GB2259180A

GB2259180A - Cooling magnetrons

Info

Publication number: GB2259180A
Application number: GB9123906A
Authority: GB
Inventors: Peter Frederick Lewis
Original assignee: EEV Ltd
Current assignee: Teledyne UK Ltd
Priority date: 1991-08-30
Filing date: 1991-11-11
Publication date: 1993-03-03
Anticipated expiration: 2011-11-11
Also published as: FR2686190A1; DE4228688A1; GB9123906D0; GB9118651D0; GB2259180B

Abstract

A magnetron including a cylindrical anode block 1 having a plurality of internal resonant cavities 4 has a pair of enclosed coolant channels 18, 19 extending about the block and connected to a respective coolant inlet and a coolant outlet, wherein the channels 18, 19 are connected to each other along their length by one or more connecting passageways 22 dimensioned relative to the channels to provide a restriction so as the enhance coolant flow velocity through the connecting passageway. As shown, grooves formed in the outer surface of the anode and separated by an annular wall 20 cooperate with a cylindrical sleeve 21 surrounding the anode block to define channels 18, 19 and the annular passageway 22 of smaller dimension which interconnects the channels. Alternatively, fig.3 (not shown), a plurality of longitudinally extending connecting passageways may be spaced circumferentially about the anode block. <IMAGE>

Description

2 2 5 91 -30 MAGNETRON The invention relates to a magnetron, and in

particular to a magnetron of relatively high power for which there is a requirement for efficient cooling. It is known to provide fins by which the magnetron can be cooled by a flow of air, but a need exists for an efficient cooling arrangement which is reliable and easy to provide.

The invention provides a magnetron comprising a cathode and an anode, the anode comprising a substantially cylindrical anode block having a plurality of internal resonant cavities, a pair of enclosed channels extending about the block, a coolant inlet being present in one of the channels and a coolant outlet being present in the other, the channels being connected to each other along their length by one or more connecting passageways dimensioned relative to the channels to provide a restriction so as to enhance coolant flow velocity, in use, through the or each passageway.

Each of the channels can be provided on the anode block by a straight forward turning operation at the same time as the anode block is made. The or each connecting P/8746/EEV passageway provides a restriction which, because of the locally enhanced velocity of the coolant, ensures that heat may be efficiently removed in the region of the passageway, and uniformly from the anode block.

In a preferred embodiment a sleeve surrounds the anode block to enclose the channels, the anode block including an outwardly extending wall which separates the channels from one another and which, together with the sleeve, defines a connecting passageway.

It is also preferred that the channels and the separating wall are integrally formed with the outer most surface of the anode block. Each channel preferably surrounds an end region of the set of resonant cavities of the anode, and the or each connecting passageway is located mid-way between the end regions. The dimensions of the or each connecting passageway are preferably selected so that turbulent flow can be induced in use, within the coolant passing therethrough. In this way heat can be efficiently removed at a greater rate where the requirement for cooling is greatest.

Although the connecting passageway may comprise an annulus defined between a wall separating the channels and a 1 P/8746/EEV sleeve enclosing the anode block, in an alternative construction a plurality of longitudinally extensive connecting passageways are circumferentially spaced about the anode block. Such longitudinally extensive connecting passageways may be provided by means of a plurality of longitudinally extending circumferentially spaced ribs present on the top of the separating wall, and which serve both to space the wall from the sleeve, and to subdivide the annular passageway into a plurality of relatively smaller passageways.

In order that the invention may be well understood, an embodiment thereof will now be described by way of example plates reference to the accompanying drawings, in which:

Figure 1 is a side view of a magnetron with the end caps removed to reveal the interior; 0 Figure 2 is a sectional view along line A-A of Figure 1; and Figure 3 is a cross-section view through an alternative embodiment in which the internal and other features have been omitted for clarity.

P/8746/EEV As shown in the drawings, a vacuum envelope for a magnetron comprises a generally cylindrical anode block 1 which includes an open ended cavity 2. Circumferentially spaced anode vanes 3 extend inwardly from the anode block 1 to define a plurality of circumferentially spaced resonant cavities 4. As shown in Figure 1, alternate vanes 3 are strapped together in known fashion by means of one of two rings 5, 6. The vanes 3 stop short of the major axis of the cylindrical anode block to define a cylindrical space 7 within which a thoriated tugsten coil cathode 8 is located. The coil 8 is supported at each end within the cylindrical space 7 by means of an elongate conducting pin 9 which extends radially out through a hole 10 in the anode block 1. The pins 9 are arranged both to support the coil 8 in spaced relation from the anode and to supply electrical current to and from the coil 8. Each pin 9 extends into a hole within the rim 11 of a top-hat shaped end cap 12. Each end cap 12 includes a spigot portion 13 which extends into and is brazed within the adjacent open end of the coil 8.

