1. MARS15 Studies of Impact of LBNF Target/Horn Optimization on the Hadron Absorber 6 th High Power Targetry Workshop Merton College, Oxford April 12, 2016 S. Striganov and N. Mokhov FermilabAccelerator Physics Center

2. Beamline Facility contained within Fermilab property ~ 21,000 m 2 4 Beamline for a new Long-Baseline Neutrino Facility MI-10 Extraction, Shallow Beam Constructed in Open Cut Constructed as Tunneled excavation All systems designed for 1.2 MW initial proton beam power (PIP-II). Facility is upgradeable to 2.4 MW proton beam power (PIP-III). Primary beam designed to transport high intensity protons (60-120 GeV) to the LBNF target

3. 3 MARS15 Source Term Simulations C-Baffle: OD=5.7cm, L=150cm ID=1.3 cm (normal) ID=3.0 cm (accident) C-target, 48 segments: 1cm(W)×2.67cm(H)×2cm(L) Starting with a proton beam at z = -7.3m from MC0, high-statistics runs for all the four scenarios to get source terms at z = 219.25 m, i.e., 1.5m upstream the absorber spoiler

4. 4 Energy Fluxes at Absorber Inclusive at 120 GeV (default) Exclusive at 120 GeV (LAQGSM)

5. Beam Hadron monitor Spoiler Water-cooled Al Mask blocks Aluminum core, 1 st 9 blocks are sculpted Water-cooled steel core Overall absorber: Poured concrete volume: 24,000 ft 3 Steel shielding: 2,500 ton Aluminum: 39 ton “Absorber core”: Spoiler block 5 Aluminum mask blocks 9 Sculpted Al blocks 4 Solid Al blocks 4 Central steel blocks which share the features: Water cooled Individually hung on removable modules Each 1 foot thick 5 Hadron monitor Insertion/extraction tower 4 m diameter Decay pipe Hadron Absorber as Designed up to Now

6. 6 Spoiler and sculpted blocks provide about factor of two reduction of maximal energy deposition y:z = 1:1 Spoiler: Coulomb scattering of fast protons and earlier start of showers followed by divergence of products in a 1.5-m air gap upstream the core Sculpted core blocks: Lower core density around axis with a more uniform ED along z

7. 7 Peak is Due to Fast Protons Inclusive at 120 GeV (default) Exclusive at 120 GeV (LAQGSM)

8. 120 GeV primary proton beam, sigma_x=1.7 mm, beta_x=110.8837 m, alpha=0 baffle radius - 0.65 cm, transverse target dimensions -2.7 cm x 1 cm Protons hitting nominal targetProtons missing nominal target 8

9. Peak at the Absorber is due to Protons Missing the Target 9 0.3% of beam misses target entirely, giving 0.9-cm RMS on absorber (7 kW) 13% of beam protons multiple scatter through target, giving 4.9-cm RMS (~300 kW)

10. 10 Mitigation of the Peak at Normal Operation Adding graphite spoiler/wings at the target upstream with diameter equal to baffle ID (= 1.3cm) spanning over ~3 segments. 6-cm long wings ensure two-fold reduction of the peak proton flux. Can provide a factor of two safety margin for the current core design.

11. Optimized setup provides 33% increase of 75% CP sensitivity Nominal setup Optimized setup 11 nominal setup – 97 cm graphite target length, optimized setup - 237 cm graphite target length, nearly same transvers dimensions

12. Longer target: up to 20-fold reduction of pedestal Longer wings decrease peak: 100 times for 48-cm wings Full MC includes target, horns …,simple MC – target only 12

13. Power on absorber for 2.4 MW beam x*yNominal +12cm wings Optimized +48cm wings cm 2 kW 6*610746166.6 12*12196862516 32*323501597162 300*300760726392382 Increase of target length reduces total energy deposition Wings decrease maximal energy deposition 13

14. Energy Deposition (mW/cm3) y-z Profile:4x10x5.35 cm bin Nominal – NuMI styleOptimized – LBNO style Maximum energy deposition density is about 5 times lower for optimized target 14

15. Energy Deposition (mW/cm3) y-z Profile: 1x1x5.33 cm bin Nominal – NuMI styleOptimized – LBNO style Peak energy deposition density is about 2 times lower for optimized target with no wings – same peak 15

16. Maximal energy deposition (mW/cm3) for different setups 16 nominaloptimized 0 cm optimized 12 cm optimized 24 cm optimized 48 cm simple* 48cm 4x10x5.35cm3 1400 230 150 100 78 100 1x1x5.35 cm3 1700 880 280 150 100 120 * simple setup – optimized setup&absorber without spoiler and without sculpting Maximal energy deposition for optimized setup can be reduced up to 17 times by using wings. Even 12 cm wings decrease maximal energy deposition about 6 times. It is possible to consider simple absorber (without spoiler and sculpting) for optimized setup and target with wings.

