JPH076900A - High frequency acceleration cavity and ion synchrotron accelerator - Google Patents

Abstract

PURPOSE:To provide a high frequency acceleration cavity and an ion synchrotron accelerator by which manufacture is facilitated and manufacturing cost is reduced by carrying out sequence control of a control system simpler than tune control of a high frequency acceleration cavity using conventional feedback control. CONSTITUTION:In a high frequency acceleration cavity 10 of an ion synchrotron accelerator, ferrite 21 having a large imaginary number part of magnetic permeability is loaded on the high frequency acceleration cavity 10, and a Q value of the high frequency acceleration cavity 10 is reduced. As the Q value is reduced, an allowable error becomes large in tuning operation to make a resonance frequency of the high frequency acceleration cavity 10 to obtain prescribed acceleration voltage and an impression frequency from high frequency electric power supply 23 coincide with each other. In this state, sequence control is carried out as tune control. The sequence control is carried out by using a digital computer 27.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion synchrotron accelerator, a high frequency acceleration cavity used in the ion synchrotron accelerator, and an acceleration method using the same.

[0002]

2. Description of the Related Art Conventionally, an ion synchrotron accelerator for accelerating ions in a circular orbit has been used in physical experiments and medical treatment. The ion synchrotron accelerator is provided with a high frequency accelerating cavity for accelerating the injected ions by applying an accelerating voltage. In order to accelerate ions using the high-frequency acceleration cavity, the orbital frequency of the ions when they orbit the synchroton must match the frequency of the high-frequency power applied from the high-frequency power source to the high-frequency acceleration cavity. I won't. Further, in order to maximize the accelerating voltage excited in the high frequency accelerating cavity, tuning control must be performed so that the applied frequency of the high frequency power and the resonant frequency of the accelerating cavity match.

The magnitude of the accelerating voltage for a constant input power of the high frequency accelerating cavity itself is expressed by the following equation: Q = 2π × (accumulated energy of cavity resonator) ÷ (from the cavity resonator during one cycle) It is evaluated by the Q value of the cavity resonator defined by (energy lost). In order to increase the acceleration voltage for a constant input power, it is necessary to use a high-frequency acceleration cavity with a high Q value.

Next, FIG. 5 shows the difference in the resonance curve depending on the Q value. From Figure 5, near the resonance frequency, the Q of the acceleration cavity
It can be seen that when the value is high, the change in acceleration voltage with respect to the change in applied frequency is large. Therefore, when the Q value of the high frequency acceleration cavity is high, the error of the acceleration voltage is large even if the error between the applied frequency of the high frequency power supply and the resonance frequency of the high frequency acceleration cavity is small. In the high-frequency acceleration cavity of the conventional ion synchrotron, the Q value is set high, so that the applied frequency and the resonance frequency must be exactly the same. In addition, when the particles are accelerated, the applied frequency changes largely (about ten times) in a short time (about 0.5-1.0 sec). For this reason, in the tuning control of the resonance frequency and the applied frequency of the high-frequency acceleration cavity, feedback control was necessary to correct a slight error in the resonance frequency (Reference "OHO '89 High Energy Accelerator Semina", Shigefumi Ninomiya. , High Energy Research Institute, V2
Page 8-V30).

[0005]

Providing a tuning device with feedback control as described in the prior art is as follows.
It is difficult to manufacture, and the manufacturing cost is high.

An object of the present invention is to provide a high-frequency accelerating cavity which is easy to manufacture and inexpensive to manufacture, and an io-synchrotron accelerator using the same.

[0007]

In order to achieve the above-mentioned object, the present invention increases the allowable error range of resonance frequency control by using an acceleration cavity having a reduced Q value. Then, sequence control is performed for resonance frequency control.

[0008]

The operation of the present invention will be described below with reference to the drawings.

FIG. 4 shows a resonance curve of the high frequency acceleration cavity.
The horizontal axis represents the applied frequency applied from the high frequency power supply to the high frequency acceleration cavity, and the vertical axis represents the acceleration voltage. The frequency f ₀ that gives the maximum acceleration voltage is the resonance frequency.

