US3426230A - Direct radiation cooling of the collector of linear beam tubes - Google Patents

Description

Feb.4.l969

JAMES E. WEBB 3,426,230 ADMINISTRATOR OF THE NATIoNAI AERoNAuTIcS AND SPACE ADMINISTRATION DIRECT RADIATION COOLING OF THE COLLECTOR OF LINEAR BEAM TUBES Filed April 18, 1967 ELECTRON BEAM FORMING CIRCUITS POWER & IODULATING CIRCUITS FIG. 2

INVENTOR United States Patent O 4 Claims ABSTRACT OF THE DISCLOSURE In a linear beam tube the normal electron beam collector is thermally isolated and made of small mass so that it is heated to incandescense by the impacting electron stream. The heated collector is made parabolic in shape to produce a favorable unidirectional heat radiation pattern and is positioned near the end of the tube opposite the cathode end. Said collector is oriented to radiate its heat out of the tubes envelope through a vacuum tight window which in this case has good heat transmitting properties, thereby cooling the collector electrode without special cooling means. The collector also includes a reflector, so positioned with respect to the parabolic section, so that most of the heat from the collector is radiated towards the window either directly from the collector or the reflector thereof. As a result about 80% of the heat generated by the thermal con-version is radiated out of the tube.

ORIGIN OF INVENTION The invention described herein was made in the performance of work under a NASA contract and is subject to the provisions of Section 305 of the National Aeronautics and Space act of 1958, Public Law 85-568 (72 Stat. 435; 42 USC 2457).

BACKGROUND OF THE INVENTION Description of the prior art One primary requirement in a high power electron tube, such as a klystron or traveling wave tube, is the removal or dissipation of heat produced by the electron collector which forms an integral part of the tube. In the prior art, various techniques have been employed to achieve such heat dissipation.

In one commercially available traveling wave tube, a combination of heat dissipation by conduction with blown fin radiative/ convective cooling is employed. In another commercially available klystron, a circulating fluid in a. heat exchanger arrangement is employed.

One of the basic disadvantages of prior art heat dissipation arrangements is the requirement of associated equipment, needed for the heat removal. Such added equipment increases the overall complexity of the electron tube system which is often undesirable, particularly in space applications where a primary design criterion is reduced system complexity and size. Also, in space applications, since systems are closely located to one another, it is often not possible to remove heat from the collector of the electron tube by conduction, since such heat removal may overheat surrounding systems which already operate near their upper temperature limit. Therefore, a new arrangement for dissipating heat from a collector of an electron tube is required, particularly for use in elec tron tubes incorporated in spacecraft systems.

OBJECTS AND SUMMARY OF THE INVENTION It is a primary object of the invention to provide a new arrangement for dissipating heat from the collector of an electron tube or the like.

Another object is to provide an arrangement for removing heat from the collector of an electron tube or the like without requiring associated equipment outside the tube itself.

A further object is the provision of a simple arrangement contained in an electron tube or the like for dissipating heat from the collector thereof without the need for associated external equipment.

These and other objects are achieved by providing within the vacuum envelope of an electron tube a collector and a reflector of selected shapes so that substantially all the heat from the collector is radiated towards one end of the tube. A reflector, external to the tube may be positioned with respect to the window to confine the heat radiation pattern from the window to a desired angular range.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention will best be understood from the following description when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a combination cross-sectional view and block diagram of an electron tube, incorporating the novel arrangement of the present invention; and

FIGURE 2 is a simplified cross-sectional view of another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Attention is now directed'to FIGURE 1 in which an electron tube 10 which incorporates the novel heat radiative arrangement of the present invention is shown. In order to distinguish between the novel aspects of the invention and the conventional parts of tube 10, the conventional parts are shown in simplified block form. As is appreciated by those familiar with the art, an electron tube such as a klystron or traveling wave tube (TWT), either of which is represented by tube 10, includes structure which is used to produce an electron beam which is directed to a collector. Such structure includes a cathode, control electrodes such as modulating and beam-shaping electrodes. These electrodes are connected to appropriate power and modulating circuits to provide a properly modulated and shaped electron beam. The tube also includes a collector which is at a selected positive potential with respect to the cathode. The electrons of the modulated and shaped beam are collected by the collector.

With a given input (DC) power applied to the collector, the proportion of this power dissipated at the collector as heat which must be removed is an inverse function of the radio-frequency (RF) modulation on the beam. With no RF modulation, all of the direct current (DC) input power is converted to heat at the collector.

In FIGURE 1, tube 10 is shown including an evacuated envelope 12 in which the cathode, and the control electrodes are represented by the electron beam forming circuits 15. Circuits 15 assumed to be supported in envelope 12 by supports 16 are shown connected through the envelope to power .and modulating circuits 20. Thus, as is appreciated, by applying appropriate power and modulating signals from circuits 20, circuits 15 provide a properly modulated and shaped electron beam, generally designated by numeral 22. The beam is assumed to be progressing along the longitudinal axis of envelope 12 towards end 12a thereof. Between end 12a and circuits 15, along the beams axis, is located a collector 25 which is electrically oriented (not shown) by circuits 20 to a positive potential with respect to the cathode in circuits 15. As a result, the beam 22 is attracted to and intercepted by collector 25.

