JP7612345B2 - Particle Therapy Equipment - Google Patents

Description

The present invention relates to an electromagnetic device, and in particular to an electromagnetic device that performs high-speed magnetic field sweeping.

Particle beam therapy devices are known that accelerate heavy particles such as protons and carbon in an accelerator to form a particle beam, which is then irradiated onto a patient's tumor or the like. In particle beam therapy devices, the beam is accelerated by an accelerator, and the particle beam emitted from the accelerator is transported to an irradiation nozzle while being deflected at required locations by a transport system, and the beam is irradiated towards the patient from the irradiation nozzle. In this case, the particle beam therapy device performs controls such as changing the energy intensity of the beam in order to control the irradiation position in the depth direction of the affected area. Specifically, for example, a multi-stage irradiation is performed in which the beam is accelerated to the maximum energy, and then the beam is transported to the affected area and injected while gradually reducing the energy according to the depth to which the beam is injected into the affected area.

The accelerator and transport system use a large number of electromagnet devices to apply a highly precise magnetic field to the beam. Some of these electromagnet devices need to change the magnetic field strength while maintaining the precision of the spatial distribution of the magnetic field. For example, some of the electromagnet devices in the transport system change the magnetic field strength accordingly when the energy intensity of the beam is changed, thereby maintaining the beam deflection direction in the desired direction.

In recent years, particle beam therapy equipment equipped with a rotating gantry that irradiates a patient with a heavy particle beam, such as heavy carbon ions, from any angle of 360 degrees is becoming practical. In order to bend a heavy particle beam in a small radius, a magnetic field stronger than that of a proton is required, so a superconducting bending magnet is used. To operate a superconducting bending magnet, a larger power supply is required than for a normal conducting magnet.

In addition, a method of irradiation (scanning irradiation) in which a finely focused beam is scanned to trace the shape of the tumor is widely used in particle beam therapy devices, and a scanning electromagnet capable of changing the magnetic field at high speed is used to scan the beam.

Electromagnet devices are also used in a variety of applications, including as static magnetic field generators and gradient magnetic field generators in MRI (magnetic resonance imaging) devices, as well as in particle beam therapy devices.

One example of a superconducting magnet device is described in Patent Document 1. In this device, the superconducting coils are divided into multiple coil groups, each of which is connected to a DC power supply, in order to suppress burnout of the superconducting coils when a quench occurs while keeping the withstand voltage and rated voltage of the superconducting coils and DC power supply low.

JP 2010-016287 A

In particle beam therapy equipment, in order to increase the throughput of treatment, it is necessary to shorten the time required for setting up the position of the affected area for treatment, and to quickly change the beam energy for multi-stage extraction. For the latter, the electromagnet device in the beam transport system needs to be able to change the magnetic field quickly.

In addition, particle beam therapy devices are also required to be compact and have a wide beam irradiation field. In this case, it is necessary to increase the (integrated) magnetic field strength generated by electromagnetic devices such as scanning magnets.

When the current supplied from the power supply is changed to change the magnetic field of an electromagnetic device, an induced voltage is generated due to the inductance of the coil. The power supply cannot change the current unless it applies a voltage greater than the induced voltage. Therefore, the speed at which the magnetic field can change is limited by the amount of voltage that the power supply connected to the coil can output.

When the electromagnetic device is a normal conducting electromagnet, in addition to the induced voltage due to the coil's inductance, a resistive voltage is generated due to the coil's electrical resistance. For this reason, the rate of change of the magnetic field of a normal conducting electromagnet is more limited by the maximum voltage that can be output by the power supply connected to the coil than is the case with a superconducting magnet.

For this reason, in order to increase the rate of change of the magnetic field of the electromagnet device, it is necessary to increase the output voltage of the power supply that supplies power to the coil, but this creates the problem of increasing the size of the power supply device. In addition, because power supplies are generally structured to control their output current using semiconductor elements such as transistors, MOSFETs (Metal-Oxide-Semiconductor Field Effect Transistors), and IGBTs (Insulated Gate Bipolar Transistors), it is difficult to output a voltage higher than the withstand voltage of the semiconductor elements.

In order to increase the rate of change of the magnetic field of a coil using a power supply with a limited output voltage, it is conceivable to reduce the inductance of each coil by dividing the coil into multiple coils, and connect each coil to a separate power supply for operation. However, when a coil is divided into multiple coils and power is supplied from separate power supplies, it is not easy to control and balance the current supplied to each coil. Therefore, when the required spatial distribution of the magnetic field is highly accurate, such as in particle beam therapy devices and MRI devices, a separate circuit is required to precisely control the output of multiple power supplies while balancing them in order to change the strength of the magnetic field at high speed while maintaining a highly accurate spatial distribution of the magnetic field.

The object of the present invention is to provide an electromagnet device with a simple configuration that can rapidly change the strength of a magnetic field while maintaining a highly accurate spatial distribution of the magnetic field.

