GB2259605A

GB2259605A - Magnetron with cooled pole piece

Info

Publication number: GB2259605A
Application number: GB9218232A
Authority: GB
Inventors: James A Eshleman
Original assignee: Burle Technologies Inc
Current assignee: Burle Technologies Inc
Priority date: 1991-09-03
Filing date: 1992-08-27
Publication date: 1993-03-17
Anticipated expiration: 2012-08-27
Also published as: GB2259605B; GB9218232D0

Abstract

A disc shaped magnet pole piece 16 of a high power magnetron tube 10 is cooled by shaping the pole piece 16 so that a substantial portion of its surface is in intimate contact with and bolted to a copper adapter flange 24 which is itself brazed to the liquid cooled anode assembly 27. The surfaces at the junction of the pole piece 16 and the copper flange 34 are finished to furnish good heat conduction characteristics across their junction. <IMAGE>

Description

MAGNETRON WITH COOLED POLE PIECE This invention deals generally with electric lamp and discharge devices and more specifically with the cooling of a magnet pole piece within a high power magnetron tube.

The typical structure and operation of a magnetron tube is well understood in the art. The structure always includes a cathode, an anode and magnet pole pieces, all of which are located in close proximity to each other. While the cathode and anode must, of course, be within the vacuum envelope of the tube, in most currently produced magnetrons the magnet pole pieces are also within the vacuum envelope.

As tube power ratings increase and the heat dissipation within the tubes also rise, the proximity of magnet pole pieces to the heat gerierated at the cathode and anode causes operational difficulties.

With the typical tungsten cathode operating at 2200 degrees centigrade, a nearby magnet pole piece is subjected to a considerable source of radiant eat, and if the temperature of the pole piece rises sufficiently, it can reach its curie temperature and begin to lose some of its magnetic properties, causing the tube to operate improperly. Under some circurnstances, the heat can become so severe that mechanical distortion of the pole piece can actually take place.

Typlcal present magnetron construction involves mounting the rretgnet pole pieces by means of a somewhat casual mechanical connection to the tube envelope or to a lip extending from the anode assembly. Since the only purpose of such arrangements is to locate the pole pieces relative to the anode and cathode, no heat transfer considerations are involved, and, typically, the actual contact between a pole piece and the anode is a very small lip. Furthermore, the typical mounting arrangement actually physically connects the pole piece to a part of the exterior envelope which is not cooled, and, since the pole piece magnetic material itself does not have particularly good heat transfer characteristics, there is little heat transfer through such pole piece mounting arrangements.Therefore, they do nothing to alleviate the problem of increasing temperatures of the pole piece.

The present invention essentially begins from the recognition that a heat transfer problem exists for the pole pieces of a high power magnetron tube, and it solves the problem by creating a highly efficient heat transfer path between the pole piece and the fluid cooled (e.g. water) anode assembly of the tube. This is achieved by inserting a cooling means with good heat transfer characteristics between the pole piece and the fluid cooled anode assembly, this cooling means having the function of collecting heat from the pole piece and passing it on to the anode assembly.

Preferably this is the sole function of the cooling means.

In order to ensure good heat collection, a large area of the cooling means should be in contact with the pole piece and in order to then ensure efficient transfer of the collected heat to the fluid cooled anode assembly, contact with other parts of the apparatus of less efficient cooling ability, and the outside environment, should be minimised. This is accomplished in part by having as far as possible areas of the cooling means which are not in contact with the pole piece or the anode assembly facing the vacuum enclosure of the apparatus. For example, by keeping the entire cooling means within the radial extent of the pole piece, most of the non-collecting/non-transferring surfaces of the cooling means face towards the vacuum enclosure of the magnetron tube.Preferably the anode assembly of the present invention comprises not only a fluid cooled anode but also a cooling jacket surrounding this fluid cooled anode to ensure fast and efficient removal of heat, and preferably the cooling means is attached to the cooling jacket rather than the anode itself.

Preferably, the cooling means comprises an annular copper flange brazed to the copper, water cooled, anode assembly and the formation of a substantial machined surface at the circumference of the face of the pole piece.

The pole piece machined surface is preferably bolted securely to the annular copper flange thereby forming an excellent conductive heat transfer path to the already fluid cooled anodes assembly.

operational tests how that this pole piece cooling structure permits magnetrons rated as ligh as 75 kilowatts to operate satisfactorily, with no degradation of the magnetic control characteristics due to overheated pole faces.

An embodiment of the invention will now be described by way of example only and with reference to tle accompanying drawing of which the FIGURE is a partial cross section assembly view of the portion of a magnetron tube which includes the preferred embodiment of the invention.

The FIGURE is a portion of a typical magnetron tube 10 shown in a partial cross section view through the axis of the tube 10. The major components shown are cathode assembly 12, anode 14, upper magnetic pole piece 16 and lower magnetic pole piece 18. A part of the microwave coupling portion of the magnetron is shown at 20.

