E. Todesco

VERY LARGE CROSSING ANGLES AND MAGNET TECHNOLOGY

E. TodescoCERN, Geneva Switzerland

Acknowledgements: R. De Maria, R. Tomas, F. Zimmermann

CERN, 15th December 20104th LHC Crab cavity workshop

E. Todesco Very large crossing angles and magnet technology - 2

CONTENTS

Dipoles

Quadrupoles

E. Todesco Very large crossing angles and magnet technology - 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 TLength: 6*3.4 m ~20 mKick: ~26 T m

D1 IP2 and IP8: RHIC-like sc magnets

Single aperture 80 mmField ~3.8 TLength: ~9.5 mKick: ~36 T m

Resistive D1 cross-section

Superconducting D1 cross-section

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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 TLength: ~9.5 mKick: ~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 D3 cross-section

Superconducting D4 cross-section

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SEPARATION DIPOLES

What one wantsLarger apertureMore compact, larger kick higher fieldRelation aperture-field-beam separation for two-in-one magnetsMargin: 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

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SEPARATION DIPOLES

Aperture - FieldIn 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 fieldThis would reduce length of resistive D1 from 20 to 3.5 m and D2-D4 from 10 to 5.5 m

Short sample field vs aperture and different coil thickness for Nb-Ti dipole at 1.9 K

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SEPARATION DIPOLES

Aperture – Field – beam separationFor a two-in-one magnet there is a minimal distance between apertures

D2: minimal distance ~ aperture+2*coil thickness+2*40 mmOne could easily reduce to 2* 30 mm the distance between coils

Minimum separation vs aperture and different coil thickness for a 60 mm distance between coils

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30 mm coil thickness

60 mm distance between coils

LHC separation dipoles

LHC main dipoles

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SEPARATION DIPOLES

More exotic designsOpen midplane dipoles [R. Gupta et al.]

To cope with places with large radiationRelies on the idea of placing coils whereLorentz forces are not pushingLess effective in terms of field-coil widthMechanical structure to be analysedVery fascinating, still on paperGood 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 coilLess effective in terms of field-coil widthMechanically viableGood field quality can be achieved

Conceptual design of open midplane dipole

Coil lay-out in a coil-free midplane dipole

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SEPARATION DIPOLES

There are two positions in the communityExploring 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 sampleGives more temperature marginIs more expensiveIs 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]

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CONTENTS

Dipoles

Quadrupoles

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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 KLength: ~5.5 – 6.3 m

MQY

Double aperture 70 mmGradient ~160 T/m at 4.2 K

MQXA cross-sectionMQXB cross-section

MQY cross-section MQY assembly

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IR QUADRUPOLES

What one wantsLarger apertureMore compact, larger gradient higher fieldRelation aperture-field-beam separation for two-in-one magnetsMargin: is it enough the 20% taken in the LHC ?

We already reached the limit with Nb-TiEither 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 apertureOr we couple both things …

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IR QUADRUPOLES

Aperture - GradientIn a quadrupole aperture is very expensive At zero order gradient is inversely proportional to aperture30 mm coil thickness in 70 mm aperture (as in the LHC IR quads) provide about 250 T/m short sampleAdding more coil does not help

Short sample gradient vs aperture and different coil thickness for Nb-Ti quadrupole at 1.9 K

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LHC MQX, MQY

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IR QUADRUPOLES

Aperture – Field – beam separationFor a two-in-one magnet there is a minimal distance between apertures

Minimal distance ~ aperture+2*coil thickness+2*25 mm50 mm is what we have in MQY – difficult to make better but …

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50 mm distance between coils

LHC MQYLHC MQ

Minimum separation vs aperture and different coil thickness for a 50 mm distance between coils

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IR QUADRUPOLES

Asymmetric coil designs [V. Kashikin, EPAC 2006]

Allows to further reduce the distance between apertures to nearly zero100 mm aperture, with ~40 mm coil thicknessThe cross-talk is compensated via the coil cross-sectionLooks viable from a practical point of view

Coil layout proposed to reduce the beam separation [V. Kashikin]

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IR QUADRUPOLES

Aperture – Field – beam separationWith the asymmetric coil we could reduce to

Minimal distance ~ aperture+2*coil thickness+2*10 mm

Minimum separation vs aperture and different coil thickness for a 20 mm distance between coils

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LARGE CROSSING ANGLE LAY OUT

8 mrad crossing angleFirst quadrupole at 23 mBeam separation starts at ~200 mmWith 200 T/m and 63 mm aperturethe 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-parallelwithin the common iron yokethis has never been done but looks viable

8 mrad crossing angle scheme [R. Tomas et al, Lumi 06]

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8 mrad

6 mrad

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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 relationsAperture - field - beam separation (dipoles)Aperture - gradient - beam separation (quadrupoles)

Several ideas have been proposed – but are still on paper

Open midplane to deal with radiationAsymmetric coils to decrease beam separation

The 8 mrad scheme is not far from the limit6 mrad could be possibleBelow it, one should change the optics