The beam is shaped and confined (focused) along the length of the tube by the forming circuits 15. The influence of these circuits normally terminates at the collector 25 entrance. As a result, the repulsive action of the beams constituent electrons spreads the beam as indicated by dashed lines 28. The electrical energy of the beam is converted to thermal energy as the spread beam physically impacts on the concave surface 25 and the total collector portion 25a rises in temperature accordingly.

The shape of collector 25 is most significant. It includes an egg-shaped or parabolic section 25a, with the concave or inner surface thereof directed toward beam 22 and the convex surface toward the end 12a. The collector also includes a cone-like section 22b with a truncated end which points towards circuits 15. The sections are integrally connected to form a single structure of collector 25. The trucated end and the center of the parabolic section 22a are aligned on the beam axis, with the beam entering the collector through the end of the section 22b. The beam 22 may be regulated so that due to its velocity and the collectors potential, the beam starts diverging so that electrons are collected near the top of the parabolic section 25a, at a selected angle with respect to the beams axis, such as a 30 angle. The convex surface of section 25a faces end 12a of envelope 12.

A heat-transmitting material, designated by numeral 30 is positioned at end 12a to form a vacuum-tight seal of the envelope. Material 30 actually serves to form a window, through which heat is radiated out of the envelope 12. The selected material is one which transmits rather than absorbs heat in the expected spectral range.

One such material is synthetic sapphire which transmits the spectral range from white hot to red, which may be thought of as between 2,400 to 46,000 angstroms. In one reduction to practice, the window used was a CA-8l00 sapphire window commercially available from Eitel-Mc- Cullough, Inc., of San Carlos, Calif. Hereafter, the material 30 may also be referred to as the sapphire window 30, although as should be appreciated materials other than sapphire may be employed.

The parabolic shape of section 25a of collector 25 is such that it is made to favor a forward radiation direction fthe heat produced therein, so that heat from the convex side of section a is favored to radiate directly to window and therefrom to the outside of envelope 12. The heat radiating directly from section 25a to window 30 is designated in FIGURE 1 by lines 32.

Although a significant portion of the heat radiates forward from collector section 25a to the window, some heat, unless prevented, will travel backwards toward cirouitry 15. To prevent this from occurring, the novel heat dissipating arrangement of the invention includes a parabolic reflector 3'5 with a truncated top or end. The convex side of reflector faces the circuits 15 and the concave side faces the collector 25 and window 30. The beam 22 enters collector 25 through the truncated end of reflector 35 which is along the longitudinal axis of the envelope. The base of reflector 35 is adjacent window 30. Brackets 37 support reflector 35 within envelope 12 while rods 40 support the collector 25 in proper relationship to the concave side of reflector 35. Basically, the function of reflector 35 is to prevent any heat from traveling back to circuits 15.

Any heat radiating from section 25!; of collector 25 is intercepted by the concave side of reflector 35 and reflected therefrom to window 30, through which it exits the envelope 12. Heat reflected by reflector 35 is designated in FIGURE 1 by numerals 36. Thus, a high percentage of the heat generated by collector 25 is radiated either directly from collector 25 to window 30, or directed to reflector 35 from which it is reflected to window 30. As a result, the particular arrangement of the collector 25 and reflector 35, both within the envelope 12 of the tube, causes most of the heat to radiate towards window 30. And, by selecting the window 30 to be of a material of high transmissivity in the expected spectral range of the heat, most of the generated heat is removed from the tube without associated equipment.

In spacecraft applications, since the environment outside the craft is a vacuum often referred to as black space, the tube 10 is preferably mounted with the sapphire window looking directly into the black space. As a result, heat transmitted through the window is dissipated by radiation into the black space, thereby removing most of the heat generated in the tube. This avoids heat contribution to the spacecraft which 'may affect surrounding equipment. :If desired, an external reflector 45 may be employed near the window to confine the radiation pattern into space to a selected number of degrees from the central axis of the tube.

In applications other than in a spacecraft in which the exterior environment is black space, other techniques may be employed to remove the heat which exits the tube 10 through window 30. The particular technique will depend on the exterior environment and is subject to the choice of the user, as is appreciated by those familiar with the art. However, irrespective of the technique involved in removing the heat once outside the envelope 12, it should be again pointed out that by using the teachings of the invention, most of the heat generated by the collector 25 is radiated out of the envelope 12 without external equipment which are expensive and add to the tubes complexit Briefly, summarized, in accordance with one embodiment of the invention, the heat dissipating arrangement of the invention includes the use of an egg-shaped collector 25 and a reflector 35 to radiate most of the heat generated by the collector towards a window at one end of the envelope 12 of an electron tube 10. The window is formed of a material which transmits heat in the expected spectral range so that the heat radiated thereto is transmitted through the window to the exterior of the tube.