Next, FIG. 5 shows the difference in resonance curve when the Q value is different. From FIG. 5, it can be seen that near the resonance frequency, when the Q value of the acceleration cavity is low, the change in acceleration voltage with respect to the change in applied frequency is small. Therefore, if the Q value of the high-frequency acceleration cavity is lowered, the error of the acceleration voltage can be small even if the error between the applied frequency of the high-frequency power supply and the resonance frequency of the high-frequency acceleration cavity is large.

To reduce the Q value of the high frequency acceleration cavity,
Utilizing the effect of the magnetic permeability of the ferrite mounted in the acceleration cavity.

Since the high frequency accelerating cavity can be described by a parallel resonant circuit, the effect of loading ferrite will be described using an LC resonant circuit.

FIG. 7 shows a diagram of an equivalent circuit when a magnetic material sample is inserted in the LC resonance circuit. When a sample having a magnetic permeability μ = μ′−jμ ″ is inserted into the inductance L ₀ , its impedance Z becomes

[0014]

## EQU1 ## Z = jωL ₀ (μ′−jμ ″) = ωμ ″ L ₀ + jωμ′L ₀ = R + jωμ′L ₀ (Equation 1) As can be seen from this, the real part μ ′ of the magnetic permeability changes the reactance and therefore the resonance frequency. The imaginary part μ ″ of the permeability increases the energy dissipation, thus lowering the Q value.

Ferrite having a large imaginary part of magnetic permeability is loaded in the high-frequency acceleration cavity to reduce the Q value of the high-frequency acceleration cavity. If an acceleration cavity with a reduced Q value is used, the allowable error of the resonance frequency with respect to the applied frequency can be increased in the tuning control for matching the resonance frequency and the applied frequency. Therefore, the tuning control for matching the resonance frequency and the applied frequency can be sufficiently performed by the sequence control without performing the feedback control.

[0016]

EXAMPLES Examples of the present invention will be described in detail below.

FIG. 1 is a view showing the arrangement of medical proton synchrotron accelerators according to an embodiment of the present invention. In the accelerator of FIG. 1, a proton having an energy of 10 MeV is incident, accelerated to 250 MeV using the high frequency acceleration cavity 10, and then emitted. The accelerator is the beam 2 from the previous stage accelerator 1.
From the injector 3. Accelerator is incident beam 2
High-frequency acceleration cavity 10 for giving energy to the beam, a bending electromagnet for bending the beam orbit 4, a quadrupole electromagnet 5 and 9 for controlling the betatron oscillation of the beam, a resonance excitation electromagnet 7 used for extraction, and an electrostatic deflector for extraction. 5, it is composed of an emitting septum electromagnet 12.

The beam of light incident from the injector 3 is bent by the deflecting electromagnet 4 in the course of orbiting. Further, the quadrupole electromagnet 9 functions to change the trajectory gradient in the direction of converging the beam in the horizontal direction, and the quadrupole electromagnet 5 functions to change the trajectory gradient in the direction of diverging the beam. In the vertical direction, each quadrupole electromagnet has the opposite function of horizontal focusing and diverging.
By controlling the amount of excitation of these quadrupole electromagnets, it is possible to stably orbit the beam during the process of incidence and acceleration.

The beam accelerates in the high-frequency acceleration cavity 1
Energy is given from 0.

FIG. 2 shows a conceptual diagram of the tuning device. The tuning device is for performing the tuning operation of the applied frequency and the resonance frequency by sequence control. The tuning device includes a digital computer 27, a bias power source 28, and a bias coil 22. The high frequency acceleration cavity 10 of FIG. 2 is shown in cross section. High frequency acceleration cavity 10
Is a Ni-Zn ferrite 21 having a large imaginary part of magnetic permeability.
To reduce the Q value of the high-frequency acceleration cavity 10. The excitation of the electromagnetic field into the high-frequency acceleration cavity is performed via the high-frequency antenna 25 by amplifying the signal generated by the high-frequency power source 23 with the quadrupole vacuum tube 24.

Tuning control for matching the resonance frequency of the high frequency acceleration cavity 10 with the applied frequency is performed by the following sequence control.

