JPS5819840Y2 - Senkei Ryuushika Sokuuchi - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a linear particle accelerator that can effectively control the dose of charged particles.

In recent years, linear particle accelerators have been increasingly used as radiation therapy devices in the medical field.

By the way, requirements for radiotherapy equipment include small size, easy handling, and low cost.

It can also be said that development of linear accelerators as radiation therapy devices is progressing along the above-mentioned direction.

This kind of linear particle accelerator is generally constructed as shown in FIG.

Here, FIG. 1 shows the structure of the accelerator, and 1 indicates an accelerating tube.

The accelerator tube 1 is formed of a metal cylinder whose interior is kept in a vacuum, and metal disks a are inserted as appropriate to form a cavity resonator array for microwaves.

The metal disc 1a has an opening of /'lL in the center so that a charged particle flow such as an electron flow can pass therethrough.

On the other hand, as a microwave source for driving the acceleration tube 1, a magnetron 2 or the like is used.

The microwave power generated by magnetron 2 is
The accelerating tube IVc is guided to generate an electric field in the axial direction inside the accelerating tube 1 to accelerate the electron flow.

An electron gun 3 is installed at one end of the acceleration tube 1 to generate the electron flow.

A target 4 made of heavy metal is attached to the other end of the acceleration tube 1, if necessary, so that the electron flow can be converted into gamma rays or X-rays.

Further, a cutoff coil 5 for controlling the electron beam dose is attached to the outside of the electron gun 3 so that a magnetic field can be applied in a direction perpendicular to the axis of the electron gun 3.

More specific operations will be explained using the control section shown in FIG.

The output of a pulse generator 5 such as a line type pulser is connected to a primary winding 7a of a pulse transformer 7.

Two secondary windings s7b, 7 of the pulse transformer 7
c is connected to the cathode of the magnetron 2 via a heater transformer.

Further, the secondary winding 7b is provided with an intermediate tap 7d, which is connected to the electron gun 30 cand via a resistor 8 inserted as required.

On the other hand, two heater transformers 9 and 10 are built into the housing of the pulse transformer 7, and a magnetron 2 and a magnetron 2, respectively.
It is connected to the heater of the electron gun 3.

Furthermore, a transformer 11 is provided outside the housing of the pulse transformer 7.

This transformer 11 appropriately steps down the output of the heater power supply 12 of the magnetron 2 and supplies the heater power to the heater of the magnetron 3 via the two transformers 11 and 9.

A heater power source 13 is a heater power source for the electron gun 3 and is connected to the heater of the electron gun 3 via a heater transformer 10 .

Next, the operation of the above-mentioned conventional device will be explained using numerical examples.

The pulse train generated by the pulse generator 6 has a peak value of 10
kV, pulse width 2μBee, repetition 600P, P, S.

This pulse train is boosted by a pulse transformer 7, and a pulse of 145 kV is applied to the cathode of the magnetron 2.

As a result, magnetron 2 has a frequency of 2998MHz, 2M
A W pulse microwave is oscillated.

This microwave output is applied to the acceleration tube 1, and
generates a standing wave electric field inside.

On the other hand, the pulse train generated by the pulse generator 6 and boosted by the pulse transformer 7 is simultaneously applied to the electron gun 30 cand via the resistor 8.

That is, the pulse train applied to the intermediate tap 7d has a peak value of -22 kV, and this negative pulse causes the electron gun 3 to
Thermionic electrons emitted from the cathode are made to enter the accelerating tube 1 and are accelerated by the standing wave electric field.

By the way, when the cutoff coil 5 shown in FIG. 1 is excited in the above-described operating state, the thermoelectrons emitted from the electron gun 30 cand are deflected in a direction perpendicular to the plane of the paper in FIG.

In this case, if the amount of excitation of the cutoff coil 5 is large, the amount by which the thermionic electrons are deflected will increase, and the thermionic electrons will not be able to enter the accelerator tube 1 through the small hole made in the front surface of the electron gun 3. It becomes possible.

In other words, the electron flow is blocked.

Therefore, if the cutoff coil 5 is continuously excited, the microwave power generated by the magnetron 2 will cause the acceleration tube 1 to
The electric field generated inside the chamber controls the accelerated flow of electrons.

That is, in the conventional device described above, a cutoff coil 5 is installed outside the electron gun 3 to control the charged particle dose and, ultimately, the gamma ray dose obtained through the target 4.

However, in the conventional device described above, the cutoff coil 5 needs to be installed around the joint between the electron gun 3 and the acceleration tube 1, resulting in a large gap between the coils.

For this reason, it is difficult to uniformly control the magnetic flux generated between the coils of the cutoff coil 5, making it impossible to perform effective dose control and increasing the size of the accelerator, making it difficult to downsize the accelerator as a whole. .

