1. DUNE/LBNF Target Studies: Physics John Back University of Warwick 12 th April 2016 1

2. Introduction DUNE/LBNF: international program for future neutrino experiment based at Fermilab: simultaneously measure mass hierarchy and CP violation – Effort underway to optimise beam & target to maximise physics potential Current “baseline” is water-cooled NuMI-like target – Proton beam: 60  120 GeV/c, width = 1  4 mm; 1.2MW, ~10 21 POT/year Investigating other target options: – Be Spherical Array Target (SAT) with He cooling – T2K-like graphite cylinder with He cooling Using Geant4 software to simulate target and comparing performance: – Estimated significance (“# of  ”) of measuring CP-violating phase  CP – Similar figure of merit: integrated  flux between E = 0 to 4 GeV 2 = n Gauss beam path length Solve for N spheres: given R, beam  and required n  physical length of SAT  15% longer than cylinder Convolution of Gauss beam path length along SAT

3. Target module geometry p beam Be He Ti He SAT support “helix” 3 He Ti He Be R SAT (or cylinder) encased in double Ti can filled with He gas inside Horn1 (3-Horn set-up) Simulation parameters: Target radius R: 3  12 mm = 3 x beam Gauss width Target length equivalent to 2  5 Proton beam momentum: 60  120 GeV/c Assume 1.2 MW beam power

4. Example CP sensitivity 4 2m NuMI target, p beam = 60 GeV, 3 years running, 1.2 MW Horizontal dotted line: “CP sensitivity” = containing top 75% of  values Need CP sensitivity to be as high as possible Estimated significance for measuring CP violation phase  CP using GLoBES software and Geant4 simulated neutrino flux at the far detector (1300km)  75%

5. Be SAT:  75% vs p 5 L = 2 L = 3 L = 4 L = 5

6. C cylinder:  75% vs p 6 L = 2 L = 3 L = 4 L = 5

7. Summary Target module CP sensitivities compared to 2m (4 ) NuMI target (assuming 3 horn set-up optimal for NuMI), all for 3 yrs running @ 1.2 MW: – Be SAT needs L = 5, R  7  2 mm, p  105  15 GeV for similar performance Longer length required owing to gaps between the spheres – C Cylinder best performance: L = 5 (2.4m), R  6  2 mm, p  110  20 GeV Caveats/issues: – The 3-horn set-up that is optimal for the NuMI target is probably not optimal for the other target modules – Horn design has strong influence on performance: Need to see what critical horn parameters we can (slightly) change Reduce target module length via horn geometry optimisation? Further work: – Split up target into two equal “mirror image” sections: Quantify impact on performance – Investigate target hybrids: low atomic Z start & high Z end Increases secondary interactions for producing useful low energy ’s Potential problems with too high energy deposition in high Z end? 7

8. LBNF Target Studies : Engineering Tristan Davenne Rutherford Appleton Laboratory High Power Targets Group Engineering Challenges Total Power Deposited [kW thermal] Pulsed power density [J/cc] Radiation damage [Protons/cm2] → dpa LBNF Requirements Beam Power = 1.2MW baseline increasing to 2.4MW with PIP Kinetic Energy = 60 – 120GeV Beam Sigma tuneable between 1mm and 4mm Target Options ‘Numi-like’ water cooled graphite target ‘T2K-like’ Cylindrical helium cooled graphite target SAT (spherical array target)

9. NUMI-like target Stress calculation assumes normal (unirradiated) graphite material properties, radiation damage may be highest at water cooling operating temperatures Stress calculated based on beam spill applied to fin initially at uniform temperature, any residual thermal stress from last pulse? Cyclic fatigue loading of a brittle material Based on the NuMI design but with: Increased target width to 10mm Increased beam sigma from 1 to 1.7mm Increased beam power from 400kW to 1,2MW Numi stress prediction at 400kW P.Loveridge C.Crowley At 1.2MW stress levels reduced from 35MPa to 10MPa C.Crowley Titanium tubes to reduce stress in cooling pipes O.Caretta C.Crowley

