GB2261319A

GB2261319A - Magnetron output probe

Info

Publication number: GB2261319A
Application number: GB9123849A
Authority: GB
Inventors: Peter Frederick Lewis
Original assignee: EEV Ltd
Current assignee: Teledyne UK Ltd
Priority date: 1991-11-09
Filing date: 1991-11-09
Publication date: 1993-05-12
Anticipated expiration: 2011-11-09
Also published as: DE4237592A1; GB9123849D0; FR2683676A1; GB2261319B

Abstract

A magnetron comprises a cathode 4, an anode 1 having a plurality of resonant cavities 3 and an elongate output probe 11 extending from the anode comprising an innermost rod 8 secured at a first end to the anode with a sleeve 11 enclosing the rod 8, the second end of the rod being spaced from the closed end 18 of the sleeve and a flexible member 15 is present between the rod and the sleeve to support the rod at a location along its length and for allowing limited relative longitudinal movement between the rod and the sleeve caused, for example, by thermal effects. The flexible member 15 may comprise a planar metal disc with a central aperture 15a within which the rod 8 is brazed and further apertures 20 may be provided to give it the required flexibility. The periphery 17 of member 15 is sandwiched between abutting end faces of sleeve part 14 and end cap 18. The thickness of flexible member 15 is selected to give adequate heat transfer from the rod 8. <IMAGE>

Description

-- 3 4, 1 VACUUM ENVELOPE FOR A MAGNETRON

The invention relates to a vacuum envelope for a magnetron. The vacuum envelope basically comprises a cathode and an anode including a plurality of resonant cavities, and the invention is particularly concerned with the output probe arrangement by which, in use, microwave radiation is emitted from the vacuum envelope when placed within a magnetic field to define the magnetron.

4 A known output probe arrangement comprises an innermost rod secured at one end to the anode and extending outwardly therefrom. A sleeve encloses the rod and is spaced apart therefrom along its length. It is known to secure the remote end of the rod within a recess at the closed end of the sleeve. The inventor has observed that such envelopes are prone to early failure, especially when used under high power conditions, and has deduced that this is due to thermal stresses set up between the rod and the sleeve.

In one aspect the invention provides a vacuum envelope for a magnetron comprising a cathode and an anode having a plurality of resonant cavities, an elongate output probe being extensive from the anode for emitting, in use, P/8769/EEV radiation from the magnetron, the probe comprising an innermost rod secured at a first end to the anode, and a sleeve enclosing the rod and spaced apart therefrom along its length, the second end of the rod being spaced from a closed end of the sleeve, a flexible member being present between the rod and the sleeve and arranged so as to provide both a means of supporting the rod at a location along its length and for allowing limited relative longitudinal movement between the rod and the sleeve.

Because the flexible member allows for limited relative longitudinal movement into the space between the rod and the closed end of the sleeve, no thermal stresses are set up which can otherwise lead to bending or distortion of the rod. Simultaneously, the flexible member provides support at a location along the length of the rod to prevent it moving from side to side, for example.

-4 The flexible member is preferably formed from a thermally conductive material, such as a metal, and is secured to a part of the sleeve that is also thermally conductive for conducting heat away from the rod and radiating it from the sleeve.

The flexible member is preferably planar and includes 6 P/8769/EEV 3 - a central through hole within which the rod is secured, e.g. by brazing. In such a case the thickness of the member is preferably selected so that the area of the side walls of the through hole contacting the rod is at least substantially equal to the cross-sectional area of the rod so as to ensure efficient heat transfer.

Because the member is secured to the rod, there will be no tendency for the rod to jam within a hole, which might be the case if the rod were allowed to slide freely through a complementary hole in a rigid support, for example. Such an arrangement might also encourage arcing. The flexible member preferably includes further holes which both provide the member with the required degree of flexibility and allow the interior of the sleeve to be evacuated on both faces of the member.

1P In order that the invention may be well understood, an embodiment thereof will now be described with reference to the accompanying diagrammatic drawings, in which:- Figure 1 is a cross sectional view through a vacuum envelope-of the invention; and Figure 2 is a cross sectional view to an enlarged P/8769/EEV scale along lines A-A of Figure 1.

A vacuum envelope for a magnetron comprises, as shown, a generally cylindrical open ended anode block 1. Anode vanes 2 extend radially inwardly to define between them a plurality of resonant cavities 3. The inner most ends 2a of the vanes are spaced from the centre of the anode block 1 to define a cylindrical space within which a cathode 4 is located. A conductor 5 is connected to each end of the cathode 4 (only one is shown in Figure 1) for supplying current to and from the cathode. Each conductor 5 extends radially outwardly of the anode block 1 and is surrounded by electromagnetic shielding 6 surmounted by an electrical terminal 7 for supplying current to each respective conductor 5.

