Transcript LEP dismantling

R. Ostojic
CERN, AT Department
LHC Insertion Magnets
Dispersion suppressor
Matching section
Separation dipoles
Final
focus
154 superconducting magnets:
• 102 quadrupoles cooled at 1.9 K,
with gradients of 200 T/m
• 52 dipoles and quadrupoles
cooled at 4.5 K, with fields of 4 T
and gradients of 160 T/m
R. Ostojic, LTC, 10 May 2006
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LHC Magnet Classes
1. MB – class (MB, MQ, MQM)
(8.5 T, Nb-Ti cable at 1.9 K; m-channel polyimide insulation)
1b. MQX- class (MQXA, MQXB)
(8.5 T; Nb-Ti cable at 1.9 K; closed-channel polyimide insulation)
2. MQY- class (MQM, MQY)
(5 T; Nb-Ti cable at 4.5 K; m-channel polyimide insulation)
3. RHIC – class (D1, D2, D3, D4)
(4 T; Nb-Ti cable at 4.5 K; closed-channel polyimide insulation)
4. MQTL – class (MQTL, MCBX and all correctors)
(3 T; Nb-Ti wire at 4.5 K; impregnated coil)
5. Normal conducting magnets (MBW, MBWX, MQW)
(1.4 T; normal conducting; impregnated coil)
R. Ostojic, LTC, 10 May 2006
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Upgrade of the Matching Sections
and Separation Dipoles
• The present matching quadrupoles are state-ofthe-art Nb-Ti quadrupoles which operate at 4.5 K.
– The upgrade of the matching sections should in the first
place focus on modifying the cooling scheme and
operating the magnets at 1.9 K.
– In case larger apertures are required, new magnets could
be built as extensions of existing designs.
• The 4 T-class separation dipoles should be replaced
with higher field magnets cooled at 1.9 K.
• The MQTL-class should be replaced by magnets
more resistant to high radiation environment.
R. Ostojic, LTC, 10 May 2006
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The LHC low-b triplet
Q2
Q3
Q1
TASB
DFBX
MQXA
6.37
MCSOX
a3
a4
b4
MCBXA
MCBXH/V
b3
b6
R. Ostojic, LTC, 10 May 2006
MQXB
2.985
MQSX
5.5
MQXB
1.0
MCBX
MCBXH/V
5.5
MQXA
2.715
6.37
MCBX
MCBXH/V
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LHC low-b triplets
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Limits of the present LHC triplets
• Aperture
70 mm coil
63 mm beam tube
60 mm beam screen
 b* = 0.55 m
• Gradient
– 215 T/m
 operational 205 T/m
• Field quality
– Excellent, no need for correctors down to b* ~ 0.6 m
• Peak power density
– 12 mW/cm3
 L = 3 1034
• Total cooling power
– 420 W at 1.9 K
R. Ostojic, LTC, 10 May 2006
 L = 3 1034
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Aperture issue
• The coil aperture was the most revisited magnet
parameter of the low-b quadrupoles.
– Aperture of 70 mm defined in the “Yellow Book” (1995,
nominal b*= 0.50 m, ultimate 0.25 m).
– Subsequent studies showed a need for increasing the
crossing angle by a factor of two.
– e-cloud instability  introduction of beam screens.
• Upgrade target remains a b* of 0.25 m (irrespective of
magnet technology).
– Luminosity increase by a factor ~1.5.
• Higher luminosity implies substantially greater load on
the cryogenic system.
– feedback to the choice of aperture and magnet design.
R. Ostojic, LTC, 10 May 2006
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Enabling operation of the LHC
with minimal disruption
• Maintenance and repair of insertion magnets:
– Large number of magnets of different type means
limited number of spare magnets ready for
exchange.
– A facility is planned at CERN for repair/rebuild of
matching section quadrupoles.
• Particular problem: low-beta quadrupoles and
separation dipoles
• Only one spare of each type (best magnets
already in the LHC).
• As of 2006, there will be no operating facility for
repair and testing of these magnets.
