GB2109625A

GB2109625A - Magnetrons

Info

Publication number: GB2109625A
Application number: GB08134082A
Authority: GB
Inventors: Alan Hugh Pickering
Original assignee: English Electric Valve Co Ltd
Current assignee: Teledyne UK Ltd
Priority date: 1981-11-12
Filing date: 1981-11-12
Publication date: 1983-06-02

Abstract

A magnetron is provided having a directly heated cathode 1 consisting of a conductive cylinder 2 having a layer of emission material 3 thereon. The cathode cylinder is supported at either end by conductive support members 7, 8 which in turn are supported by the pole pieces 5, 6 of the magnet to each of which a different end of the strip line secondary 15 of a transformer 12 is connected in order to supply said cathode with cathode heating current. <IMAGE>

Description

SPECIFICATION Improvements in or relating to magnetrons This invention relates to magnetrons.

A typical magnetron as at present known, comprises an electron emitter forming the cathode arrangement which requires to be accurately located and to be of such nature that its location remains stable during operation. This implies the use of a relatively massive cathode arrangement which requires considerable heating effect to raise its temperature to the required high value, typically, 800--2 5000C.

In order to provide sufficient heating effect, it is common practice to heat the emitter by radiation or conduction from a coil of tungsten wire placed next to or, inside the cathode if this comprises a hollow cylinder or cup.

Such practice involves a number of disadvantages in practice. Of these the more serious are the extent of the delay which tends to occur in heating the cathode and the relatively fragile nature of the heater coil which may exhibit a tendency to fail under shock or vibration.

One object of the present invention is to provide an improved magnetron in which one or more of the above disadvantages are avoided.

According to this invention, a magnetron includes an electron emitting cathode member and means for passing heating current through said member, whereby to directly heat said member.

Said cathode may take a number of different forms including that of a strip or rod, but preferably said cathode is cylindrical and supported at either end by cathode support members which are arranged to conduct said heater current.

Normally in this case said cathode comprises a cylindrical member of conductive material carrying a layer of electron emissive material thereon.

Preferably said layer of electron emissive material extends over a length of said cathode cylindrical member approximately corresponding to the axial length of an anode member which coaxially surrounds said cathode.

Preferably said cathode support members are of an electrically conductive material, and are supported by pole pieces and through which also said heater current is arranged to pass.

Preferably said heater current is provided by a transformer having a secondary comprising a conductive strip one end of which is connected to a pole piece to one end of said cathode cylinder and the other end of which is connected to a second pole piece to the other end of said cathode cylinder whereby said heater circuit comprises said conductive strip, said pole pieces, said cathode support members and said cathode cylinder. Said heater circuit may also comprise electrically conductive closure members at either end of said magnetron, beyond said pole pieces and between said pole pieces and the respective ends of said transformer secondary conductive strip.

Said transformer may be arranged to be supplied in operation from an A.C. supply or via a transistor oscillator for example, from a D.C.

supply.

Preferably any such transistor oscillator is integral with said magnetron.

The invention is further described with reference to the accompanying drawing which is a cross-sectional diagram of one example of magnetron in accordance with the present invention.

Referring to the drawing the magnetron includes a cathode 1 which comprises a cylindrical member 2, upon the outer surface of which is a layer 3 of electron emitting cathode material.

The cathode 2 is surrounded by an annular anode 4, both being co-axial about axis X. As will be seen, the layer 3 of cathode emitting material extends on the cathode cylinder 2 over the axial length of the anode 4.

On either side of the anode 4 are shaped soft iron pole pieces 5, 6 having hollow interiors in which cathode support members 7, 8 are located, which support members in turn support and locate the cathode cylinder 2, as known per se.

The anode 4 is carried by an anode support member 9, 10 which pass through and are themselves supported by an annular member 11 of electrically insulating material. Member 11 is in turn carried by the pole pieces 5, 6. One of the anode support members that referenced 9, is provided as a magnetron output electrode.

Not shown are external magnets provided in operation to produce the magnetic field which is collimated and shaped by the pole pieces 5, 6.

Unlike conventional magnetrons of otherwise similar construction, the magnetron illustrated in the drawing contains no heater element within the cathode cylinder 2. The cathode is in fact of the directly heated kind, there being provided means for passing the relatively large current required through the cathode, as now to be described, to provide the required operating temperature. The required cathode heating current is arranged to pass through the cathode support members 7, 8 which are of electrically conductive material, in this case copper. In order to generate the required current a transformer 12 is provided in the base (as viewed) of the magnetron.

