JPS6380436A - Embedded heater type indirectly heated cathode structure - Google Patents

Abstract

PURPOSE:To prevent leg parts from being broken and to obtain excellent application to a preparatory ionizing device for nuclear fusion equipment by embedding partial end parts of auxiliary members, which are juxtaposed to the leg parts of a heater filament, into an insulating substance. CONSTITUTION:A heater filament 24 is used in pairs and conductors made of the same tungsten as the filament 24 are added as auxiliary members 26 to the leg parts of the filament 24. The filament 24 and the auxiliary members 26 are welded/fixed with each other on many positions and tightly bundled with tungsten thin wires 28. During manufacturing of an indirectly heated cathode structure, a cathode susceptor 21 made of molybdenum alloy is jointed with a holder 22 made of molybdenum and successively the filament 24 except for the most part of its leg parts together with partial end parts of the auxiliary members 26 are embedded into alumina powder. Then the alumina is sintered in a high-temperature heating process under a vacuum atmosphere, and so the filament 24 is embedded into an insulating material 23.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to an indirectly heated cathode with an embedded heater used under a high magnetic field such as in a nuclear fusion device.

(Technical background of the invention and its problems) Nuclear fusion devices, which are attracting attention as a new power generation system, use a thermionic emission cathode to generate plasma, and
It is functioning as a device. That is, the hot cathode can reliably generate plasma for causing nuclear fusion.

Fusion devices use strong magnetic fields to confine and control plasma. The strength of this magnetic field can reach several Teslas or more. Conventionally, a filament-shaped directly heated cathode has been used as the cathode for this preionization device. However, as the strength of the magnetic field increases in recent years due to higher output, the interaction between the filament ffi flow and the magnetic field causes the filament to receive force, and accidents such as deformation or wire breakage are expected. Therefore, in order to obtain stable electron emission, an embedded heater type indirectly heated electrode with a planar electron emitting surface is considered to be a desirable form.

FIG. 3 shows a cross-sectional view of the main parts of the internally heated cathode with an embedded heater.

In FIG. 3, a cathode substrate 11 having an electron emitting surface;
A heater filament 14 is disposed through an electrically insulating material 13 in the space created by the cathode support 12.
Both ends of the leg portions of the heater filament 14 are joined to heater leads 15 for electrical heating.

Incidentally, in a strong magnetic field, this cathode structure is also subjected to large stress due to the interaction between the current and the magnetic field, similar to the filament-shaped directly heated cathode. In this case, since the coil portion of the heater filament is fixed to the electrically insulating material 13 and the leg end portion is fixed to the heater lead 15, stress is concentrated on the leg portion of the heater filament. In addition, in an indirectly heated cathode with an embedded heater, when the heater filament is energized to emit electrons, the heater filament leg also generates heat, and the strength of the heater filament leg decreases due to the rise in temperature.

Therefore, severe high-temperature fatigue and stress can cause heater filament leg breakage at the end of the filament's life.

[Purpose of the invention]

The present invention prevents breakage of the heater filament leg in an embedded heater-type indirectly heated cathode, and is particularly suitable for use in a nuclear fusion device preliminary (iiiffi 5A remote location). The purpose is to provide a thermal cathode.

[Summary of the invention]

The present invention provides an implant having a cathode substrate having an electron emitting surface, a cathode support joined to the cathode substrate, and a heater filament disposed through an electrically insulating material in a container formed by the cathode substrate and the cathode support. The heater-type indirectly heated cathode assembly is characterized in that an auxiliary member is arranged in parallel to the heater filament leg to lower the electrical resistance of the heater filament leg and to improve the strength.

Therefore, according to the present invention, since the temperature rise of the heater filament leg portion when energized is suppressed and strengthened, a long-life cathode that can withstand stress caused by the interaction between current and magnetic field can be realized.

The present invention will be explained in more detail below using Examples.

[Embodiments of the invention]

A heater filament with a coil length of 160 am and a single leg length of 20111 was manufactured using tungsten wire with a wire diameter of 0.55 all, and was assembled into an embedded heater-type indirectly heated cathode as shown in FIG. 1, a cross-sectional view of the main part. To explain in detail, the heater filament 24 has a shape as shown in FIG. 2, and two heater filaments 24 are used in a set.
A length of 51 m and a length of 23 nv is added as an auxiliary member 26. The heater filament 24 and the auxiliary member 26 are welded and fixed to each other at multiple locations, and have a wire diameter of approximately 0.00.
6mm tungsten wire? It is tied tightly with 328.

The cathode structure of this example was manufactured as follows.

In FIG. 1, a cathode substrate 21 with a diameter of 20 ma+ made of a molybdenum alloy containing double a% of 1a20a is joined to a cathode support 22 made of molybdenum, and then the above-mentioned filament 24 is attached except for most of the legs. Auxiliary member 26
Embedded in alumina powder along with one end. The invasion,
The alumina was heated in a vacuum at 1800° C. for 3 hours to sinter the alumina, thereby producing an indirectly heated cathode horizontal body in which the heater filament was embedded in the electrical insulating material 23.

In order to evaluate this cathode structure, the heater filament 2
The end of the leg of No. 4 was welded to the heater lead 25 of a glass dummy tube (not shown) together with the end of the auxiliary member 26, and then the dummy tube was evacuated. Using the dummy tube thus manufactured, a strength test was conducted by applying a magnetic field to the heater filament leg. That is, a dummy tube was placed in a capacitor discharge type magnetic field generating coil that generates a maximum magnetic field strength of 4.6 Tesla, and while a filament current of 75 A was being applied, a magnetic field was generated to apply stress to the heater filament. I was able to turn the current on and off 1000 times under the conditions that the filament was energized for 3 seconds and rested for 171 seconds.
No abnormalities such as deformation were observed in the heater filament legs.

〔Effect of the invention〕

According to the present invention, the heater filament leg is reinforced by the auxiliary member, and by arranging the auxiliary member in parallel, electrical resistance is reduced, heat generation in the heater filament leg is reduced, and temperature rise is suppressed. Therefore, even when used under a strong magnetic field, there is no deformation or disconnection, and a long-life cathode structure can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view showing the cathode structure of the present invention, FIG. 2 is a perspective view of a heater filament showing the arrangement of auxiliary members according to the present invention, and FIG. 3 is a conventional indirectly heated cathode with an embedded heater. FIG. 3 is a partial cross-sectional view showing the structure. 11.21...Cathode substrate, 12.22...Cathode supporter, 13.23...Electrical insulating material, 14.24...
...Heater filament, Is, 25...
Heater lead, 26... Auxiliary member, 33... Tungsten wire. People buried (Yakei Toki no Renkakun 5) Ra (-what-
P-(Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] An embedded heater having a cathode base having an electron emitting surface, a cathode support joined to the cathode base, and a heater filament disposed through an electrically insulating material in a space created by the cathode base and the cathode support. In the indirectly heated cathode structure, an auxiliary member is provided in parallel to the leg of the heater filament, and one end of the auxiliary member is embedded in the electrically insulating material. Shaped cathode structure.