Analysis and Reduce on Magnetic Moment of AMS01 Magnet

1
Analysis and Reduce on Magnetic Moment of AMS01
Magnet
Song Tao, Qiuliang Wang, Housheng Wang , Zhen Wang

• Institute of Electrical Engineering, CAS
• 2006.4.24

2
Contents

• Background
• Magnetic Moment of AMS-01 Magnet
• Measurement of the Magnetic Moment of 1/3 AMS
  Model Magnet
• Methods to Reduce the Magnetic Moment of AMS-01
  Magnet
• Conclusion

3
Background (1)

• Magnetic Moment of Current Loop

4
Background (2)

• Magnetic Moment of Permanent Magnet

The permanent magnet can be equivalent to a set
of current loops.
5
Background (3)
6
Background (4)
AMS magnet will operate in the space. NASA
requires that the torque of the magnet must be
less than 2.7 Nm in the Earths magnetic field,
which corresponds to a limit on the magnetic
moment of 5.4104Am2 in the B field of 0.5Gs on
orbit.
7
Numerical and theoretical analysis on Magnetic
moment For AMS01
8
Structure of AMS-01 magnet (1)

• The AMS-01 magnet is made of 64 magnetic blocks.
  
• The arrangement of the blocks is symmetric about
  Z0 and Y0 section, and it is antisymmetric
  about X0 section.

Cross-section of AMS-01 magnet at Z0
9
Three dimensional structure of AMS01
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Magnetic Moment of AMS-01 magnet (2)

• The volumes of magnetic blocks are equal to each
  other.
• According to the symmetry, the z-component and
  y-component of the magnetic moment are zero.
• Px ??

11
Magnetic Moment of AMS-01 magnet (3)

• Assume the relative permeability of Nd-Fe-B
• µr1
• that means magnetization of each magnetic block
  is a constant.
• So the magnitudes of the magnetic moment of each
  block are the same.

12
Magnetic Moment of AMS-01 magnet (4)

• According to the directions of magnetization,
• So the magnetic moment is zero.

13
Magnetic Moment of AMS-01 magnet (5)

• In fact µr1.05
• magnetization is changed with the working point
  of the magnet.

14
Average working point of each magnetic blocks
15
P
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Magnetic Moment of AMS-01 magnet (6)

• Using above method, we have estimated the
  magnetic moment of AMS-01 magnet.
• P 4.1103Am2ltlt 5.4104Am2
• It is considered that three kinds of magnetic
  material are used in fact.
• This estimation is based on theoretic analysis
  and the calculation of working point.
• --- Numerical calculation will be introduced

17
Analysis Software comparison

• Using ANSYS and Ansoft software
• Ansoft with good accuracy and convergence with
  adaptive mesh

18
Ansoft Calculation Model

• Half of the model to be studied due to symmetry
  of the AMS01 magnet.
• Balloon(infinite) boundaries applied, except the
  symmetry plane.
• Gaps between the adjacent bars are neglected.

19
Test the Model Magnetic field distribution for
AMS01 based on Ansoft Model calculation
Center magnetic field Calculation B0
1380Gauss
Measurement B0 1360 Gauss
Error1.45
20
Calculation methods for magnetic moment
??????
P
Where P is the magnets dipole moment , B is the
background magnetic field and T is the torque
that the magnet be subjected. A given uniform
background magnetic field which is normal to the
main magnetic flux of AMS01.
P
21
Calculation flowchart for magnetic moment
Ansoft Numerical Calculation
P Magnetic moment of the AMS Magnet
B Uniform Background Field
T The Torque of the AMS Subjected
22
Calculation of Magnetic Moment
According to the formula, when the B
perpendicular to P
the magnetic moment of the magnets is about
P 7313 Am2 Direction
is from bottom to top is reversed to the B
Element numbers 230000
23
Calculation and measurement of magnetic
moment For 1/3 model AMS01
24
Measurement of the Magnetic Moment of 1/3 AMS
Model Magnet (1)

• To verify the calculation, the magnetic moment
  of an 1/3 AMS model magnet was measured.

25
Measurement of the Magnetic Moment of 1/3 AMS
Model Magnet (2)

• The model magnet is suspend by a permanent
  magnetic bearing.
• Applied magnetic field B is 2 mT produced by
  four coils.
• Measured the torque T which make the magnet turn
  90º.
• Calculate the magnetic moment PT/B.

26
Measurement of the Magnetic Moment of 1/3 AMS
Model Magnet (3)

• The measured result is
• P120Am2
• Its direction is opposited to the direction
  of the main magnetic field of the magnet.
• Using above analysis method, we have estimated
  the magnetic moment of model magnet
• P 97Am2 (Error rate related measured result is
  17)
• The calculated result by Ansoft is
• P 130Am2 (Error rate related measured result is
  8)

27
Measurement of the Magnetic Moment of 1/3 AMS
Model Magnet (4)

• Above measured work was done about 10 years ago.
  
• In order to verify it, we measured the magnetic
  moment again one month ago.

