JPS5846516Y2 - helical traveling wave tube - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a helical traveling wave tube equipped with a helical slow wave circuit.

As shown in FIG. 1, a spiral traveling wave tube 1 includes an electron gun 2 that emits an electron beam, a helical slow-wave circuit 3 in which the electron beam and a high-frequency signal interact and the amplified high-frequency signal propagates, and a slow-wave circuit 3. A magnetic field focusing device 4 that focuses the electron beam into a certain shape along the central axis, a collector 5 that contributes to amplification and captures the electron beam that is no longer needed, and an input circuit 6 that inputs high-frequency signals from the input side. , an output circuit 7 for extracting the amplified high-frequency signal, a cooler (not shown) for dissipating heat generated in the collector 5, and the like.

Now, as shown in the figure, the helical slow wave circuit 3 consists of a helix 11 and a plurality of insulating rods 12 arranged around it, and is fixed inside the vacuum envelope 8, and both ends of the helix 11 are connected to input circuits. 6 and an output circuit 7.

In order to stabilize the operation of the traveling wave tube, a high frequency attenuator 13 is coated on the outer peripheral surface near the center of the insulating rod 12 to constitute an oscillation prevention attenuator. It is separated into an input side part and an output side part.

The metal material for the spiral 11 is generally a material having a high melting point, such as hollybdenum or tungsten.

The high frequency signal inputted from the input circuit 6 is emitted from the electron gun 2 while propagating on the spiral 11, and is transmitted to the magnetic field focusing device 4.
It interacts with the focused and shaped electron beam, is amplified, and is output from the output circuit 7 to an external circuit (not shown).

The second diagram shows how the high frequency signal is amplified along the spiral 11.
As shown in the figure, the high frequency power on the spiral 11 is once attenuated by the high frequency attenuator 13, and then increases exponentially with distance, and eventually reaches saturation.

In addition to the high-frequency power, Figure 2 also shows the characteristics of the high-frequency loss generated on the helix 11 due to the dielectric loss of the insulating rod and the skin effect within the helix 11 versus distance. 1
3, it can be seen that the high frequency power level is generated in the output side portion where the high frequency power level is high, especially in the portion several wavelengths from the output end.

High-frequency loss not only reduces the actual conversion efficiency from DC energy to high-frequency energy, but also the generated heat heats the helix 11 and releases the occluded gas in the helix 11 into the tube, reducing the vacuum inside the tube. This causes deterioration, increases noise, and further shortens the life of the tube.

Conventionally, as a method for reducing the above-mentioned high frequency loss, there has been a method of manufacturing the entire spiral 11 using a thin wire whose surface is plated with gold or copper using molybutton as a base material.

It is true that by doing this, as is clear from Table 1, the electrical resistance of the surface of the helix 11 decreases, and the skin effect decreases.
High frequency loss is reduced.

As a result, there were advantages in that the gain per unit length was increased and the efficiency of the traveling wave tube was improved.

However, since the entire surface of the helix 11 is plated with copper and gold, which have low melting points, the allowable power of the helical slow-wave circuit 3 (maximum allowable slow-wave circuit current without sputtering of the helical metal x slow-wave circuit voltage) The disadvantage was that it was not possible to obtain a large value.

That is, when the electron beam emitted from the electron gun 2 locally collides with the helical slow-wave circuit 3, the temperature of the helical slow-wave circuit 3 locally increases, causing the melt plated on the helix 11 to rise. The metal material with low points sputters on the surface of the insulating rod 12, and the high frequency waves are reflected at that part, resulting in a reduction in the high frequency amplification effect and a decrease in the high frequency output.

The present invention aims to eliminate such drawbacks, and it is based on the fact that most of the high frequency loss occurs in the part closest to the output side of the slow wave circuit, especially in the part several wavelengths from the output end.
Furthermore, we focused on the fact that the electron beam collides with the slow-wave circuit more easily at the input end, and that this part is most prone to sputtering due to its small heat capacity, and divided it into several parts in the axial direction with the high-frequency attenuator as the boundary. To provide a helical traveling wave tube that reduces high frequency loss and improves efficiency by plating the helical surface of the most output side part of a helical slow wave circuit with a metal whose electrical resistance is smaller than that of the helical base material. It is in.

