JPH0441564Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an electrode structure for use in, for example, a linac.

[Technical background of the invention and its problems]

A linear accelerator is a device that accelerates electrons using microwaves, and is used in medical applications to irradiate affected areas of the human body with high-energy radiation to destroy cancer cells.

The electrode structure used as a chamber in this linac is a combination of a pipe-shaped high-voltage electrode and a linear collector electrode inserted into the high-voltage electrode, and is an insulating tube with a metal ring at the end of the high-voltage electrode. The collector electrode is inserted through an insulating cylinder and a metal ring, and then joined to the metal ring. Also, nickel was used for the high-voltage electrodes, and a nickel-iron alloy with excellent conductivity and strength was used for the collective electrodes.

Therefore, in conventional electrode structures, soldering was used as a method of joining the collector electrode to the metal ring. In this joining method, when the collector electrode was soldered to the metal ring, molten solder or solder flux sometimes entered the inside of the insulating cylinder through the gap between the collector electrode and the metal ring.
Also, the airtightness due to solder was not sufficient. Therefore, it is affected by flux contamination and external humidity,
The electrical insulation between the high-voltage electrode and the collector electrode provided by the insulating tube deteriorated over time, causing the electrode structure to lose its function.

[Purpose of invention]

The present invention was made based on the above-mentioned circumstances, and an object of the present invention is to provide an electrode structure that greatly improves the reliability of insulation between electrodes.

[Summary of the idea]

The electrode structure of the present invention consists of a metal ring joined to an insulating cylinder that insulates between a rod-shaped (including pipe-shaped) second electrode that is inserted into a pipe-shaped first electrode;
The feature is that the electrodes are joined by brazing.

An example in which the electrode structure of the present invention is applied to a liner chamber will be described with reference to the drawings.

In the figure, reference numeral 1 denotes a pipe-shaped high-voltage electrode, which is made of, for example, nickel. Insulating cylinders 2, 2 are fitted into openings at both ends of the high voltage electrode 1, and are joined by brazing via molybdenum or tungsten metallization and nickel plating applied to the insulating cylinders. The insulating cylinders 2, 2 are made of a dense ceramic such as alumina that has high voltage resistance, high electric insulation, and vacuum tightness, and the joints with the electrodes are metalized. Metal rings 3, 3 are similarly joined to the outer end surfaces of the insulating cylinders 2, 2 by brazing. The metal rings 3, 3 are made of a ceramic bonding metal such as a cobalt-nickel-iron alloy. In the figure, reference numeral 4 denotes a linear collector electrode, which is made of a material having a thermal expansion coefficient similar to that of the material forming the high-voltage electrode 1, such as nickel. The collector electrode 4 is inserted into the high voltage electrode 1, and both ends thereof are inserted into the insulating cylinders 2, 2 and the metal rings 3, 3 and protrude to the outside. The collector electrode 4 is bonded and sealed to the metal rings 3, 3 by brazing using, for example, silver solder 5, 5.

When manufacturing this electrode structure, first, the high-voltage electrode 1, the insulating tubes 2, 2, and the metal rings 3, 3 are combined, and each is joined by brazing using, for example, silver solder in a brazing furnace. do. Next, the collector electrode 4 is inserted into the high voltage electrode 1, the insulating cylinders 2, 2, and the metal rings 3, 3, and the collector electrode 4 and the metal rings 3, 3 are connected.
and are joined and sealed by silver brazing in the same manner as above.

For brazing, an appropriate amount of brazing metal is placed at the joint, fixed with a jig, and then heated in a brazing furnace. The joints are hermetically sealed and sealed with stable, low-humidity gas, and the molten brazing filler metal passes through the gap between the collector electrode 4 and the metal rings 3, 3 into the insulating tubes 2, 2. No intrusion. Therefore, the insulation between the high voltage electrode 1 and the collector electrode 4 is maintained without being contaminated from the outside or inside of the electrode structure, and the occurrence of insulation defects can be prevented.