The transformer 12 consists of a magnetic core 13 of annular form. Part of the core 13 is surrounded by a wire wound primary coil 14 whilst diametrically opposite primary coil 14 is a strip wire secondary 1 5. Strip wire secondary 15 is provided to continue up one side of the magnetron, with insulators such as those referenced 16, 1 7 being provided where necessary, to contact pole piece 5 via the intermediary of a conductive end closure plate 18.

The other end of the secondary 1 5 is electrically connected to the pole piece 6 via the intermediate of a conductive end closure plate 1 9.

The path for cathode heating current is thus via the continuation of the strip secondary 1 5, through end closure plate 18, pole piece 5, cathode support member 7, the cylindrical cathode 1, cathode support member 8, end closure plate 1 9 and pole piece 6 back to the other end of the secondary 1 5.

As will be appreciated the constituent parts of the magnetron which form the path for heater current are inherently robust and are readily adapted to carry the amount of current required for the functioning of the directly heated cathode arrangement.

Claims

1. A magnetron including an electron emitting cathode member and means for passing heating current through said member whereby to directly heat said member.

2. A magnetron as claimed in claim 1 and wherein said cathode is cylindrical and supported at either end by cathode support members which are arranged to conduct said heater current.

3. A magnetron as claimed in claim 2 and wherein said cathode comprises a cylindrical member of conductive material carrying a layer of electron emissive material thereon.

4. A magnetron as claimed in claim 3 and wherein said layer of electron emissive material extends over a length of said cathode cylindrical member approximately corresponding to the axial length of an anode member which coaxially surrounds said cathode.

5. A magnetron as claimed in any of claims 2 to 4 and wherein said cathode support members are of an electrically conductive material and are supported by pole pieces and through which also said heater current is arranged to pass.

6. A magnetron as claimed in claim 5 and wherein said cathode support members are of copper.

7. A magnetron as claimed in claim 5 or 6 and wherein said heater current is provided by a transformer having a secondary comprising a conductive strip one end of which is connected to a pole piece to one of said cathode cylinder and the other end of which is connected to a second pole piece to the other end of said cathode cylinder whereby said heater circuit comprises said conductive strip, said pole pieces, said cathode support members and said cathode cylinder.

8. A magnetron substantially as hereinbefore described with reference to the accompanying drawing.

8. A magnetron as claimed in claim 7 and wherein said heater circuit also comprises electrically conductive closure members at either end of said magnetron, beyond said pole pieces and between said pole pieces and the respective ends of said transformer secondary conductive strip.

9. A magnetron as claimed in claim 7 or 8 and wherein said transformer is arranged to be supplied in operation from an A.C. supply.

10. A magnetron as claimed in claim 7 or 8 and wherein said transformer is arranged to be supplied in operation via a transistor oscillator from a D.C. supply.

1 A magnetron as claimed in claim 10 and wherein said transistor oscillator is integral with said magnetron.

12. A magnetron susbstantially as herein described with reference to the accompanying drawing.

New claims or amendments to claims filed on 21st May 1982 Superseded claims 1-12 New or Amended Claims:-

1. A magnetron including a generally elongate electron-emitting cathode member supported at either end by electrically conductive cathode support members themselves supported by electrically conductive pole pieces, and means for passing heating current through said cathode member via said support members and pole pieces whereby to directly heat said cathode member, wherein said heating current is provided by a transformer having a secondary comprising a conductive strip one end of which is connected via a pole piece and cathode support member to one end of said cathode member and the other end of which is connected via a second pole piece and cathode support member to the other end of said cathode member, whereby the heater circuit comprises said conductive strip, said pole pieces, said cathode support members and said cathode member.

2. A magnetron as claimed in claim 1 and wherein said cathode member comprises a cylindrically tubular member of electrically conductive material carrying a layer of electronemissive material thereon.

3. A magnetron as claimed in claim 2 and wherein said layer of electron-emissive material extends over a length of said cathode member approximately corresponding to the axial length of an anode member which co-axially surrounds said cathode.

4. A magnetron as claimed in any of claims 1 to 3 which also includes electrically conductive closure members at either end thereof beyond said pole pieces, and wherein said heater circuit additionally comprises these closure members between said pole pieces and the respective ends of said conductive strip.

5. A magnetron as claimed in any of claims 1 to 4 and wherein said transformer is arranged to be supplied in operation from an A.C. supply.

6. A magnetron as claimed in any of claims 1 to 4 and wherein said transformer is arranged to be supplied in operation via a transistor oscillator from a D.C. supply.

7. A magnetron as claimed in claim 6 and wherein said transistor oscillator is integral with said magnetron.