US3365601A - High power vacuum tube with magnetic beaming - Google Patents

Description

Jan. 23; 1968 y H DOOUTTLE 3,365,601

HIGH POWER VACUUM TUBE WITH MAGNETIC BEAMING Original Filedqan. 28, 1965 Y 3 Sheets-Sheet 1 W2 Q F53 I P J t 60 INVENTOI? HOWARD D. 000L/ 7 7' LE J 1968 H. D. DQOLITTLE 3,

HIGH POWER VACUUM TUBE WITH MAGNETIC BEAMING Original Filed Jan. 28, 1965 3 Sheets-Sheet 2 lNl/E/VTOI? HOW 1 RD 0 DOOL TTLE Jan. 23, 1968 H; D. DOOLITTLE 3,365,601

HIGH POWER VACUUM TUBE WITH MAGNETIC BEAMING Original Filed Jan. 28, 1965 I BSheets-Shes 3 CONSTANT GRID-VOLTAGE CHARACTERISTICS er"=7.6 v o LTS PLATE CURRENT 5 GRID CURRENT----- I C=PEAK POSlTlVE 6 I400 GRID VOLTAGE 'F/ae 4 PEAK PLATE CURRENT AMPERES PEAK GRID CURRENT AMPERES o O'I-23456789l0 PLATE VOLTAGE KILOVOLTS llVl/E/VTOR HOW/1D [7. DOOL/TTLE United States Patent 3,365,601 HlGH POWER VAQUUM TUBE WITH MAGNETEQ BEAJVHN'G Howard D. Doolittle, Stamford, Conn, assignor to The Machlett Laboratories, incorporated, Springdale, Conn, a corporation of Connecticut fiontinnation of application Ser. N 428,687, Jan. 2% 15 65. This application Fan. 24, 1967, Ser. No. 611,474 12 Claims. (6i. 313-21) ABSTRACT (PF THE DISCLOSURE An electron discharge device employing magnetic fields for eifecting controlled how of electrons and comprising an electrode structure embodying an anode having an open ended cavity therein, an array of cathode filaments within the cavity, grid wires in the cavity on either side of said filament array, and a magnet enclosing said anode.

This application is a continuation of application Ser. No. 428,687, filed Ian. 28, 1965, and now abandoned.

This invention relates to electron discharge devices and has particular reference to novel high power electron tube structures employing magnetic fields for eifecting controlled fiow of electrons to prevent production of grid current.

In the manufacture of high power tubes requiring emission from a cathode of extremely large numbers of electrons, a serious problem has prevailed due to the fact that critical control of electron flow is necessary to prevent electron impingement upon grid elements with resultant production of undesirable grid current. Such control in the past has taken many forms, among them being specially shaped cathode structures, shielded grid structures, deflecting electrodes, and other means designed to beam the flow of electrons between cathode and anode by creation of appropriately shaped electric fields whereby the electrons will reach the anode without being substantially intercepted by grid elements and without substantial bunching at the anode.

Grid current is undesirable since it increases the drive power required to operate the tube, raises the grid temperature, and produces relatively large secondary electron emission from the grid. The driving power for a tube is a product of the grid voltage swing and the grid current. Except for circuit losses, the driving power may be reduced to zero if the grid intercepts no electrons and produces no grid current at all. Since in the presently described tube structure grid current is reduced by a factor of 10 or more over that of a conventional triode, the driving power is also reduced by the same order of magnitude. In power triodes a serious power limitation is due to high grid temperatures. Current to the grid heats the grid wires. If the grid wires get too hot they can act as primary emitters and cause excessive plate dissipation, as Well as loss of grid control. By substantially reducing the current produced in the grid, this problem is solved. Most triodes show regions of reverse grid current due to secondary electron emission from the grid. This can cause loss of control by the grid, resulting in pulse stretching in pulse modulator tubes and/or flash arcing to the plate. In general, this can be counteracted only by putting a resistor in parallel with the grid and cathode such that the current in this swamping resistor is greater than the reverse grid current. Obviously, the input resistor absorbs power from the driving stage, and it is desirable to keep this resistor as large as possible. In tubes such as described herein, the secondary emission current is much smaller than in conventional tubes, since it is directly related to the current produced in the grid by interception of electrons from the cathode. Furthermore, the magnetic field will tend to return some secondary electrons to the grid.

Grid current produces secondary emission effects which sometimes result in pulse stretching in conventional tube structures. This and other disadvantages are overcome in the presently described tube wherein grid current is reduced by magnetically beaming electron flow so that it will not be substantially intercepted by the control grid elements.