In order to achieve the above object, a particle beam therapy device according to the present invention includes a duct that transports a particle beam and is partially curved, a plurality of superconducting coils that deflect the particle beam by applying a magnetic field with a predetermined intensity distribution to the particle beam transported through the curved portion of the duct while maintaining the predetermined intensity distribution and changing the intensity of the magnetic field in response to a change in the energy of the particle beam, and two excitation power sources that excite the plurality of superconducting coils, the number of the plurality of superconducting coils being four, the four superconducting coils being disposed such that at least a portion of the magnetic fields they generate overlap, and the predetermined magnetic field is generated by the at least a portion of the overlapping magnetic fields. a magnetic field having a constant intensity distribution, the four superconducting coils are arranged in four directions around the curved portion of the duct, two of the four superconducting coils are arranged on either side of the duct and connected in series to form a first superconducting coil, and the remaining two superconducting coils are arranged on either side of the duct and connected in series to form a second superconducting coil, the first superconducting coil, the second superconducting coil, and the two excitation power sources are connected in series in the order of the first superconducting coil, the excitation power source, the second superconducting coil, and the excitation power source, and currents of the same magnitude pass through them in sequence.

The electromagnetic device of the present invention has a simple configuration because the current values flowing through multiple coils are the same, making it possible to change the strength of the magnetic field quickly while maintaining a highly accurate spatial distribution of the magnetic field.

1 is a circuit diagram showing a configuration of an electromagnetic device according to a first embodiment of the present invention. FIG. 2 is an equivalent circuit diagram of the electromagnetic device of FIG. 1 . 1 is a block diagram showing the overall configuration of a particle beam therapy system according to a first embodiment. FIG. 2 is a side view of a bending magnet 203 for a heavy particle beam therapy apparatus to which the electromagnetic device of the first embodiment is applied. A-A' cross-sectional view of Figure 4. 5 is a perspective view showing the arrangement of superconducting coils 20 and 21 in the bending magnet 203 of FIG. 4. 6A and 6B are circuit diagrams of an electromagnetic device according to a comparative example. FIG. 6 is a circuit diagram of an electromagnetic device according to a second embodiment. 10A is a circuit diagram of an electromagnetic device according to a third embodiment, and FIG. 10B is a diagram showing a current flow in the circuit of FIG. FIG. 11 is a circuit diagram of an electromagnetic device according to Comparative Example 3. 10A is a circuit diagram of an electromagnetic device according to a fourth embodiment, and FIG. 10B is a diagram showing a current flow in the circuit of FIG. 13A is a circuit diagram of an electromagnetic device according to a fifth embodiment, and FIG. 13B is a graph showing the change over time in the power supply current value and the coil current value of the circuit shown in FIG.

One embodiment of the present invention will be described below. However, the present invention is not limited to the embodiment described here, and appropriate combinations and improvements are possible without departing from the gist of the invention.

<<Embodiment 1>>
As shown in Fig. 1, the electromagnet device of this embodiment is configured with a plurality of coils 20, 21 arranged so that at least a portion of the magnetic fields 20m, 21m generated overlap each other, and a plurality of power sources (excitation power sources) 8a, 8b. The plurality of coils 20, 21 and the plurality of power sources 8a, 8b are connected in series so that the coils and the power sources are arranged alternately. For example, in the example of the electromagnet device of Fig. 1, its equivalent circuit is a closed circuit in which the coil 20, the power source 8a, the coil 21, and the power source 8b are connected in series in this order, as shown in Fig. 2.

In an electromagnetic device with such a circuit configuration, currents of the same magnitude pass through the multiple coils 20, 21 connected in series in sequence. In other words, each coil 20, 21 is operated with a continuous current.

Therefore, by dividing the coil that forms the desired magnetic field distribution into multiple coils 20 and 21, the inductance of each coil can be reduced, and it becomes possible to change the magnitude of the current supplied to coils 20 and 21 more quickly than if the coils were not divided, while using power supplies 8a and 8b with a limited output voltage.

In addition, because the same value of current flows through the divided coils 20 and 21, the strength balance between the magnetic field 20m generated by coil 20 and the magnetic field 21m generated by coil 21 can be maintained even when the current value is changed. Therefore, the magnetic field strength can be changed quickly while maintaining a highly accurate magnetic field spatial distribution formed by the overlap of the magnetic fields 20m and 21m.

Furthermore, the electromagnet device of this embodiment has a simple circuit configuration in which multiple coils 20, 21 and multiple power sources (excitation power sources) 8a, 8b are alternately connected in series, and when changing the current, it is sufficient to adjust power source 8a and/or power source 8b so as to change the value of the current flowing through the circuit, thereby maintaining the magnetic field distribution. Therefore, the electromagnet device of this embodiment does not require a circuit that precisely controls the output of power sources 8a and 8b while balancing them in order to maintain the magnetic field distribution, and can be made into a small device with a simple circuit configuration.

