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Magnets for Pamela

Magnets for Pamela. H Witte, T Yokoi, S Sheehy, J Cobb, K Peach John Adams Institute for Accelerator Science, Keble Road, Oxford, OX1 3RH, UK. Introduction. Magnet requirements for S. Machida’s lattice Combined function magnets (up to decapole )

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Magnets for Pamela

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  1. Magnets for Pamela H Witte, T Yokoi, S Sheehy, J Cobb, K Peach John Adams Institute for Accelerator Science, Keble Road, Oxford, OX1 3RH, UK

  2. Introduction • Magnet requirements for S. Machida’s lattice • Combined function magnets (up to decapole) • Magnets need to be short, little space in lattice • Large beam aperture • High field quality required • Helical coil approach (double helix technology) • Solution for S. Machida’s lattice • Performance • Fringe Field • Loadlines • Conclusion • Outlook

  3. Magnet Requirements • Lattice by S. Machida • semi-scaling FFAG for proton therapy • QF • Dipole 1T • Quad 4 T/m • Sextupole 0.76 T/m2 • Octupole 0.0912 T/m3 • Decapole 0.007752 T/m4 • QD • 80% of QF • Envisaged coil length: 0.314 m • Additional Space: 0.314 m between magnets • Maximum coil length: 0.45 m? • Focus on QF (worst case) 4.4 T with 314 mm space

  4. Magnet Requirements QF

  5. Magnetic Field Aperture

  6. Double Helix Concept • Double-helix concept • Two oppositely tiled solenoids create dipole field • Higher order multipoles follow same logic • Advantage: No coil end problem • S. Machida’s lattice • At least one double-layer per multipole = 5 rings • In practise: more layers to reduce peak field on wire • Order • Dipole innermost (1) • ... • Decapole outermost (5)

  7. Double-Helix: Combined Function Magnets

  8. Magnet Details

  9. Performance • Field equivalent to coil with length of 0.314 m • Integrate magnetic field • Figure shows field equivalent for a coil length of 314 mm • Aperture: 290x30 mm2 • Note: Deviation in polynomial coefficients is not identical to field quality!

  10. Field Quality • Multipole components can be tuned to target values • Field quality is probably more determined by manufacturing tolerances

  11. Stray Field

  12. Loadlines: Dipole Dipole Margin: 0.8-1.7K • Dipole suggests that T ≈ 1.8K is required

  13. Loadlines: Cont. Quadrupole Margin: 1.7-2.3K Sextupole

  14. Loadlines cont. Octupole Decapole • Sextupole, octupole and decapole relatively unproblematic

  15. Conclusions • Magnets for S. Machida’s lattice: • Coils based on double-helix approach look promising • Dipole most challenging • requires probably NbTi at 1.8K • 1.8K: Cryogenics more complicated, but there are advantages • He is superfluid – much better thermal conductivity • (LHC runs on 1.8K) • Operation at 4.2K? • Magnets need to become longer or • Lower field or • Smaller beam aperture • Higher order multipoles ok • Decapole field contribution – do we need it (3.4 mT at r=145mm)? • Stray field relatively large

  16. Conclusions • Carbon lattice? • Proton lattice seems to be pushing limits of NbTi • Carbon more challenging? • Nb3Sn • Answer? • Technically feasible • Active area of development (ITER) • Cost!

  17. Thank you for your attention!

  18. Picture Frame Magnets • Idea: M Green. • A Design for a Combined Function Superconducting Dipole for a Muon Collider FFAG Accelerator. Fourth European Conference on Applied Superconductivity Sitges, Spain, LBNL-44190, Sept.1999. • Superferric coil • Initial design: Dipole+Quad+Sextupole • Advantages: • Iron • Rectangular bore • Stray fields

  19. Picture Frame Magnets Dipole Quadrupole (Panofsky)

  20. Picture Frame Magnet: Sextupole Current Density Field in Coil Centre

  21. Shinji: Picture Frame Magnet? • Just dipole, quad and sextupole field • Unshifted field centre • Bdp=1T • Iron: 1.5 x 0.75 m2 • Bore: 240x30 mm2 • Higher order field components? • Up to 20 independent current sources to create octapole and decapole fields

  22. KST Lattice: Ring 2D Aperture: 80x26 mm2 Field: Dipole and Quad

  23. KST Lattice: Ring 2D • Picture Frame Magnet seems to be an option for KST lattice (ring 2) • Iron is not saturated • Good field quality seems to be achievable • Further studies required • 3D model • Field quality

  24. Jc of NbTi and Nb3Sn

  25. Limits of Helical Coil Technology • Field in coil depends on • Current (density) • Tilt angle alpha • No. turns • (coil length, layer thickness) • Efficiency: • Small tilt angle • Lower J • Large tilt angle: • More turns • Lower peak field • Example: • 45 and 60 degrees • Difference: 1.5T • Tc(J, B) • Optimum?

  26. Limits Critical Temperatures Influence of coil length (Dipole)

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