R. Ostojic, LTC, 10 May 2006
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Quadrupole-first layouts
Q3
Q2B
Q2A
Q1
LHC Low-b Triplet
6.3
3.0
5.5
1.0
5.5
2.7
6.3
Symmetric Triplet
8.0
2.0
8.0
2.0
8.0
2.0
8.0
2.0
8.0
2.0
8.0
2.0
8.0
L* = 23 m
Triplet with "long" Q3
10.0
Optimize the aperture and
length of the quadrupoles
according to their position in
the triplet.
Triplet with "short" Q1
8.0
2.0
8.0
2.0
8.0
2.0
4.0
140.00
0.90
L < 10 m
0.80
120.00
0.70
100.00
0.60
80.00
0.50
60.00
0.40
Fp
Dmin [mm]
L ~ Fp/b*
0.30
40.00
0.20
Q2/Q3
Q1
20.00
0.00
0.00
0.10
0.20
0.30
b*[m]
R. Ostojic, LTC, 10 May 2006
0.40
0.50
0.10
0.00
0.60
Use of aperture:
• Increase the aperture to
reduce heat loads (peak and
total)
• Profit from better field quality
to reduce the number of
correctors and introduce
stronger orbit correctors
• Decrease b* to complement
other ways of increasing
luminosity.
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Large aperture quadrupoles using
existing LHC cables
Cable parameters
Width [mm]
Mid-thickness [mm]
Critical current,
Ic [A] @ 9 T, 1.9K
dIc/dB [A/T]
MQY
8.3
0.84/
1.28
5070/
9110
1350/
2550
R. Ostojic, LTC, 10 May 2006
MQ
15.10
1.48
MB
15.10
1.90
12960
13750
3650
4800
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Large aperture quadrupoles
240
Operating current at
80% of conductor limit
As the quadrupole aperture
increases, the operating gradient
decreases by 20 T/m for every
10mm of coil aperture.
220
Gradient [T/m]
200
To get a GL similar to the present
triplet, quadrupole lengths need
to be increased by 20-30%.
180
160
140
MQY cable
MB/MQ cable
120
MQ cable
The Nb-Ti technology proven for
quadrupoles up to 12 m long.
100
50
60
70
80
90
100
110
120
Coil aperture [mm]
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R&D directions for Nb-Ti quads
• Technology and manufacturing issues are well
mastered.
• Relatively easy extension of main magnet
parameters (aperture and length) without
extensive R&D.
LHC
dipoles
• Focus R&D on magnet “transparency”:
– Cable and coil insulation
– Thermal design of the collaring and yoking structures
– Coupling to the heat exchanger
C. Meuris
et al, 1999
FRESCA,
10 T, 88 mm
R. Ostojic, LTC, 10 May 2006
D. Leroy et al., 1999
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Summary
• LHC contains several generations of Nb-Ti magnets. Extensive
experience exists in building magnets of different aperture
and length. Upgrading the magnets to a higher class should
be considered as a first option.
• Nb-Ti (1.9K) technology is a clear choice for upgrading the
large number of magnets in the LHC insertions (dipoles and
quadrupoles) of the 4 T class.
• The availability of spare low-b triplets and separation dipoles
is a serious concern. Any proposal for the upgrade must take
this issue into account and provide an appropriate solution.
– The shortest route for providing new magnets in a time frame
compatible with LHC luminosity runs is to use Nb-Ti technology.
• Nb-Ti (1.9K) technology has reached its limits for large series
production with the LHC main dipoles; improvements for
small series are still possible.
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Comment
• It is generally accepted that a new generation of magnets
(Nb3Sn, HTS,…) will be required for the next hadron collider.
CERN should take part in a wider effort to develop and
demonstrate the feasibility of the new technology.
– In the interest of LHC operation, we must have an alternative;
Nb-Ti technology can offer an appropriate intermediate solution.
• The pitfalls in building Nb-Ti magnets should not be
underestimated. There is a need to start design studies and
development before LHC construction teams move on to
other projects.
• Initial experience from operating the LHC with beam is
crucial for refining magnet parameters and making sure
there are no “unknown unknowns”.
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