US3449617A - Electron discharge device having at least one electrode mounted by a meander-type insulator - Google Patents

Description

June 10, 1969 R c, KREUCHEN ET AL 3,449,617 ELECTRON DISCHARGE DEVICE HAVING AT LEAST our; ELECTRODE MOUNTED BY A MEANDER-TYPE INSULATOR Filed on. 24, 1966 Sheet 3,449,61 7 CTRODE June 1969 K. H. R. c. KREUCHEN ETAI- ELECTRON DISCHARGE DEVICE HAVING AT LEAST ONE ELIE MOUNTED BY A MEANDER-TYPE INSULATQR Sheet Filed Oct. 24, 1966 FIGZ FIG. 3

United States Patent US. Cl. 315-5.34 8 Claims ABSTRACT OF THE DISCLOSURE An electron discharge device, such as a klystron comprises means for producing electrons, electrostatic focussing means for constraining said electrons to travel as a beam past energy interchange means, and means for collecting said electrons. The focussing means includes one electrode having a central aperture for the beam located closely adjacent to a conducting surface of said energy interchange means. The said electrode is mounted by means of an insulator which contacts said electrode and said conducting surface and is formed as a meander so that there is no direct path on the surface of said insulator from a point of contact with said electrode to a point of contact with said conducting surface.

This invention relates to electron discharge devices and it relates especially although not exclusively to klystrons.

In a klystron, the electrons from the cathode are focussed to form a beam which passes through successive cavities before being collected by a collecting electrode. The focussing means have usually been electromagnetic, but such means render the klystron heavy and bulky, and it has therefore been proposed to substitute electrostatic focussing for electromagnetic focussing. This proposal has however encountered problems of insulation having regard to the high potential differences required between electrodes to achieve electrostatic focussing. The insulation problem is for example encountered in mounting focussing electrodes accurately in position close to but insulated from the walls of the cavities, a large potential difference being required between the focussing electrode and the cavity wall.

It has been found that conducting particles are liable to be deposited on the surface of insulators. within the envelope of the klystron causing leakage across the insulators, such deposition occurring especially during the degasing baking operation which is a final stage in the manufacture of the tube.

Similar problems may be encountered in other electron discharge devices which incorporate electrostatic focussing means for constraining electrons to travel as a beam past energy interchange means, and the object of the invention is to reduce the problem of insulation encountered in such a device.

According to the present invention there is provided an electron discharge device comprising means for producing electrons, focussing means for constraining said electrons to travel as a beam, and means for collecting said electrons, and wherein said focussing means includes at least one electrode having a central aperture for the beam, a conducting surface adjacent said electrode, which may be a surface of said energy interchange means, said electrode being mounted by means of an insulator which contacts said electrode and said conducting surface and is formed as a meander so that there is no direct path on the surface of said insulator from a point of contact with said electrode to a point of contact with said conducting surface.

In order that the present invention may be clearly understood and readily carried into etfect it will now be described with reference to the accompanying drawings of which:

FIGURE 1 illustrates a longitudinal sectional view of a klystron according to one example of the invention,

FIGURE 2. is a sectional view taken on the line II of FIGURE 1, and

FIGURE 3 is a perspective view of a focussing electrode of the klystron.

Referring to FIGURE 1, the klystron which is illustrated comprises an electron gun 1 including a thermionic cathode, four resonant cavities 2, 3, 4 and 5 and a collector electrode 6, arranged in that order along the axis of the klystron. The electron gun may be of any suitable construction but it is preferably of the construction described and claimed in co-pending United States application Ser. No. 588,777 filed Oct. 24, 1966 by Karl Heinz Robert Christian Kreuchen one of the applicants of the present application. Each of the cavities is formed by two transverse copper walls and by part of the copper envelope of the klystron, the transverse walls being denoted by the references 7 and 8 in the case of each cavity and the copper envelope or the klystron being denoted by the reference 9. The walls 7 and 8 are formed with drift tubes 10 and 11 in known manner, having central apertures which are co-axial. All the cavities have plungers 12 which can be moved radially within the cavities for the purpose of tuning. The cavity 2 is the input cavity and high frequency signals can be fed to this cavity by way of a coupling loop 13. The cavity 5, on the other hand, is the output cavity and is coupled to an output waveguide 14 through a dielectric window 15.