10. NUMI-like target May require additional helium cooling for downstream window and outer can? Good physics performance due to small beam sigma Could eliptical beam spot improve physics further? Water cooling means graphite operates at less than 400C, not benefitting from damage annealing effects that occur at higher temperatures in NoVA & T2K C.Crowley Stress concentrations at join between graphite fins and cooling tubes C.Crowley

11. T2K-like Helium cooled cylindrical graphite target preliminary calculations with LBNF beam parameters Beam Parameters Beam Energy = 120GeV Beam pulse length = 10 μ s Beam sigma = 3.5mmRepetition period = 1.33s Beam Power = 2.3MWProtons per pulse = 1.6x10 14 FLUKA output for 2m long cylinder of graphite Plan to have two targets back to back about 1m long each Power deposited in target 1 (i.e. 0m<z<1m) = 30kW Power deposited in target 2 (i.e. 1m<z<2m) = 19kW T2K 750kW 30GeV 4.24mm sigma 3.3e14ppp 2.1s 266J/cc/pulse 15kW LBNF 2.3MW 120GeV 3.5mm sigma 1.6e14 ppp 1.33s 280J/cc/pulse 30kW

12. Predicted operating Temperature of target 1 Assume target has average surface heat transfer coefficient of 1000W/m2K feasible with pressurised helium, IG43 temperature dependant thermal conductivity reduced by factor of a third before beam pulse after beam pulse

13. Predicted stress in target 1 before beam pulse after beam pulse Pulsed energy density no higher than T2K at 750kW Stress levels higher than T2K predictions but in same ball park Off axis beam?

14. Spherical array target Good cooling near target core Scalability to 2.4MW Smaller beam sigma than for the graphite cylinder maybe possible Use of beryllium target material possible in the event that radiation damage becomes a limiting factor for graphite Possibility of using different density target materials, although much higher density than beryllium will be hard without going to very small segments

15. Stress Wave simulations Common theme for neutrino facilities is large pulsed energy deposition which result in stress waves in beam windows and targets Simulations often done with Autodyn, LS-Dyna, ANSYS However simulations are sensitive to parameters such as Courant number but also mesh size and cell type As such attractive to have an exact solution for stress wave propagation in order to benchmark simulations Search for an analytical solution for the case of stress waves in a disc -Sievers 1974 and 2000 –uniform heating case and initial energy deposition with a discontinuity (top-hat profile) -Zheng & Taleyarkhan 2004 –solution with smooth energy deposition but appears unstable when increasing number of terms in summation? -Bertarelli – modal summation method for analytical stress wave simulations

16. After some years of searching we arrived at the following expression for stress waves propagation in a disc as a result of an initial Gaussian temperature distribution A. D. Polyanin. Handbook of Linear Partial Differential Equations for Engineers and Scientists. CRC Press, 2002. P Loveridge

17. Backup 17

18. Be SAT: CP  75% for L = 5 18 Bold: Maximum CP  for NuMI Red : CP  higher than NuMI maximum  0 Blue: CP  below but within NuMI maximum;  0 -  < |  0 | + |  | Uncertainties are   0.02 for all CP 

19. C Cylinder: CP  75% for L = 5 19 Bold: Maximum CP  for NuMI Red : CP  higher than NuMI maximum  0 Blue: CP  below but within NuMI maximum;  0 -  < |  0 | + |  | Uncertainties are   0.02 for all CP 

20. Mary Bishai BACK UP SLIDES High z cooling tube or downstream plug? A high z plug downstream of the target and/or high z target outer tube shown to increase pion yield relative to a 2 interaction length graphite target. Graphite cylinder inside a tantalum tube gives best increase in yield

21. How could we make a downstream high z target plug? Longer (2m) target helps some what Tantalum plug looks challenging If downstream plug made of an inconel packed bed - max temp jump per pulse would be 265K - power density 0.7kW/cc Merits further investigation

22. Steady state test Air mass flow = 34grams/s Inductive power transferred to packed bed = 3.9kW Maximum sphere surface temperature = 165°C Outlet air temperature = 112°C Average power density = 0.19kW/cc Average heat transfer coefficient = 2kW/m 2 K Induction heating test at RAL with packed bed of 3mm diameter spheres