CATHODES FOR MAGNETRONS

Abstract: A magnetron includes a cathode assembly 1 which comprises a helically wound wire 2 supported by a ceramic cylindrical member 3. Emissive material 4 is located between adjacent turns of the conductor 2 and connection is provided to the conductor via a rod 6 and tube 7. When current is passed through the conductor 2, the emissive material 4 is directly heated.

Description: This invention relates to magnetrons and more particularly to magnetron cathodes. The time required for a magnetron to become operational is governed by the warm-up time of its cathode, that is, the time required for the cathode to reach an operating temperature at which sufficient electrons are emitted for proper operation to be achieved. US-A-2,653,268 discloses a magnetron including a cathode which comprises an electrical conductor wound on an electrically insulating member and electron emissive material located adjacent the conductor such that, when current is passed through the conductor, the emissive material is directly heated. As the conductor is in direct contact with the emissive material, heating it to the operating temperature is readily achieved. It is an object of this invention to provide a cathode of this general type having enhanced rigidity and therefore electrical stability. In a first aspect of the present invention a magnetron as disclosed in US-A-2,653,268 above is characterised in that the insulating member includes a groove within which the electrical conductor and the electron emissive material is located. In a second aspect of the present invention a magnetron as disclosed in US-A-2,653,268 above is characterised in that the insulating member includes a groove within which the electrical conductor is located, the electrical conductor being partially extensive of the groove, the electron emissive material being located between adjacent parts of the conductor. In each aspect, the interengagement of the insulating member, electron emissive material and conductor by means of the groove results in a relatively strong and rigid structure having good electrical stability. It is preferred that the conductor is helical, as this configuration has particularly satisfactory operational characteristics. Preferably, the insulating member is a ceramic cylinder. Advantageously, where the conductor is helical, electron emissive material is located between adjacent turns of the conductor. Emissive material is therefore heated by two adjacent turns and the helical conductor ensures that the electrical field between the magnetron cathode and anode is kept constant as the emissive coating evaporates. Some ways in which the invention may be performed are now described by way of example with reference to the drawings, in which: Figure 1 is a schematic sectional diagram of part of a magnetron, generally in accordance with that disclosed in US-A-2,653,268. Figure 2 is a view along the line II-II of Figure 1; Figure 3 is a schematic sectional diagram of part of a magnetron in accordance with one aspect of the invention; and Figure 4 is a schematic sectional drawing of part of another magnetron in accordance with a second aspect of the invention. With reference to Figure 1, a magnetron includes a cathode indicated generally at 1 which comprises a helically wound wire 2 of tungsten rhenium which is supported by a ceramic cylindrical member 3. Electron emissive material 4, which is a mixture of oxides of barium, strontium and calcium, is laid down between the turns of the helical conductor 2 so that if fills the spaces between them. The ceramic member 3 includes a slot 5 at each end, as shown in Figure 2, in which the ends of the helical conductor 2 are located and fixed. Connection to the lower end as shown of the conductor 2 is made via a nickel rod 6, which passes through the member 3 along its axis, and a metallised region on the member 3 in the region of the slot 5. The connection to the upper part of the conductor 2 is made via a nickel tube 7 which is located coaxially about the rod 6. Nickel end caps 8 and 9, located at the ends of the member 3, hold the assembly together. With reference to Figure 3, in another magnetron in accordance with the invention, the magnetron cathode includes a cylindrical ceramic member 10 which has a helical groove 11 in its outer curved surface. A conductor 12 is wound around the ceramic member 10, being located in the groove 11. Electron emissive material 13 is also included in the groove 11 and is arranged to surround the conductor 12. With reference to Figure 4, in another advantageous embodiment of the invention, a ceramic member 14 includes a helical groove 15 in its outer curved surface similar to that shown in Figure 3. A rectangular section conductor 16 is wound in the groove such that part of it stands proud of the ceramic surface. Electron emissive material 17 is coated between the portion of the conductor 16 which are extensive from the ceramic surface. Of course, although a rectangular section conductor is used in this embodiment of the invention, other configurations could be used.

Claims: A magnetron including a cathode (1) which comprises an electrical conductor (2, 12, 16) wound on an electrically insulating member (3, 10, 14) and electron emissive material (4, 13, 17) located adjacent the conductor (2, 12, 16) such that, when current is passed through the conductor (2, 12, 16), the emissive material (4, 13, 17) is directly heated characterised in that the insulating member (10) includes a groove (11) within which the electrical conductor (12) and the electron emissive material (13) is located. A magnetron including a cathode (1) which comprises an electrical conductor (2, 12, 16) wound on an electrically insulating member (3, 10, 14) and electron emissive material (4, 13, 17) located adjacent the conductor (2, 12, 16) such that, when current is passed through the conductor (2, 12, 16), the emissive material (4, 13, 17) is directly heated characterised in that the insulating member (14) includes a groove (15) within which the electrical conductor (16) is located, the electrical conductor (16) being partially extensive of the groove (15), the electron emissive material (17) being located between adjacent parts of the conductor (16). A magnetron as claimed in claim 1 or claim 2 wherein the conductor (2, 12, 16) is helical. A magnetron as claimed in any preceding claim wherein the member is a ceramic cylinder (3, 10, 14). A magnetron as claimed in any preceding claim wherein the member (3, 10, 14) includes a slot (5) in which an end of the conductor (2) is located. A magnetron as claimed in any preceding claim and including a conductive rod (6) which is extensive through the member (3, 10, 14) and which is arranged to provide a connection to the conductor via a metallised region of the member (3, 10, 14). A magnetron as claimed in claim 2 wherein the sectional configuration of the conductor (16) corresponds to the configuration of the groove (15). A magnetron as claimed in any of claims 2 to 7 wherein, where the conductor is helical, electron emissive material (17) is located between adjacent turns of the conductor (16). A magnetron as claimed in any preceding claim wherein the conductor is a wire (2). A magnetron as claimed in claim 9 wherein the conductor is of tungsten rhenium.

Inventors: JERRAM, PAUL ANDREW, KERR, JOHN WALTER, PITT, IAN DAVID
Applicants: EEV LIMITED
Application year: 1989
Main classification: H01J23
IPC codes: H01J23