The coils (electromagnets) that make up the electromagnetic device may be normal conducting coils or superconducting coils. From the standpoint of improving the performance and miniaturization of the electromagnetic device, it is preferable to use superconducting magnets.

The coils 20, 21 of the electromagnet device are preferably driven at high voltage by the power sources 8a, 8b, but from the viewpoint of simplifying the insulation structure of the electromagnet device, it is preferable that the power sources 8a, 8b are internally grounded (midpoint grounded) and are capable of outputting AC voltages of both positive and negative polarities (i.e., AC voltages with a positive potential at the maximum value and a negative potential at the minimum value). As a result, for example, an electromagnet device equipped with an insulation structure capable of insulating a voltage value V against a ground voltage can apply a voltage from +V to -V to the coils 20, 21, so that a voltage twice as large (-V to +V) can be applied compared to the case where a voltage of +V or -V is applied. Therefore, the current in the coil can be changed twice as fast, and the magnetic field generated by the coil can be changed twice as fast.

When the power supplies 8a and 8b are bipolar, the power supplies 8a and 8b are configured with, for example, a full bridge circuit in the output stage. In this case, it is desirable to drive the gates of the IGBT elements and the like in the output stages of the multiple power supplies at the same timing in all of the power supplies 8a and 8b. This allows for the simplest power supply configuration.

<Particle beam therapy equipment>
Next, a particle beam therapy system using the electromagnetic device of this embodiment will be described in detail with reference to the drawings.

The overall configuration of a particle beam therapy device is shown in Figure 3. As shown in Figure 3, the particle beam therapy device is configured with an accelerator 500 that forms a particle beam, a beam transport system 200 that transports the particle beam, an irradiation device 300 that irradiates a patient 301 with the particle beam, and a bed 302 on which the patient 301 is placed.

In the example shown in FIG. 3, the accelerator 500 is configured to include a linac 501, which is a pre-stage accelerator, and a synchrotron 502, which further accelerates the particle beam formed by the linac 501, but it is not limited to this configuration and it is of course possible to use a cyclotron or the like.

The beam transport system 200 includes a duct 204 that transports the particle beam formed by the accelerator 500, deflection magnets 201, 202, and 203 that apply a deflection magnetic field to the particle beam in the duct 204, a quadrupole magnet 211 that applies a magnetic field to focus the particle beam, and an orbit correction magnet 212.

The duct 204 is provided with a rotary coupling 214, and the tip side of the rotary coupling 214 can rotate by the mechanism of the rotary coupling 214 with respect to a fixed part closer to the accelerator 500 than the rotary coupling 214.

The beam transport system 200, which is located further distal than the rotary connection 214, is mounted on a rotating ring (not shown) and rotates about the rotation axis 1213 as the rotating ring is rotated by the drive unit.

As a result, the beam transport system 200, together with the rotating ring and drive unit, constitutes the rotating gantry 400.

The scanning device 300 is equipped with a scanning electromagnet 303 for moving the beam irradiation position according to the shape of the affected area.

As the beam emitted from the accelerator 500 passes through the beam transport system 200, it is bent and transported along the beam transport path by the deflection magnets 201, 202, and 203, and the shape and position of the beam are adjusted by the quadrupole magnet 211 and the trajectory correction magnet 212. In addition, the beam is deflected in a direction perpendicular to the beam axis by the scanning electromagnet 303 installed in the irradiation device 300, so that the affected area is irradiated in a tracing manner.

The strength of the magnetic field generated by these magnets 201-203, 211, 212, and 213 is changed according to the energy of the beam. The energy of the beam may be changed in the accelerator 500, or a degrader may be placed midway along the transport system 200 to attenuate the energy by the desired amount.

<Configuration example of bending electromagnet 203>
An example in which the electromagnet device of this embodiment is used as a bending magnet 203 for a heavy particle beam therapy device will be described below with reference to Figures 4, 5 and 6. The bending magnet 203 is configured such that three electromagnets that bend a particle beam by 30 degrees are arranged along a duct 204, and bend the particle beam by 90 degrees. Note that the bending magnets 201 and 202 also differ from the bending magnet 203 in the number of superconducting coils that constitute them, but have the same basic configuration.

Figure 4 is a side view of the deflection magnet 203, and Figure 5 is a cross-sectional view taken along line A-A' in Figure 4. Figure 6 is a perspective view showing the arrangement of superconducting coils 20, 21 within the deflection magnet 203. The deflection magnet 203 comprises multiple superconducting coils 20, 21 (101-104), power sources 8a, 8b, a thermal insulation container 110, a refrigerator 120, and multiple pairs of leads 30a, 30b, 31a, 31b.

