JPS6314456B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of a helical traveling wave tube focusing device using a periodic permanent magnet (PPM) as an electron beam focusing device.

A traveling wave tube generally includes an electron gun section that generates an electron beam, a high frequency circuit section that interacts with the electron beam and amplifies the microwaves, a collector section that captures the electron beam, and an input section that inputs and outputs the microwaves. It consists of an output coupling section, a beam focusing device that focuses the electron beam, a tube support mechanism, etc.

As a recent general trend, there is a demand for higher output from high-power microwave tubes, and periodic permanent magnets (PPM)
Helical traveling wave tubes that are used as electron beam focusing devices are also expected to have higher output than conventional ones. However, since the helical traveling wave tube has a relatively heat-resistant structure, high output cannot be achieved without special measures.

FIG. 1 shows a cross section of a high frequency circuit section and a PPM at a high frequency output section of a helical traveling wave tube having a conventional structure. To briefly explain this figure, 1 is a helix, 2 is a helix support made of an insulator, 3 is a pipe (which also serves as a vacuum envelope), 4 is a central convex part of a pole piece, and 5 is a magnet. shows. At the high frequency output, the helix 1 is coupled once to a coaxial circuit 6 and further to a waveguide 7. In the portion where the coaxial circuit 6 is present, the magnet 5 is cut into a substantially C-shape as shown in the figure. In addition, some traveling wave tubes have a structure in which the helix is suddenly connected to the waveguide without passing through the coaxial circuit, but in this case, the amount of cut of the magnet at that part is too large, causing the beam to fail. Since it becomes very difficult to secure the magnetic field necessary for focusing, the structure shown in FIG. 1 is more common.

When increasing the output power of a helical traveling wave tube having such a structure, one problem is that the temperature of the inner conductor of the coaxial circuit increases. That is, since the coaxial inner conductor is only supported by the vacuum sealing ceramic 8, heat escape from the inner conductor is extremely poor, and the tip of the inner conductor in particular may reach an abnormally high temperature.

An object of the present invention is to provide a helical traveling wave tube having a new output extraction mechanism that improves the drawbacks of the conventional structure and can operate stably even at relatively high power levels.

The present invention provides a helical traveling wave tube using a periodic permanent magnet as a beam focusing device, in which an output extraction section is connected from the helix to a waveguide via a coaxial circuit, and the magnet is connected near the coaxial circuit section. The pole piece is characterized in that part or a plurality of places on the outer periphery thereof are cut into a flat shape.

The present invention will be explained below using the drawings.

FIG. 2 shows an embodiment of the output extraction mechanism of a helical traveling wave tube according to the present invention. In the present invention, a part of the outer side of the magnet 5' and the pole piece near the output take-out part is further cut into a flat shape as shown in the figure. The waveguide 7 is moved closer to the helix 1 side, resulting in a shorter coaxial portion. The reason for doing this is to lower the thermal resistance of the coaxial inner conductor and, in turn, to lower the operating temperature at the coaxial tip 9. Although the axial magnetic field will be reduced somewhat by cutting the magnet and pole piece on one side, it may be necessary to change the material of the magnet or reduce the PPM in areas other than the cut part.
This can be easily corrected by enlarging the outer circumference. Furthermore, if there is a concern that the axial symmetry of the PPM will be disrupted by cutting, the symmetry can be almost compensated for by cutting the side 180° opposite the cut surface in the same way, as shown in Figure 3. Further, as shown in FIG. 4, it is possible to cut it into a rectangular shape to further improve the symmetry.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the high frequency circuit and PPM of a helical traveling wave tube with a conventional structure, Figures 2 and 3
4 and 4 are cross-sectional views showing an output extraction mechanism of a helical traveling wave tube according to the present invention. 1... Helix, 2... Helix support (insulator), 3... Pipe, 4... Pole piece convex part,
5... Magnet, 6... Coaxial circuit, 7... Waveguide, 8... Ceramic for vacuum sealing, 9... Coaxial section tip.

Claims (1)

[Claims] 1. Connecting the waveguide to the coaxial circuit in a helix-shaped traveling wave tube that uses a periodic permanent magnet as a beam focusing device and has an output section connected from the helix to the waveguide via the coaxial circuit. A helical traveling wave tube characterized by cutting the outer periphery of the permanent magnet and pole piece into a flat shape, and connecting the coaxial circuit and the waveguide at this cut part.