JPS5818837A - Spiral delayed wave circuit - Google Patents

Abstract

PURPOSE:To obtain an easy to manufacture spiral delayed wave circuit with excellent heat resistant characteristics by melting and joining a metal wire and a metal enclosure using a low-melting metal in a traveling-wave tube. CONSTITUTION:A spiral 1 composed of tungusten as a high-melting metal and three beryllia rods 2 are fixed by a cupro-nickel wire 3 whose surface is wound tightly. Their assembly body is inserted in a metal enclosure 4 made of cupro- nickel. Then a low-melting metal 5 with a melting point of approximately 900 deg.C is melted and joins the metal wire 3 and the metal enclosure 4. Since the outer shape of the metal wire 3 wound tightly and the inner wall shape of the metal enclosure 4 are fit to each other, the joining surface ranges over all surfaces of the inner wall of the metal enclosure 4. As a result, as compared with the spiral delayed wave circuit by the conventional ''squeeze method'', the heat resistance between the spiral 1 and the metal enclosure 4 is reduced one third to one tenth and resistance to power is improved only for the same ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improving the power durability of a helical slow wave circuit used in a traveling wave tube.

Spiral circuits are widely used as slow-wave circuits in concentrating wave tubes, but they have a higher coupling impedance to the electron beam than other types of slow-wave circuits, and their phase velocity hardly changes with frequency. This is because it has such excellent properties. A helical slow-wave circuit usually involves spirally winding a high-melting point metal such as molybdenum or tungsten, and wrapping it concentrically with the tube axis using several dielectric rods inside a metal envelope that also serves as a vacuum envelope. It is designed to support the system. The dielectric rod electrically insulates the helical melt and the metal envelope, supports them concentrically, and prevents high frequency loss that occurs when electromagnetic waves are transmitted through the helical slow-wave circuit and electron beams that pass through the circuit. It plays the role of conducting the heat generated by the spiral to the outside.

However, the thermal conductivity of dielectrics is smaller than that of metals, and large thermal resistances exist at the contact areas formed between the helix and the dielectric rod and between the dielectric rod and the metal envelope. The drawback is that the allowable power is small.

Various efforts have been made to improve the heat resistance of helical slow-wave circuits and apply them to high-power traveling wave tubes. For example, at the French painting company Thomnon C.N.F., the spiral-dielectric rod and the dielectric rod-metal envelope are joined using a low-melting metal (brazing material) to reduce the thermal resistance of the contact area. 1
The tabular structure shown in the figure is adopted (International Electron Device Meeting, 1977
A prestigious international conference held in December 2016 in Washington, D.C., USA).

Additionally, R.C.N., Inc. in the United States has adopted the configuration shown in Figure 2, in which a metal wire is wrapped around the helix and the dielectric rod, and the metal wire and metal envelope are bonded using a brazing material. (Famous magazine, Microwave Journal, vol. 16,
10, October 1973). In the first method, the spiral metal envelope must be made of plastic copper in order to prevent the dielectric rod from breaking during bonding due to the difference in coefficient of thermal expansion between the metal and the dielectric. For this reason, mechanical strength and melting point decrease, which is undesirable. In addition, the dielectric rod has
Since metallization must be applied to each helical pitch that comes into contact with the helix, high precision is required for assembly, making it very expensive. On the other hand, the second method does not have the same problems as the first method because the bonding is limited to metals, and the heat resistance of the helical slow-wave circuit is also comparable to that of the conventional "squeeze method." Very improved and excellent.

An object of the present invention is to further improve the second method described above, and to provide a complete spiral slow-wave circuit that is inexpensive, easy to manufacture, and has excellent heat resistance characteristics.

The helical slow wave circuit according to the present invention includes a spiral made of a high-melting point metal, a plurality of dielectric rods, a metal wire tightly wound and fixed around them, and an inner wall shape that matches the outer circumferential shape of the metal wire. and a metal envelope disposed coaxially with the spiral, and the metal wire and the metal envelope are fused and joined with a low melting point metal.

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 3 shows a cross-sectional view of a helical slow wave circuit according to the present invention. The helix 1 and three bars 2 made of tungsten, a high-melting point metal, are fixed by a cupnickel ring 3 tightly wound with gold around them, and the assembly is made of cupnickel. After the metal envelope 4 is attached, a low melting point metal 5 having a melting point of about 900° C. is melted to join the metal wire 3 and the metal envelope 40. The outer circumferential shape of the tightly wound metal wire 3 and the inner wall shape of the metal envelope 4 match each other, so that the joint surface covers the entire inner wall of the metal envelope 4. Therefore, the thermal resistance between the helix 1 and the metal envelope 40 is lower than that of a helical slow-wave circuit using the conventional "squeeze method."

, and the power durability has also improved by the same proportion.

One thing to note when implementing the present invention is:
The inner wall of the metal envelope 40 is precisely machined to make the clearance with the outer circumference of the metal as small as humanly possible. It is manufactured using a precision machining method.The low melting point metal 5 for joining is used in the form of a rod, which is inserted into the groove 6 cut into the metal envelope 4 shown in Fig. 4, and hydrogen Heat and melt in a furnace or vacuum furnace.

A second embodiment of the present invention is shown in Figure 5, which is the same as the first embodiment except that the number of dielectric rods 2 is four. In this case, since the contact area between the helix 1 and the dielectric rod 2 is increased, the heat resistance as a helical slow wave circuit is further improved.

In the above-described embodiments, the low melting point metal 5 for joining is used in the form of a rod, but the metal wire 3 may be plated with low melting point metal 5 gold and then heated and melted. Further, the present invention can be applied even if there are 11 dielectric rods 2 in the case of 5 or more.

As explained above, according to the present invention, it is possible to realize a helical slow wave circuit that is easy to manufacture and has significantly improved heat resistance and hence power resistance.
A spiral traveling wave tube with continuous output greater than IKW becomes possible.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views of a conventional helical slow-wave circuit with improved power durability, FIG. 3 is a cross-sectional view of a first embodiment of the present invention, and FIG. 4 is a cross-sectional view of a metal according to the present invention. Perspective view of the envelope;
FIG. 5 is a cross-sectional view of a second embodiment according to the invention. 1... Helix, 2... Dielectric rod, 3.
... Metal wire wound around and fixed around the helix and dielectric rod, 4 ... Metal envelope, 5 ... Low melting point metal for bonding, 6 ... ... A large groove on a low melting point metal rod for joining. Mine 1 Funuma 2 times

Claims (1)

[Claims] A spiral made of high melting point metal, multiple dielectric rods,
a metal wire tightly wound and fixed around the metal wire; and a metal envelope having an inner wall shape that matches the outer peripheral shape of the metal layer, and a metal envelope disposed coaxially with the spiral. A spiral slow wave circuit characterized in that the wire and the metal envelope are fused and bonded using a low melting point metal.