The superconducting coils 101 and 102 are connected in series as shown in FIG. 5 to form the superconducting coil 20. The superconducting coils 103 and 104 are connected in series to form the superconducting coil 21. The superconducting coils 20 and 21 are alternately connected in series to the power sources 8a and 8b as shown in FIG. 5 to form the electromagnet device of this embodiment shown in FIG. 1 and FIG. 2. The superconducting coils 101 to 104 superimpose the magnetic fields they respectively form to form and apply a magnetic field 213 with a predetermined intensity distribution to the particle beam transported within the duct 204. Specifically, the magnetic field 213 perpendicular to the traveling direction 214 of the particle beam is applied. This deflects the particle beam in a direction 215 perpendicular to the magnetic field direction 213 and the traveling direction 214 of the particle beam.

As an example, as shown in FIG. 6, the superconducting coils 20, 21 (101-104) are wound in a flat shape having a major axis and a minor axis in the main plane, and are arranged so that the major axis is along the axial direction of the duct 204. The major axis direction is curved so as to follow the curvature of the duct 204. The superconducting coils 20, 21 (101-104) are arranged in four directions around the duct 204 so that the main plane is parallel to the plane in which the particle beam is deflected. The superconducting coils 101 and 102, and the superconducting coils 103 and 104 face each other across the duct 204 through which the particle beam is transported.

The thermal insulation container 110 houses multiple superconducting coils 20, 21 (101 to 104) in its internal space. In the example of FIG. 5, the thermal insulation container 110 includes a vacuum container 111 and a radiation shield 112 arranged inside the vacuum container 111.

The refrigerator 120 is mounted in the insulated container 110. For example, the first stage (e.g., 40k) of the refrigerator 120 is thermally connected to the radiation shield and cools the radiation shield 112 to the temperature of the first stage. The second stage (e.g., 4k) is thermally connected to the superconducting coils 101-104 by a copper mesh or the like (not shown) and cools the superconducting coils 101-104 by conduction cooling.

Multiple pairs (two pairs in this case) of leads (hereafter also referred to as power leads) 30a, 30b, 31a, 31b have one end connected to the end of each of the superconducting coils 20, 21 (101-104) and the other end extended from the inside of the insulating container 110 to the outside.

In addition, although not shown, a protective element that receives and consumes the current flowing through the superconducting coils 20, 21 (101-104) via leads 30a, 30b, 31a, and 31b when the superconducting coils 20, 21 (101-104) are quenched is disposed outside the insulating container 110.

In this way, in the deflection magnet 203 of this embodiment, the coil that generates the magnetic field 213 required for deflecting the particle beam is divided into superconducting coils 20 and 21, which are connected in series to the power sources 8a and 8b in the structure. In this way, by dividing the coil that forms the desired magnetic field 213 into multiple coils 20 and 21, the inductance of each coil can be reduced, so that while using power sources 8a and 8b with a limited output voltage, it is possible to change the magnitude of the current supplied to the coils 20 and 21 more quickly than if the coils were not divided.

In addition, because the same current flows through the divided coils 20 and 21, the strength balance between the magnetic field generated by coil 20 and the magnetic field 213 generated by coil 21 can be maintained even when the current value is changed. Therefore, the strength of the magnetic field 213 can be changed at high speed while maintaining the spatial distribution of the magnetic field 213.

Furthermore, the deflection magnet 203 of this embodiment has a simple circuit configuration, and when changing the current, it is sufficient to adjust the power supply 8a and/or the power supply 8b so as to change the value of the current flowing through the circuit. Therefore, a small deflection magnet 203 can be provided.

As a specific example, the deflection magnet 203 in FIG. 4 deflects 430 MeV/u carbon ions by 90 degrees with an equivalent radius of 2.4 m, and three magnets (superconducting coils 20, 21) that deflect the particle beam by 30 degrees are arranged along the duct 204 and housed in a cryostat (insulated container 110). They are cooled by multiple GM refrigerators 120 and operated in a superconducting state.

The magnetic field 213 generated by the magnet (superconducting coils 20, 21) that deflects by 30 degrees is approximately 3.7 T at the center of the magnet, and the stored energy of the 30-degree magnet in rated operating conditions is approximately 430 kJ.

When the superconducting coils 20, 21 are not divided and are operated with a single 600V power supply, the magnetic field change speed is 0.43 T/sec. However, in the deflection magnet 203 of this embodiment, the superconducting coils 20, 21 and the power supplies 8a, 8b are alternately connected in series, and the speed can be increased to approximately double that, 0.80 T/sec, with the power supplies 8a and 8b each being 600V. In addition, the magnetic field change time associated with the energy change per layer can be reduced to less than 30 msec.

<Configuration Example of Scanning Electromagnet 303>
The electromagnet device of this embodiment can also be applied to the scanning electromagnet (normally conductive) 303 mounted on the irradiation device 300 of a particle beam therapy device.

As a result, the scanning electromagnet 303 can generate a magnetic field with an integrated magnetic field strength 2.0 times that of the conventional one, so the nozzle length of the emission section can be reduced by, for example, 1.2 m while maintaining the size of the conventional irradiation field. In this case, the diameter of the rotating gantry on which the irradiation device 300 is mounted can be reduced by 2.4 m, and the weight of the rotating gantry can be reduced by 20 tons.