In one actual reduction to practice, the collector 25 was made of tungsten of a thickness to produce a temperature of about 1500 C. for a selected beam power.

Support rods 40 were made of a rhenium tungsten alloy which has a high temperature gradient so that collector 25 was substantially insulated from reflector 35. The reflector 35 was made of a plurality (three) of concentric spaced tungsten shells to minimize the heating of the convex side thereof. In this reduction to practice the magnitude of radiative heat was observed to reach of the total heat generated by the thermal conversion of the electron beam.

From the foregoing it should be appreciated that once the heat is radiated out of the window, any external cooling means may be employed to remove the heat from the surroundings external to the tube. For example, any known convective cooling techniques may be employed if the environment outside the tube is not a vacuum. Also, herebefore the invention has been described in conjunction with a collector which is completely enclosed within the housing 12. However, the invention need not be limited thereto. Thus, for example, in situations where the high potential of the collector 25 does not present a hazard, the tube may be designed so that the parabolic section 25a of collector 25 is located at the open end 12a of the envelope, forming a vacuum seal thereat, thereby eliminating the need for window 30.

Such an arrangement is diagrammed in FIGURE 2, in which like elements are designated by like numerals. In FIGURE 2, the collector 25 is mounted at end 12a, forming part of the vacuum wall of envelope 12. As in FIGURE 1, lines 28 represent diverging streams of electrons attracted to the collector. Heat is prevented from radiating back to the circuits 15 by one or more reflectors 35, which may be supported within envelope 12 by a thermal isolator 50, such as ceramic metal.

The latter described embodiment is particularly advan- 5. tageous in applications in which the collector is to be 0perated at lower temperatures. As is appreciated by those familiar with the art, when the collector is operated at lower temperatures efliciency decreases so that larger collector area is required. Also at lower collector temperatures the wavelength of the radiation increases. However, by eliminating the window material 30 the cooling arrangement is no longer limited by the longest wavelength which can be efiiciently transmitted through the material, and the area of the collector can be optimized to achieve a desired efliciency even at lower temperatures.

There has accordingly been shown and described a novel arrangement for removing heat generated by a collector in an electron tube or the like, from the tube without the use of complex associated equipment. The novel arrangement is contained within and forms part of the electron tube. It is appreciated that those familiar with the art may make modifications and/ or substitute equivalents in the arrangement as shown without departing from the spirit of the invention. Therefore, all such modifications and/or equivalents are deemed to fall within the scope of the invention as claimed in the appended claims.

What is claimed is:

1. In an electron tube of the type including an evacuated envelope, means positioned within said envelope for providing a beam of electrons propagating along a selected axis and directed to a collector in said envelope, an arrangement for collecting said electrons and for radiating heat, generated by said collector as a function of the electrons collected thereby, to the outside of the envelope, comprising:

an evacuated envelope defining a longitudinal axis and one end perpendicular thereto;

first means in said envelope for generating a beam of electrons along said longitudinal axis towards said one end of said envelope at which said windowforming member is positioned;

an electron collector having at least a hollow parabolically shaped section with concave and convex surfaces, said collector by forming a vacuum-tight seal at said one end, the center of said collector substantially coinciding with said longitudinal axis, with the concave surface thereof directed toward said beam, whereby said collector collects the electrons thereof; and

at least one reflector supported in said envelope adjacent said one end, said reflector having a truncated top with the center thereof coinciding with said longitudinal axis to provide a path for electrons therethrough, whereby heat is radiated to the exterior of said envelope through the convex side of said collector, with said at least one reflector preventing heat from the collector from radiating to said first means.

'2. The arrangement defined in claim 1 including at least one hollow parabolic reflector, with concave and convex surfaces the convex surface thereof being directed to the concave surface of said collector.

3. In an electron tube of the type comprising an evacuated envelope including an electron collector forming one end of the envelope and adapted to radiate heat, and means for propagating a beam of electrons along a predetermined path exending to the collector, the improvement comprising, in combination:

At least one reflector, including means defining an opening disposed in concentric alignment with the predetermined path, whereby at least a portion of the heat radiated by said collector is caused to be reflected back toward said collector by said reflector, to thus protect the means for propagating electrons from the effect of the heat radiated by the collector.

4. The combination of claim 3 wherein said collector is provided with a concave surface and said reflector is pro vided with a convex surface in juxatoposition with the concave surface of said collector.

References Cited UNITED STATES PATENTS 2,466,430 4/1949 Hutchison 3131 12 X 2,935,633 5/1960 Peters 31346 X 2,999,163 9/1961 Beese 31340 X JAMES W. LAWRENCE, Primary Examiner.

C. R. CAMPBELL, Assistant Examiner.

US. Cl. X.-R. 313-45, 46

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