JPS63284736A - Beam collector with low electric leakage - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION INDUSTRIAL APPLICATION The present invention relates to traveling wave tubes (TWT's) and klystrons, which are conventionally used in traveling wave tubes (TWT's) and klystrons that It relates to such electron beam tubes having separate electrodes for focusing the beam. The conversion efficiency of these electron tubes, especially of T W T's, is determined by applying a negative potential to the ground (“potential reduction”) so that the electrons release kinetic energy before dispersing the residue on the collector surface. The reduction is often improved by the high impedance beam required to focus the beam through a small circuit, the resulting weak coupling between the beam and the circuit, and the relatively high circuit losses. Effective for millimeter wave tubes with low inherent interaction efficiency.

The use of a high voltage, low current beam makes any electrical leakage from the collector to ground a significant fraction of the output, and also puts beam current interruption on the circuit, which must be minimized to reduce heating and maintain conversion efficiency.

BACKGROUND OF THE INVENTION When a rectifier is reduced, the heat generated within it must be transferred through an electrically insulated path to a ground potential heat sink. In large electron tubes, the heat sink often has air, using a cooling fan on the collector in a forced air stream.

In small millimeter tubes, insulation between the collector and the grounded tube becomes a problem with high exposed voltages and short leakage paths.

A prior art non-separable potential reduction collector is shown in FIGS. 1 and 2. TWT is copper metal vacuum envelope 10
It is contained within. Electron beam from a gun (not shown)! 2 is an interaction circuit, which is a helical tungsten wire 2 supported by a number of dielectric rods 16 of sapphire in a steel tube 32 that is part of the envelope 10, and traverses therethrough. The end of the spiral (2) extends as an external conductor 18 via an insulating vacuum seal 2G. beam! 2 is the axial magnetic field (
After passing through circuit (2), which is confined to a small cylindrical shape by (not shown), it expands into a hollow collector electrode 22 made of copper. A plurality of dielectric rods 24 are shrink-fitted between the collector electrode 22 and the envelope 10, and the rods are made of beryllium oxide ceramic, for example.
The envelope is cooled by a grounded heat sink (not shown) such as sir fins, liquid channels or conductive paths.

Current is supplied to collector 22 by conductor 26 through an insulating vacuum seal 28 .

The prior art collectors of FIGS. 1 and 2 suffer from several inherent problems. Since the dielectric structure is in a high vacuum, thermal conductivity through the small area that contacts rod 24 is poor. (In a vacuum, except for physical contact at the atomic level,
Only radiative transfer is possible. ) Another problem that arises with low current, high voltage, such as millimeter wave tubes, is that the conductive coating is deposited onto the dielectric rond in a vacuum. Some metal evaporates from the hot part and some sputtering appears from the gas left in the high electric field. The increase in current leakage across these coatings is due to the compression on the rod being reduced during heating and cooling cycles, thereby causing the rod to rotate and expose a new surface to the coating process. Nevertheless, cylindrical rods are widely used because they are easy and inexpensive to manufacture.

In some prior art electron tubes, attempts have been made to reduce leakage by filling the space between the collector and the case with a dielectric liquid.

Under embodiments of the invention as described below, this reduced high vacuum is released so that a conductive layer is created. but,
Significant electrical leakage remains.

OBJECTS OF THE INVENTION It is an object of the invention to provide a potential reduction collector with minimized electrical leakage.

A further object of the invention is to provide a potential reduction collector with improved cooling capacity.

A further object of the invention is to provide a collector that is inexpensive and easy to assemble.

A further object of the invention is to provide an electron tube in which the collector insulator is attached after vacuum treatment.

These objectives are achieved by a collector having two concentric bands of insulator with minimal electrical contact. Preferably, the bands are arranged such that the radial gap of one band is covered by a solid member, while minimizing continuous leakage current. In a preferred embodiment, the insulator is encased in a dielectric liquid in which electrical discharges that might cause a leaky coating are prevented and heat transfer is increased.

Preferred Embodiment FIG. 3 is a suggested cross-sectional view of a collector embodying the invention. After passing through a TWT interaction structure (not shown) contained within the vacuum envelope 10', the electron beam 12' enters a hollow beam collector electrode 22' where it diverges and is intercepted by an inner wall. The collector 22'' is preferably constructed like the inner and outer surfaces of a right circular cylinder for ease of manufacture and cooling. The collector B' is formed by an insulating hollow dielectric cylinder 30 of high alumina ceramic, for example, into the vacuum envelope 10' of the tube. The heat generated within the collector 22' is conducted radially outward to the surrounding casing 32' (e.g. copper), which eventually becomes part of the end closure. It is sealed by welding the lip 34 of 33 to the lip 36 of the case 32'.

Space 4 between collector 22' and enclosure 32'
4 is mostly filled with two concentric bands of solid dielectric material H', 4G, such as beryllia ceramic, which has high thermal conductivity. In the preferred embodiment, the inner band is a layer of closely packed dielectric rods 24' and the outer band is a hollow dielectric cylinder 40. The dielectrics 24', 40 are tightly interlocked for the most effective heat transfer.

Electrical connections to collector 22' are made by electrical wires 26' passing through case 31' through insulator seals 28''.

The insulating bands 24', 40 are preferably inserted after vacuum treatment of the tube to prevent contamination during bakeomt with volatile materials.

