Thyratrons

Abstract

 A thyratron includes an anode 1, a cathode 2 and a grid 3 located between them. The grid 3 has a passage 7 therethrough, through which in operation cooling fluid is passed.

Description

[0001] This invention relates to thyratrons.

[0002] Generally, a thyratron comprises a cathode and an anode contained within a gas-filled envelope and having one or more apertured control grids located between them.

[0003] Previously, it has often proved difficult to maintain interior components of thyratrons at the temperatures desired for optimum performance. In particular, the temperatures of thyratron grids tend to be unsatisfactorily high.

[0004] The present invention seeks to provide an improved thyratron.

[0005] According to a first aspect of this invention there is provided a thyratron comprising a grid having at least one passage therein through which, in operation, cooling fluid is arranged to flow and at least one aperture through which a discharge is established.

[0006] By arranging that cooling fluid is passed through the grid itself, heat may be dissipated. The cooling fluid may be air, water, oil or some other suitable gas or liquid. The passage or passages may be straight or curved, for example in a serpantine shape. If a plurality of passages are included, they may be arranged in different planes in a uniform distribution. It is preferred that the grid is of solid metal except for the passage or passages and the aperture or apertures. This aids in conducting heat from the grid to the cooling fluid. The grid could be of a laminated or sectional construction to enable a passage of a desired configuration to be used.

[0007] In one advantageous embodiment of the invention, the or a passage is extensive across an aperture. The passage may then be arranged to support a centre portion of the grid where the aperture is annular, for example. It could also be arranged to support the whole grid within the envelope.

[0008] Preferably, the or a passage is extensive in a direction substantially normal to the longitudinal axis of the thyratron, the longitudinal axis being that about which the thyratron anode and cathode are co-axial. Temperature control may then be achieved at a particular region along the longitudianal axis without the need to consider what effects will be exerted by the anode and cathode on the cooling fluid, and no redesign of the anode or cathode is necessary to accommodate this form of cooling.

[0009] It is preferred that the path length through the or an aperture is greater than the smallest transverse dimension of the aperture so that the grid is what may be termed a "thick" grid. Normally said path length will be substantially greater than the smallest transverse dimension of the aperture, that is to say at least five times greater. Preferably, said path length is at least ten times greater than the transverse dimension.

[0010] In previous thyratrons, the dimensions of the aperture or apertures in a grid have been chosen to give field penetration through the aperture, so that the preferred route of the discharge is through the aperture. This has led to the porvision of grid apertures which have relatively large transverse dimensions in comparison with their lengths to ensure that the discharge path from cathode to anode is through the aperture or apertures in the grid rather than by a route involving grid arcing, in which the discharge path goes from the cathode to the grid surface and then from another part of the grid surface to the anode. However this approach has limited the surface area for recombination presented by an aperture.

[0011] The present inventors have discovered that, surprisingly, thyratrons in accordance with the invention with "thick" grids can be operated without grid arcing. A thyratron with a "thick" grid in accordance with the invention may have larger operating voltages than a conventional "thin" grid thyratron. Also it may be operated at a higher pulse repetition rate than a conventional thyratron, since the walls of the aperture present a relatively large surface area over which recombination may occur, thus giving faster recovery rates. The relatively large surface area of the aperture is also advantageous in improving cooling.

[0012] In one configuration, the aperture is arranged in a direction parallel to the longitudinal axis of the thyratron. Thus in this arrangement the aperture is a straight passage through the grid from the anode to the cathode facing side. However, in some applications it may be convenient to have an aperture which is curved or otherwise convoluted. The aperture could be straight but inclined to the anode and cathode facing grid surfaces.

[0013] In one advantageous configuration, the aperture is arranged to lie along the longitudinal axis of the thyratron. This enables the thickness of the grid to be maximised for a given path length through the aperture, the grid then having a high thermal capacity, permitting low temperature operation. Another convenient configuration may include an annular aperture, the transverse dimension in this case being the distance between the inner and outer parts of the grid which define the aperture, that is, the width of the annulus, and not the diameter of the annulus. In a further advantageous arrangement a plurality of apertures are included. These may be arcuate slots arranged coaxially about the longitudial axis of the thyratron, each slot having similar dimensions to the other or others.

[0014] The aperture may be such that there is no straight-­through path through the aperture parallel to the longitudinal axis of the thyratron. Thus where the aperture is an annulus, say, there is no overlap in a direction parallel to the longitudinal axis between the opening at one face of the grid and that at its other face. This configuration gives an increase in breakdown voltage over that where there is a straight through path parallel to the longitudinal axis of the thyratron, since the component of the electric field in the direction of the aperture is less than the electric field normal to the grid surfaces facing the anode and cathode. Again, as realised by the present inventors, there need not be field penetration through the aperture to prevent grid arcing.

[0015] Advantageously, the grid forms part of the envelope of the thyratron, enabling radiative cooling to take place from the outer surfaces of the grid into the surroundings, and preferably cooling fluid is arranged to flow adjacent to that part of the grid which forms part of the envelope. Thus, internal cooling of the grid, by the flow of cooling fluid through the passage, and external cooling may be employed, and if the grid is a "thick" grid, there are additional cooling and operational benefits.

[0016] The invention is now further described by way of example with reference to the accompanying drawings, in which:

Figures 1 and 2 are schematic tranverse and longitudinal sections respectively of a thyratron in accordance with the invention;

Figure 3 is a schematic transverse section of part of another thyratron in accordance with the invention;

Figure 4 is a schematic transverse section of part of another thyratron in accordance with the invention;

Figures 5 and 6 are schematic longitudinal and transverse sections respectively of another thyratron; and

Figures 7 and 8 are schematic longitudinal and transverse sections of yet another thyratron in accordance with the invention.

