JPH03236862A - Medical electron accelerating device - Google Patents

Abstract

PURPOSE:To deflect a beam with excellent reproducibility not being affected by fluctuations in magnetic flux density by hysteresis by providing a deflecting electromagnet for deflecting in the vertical direction an electron beam from an accelerating tube, a constant current power source for exciting the deflecting electromagnet, a processor for controlling the constant current power source, and a voltage generator. CONSTITUTION:An electromagnet 4A is excited when supplied with a current by a constant current power source 3. The constant current power source 3 has its current output controlled by the output voltage of a voltage generator 2. A processor 1 controls the voltage generator 2 in such a manner that the output voltage of the voltage generator 2 is freely varied. Each time a medical electron accelerating device for generating desired radiation output energy is set up, the processor 1 controls the voltage generator 2 so that the constant current power source 3 outputs an exciting current Is for adjusting the magnetic flux density of the deflecting electromagnet 4 to saturated magnetic flux density Bs. Until the magnetic flux of the deflecting electromagnet 4 is sufficiently saturated (for the duration of about 6 minutes in an actual case), the exciting current Is is applied to the deflecting electromagnet 4, and then the exciting current Is is automatically lowered and fixed to an exciting current Ip by which desired magnetic flux density Bp is obtained.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is applied to medical electron accelerators, and particularly to electromagnets for deflecting electron beams from an acceleration tube or for magnetrons, which are high-frequency sources for accelerating electrons. The present invention relates to a method of setting magnetic flux density determined for each output energy.

[Conventional technology]

Conventionally, this type of medical electron accelerator has been simply controlled by simply applying a current to the electromagnet to obtain a desired magnetic flux density.

[Problem to be solved by the invention]

The saturation excitation characteristics of an electromagnet are shown in Figure 3, a graph (B
0-8-Br-8' ・
It has a hysteresis characteristic shown by the -Br-S curve. In the figure, Bs is the saturation magnetic flux density, and Br is the residual magnetic flux density. Since the magnetic flux of an electromagnet in a bending electromagnet or a magnetron is unidirectional, the diagonally shaded range surrounded by 0-8-Br in the figure is used.

According to the conventional method described above, the magnetic flux density Bp for a desired excitation current rp is changed each time the excitation current changes from zero to rp.
It varies depending on the history of band increase until it becomes , and there is a possibility that the output beam from the accelerator tube cannot be deflected correctly or the output of the magnetron may fluctuate. This causes problems such as fluctuations in the output of radiation extracted in the vertical direction and deviations in the beam axis.

[Means to solve the problem]

A first aspect of the medical electron accelerator of the present invention is a medical electron accelerator having an electron beam output or an X-ray output of a plurality of energies, which includes a deflecting electromagnet that deflects an electron beam from an accelerating tube in a vertical direction. , a constant current power supply that excites the deflection electromagnet, a processor that excites the constant current power supply, and a voltage generator.

A second invention of the medical electron accelerator of the present invention is a medical electron accelerator having electron beam output or X-ray output of a plurality of energies, which has a magnetron as a high frequency source for accelerating electrons, Electromagnets used in magnetrons,
The device includes a constant current power source that excites the electromagnet, a processor that controls the constant current source, and a voltage generator.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of essential parts of a first embodiment of the present invention. Output beam 102 from accelerator tube 101 can be switched to multiple energies. The electromagnet 4A that deflects the output beam 102 has a magnetic flux density uniquely determined for each energy, and deflects the beam in a determined direction (here, rotated counterclockwise toward the right in FIG. 1).

The electromagnet 4A is supplied with current by the constant current power source 3 and is excited. The current output of the constant current power supply 3 is controlled by the output voltage of the voltage generator 2. The processor 1 controls the voltage generator 2 so as to arbitrarily vary the output voltage of the voltage generator 2. In this embodiment, each time the medical electronic accelerator is set up to generate a desired radiation output energy, the processor 1 adjusts the magnetic flux density of the bending electromagnet 4 so that the excitation current Is becomes a constant current, so that the magnetic flux density becomes the saturation magnetic flux density Bs shown in FIG. The voltage generator 2 is controlled to output from the power supply 3. This excitation current Is is applied while the magnetic flux of the bending electromagnet 4 is sufficiently saturated (about 6 seconds in the embodiment), and then it is automatically lowered and fixed to an excitation current Ip that provides the desired magnetic flux density Bp. These series of operations are incorporated into the setup sequence and are all performed automatically.

As is clear from FIG. 3, when the magnetic flux density is lowered from the saturation point (Bs), the magnetic flux density with respect to the excitation current is uniquely determined on the 5-Br saturation curve.

FIG. 2 is a block diagram showing a second embodiment of the invention. The magnetron 5 emits an output proportional to the magnetic flux density of the electromagnet 4B. This magnetic flux density is varied according to a plurality of radiation output energies. Constant current power supply 3 supplies current to electromagnet 4 to excite it. The current output of this constant current power supply 3 is controlled by the output voltage of the voltage generator 2. The processor 1 controls the voltage generator 2 so that the output voltage of the voltage generator 2 can be arbitrarily varied.

In the second embodiment, each time the medical electronic accelerator is set up to generate a desired radiation output energy, the processor 1 determines the magnetic flux density of the electromagnet 4 so that the excitation current Is becomes the saturation magnetic flux density Bs shown in FIG. The voltage generator is controlled to output from the current power source 3. This excitation current Is is applied while the magnetic flux of the electromagnet 4 is sufficiently saturated (in the embodiment, about 6
seconds), followed by an excitation current I that obtains the desired magnetic flux density Bp.
p is automatically lowered and fixed.

These series of operations are incorporated into the setup sequence and are all performed automatically. Furthermore, as is clear from FIG. 2, when the magnetic flux density is lowered from the saturation point (Bs), the magnetic flux density with respect to the excitation current is uniquely determined on the 5-Br saturation curve.

[Effects of the Invention] As explained above, the present invention saturates the magnetic flux density of the electromagnet every time it is set up and then fixes it at a desired value. Therefore, the reproducibility is not affected by fluctuations in the magnetic flux density due to hysteresis. Excellent beam deflection is possible. This has the effect of stabilizing the output radiation of the medical electron accelerator.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the excitation current control of the bending electromagnet of the medical electron accelerator of the present invention, FIG. 1 is a block diagram showing the configuration of the first embodiment of the present invention, and FIG. FIG. 3 is a block diagram showing the configuration of the second embodiment, and FIG. 3 is an excitation characteristic curve of the electromagnet. DESCRIPTION OF SYMBOLS 1...Processor, 2...Voltage generator, 3...Constant current power supply, 4A/4B...Bending electromagnet, 5...Magnetron, 101...Acceleration tube, 102...Output beam .

Claims (1)

[Scope of Claims] 1. A medical electron accelerator having electron beam output or X-ray output of a plurality of energies, including a deflecting electromagnet that deflects an electron beam from an accelerating tube in a vertical direction, and exciting the deflecting electromagnet. 1. A medical electronic accelerator comprising: a constant current power supply; a processor that controls the constant current power supply; and a voltage generator. 2. A medical electron accelerator having multiple energies of electron beam output or A medical electronic accelerator comprising a constant current power source, a processor that controls the constant current source, and a voltage generator.