<Detailed explanation of the concept of this embodiment>
The electromagnetic device of this embodiment will be described in further detail below.

It is generally known that in order to rapidly change the magnetic field strength generated by an electromagnetic device, it is necessary to apply a voltage from an excitation power supply to the magnet so that it overcomes the induced voltage, which is determined by the product of the time change in operating current and the inductance of the magnet.

Electromagnet devices (such as bending magnet 203) used in particle beam therapy devices must accurately generate a magnetic field strength that is set relative to the beam energy, and therefore the superconducting coils (hereinafter, the superconducting coils of an electromagnet device will be referred to as electromagnets) must be operated accurately at a set current value. For this reason, a controlled power supply is used as the power source to operate these electromagnets. Semiconductor elements such as transistors, MOSFETs, and IGBTs are arranged in the output stage of the circuit in the controlled power supply, and a specified current is passed through the electromagnets by controlling the output current (voltage) using these elements. An example of the arrangement of the semiconductor elements will be explained later.

The maximum voltage that can be output from an excitation power supply is restricted by the withstand voltage of the semiconductor elements in the output stage, so the sweep speed of the electromagnet's magnetic field is limited by this voltage. For example, if a semiconductor element with a withstand voltage of 600V is used to output voltages of ±600V with both polarities, the electromagnet will be driven at 1200V. The sum of the inductive and resistive voltages generated by the electromagnet can be operated within a range that does not exceed 1200V.

<Comparative Example 1>
As a comparative example, consider the circuit of an electromagnet device in which an electromagnet (coil) and an excitation power supply are connected in series as shown in Fig. 7(a). The inductance of the electromagnet in this electromagnet device is 2L, and the voltage applied to the electromagnet is 2Vo, so if we ignore the voltage generated by the resistance component, the rate of change of the current passing through the electromagnet is Vo/L (A/sec). Since the rate of change of the magnetic field is proportional to the rate of change of the current, the rate of change of the magnetic field becomes smaller for magnets with larger inductance in Fig. 7(a).

<Comparative Example 2>
As mentioned above, the operating speed of an electromagnet is limited by the power supply voltage, so an electromagnet with a large inductance cannot increase its operating speed due to inductive voltage. One way to avoid this is to divide the electromagnet and drive each of the divided electromagnets with a power supply, as shown in Figure 7(b). In this case, the electromagnet is divided and its inductance as seen from the power supply becomes smaller, so the rate of change of the magnetic field can be increased.

In a divided circuit such as that shown in Figure 7(b), two electromagnets with inductance L are each driven by a voltage of 2Vo, so if we ignore the voltage generated by the resistance component, the rate of change of the current passing through the electromagnets is 2Vo/L (A/sec). When comparing the circuit in Figure 7(b) with a circuit in which the magnets are not divided, such as that shown in Figure 7(a), we can see that the rate of change of the current is twice as high, and therefore the rate of change of the magnetic field can be doubled.

In the circuit in Figure 7(b), the electromagnet is divided and each part is operated by a separate power source, so there are multiple independent electromagnets. Therefore, any amount of current can be passed through each magnet.

However, there are magnet devices that require precise control of the magnetic field strength distribution, such as magnets that apply a magnetic field to beams in particle beam therapy devices. As shown in Figure 7(b), if what was originally a single electromagnet is split into two and driven by separate power supplies, it is difficult to precisely match the current values flowing through the two electromagnets. Therefore, the electromagnet device of Figure 7(b) requires a separate control device to match the currents in the two electromagnets. Also, compared to driving an unsplit magnet with a single power supply as in Figure 7(a), this is disadvantageous in terms of magnetic field precision and magnetic field stability.

<Electromagnet device of this embodiment>
Therefore, in the electromagnet device of this embodiment, the divided electromagnets (superconducting coils) 20, 21 and the excitation power supplies 8a, 8b are connected in series so as to be arranged alternately as shown in Fig. 2. By configuring the circuit as shown in Fig. 2, the current flows through one closed circuit, so that the currents flowing through the two magnets 20, 21 can be made to match each other.

In a circuit like that shown in Figure 2, two electromagnets 20, 21 with inductance L are driven by the voltage of two excitation power supplies 8a, 8b with a voltage of 2Vo. If we ignore the voltage generated by the resistance component, the rate of change of the current passing through the magnets is (2Vo+2Vo)/(L+L)=2Vo/L (A/sec).

Comparing the circuit in Figure 2 with a circuit in which the magnet is not divided, as in Figure 7(a), the rate of change of the current is doubled, and therefore the rate of change of the magnetic field can be doubled.

