Superconducting Solenoids for COMET

1. Superconducting Solenoidsfor COMET KEK Cryogenics Center, Osaka Univ. Kuno-san’s Team, J-PARC MLF Muon Group

2. Layout of Beam Line Magnets • Pion Capture • High Field • High Radiation • Transport & Decay • Medium Field • Curved solenoid • Experiment • Low Field • Large volume • Curved solenoid

3. Pion Capture Solenoid Requirement • High Field • More pion to capture • More (better) conductor • Larger stored energy • High Radiation • High Power Beam • Heat Load • Radiation Damage

4. Heat Load ~10kW Cost ~100M$ Big SC Solenoids in Real World Heat Load ~100W Cost ~10M$ Heat Load ~1W Cost ~1M$ Fusion (ITER CS model) Field: ~13T (Nb3Sn) Cooling: Direct Cable in Conduit Detector Solenoids Field: 1~4T (NbTi) Cooling: Indirect Al Stabilized Cable With Cooling pipes MRI Magnets Field: 1~4T Cooling: He Free?

5. Technology ChoiceConductor Material • NbTi (~5T) choice for now • Well established • Not Expensive • Nb3Sn or Nb3Al (~12T) • Established for solenoids • Expensive (x5:conductor, x2:assebly to NbTi) • High Tc (~20T??) • Not established for high field magnets • Very expensive

6. Technology ChoiceHeat Load • 50GeV x 15mA • Beam: 750kW • Coil: ~100W • Cable in Conduit? • 8GeV x 7mA • Beam: 56kW • Coil: ~10W • Detector Solenoid

7. Detector Solenoids • Mostly Common Feature • Aluminum stabilized cable • quench stability • quench protection • transparency • Indirect cooling with cooling pipe • 2 phase forced flow • Thermo siphon • Technology well established • Many solenoids are in use • Familiar to people in high energy physics • Good for field up to ~5T • 4T already achieved • Good Solution for near future plan • With modest budget

8. Capture Solenoid Design 30mm 5mm

9. Temperature Margin Indirect cooling Cooling path from conductor to cooling pipe i.e. Temp. gradient We choose 5T version More temp margin 2 < 4 layer (transparency) Lower peak field

10. Quench Protection • Quench • Stored energy • partly extracted • partly into coil • To protect coil • spread heat evenly • Still there are limit • Parameter to look • Stored Energy to • Coil Mass Ratio M-E conversion

11. Yield Strength VS RRR Good RRR: for quench stability and protection High Yield Strength: for high EM force

12. High Yield Strength Al stabilized Conductor R&D • For High Energy Physics • Higher Field：　> 5 Tesla • Larger Size：　Diameter〜10m • Combination of Various Technology • ATLAS Al Ni Alloy • Ni-0.5 ~ 1 % • CMS-Hybrid Support • A6058 -->> A7020 Y.S.(0.2%) = 400 MPa RRR = ~ 400

13. An R&D Work using ATLAS-CS Conductor + A6061-T6 • T.S. is > 50 % reinforced with A6061 using Electron Beam, and Laser Beam Welding • LBW may be a potential technology Laser Beam Welding EBW, LBW

14. Refrigerator • Cryocoolers (GM or pulse tube) may not be strong enough • Maybe Helium refrigerator plant needed

15. Guideline for magnet design • Optimize the magnetic field design below 6 T • As base-line, using NbTi superconductor • (with a future option for > 10 T Nb3Sn, Nb3Al magnet for the pion capture solenoid) • Apply “thin solenoid” design concept with Al-stabilized superconductor and indirect-cooling to • Minimize radiation heating, • Refer technology established at, • ATLAS, BESS, and CMS Solenoid

16. Toward Higher Field • Al-stabilized Nb3Sn/Nb3Al Solenoid beyond 10 T • An R&D may be proposed in cooperation with NIFS.

17. Toward Higher Beam Power • Cable in conduit • Removal of large heat load • ITER CS Experienced by model Nb3Sn ready Up to 13 T Can be ideal If affordable… ITER CS: 170M€

18. Capture SolenoidSummary & Issues • For Pion Capture Solenoid for J-PARC • Detector Solenoid Technologies can be good solution • Field ~5T, Heat Load ~10W (Beam Power ~56kW) • More advanced technologies are also available • with some more money… • Issues • High Radiation Doze • Insulation material: Organic < 107 Gy • High Neutron Fluence • Al and Cu: Resistivity change • Superconductor: Jc change

19. What about others • Pion Capture • High Field • High Radiation • Transport & Decay • Medium Field • Curved solenoid • Experiment • Low Field • Large volume • Curved solenoid

20. Transport solenoid • COMET is not the only project needing muon transport solenoid • Even in J-PARC there is a similar curved solenoid needed • J-PARC MLF muon beam line • Lot of similarity in spec • Joint R&D • Osaka Univ • KEK muon group • KEK cryogenics center

21. J-PARC Muon Beam Line • Field; ~2T • Aparture; ~0.4 m • Limited Access to shielded area • Refrigerator must be outside of shield • Limited Space for the refrigerators • Long distance to cold head to coil front • Conduction Cooling with Higher Temperature

22. Trial Winding of Curved Section with MgB2 conductor R&D Coil made at KEK in house NbTi Already wound Test just started • Purchase two kinds of MgB2 conductor from Columbus SC • 1 is the 1.13 mm diameter round wire • Will be wound by a company • 2 is the 1.5 * 2.5 mm square wire • Will be wound by Nakahara and Adachi at KEK • They will be wound this winter and Tested in next spring

23. R&D on Transport SC R&D on trim dipole coil Solenoid Coil by company will be wound till Mar.

24. Trial Winding of Curved Section with MgB2 conductor • Purchase two kinds of MgB2 conductor from Columbus SC • 1 is the 1.13 mm diameter round wire • Will be wound by a company • 2 is the 1.5 * 2.5 mm square wire • Will be wound by Nakahara and Adachi at KEK • They will be wound this winter and Tested in next spring

25. MgB2 conductor actually purchasing Monel 400 sheathed Diameter: 1.13mm Composition MgB2 (Vol %) 14.6 Fe (Vol %) 10.8 Cu (Vol %) 13.8 Ni (Vol %) 15.8 Monel 400 (Vol %) 45.0 Cost: 3€/m There is also 1.5 mm * 2.5 mm conductor

26. Themal Conductivity and Specific Heat of Cu and Al Thermal Conductivity: ~ 3 times better Cp: about 10 times larger NbTi MgB2

27. Refrigerator Performance • Refrigerator Efficiency • Improve significantly at higher temperature 7.2 kW

28. Transport SolenoidSummary • MgB2 can be a good candidate • Operation Temperature 10~20 K • Better Refrigerator Performance • Best Thermal Conductivity • Better Specific Heat • Good Cost saving solution