9/19/2005 1

Permanent Magnet Diploes and Quadrupolesfor FFAGs

Jinfang Liu and Peter DentElectron Energy Corporation

924 Links Ave, Landisville PA 17538

Phone: 717-898-2294 Fax: 717-898-0660

9/19/2005 2

(1) Permanent Magnet Overview

(2) Some Design Considerations

(3) Radiation Effect

(4) Permanent Magnet Dipoles

(5) Permanent Magnet Mangles

(6) Permanent Magnet Quadrupoles

(7) Summary

Outline

9/19/2005 3

Types of Commercial magnets

Nd-Fe-B MagnetsNd-Fe-B Magnets

Sm-Co MagnetSm-Co Magnet

Strontium FerriteStrontium Ferrite

Barium FerriteBarium Ferrite

Permanent Magnets

Permanent Magnets

Bonded Magnets(Rubber/Plastic)

Bonded Magnets(Rubber/Plastic)

Metal Magnets

Metal Magnets

Ferrite MagnetsFerrite Magnets

RE MagnetsRE Magnets

Alnico MagnetsAlnico Magnets

Bonded Ferrite MagnetsBonded Ferrite Magnets

Bonded RE MagnetsBonded RE Magnets

SmCo 1:5SmCo 1:5

SmCo 2:17SmCo 2:17

Other MagnetsOther Magnets

Overview

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(BH)max versus Maximum Operating Temperature

Overview

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Some factors to consider:

(1) Magnetic performance(2) Corrosion resistance(3) Thermal stability(4) Radiation resistance(5) Magnetization direction(6) Manufacturability(7) Cost

Permanent Magnet Selection

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Typical magnetic properties, in terms of energy product, of selected commercial magnets:

Sintered Nd-Fe-B magnets: up to 50 MGOe

Sintered Sm-Co magnets: up to 32 MGOe

Isotropic bonded Nd-Fe-B magnets: up to 10 MGOe

Sintered ceramic magnets: up to 4 MGOe

Cast Alnico magnets: up to 9 MGOe

Permanent magnets --- properties comparison

9/19/2005 7

Maximum operating temperature of sintered magnets

Magnets Maximum Operating Temp.*

NdFeB with iHc =12 kOe 80°C

NdFeB with iHc =17 kOe 120°C

NdFeB with iHc =20 kOe 150°C

NdFeB with iHc =25 kOe 180°C

Conventional SmCo magnets 300°C

EEC24-T400 magnets (patented & available) 400°C

EEC20-T500 magnets (patented & available) 500°C

EEC16-T550 magnets (patented & available) 550°C

Rare Earth Magnets

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15

20

25

30

35

40

45

50

100 200 300 400 500 600

Maximum Operating Temp. (oC)

(BH

) max

(M

GO

e)

NdFeB

SmCo

(BH)max Versus Maximum Operating Temperature

Rare Earth Magnets --Properties vs. Temperature

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Long-term Thermal Stability of SmCo Magnets at 300°C in Air

0 4000 8000 12000 16000 20000 24000 28000-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

1 Year

Magnet Dimensions:1 cm OD x 1 cm THK

2 Years 3 Years

T550C-16MGOe w/coating T550C-16MGOe T500C-20MGOe T400C-24MGOe T330C-27MGOe T250C-31MGOe

Time at 300°C (Hours)

Mag

netic

Irre

vers

ible

Los

ses

(%)

-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

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High temperature magnets

DoD initiated the More Electric Aircraft program, which requires magnets with maximum operating temperature more than 400°C

Funded by the Department of Defense, a series of sintered SmCo 2:17 magnets were developed at EEC with maximum operating temperature as high as 550°C

These patented SmCo UHT magnets were introduced to the industry in 1999.

Rare Earth Magnets --- Materials Selection

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SmCo Rare Earth Magnets

PM Grades Br (kG) (kG)

(BH)max(MGOe)

Max. operating temp (oC)

EEC2:17-31 11.6 31 250

EEC2:17-27 10.8 27 300

EEC24-T400 10.2 24.5 400

EEC20-T500 9.3 21 500

EEC16-T550 8.6 17 550

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Nd-Fe-B sintered magnets

Key features:

Highest (BH)max available (up to 50 MGOe)

Less expensive than Sm-Co magnets

Corrosion resistance is not good

Special coating is required

Maximum operating temperature is very low compared to SmCo magnets

Rare Earth Magnets --- Materials Selection

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Nd-Fe-B Type Rare Earth Magnets

PM Grades Br (kG) (kG)

(BH)max(MGOe)

Max. operating temp (oC)

N50 14-14.5 48-51 70

N45 13.2-13.8 43-46 70

N45M 13.2-13.6 43-46 100

N42SH 12.8-13.2 40-43 120

N33UH 11.3-11.7 31-34 180

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Permeance Coefficient Pc

Also known as load line or operating point

It is related to the dimensions of the magnets and the associated magnetic circuit

In the magnetic circuit, a magnet will operate at a specific point on its extrinsic demagnetization curve:

Pc = Bd/HdBr

Bd

HdHcPc=Bd/Hd

Some Design Considerations

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Why straight-line demagnetization curves?