To enable the electrons from the source 1 to be focussed so as to form a concentrated axial beam which passes through the cavities 2, 3, 4 and 5- and is finally collected by the collector electrode 6, electrostatic focussing electrodes 16, 17 and 18 are provided between each pair of cavities. When the klystron is operational, a high potential is maintained on the electrodes 16, 17 and 18 relative to the walls 7 and 8 of the cavities and to the envelope 9', and the electrodes 16, 17 and 18 co-act with the apertured walls 7 and 8 to form converging electrostatic lenses. Each of the electrodes 16, 17 and 18- is at a fixed distance from the respective walls 7 and 8 of the two adjacent cavities, and the mounting is achieved, in the case of each focussing electrode, by means of a ceramic insulator 19. Each focussing electrode and insulator is of the same construction, and the following description of the electrode 17 and its respective insulator is therefore applicable to all. As can be seen especially from FIGURE 3, the electrode 17 is in the form of a planar member having a central aperture for passage of the beams. Lips 21 and 22 of the electrode 17 at four angularly spaced positions, all the lips 21 being shown by dotted lines in FIGURE 2. The lips 21 and 22 thus form four arcuate grooves, equiangularly spaced round the circumference of the electrode 17, the angular extent of each groove being less than 45 The insulator 19 has a central aperture, in which there are four equi-angularly spaced tongues 23 complementary to the four grooves formed by the lips 21 and 22. The size of the electrode 17 relative to the aperture in the insulator 19* is such that the electrode can be inserted in an axial direction into the aperture with the circumferential grooves located between the tongues 23, whereupon the are provided on both edges electrode can be rotated by approximately 90 to cause v the tongue to enter the grooves, restraining the electrode from axial movement. The electrode 17 is located in the aperture of the insulator 19 so that a tapped radial hole 51 in the electrode is aligned with a radial hole 52 in the insulator 19. The lead passes through the hole 52 and an aligned hole 53' in the metal envelope 9 and terminates in an end cap 54. Between the insulator 19 and the end cap 54, the lead is sheathed by a ceramic sleeve 55, which has an end portion 56 of reduced diameter projecting into the hole 52 in the insulator 19. To insulate the end cap 54 from the metal envelope 9, it is secured to one end of a stand-off insulator 57, the other end of which is secured to a flanged metal piece 58- welded to another flanged metal piece 59, the inner end of which is in turn welded to the envelope 9 around the edge of the hole 53. The end cap 54 and the flanged metal piece 58 are each secured to the insulator 57 by a multi-step brazing process such as described in British patent specification No. 891,705.

The insulator 57 is of a fluted cylindrical form, formed on its internal surface with three annular grooves, being as can be seen in FIGURE 2, re-entrant towards the envelope 9. It has been found that this construction of in-- sulator reduces the risk of conducting particles being deposited over the inner surface of the insulator 57 in such a way as to cause electrical leakage from the envelope 9 to the end cap 54.

The mounting insulator 19 for the electrode 17 is a one piece member formed of high grade ceramic and the apertured central part thereof has three limbs 33 each in the form of a zig-zag or meander. The outer end of each limb is enlarged to form a foot 34 which, as can :be seen in FIGURE 1, is thicker, measured in the axial direction, than the rest of the insulator 19. Both the circumferential and axially facing surfaces of the feet 34 are accurately ground, after the ceramic insulator has been fired, in relation to the central aperture of the insulator 19 and the tongues 23, and the axial facing surfaces of the feet 34 contact walls 7 and 8 of the adjacent cavities, whilst the circumferential surfaces of the feet contact the inner surface of the envelope 9. In this way, the location of the electrode is accurately determined. Moreover, as will be appreciated from a consideration of FIGURES 1 and 2, there is no direct path on the surface of the insulator 19 from the electrode 17 to either of the adjacent walls 7 and 8, or the envelope 9-. Any path on the surface of the insulator 19 is long compared with the shortest distance from a point of contact with the electrode and a point of contact with the conductive surfaces 7, 8 and 9. This feature serves to reduce the risk of the klystron being rendered inoperative by reason of the surface of the insulator becoming conductive. Other meander forms for the insulator 17 could produce a similar result to the zigzag meander illustrated.

Although the invention has been described herein as applied to a klystron, it is also applicable to other high power tubes such as tra'velling wave tubes.

What we claim is:

1. An electron discharge device comprising means for producing electrons, focussing means for constraining said electrons to travel as a beam past energy interchange means, and means for collecting said electrons, and wherein said focussing means includes at least one electrode having a central aperture for the beam a conducting surface adjacent said electrode, said electrode :being mounted by means of an insulator which contacts said electrode and said conducting surface, and is formed as a meander so that there is no direct path on the surface of said insulator from a point of contact with said electrode to a point of contact with said conducting surface.

2. A device according to claim 1 in which said electrode and said insulator are coplanar and said insulator comprises a plurality of limbs each formed as a zig-zag.

3. A device according to claim 1 and said adjacent conducting surface being a part of said energy interchange means.

4. A device according to claim 3 in which said electrode and said insulator are co-planar and said insulator comprises a plurality of limbs each formed as a zig-zag, and the outer end of each of said limbs is formed with a foot having a circumferential surface engaging the inner circumferential surface of a conducting part of the envelope of said device and having at least one axially facing surface engaging said conducting surface of said energy interchange means.

5. A device according to claim 4 in which the foot on each of said limbs has oppositely facing axial surfaces engaging conducting surfaces of two successive energy interchange means, the arrangement being'such that said focussing electrode is held by said insulator spaced from both said energy interchange means.

6. A device according to claim 1 in which said insulator has a central aperture in which said electrode is secured, said electrode and said insulator being formed with interengaging parts such that the electrode can be withdrawn from the central aperture following a rotation of said electrode.

7. A device according to claim 6 in which said electrode when secured in position is held against rotation in said central aperture by a lead which is connected to the electrode and passes through the insulator.

8. A device according to claim 1 in which said insulator comprises a one piece ceramic member.

References Cited UNITED STATES PATENTS 8/1960 Albert 313-254 X 5/1961 Vaccaro et al. 3155.34

US. Cl. X.R.. 313-254; 3153.5

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