[0017] With reference to Figures 1 and 2, a thyratron in accordance with the invention includes an anode 1, a cathode 2 and a control grid 3 located between them. The control grid 3 includes an annular aperture 4 therethrough, such that the grid 3 comprises an inner core 3A and an outer portion 3B. The path length l through the aperture 4 is substantially greater than the transverse dimension a, which in this case is the distance between facing surfaces defining the annulus. A tube 5 is arranged to pass through a containing envelope 6 and to connect with a passage 7 in the control grid 3. In operation, a cooling fluid, which in this embodiment is water, is arranged to flow through the passage 7 to effect cooling of the grid 3. The passage 7 includes tubular parts 8 which are arranged to support the centre portion 3A of the grid and has extensive portions 9 which hold the grid 3 in position.

[0018] With reference to Figure 3, in another thyratron a thick control grid 10 includes three arcuate apertures 11 therethrough, and three curved passages 12 for cooling fluid which are uniformly distributed through the thickness of the grid 10.

[0019] With reference to Figure 4, a control grid 13 in a thyratron includes an aperture 14 therethrough which is annular, the diameter of the annulus being larger at the surface facing the cathode than at the anode-facing surface. In this configuration, the path length l through the aperture 14 is greater than the thickness t of the grid 13, and the transverse dimension a is smaller than the width b of the aperture 14 at the grid surfaces. Again, the path length l is substantially greater than the transverse dimension a. In this embodiment there is no overlap between the opening of the aperture 14 in the surface facing the anode and that in the surface facing the cathode. A serpantine passage 15 for cooling fluid is also included.

[0020] With reference to Figures 5 and 6, another thyratron in accordance with the invention is similar to that shown in Figures 1 and 2, but in this embodiment, the grid 16 extends across the envelope 17 and forms part of its wall, enabling radiative cooling to occur from the outer surface 18 of the grid 16 in addition to that provided by the flow of cooling fluid through passage 19.

[0021] With reference to Figures 7 and 8 a thyratron includes an anode 20 and a cathode 21 located within a ceramic envelope 22 which also contains a gas. A control grid 23 is located between the anode 20 and cathode 21 and has an aperture 24 therethrough which is arranged to lie on the longitudinal axis X-X of the thyratron. The dimension of the apertures are such that the path length l through the aperture 24 is about ten times longer than the transverse dimension a normal to the path length.

[0022] Two passages 25 and 26 are included in the grid through which, in operation, cooling fluid is passed. The grid 23 is extensive across the thyratron and forms part of the envelope 22. A metal tube 27 is arranged adjacent the grid 23 and cooling fluid passed through that also.

[0023] During operation, the thyratron is initially non-­conducting. A voltage is applied between the anode 20 and cathode 21 and an electrostatic field exists between the anode 20 and the grid 23 of about 30kV, and between the grid 23 and cathode 21 of about 1kV. Equipotentials in the region of the grid 23 are illustrated by lines 28, where it can be seen that the field penetrates only a small distance into the aperture 24 and that the anode and cathode-facing surfaces of the grid 23 are equipotential surfaces. When a trigger pulse is applied to the grid 23 a discharge is established and conduction occurs. When conduction ceases, recombination of charge is facilitated because of the relatively large surface presented by the aperture 24 and because of its small transverse dimension. The thickness of the grid 23 also gives improved cooling over conventional 'thin' grids, since it has a large thermal capacity.

[0024] Of course, a plurality of grids may be included in a thyratron, and more than one of these may include a passage along which cooling fluid is passed.

Claims

1. A thyratron comprising a grid having at least one passage therein through which, in operation, cooling fluid is arranged to flow and at least one aperture through which a discharge is established.

2. A thyratron as claimed in claim 1 wherein the grid is of solid metal except for the passage or passages and the aperture or apertures.

3. A thyratron as claimed in claim 1 or 2 and wherein the or a passage is extensive across an aperture.

4. A thyratron as claimed in claim 1,2 or 3 and wherein the or a passage is extensive in a direction substantially normal to the longitudinal axis of the thyratron.

5. A thyratron as claimed in claim 1,2,3 or 4 wherein the path length through the or an aperture is greater than the smallest transverse dimension of the aperture.

6. A thyratron as claimed in claim 5 wherein the path length through the or an aperture is substantially greater than the smallest transverse dimension.

7. A thyratron as claimed in claim 6 and wherein the path length is at least ten times greater than the transverse dimension.

8. A thyratron as claimed in any preceding claim wherein the aperture is arranged in a direction parallel to the longitudinal axis of the thyratron.

9. A thyratron as claimed in claim 8, wherein the aperture is arranged to lie along the longitudinal axis of the thyratron.

10. A thyratron as claimed in any of claims 1 to 8 wherein the aperture is annular and the passage is arranged to support a centre portion of the grid.

11. A thyratron as claimed in any preceding claim wherein a plurality of apertures, which are arcuate slots, are arranged co-axially about the longitudinal axis of the thyratron, each slot having similar dimensions to the other or others.

12. A thyratron as claimed in any preceding claim wherein part of the passage is extensive of the grid and is arranged to support it.

13. A thyratron as claimed in any preceding claim wherein the grid forms part of the envelope of the thyratron.

14. A thyratron as claimed in claim 13 wherein cooling fluid is arranged to flow adjacent to that part of the grid which forms part of the envelope.

Drawing