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Innovative Magnet Design for S. Machida’s Proton Therapy Lattice

This study focuses on magnet requirements for S. Machida’s lattice for proton therapy, emphasizing double-helix technology. The design includes combined-function magnets with a high field quality and large beam aperture. Performance, fringe field, loadlines, and conclusions are discussed. The study evaluates the potential of helical coils in meeting the lattice demands and explores the impact of higher-order multipoles. The use of innovative design concepts and materials like NbTi and Nb3Sn is considered to achieve optimal magnet performance for the lattice. Conclusion and outlook provide valuable insights for future developments.

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Innovative Magnet Design for S. Machida’s Proton Therapy Lattice

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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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