While magnetic beaming of electron flow in electron tubes has been explored in the past, this has been done in connection with relatively low power devices and has not been heretofore successful when utilized in high power pulse modulator, amplifier or oscillator tubes capable of delivering from up to seventy mw. of pulse output at 1200 amperes with pulse widths up to 10,000 microseconds or 2.5 mw. of CW power at frequencies up to 30 inc. Tubes capable of high power performance have been made with complicated electrode structures for the purpose of beaming the electron flow from specially designed cathodes and grid structures to the anodes, and generally included shield grid structures which were operated at cathode potential in order to achieve efiicient operation.

The present invention achieves the described ellicient high power operation with a simple triode 0r tetrode structure utilizing simple uncomplicated wire-like electrodes by virtue of magnetic electron focusing together with novel and efiicient liquid cooling. This is accomplished by the novel combination of an annular array of longitudinally extendin" cathode filament wires, which array is located between two or four annular arrays of control grid wires. The grids and cathode are themselves both located between inner and outer annular anodes so that electron emission from the filaments may pass in both directions radially onto one or the other of the anodes. Beaming is efiected by a magnetic field extending radially of the tube from one pole of a magnet inside the inner anode to a second pole encircling the outer anode, and cooling is achieved by encircling the magnet and electrode structures with a water jacket through which a coolant is introduced into the interior of the tube around the anode as well as around the magnet for efliciently dissipating heat. This combination of features, together with the novel cathode and grid structures, results in the production of a novel but simple tube structure which achieves the desired exceedingly high power output.

These and other novel features of this invention will become apparent from the following description taken in connection with the accompanying drawings, wherein:

FIG. 1 is a front elevational view of a tube embodying the invention;

2 is a vertical sectional view talren substantially along the axis of the tube of FIG. 1;

PEG. 3 is a fragmentary view of the cathode and electrode structures of the tube;

FIG. 4 is an enlarged fragmentary sectional view of the devices connecting the cathode and grid electrodes to supporting decks;

PEG. 5 is a fragmentary view of cathode and grid wires arranged as in a tetrode structure; and

FIG. 6 is a graph showing plate and grid currents for various plate and grid voltages.

Referrin more particularly to the drawings wherein like characters of reference designate like parts throughout the several views, the tube structure embodies an annular metal anode 1i) (FIG. 2), preferably of copper, which is provided with an axially extending channel 11 throughout the annulus, thus forming inner and outer annular walls 12 and 33 respectively. The open mouth of the channel l]. is directed toward the terminal structure to 7 heavy rugged ring to be used additionally as a support for mounting the tube in a coolant jacket, as will be described later.

Depending into the cavity within the anode walls is a plurality of thcriated tungsten filaments 17 forming part of an assembled cathode electrode structure 15.

Qathode structure 1% comprises a pair of axially spaced supporting rings 18 and 19 which are connected at their inner peripheries to respective concave decks 29 and 21. As can be seen best in FIG. 4, supporting rings 18 and 19 are connected together but are insulated from each other by an intermediate ceramic spacer ring 22. A screw 23 or the like is preferably used as a connecting member and is mounted in ring 19 while being suitably insulated from ring 18. Rim 18 is preferably flanged as shown and is attached to deck ill by the flange.

As shown best in FIG. 3, the filaments 17 are U-shaped wires, preferably of thoriated tungsten, mounted at the ends in the ends of elongated studs 24 and 24a respectively. Studs 24a extend through supporting ring 1% into ring 18 to which they are conductively affixed, while studs 12d terminate at and are fixed to ring 19. Thus, filament power can be applied to the filaments from one ring, through the respective studs and filament wire, and then through the other studs to the second ring. Copious emission of electrons from the filaments will result.

lhe inner deck 21 is of relatively thick heavy metal such as copper and has a central opening 25. One end of a tubular metal support as is sealed to this deck adjacent the periphery of opening 25, as shown in FIG. 2, Outer deck 20 likewise has a central opening .27 and one end of a second tubular metal support 28 is fixed thereto adjacent the periphery of opening 27, support 28 encircling support 26 in spaced relation thereto. The opposite end of support 2% extends toward the adjacent end extremity of the tube and with encircling terminal ring 29 forms a cathode terminal to which may be attached means for supplying power to the filament. The inner support 26 extends only part way along the length of outer support 23 and is mounted on and supported by support 28 through an insulating seal comprising a pair of metal rings 3d and 31 connected together by a ceramic ring 32, one metal ring 36 being sealed to the extreme end of support 26 and the other ring 31 being sealed to a metal ring 33 which is carried by the inner surface of support 28. To provide a second cathode connection, a metal disc 34 is sealed at its periphery to the inner surface of support 2:; and has a central opening in which is fixed one end of a hollow elongated exhaust tubulation 35, the other end of tubulation 35 being capped as at 36. During tube processing the interior of the vacuum chamber may be outgassed through tubulation 35 and sealed off by cap 36, after which the cap and tubulation provide a second terminal means for connection of the second side of the cathode circuit to the external source of cathode power (not shown).