Therefore, the present invention was developed in view of the above-mentioned circumstances, and by using a thyristor to control *+m of the charged particle flow emitted from the electron gun, it is possible to perform effective control, and the cutoff coil can also be controlled. It is an object of the present invention to provide a linear particle accelerator which can reduce the size of the entire device by eliminating the need for such a device.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings in which the same parts as in FIG. 1 are denoted by the same reference numerals.

FIG. 3 is a sectional view showing the structure of the accelerator of the present invention,
FIG. 4 is a wiring diagram of the control section of the present invention.

First, referring to FIG. 3, it is the same as the conventional device shown in FIG. 1, except that the cutoff coil 5 is removed, and the other functions are the same as the conventional device.

On the other hand, in the control section shown in FIG. 4, 14 is Cyrisk;
15 is a control pulse generator for this thyristor 14, and 16 is a DC power supply for generating a retrospective bias voltage for the thyristor 140.

That is, the device of the present invention attempts to control the dose by using the cyrisk and its control circuit instead of using the cutoff coil.

Next, the operation of the device of the present invention in the above configuration will be described with specific numerical examples.

The pulse train generated by the pulse generator 6 has a peak value of 10 as in the conventional example described above.Pulse width is 2μsea and repetition rate is 600.
P, P, S toss.

This pulse train is boosted by a pulse pulse 7, and a pulse of 145 kV is applied to the cathode of the magnetron 2.

This high voltage pulse causes magnetron 2 to reach 2998MH
z, a 2 MW pulsed microwave is oscillated.

This microwave output is applied to the accelerating tube 1 to generate a standing wave electric field inside the accelerating tube 1.

On the other hand, the pulse train generated by the pulse generator 6 and boosted by the pulse transformer 7 is simultaneously applied to the electron gun 30 cand via the resistor 8.

That is, the pulse train applied to the intermediate tap 7 b Vc6 has a peak value of -22 kV, and the thermoelectrons emitted from the cathode of the electron gun 30 are accelerated by the standing wave electric field into the interior of the accelerator tube 1 due to this negative pulse.

Here, a trigger pulse is generated from the control pulse emitter 15 in synchronization with the pulse generator 6.

The thyristor 14 is then fired by the trigger pulse, and the high voltage pulse applied via the resistor 8 bypasses the cathode of the electron gun 3 and flows to the thyristor 14 side.

That is, when the thyristor 14 becomes conductive, the voltage pulse from the pulse transformer 7 is not applied to the cathode of the electron gun 30, and no thermoelectrons are generated from the cathode of the electron gun 30.

On the other hand, when the high voltage pulse from the pulse transformer 7 disappears, the thyristor 14 is reversely biased by the DC power supply 16 and shut off.

Therefore, the trigger of the thyristor 14 now output from the control pulse generator 15? (By appropriately controlling the pulse train, that is, by generating a trigger pulse at a certain ratio to the output pulse of the pulse generator 6, the generation of charged particles can be controlled when this trigger pulse is generated. For example, the dose rate of γ-rays output from the acceleration tube 1 to the outside is controlled.

The control amount in this case can be arbitrarily controlled by changing the output trigger pulse generation ratio of the control pulse generator 15 to the output pulse of the pulse generator 6.

As described above, according to the present invention, a bypass circuit using a thyristor is provided in the high-voltage pulse supply path to the electron gun,
Since the thyristor is made conductive at a settable ratio to the high-voltage pulse, the high-voltage pulse is bypassed, and the generation of particle electrons generated from the electron gun is suppressed, so the output dose rate can be controlled reliably and easily. It can be done.

Further, since there is no need for a cutoff coil or the like for generating a magnetic field, which was conventionally required, the overall size of the device can be reduced, and a linear particle accelerator that is effective as, for example, a radiation therapy device can be provided.

[Brief explanation of the drawing]

1 and 2 are a block diagram and a control section wiring diagram showing a conventional linear particle accelerator, and FIGS. 3 and 4 are a block diagram and a control section wiring diagram showing an embodiment of the present invention. 6... High voltage pulse generator, 14... Thyristor, 15... Control pulse generator, 16... DC power supply.

Claims (1)

[Scope of utility model registration request] In a linear particle accelerator, a high-voltage pulse generation section that drives an electron gun that generates charged particles, a thyristor that bypasses the electron gun by conducting an output pulse train of the high-voltage pulse generation section, and the high-voltage pulse generation section. A linear particle accelerator comprising: a control pulse generator that generates a trigger pulse for the thyristor at a settable ratio to an output pulse train of the thyristor; and a power source that generates a bias voltage that normally cuts off the thyristor.