GB2081968A - Magnetically-focussed power valves - Google Patents

Abstract

The gate electrode (2), eg U shaped, of a magnetically focussed power valve has a groove (5) in each limb adjacent the cathode (14) enabling manufacturing tolerances to be less critical thus easing manufacture whilst maintaining performance. Preferably the gate (2) is made of sheet metal. The grooves need not be of circular arc section and may even be slots. In multicathode valves the gate electrodes may be slots, grooved on both faces between adjacent parallel cathodes. <IMAGE>

Description

SPECIFICATION Magnetically-focussed power valves This invention relates to magnetically-beamed or focussed power valves. Such valves are described in our British Patent Specification Nos. 1 195 703, 1 434984 and 1 534 495.

UK Patent Specification No. 1 434 984 discloses for the first time a magneticallyfocussed power valve in which the grid or gate electrode is formed as a main structural unit supporting within it a cathode by means of intermediate insulating spaces. UK Patent Specification No. 1 534 495 describes a magnetically-focussed power valve of high power handling capacity with a water cooling jacket for cooling the anode and a separate cooling device for cooling the gate/cathode assembly.

It is an object of the present invention to simplify the construction of a magneticallybeamed or focussed power valve.

According to the present invention there is provided a magnetically-focussed power valve comprising a tubular anode, an elongate electron emissive cathode structure and a gate electrode structure each extending axially within the anode, the cathode being located in a slot defined between opposed limbs of the gate electrode, the limbs having a groove or aperture adjacent the cathode so that the slot is wider adjacent the cathode than further away from the cathode, in directions extending out of the slot.

Preferably the grid or gate electrode is fabricated from sheet metal.

In order that the invention can be clearly understood reference will now be made to the accompanying drawings in which:- Figure I shows a single-cathode magnetically-focussed power valve according to an embodiment of the invention, Figure 2 shows schematically part of the valve of Fig. 1 within the dot-dash balloon X of Fig. 1, Figure 3 is a side view of a gate structure for a 4-cathode magnetically-focussed power valve, according to another embodiment of the invention, Figure 4 shows in perspective and not to scale one of the gate slats of Fig. 3, and Figure 5 shows very schematically a cutaway view of a magnetically-beamed power valve incorporating the gate/cathode structure of Figs. 3 and 4.

Referring to Figs. 1 and 2 of the drawings the valve comprises a tubular anode 1 formed of copper and shown in broken line. Around the anode is a cooling jacket 1 A defining between itself and the anode water cooling channels (not shown) for cooling the anode of the valve. Coolant supply ports 1 B and 1 C are shown.

Extending axially within the anode 1 is a metallic gate electrode structure 2 formed from sheet metal (copper) with legs 3 by which it is mounted on a gate flange 4 by brazing or welding. The gate electrode 2 has extending along the length of both limbs down to and including its legs 2, a groove 5, illustrated more clearly in Fig. 2. A corresponding rib 6 appears on the outside of the gate. The groove and rib formation has been formed in an originally straight sheet metal part which has been cold-formed to produce the rib and groove formation, followed by bending the metal part at 2A into the Ushaped gate electrode and at 2B to form the diverging legs 3, as shown in the drawings.

An insulating intermediate spaced 7 fits in a hole 8 (shown in dashed line) in the U-end 2A of the gate and is held in position by straps 9.

A similar spacer 10 sits in a hole 11 in a cross member 1 2 of copper which is welded or brazed to the gate electrode at the point where the legs 3 begin in diverge from the gate limbs. Similar straps 1 3 hold the spacer 10 in position on the cross member 1 2. The spacers are made from alumina.

A cathode 14 extends along and within the slot defined between the limbs of the gate 2 and, adjacent the cathode the slot is wider owing to the existance of the groove 5 on both sides, than further away from the cathode as one proceeds in direction out of the seat towards the anode.

The cathode has a heater element 1 4A and an electron emissive coating 14B. Connection leads to the heater element are connected to the heater terminals 1 5 and 1 6. The left-hand terminal 1 6 also functions as a cathode terminal.

As shown in Fig. 1 a ceramic annular spacer 1 7 provides insulation between the gate flange 4 and an anode connecting flange 1 8 is provided.

We have discovered that the provision of the groove 5 in the gate electrode on opposite sides of the cathode enables larger manufacturing and assembly tolerances without significantly affecting the performance of the valve, in particular the gate current. Thus alignment of the cathode relative to the gate becomes considerably less critical using this feature.

