R. Ostojic CERN, AT Department

R. Ostojic

CERN, AT Department

R. Ostojic, LTC, 10 May 2006 2

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


LHC Magnet Classes

1. MB – class (MB, MQ, MQM)(8.5 T, Nb-Ti cable at 1.9 K; -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; -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)


Upgrade of the Matching Sections and Separation Dipoles

• The present matching quadrupoles are state-of-the-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.


The LHC low- triplet

MQXA MQXB MQXAMQXB

6.372.985

5.5 5.52.715

6.37

MCBXAMCBXH/V

b3b6

MCBXMCBXH/V

MQSX

1.0

TASB

MCBXMCBXH/V

Q3 Q2 Q1

MCSOXa3a4b4

DFBX


LHC low- triplets


Limits of the present LHC triplets

• Aperture70 mm coil63 mm beam tube 60 mm beam screen * = 0.55 m

• Gradient– 215 T/m operational 205 T/m

• Field quality– Excellent, no need for correctors down to * ~ 0.6 m

• Peak power density– 12 mW/cm3 L = 3 1034

• Total cooling power– 420 W at 1.9 K L = 3 1034


Aperture issue

• The coil aperture was the most revisited magnet parameter of the low-quadrupoles.– Aperture of 70 mm defined in the “Yellow Book” (1995,

nominal *= 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 * 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.


Enabling operation of the LHCwith 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.


Quadrupole-first layouts

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 * to complement other ways of increasing luminosity.

0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

0.00 0.10 0.20 0.30 0.40 0.50 0.60

*[m]

Dm

in [

mm

]

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

Fp

Q2/Q3

Q1

L < 10 m

L ~ Fp/*

Optimize the aperture and length of the quadrupoles according to their position in the triplet.

Q3 Q2B Q2A Q1

LHC Low- Triplet

1.0

Symmetric Triplet

2.0 2.0 2.0 L* = 23 m

Triplet with "long" Q3

2.0 2.0 2.0

Triplet with "short" Q1

2.0 2.0 2.0

10.0 8.0 8.08.0

8.0 8.0 8.0 4.0

8.0 8.0 8.0 8.0

6.3 5.5 6.32.73.0 5.5


Large aperture quadrupoles using existing LHC cables

Cable parameters MQY MQ MB Width [mm] 8.3 15.10 15.10 Mid-thickness [mm] 0.84/

1.28 1.48 1.90

Critical current, Ic [A] @ 9 T, 1.9K

5070/ 9110

12960 13750

dIc/dB [A/T] 1350/ 2550

3650 4800


Large aperture quadrupoles

100

120

140

160

180

200

220

240

50 60 70 80 90 100 110 120

Coil aperture [mm]

Gra

die

nt

[T/m

]

MQY cable

MB/MQ cable

MQ cable

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.

To get a GL similar to the present triplet, quadrupole lengths need to be increased by 20-30%.

The Nb-Ti technology proven for quadrupoles up to 12 m long.


• Technology and manufacturing issues are well mastered.

• Relatively easy extension of main magnet parameters (aperture and length) without extensive R&D.

• 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

LHC dipoles

R&D directions for Nb-Ti quads

FRESCA, 10 T, 88 mmD. Leroy et al., 1999


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- 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.


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”.

Documents

R. Ostojic CERN, AT Department