The case 32'' is then sealed by attaching the end closure 38. In the next manufacturing step the collector 2
The space 44 between the 2° and the case 40 is filled with a dielectric fluid, such as nitrous oxide having good thermal conductivity and voltage breakdown properties, or an I-rogenated organic gas having excellent voltage breakdown properties, through a tube 46 filled with In applications where voltage breakdown is not a limiting factor, improved heat transfer can be obtained with lower molecular weight gases such as hydrogen or helium. Alternatively, a dielectric liquid may be used, but this is more unstable to fill and also has thermal expansion problems. For applications requiring low voltage breakdown, air filling is sufficient. In any case,
Dielectric fluids improve heat transfer by creating convection between tightly joined parts. In prior art configurations, heat conduction is limited except through small areas by actual molecular contacts.
It appears only by radiation that traverses the vacuum. After filling,
Space 44 is sealed by a closure tube 46 .

As discussed under the "Prior Art" section, the insulating band h is coated with metal from where it contacts the metal portion 22, thereby making it conductive. As the tube is heated and cooled by cyclic operation, rods such as 24 become free to rotate during the thermal expansion cycle and are somewhat conductive over their entire surface. In the present invention, such a rod does not contact the second metal electrode opposite the first electrode, but contacts the second insulator. The formation of leakage paths across electrically series bridges is suppressed. Preferably, the second dielectric band is such that any radial gap planes present, such as those due to accidental pyrolysis of the tube, have only a very small chance of lining up with the leakage path of the first band 24'. As shown, the cylinder 40 is formed as described.

FIG. 5 is a schematic axial cross-sectional view of an alternative embodiment in which an external dielectric band is cut into the segment 42 to reduce cracking due to thermal stress.

The segments are shaped so that they do not rotate during repetition, so the radial paths are not coated with contact and there is a small chance of radial cracks aligning with the gaps between the inner band cylinders 24''.

FIG. 6 is a schematic axial sectional view of another embodiment.

Where heat conduction is less important, the second band may be made from a second layer of cylindrical rods 44. As mentioned above, these rods are inexpensive and easily obtained. The external leakage paths are broken by cuts between the rods, and the gaps are generally not aligned.

It will be apparent to those skilled in the art that many different embodiments may be made within the scope of the invention described by way of example. The shape of the dielectric elements can be very different. Cylindrical rod 2
4' is inexpensive and easily obtained. A large number of shapes can be used for the second pan mill O. Preferably, these elements are not rotatable. Although it is not completely essential that the insulation space be filled with dielectric fluid, it is desirable. The invention is limited only by the scope of the claims appended hereto.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of an insulated collector according to the prior art. FIG. 2 is a suggested cross-sectional view in a plane perpendicular to the axis of the collector of FIG. 1; FIG. 3 is a suggested cross-sectional view of a collector embodying the invention. FIG. 4 is a suggested cross-sectional view in a plane perpendicular to the axis of the collector of FIG. 3; FIG. 5 is a suggested cross-sectional view in a plane perpendicular to the axis of a different embodiment. FIG. 6 is a suggested cross-sectional view of another embodiment. Explanation of main symbols 10'...Vacuum envelope 2! ″・・・・・・
--- Collector electrode 2C --- Inner band 32' --- Case 40 --- Outer band Patent applicant: Parian Associates Incoholated

Claims (1)

Claims: 1. Collector means for a linear beam electron tube comprising: a) a conductive inner collector electrode having a cylindrical outer surface; b) a conductive case surrounding said collector electrode; c) said collector means comprising: an inner band of thermally conductive dielectric surrounding and in contact with the collector; d) an outer band of thermally conductive dielectric between and in contact with said inner band and said case; Collector means for a linear beam electron tube as claimed in claim 1, wherein the bands are shaped such that a gap or cut extending outwardly through one of the bands is generally aligned with a solid portion of another band. 3. Collector means for a linear beam electron tube according to claim 2, wherein at least one of said bands is a substantially complete hollow cylinder. 4. Collector means for a linear beam electron tube according to claim 1, wherein said hollow cylinder is comprised of a plurality of adjacent segments. 5. Collector means for a linear beam electron tube as claimed in claim 4, wherein said segments are distributed around said cylinder. 6. Collector means for a linear beam electron tube according to claim 4, wherein said segments are separated by pressure cracks. 7. Collector means for a linear beam electron tube according to claim 1, wherein at least one of said bands comprises a layer of parallel rods shaped like a right cylinder. 8. Claim 7, wherein the other of the bands does not consist of a right circular cylinder.
Collector means for the described linear beam electron tube. 9. Collector means for a linear beam electron tube as claimed in claim 7, wherein the other of said bands comprises a second layer of right circular cylinders. 10. Collector means for a linear beam electron tube according to claim 1, wherein said case is hermetically closed. 11. Collector means for a linear beam electron tube as claimed in claim 10, wherein said case is part of said tube. 12. The case is adapted to be sealed from the vacuum envelope of the tube and to allow the inductive band to be placed in front of the airtight closure after vacuum treatment of the tube. Collector means for the described linear beam electron tube. 13. Collector means for a linear beam electron tube as claimed in claim 10, wherein the open space between the case and the collector is filled with a guiding fluid. 14. Collector means for a linear beam electron tube according to claim 13, wherein said fluid is a gas. 15. Claim 1, wherein the fluid is a halogenated organic compound.
3. Collector means for a linear beam electron tube according to claim 3. 16. Collector means for a linear beam electron tube as claimed in claim 14, wherein said gas is a glass member comprising hydrogen and helium. 17. Collector means for a linear electron tube according to claim 14, wherein said gas is nitrogen oxide.