In addition, the circuit diagram in Figure 2 does not show the location of the ground, but for example, if the internal midpoint of each power supply is grounded, the potentials at both ends of each coil (inductance L) will be +Vo and -Vo, and they will be operated at a voltage of 2Vo. Looking at the circuit clockwise from power supply 8a as the starting point, we can see that the potential at the outlet side of power supply 8a is Vo, +Vo at the inlet of coil 20 and -Vo at the outlet, which connects to power supply 8b, and power supply 8b raises the voltage by 2Vo, becoming +Vo at the inlet of coil 21 and -Vo at the outlet, which returns to power supply 8a, and the potential relationship between power supplies 8a, 8b, and both ends of electromagnets 20, 21 is not broken. In this case, the magnet as a whole is operated at a voltage of 4|Vo|, but the maximum voltage to ground of the circuit is |Vo|.

The power source generates an AC voltage, the maximum value of which is a positive potential and the minimum value of which is a negative potential.
If the power supplies 8a, 8b and the electromagnets 20, 21 in the circuit of Fig. 2 were not alternately arranged, but the power supplies 8a, 8b were connected together in one place in series, short-circuit current would flow, making it impossible to ground the midpoint inside each of the power supplies 8a, 8b. Even if the power supplies were grounded at one suitable point inside the circuit, including the power supplies, the maximum voltage to ground in this circuit would be 2|Vo|, which would exceed the withstand voltage |Vo| of the semiconductor elements that make up the power supplies. In addition, the electromagnets 20, 21 themselves would need to be insulated against 2|Vo|, which would require a complex insulation structure.

So far, we have explained the configuration of a bipolar power supply (bipolar power supply) capable of outputting ±Vo as the power supply. A bipolar power supply is desirable in order to maximize the operating voltage of the coil while keeping the voltage to ground at Vo. However, if you want to configure it using an inexpensive power supply, or if you do not need high-speed demagnetization and do not require a large negative voltage, it is also possible to configure it in the same way using a unipolar power supply that generates a voltage of 0-Vo. In this case, you can simply ground the point where the voltage becomes 0V.

<<Embodiment 2>>
Next, an electromagnet device of embodiment 2 will be described. The electromagnet device of embodiment 2 is similar to embodiment 1 in that a plurality of coils 20, 21 and power sources 8a, 8b are connected in series so as to be arranged alternately as shown in Fig. 8, but differs from embodiment 1 in that the magnitudes of inductance of two coils 120, 121 are different, L1 and L2, respectively, and the voltage 2|Vo1| of the power source 18a and the voltage 2|Vo2| of the power source 18b are also different.

In the electromagnet device of FIG. 8, the coils 120, 120 of the inductances L1, L2 are connected in series to the power supplies 8a, 8b of ±Vo1, ±Vo2, so the inductance (L1+L2) is driven by a voltage of 2(Vo1+Vo2), and the current change rate of the entire circuit is 2(Vo1+Vo2)/(L1+L2). In addition, the voltages applied to the coils 20, 21 of the inductances L1, L2 are automatically divided and become 2(Vo1+Vo2)L1/(L1+L2) and 2(Vo1+Vo2)L2/(L1+L2), respectively.

Therefore, in the electromagnet device of this embodiment, even if the inductances of the coils 120 and 121 are different, or even if the voltages of the power sources 8a and 8b are different, the voltages are divided without any problems, and the same effect as in embodiment 1 can be achieved. In other words, there is no need for a circuit or the like for specially controlling the power sources 8a and 8b, which have different voltage values.

<<Embodiment 3>>
As a third embodiment, a specific example of the electromagnetic device of the first embodiment shown in FIG. 1 in which the output stages of the excitation power supplies 8a and 8b are full-bridge circuits using IGBTs 80 will be described with reference to FIG. 9(a).

As shown in FIG. 9(a), the excitation power supply 8a is a full bridge circuit in which arms 82a-1 and 82a-2 are connected in parallel, and each arm is configured with two IGBTs 80 connected in series, with a diode 83 connected in anti-parallel. The excitation power supply 8b is also a full bridge circuit in which arms 82b-1 and 82b-2 are connected in parallel. Both ends of the coil 20 are connected to the midpoint of the arm 82a-1 and the midpoint of the arm 82b-1. Both ends of the coil 21 are connected to the midpoint of the arm 82a-2 and the midpoint of the arm 82b-2. In other words, the coils 20 and 21 are arranged across the two power supplies 8a and 8b.

The rectifier circuit sections upstream of the arms of each power supply 8a, 8b must be insulated from each other.

Note that this is a simplified circuit to explain the load inductance and the current flowing inside the power supply, and does not show a control circuit for constant current control, but a control circuit that outputs a gate signal to switch the gate is connected to the IGBT 80 in the full bridge circuit.

Figure 9(b) shows the current flow at the moment when current is applied to coils 20, 21. As is clear from Figure 9(b), the current flowing through coils 20, 21 is continuous, and is configured so that the voltage supplied from power sources 8a, 8b and the inductance of coils 20, 21 are arranged alternately. In this way, in the electromagnet device of embodiment 3, the current path is one closed circuit, so the current flowing through the two coils 20, 21 automatically becomes the same value.

