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VERY LARGE CROSSING ANGLES AND MAGNET TECHNOLOGY

CERN, 15 th December 2010 4 th LHC Crab cavity workshop. VERY LARGE CROSSING ANGLES AND MAGNET TECHNOLOGY. E. Todesco CERN, Geneva Switzerland Acknowledgements: R. De Maria, R. Tomas, F. Zimmermann. CONTENTS. Dipoles Quadrupoles. SEPARATION DIPOLES.

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VERY LARGE CROSSING ANGLES AND MAGNET TECHNOLOGY

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  1. CERN, 15th December 2010 4th LHC Crab cavity workshop VERY LARGE CROSSING ANGLES AND MAGNET TECHNOLOGY E. Todesco CERN, Geneva Switzerland Acknowledgements: R. De Maria, R. Tomas, F. Zimmermann

  2. CONTENTS • Dipoles • Quadrupoles

  3. SEPARATION DIPOLES • In the present LHC lay out the separation dipoles are not at the limit of Nb-Ti technology • D1 IP1 and IP5: resistive magnets • Single aperture • Field ~1.3 T • Length: 6*3.4 m ~20 m • Kick: ~26 T m • D1 IP2 and IP8: RHIC-like sc magnets • Single aperture 80 mm • Field ~3.8 T • Length: ~9.5 m • Kick: ~36 T m Resistive D1 cross-section Superconducting D1 cross-section

  4. SEPARATION DIPOLES • In the present LHC lay out the separation dipoles are not at the limit of Nb-Ti technology • D2: RHIC-like sc magnets • Double aperture 80 mm • Field ~3.8 T • Length: ~9.5 m • Kick: ~36 T m • D3 • Double magnet 80 mm • ~3.8 T ~9.5 m ~36 T m • D4 • Double aperture 80 mm • ~3.8 T ~9.5 m ~36 T m Superconducting D2 cross-section Superconducting D4 cross-section Superconducting D3 cross-section

  5. SEPARATION DIPOLES • What one wants • Larger aperture • More compact, larger kick  higher field • Relation aperture-field-beam separation for two-in-one magnets • Margin: if these magnets work in a place with radiation, more margin may be needed • 33% instead of the usual 20% we have in cell magnets

  6. SEPARATION DIPOLES • Aperture - Field • In a dipole aperture comes without losing much field – you just have to pay for the cable … • 30 mm coil thick (as in the LHC dipoles) gives ~10 T short sample • 6.5 T with 33% margin is a reasonable operational field • This would reduce length of resistive D1 from 20 to 3.5 m and D2-D4 from 10 to 5.5 m Short samplefield vs aperture and differentcoilthickness for Nb-Ti dipoleat 1.9 K

  7. SEPARATION DIPOLES • Aperture – Field – beam separation • For a two-in-one magnet there is a minimal distance between apertures • D2: minimal distance ~ aperture+2*coil thickness+2*40 mm • One could easily reduce to 2* 30 mm the distance between coils 80 mm Minimum separation vs aperture and differentcoilthickness for a 60 mm distance betweencoils

  8. SEPARATION DIPOLES • More exotic designs • Open midplane dipoles [R. Gupta et al.] • To cope with places with large radiation • Relies on the idea of placing coils where Lorentz forces are not pushing • Less effective in terms of field-coil width • Mechanical structure to be analysed • Very fascinating, still on paper • Good field quality can be achieved • Coil-free midplane[J. Bruer, E. Todesco, IEEE Trans. Appl. Supercond. (2009)] • The midplane is not open, but there is no coil • Less effective in terms of field-coil width • Mechanically viable • Good field quality can be achieved Conceptual design of open midplanedipole Coil lay-out in a coil-free midplanedipole

  9. SEPARATION DIPOLES • There are two positions in the community • Exploring open midplane to get rid of radiation • Shielding in not enough effective! • Make the dipole larger and shield it • A standard design with larger aperture requires less conductor than an open midplane! • What about Nb3Sn? • It can give about 50% more field, i.e. reaching the 15 T short sample • Gives more temperature margin • Is more expensive • Is more strain sensitive, even though latest results show good performance up to 200 MPa[M. Bajko, S. Caspi, H. Felice, et al. TQ test at CERN]

  10. CONTENTS • Dipoles • Quadrupoles

  11. IR QUADRUPOLES • In the present LHC lay out the IP quadrupoles ARE at the limit of Nb-Ti technology • MQXA-B • Single aperture 70 mm • Gradient ~220 T/m at 1.9 K • Length: ~5.5 – 6.3 m • MQY • Double aperture 70 mm • Gradient ~160 T/m at 4.2 K MQXA cross-section MQXB cross-section MQY cross-section MQY assembly

  12. IR QUADRUPOLES • What one wants • Larger aperture • More compact, larger gradient  higher field • Relation aperture-field-beam separation for two-in-one magnets • Margin: is it enough the 20% taken in the LHC ? • We already reached the limit with Nb-Ti • Either we explore new ways in the optics satisfying the gradient-aperture-separation requirement[S. Fartoukh, sLHC-PROJECT-Report-0049 (2010)] • Or we use Nb3Sn – 50% larger gradient for the same aperture • Or we couple both things …

  13. IR QUADRUPOLES • Aperture - Gradient • In a quadrupole aperture is very expensive • At zero order gradient is inversely proportional to aperture • 30 mm coil thickness in 70 mm aperture (as in the LHC IR quads) provide about 250 T/m short sample • Adding more coil does not help Short sample gradient vs aperture and differentcoilthickness for Nb-Ti quadrupoleat 1.9 K

  14. IR QUADRUPOLES • Aperture – Field – beam separation • For a two-in-one magnet there is a minimal distance between apertures • Minimal distance ~ aperture+2*coil thickness+2*25 mm • 50 mm is what we have in MQY – difficult to make better but … Minimum separation vs aperture and differentcoilthickness for a 50 mm distance betweencoils

  15. IR QUADRUPOLES • Asymmetric coil designs [V. Kashikin, EPAC 2006] • Allows to further reduce the distance between apertures to nearly zero • 100 mm aperture, with ~40 mm coil thickness • The cross-talk is compensated via the coil cross-section • Looks viable from a practical point of view Coillayoutproposed to reduce the beamseparation[V. Kashikin]

  16. IR QUADRUPOLES • Aperture – Field – beam separation • With the asymmetric coil we could reduce to • Minimal distance ~ aperture+2*coil thickness+2*10 mm Minimum separation vs aperture and differentcoilthickness for a 20 mm distance betweencoils

  17. LARGE CROSSING ANGLE LAY OUT • 8 mrad crossing angle • First quadrupole at 23 m • Beam separation starts at ~200 mm • With 200 T/m and 63 mm aperture the quadrupole is viable • But one is at the limit, one cannot go much lower: 150 mm – 6 mrad with the same apertures • Quadrupole coils would be non-parallel within the common iron yoke this has never been done but looks viable 8 mradcrossing angle scheme[R. Tomas et al, Lumi 06]

  18. CONCLUSIONS • LHC is at the limit for Nb-Ti technology for IR quadrupoles, and well below for separation dipoles • Much room for improving dipoles staying with Nb-Ti – both for quads and for dipoles Nb3Sn gives 50% more • We sketched the mail relations • Aperture - field - beam separation (dipoles) • Aperture - gradient - beam separation (quadrupoles) • Several ideas have been proposed – but are still on paper • Open midplane to deal with radiation • Asymmetric coils to decrease beam separation • The 8 mrad scheme is not far from the limit • 6 mrad could be possible • Below it, one should change the optics

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