Embodiments of the present invention will be described below with reference to the drawings.

The helical traveling wave tube according to the present invention has a structure similar to that shown in FIG. The surface is plated with copper, which has a lower electrical resistance than molybdenum, over a length corresponding to five wavelengths.

In other words, as shown in Fig. 3, the helix 11 wound around the winding core 14 at a predetermined pitch is subjected to chemical treatment and heat treatment, then shifted from the winding core by a length corresponding to five wavelengths, and only this portion is removed. It is placed in a plating bath, and a few μm of copper plating 15 is applied to the surface.

About improving the high frequency output of a traveling wave tube when the output side portion of the helix 11 is coated with copper plating 15, which has a lower electrical resistance than the base metal of the helix 11. 11G east traveling wave tube (helix inner diameter: 1.4φ, wire diameter: 0.2φ, helical material: molybdenum, helical length: 150 mm, helical voltage: 4 kV, and electron beam current: 40 mA).

As shown in Table 2, this result shows that if copper plating 15 is applied locally to the helical surface with a length corresponding to approximately 5 wavelengths of the operating center frequency from the output end, copper plating will be applied over the entire length of the helix. It is found that the output improvement of the traveling wave tube is almost equal to that of the traveling wave tube.

Furthermore, through experiments, it was confirmed that by applying copper plating to a length corresponding to five wavelengths, it was possible to sufficiently improve the output of the traveling wave tube, or in other words, to improve the efficiency.

Generally, the total length of the helix 11 of a traveling wave tube is 30 to 40 wavelengths in terms of the wavelength of the operating center frequency, and in the case of a molybdenum-based helix 11, the total length is 1/6 to 1/6 of the total length.
Copper plating is applied to the length of 8, and the spiral 11
The high frequency loss on the output side of the tube can be reduced, and the efficiency of the traveling wave tube can be improved by about 10%.

In this case, the length of the helix 11 from 5/6 to 7/8 is
Since the portion of the helix 11 near the input end, which is not copper-plated and is most prone to sputtering, is not plated, the drop in allowable power of the helical slow-wave circuit 3 is extremely small.

In addition, since the helix 11 is locally plated after heat treatment, the heat treatment temperature is not limited by the melting point temperature of the plating material copper or gold, and can be processed according to the material of the helix 11. Heat treatment at a sufficiently high temperature is possible in terms of the manufacturing process.

Even if the helix 11 is heated by an electron beam colliding with it during operation of the traveling wave tube, gas generation from the helix 11 is small.
It is possible to maintain a high vacuum inside the tube, which is advantageous in terms of noise and life of the traveling wave tube.

As explained above, according to the present invention, a helical traveling wave tube with reduced high frequency loss and improved efficiency can be obtained without substantially reducing the allowable power of the helical slow wave circuit.

[Brief explanation of drawings]

Figure 1 is a longitudinal cross-sectional view of a spiral traveling wave tube, Figure 2 is a characteristic diagram showing the magnitude of high-frequency power and high-frequency loss versus axial distance, and Figure 3 is a method of applying local plating to a spiral. FIG. In the figure, 1... spiral traveling wave tube, 2...
...Electron gun, 3...Spiral slow wave circuit, 4.
...Magnetic field focusing device, 5...Collector, 6
...Input circuit, 7...Output circuit, 8.
...Vacuum envelope, 11 ... Spiral, 12
...Insulating rod, 13...High frequency attenuator,
14... Winding core, 15... Copper plating.

Claims (1)

[Scope of utility model registration request] In a traveling wave tube having a helical slow wave circuit, a helical base metal is applied from the output end of the helical delay circuit to a length range corresponding to 5 to 7 wavelengths when the operating frequency of the traveling wave tube is converted into a wavelength. A spiral traveling wave tube characterized in that it is plated with a metal having an electrical resistance smaller than the electrical resistance of the tube.