Magnet designs for the ESRF-SR2 G. Le Bec, J. Chavanne Compact and Low Consumption Magnet Designs...

Magnet designs for the ESRF-SR2 G. Le Bec, J. Chavanne

Compact and Low Consumption Magnet Designs for Future Linear and Circular Colliders

Geneva, November 26-28, 2014

G. Le Bec, Magnet designs for the ESRF-SR2, Compact and Low Consumption Magnets Workshop, Geneva, November 2014

OUTLINE

•Introduction: the ESRF-SR2

•Generalities about compact and efficient magnets

• Reducing the aperture• Minimum aperture magnets• Permanent magnets?

•Compactness and power efficiency for the ESRF-SR2

• PM dipole with longitudinal gradient• EM high gradient quadrupole• EM combined dipole-quadrupole

•Conclusion


OUTLINE

Introduction


INTRODUCTION

ESRF Upgrade Phase II

•Reduced horizontal emittance: 4000 147 pm.rad

•Same insertion devices source points

•New storage ring

•Increased number of magnets: 7-bend achromat

•Reduced longitudinal space

•Reduced power consumption


INTRODUCTION

ESRF Upgrade Phase II magnets: one cell

32 cells~1000 magnets (without correctors)


INTRODUCTION

Design challenges

•High gradient quads (up to 85 T/m)

•High gradient combined magnets

•Dipoles with longitudinal gradient

•Longitudinal compactness required

•Integration of vacuum chambers and beam ports


OUTLINE

Compact and efficient magnets

Reducing the aperture

Compactness and power consumption


SMALL APERTURE MAGNETS

Power consumption and bore radius

If the magnets are not saturated:• Dipole power consumption g 2

• Quadrupole power consumption R 4

• Sextupoles power consumption R 6

Low power and compactness Reduced magnet apertures

Main limitations• Integration: vacuum chambers, beam ports, etc.• Sensitivity to mechanical errors

Compact magnetMinimum aperture reachedCompactness refers to the external dimensions


SMALL APERTURE MAGNETS

Assembly errors

Errors at the GFR boundary

,0

0

x yNB

Multipolar error at the bore radius

Mechanical error

Bore radius

1

00

N

N NB B

(GFR radius = r)

Error @ r =R/4 r0=R r0=R/2

Quadrupolar e2 4e2

Sextupolar e3 8e3

Octupolar e4 16e4

Compact & low consumption Tigh mechanical tolerances


COMPACT MAGNETS

Compactness… in which direction?

L

H 00

0 0

BLH H

ML BL

At constant integrated field(in first approximation: no saturation, no flux leakage, etc.)

Transverse size variation is much faster if the magnet is saturated

Longitudinal compactness

Transverse compactness

Compromise

(also true for EM magnets)


TRANSVERSE COMPACTNESS VS. POWER CONSUMPTIONW

YO

KE

WPOLE

WCOIL

H COIL

Fixed parametersNIWPOLE & WYOKE

WCOIL (magnet length is fixed)

1mass and powerCOIL COILH H

Compact Low power

High J Low J


LENGTH, TRANSVERSE DIMENSIONS AND POWER CONSUMPTION

•Fixed integrated gradient: 50 T•Variable length•Variable NI and outer radius•Bore radius: 12.5 mm•Constant current density: 5 A/mm2


OUTLINE

Compact and efficient magnets

Normal conducting vs. permanent magnets


mm m

PM micro-motor PM DC motor Asynchronous motor Power plant generator

Short period undulator Lattice magnets


SCALE FACTOR

gg

0

23PMB M

gg

g

02JB g JCharacteristic aperture

(g0 is obviously design dependent, this is a very first approximation)

0 if 3PM JB B g M J g 2

0 06 cm if 1.1 T and 5 A/mmg M J

Gap < a few centimeters PM dipoles are more compact than EM dipoles


PERMANENT MAGNETS

PM systems advantages

•More compact for small aperture magnets

•No coil head: iron length = magnet length

•No power consumption

But…

•Risk of radiation damage? No if Sm2Co17 material is used

•Temperature variation? Can be compensated passively

•Mechanical complexity, tolerance stack-up

•Limited tunability


PERMANENT MAGNETS

Mechanical complexity

Yoke+pole: rigid assembly Yoke+pole: different partsNeed spacersTolerance stack-upNot compatible with laminated designs


PERMANENT MAGNETS TUNABILITY

Trimming coils

•Permanent magnets = air gaps for coils

•Field in the gap:

•Optimization of PM volume:

•Coil field at optimum PM dimensions:

x2 Amp turns needed!

wY

wP

Coils

Yoke

h

0P

Y

NI MhB

wg h

w

0 0

2 2 and P

Y

Bw Bgw h

M M

0 2NI

NIB

g

g


Rx1

x2

w h


Trimming coils

•Similar result for quad

(Tosin, NIMA 2012)

•Optimization of PM volume:

•Coil induced gradient at optimum PM dimensions:

22

1 2 20

1 2 1

1ln

2 2x h x xR

G NI Mhw x x x

221 2 2

0 0 2 1 1

2 and ln 1

G x x xR Gh w

M M x x x

0 02

12

NIG G

R where G0 is the gradient obtained without PM

Coil efficiency reduced by a factor 2



10% of these Amp turns 5% tuning range



Moving parts?

