JPS6110937B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a straight beam multi-cavity klystron structure using permanent magnets as beam focusing devices.

This type of multi-cavity klystron is shown in Figure 1a,
As shown in FIG. 1B, an example is shown in FIG. The main components include a side magnetic pole piece 4, a collector side magnetic pole piece 5, an electron gun side permanent magnet 6, a collector side permanent magnet 7, and a yoke 8 stretched between the permanent magnets 6 and 7. Because they are small, lightweight, and have high electrical performance, they have come to be widely used in a variety of applications. However, in the case of klystrons that operate at high frequencies above GHz, the operation of the klystron often becomes unstable, or the electron beam intensively heats the lower part of the collector (near the entrance). Conventional measures to solve the former of these problems include making the collector with ferromagnetic material to improve magnetic shielding and preventing electrons from moving backwards from the collector to the high-frequency circuit. There have been methods to improve unstable operation, such as increasing the thickness of the collector to improve the cooling effect of the collector as a solution to the latter problem, but each of them has advantages and disadvantages and is not a complete solution to the problem. Ta.

In order to solve these problems, in FIG. 1, the collector side magnetic pole piece 5 is made thinner to achieve appropriate magnetic saturation, and the magnetic pole tip surface of the magnet 7 to which the magnetic pole piece 5 is connected is partially exposed and inserted into the collector. A method has been proposed in which a leakage magnetic field for beam refocusing is formed to cause the electron beam to almost uniformly impinge on the upper part of the collector. It was found that this method improved the unstable operation of the klystron and localized overheating near the collector inlet. However, when this method is actually applied, the trajectory of the beam within the collector changes considerably due to variations in the strength of the magnetic field of the permanent magnet, variations in the structure of the electron gun, or variations in the characteristics of the high-frequency circuit. It was found that in some cases, the beam could centrally heat the top of the collector.

FIG. 2 shows a typical beam trajectory when there is a leakage magnetic field in the collector. FIG. 2a shows a case where the amount of leakage magnetic field is just appropriate, and the upper part of the collector is heated almost uniformly. On the other hand, b indicates a case where the amount of leakage magnetic field is too strong, that is, a case where the leakage magnetic field is generated over almost the entire length of the collector, and even at the apex of the collector with a taper angle of 45°. Because of the magnetic field, the focused beam 11 having four antinodes and nodes collides intensively, which may lead to gas release from the apex or melting of the apex. Of course, if the length of the collector is made very long, the electron beam will eventually diffuse, eliminating the risk of concentrated heating at the top, but an unnecessarily long collector is undesirable because it becomes inconvenient to handle in practical terms.

The present invention aims to solve the above-mentioned problems by processing the inner surface of the collector into a special shape, thereby preventing concentrated heating at the collector vertex.

FIG. 3 shows the shape of the inner surface of the collector according to the present invention. In Figure 3, the taper angle of the collector cone with respect to the central axis is much more acute than before, about 6
I do it every once in a while. Therefore, if the amount of leakage magnetic field inside the collector is too strong, that is, when the leakage magnetic field is generated over almost the entire length of the collector, as shown in FIG. 33% because it collides at point A, which is the second antinode of
The energy of is absorbed in part A. The remaining beam then leaves the inner wall of the collector, and at the next third antinode, point B, about 33% of the energy is absorbed by the collector. Since the energy of the beam 11 is gradually absorbed by the collector in this way, the risk of concentrated heating at the top is greatly reduced.
The ideal way to determine the taper angle of the collector shown in Figure 3 is to absorb 1/n-1 of the beam energy at the second antinode of beam 11, assuming that there are n antinodes in the collector. , even the third belly is 1/
It is determined as n-1.

The main type of multi-cavity klystron that uses a permanent magnet as a beam focusing device is a klystron in the 2 to 30 GHz band. If the taper angle with respect to the central axis of the collector cone is set to 5 degrees to 20 degrees, even if the energy distribution ratio is not at face value, it is possible to achieve a level distribution that is one step closer to this. There is no significant difference in the cooling effect of the collector due to changes in the beam trajectory due to changes in various conditions, and this is extremely effective for stable klystron operation.

[Brief explanation of the drawing]

Figure 1a is a vertical cross-sectional view showing the schematic structure of a conventional klystron, Figure b is a cross-sectional view taken along the line A-A in Figure a, and Figure 2a is an ideal view of the collector of the conventional klystron in Figure 1. A diagram showing an example of electron beam diffusion, FIG. 2b is a diagram showing the electron beam state when the leakage magnetic field in the collector of a conventional klystron is too strong, and FIG. 3 is a diagram showing the collector structure and leakage magnetic field in the present invention. FIG. 4 is a diagram showing the state of an electron beam when the beam is too strong. In the figure, 1 is an electron gun section, 2 is a high frequency circuit section, 3 is a collector, 4 is a magnetic pole piece on the electron gun side, 5 is a magnetic pole piece on the collector side, 6 is a permanent magnet on the electron gun side, 7 is a permanent magnet on the collector side, 8 indicates a yoke.

Claims (1)

[Claims] 1. An electron gun section that emits an electron beam, a high frequency circuit section where the electron beam and high frequency interact with each other, a collector that collects the electron beam after the interaction, and a focusing main unit in the high frequency circuit section. In a straight beam type klystron comprising a magnetic field and a permanent magnet-type focusing magnetic field device that generates a leakage magnetic field for refocusing in the collector, the leakage magnetic field for refocusing is generated over substantially the entire length of the collector. and a taper angle of the top conical portion inside the collector with respect to the central axis is selected to be 5 degrees to 20 degrees.