In addition, in the electromagnet device of FIG. 9(a), even if there is a difference in the voltage of the exciting power sources 8a and 8b or the inductance of the coils 20 and 21, the currents flowing through the coils 20 and 21 are the same.

Therefore, essentially, the full bridge circuits of the power supplies 8a and 8b monitor the current flowing through the circuit and turn on and off the gates of the IGBTs at the same timing to achieve the desired current value. Since the current to be monitored needs to be monitored at one location, only one control circuit (not shown) is required to output a control signal for turning on and off the gates. A control signal is sent from this control circuit to the IGBTs of the two power supplies 8a and 8b, and when a current is supplied to the plus (+) side (current is added to the coil), the upper IGBT of the arm 82a-1, the lower IGBT of 82b-1, the lower IGBT of the arm 82a-2, and the upper IGBT of the arm 82b-2 are switched (turned on) at the same timing to flow current as shown in FIG. 9B, and when a current is supplied to the minus (-) side (current is drawn from the coil), the remaining IGBTs are turned on at the same timing.
In this way, by changing the switching timing of the full bridge circuit of the power supplies 8a and 8b to change the current flowing through the coils 20 and 21, it is possible to change the magnetic field strength while maintaining the magnetic field distribution formed by the overlapping magnetic fields of the coils 20 and 21.

<Comparative Example 3>
An electromagnetic device as a comparative example of the third embodiment is shown in FIG.

As shown in Figure 10, this circuit configuration uses a power supply whose output stage is a full-bridge IGBT to excite two coils in parallel. Because two coils are driven in parallel, the excitation operation of the two coils is equivalent to exciting separate coils with independent power supplies, and is equivalent to the circuit in Figure 7(b).

<<Embodiment 4>>
11A shows a circuit configuration of the electromagnet device of the first embodiment shown in FIG. 1, in which a series dropper using a transistor 81 is used as the excitation power supplies 8a and 8b. As in the third embodiment, the coils 20 and 21 are arranged across the two power supplies 8a and 8b.

Figure 11(b) shows the current flow at the moment when current is applied to coils 20, 21. As shown in Figure 11(b), the current flowing through coils 20, 21 is continuous, and the power sources 8a, 8b that apply voltage and the coils 20, 21 with inductance are arranged alternately. Since the current path is one closed circuit, the current flowing through the two electromagnets is automatically the same. In the case of a series dropper, it is desirable to configure the transistors to operate in cooperation, such as by forming a current mirror circuit, so that the same current flows, and to have a single control unit that controls the current.

The effects of the electromagnet device of this embodiment 4 are similar to those of embodiment 1, so a detailed explanation will be omitted.

<<Embodiment 5>>
As a fifth embodiment, a superconducting magnet device for an MRI apparatus, which is composed of two power sources with different power source performance, will be described with reference to Figs.

Fig. 12(a) is a schematic representation of a superconducting magnet device for MRI. The superconducting magnet device for MRI uses coils 20 and 21 wound with _MgB2 , which is a high-temperature superconducting material. This superconducting magnet device for MRI is not a persistent current mode magnet like the conventional superconducting magnet device for MRI that uses NbTi coils, but a drive mode magnet that generates a magnetic field by constantly supplying current from power sources 18a and 18b.

Unlike the first embodiment, the power supplies 18a and 18b are DC current sources. As shown in FIG. 12(b), the power supply 18a is a power supply with both a small output current and output voltage and a small current ripple (current noise), while the other power supply 18b is a power supply with both a large output current and output voltage and a relatively large current ripple (current noise). The former power supply is a so-called high-performance power supply that uses a series dropper method and has low noise, while the latter is an inexpensive, general-purpose switching power supply.

The superconducting magnet device also has diodes 22 and 23 for circulating the current flowing through the superconducting coils 20 and 21, respectively, so that the coil current circulates when the magnet is in operation. By installing these diodes 22 and 23, interference between power sources 18a and 18b can be avoided, and the currents supplied from the respective power sources 18a and 18b are superimposed and supplied to the superconducting magnets 20 and 21.

Figure 12(b) shows the time change of the output current of the two power supplies 18a and 18b and the current flowing through the coils 20 and 21. The current noise of the power supply 18b is approximately 70 mArms. The current flowing through the coils 20 and 21 is estimated by appropriate measurements (measurement of the inductive voltage generated in the coils 20 and 21 or measurement of the magnetic field using a SQUID or NMR probe). A current is supplied from the power supply 18a so that feedback is applied to cancel the current fluctuations (noise) in the coils 20 and 21 caused by the current noise of the power supply 18b. Therefore, the current in the coils 20 and 21, which is the superposition of the currents supplied from the power supplies 18a and 18b, has noise (current fluctuations) removed, and the superconducting magnet device can generate a stable (noise-free) magnetic field.

