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Target Studies

Target Studies. Rob Edgecock. Outline. Introduction Mercury jet - current IDS baseline Solid targets – main focus in UKNF Powder jets – studied in EID for NF and superbeam Conclusions. 4MW beam: ~0.75MW in target → Δ T ~ 100K/pulse → must change target between pulses

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Target Studies

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  1. Target Studies Rob Edgecock

  2. Outline • Introduction • Mercury jet - current IDS baseline • Solid targets – main focus in UKNF • Powder jets – studied in EID for NF and superbeam • Conclusions

  3. 4MW beam: • ~0.75MW in target → ΔT ~ 100K/pulse → must change target between pulses • most of rest: beam dump or target station, depending on E • Small beam → large energy density: ~300J/cm3 • shock/cavitation: 300MPa stress wave → effect must be determined • Activation: • small nuclear plant • ~30MCi after 10 years operation • possible significant radiation damage → difficulty in obtaining a license shouldn’t be underestimated • heat load into SC magnets is a problem Introduction

  4. 1 - Mercury Jet • IDS baseline • DC jet, ~1cm diameter, ~20m/s → 21kg/s

  5. Solenoid Jet Chamber Syringe Pump Secondary Containment Proton Beam 1 2 3 4 Feasibility in proton beam & B-field: tested by MERIT. Ran at CERN using PS in Autumn 2007. MERIT Experiment

  6. MERIT Experiment 20TP, 10T V = 65 m/s • Conclusions: - It worked! - B-field improved jet quality - Droplet velocities reduced by B-field - Disruption length OK (energy density 4±2 MW) • Technical issues for NF use to be dealt with t=0.375 ms t=0.050 ms t=0.175 ms t=0

  7. Mercury in NF • DC loop - pump - quality of jet - nozzle and erosion by mercury - mercury splash • Impact of droplets • Downstream beam window • Radioprotection & license Tristan Davenne

  8. Target Cart Mercury Pump Mercury Experience Ventilation Supply • Contained mercury used in SNS and JSNS • In SNS, works better than expected • Problems after target change Ventilation Exhaust Mercury condensate on Target Cart surfaces • For 2nd target station, choice between - copy of 1st - tungsten on rotating wheel Service Bay Size: 31.4 m x 4.3 m

  9. In Europe • PSI: - studied mercury - used lead-bismuth eutectic (solid at RT) • ESS Sweden: - lead-something (gold?) eutectic - or tungsten on rotating wheel

  10. In Europe

  11. Solid means • tungsten bars, each ~2x20cm • 150-200 bars • changed between beam pulses • cooled radiatively or possibly by helium • Why? • lots of experience world-wide & safer • already have a license at RAL • Issues for solids: • shock – original show-stopper • radiation damage • target change • Focus has been on shock - but now moving on 2 - Solid Targets

  12. Ideally, high energy density proton beam for >1 year • Not possible, so use pulsed electric current • Relationship to target made via LSDyna Shock Aims: measure lifetime validate LSDyna model understand W behaviour 60kV, 8kA PSU, 100ns rise time

  13. Laser beam Wire Laser beam • Lifetime - more than sufficient demonstrated: > 20 years in 3cm diameter target > 10 years in 2cm “ “ More at lower temperature • Validation of LSDyna model: Use Laser Doppler Vibrometer Measure surface velocity of shocked wires Extract oscillation frequencies Results 200 targets 1500oC Longitudinal and radial measurements possible

  14. LDV Measurements Frequency analysis Longitudinal oscillations vs LSDyna

  15. LDV Measurements Radial oscillations: frequency analysis vs LSDyna Radial oscillations vs LSDyna

  16. Young’s Modulus - Tungsten Young’s modulus remains high at high temperature & high stress! Encouraging but not conclusive enough.

  17. Young’s Modulus - Tantalum E of Ta < 0.5 W at 1500oC Don’t see expected fall off …but we noticed something interesting when tried to reach highest possible temperature…

  18. High temperature tests - Ta wire – 0.8 mm diameter 35 kV 45 kV ~ 1000 ºC

  19. High temperature tests - Ta wire – 0.8 mm diameter 35 kV 45 kV ~ 1400 ºC

  20. High temperature tests - Ta wire – 0.8 mm diameter 35 kV 45 kV ~ 1800 ºC

  21. High temperature tests - Ta wire – 0.8 mm diameter 35 kV 45 kV Started bending here; same temperature but higher shock per pulse ~ 2100 ºC

  22. Combination of visual observation of the wire and LS-DYNA simulations In our case: high strain-rate… Stress in NF target

  23. Would like to measure strength of W • No sign of bending before failure Tensile Strength - Tungsten • Some ideas in mind • Three papers in preparation

  24. Repeat lifetime tests, with LDV measurements • Stress bulk samples: • Oscillation frequencies different • Manufacture techniques different • Show targets will work • Needs high density proton beam: • ISIS possible, but not trivial • HiRadMat facility or ISOLDE at CERN looks best • Strength after irradiation – various possibilities: • Measure ISIS targets – expensive; consortium investigated • Join radiation damage tests at GSI • Measure various ISOLDE targets Next Steps

  25. Radiation Damage NB Static measurements. 300 1500

  26. Detailed engineering starting Target Change Outer diameter: 5m Speed at rim: 5m/s Revolution time: 3.14s Target spacing: 100mm # of targets: 157 Wheel Moving parts out of radiation Structurally ok Radiation shielding Forces on Helmholtz coils

  27. Target Change ~7kt bending force on SC coils: “very difficult” So, studying other magnet arrangements. First priority: sufficient pion capture cf Study II

  28. Target Change Helmholtz Pion capture into ~Study II acceptance: ~100%

  29. Target Change Coils only downstream of target Pion capture into ~Study II acceptance: ~60%

  30. Target Change Helmholtz structure, but only with NC coils Pion capture into ~Study II acceptance: ~75%

  31. Target Change Helmholtz structure, with larger NC coils Pion capture into ~Study II acceptance: ~90% New option – minimal solenoid impact – under study

  32. 3 - Fluidised Powder Jet • ~250μm tungsten powder driven by gas • Number of potential advantages • can deliver material without splitting solenoid • carries heat away • but not a liquid • Number of issues • never used as a target before • will need to be licensed • density, erosion, DC operation, etc • Test rig built at RAL to test

  33. Powder • Rig contains 150 kg Tungsten • Particle size < 250 microns • Total ~8,000 kg powder conveyed • 90 ejection cycles • Equivalent to 15 mins continuous operation • Batch mode • Test out individual handling processes before moving to a continuous flow loop 2 1 3 4 1. Suction / Lift 2. Load Hopper 3. Pressurise Hopper 4. Powder Ejection and Observation

  34. It works! • Initial density measurement: • 42 ± 5% • Various improvements planned: • prevent phase separation • DC operation • minimise erosion • etc • Turbulent flow ~3bar • Dune flow ~1.5bar • Pulsing flow ~1.5bar • Coherent jet ~2bar

  35. SC1 SC2 SC3 SC4 SC5 Air FeCo WC Shield Hg Jet Hg Jet STST Env (Bottle) Pre-Trgt Res Sol Hg Pool BeWindow (z=600cm) Energy Deposition of Beam X.Ding UCLA

  36. Energy Deposition of Beam

  37. Energy Deposition of Beam More shielding helps. Further study required. May require higher proton energy.

  38. Conclusions • Target + target station: one of biggest challenges for NF • Three complementary target technologies under study - mercury - solid tungsten - tungsten powder • Each have advantages and disadvantages • None yet fully proven • Lots of work still to be done

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