When the beam is incident on the synchrotron accelerator from the injector 3, a signal is sent from the injector 3 to the timing pulse generator. The timing pulse generator sends a signal to the digital computer 27, and the digital computer 27 receiving the signal controls the bias power supply 28 according to the bias current program calculated in advance. A current is sent from the bias power supply 28 to the bias coil 22 to generate a bias magnetic field. The real part of the magnetic permeability of the ferrite 21 is changed according to the strength of the bias magnetic field generated by the bias coil 22, and the resonance frequency of the electromagnetic field excited in the high frequency acceleration cavity 10 is controlled.

The bias current program is set as follows. FIG. 3 is a flowchart showing a calculation procedure performed by the digital computer 27 as a specific example. A time change pattern of the magnetic field strength of the bending electromagnet 4 is input from the console. The time change pattern of the beam energy is calculated according to the time change pattern of the magnetic field strength. Since the circumference of the synchrotron accelerator is constant, the time change of the orbital frequency of the beam is calculated based on the time change pattern of the beam energy. Since the applied frequency is controlled by another control system so as to match the circulation frequency, the current value of the bias coil is changed with time so that the time variation of the resonance frequency becomes equal to the circulation frequency. The bias current value for obtaining the desired resonance frequency is calculated by a digital computer based on the resonance frequency characteristics of the bias current measured in advance.

After the beam has been accelerated to the target energy,
The orbit is deflected by the emitting electrostatic deflector 11 and the septum electromagnet 12 and sent to the treatment room 14.

[0025]

According to the present invention, it is possible to provide a high-frequency accelerating cavity that is easy to manufacture and is inexpensive to manufacture, and an ion cyclotron accelerator using the same.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an accelerator according to a fifth embodiment of the present invention.

FIG. 2 is an explanatory diagram of a tuning device according to a second embodiment of the present invention.

FIG. 3 is a flowchart showing a procedure for setting a bias current program.

FIG. 4 is a characteristic diagram of a resonance curve showing frequency dependence of acceleration voltage.

FIG. 5 is a characteristic diagram showing changes in the resonance curve when the Q value changes.

FIG. 6 is an equivalent circuit diagram when a ferromagnetic material is inserted in a resonance circuit.

[Explanation of symbols]

10 ... High frequency acceleration cavity, 21 ... Ferrite, 22 ... Bias coil, 23 ... High frequency power supply, 24 ... Quadrupole vacuum tube, 2
5 ... high frequency antenna, 27 ... digital computer,
28 ... Bias power supply.

Claims (5)

[Claims] 1. A high frequency accelerating cavity used in an ion synchrotron accelerator, comprising means for changing a resonance frequency, and performing sequence control so that the resonance frequency becomes equal to the rotation frequency according to a change in the rotation frequency. High frequency acceleration cavity. 2. A high frequency accelerating cavity used in an ion synchrotron accelerator, wherein a resonance frequency controlling ferrite and a bias coil for generating a magnetic field for adjusting the permeability of the ferrite are loaded, and a current value of the coil is loaded. A high-frequency accelerating cavity in which the resonance frequency is sequence-controlled so that the resonance frequency becomes equal to the orbiting frequency. 3. A method of accelerating charged particles in an ion synchrotron accelerator, wherein a high-frequency acceleration cavity provided with a means for changing a resonance frequency is used, and the resonance frequency of the high-frequency acceleration cavity is rotated in response to a change in the rotation frequency. A method of accelerating charged particles, characterized by performing sequence control so that the frequency becomes equal to the frequency. 4. A method for accelerating charged particles carried out by an ion synchrotron accelerator, comprising: a high-frequency accelerating cavity equipped with ferrite and a bias coil for generating a magnetic field for adjusting the permeability of the ferrite; A method of accelerating charged particles, characterized in that the current value of the coil is sequence-controlled so that the resonance frequency of the high-frequency accelerating cavity becomes equal to the orbiting frequency according to a change in frequency. 5. An ion synchrotron accelerator provided with the high-frequency acceleration cavity according to claim 1 or 2.