam Dimensions • For target lifetime – the bigger the better? • Lower power density – lower temperatures, lower stresses • Lower radiation damage density • Lower current density in inner conductor • For integrated neutrino flux, need to take both neutrino flux and lifetime factors into account • Hope for this study is to make an assessment of trade off between target lifetime vs beam and target dimensions • Answer will depend on Target Station engineering (time to change over target and horn systems)

7. Target / horn geometry preferences (in order) • Single horn, 3 m long, target integral over initial 1 m. • Simplest configuration • Issues to study • Vibrations from off-axis effects • Minimise discontinuity at transition (stresses, currents) • Double horn, 1 m horn integral with target + 2 m horn • Longer lifetime for second horn expected, less waste for target change • Issues to study • Possible longer life for combined 1st horn and target cf 3 m? • More complex geometry (striplines, remote exchange) • Possible reduction in neutrino flux

8. Simulation Inputs - Typical energy deposition contour plots Target radius = 10.5mm or 4.5mm Target length = 1m Beam sigma = radius/3 Beam kinetic energy = 60GeV or 120GeV Particles per spill = 1.6e14 Materials = Beryllium, Aluminium & Albemet Albemet has 38% Aluminium and 62% beryllium by mass

9. Results summary

11. Ansys thermal analysis HTC = 3000 W/m2.K @ 300K Target material = Beryllium CFX Conjugate Heat Transfer Helium flow rate = 130g/s @ 300K Target material = Beryllium 408K 384K BEAM BEAM Largest differences between Ansys and CFX are seen at downstream end of target due to fluid temperature rise

12. Contained waterSummary of empirical calculations: Results for 21mm diameter target in 30mm concentric tube Heat deposition is 23kW uniform internal heat generation • Sufficient cooling can be easily achieved with water cooling • Pressure drops are small although operating at pressure will reduce cavitation • Shock waves in water needs to be considered. • Gas bubbles could dampen shock waves in water and literature suggest it could also increase the heat transfer. • Cooling of smaller radius target is more demanding due to decreased area for heat exchange

13. Direct water cooling – secondary heating of water

14. Water jets: modelling approach • ¼ Symmetry model • 6 water jets modelled by coordinate systems normal to surface • Profile of water jets customisable using function Target diameter = 21mm Average HTC ≈ 12,000 W/(m2.K) Beam heating from Fluka data, 60GeV, 0.76Hz, 3.5mm sigma(23kW)

15. Heat Transfer Coefficient Peak = 54,000W/(m2.K) Sigma = 0.1m

16. Results Summary • Target seems tolerant to the water jet profile so long as there is reasonable coverage along the whole target. • When gaps between jets appear, the target temperature and stresses rise significantly • A realistic water jet profile of heat transfer coefficient is needed

18. Model Strategy ANSYS axisymmetric FE model (Peter Loveridge) FLUKA model (Tristan Davenne) Material properties Proton beam parameters Read thermal results into ANSYS mechanical Read element heat input from FLUKA output file Calculate heat deposition as a function of r and z ANSYS thermal transient (thermal conduction) ANSYS static mechanical run at each thermal time step Power density distribution in table format (.csv file) Temperature distribution during/after the spill Stress/strain due to temperature gradients in the target

19. Transient Results Temperature and stress evaluated during and after the beam spill Example case shown: 120 GeV, Beryllium target, Ø21mm

20. Energy Deposition in Autodyne • Use a fit to FLUKA energy deposition data as input to AUTODYNE • Energy deposited = 31kJ/spill or 60J/bunch • Temperature rise = 80K

21. Gauge points Stress wave propagation in Autodyne Longitudinal oscillation period ≈ 0.14ms

22. Increase in peak stress as a result of longitudinal stress waves meeting in the middle of the target Radial oscillation period = 3microseconds

23. Analysis Process Combined Target + Inner Conductor

24. Combined Target + Inner Conductor • Skin Effect

25. Combined Target + Inner Conductor • Results

26. Finally, something relevant for SPL based Superbeam:Cooling data (from empirical formula spreadsheet by Mike Fitton, benchmarked by CFX simulations) • 50 kW heat load assumed per target • 1 GW/m3 peak power deposition assumed (more or less arbitrary, need to use value calculated by Andrea/Christophe)

27. Helium cooling

28. Water cooling