28
Measurement of the Magnetic Moment of 1/3 AMS
Model Magnet (5)

• The model magnet is suspend by line.
• Applied magnetic field B is 1 mT produced by a
  group of Helmholtz coils.
• Measured the torque T which make the magnet turn
  90º.
• Calculate the magnetic moment PT/B.
• This method is easy. So it can be used to
  measure the AMS-01 magnet.

29
Measurement of the Magnetic Moment of 1/3 AMS
Model Magnet (6)

• The result is P22015 Am2
• Its direction is almost opposited to the
  direction of the main magnetic field of the
  magnet, but they lie at an angle of 5º .

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Measurement of the Magnetic Moment of 1/3 AMS
Model Magnet (7)

• The measured magnetic moment is increased , the
  possible reasons are
• Effects of temperature, which could make the
  magnetic blocks at low working point demagnetize.
  
• There is difference between two measured methods.

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Reduce magnetic moment For 1/3 model AMS01
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Methods to Reduce the Magnetic Moment of AMS-01
Magnet (1)

• There are two methods can be chosen to reduce
  the magnetic moment
• Adding irons.
• Adding magnetic pieces
• Using the 1/3 model magnet, we have taken
  experiments on reducing its magnetic moment.

33
Methods to Reduce the Magnetic Moment of AMS-01
Magnet (2)
I

• Adding irons (1)
• A Adding irons around the magnet.
• B Adding irons at Area II and Area IV
• C Adding irons at Area I and Area III
• - Measured its magnetic moment

IV
II
III
34
Methods to Reduce the Magnetic Moment of AMS-01
Magnet (3)

• Adding irons (2)
• We found the magnetic moments are not be reduced
  by method A and B.
• Method C can reduce the magnetic moment of model
  magnet
• The magnetic moment was reduced 10 by 1.3 kg
  iron pieces for model magnet.
• We estimated that the magnetic moment of AMS-01
  magnet could be reduced 10 by 40kg irons.

35
Methods to Reduce the Magnetic Moment of AMS-01
Magnet (4)

• Adding magnetic pieces (1)
• According to the analysis of magnetic moment of
  AMS magnet, it is a useful method to reduce the
  magnetic moment by permanent magnetic pieces.
• The magnetic pieces are fixed on the magnet, and
  their magnetization directions are same with
  that of main magnetic fields.
• The volume of the magnetic material is P/M.
• M is the magnetization of magnetic pieces
• P is the value that will be reduced.

36
Methods to Reduce the Magnetic Moment of AMS-01
Magnet (5)

• Adding magnetic pieces (2)
• For model magnet, the magnetic moment (220Am2) is
  the same as that of 232cm3 (i.e. 5 cm5cm9.28cm)
  Nd-Fe-B which maximum energy product is 35 MGOe
  (N35).
• We fixed the magnetic pieces on the Area I and
  Area III to measure the magnetic moment.

I
III
37
Methods to Reduce the Magnetic Moment of AMS-01
Magnet (6)

• Adding magnetic pieces (3)
• Fixed two magnetic pieces (N35) on the two sides
• The size of each piece is 5 cm5cm 2.5cm
• We measured the magnetic moment is 110Am2.

38
Methods to Reduce the Magnetic Moment of AMS-01
Magnet (7)

• Adding magnetic pieces (4)
• Fixed two magnetic pieces (N35) on the two sides
• The size of each piece is 5 cm5cm 4.5cm
• We measured the magnetic moment is closed to zero.

39
Methods to Reduce the Magnetic Moment of AMS-01
Magnet (8)

• According to the experiments, a useful method to
  reduce the magnetic moment of AMS-01 magnet is to
  fix a permanent magnetic pieces on magnet.
• 7 kg Nd-Fe-B (50MGOe) can reduce 1000Am2
  magnetic moment.
• It is necessary to fix the magnetic material on
  the magnet rigidly.
• It is noticed the effects of flux leakage of
  magnetic peaces.

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• The compensation effect is independent of the
  location where PM bulks are placed but only
  relate to their weight, and every 7kg PM pieces
  can reduce magnetic moment about 1000Am2.

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Further test and decide the position of Permanent
magnet pieces

• Numerical calculation of optimal distance between
  pieces and AMS01.
• Experimental test of magnetic moment and field
  distribution after install the PM pieces in
  AMS01.
• .

43
Methods to Reduce the Magnetic Moment of AMS-01
Magnet (10)

• What places can be used to fixed the magnetic
  pieces?
• --- Depend on the structure and the requirements
  on the flux leakage.

44
Conclusion

• The AMS-01 magnet has a magnetic moment which
  direction is opposited with the main magnetic
  fields.
• The calculated magnetic moment of AMS-01 magnet
  is 7300Am2 by Ansoft.
• It is most important to measure the magnetic
  moment of AMS-01 magnet, because the moment may
  be increased.
• A useful method to reduce the magnetic moment of
  AMS-01 magnet is to fix a permanent magnetic
  pieces on the magnet.
• 7kg Nd-Fe-B (50MGOe) can reduce 1000Am2 magnetic
  moment.

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• Thank you!