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Main Linac Quadrupoles

Th. Zickler

CERN

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Outlook

Introduction Drive Beam Quadrupoles (DBQ)

– Requirements and constraints

– The ‘two-current’ proposal

– Proposed quadrupole layout

– Magnetic field calculations and characteristics

Main Beam Quadrupoles (MBQ)– Requirements and constraints

– Proposed quadrupole layout

– Magnetic field calculations and characteristics

– Open issues

Conclusions and future work

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Introduction

Drive Beam

– 24 Drive Beam Decelerating Sectors (DES) per CLIC Linac

– 856 quadrupoles (428 focusing and 428 defocusing) per DES

– Linear beam energy decrease from 2.38 GeV to 0.24 GeV

– 41 100 quadrupoles needed per Linac

Main Beam

– 2001 Main Beam quadrupoles per CLIC Linac

– Beam energy increase requires variation of integrated gradient in the range between 15 Tm/m and 370 Tm/m

– Baseline: 4 magnet types of different length

– Alternative: several magnets of one type connected in series

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Drive Beam Quadrupoles DBQ

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DBQ Requirements and Constraints

Aperture and field requirements

– Nominal beam energy: 2.5 GeV

– Integrated gradient / beam energy: 5.7 T/GeV

– Integrated gradient: 14.3 Tm/m

– Aperture radius: 13 mm

– Total length (incl. BPM): < 344 mm

Keep heat dissipation into tunnel as low as possible

– Indirect water cooling

No redundancy possible

– High reliability and very robust design (low MTBF)

Large number of magnets (> 40 000!)

– Automated production (50/day in 3 years)

– To be respected already in the preliminary design

– Cost optimization (also for cables and power converters)

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‘Two-Current’ Proposal

‘Two-current’ proposal by H. Braun:

– Splitting the coils in two sub-coils (red & blue)

– Connect all sub-coils of the same type in series (string)

– Power the strings with different current (Ired & Iblue)

– Linear gradient decrease along the string

first quadrupole

mid sector quadrupole

last quadrupole

second quadrupole

second to last quadrupole

Picture by courtesy of H. Braun

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‘Two-Current’ Proposal

Advantages:

– Reduced number of power converters (minimum 4)

– Reduced cable length

Disadvantages:

– Number of turns must be multiple integer of number of magnets per string

– Large number of coil types issue for mass production

– High voltage drop

– Longitudinal beam dynamics in case of PETS failure

– Non-linearity of magnetic field along the string due to iron saturation

Open questions:

– Coupled circuits (power converter design)

Optimum number of magnets per string has to be found

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Proposed DBQ Layout

Assumption: 16 quadrupoles per string

2.5 GeV nominal beam energy

Aperture radius: 13.0 mm

Integrated gradient: 14.3 Tm/m

Nominal gradient: 67.1 T/m

Nominal current: 35.3 A

Nom. power consumption: ~ 400 W

Iron length: 200 mm

Magnetic length: 213 mm

Total length: 270 mm

Magnet width: 390 mm

Magnet total mass: 180 kg

Space available for BPM: 109 (74) mm

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DBQ Magnetic Field Calculations

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DBQ Magnetic Field Quality

Gradient homogeneity along the x-axis

0.0E+00

5.0E-05

1.0E-04

1.5E-04

2.0E-04

2.5E-04

3.0E-04

3.5E-04

4.0E-04

4.5E-04

5.0E-04

-12.5 -7.5 -2.5 2.5 7.5 12.5

x [mm]

dB

y/d

x w

rt G

0

2.50 GeV 2.42 GeV 2.31 GeV 2.08 GeV 1.50 geV 0.70 GeV

0.24 GeV GFR

Gradient homogeneity along the GFR boundary

-4.0E-04

-3.0E-04

-2.0E-04

-1.0E-04

0.0E+00

1.0E-04

2.0E-04

3.0E-04

4.0E-04

5.0E-04

0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0

angle [degree]

d|B

|/d

r w

rt G

0

2.50 GeV 2.42 GeV 2.31 GeV 2.08 GeV 1.50 geV 0.70 GeV 0.24 GeV

Gradient homogeneity:

Better than 5 * 10-4 inside good-field-region (GFR)

GFR radius: 11 mm

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DBQ Magnetic Field Quality

Magnetic Field Quality

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DBQ Excitation Curve

0

10

20

30

40

50

60

70

80

90

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Beam energy [GeV]

Gra

die

nt

[T/m

]

0.0%

1.0%

2.0%

3.0%

4.0%

5.0%

6.0%

7.0%

Sat

ura

tio

n [

%]

Theor. gradient Calc. gradient Series4 Saturation

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TBL Quadrupole

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Main Beam Quadrupoles MBQ

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MBQ Requirements and Constraints

Aperture and field requirements

– Magnetic length: between 350 and 1850 mm

– Field gradient: 200 T/m

– Aperture radius: 4 mm

Indirect water cooling

– Max. current density 3 A/mm2

Integrated pulsed (20 ms) H/V steering coils (2 mT)

Large number (4000)

– High reliability, very robust design, low MTBF

Small aperture, long structure

– High mechanical precision

– Tight manufacturing and assembly tolerances

– Good mechanical stability

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MBQ Design Parameters

Aperture radius: 4.00 mm

Integrated gradient: 70 (170, 270, 370 ) Tm/m

Nominal gradient: 200 T/m

Iron length: 346 (846, 1346, 1846) mm

Magnetic length: 350 (850, 1350, 1850) mm

Magnet width: < 200 mm

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MBQ Magnetic Field Calculations

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MBQ Gradient Homogeneity

Gradient homogeneity along the GFR boundary

-4.0E-04

-3.0E-04

-2.0E-04

-1.0E-04

0.0E+00

1.0E-04

2.0E-04

3.0E-04

4.0E-04

0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0

angle [degree]

d|B

|/d

r w

rt G

0 [%

]

Pure quadrupole Pure dipole

Gradient homogeneity:

Better than 4 * 10-4 inside good-field-region (GFR)

GFR radius: 2.5 mm

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MBQ Corrector Field Homogeneity

Gradient resp. dipole field homogeneity along the x-axis

0.0E+00

5.0E-05

1.0E-04

1.5E-04

2.0E-04

2.5E-04

3.0E-04

3.5E-04

4.0E-04

4.5E-04

5.0E-04

-3.0 -2.0 -1.0 0.0 1.0 2.0 3.0

x [mm]

dB

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x w

rt G

0

0.00E+00

5.00E-02

1.00E-01

1.50E-01

2.00E-01

2.50E-01

3.00E-01

3.50E-01

4.00E-01

4.50E-01

5.00E-01

By

wrt

By(

0)

Pure quadrupole GFR Pure dipole

Dipole field homogeneity:

Better than 4 * 10-1 inside good-field-region (GFR)

GFR on x-axis: ± 2.5 mm

Strong sextupolar component (b3)

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Open Issues

Detailed cooling circuit study

– Long term reliability

– Heat dissipation into tunnel

– Cooling efficiency

– New insulation materials

Mechanical and thermal stability

– Thermal expansion

– Cooling flow induced vibrations

Manufacturing and assembly tolerances

– Small aperture

– Long and slim structure

– Large series prodution

– New technologies required

Magnetic measurements, vacuum chamber integration, corrector optimization

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Conclusions and Future Work

A preliminary design for the CLIC DB and MB quadrupoles has been presented

A classical and robust layout has been chosen to maximize reliability and machine availability

The proposed designs fullfill the basic requirements and constraints, in particular the required dimensional limitations

DB Quadrupoles:

– The ‘two-current' proposal (DB) seems to be feasible and a good alternative to individually powered quadrupoles

– Number of magnet per string has to be optimized in view of the longitudinal beam dynamics constraints

– Protoypes for TBL and study their performance

MB Quadrupoles:

– Future studies and work addressing open issues

– Prototype needed to verify design and to study stability of assembly