JPS6211449B2 - - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetron having an annular groove at the cathode end to suppress axial oscillations that may occur during warm-up.

BACKGROUND ART Rare earth magnets such as samarium-cobalt and cerium-cobalt are used as magnets in microwave tubes, as described, for example, in US Pat. No. 3,781,592. However, such devices are generally located far enough away from the heat source within the microwave tube that relatively low temperatures such as 125° C. are not exceeded. As a result, the weight of the pole piece material increases and an additional amount of permanent magnet material is required. Additionally, when rare earth permanent magnet materials are used in air for extended periods of time, even at temperatures slightly below 125°C, the magnetic properties of the rare earth permanent magnets are altered and the amount of energy produced decreases. The operating characteristics of devices such as microwave tubes could change.

SUMMARY OF THE INVENTION According to the present invention, rare earth magnets can be operated at significantly high temperatures for long periods of time in a protected environment such as a vacuum or inert gas without permanent change in magnetic properties. This is disclosed. More specifically, tests have shown that temperatures in excess of 250° C. can be used without any substantial permanent change in the magnet material.

In the present invention, a shield is provided at the end of the cathode to prevent electrons from being emitted from the cathode to the permanent magnet, thereby suppressing the temperature rise of the magnet, and an annular groove is provided at the cathode end to prevent electrons from being emitted from the cathode to the permanent magnet. Suppresses axial mode oscillation.

According to the present invention, various applications of rare earth permanent magnets for magnetrons can use the magnetic material directly in the desired area without the need for field concentration or additional pole pieces for the return path of the magnetic flux. The reason for this advantage is that the energy production of rare earth magnetic materials is large, and that such energy production is achieved by using a heated cathode with a transverse magnetic field of several thousand gauss produced by a rare earth permanent magnet system. This is because it cannot be permanently altered by the high frequency electromagnetic field within the magnetron used.

In addition, the present invention provides a method for determining the rate at which the thermal energy radiated into the rare earth magnet material by the hot portion of the tube, such as the cathode or anode, causes thermal equilibrium of the magnet material at a temperature below the long-term degradation temperature of the magnet material. It is disclosed that the magnetic material can be cooled by conduction of heat through the support structure to the external surface structure of the tube so that it escapes at a temperature of 1.

The present invention further discloses that the permanent magnetic material can be sheathed in a thin layer of a conductive, substantially thermal, radiation reflective material such as copper, which further impedes heating of the magnetic material; are generally insufficiently thick to provide a wall between the evacuated region and ambient pressure, and to conduct heat generated by stray electron bombardment or thermal radiation away from the region. It is made thick enough to escape.

(Example) The present invention will be described below with reference to the drawings.

1 and 2, a magnetron 10 is shown comprising an anode cylinder 12 made of a material with high magnetic permeability, for example copper-coated steel. A plurality of anode members 14 extend radially inwardly from the anode cylinder 12 to a central hole 16 .
6 includes a directly heated cathode 18 using a tungsten carbide filament 20. The filament 20 is helically wound and attached at its upper end to a central support rod 22.

The lower end of the filament 20 is connected to the conductive support cylinder 2
4, the electrically conductive support cylinder 24 is disposed coaxially with respect to the support rod 22 and is sealed thereto in an insulative relationship via the ceramic cylinder 26 and caps 28 and 78.
Upper cathode end shield 30 and lower cathode end shield 32 are attached to the upper end of support rod 22 and the upper end of conductive support cylinder 24, respectively.

In accordance with the present invention, an upper annular rare earth permanent magnet member 34 and a lower annular rare earth permanent magnet member 36, such as S _n C _p5 , are disposed coaxially with the cathode 18 and are connected to the upper cathode end shield 30 and the lower cathode end shield, respectively. 32 and below.

As shown here for illustrative purposes only:
The upper permanent magnet member 34 and the lower permanent magnet member 3 are preferably polarized in the same axial direction relative to the cathode 18 to generate a single magnetic field.
6 is disposed substantially coaxially with cathode 18 and extends radially from a point inside the diameter of filament 20 to a point outside the diameter of central hole 16 .

In accordance with the present invention, the upper permanent magnet member 34 and the lower permanent magnet member 36 are arranged at the circular ends of the plurality of anode members 14 and filaments 20 to minimize the amount of magnetic material required to produce the desired magnetic field strength. placed as close as possible to the interaction space between.

