JPH02168537A - Cyclic magnetic field generating device - Google Patents

Abstract

PURPOSE:To easily provide a uniform on-axis mag. field distribution by arranging a plurality of shims having a body in specific shape at a certain spacing in the axial direction, and using permanent magnets in the same shape which allows tight fit in the space between adjoining shims. CONSTITUTION:A plurality of shims 12 are arranged at a certain spacing on one axis with spacers 13 interposed. The body 12A of each shim 12 reduces its thickness in axial direction from the internal end toward the external so as to assume a taper. A plurality of ring-shaped permanent magnets 11 in an identical form are fitted between adjoining shims. The permanent magnets 11 are in close contact with respective shims. Thereby the magnetic resistance to the flux leaking to the outside can be increased compared with the case in which the thickness in the axial direction is uniform, and accordingly the leak mag. field is reduced. This lessens the influence of the leak mag. field upon the on-axis mag. field distribution, which will thus be more uniform.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates primarily to improvements in periodic magnetic field generators used for converging electron beams in traveling wave tubes.

[Conventional technology]

FIG. 3 is a schematic cross-sectional view of a periodic magnetic field generating device for a traveling wave tube described in, for example, Japanese Utility Model Publication No. 51-49874. In the figure, l is an annular permanent magnet (the front view is shown in FIG. 4), 2 is a shim, 3 is a spacer, and 4 is an envelope consisting of the shim 2 and spacer 3.

This periodic magnetic field generator consists of a permanent magnet 1 magnetized in the axial direction.
are arranged between shims 2 so that the same polarity faces each other, and a periodic magnetic field (a magnetic field having a magnetic field distribution as shown in FIG. 6) is generated on the axis.

Even if the size and characteristics of each permanent magnet 1 are equal, the periodic magnetic field will have uneven peak values as shown in Figure 5, and it is difficult to have an even distribution. As shown in Fig. 6, the magnetic field distribution generated on the axis when only one permanent magnet 1k is used is also generated between the shims 2a and 2b due to the leakage magnetic field 5. There is. When a large number of permanent magnets 1 are combined, the leakage magnetic fields influence each other, and the total becomes the axial magnetic field distribution, but towards the end of the device, the number of neighboring permanent magnets 1 This is because the total magnitude of the leakage magnetic field varies from place to place, causing inconsistency. When this magnetic field distribution is uneven, a part of the electron beam is housed coaxially within the envelope 4 and is insulated and supported by the slow wave circuit structure (
As it progresses through the helix (not shown), it collides with the wax. This collision increases the temperature of the helix and generates gas, which adversely affects the electrical properties of the traveling wave tube device.

[Problem to be solved by the invention]

In order to prevent the above-mentioned collision of the electron beam, conventionally, iron pieces were attached to the outer periphery of the permanent magnet 1 and shims on the envelope of the traveling wave tube device, and the magnetic field distribution was adjusted to prevent the above-mentioned collision of the electron beam from occurring. However, since the installation of this iron piece is different for each traveling wave tube, it is troublesome and takes time and effort.

This invention was made to solve the above problem.
It is an object of the present invention to provide a periodic magnetic field device that can easily obtain a uniform axial magnetic field distribution compared to the prior art.

[Means to solve the problem]

In order to achieve the above-mentioned object, in the invention of claim 1, the shim of the envelope has a tapered shape in which the thickness in the axial direction becomes narrower at the outer peripheral part, and the side surface of the shim of the magnet is aligned with the tapered shape. According to the second aspect of the invention, the magnet is a combination of a plurality of magnet pieces having the same shape.

[Effect]

In the first aspect of the invention, since the axial thickness of the outer circumferential portion of the shim is reduced, the magnetic resistance to the magnetic flux leaking to the outside is increased, and the influence of the leaked magnetic field is significantly reduced compared to the prior art. Furthermore, in the invention of claim 2, the annular magnet can be assembled with selected magnet pieces to obtain a uniform field distribution on the axis before being attached to the traveling wave tube device, so that the adjustment after the above-mentioned attachment is possible. This becomes unnecessary and the adjustment work becomes easy.

