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
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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
80 mm100
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Min
im b
eam
sep
arat
ion
(mm
)
Aperture (mm)
10 mm coil thickness
20 mm coil thickness
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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50 100 150 200
Sho
rt s
ampl
e gr
adie
nt (
T)
Aperture (mm)
10 mm coil thickness
20 mm coil thickness
30 mm coil thickness
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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50 100 150 200
Min
im b
eam
sep
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(mm
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Aperture (mm)
10 mm coil thickness
20 mm coil thickness
30 mm coil thickness
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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50 100 150 200
Min
im b
eam
sep
arat
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(mm
)
Aperture (mm)
10 mm coil thickness
20 mm coil thickness
30 mm coil thickness
20 mm distance between coils
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