Normally, when a magnet is operated with a single power supply, the rated current value for generating the rated magnetic field is 200 to 500 A. Even if a high-precision power supply is used as the power supply, the ripple is 10 to 100 ppm. Since 10 ppm of current noise (magnetic field change) is unacceptable for NMR and MRI equipment, an ultra-high-precision power supply with even lower noise must be used to achieve drive mode operation, but such power supplies are very expensive and large. The current ripple and voltage ripple supplied from the power supply generally tend to be proportional to the magnitude of the full-scale output, and the smaller the full-scale value, the smaller the absolute value of the ripple.

In this embodiment 4, by combining a small current/small voltage high precision power supply 18a with a large current/large voltage general purpose switching power supply 18b, it is possible to realize a magnetic field equivalent to an ultra-high precision power supply inexpensively and compactly.

Therefore, an MRI apparatus that uses the superconducting magnet device of embodiment 4 as a static magnetic field generating magnet can generate MRI images with less noise because of the high accuracy of the magnetic field. In addition, the superconducting magnet device of embodiment 4 is inexpensive and compact, so the MRI apparatus can be made smaller and provided at a low cost.

The electromagnets described in embodiments 1 and 2 can also be used as gradient magnetic field generating magnets for an MRI device.

The electromagnet device of the present invention described above makes it possible to increase the excitation speed regardless of the maximum voltage constraints of the excitation power supply and regardless of the magnitude of the magnet inductance.

In electromagnet devices that require rapid magnetic field changes, the ability to eliminate power supply voltage constraints allows for even faster operation, and the ability to accommodate increased magnetomotive force also contributes to the miniaturization of magnet devices.

The electromagnet device of the present invention can be applied to various devices, and is particularly suitable for electromagnet devices that change the magnetic field strength at high speed while maintaining a highly accurate magnetic field distribution. For example, it is useful as an electromagnet for a particle beam therapy device, and can improve the performance and reduce the size of the particle beam therapy device.

It is also useful as an electromagnet that generates static magnetic fields and gradient magnetic fields in MRI devices, making it possible to achieve highly accurate magnetic field distributions using a low-cost electromagnet device.

8a, 8b...power supply (excitation power supply), 20, 21...coil, 20m, 21m...magnetic field, 30a, 30b, 31a, 31b...leads, 101-104...coil, 110...thermal insulation container, 120...refrigerator, 200...beam transport system, 201, 202, 203...deflection magnet, 204...duct, 211...quadrupole magnet, 212...orbit correction magnet, 214...rotation connection, 301...patient, 300...examination device, 302...bed, 303...scanning electromagnet, 400...rotating gantry, 500...accelerator, 501...linac, 502...synchrotron, 1213...rotation axis

Claims (5)

A duct for transporting a particle beam and having a curved portion;
a plurality of superconducting coils for applying a magnetic field having a predetermined intensity distribution to the particle beam transported through the curved portion of the duct while changing the intensity of the magnetic field in response to a change in the energy of the particle beam while maintaining the predetermined intensity distribution, thereby deflecting the particle beam;
two excitation power sources for exciting the plurality of superconducting coils;
the number of the plurality of superconducting coils is four , the four superconducting coils are arranged so that at least a portion of the magnetic fields they generate overlap, and the magnetic field having the predetermined intensity distribution is formed by the at least a portion of the overlapping magnetic fields, the four superconducting coils are arranged in four directions around the curved portion of the duct, two of the four superconducting coils are arranged on either side of the duct and are connected in series to form a first superconducting coil, and the remaining two superconducting coils are arranged on either side of the duct and are connected in series to form a second superconducting coil,
The first superconducting coil, the second superconducting coil, and the two excitation power sources are connected in series in the order of the first superconducting coil, the excitation power source, the second superconducting coil, and the excitation power source, and currents of the same magnitude pass through them in sequence. The particle beam therapy device according to claim 1, characterized in that the two excitation power sources generate an AC voltage, the maximum value of the AC voltage being a positive potential, and the minimum value being a negative potential. 2. The particle beam therapy device according to claim 1, wherein the two excitation power sources have full bridge circuits including a plurality of semiconductor elements, and both ends of the first superconducting coil and the second superconducting coil are each connected to a full bridge circuit of a different excitation power source. 4. The particle beam therapy device according to claim 3, wherein the two excitation power supplies include a control circuit that outputs a gate signal for switching the plurality of semiconductor elements of the full bridge circuit, and the control circuit outputs the gate signal to the two excitation power supplies at the same timing. 2. A particle beam therapy device according to claim 1, wherein the two excitation power supplies generate DC current , and one of the excitation power supplies has an output current, an output voltage and a current noise smaller than those of the other excitation power supply, and the current noise of the other excitation power supply is reduced by superimposing the current of the other excitation power supply on the current of the one excitation power supply.

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