The cathode structure becomes severely heated during operation of the device, and the resultant thermal expansion sometimes causes movement of the decks 29 and 21 with respect to one another, thus resulting in bowing of the filament wires as a result of shifting of one end of a wire with respect to its other end. To overcome this problem, cathode-supporting deck as is made relatively thin and flexible and is clamped to deck 21 as described so that upon thermal expansion of the elements of the cathode the deck 29 will flex without affecting the filament Wires.

The filaments 17 are so disposed as to lie in an annular arrangement throughout the length of the annular cavity 11 in the anode, with each side of the filaments lying equidistant from the axis of the tube. A grid electrode 37 is provided and includes a plurality of U-shaped grid vires 38 of molybdenum or other selected metal, one grid wire 33 being associated with each filament wire 17 but at right angles thereto and midway thereof as shown best in FlG. 3. Grid wires 38 are longer than filament wires 17 and extend slightly beyond wires 17 as shown, and are maintained in preset spaced relation by a concave hoop 39 to' which the outer ends are attached. The opposite ends of grid wires 38 are mounted on adjacent ends of respective inner and outer supporting sleeves 40 and 41 respectively Outer sleeve 41 has its other end conductively connected to a frusto-conical supporting deck 42, the inner peripheral portion of which is mounted upon a tubular grid support 43. Grid support 43 encircles cathode support 28- in spaced relation therewith and is connected to a grid terminal structure which includes a heavy metal ring 44 sealed to the end thereof and a frusto-conical flanged metal terminal member 45 which is disposed to flare outwardly therefrom, as shown best in FIG. 2, for ease in attaching external means (not shown) for supplying grid potential.

The inner grid sleeve 4% is mountedon a rigid ring 4-6 which is in turn supported by studs 47 carried by grid-supporting ring 42, the studs extending freely through slots or openings in cathode-supporting rings 20 and 21 to prevent shorting therewith.

The tube envelope encloses the grid and cathode supporting structures and comprises a hollow insulating ceramic cylinder 48 attached at one end by a kovar ring 49 to the grid terminal 45 and at the other end by a series of ring seals 59, 51, 52, and 53 to the terminal end portion of the anode ill.

From the foregoing it can be seen that the tube utilizes a cathode which comprises a cylindrical array of axially disposed thoriated tungsten wires, preferably one hundred ten in number. The grid is ellectively comprised of an inner cylindrical array of axially extending wires on a smaller diameter than the cathode wires, and an outer array of larger diameter than the cathode wires, whereby each set of grid wires is radially disposed midway between each of a set of cathode wires. A novel anode structure is provided for effectively placing two anodes in surrounding relation to the grids, one on a smaller inner diameterand the other on a larger outer diameter.

Electrons emitted from the filament wires 17 will be drawn, under the influence of the grid wires 33, from the filaments toward the anode portions 12 and 13. However, since in normal tube operation electrons are emitted from all sides of the filament wires, many thereof will impinge upon the grid wires, causing undesired grid current, grid dissipation and secondary emission eflects which sometimes result in pulse stretching. To overcome this undesirable condition, the presently described tube is provided with means for providing a magnetic field in the intended direction of electron flow, that is, radially of the tubes axis. To achieve this, there is provided an annular magnet 54 with a central annular cavity 55 in which is suspended the anode structure 10. The portions 56 and 57 of the magnet forming the inner and outer walls of the cavity comprise the north and south pole pieces of the magnet. Thus, the magnet flux extends radially of the pole pieces and, consequently, also extends in the directions of electron fiow. This magnetic field thus beams electrons from each cathode filament wire, directing the electrons in beams radially toward each anode section 12 and 13 without substantial impingement of the electrons upon the grid wires.

The anode and magnet structures are located within an enclosing jacket through which water or other selected coolant is made to flow for cooling purposes. The jacket comprises a cylindrical outer side wall 58 which is closed at one end by a base 59 and has a flange 60 at its other end by which it may be bolted or otherwise secured in leakproof fashion to the anode terminal 15. Coolant is introduced from a suitable source (not shown) through one of a pair of pipes 61 directly into a cavity 63 provided at the base of the magnet 54 by means of a U- shaped section in annular conduit 64, from which it is urged through openings 65 in magnet 54 to the anode 10, as shown by arrows in FIG. 2. The coolant flows upward over the entire outer surface of the anode l and then down around the outer surface of the magnet 54 into the space 65 between the jacket conduit 64 and base 59, from which it is expelled through pipe 62. Thus, the magnet has been made to become part of the means for controlling flow of coolant in a manner to efliciently cool the heated elements of the tube. An inner cylindrical jacket wall 67 is suitably sealed at its inner end as by ring 68 to anode disc 14 and at its outer end by a metal bellows 69 and disc 70 to complete the jacket enclosure. The space within the wall '67 may be utilized to house a vac-ion pump or other associated equipment, if desired.