Application with load line #1: Both magnets are okay to use

Application with load line #2: Only magnet #1 is suitable

Bd1

Normal demagnetization curve for magnet #1

load line 2

Br

Hc 0

Knee

load line 1

Bd2

Hd1 Hd2

Br

Hc

Normal demagnetization curve for magnet #2

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The effects of radiation on permanent magnets was studied at EEC under a NASA STTR Contract

All Samples have a L/D ratio of 1.25

Permanent Magnets Studied: EEC T500 and T300 SmCo 2:17 magnets

Nd-Fe-B Magnets

Radiation Source: Ohio State University Research Reactor

Radiation Effect

OSU Reactor

Samples in quartz tubes

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Permanent Magnets and Radiation Effect

C.H. Chen, J. Talnagi, J.F. Liu, P. Vora, A. Higgins and S. Liu, IEEE Trans. Magn. 41(2005)3832

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-100

-80

-60

-40

-20

0

20

1.E+13 1.E+14 1.E+15 1.E+16 1.E+17 1.E+18 1.E+19 1.E+20

Neutron Fluence (neu/cm2)

Mag

netic

Flu

x Lo

ss (%

)

L/d = 8.9

L/d = 4.8

L/d = 4.4

L/d = 3.1

L/d = 2.0

L/d = 0.9

L/d = 0.4

1013 1014 1015 1016 1017 1018 1019 1020

Cost et al.[ 7]

Recorded T = 78°C, TL was likely ~ 160°C

(Hci >17kOe)

If TL ≥ Tc, the loss will be 100% for all the samples

E = 0.1 to 10 MeV

Nd-Fe-B

J.R. Cost et al, IEEE Trans. Mag.24 (3), 2016-2018 (1988).

Working Point and Radiation Effect

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Radiation Effect

The major radiation damage is caused by radiation-induced thermal spikes

The dominant factor for radiation tolerance is thermal stability, which is related to the following factors:

(1) Curie temperature of permanent magnets

(2) Working point of permanent magnet in the system

(3) Intrinsic coercivity

9/19/2005 20

Permanent Magnet Dipoles

Magnets

Magnets

Return Path

d Bg = –––––BmAm

k1Ag

Am =Magnet area perpendicular to the direction of magnetization;Bm =Flux density of the magnet corresponding to the operating pointof the demagnetization curve;Bg =Flux density desired in the air gap;Ag =Cross section area of the air gap perpendicular to the flux lines.

The Air Gap Flux Density Is A Lot Lower Than The Br Of The Permanent Magnets

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Permanent Magnet Dipoles

Halbach PM Dipole Structures:

Bg = Br ln(OD/ID)ODID

There is no upper limit for air gap flux density in Halbach dipole structures according to above equation. But in reality it would be limited by:

(1) The realistic size

(2) The demagnetization effect

9/19/2005 22Flux Density Map Vector Map

Halbach Dipole Example

9/19/2005 23Vector MapFlux Density Map

Halbach Dipole Structure

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0o Position

Magnetic Mangles

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45o Position

Magnetic Mangles

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90o Position

Magnetic Mangles

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135o Position

Magnetic Mangles

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Combination of magnetic mangles and Habachstructures can make the air gap flux density adjustable to some degree

9/19/2005 29

4 Tesla PM prototype Halbach cylinder was made in Japan.*

EEC has produced many Halbach structures for a variety of applications.

Sintered SmCo or high Hci NdFeB magnets are good choices

Halbach Dipole for FFAGs

*M. Kumada et al, PAC2001, 3221.

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A Example of Halbach PM Quadrupole

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Adjustable magnetic quadrupoles as reported by Fermi lab and SLAC*:

Diametrically magnetized SmCo 2:17 tuning rods

Tuning rods rotation changes the strength of field gradient

* J. T. Volk et al, PAC2001, p217

Adjustable Magnetic Quadrupoles

9/19/2005 32

SummaryPermanent magnet dipoles and quadrupoles can

have high air gap flux density if designed with Halbach principles.

Innovative designs can make the air gap flux density adjustable.

Permanent magnet selection might include trade-offs between cost and performance.

SmCo magnets are far superior to NdFeB magnets with respect to radiation resistance.

9/19/2005 33

Contact InformationJinfang Liu, Director of TechnologyPeter Dent, Director of Sales and MarketingMichael Walmer, President

Electron Energy Corporation924 Links Ave.Landisville, PA 17538(717) 898-2294 Phone(717) 898-0660 Faxeec@electronenergy.comwww.electronenergy.com