An output probe arrangement for emitting microwave radiation comprises a metal rod 8 of circular cross section brazed or otherwise electrically and mechanically secured at one end 9 within a complementary slot formed within an anode vane 2b. The rod 8 extends radially outwardly of the anode block 1 through a circular hole 10 of relatively much larger diameter than the rod 8. A generally cylindrical sleeve arrangement 11 surrounds and encloses the rod 8, and is spaced apart therefrom along its length. The sleeve o P/8769/EEV - 5 arrangement 11 comprises a first stepped generally cylindrical metal part 12, one end of which is brazed within a stepped recess within the walls of the hole 10. A disc shaped flange 12a surrounds the first part 12 for securing the envelope within a housing, for example. A further metal cylindrical ring 13 is attached in end-to-end relation to the first part 12. Beyond that, a ceramic or similarly electrically insulating cylindrical sleeve part 14 is attached in end-to-end relation.

A A flexible planar member 15 formed from a metal material includes a central through hole 15a, as with a washer, within which the other end 16 of the rod 8 is brazed or otherwise mechanically attached (see Figure 2). The periphery 17 of the planar member is sandwiched between opposing end faces of sleeve part 14 and of an end cap 18, formed from a thermally conductive material such as a metal, which includes a central recess 19 and which closes off the free end of the sleeve 11. The thickness of the member is selected so that the sidewalls of the through hole 15a contracting the rod 8 have an area substantially equal to the crosssectional area of the rod 8. In this way heat can be efficiently transferred from the remote end regions of the rods, through the flexible member 15 to the end cap 18 from where it can be radiated.

P/8769/EEV 6 - The interior of the sleeve 11 and the resonant cavities 3 are, in use, evacuated. The flexible planar member 15 includes further holes 20, three as shown, which both provide the member with the required flexibility and allow gas communication to allow the interior of the sleeve on both sides of the member to be evacuated.

The use of a flexible member as defined can both support the free end of the rod preventing movement from side to side to maintain the rod centrally within the sleeve, while at the same time can allow relative longitudinal movement, i.e. elongation or contraction, of the rod with respect to the sleeve caused by thermal effects of up to, say, 3/4 M or more. Furthermore excess heat can be removed from both ends of the rod, as discussed above.

A Although, as shown, the flexible member is located at the end of the rod 8, it is to be understood that it may be located at any suitable position intermediate the ends of the rod. Similarly the member need not be discshaped but could be, e.g. star or otherwise shaped, or even a solid member without any holes. Although, as described, no magnets are located within the envelope, that could be the case.

1 P/8769/EEV

Claims

1. A vacuum envelope for a magnetron comprising a cathode and an anode having a plurality of resonant cavities, an elongate output probe being extensive from the anode for emitting, in use, radiation from the magnetron, the probe comprising an innermost rod secured at a first end to the anode, and a sleeve enclosing the rod and spaced apart therefrom along its length, the second end of the rod being spaced from a closed end of the sleeve, a flexible member being present between the rod and the sleeve and arranged so as to provide both a means of supporting the rod at a location along its length and for allowing limited relative longitudinal movement between the rod and sleeve.

2. A vacuum envelope, according to Claim 1, in which the flexible member and rod are formed from a thermally conductive material and the member is secured to a part of the sleeve that is also thermally conductive, whereby heat can be conducted from the rod through the flexible member and radiated from the sleeve.

3. A vacuum envelope, according to Claim 1 or 2, in which the flexible member is planar and disc shaped and P/8769/EEV - 8 includes a central through hole within which the rod is secured.

4. A vacuum envelope, according to claim 3, in which the thickness of the member is selected so that the area of the sidewall of the through holes contacting the rod is at least substantially equal to the cross-sectional area of the rod.

5. A vacuum envelope, according to any one of Claims 1 to 4, in which the flexible member is made from metal and includes further holes disposed about the rod.

6. A vacuum envelope, according to any one of Claims 2 to 5, in which the sleeve is formed from a plurality of sleeve members joined in end-to-end relation including a metal cap providing the closed end of the sleeve which, together with a sleeve member formed from an electrically insulating material, sandwiches peripheral regions of the flexible member. to secure the member to the sleeve.

7. A vacuum envelope for a magnetron substantially as described with reference to any one of the accompanying drawings.

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