Since the tube shown is of the type designed for microwave output powers up to 75KW, anode 14 is liquid cooled. This is accomplished with liquid passages 22 which are located within anode 14 and are attached to and fed liquid from liquid passages 24 within anode cooling jacket 26 which forms the outer portion of anode assembly 2. The cooling liquid is supplied through pipe 28, and the heated liquid is removed by a similar pipe. not shown.

Lower pole piece 18 of magnetron tube 10 is located near the electrical power connectors and support structure 30 of cathode 12 and is remote from the high temperature region of cathode 12. Therefore, it does not require a special cooling arrangement, Because of its cooler location and no need for special cooling, lower magnet pole piece 18 is an excellent example of the prior art means of mounting magnet pole pieces.

The contact of lower pole piece 18 with anode assembly 27 is limited to the small area of lip 32 and there is no mechanical attachment of the parts at that location, or even any assurance that the contact between anode assembly 27 and pole piece 18 is continuous. The function of lip 32 is merely to ensure that pole piece 18 is located properly along the axis of magnetron tube 10, so that the operation of pole piece 18 in the magnetic circuit is correct. Pole piece 18 is held against lip 32 only by support ring 35 which abuts its lower surface.

The preferred embodiment of the invention is shown in relation to the arrangement for attaching upper pole piece 16 to anode cooling jacket 26. Since upper pole piece 16 is located directly opcsite the end of cathode 12 which Is operating at approximately 2200 degrees centigrade. it is pole piece 16 which must be cooled in order for it to operate properly.This cooling is accomplished by conduction heat transfer from upper pole piece 16 to cooling jacket 2d'of anode assembly 27 The means by which this is accomplished is t() attach copper cooling flange 34 directly to anode cooling jacket 26 by brazing it to the top of anode cooling jacket 26 thereby forming a larger and better heat conducting support structure for upper pole piece 16 than is conventionally available. The lower face of upper pole piece 16 is also machined to create a surface which accurately matches the upper surface of cooling flange 34, so that the heat transfer between them is aided by complete and intimate contact between the mating surfaces.The assembly is completed by securely attaching pole piece 16 to cooling flange 34 with several screws 36 < only two shown) inserted through holes 38 formed in pole piece 16, with the screws threaded into threaded holes 40 in cooling flange 34.

This simple but effective structure permits the magnet pole pieces of even the highest power magnetrons to operate well below their curie temperatures, and assures reliable operation with no degradation of the magnetic characteristics.

It is to be understood that the form of this invention as shown is merely a preferred embodiment. Various changes may be made in the function and arrangement of parts; equivalent means may be substituted for those illustrated and described; and certain features may be used independently from others without departing from the scope of the invention as defined in the following claims.

For example, materials other- than copper could be used tor- cooling flange 3a. Moreover, the invention could also be used in air cooled magnetrons, by conducting heat from the pole pieces to an air cooled anode assembly. Furthermore, the structure used to conduct heat from the pole piece to the fluid cooled anode assembly could be of a configuration other than an annular flange.

Claims

CLAIMS:

1. A magnetron tube comprising: a vacuum enclosure; a fluid cooled anode assembly, at least part of which is within the vacuum enclosure; a cooling means constructed of thermally conductive material and being attached to the anode assembly whereby heat may be transferred by conduction from the cooling means to the fluid cooled anode assembly; and a magnet pole piece located at least partially within the vacuum enclosure and held in thermally conductive contact against the cooling means by attachment means included in the magnet pole piece, and the cooling means.

2. The magnetron tube of claim 1, wherein said anode assembly comprises an anode and an anode cooling jacket surrounding the anode.

3. The magnetron tube of claim 1 or 2, wherein the anode assembly is liquid cooled.

4. The magnetron tube of claim 2 or 3, wherein the cooling means is attached to the anode cooling jacket of the anode assembly.

5. The magnetron tube of claim 2, 3 or 4, wherein said cooling means is attached only to said pole piece and said cooling jacket.

6. The magnetron tube of any preceding claim, wherein said cooling means is within the radial extent of said pole piece.

7. The magnetron tube of any preceding claim, wherein the cooling means is a flange constructed of copper material which is attached to the anode assembly by means of a brazed joint between the flange and the anode assembly.

8. The magnetron tube of any preceding claim, wherein the cooling means are attached to the magnetic pole piece by means of screws passing through threaded holes in the cooling means and the magnetic pole piece.

9. The magnetron tube of any preceding claim, further including a machined surface on the magnet pole piece, the machined surface being the thermally conductive contact between the magnet pole piece and the cooling means.

10. A magnetron tube substantially as hereinbefore described by reference to the accompanying drawing.