Magnetic field simulation for the 10D45 magnet
N.A.Morozov
Dubna, June 2005
The magnetic field simulation for the 10D45 magnet was provided by the 3D TOSCA code [1].
The magnet dimensions were taken from the SLAC drawings, the pole gap was increased by 2
mm (66 mm for the main part and 60 mm for the edge shim). The magnet excitation current
provided the 0.1 T pole center magnetic. Due to the magnet symmetry the computer model has
been used 1/8 part of the iron. The views of the model are in Fig.1-3.
Fig.1. Overall view of the TOSCA model of the 10D45 magnet
Fig.2. TOSCA model with 1/8 part of the iron yoke
The mesh size in the three parts of the pole (part 1, 2 and edge shim, Fig.3) was varied (Tab.1)
and it influence on the simulated magnetic field was studying. The case meshing 4 was the limit
for the TOSCA simulation, it takes about one million elements. The normalized magnetic field
for the middle transverse cross-section of the magnet is in Fig.4-5 and the transverse dependence
of the longitudinal magnetic field integral is in Fig.6. The normalized distributions for the
longitudinal magnetic field integral are shown in Fig.7. The magnet effective length is 1.075 of
the pole length.
Fig.3. Meshing of the 1/8 part of the iron yoke
Table 1. Mesh size (cm) in the different pole parts
Number of curve
1
2
3
4
Part 1
2
2
1
0.7
Part 2
0.5
0.3
0.3
0.3
Edge shim
0.3
0.2
0.2
0.2
mesh 1
mesh 2
mesh 3
mesh 4
1,020
1,015
B/B0
1,010
1,005
1,000
0,995
0,990
0
1
2
3
4
5
6
7
8
9
10
11
12
X(cm)
Fig.4. Normalized magnetic field in the middle cross-section of the magnet (mesh number is
from Tab.1).
mesh 1
mesh 2
mesh 3
mesh 4
1,00060
1,00055
1,00050
1,00045
1,00040
1,00035
1,00030
B/B0
1,00025
1,00020
1,00015
1,00010
1,00005
1,00000
0,99995
0,99990
0,99985
0,99980
0
1
2
3
4
5
X(cm)
Fig.5. Normalized magnetic field in the middle cross-section of the magnet (mesh number is
from Tab.1).
mesh 1
mesh 2
mesh 3
mesh 4
1,00060
1,00055
1,00050
Int(B*dz)/Int 0(B*dz)
1,00045
1,00040
1,00035
1,00030
1,00025
1,00020
1,00015
1,00010
1,00005
1,00000
0,99995
0,99990
0,99985
0,99980
0
1
2
3
4
5
6
X(cm)
Fig.6. Normalized magnetic field longitudinal integral in the transverse direction of the magnet
gap (mesh number is from Tab.1).
The typical magnetic field uniformity requirement for the NMR sensor (METROLAB) for the
field 0.1 T is less 600ppm/cm. This means magnetic field gradient less 0.6 G/cm. Fig.7 presents
the magnetic field gradient in the magnet middle cross-section for the pole gap median plane and
for y=2.5 cm. The red box marks the 0.6 G/cm limit. The field gradient in the vertical direction is
presented in Fig.8.
y=0
y=2.5 cm
2,0
1,8
1,6
1,4
1,2
dB/dx (G/cm)
1,0
0,8
0,6
0,4
0,2
0,0
-0,2
-0,4
-0,6
-0,8
-1,0
0
1
2
3
4
5
6
7
8
X(cm)
Fig.7. Magnetic field gradient in the middle cross-section of the magnet (y=0, 2.5 cm).
x=3 cm
x=6 cm
1,0
0,8
0,6
dB/dy (G/cm)
0,4
0,2
0,0
-0,2
-0,4
-0,6
-0,8
-1,0
0,0
0,5
1,0
1,5
2,0
2,5
3,0
Y(cm)
Fig.8. Magnetic field gradient in the vertical direction in the middle cross-section of the magnet
(x=3 and 6 cm).
The possible region (for the sensor center) of the NMR probe positioning for the magnet pole
gap transverse cross-section is marked in Fig.9 by green line.
10
9
8
7
pole
Y(cm)
6
5
4
3
region of
NMR probe
location
2
vacuum 1
chamber 0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
X(cm)
Fig.9. Region for NMR probe positioning (middle transverse cross-section)
X=3 cm
X=6 cm
1,0
0,8
0,6
dB/dz (G/cm)
0,4
0,2
0,0
-0,2
-0,4
-0,6
-0,8
-1,0
0
5
10
15
20
25
30
35
40
45
50
Z(cm)
Fig.10. Magnetic field gradient in longitudinal direction in the pole gap median plane (x=3 and
6 cm).
The field gradient in the longitudinal direction is presented in Fig.10. This gives the possible
region in the longitudinal direction of the NMR probe installation ±47 cm.
Conclusions
1. The computer model for the 10D45 magnet was realized by TOSCA code.
2. The magnetic field map was simulated. The comparing of this field map with the future
experimental results will give the information about the accuracy of the TOSCA
simulation of the dipole magnets.
3. The region for possible NMR probe placement was determined. It is (outside vacuum
chamber) X*Y*Z= (2.5-5.5)*±2.7*±47 cm.
References
[1] OPERA 2D and 3D, Vector Fields, UK, www.vectorfields.com