US3886384A - Collector electrode - Google Patents

Abstract

An improved collector electrode for a high powered traveling wave tube is shown to consist of a laminated assembly wherein both sides of a metallic core layer resistant to cracking under operating conditions of such a tube are bonded to oxygen free high conductivity copper.

Description

0 United States Patent 11 1 1111 3,886,384 Tuinila May 27, 1975 l l COLLECTOR ELECTRODE 3,260,885 7/1966 Craduchettes 315/538 3.317.780 5/1967 Ayers i A BIS/5.38 X {75] inventor: Raymond P. Tumlla, Beverly, Mass 3368J02 2/l968 Sahan-an n 5,538 X 73 Assignee; Raythean Company, Lexington, 3,662,2l2 5/1972 Ravvls i 3l5/5138 Mass 3,748,5l3 7/1973 Levm H 315/538 [22l Filed: 1974 Primary ExaminerSaxfield Chatmon, Jr. {21] A l N 439,180 Attorney, Agent. or Firm-Philip J. McFarland;

Richard M. Sharkansky; Joseph D. Pannone [52] US. Cl. 313/39; 3l3/32; 3l3/46;

3l5/3.5; 3l5/5.38 [5 ABSTRACT 'l Cl Holk An improved collector electrode for a high powered [58] F'eld Search 3 [5638' traveling wave tube is shown to consist of a laminated 3 I 3/39 39 assembly wherein both sides of a metallic core layer resistant to cracking under operating conditions of [56] References C'ted such a tube are bonded to oxygen free high conductiv- UNlTED STATES PATENTS ity coppep 3,104.3311 9/1963 Symons 1. 315/538 x 3.259.790 7/1966 Goldfinger .4 315/533 x 2 2 Drawmg Fgures SOURCE COOLANT INLET FROM MODULATION COOLANT OUTLET COLLECTOR ELECTRODE BACKGROUND OF THE INVENTION This invention pertains generally to high powered electron discharge devices and particularly to devices of such type amplifying a modulated electron beam.

It is known in the art that an electron beam may be modulated and amplified in a so-called traveling wave tube (TWT) to provide radio frequency signals at high power levels. In devices of such type, especially when the desired power level is very high, it is known to provide a collector electrode to allow the remanent electrons in an intense, modulated beam to be dissipated after a required radio frequency signal has been produced. In a commonly used TWT, wherein the density of electrons in a modulated beam is extremely high, it is known that a useful collector electrode may include a hollow cylinder to receive the electron beam to be dissipated. Such a cylinder is disposed within a fieldfree space with its longitudinal axis colinear with the electron beam to be dissipated. Mutual repulsion between electrons in such a beam then is effective to cause electrons entering such hollow cylinder to travel in arcuate paths until impinging upon the inner surface of the cylinder. The heat generated by the electrons impinging on the inner surface of the hollow cylinder is dissipated by conduction through the wall of the cylinder. The efficiency of such an arrangement is increased by providing cooling fins projecting outwardly from the outer wall of the cylinder to increase the area of the collector electrode in contact with a coolant forced around such fins.

Because the inner surface of the cylinder making up the collector electrode in a TWT of the type being discussed defines a portion of the walls making up the re quired vacuum chamber for the TWT, it is necessary that the material from which such cylinder is made be free from occluded gases. When such a requirement is considered along with the requirement that the collec tor electrode also be a good conductor of heat, the most practical material for the collector electrode in a high powered TWT is, as is well known in the art, a particular kind of copper called oxygen-free high conductivity" copper (OFHC).

Unfortunately, the physical characteristics of OFHC copper are not ideal for application in situations where high energy density electron beams impinge upon it, as in the collector electrode of a high power TWT. Under normal operating conditions, in such an application the density of the electrons impinging on different portions of a cylindrical collector electrode varies, thereby causing unequal heating. Further, the density and velocity of the electrons falling on some portions of such an electrode may be so great as to cause the generation of intergranular cracks in the illuminated surface. Further, stresses engendered for either, or both, justmentioned reasons may combine to cause fatigue of the OFHC copper as evidenced by cracking which ulti mately makes the collector electrode ineffective by destroying the required vacuum with the tube.

SUMMARY OF THE INVENTION Therefore, it is a primary object of this invention to provide an improved collector electrode for a traveling wave tube.

Another object of this invention is to provide an improved collector electrode for a traveling wave tube, such electrode being fabricated in such a manner that cracking is reduced when such electrode is subjected to heating from intense electron bombardment.

These and other objects of this invention are attained generally according to my concepts by providing a hollow cylindrical collector electrode in a TWT, such electrode being made by laminating a cylinder of stainless steel between an inner cylinder of OFHC copper and an outer generally cylindrical member, also formed of OFHC copper, but having cooling fins projecting therefrom.

BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding of this invention, reference is now made to the following description of the accompanying drawings wherein:

FIG. 1 is a cross-sectional view, somewhat simplified, of a TWT incorporating a collector electrode according to my inventive concepts, and

FIG. 2 is a cross-sectional view, somewhat distorted, to show my contemplated laminations, of a collector electrode according to my inventive concepts.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, it may be seen that a high powered TWT incorporating a collector electrode according to my concept may be conventional in appearance. Thus, an electron beam source 10 may be formed in any convenient manner and passed through an amplifying section 12 after modulation from a modulation source (not shown). After amplification, such a modulated beam is passed through an aperture (not numbered) in a pole piece 14 and is coupled to an output line 16 in a conventional manner. The electron beam finally is caused to pass into a substantially field-free space defined in part by a magnetic shield 18 and a plate 20. A collector electrode 22, to be described in detail in connection with FIG. 2, is disposed in the field free space as shown. Suffice it to say here that the collector electrode 22 is arranged to define an evacuated volume within the field-free space. It may be seen, therefore, that mutual repulsion between the electrons in the beam (after passing through the aperture in the pole piece 14 into the field-free space) causes individual electrons to follow arcuate paths toward the inner wall of the collector electrode 22. The exact path followed by any particular electron is a function of its velocity on passing through the aperture in the pole piece 14 and the density of the beam at that point. It will be recognized, however, that if there is little dispersion in velocity of the electrons in the beam passing through the aperture in the pole piece 14, the arcuate paths of the individual electrons will be such as to cause a majority of the electrons to impinge on a relatively small portion of the collector electrode 22. It follows then that localized heating of the collector electrode 22 occurs.

Referring now to FIG. 2 it may be seen that my con templated collector electrode is designated to affect conduction of heat resulting from electron bombardment. Thus, my assembled collector electrode comprises substantially a cylindrical assembly comprising an inner liner 25 of OFHC copper, a core 27 (here made of nonmagnetic stainless steel) and an outer shell 29 of OFI-IC copper with a substantially conical cover over one end. The cylindrical assembly and conical cover, after being laminated, are machined as shown to provide cooling fins (not numbered) running longitudinally along the outside of the outer shell 29. The lands of such fins in the cylindrical assembly are then brazed to the inside of the magnetic shield 18 so that the grooves between adjacent fins form channels for a coolant, as oil or water.

It is preferred that the elements making up my collector electrode be (except as just mentioned) joined together without use of any technique such as brazing. To accomplish an intimate and continuous joint between the elements, I prefer that a so-called explosive cladding" process be followed. In such a process, the three elements are assembled and placed in a mold. The inner surface of the inner liner 25 is covered with an ex plosive which is detonated to force the three elements into intimate Contact as shown in FIG. 2.

In operation, the core 27 has no effect on the fieldfree space but such core does affect the manner in which heat is conducted through the collector electrode and the mechanical stability of such electrode. That is, the core 27, being fabricated from stainless steel, maintains its strength even though localized heating is encountered. Further, it is thought that the core 27 reduces the effect of localized heating at the roots of the cooling fins, thereby reducing the occurrence of cracking at such sites due to fatigue. Still further, and perhaps most importantly, the core 27 prevents any crack which may start on either side of my collector electrode from propagating through the full thickness of the copper portions of the wall of such electrode.

Having described a preferred embodiment of my improved collector electrode, it will now become evident to one of skill in the art that changes may be made without departing from my inventive concepts. For example, because a substantially field free space is desired within the collector electrode of a high powered TWT, the material from which the core of my collector electrode is made need not be non-magnetic. That is, so long as the selected material is capable of maintaining its physical characteristics under operating temperatures, its magnetic qualities are of secondary importance. As a matter of fact, the core need not be made of stainless steel, but rather may be made of any metal which has superior thermal conductivity (such as beryllium copper or titanium) and which is immune to cracking under operating conditions.

It is felt, therefore, that this invention should not be restricted to its disclosed embodiment but rather should be limited only by the spirit and scope of the appended claims.

What is claimed is:

1. In an electron discharge device wherein a beam of electrons is directed toward a collector electrode, an improved collector electrode comprising a hollow substantially cylindrical portion and a hollow conical portion covering one end of such cylindrical portion, both such portions being laminated and consisting of a core layer of a material selected from the group of stainless steel, beryllium, copper and titanium between an inner and an outer layer of oxygen-free high conductivity copper.

2. The improved collector electrode as in claim I wherein each side of the core layer is intimately bonded to both the inner and the outer layer of oxygen-free high conductivity copper.

Claims (2)

1. In an electron discharge device wherein a beam of electrons is directed toward a collector electrode, an improved collector electrode comprising a hollow substantially cylindrical portion and a hollow conical portion covering one end of such cylindrical portion, both such portions being laminated and consisting of a core layer of a material selected from the group of stainless steel, beryllium, copper and titanium between an inner and an outer layer of oxygen-free high conductivity copper.

2. The improved collector electrode as in claim 1 wherein each side of the core layer is intimately bonded to both the inner and the outer layer of oxygen-free high conductivity copper.

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