Simulation of An Octupole Scanning Magnet for Spot Scanning in Proton Therapy BOlei Jia, Lianhua Ouyang, and Zhentang Zhao Shanghai Institute of Applied Physics, C. A. S., Shanghai 201800, P. R. China Current proton therapy scanning systems always use two independent dipole magnets for spot scanning in proton therapy. However, the space occupied by these two dipole magnets located after the final gantry bending magnets is very large and increases the overall size of the gantry. In order to construct a compact nozzle and decrease the size of the gantry, we decide to design an octupole scanning magnet to replace these two separate dipole magnets. The octupole scanning magnet, which is completely different from traditional octupole magnet, can generate rotating dipole magnetic field with the change of the loaded sinusoidal current phases. In the paper, we have finished the static optimization of an octupole scanning magnet model, including the length and shape of the poles, the diameter of the gap and the shims on the pole edges, both in Opera 2D and 3D. The corresponding relationship between the size of the gap and the good field region was also studied. The effect of eddy currents on magnetic field stability was also simulated in Opera 3D. Design parameters Dynamic simulation Static simulation Abstract MT25-Wed-Af-Po3.04-02 To increase the critical photon energy, and to save space for accomodating more insertion devices, four normal bend magnet will be replaced by high field ones during the phase-II beamline project of the Shanghai Synchrotron Radiation Facility(SSRF). The design of these super bends has been finished, the first one has been manufactured and measured recently at SSRF. This water cooled electro-magnet has a total length of 1000 mm and a steering field of 2.29~Tesla. An air slot in the magnet pole was used to control the uniformity field integral distribution. The d The main parameters of the simulated magnet model Distance away from the iso-center 2.1 Integrated field Mechanical length 0.1679 35 Good field region Aperture 20 (radius) 104 Field homogeneity Pole tip width ±2.5×10 -3 26 3D simulation model with coils Conclusions • The integrated field reached 0.2175 which is larger than the required. • The radius of the good field region is approximately proportional to the aperture of the model. • The uniformity of the field integral was controlled below 2.5× 10 −3 within the good field region using the tangent shims. • The effect of the eddy currents on the stability of field can be negligible and the stability time is very short. 0 5 10 15 20 25 60 70 80 90 100 110 Radius of the good field region r (mm) Aperture of the model d (mm) 1.50E-03 2.00E-03 2.50E-03 The distribution of the magnetic field along z axis. The relationship between the aperture and the radius of the good field region in different field homogeneity. It indicates that the radius of different good field region is approximately proportional to the aperture of the model and the scale factor dependents on the required field homogeneity. -3.00E-03 -2.00E-03 -1.00E-03 0.00E+00 1.00E-03 -30 -20 -10 0 10 20 30 dB/B Radial distance -0.002 -0.0015 -0.001 -0.0005 0 0.0005 -30 -20 -10 0 10 20 30 Integrated field homogeneity Radial distance (mm) Field error at B= 4673 Integrated field error in the good field region （1）Principle The octupole scanning magnet can generate a rotating dipole field when each pair of opposing poles is given a regular sinusoid independently. All the currents are with a same amplitude. The current amplitude determines the field strength. The phases of the currents determines the deflection angle of the dipole field. The field can rotate with the change of the current phases and the deflection angle of the field is equal to the magnitude of the phase change. （2）Simulation of the field strength increasing （3）Simulation of the field rotation The distribution of the eddy currents at t = 1 ms. The deflection angle of the field varying with time. The distribution of the eddy currents at t = 1 ms. The field strength varying with time
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Simulation of An Octupole Scanning Magnet for Spot Scanning in Proton TherapyBOlei Jia, Lianhua Ouyang, and Zhentang ZhaoShanghai Institute of Applied Physics, C. A. S., Shanghai 201800, P. R. China
Current proton therapy scanning systems always use two independent
dipole magnets for spot scanning in proton therapy. However, the space
occupied by these two dipole magnets located after the final gantry
bending magnets is very large and increases the overall size of the
gantry. In order to construct a compact nozzle and decrease the size of
the gantry, we decide to design an octupole scanning magnet to replace
these two separate dipole magnets. The octupole scanning magnet, which
is completely different from traditional octupole magnet, can generate
rotating dipole magnetic field with the change of the loaded sinusoidal
current phases. In the paper, we have finished the static optimization of
an octupole scanning magnet model, including the length and shape of
the poles, the diameter of the gap and the shims on the pole edges, both
in Opera 2D and 3D. The corresponding relationship between the size of
the gap and the good field region was also studied. The effect of eddy
currents on magnetic field stability was also simulated in Opera 3D.
Design parameters
Dynamic simulationStatic simulationAbstract
MT25-Wed-Af-Po3.04-02To increase the critical photon energy, and to save space for accomodating more insertion devices, four normal bend magnet will be replaced by high field ones during the phase-II beamline project of the Shanghai Synchrotron Radiation Facility(SSRF). The design of these super bends has been finished, the first one has been manufactured and measured recently at SSRF. This water cooled electro-magnet has a total length of 1000 mm and a steering field of 2.29~Tesla. An air slot in the magnet pole was used to control the uniformity field integral distribution. The design as well as the magn
The main parameters of the simulated magnet model
Distance away from the iso-center 2.1 𝑚
Integrated field
Mechanical length
0.1679 𝑇𝑚35 𝑐𝑚
Good field region
Aperture
20 𝑚𝑚(radius)
104 𝑚𝑚
Field homogeneity
Pole tip width
±2.5×10-3
26 𝑚𝑚
3D simulation model with coils
Conclusions
• The integrated field reached 0.2175 𝑇𝑚 which is larger than the
required.
• The radius of the good field region is approximately proportional
to the aperture of the model.
• The uniformity of the field integral was controlled below 2.5×10−3 within the good field region using the tangent shims.
• The effect of the eddy currents on the stability of field can be
negligible and the stability time is very short.
0
5
10
15
20
25
60 70 80 90 100 110
Radi
us o
f the
good
fiel
d re
gion
r (m
m)
Aperture of the model d (mm)
1.50E-03 2.00E-03 2.50E-03
The distribution of the magnetic field along z axis.
The relationship between the aperture and the radius of the good
field region in different field homogeneity. It indicates that the
radius of different good field region is approximately proportional to
the aperture of the model and the scale factor dependents on the
required field homogeneity.
-3.00E-03
-2.00E-03
-1.00E-03
0.00E+00
1.00E-03
-30 -20 -10 0 10 20 30
dB
/B
Radial distance
-0.002
-0.0015
-0.001
-0.0005
0
0.0005
-30 -20 -10 0 10 20 30
Inte
grat
ed fi
eld
ho
mo
gen
eity
Radial distance (mm)
Field error at B= 4673 𝐺𝑠 Integrated field error in the good field region
（1）Principle
The octupole scanning magnet can generate a rotating dipole field
when each pair of opposing poles is given a regular sinusoid
independently. All the currents are with a same amplitude. The
current amplitude determines the field strength. The phases of the
currents determines the deflection angle of the dipole field. The field
can rotate with the change of the current phases and the deflection
angle of the field is equal to the magnitude of the phase change.
（2）Simulation of the field strength increasing
（3）Simulation of the field rotation
The distribution of the eddy currents at
t = 1 ms.The deflection angle of the field varying
with time.
The distribution of the eddy currents at
t = 1 ms.The field strength varying with time
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