According to the present invention, it is disclosed that rare earth magnets in an inert environment such as a vacuum can withstand high temperatures while maintaining stable magnetic properties. For example, temperatures in the range between 150°C and 250°C can be achieved in continuous operation, and temperatures as high as 500°C for short periods per day. For example, filament 20 and anode member 14
A magnetron such as the one shown here can be used in a microwave oven operated with a voltage between about 4000 volts. At an average current of about 300 milliamps, the heating of the tip of the anode member 14 is several hundred degrees. In addition, filament 20 is heated from 1400℃
Preferably it is heated to a temperature in the range up to 1700°C. Heat from the tip of the anode member 14 that does not produce an effective function is conducted away to the anode cylinder 12 of the anode member 14, where the anode cylinder 12
for example by fins (not shown) in contact with the outside of the However, anode member 1
Thermal radiation from the inner end of 4 and from filament 20 reflected by the bright copper surfaces of anode member 14 and anode cylinder 12 is reflected by upper permanent magnet member 34 and lower permanent magnet member 36.
It can be radiated towards. In addition, an upper cathode end shield 30 and a lower cathode end shield 3
Some stray electrons that may escape from the interaction area of the central hole 16 between the two move towards the upper permanent magnet member 34 and the lower permanent magnet member 36. Therefore, the thermal energy absorbed by the upper permanent magnet member 34 and the lower permanent magnet member 36 is, for example, 150
Preferably, it is dissipated so as not to exceed a temperature of between 250°C and 250°C.

Upper cup 44 and lower cup 4 made of a material with high thermal reflectance and thermal conductivity such as copper.
6 are arranged around the upper permanent magnet member 34 and the lower permanent magnet member 36, respectively, to reflect the radiated thermal energy towards the upper permanent magnet member 34 and the lower permanent magnet member 36 and away from the interaction region. The upper permanent magnet member 34 escapes.
Alternatively, stray electrons directed toward the surface of the lower permanent magnet member 36 are blocked. Upper cup 44 and lower cup 46 are attached to upper cover 40 and lower cover 42. These upper cover 40 and lower cover 42 are made of steel or other material with high magnetic permeability and thermal conductivity, and each of the anode cylinder 1
Attached to the upper and lower ends of 2. The upper cup 44 and the lower cup 46 connect the upper permanent magnet member 34 and the lower permanent magnet member 36 to the upper cover 4.
0 and the lower cover 42 to prevent gases within the upper permanent magnet member 34 and the lower permanent magnet member 36 from escaping during magnetron exhaust and bakeout. It has an opening 33 for opening.

Since the anode cylinder 12 and the upper and lower covers 40 and 42 are made of high magnetic permeability material, a low magnetic resistance magnetic path is formed therethrough, generated by the upper permanent magnet member 34 and the lower permanent magnet member 36. and a plurality of anode members 14 and cathodes 18
Most of the magnetic flux that passes through the electron interaction space between the tips of the is returned through the anode cylinder 12 and the upper and lower covers 40 and 42. as a result,
High densities such as 1000-3000 Gauss, e.g.
Interaction spatial magnetic flux densities of 1500 to 2000 Gauss can be achieved using relatively small rare earth permanent magnets, where these permanent magnets are placed inside the magnet's return path structure to provide extremely low leakage to the outside of the magnetron. Produces a magnetic field. The upper cup 44 and the lower cup 46 are placed in a region away from the upper permanent magnet member 34 and the lower permanent magnet member 36, e.g. 48, to prevent them from overheating.
and is attached to the upper cover 40 and lower cover 42 by spot welding or the like at the points indicated at 50. Upper permanent magnet member 34
It will be appreciated that the size, shape and spacing of the lower permanent magnet member 36 can be adjusted to produce any desired strength of magnetic field within the interaction space.

Referring now to FIG. 3, there is shown a graph of second quadrant hysteresis characteristics of various magnetic materials with the unit of magnetizing force H in Oersteds and the unit of magnetic flux density B in Gauss. Curve 50 shows a rare earth cobalt such as S _n C _p5 , which has a majority of dimensions smaller than the size that contains two magnetic domains, called “single domain type particles of S _n C _p5 ”. Preferably, it is formed from particles of S _n C _p5 . Preferably, the particles are glued together with a material containing samarium oxide or other samarium-cobalt compounds that inhibits particle growth. A more detailed description of such materials is provided in US patent application Ser. No. 416,700. For example, at a magnetic flux density of 1800 Gauss as shown at the point on curve 50, about 7500
Ersted coercive force is given. In this way, the primary reluctance is within the interaction space between the magnetic members, so that the spacing between the gaps and the like can be on the order of five times the total axial distance through the upper and lower permanent magnet members 34 and 36. . Thus, it should be understood that such magnetic materials can actually be used without a return path by using a larger weight of magnetic material. However, it is preferred that the anode cylinder 12 and upper and lower covers 40 and 42 be constructed of a material with a high strength-to-weight ratio, such as steel (the inner surface thereof may be made of a material such as 1 mil thick copper). (preferably plated with a material of high conductivity), it is economically advantageous to use these elements as return paths. The substantial improvement of rare earth magnets over alnico 5, alnico 8, ferrite, and platinum cobalt permanent magnets is illustrated by curves 54, 56, 58, and 60, respectively. At 1800 Gauss, Alnico 5 has a coercivity less than 500 Oersted, as shown by curve 54, and the total magnet length must be 4 to 5 times the air gap spacing; This considerably increases the total path length of the alnico magnet and adds substantially to its weight. Ferrite, Alnico-8, and platinum-cobalt require large magnets as well, and the best of the group is platinum-cobalt, which is extremely expensive and therefore economically impractical.