〔Example〕

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

In FIG. 1, 1) is an annular permanent magnet magnetized in the axial direction, 12 is a shim, 12A is a shim main body 12B is a base of the shim, 13 is a spacer, and 14 is an envelope. This envelope 14! : [Several shims 12 are sandwiched between spacers 13 and sequentially connected coaxially, and the shim body portions 12 are arranged in a protruding manner at a predetermined distance in the axial direction from the outer periphery. The shim main body 12A has a tapered shape in which the thickness in the axial direction decreases as it goes from the base side to the outer peripheral end. A trapezoidal annular space G smaller than the axial length is defined. The annular permanent magnets 1) have a shape that tightly fits into this annular space G, and are arranged so that the same polarity sides face each other.

In this configuration, since the thickness of the outer end of the shim main body 12A is smaller than that of the base, the magnetic resistance against the magnetic flux leaking to the outside is lower than in the conventional case where the thickness in the axial direction is uniform. The leakage magnetic field can be reduced accordingly.

Therefore, the influence of the leakage magnetic field on the axial magnetic field distribution is reduced, and the axial magnetic field distribution can be made more uniform than in the past.

In the above embodiment, the shim main body 12A has a tapered shape, but the shim main body 12A has a smaller thickness at the outer end than the axial thickness on the base side. It is sufficient if the shape is symmetrical with respect to the center.

FIG. 2 shows another embodiment of the present invention, in which a combination of a plurality of magnet pieces IA of the same shape is used as the annular permanent magnet 1. Many types of magnet pieces IA with different magnetic forces are prepared.

When carrying out this invention, permanent magnets are installed in an envelope with shims interposed between them, and the axial magnetic field is measured with a magnetic field measuring device, so that the axial magnetic field distribution has a desired degree of uniformity. Each magnet piece IA is replaced and adjusted, and after the adjustment is completed, it is reattached to the envelope of the traveling wave tube device.

In this way, after it is attached to the traveling wave tube device, there is no need for adjustment or only fine adjustment is required, so that the effort and time required for adjustment can be reduced.

〔Effect of the invention〕

As explained above, in this invention, since the magnet formed by the magnet piece does not require substantially any adjustment after being attached to the traveling wave tube device, it is possible to make the adjustment to make the axial magnetic field distribution uniform compared to the conventional one. By reducing the thickness of the outer end of the shim, it is possible to reduce the influence of leakage magnetic field, making it easier to obtain a uniform axial magnetic field distribution and eliminating the need for adjustment. All it takes is a little adjustment.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing an embodiment of the present invention, Fig. 2 is a front view showing the main parts of an embodiment of another invention, Fig. 3 is a sectional view showing a conventional device, and Fig. 4 is a sectional view showing the above-mentioned conventional device. FIG. 5 is a front view of the annular magnet in the device, FIG. 5 is a diagram showing the axial magnetic field distribution in the conventional device, and FIG. 6 is a diagram showing the leakage magnetic flux in the conventional device. In the figure, 1ll-ring magnet, 12- shim, 12
A~・-Shim body, 13-・-Spacer, 14・・-
envelope. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (2)

[Claims] (1) In a periodic magnetic field generating device in which an annular magnet is attached to each of the shims protruding in the radial direction at a predetermined axial distance from the outer circumference of the envelope, the shims are located at the outer end of the shim. A periodic magnetic field generator characterized in that the magnet has a shape in which the axial thickness is smaller than the axial thickness of the base, and a shim side surface of the magnet has a shape that follows the shape. (2) In a periodic magnetic field generator in which annular magnets are attached to each of the shims protruding from the outer periphery of the envelope at a predetermined distance in the axial direction, the magnets are made of a plurality of magnet pieces of the same shape. A periodic magnetic field generator characterized by comprising a combination body.