A choke arrangement 15 surrounds the portion of the pin 9 extending outwardly of the anode block 1 to shield the pin against the emission of electromagnetic radiation. A terminal 16 is attached to the free end of each pin 9 for supplying electrical current to and from the cathode coil 8.

z P/8746/EEV A pair of ring shaped channels 18, 19 surround the central region of the anode block 1 within which the anode vanes 3 are located. The channels 18, 19 are separated along their length from one another by means of an annular ring shaped wall 20 extending outwardly of the anode block. The channels 18, 19 and wall 21 are arranged co-axially with the major axis of the anode block 1. A cylindrical sleeve 21 surrounds the anode block 1 and includes appropriate holes to receive the two choke arrangements 15 and an output probe 17, discussed later on. The wall 20 stops short of the sleeve 21 to define an annular passageway 22 connecting the channels together along their length. The channels 19 each surround a region of the anode block adjacent the ends of the anode vanes, with the wall 20 being located about a region intermediate the ends of the vanes 3.

0 An inlet and an outlet pipe 23, 24 extend into a respective one of the channels 18, 19 for supplying a liquid coolant, e.g. water, which flows round one of the channels 18. From theref the layer of coolant adjacent the passageway 22 will pass through the passageway before passing into the second channel and out of the outlet 24, the flow being generally helical in direction. The output probe assembly 17, for emitting the produced energy, extends P/8746/EEV 6 out through a complementary hole 26 in the anode block which passes through the wall 22 and into portions of the channel, as is shown in Figure 2. The probe 17 is sealed within the hole 26 so that coolant cannot flow from channel to channel around the probe. A pair of anode end plates 25 seal off each end of the cavity 2.

A The cross-sectional area of the connecting passageway 22 in the direction of fluid flow, i.e. parallel to the major axis of the cylindrical anode block, is much reduced compared to the cross-sectional area of each of the channels 1 8, 19. In this way the connecting passageway provides a restriction within which the fluid flow velocity can be increased, depending on the coolant flow rate, to such an extent that the fluid flow within that region is turbulent, i.e. the Reynolds number is greater than about 2,000. In this way the cooling effect is enhanced in the central region of the anode block adjacent to the wall 22, where the requirement for cooling is greatest. Furthermore the construction of two parallel channels 18, 19 is relatively easy to provide with a turning operation using a lathe or milling machine at the same time as the anode block is made.

In an example, channels about 6mm wide and about 4mm high were separated by a wall 4mm wide having a connecting f- P/8746/EEV passageway of height 0.75mm. With a flow rate of water of about 10 liters per minute, it was found that the magnetron was well cooled.

The invention is not limited to the embodiment shown in Figures 1 and 2. For example, as shown in Figure 3, a wall 30 separating a pair of channels 31 (shown in dotted outline) includes a plurality of circumferentially spaced longitudinally extending ribs 32 which, in effect, subdivides the annular passageway of the Figures 1 and 2 embodiment into a plurality of smaller passageways 33 and serve to space the wall from an enclosing sleeve 34. In other alternative arrangements, the sleeve may include an inwardly extensive partition which divides a relatively large recess into the two channels. More than two channels may be present. The channels need not be ring shaped, as shown, but could be, eg, generally wavy or sinusoidal, when viewed from the side.

1 0 P/8746/EEV

Claims

1. A magnetron comprising a cathode and an anode, the anode comprising a substantially cylindrical anode block having a plurality of internal resonant cavities, a pair of enclosed channels extending about the block, a coolant inlet being present in one of the channels and coolant outlet being present in the other, the channels being connected to each other along their length by one or more connecting passageways dimensioned relative to the channels to provide a restriction so as to enhance coolant flow velocity, in use, through the connecting passageway.

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2. A magnetron according to claim 1, in which a sleeve surrounds the anode block to enclose the channels, the anode block including an outwardly extending wall which separates the channels from one another and which together with the sleeve defines a connecting passageway.

3. A magnetron according to claims 1 or 2, in which the connecting passageway is of annular shape.

4. A magnetron according to claim 2 or claim 3, in which the channels and the separating wall are of ring-like 1 -Q P/8746/EEV - 9 shape and are arranged in side-by-side relation co-axially with the major axis of the cylindrical anode block.

5. A magnetron, according to any preceding claim, comprising a plurality of longitudinally extensive connecting passageways circumferentially spaced apart about the anode block.

6. A magnetron, according to any preceding claim, in which the channels and a separating wall are integral with the outermost surface of the anode block.

7. A magnetron, according to any preceding claim, in which each channel surrounds an end region of the set resonant cavities of the anode, and the or each connecting passageway is located midway between the end regions.

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8. A magnetron, according to any preceding claim, in which the dimensions of the or each connecting passageway are selected so that turbulent flow can be induced, in use, within the coolant passing therethrough.

9. A magnetron, according to any preceding claim, in which the channels are of rectangular transverse cross-section.

P/8746/EEV - 10

10. A magnetron, substantially as described with reference to either one of the drawings.

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