It should be understood that S _n C _p5 is shown for example only and that other rare earth cobalts such as cerium cobalt may also be used for the magnet material. By maintaining the materials of the upper permanent magnet member 34 and the lower permanent magnet member 36 at a temperature below 250° C., significant changes are made in the properties of those magnet members that substantially affect the efficiency of the magnetron. It can be operated for thousands of hours without experiencing any problems. In addition, during the internal evacuation and baking out of the magnetron after its manufacture.
It is possible to heat to temperatures as high as 400-450℃ or even 500℃.

In operation, microwave energy generated by the magnetron is extracted by the output probe 62, which probe is connected to one of the plurality of anode members 14.
opening 6 of the upper cover 40 and connected to the upper edge of the upper cover 40
4 and extends upwardly through a metal cylinder 66 coaxial with the axis of the magnetron to a seal tube 68 that vents the magnetron. A seal tube 68 is attached to the metal cylinder 66 through a ceramic cylinder 70 to provide a vacuum seal that isolates the seal tube 68 from the metal cylinder 66 and to output microwave energy to the probe 62.
provides an output aperture for radiation to a microwave energy load such as a microwave oven. Seal tube 6
8 is covered by a cap 72 to protect the tube and provide a smooth outer surface radiation.

To prevent modeding of the magnetron,
Straps 82 alternately connect the upper and lower edges of the inner ends of the plurality of anode members 14 in a known manner. If desired, upper cathode shield 3
The zero and lower cathode end shields 32 have grooves 84 inside to suppress axial mode oscillation during magnetron warm-up.

During warm-up before thermionic emission or π mode operation begins, an impact voltage may be generated due to electron vibrations reciprocating between the upper cathode end shield 30 and the lower cathode end shield 32. These electrons are axially spiraled from one shield to the other by magnetic and electric fields during warm-up. Those electrons that have gained energy are accelerated and collide with the shield, causing secondary electron emission and generating an impact voltage. However, when the grooves 84 are provided in the upper cathode end shield 30 and the lower cathode end shield 32, regions of low electric field are created there, whereby many of the secondary electrons are returned to the grooves, and axial mode oscillation is caused. suppressed.

The cathode 18 couples the conductive support cylinder 24 to the cup 7.
8. Ceramic cylindrical body 76 and metal cylindrical body 74
The lower cover 42 is securely secured within the central hole 16 by insulatively sealing the lower cover 42 through the lower cover 42 .

Although upper cup 44 and lower cup 46 are shown here as having openings 33 for evacuating the magnet member within the magnetron, if desired, upper and lower permanent magnet members 34 and 46 may be Member 36 is connected to upper cup 44 and lower cup 46 and upper cover 40, respectively.
It can also be encapsulated between the lower cover 42 and the lower cover 42.

[Brief explanation of the drawing]

1 is a longitudinal sectional view taken along line 1--1 in FIG. 2, showing a magnetron embodying the present invention; FIG. 2 is a longitudinal sectional view taken along line 2--2 in FIG. FIG. 3 is a diagram illustrating the properties of several rare earth-containing permanent magnets of the type useful for use in the present invention. Explanation of symbols, 10: Magnetron, 12: Anode cylinder, 14: Plural anode members, 16: Central hole, 1
8: Cathode, 20: Filament, 24: Support cylinder, 26: Ceramic cylinder, 28, 78: Cap, 30: Upper cathode end shield, 32: Lower cathode end shield, 34: Upper permanent magnet member, 36:
Lower permanent magnet member, 40: upper cover, 42: lower cover, 44: upper cup, 46: lower cup, 84: groove.

Claims (1)

[Scope of Claims] 1. An evacuated anode cylinder having an anode member having a plurality of resonators formed therein and surrounding a central hole accommodating a cathode; a device for generating a magnetic field across said cathode, said device comprising a rare earth permanent magnet supported entirely in a vacuum within said anode cylinder adjacent to the end of said cathode, said permanent magnet being emitted from said cathode; A magnetron comprising: a device for shielding from electrons; and a cathode end shield having an annular groove at each end of the cathode for substantially shielding a region proximate the ends of the cathode. 2. The magnetron of claim 1, wherein the rare earth permanent magnet is at an anode potential and generates a magnetic field substantially coaxial with the cathode.