Furthermore, in this embodiment the use of sheet metal parts is possible because the groove / rib formation significantly stiffens the sheet metal part enabiing it to be satisfactorily used without additional stiffening/support components other than the cross-member 12.

Referring now to Figs. 3, 4 and 5 of the drawings, Fig. 3 shows the gate structure of a 4-cathode valve capable of operating at around 25 kW. The gate structure is formed completely from sheet metal parts of copper and comprises a pair of uprights 21 and 22 of U-channel cross section and a pair of Uchannel bridge members 23 and 24. Each bridge member carries four apertures 25 (only those for 23 are visible). These apertures hold in position tubular intermediate insulating spacers 50 and 51 similar to the ones shown in Figs. 1 to 3 and designated by the reference numerals 7 and 10. These supports are similarly held in place by straps 52 and 53 similar to those designated 9 or 1 3 respectively, as shown in Fig. 15. These supports locate respective cathodes such as 54, each similar to the one 14 shown in Fig. 3.Only one 54 is shown in Fig. 3 for the sake of clarity.

Between the bridge members 23 and 24 are located five gate slats such as 26 shown in greater detail in Fig. 4. Each slat has on each side a groove such as 27 and 28, each of circular section. Each slat has corresponding notches (not visible) in the edges of the bridge members 23 and 24, thereby maintaining the five gate slats fixed in parallel alignment. The surface of the grooves 27 and 28, in cross section, lies on the circumference of a circle centred on the axis of the circular cathode and as seen more clearly in Fig. 2.

As mentioned above the gate electrode parts are made from sheet metal and the gate slats are also made from sheet metal which has been subsequently cold-formed to produce the grooves 27 and 28 on opposite sides.

The uprights 21 and 22 have bent away tabs 30 and 31 by which the structure is brazed or welded to the gate flange of the valve.

The bridge members 23 and 24 are welded or brazed to the uprights 21 and 22 to form a rigid structure.

The holes such as 33 and 34 enable the straps to locate the insulating spaces relative to the bridges.

As shown very schematically in Fig. 5, a tubular anode 35 and a surrounding water cooling jacket 36 are brazed to a top 37 and anode connecting flange 38 defining an annu lar water coolant chamber 39 fed from water coolant ports (not shown). This structure is mounted on an annular alumina insulator 40 which is secured in turn to a gate flange 41 designed to act as a second cooler for the valve having cooling pins 42. Heater connection leads 43, 44 extend from cathode bus bars 43a and 44a to heater connection terminals 45 and 46, which are similar to those designated 15 and 16 in Fig. 1, and similar also to the arrangement described in Fig. 1 of UK Patent No. 1 534 495.

We have tried as an alternative a groove which in cross-section is cuspshaped and this gave good results. Other groove shapes are also possible.

It would also be possible to have a "bottomless" groove i.e. an elongate aperture in the limbs of the gate electrode. Furthermore it would be possible for the groove or aperture to be discontinuous in the longitudinal direction i.e. a series of grooves or apertures. In this case the electron emissive surface could also be discontinuous in a correspoRcling manner.

Claims (7)

1. A magnetically-focussed power valve comprising a tubular anode, an elongate electron emissive cathode structure and a gate electrode each extending axially within the anode, the cathode being located in a slot defined between opposed limbs of the gate electrode, the limbs having a groove or aperture adjacent the cathode so that the slot is wider adjacent cathode than further away from the cathode, in directions extending out of the slot.

2. A power valve as claimed in claim 1 wherein the surface of each limb adjacent the cathode is formed by a groove extending.

parallel to the cathode, each groove in crosssection defining an arc of a circle.

3. A valve as claimed in claim 1 or claim 2, wherein said gate electrode is formed from sheet metal, said grooves being created by plastic deformation of the sheet metal.

4. A valve as claimed in daim 3, and having a single cathode, opposed limbs of said gate electrode being formed from a single sheet metal part which is bent to form an elongate U-shape.

5. A valve as claimed in daim 1, 2 or 3, comprising a plurality of cathodes, the gate for each cathode being formed by a pair of gate slats located in notches in respective upper and lower bridge members.

6. A valve as claimed in claim 6, wherein the gate structure comprises a pair of up rights, a pair of bridge members connected thereto, and a plurality of gate slats located in respective notches in the bridge members.

7. A magnetically-focussed power valve substantially as hereinbefore described with reference to Figs. 1 to 3 or Figs. 4 to 8, of the accompanying drawings.