JPH0117082Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a traveling wave tube electron beam focusing device using a periodic permanent magnet (PPM) as an electron beam focusing device.

A traveling wave tube is an electron gun that emits an electron beam, a collector that captures the electron beam, a slow wave circuit that amplifies the circuit wave through interaction with the electron beam, and an input that allows the circuit wave to enter the slow wave circuit without loss. It consists of a coupling section, an output coupling section for transmitting the circuit wave from the slow wave circuit section to the load without loss, and an electron beam focusing device that provides a magnetic field for focusing the electron beam.

Electron beam focusing using PPM is often used in helical traveling wave tubes, which have a relatively simple slow-wave circuit structure and a relatively small outer diameter, but can be made smaller and lighter. It is also used in coupled cavity traveling wave tubes because it is easy to use and handle.

Here, we will discuss a helical traveling wave tube as an example. Generally used helical traveling wave tubes have helices (helical lines) that are thermally weak, so when designing a PPM that focuses electron beams, consideration must be given to maintaining sufficiently good electron beam transmission characteristics. Must be. Normally, the magnetic field strength provided by PPM is designed to be approximately twice as strong as the Brilliant focusing magnetic field strength. Further, the strength of the magnetic field crossing the cathode is determined so that the electron beam passes through the slow wave circuit section stably and with as little beam ripple as possible.

In this way, the magnetic field strength of PPM is composed of the magnetic field strength crossing the cathode, the uniform magnetic field strength part, the transition region thereof, and the magnetic field strength crossing the collector part. In the case of a helix type traveling wave tube, as mentioned in the section on light, the helix is thermally weak, so if the electron beam transmission characteristics are not maintained well, in the worst case, the helix will burn out and the reliability of the traveling wave tube will drop significantly. It is something. Therefore, when designing a helical traveling wave tube, the PPM design will significantly reduce the reliability of the traveling wave tube unless sufficient consideration is given.

The present invention achieves stability of the electron beam by making the outer diameter of the pole piece that constitutes the PPM smaller than the outer diameter of the permanent magnet by at least one point in order to maintain a good magnetic field in the uniform magnetic field strength part of the PPM. The present invention provides a traveling wave tube characterized by:

FIG. 1 shows a commonly used traveling wave tube electron beam focusing device. In FIG. 1, the focusing device (PPM) consists of a plurality of pole pieces 1 and a plurality of permanent magnets 2. Further, input/output couplers 3 are provided almost at both ends of the slow wave circuit. The input/output coupler 3 is normally connected to the outside through a part of one permanent magnet. The permanent magnet at the location where the input/output coupler 3 is provided is partially cut out as shown in FIG. Therefore, the magnetic field strength obtained from this magnet is lower than that of other parts, and uniformity of the magnetic field strength cannot be obtained. To compensate for this, the outer diameter of the permanent magnetic field in this area is increased to keep the magnetic field strength uniform.

However, in order to maintain good electron beam transmission characteristics, a traveling wave tube with a support structure as shown in FIG. 3 has been devised. This structure increases the mechanical strength of the long and thin helical traveling wave tube, and at the same time
By controlling the outer diameter dimensions of the permanent magnets 2 and the pole piece 1 with high precision, it is possible to obtain good concentricity between the plurality of permanent magnets 2 and the pole piece 1, and as a result, it is possible to maintain good electron beam transmission characteristics. .
It also has the advantage that the heat generated in the slow wave circuit section can be dissipated well and the stability of the traveling wave tube can be sufficiently obtained.

However, the permanent magnet on which the input/output coupler 3 is installed requires a notch as shown in FIG. As a result, the magnetic field strength at this portion decreases, making it impossible to maintain good electron beam transmission characteristics.

However, when the support structure shown in FIG. 3 is used, it is not possible to increase the outer diameter of the permanent magnet 2 in the input/output coupler 3 to obtain uniformity in magnetic field strength.

In the present invention, the outer diameter of at least one of the pole pieces 1 installed on both sides of the notched permanent magnet 2 shown in FIG. 2 is made smaller than the outer diameter of the permanent magnet 2. It is possible to increase the magnetic field strength and maintain good electron beam transmission characteristics.

By adopting this invention, it is possible to increase mechanical strength, maintain good concentricity between multiple permanent magnets and pole pieces, and improve heat dissipation in the slow wave circuit section, as shown in Figure 3. Even in this structure, it is possible to obtain a good magnetic field strength at the extraction part of the input/output coupler, and to maintain good electron beam transmission characteristics.

[Brief explanation of drawings]

FIG. 1 shows a conventional helical traveling wave tube electron beam focusing device. FIG. 2 shows the permanent magnet at the input/output coupling section. FIG. 3 shows an electron beam focusing device according to the present invention. 1...Pole piece, 2...Permanent magnet, 3...
Input/output coupler, 4... circuit support.

Claims (1)

[Scope of utility model registration request] In a traveling wave tube using a periodic permanent magnet made of a rare earth monocobalt system as an electron beam focusing device, the outer diameter of at least one pole piece of the focusing device consisting of a pole piece and a permanent magnet is smaller than the outer diameter of the permanent magnet. A traveling wave tube characterized in that it has a small focusing device.