•Gap motions on insertion devices: 100% field tunability

But…

•Field quality and magnet centre may depends on the position of the moving parts

•Possible reliability issues (may be improved using stepper motors)

•Accuracy of mechanical assembly is not easy to reach, even without motion

•Complex mechanical system high cost


OUTLINE

Compactness and power efficiency for the ESRF-SR2

Dipoles with longitudinal gradient (DL)


ESRF DIPOLE WITH LONGITUDINAL GRADIENT (DL)

• Field ranging from 0.17 T up to 0.55 T or 0.67 T • Total length: 1.85 m• Gap: 25 mm• Magnet mass: 400 kg

• PM Mass: 25 kg/Sm2Co17 and 25 kg Strontium ferrite per dipole

(Design and measurements of the DL magnet: J. Chavanne)



DL moduleNumber of PM blocks is module dependentTemperature compensation is not shown here

Complete DL magnet on its support

PM blocksIron pole and yoke Aluminium spacers



Homogeneity of central field

• Quality dominated by pole faces parallelism

• May need refinement of mechanical tolerances

• Easy and fast mechanical correction (shimming)

• Tolerance: DB/B < 10-3 @13 mm

Module 2 without shims (Hall probe meas.)Module 1 without shims (Hall probe meas.)


Integrated field

• Preliminary study on straight integrals

• Stretched wire method

• Two modules with 0.62 T and 0.41 T

• Longitudinal gap 5 mm between poles

• End effect (sextupole) shims not installed

• Will improve with additional modules




Longitudinal field

• Flat top field at longitudinal gap gs = 5 mm

•The optimum gs may change between the modules of the full magnet (field step dependence)

gs


OUTLINE


High gradient quadrupoles


HIGH GRADIENT QUADRUPOLES

ESRF-SR2

•85 T/m nominal gradient

•12.8 mm bore radius, 0.5 m long

•Normal conducting

•Longitudinal compactness optimized

•90 A, 69 turns

•Low power consumption (1.6 kW)

•Total mass ~1 ton

•Fast pole shaping algorithm developed

•Prototype being manufactured

600

mm

600 mm500 mm



Magnetization m0M [T] of a moderate gradient (a) and high gradient (b) quadrupoles at nominal current.

Excitation curves

1.5 T

(a) (b)

1 T

0.5 T

2 T

1.5 T

1 T

0.5 T

Excitation curves and saturation

• Moderate gradient quads optimized at a linear working point

• High gradient quads optimized at a saturated working point



Energy savings and compactness

Low power quadrupole

Compact quadrupole

Current density 3.25 5 A/mm2

Power 1.65 2.50 kW

Height 605 535 mm

Mass 860 740 kg


OUTLINE


Combined dipole-quadrupoles (DQ)


COMBINED DIPOLE-QUADRUPOLES

Bz

x

Bz

x

Tapered dipoleHigh field, low gradient

Offset quadrupoleHigh field, high gradient



Bz

x

Offset quadrupoleHigh field, high gradient

DQ specificationsGFR radius 7 mmField 0.54 TGradient 34 T/mm



GFR

x

Bz

Region of interest

Additional power consumption, weight, etc.

Field of an offset quad



GFR

x

Bz

A new target for DQ field

Pro• Lower power consumption and weight• Easy access on one side (vacuum chamber, magnetic measurements)

Cons

• Design and construction are more complex



Single-sided dipole-quadrupole

• 2 poles + 2 “half” poles• 0.54 T field, 34 T/m gradient• Iron length: 1.1 m• Magnet mass ~ 1 ton• Power consumption: 1.5 kW

Main coil

Auxiliary coil(in series with main coil)

Trimming coil

Auxiliary poleMain pole



Magnetic design

GFR

Vertical field vs. position.Field is almost zero on one side.

DG/G expressed in 10-3. Specification: DG/G < 10-2.GFR: 7x5 mmField integration along an arc.



Energy savings and compactness

Single-side DQ vs. offset quadrupole

Single-sided DQ

Compact offset quadrupole

Low power offset quadrupole

Current density 3.25 5 3.25 A/mm2

Power 1.5 3.9 2.5 kW

Width x height 330 x 470 415 x 415 465 x 465 mm

Mass 900 940 1050 kg

CONCLUSIONS

Compactness and efficiency

•Small aperture magnets (tight tolerances)

•Trade off between compactness and power consumption

•Trade off between length and transverse dimensions

PM magnets?

•Good choice if reduced a tuning range is accepted (coil efficiency x1/2 for dipole and quadrupoles)

•Tight tolerances to be anticipated (more parts, tolerances stack-up)

ESRF-SR2 magnets: lower power and compact designs

•Dipole with longitudinal gradient: PM, compact, no power consumption

•Quadrupoles: low power, not so compact

•Combined dipole-quadrupoles: low power, single-sided design


MANY THANKS FOR YOUR ATTENTION


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Magnet designs for the ESRF-SR2 G. Le Bec, J. Chavanne Compact and Low Consumption Magnet Designs...

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