17. Muon neutrino at far detector optimized setup: G4LBNF vs two MARS hadron-production models Linear scaleLog scale 17

18. Muon neutrino spectra at far detector – optimized setup: dependence on wings length Wings reduce muon neutrino flux less than few percent in region of interest (<5 GeV) 18 24 cm wings48 cm wings

19. 19 Muon/Hadron Fluxes (cm -2 s -1 ) with Steel Kern Rock Soil Z=360m, S=113 m Z=277 m, S=30 m Ground-water design goal Soil Rock ND L=459m, Z=456.7 m 30-m steel kern: R 1 =3.5m, R 2 =1.5m Muons Hadrons

20. Ratios of positive muon spectra in muon detectors –nominal/optimized 0cm – green, nominal/optimized 24cm – black, nominal/optimized 48cm – blue 20

21. Conclusions Using optimized (long) target with 12-48 cm wings reduces maximal energy deposition in LBNF absorber 6-20 times. It is possible to consider simple absorber without spoiler and sculpted blocks for optimized setup. Such simple absorber can survive even for significantly increased beam power beyond 2.4 MW. Muon neutrino flux decreases a few percent for target with 48 cm wings and less than one percent with 24 cm wings for neutrino energies important for LBNF/DUNE experiment. High energy muon flux after fourth alcove is reduced by factor of 2-3 for long target setup. It significantly decreases ground water activation in rock after absorber. 21

22. Backup 22

23. Analytical model: convolution of multiple Coulomb and quasi-elastic and elastic scatterings Blue line – only MCR in target red line –MCR*elastic scattering pink – coherent elastic green – quasi-elastic 23

24. Muon neutrino in near detector - optimized setup: G4LBNF vs two MARS hadron-production models Linear scaleLog scale 24

25. Muon neutrino spectra in near detector – optimized case: dependence on wings length Wings reduce muon neutrino flux less than few percent in region of interest (<5 GeV) 25

26. Target Hall/Decay Pipe Layout 26 DECAY PIPE SNOUT DECAY PIPE UPSTREAM WINDOW WORK CELL 50 TON CRANE Decay Pipe: 194 m long, 4 m in diameter, double – wall carbon steel, helium filled, air-cooled. Target Chase: 2.2 m/2.0 m wide, 34.3 m long air- filled and air & water-cooled (cooling panels). Sufficiently big to fit in alternative target/horns. Cooling panels Bea m 5.6 m ~ 40% of beam power in target chase ~ 30% of beam power in decay pipe Main alternatives for gas atmosphere: N 2 or He

27. 27 Hadron Absorber The Absorber is designed for 2.4 MW ~ 30% of beam power in Absorber 515 kW in central core 225 kw in steel shielding Core blocks replaceable (each 1 ft thick) Beam Muon Shielding (steel) Beam Muon Alcove Sculpted Al (9) Hadron Monitor Absorber Cooling Core: water-cooled Shielding: forced air-cooled Flexible, modular design

28. Energy Deposition (mW/cm3) y-z Profile:4x10x5.35 cm bin Nominal – NuMI style Optimized – LBNO style + 24cm wings Maximum energy deposition density is about 14 times lower for optimized target with 24 cm wings 28

29. Energy Deposition (mW/cm3) y-z Profile: 1x1x5.33 cm bin Nominal – NuMI styleOptimized – LBNO style+24cm wings Peak energy deposition density is about 11 times lower for optimized target with 24cm wings 29

30. Energy Deposition (mW/cm3) y-z Profile:4x10x5.35 cm bin Nominal – NuMI style Optimized – LBNO style + 48cm wings Maximum energy deposition density is about 21 times lower for optimized target with 48-cm long wings 30

31. Energy Deposition (mW/cm3) y-z Profile: 1x1x5.33 cm bin Nominal – NuMI style Optimized – LBNO style + 48cm wings Peak energy deposition density is about 21 times lower for optimized target with 48-cm long wings 31

32. Energy Deposition (mW/cm3) y-z Profile:4x10x5.35 cm bin Nominal – NuMI style Optimized – LBNO style + 48cm wings Maximum energy deposition density is about 14 times lower in simple absorber without spoiler and sculpted blocks (optimized target with 48-cm long wings) 32

33. Energy Deposition (mW/cm3) y-z Profile: 1x1x5.33 cm bin Nominal – NuMI style Optimized – LBNO style + 48cm wings Maximum energy deposition density is about 14 times lower in simple absorber without spoiler and sculpted blocks (optimized target with 48-cm long wings) 33