Since the entire electrode structure is placed in a brazing furnace and subjected to high-temperature heat treatment, each component is heated and undergoes large thermal expansion, particularly in the axial direction. Therefore, if the coefficients of thermal expansion of the materials forming the long electrodes 1 and 4 are different, since both ends of the collector electrode 4 are bonded and fixed to the metal rings 3, 3, the collector electrode 4
The collector electrode 4 may be bent and come into contact with the high-voltage electrode 1, or conversely, the collector electrode 4 may be pulled and cut internally. For example, when the collector electrode 4 is made of a nickel-iron alloy that has a higher coefficient of thermal expansion than nickel, which is the material of the high-voltage electrode 1, the collector electrode 4 is Although it undergoes large thermal expansion and contraction,
After brazing is completed and cooled, both ends are metal rings 3, 3
Since the collector electrode 4 is prevented from moving outward in the axial direction, the collector electrode 4 bends inside the high voltage electrode 1 and comes into contact with the high voltage electrode 1. For this reason, it becomes difficult to braze the collector electrode 4 and the metal ring 3 in practice. In contrast, in the electrode structure of the present invention, the collector electrode 4 is made of a material with similar thermal expansion coefficients, for example, nickel, so that both electrodes 1 and 4 thermally expand and contract by the same length in the axial direction. Therefore, the above-mentioned problems will not occur. Therefore, the collecting electrode 4 and the metal rings 3, 3 can be easily brazed together.

[Example of idea]

A high-voltage electrode made of a nickel pipe with a diameter of 4.2 mm and a thickness of 0.1 mm is connected to an insulating cylinder made of alumina ceramics with ordinary Mo metallization and Ni plating, and a cobalt-nickel-iron alloy (sealing metal for alumina). The parts were fitted and assembled, silver solder was placed at the fitting parts, and each part was integrated and hermetically sealed in a hydrogen atmosphere at approximately 820°C for 10 minutes in a brazing furnace. Next, a collector electrode made of nickel wire with a diameter of 1.0 mm was inserted into this and joined by brazing in the same manner. The brazing material in this case is eutectic silver solder (72% silver, 28% copper). As a result, the collector electrode and the metal ring are airtightly sealed at the joints of each part (airtightness 1×10 ^-9 cc/sec or less, 1 in the case of soldering) without the brazing material entering between the joints of the collector electrode and metal ring.
×10 ^-5 cc/sec). In addition, the condition of the collector electrode was inspected by transmitting X-rays through the electrode structure.
It was confirmed that no bending occurred. The insulation resistance between the high voltage electrode and the collector electrode was 1×10 ¹³ Ω or more at DC1000V. In addition, after leaving it in a humidity test tank at a relative humidity of 98% and a temperature of 100℃ for 1000 hours, it was taken out.
After cooling and drying, the insulation resistance was remeasured and found to be 1×
10 ¹³ Ω or more, and it was confirmed that there was no deterioration of the insulation properties at all.

[Effect of idea]

As explained above, according to the present invention, it is possible to obtain a high-quality electrode structure suitable for a liner cutter.

[Brief explanation of the drawing]

The drawing is a longitudinal sectional view showing the airtight electrode structure of the present invention. 1... High voltage electrode, 2... Insulating tube, 3... Metal ring, 4... Collector electrode, 5... Brazing metal.

Claims (1)

[Claims for Utility Model Registration] (1) A first electrode having a pipe shape, a second electrode having a wire shape inserted into the first electrode, and a second electrode having a wire shape inserted into the first electrode;
An electrode structure comprising: an insulating tube fixed to an end of an electrode to hold the collective electrode; and a metal ring fixed to the insulating tube and joined to the second electrode by brazing. (2) The electrode structure according to claim 1, wherein the second electrode is formed of a material having a coefficient of thermal expansion similar to that of the material of the first electrode. (3) The electrode structure according to claim 2, wherein the first electrode and the second electrode are made of nickel. (4) The electrode structure according to claim 1, which is used in a linear accelerator. (5) The electrode structure according to claim 4, wherein the first electrode is a high voltage electrode and the second electrode is a collector electrode. (6) The insulating tube is made of ceramics, and the first electrode and the metal ring are brazed to each other via a conductive layer.
The electrode structure according to claim 1, wherein each joint is vacuum-tight.