The tube described in the foregoing has been found to operate very efficiently at DC plate voltage of 65 v. By operating at a tube drop of kv., the plate eificiency is 92%. The cutoff [A is 20, which requires a bias voltage of -3500 to 4000 volts. A positive grid drive voltage of 3009 volts will give a plate current of 1150 amps. at 5 kv. tube drop. Grid current is less than 15 amps. This tube is capable of CW operation in excess of 2.5 mw. or pulsed RF. operation up to mw. at high duty. Filament power requires 7.6 volts at 1900 amperes or slightly less than kw. Since primary grid current is low, secondary emission effects are easily neutralized.

Although the foregoing description specifically describes a triode tube structure, the present invention is as readily adaptable to a tetrode structure utilizing a second or screen grid comprising a number of U-shaped wires 7i (FIG. 5) radially aligned with and straddling the control grid wires 38a, the legs Tia and 71b of wires 71 being located in two respective annular configurations, one on either side of the grid 38a between it and the opposed sides of the anode portions. This second grid may be operated at a positive DC potential of, for example, from 2000 to 4006 volts or may be operated at ground potential in a shielded grid triode. The [1. of this grid with respect to grid 37 would be of the order of five. Such a structure would possess the usual desirable characteristics of conventional tetrodes over conventional triodes, such as reducing the control grid swing necessary to extract maximum permissable current from the cathode and substantially reducing the capacitance between the plate and control grid. This latter feature is of particular importance at frequencies above a few megacycles on tubes of this size. Conven tional screen grid tetrodes are limited in power output by screen grid dissipation. However, a magnetic field tetrode as described herein will substantially reduce the screen grid dissipation and permit higher power output.

An additional interesting and advantageous feature relating to magnetic field electron beaming is that the magnetic field acts to oppose spreading or contraction of the electron beam. That is, in the cathode-to-grid area, the magnetic field restricts beam spreading. it the beam normally tends to focus on a localized anode area by contraction, the magnetic field will tend to widen the beam. In triodes using electrostatic beaming, there are a certain set of plate and grid voltages which cause sharp focusing of the beam on the anode, giving rise to high power density on restricted anode areas and leading to excessive local anode temperatures. This type of undesirable focusing is opposed in a magnetic structure.

From the foregoing, it will be apparent that a novel high power electron tube has been achieved. It will also be apparent that many modifications and changes may be made in the structures and methods described by those skilled in the art. Accordingly, it should be understood that the foregoing description is illustrative only and should not be interpreted in a limiting sense.

I claim:

1. A high power electron discharge device comprising an envelope, an annular anode connected at one end to the envelope and having an annular open-ended cavity therein, an annular array of cathode filaments extending within said cavity, a pair of annular arrays of grid wires extending into said cavity one on either side of said filament array, terminals connected to said filaments and grid wires extending externally of said envelope, and an annular magnet enclosing said anode, the magnet having inner and outer walls defining an annular cavity within which the anode is suspended, the inner and outer walls of the magnet being pole pieces influencing flow of electrons radially from said filaments to said anode.

2. A high power electron discharge device comprising an envelope, an annular anode connected at one end to the envelope and having an annular open-ended cavity therein, an annular array of cathode filaments extending within said cavity, a pair of annular arrays of grid wires extending into said cavity one on either side of said filament array, a pair or" substantially parallel filamentsupporting decks, the filaments being connected at 0pposite ends to respective decks, terminal members extending from respective decks and from said grid wires externally of the envelope, and an annular magnet enclosing said anode, the magnet having inner and outer walls defining an annular cavity within which the anode is suspended, the inner and outer walls of the magnet being pole pieces influencing flow of electrons radially from said filaments to said anode.

3. A device as set forth in claim 2 wherein one of said decks is rigid and the other is flexible, said flexible deck comprising means for maintaining the filaments stress free under conditions of varying temperature.

4. A high power electron discharge device comprising an envelope, an annular anode connected at one end to the envelope and having an annular open-ended cavity therein, an annular array configuration of cathode filaments extending within said cavity, a pair of annular arrays of grid wires extending into said cavity one on either side of said filament array, terminals connected to said filaments and grid wires extending externally of said envelope, said filaments comprising wires formed substantially in U-shapes and disposed in planes extending substantially in the arc described by said annular configuration, said grid wires each defining a U-shaped configuration and each disposed in a plane radially of the device and substantially at right angles to the planes of the filament wires, and an annular magnet enclosing said anode, the magnet having inner and outer walls defining an annular cavity within which the anode is suspended, the inner and outer walls of the magnet being pole pieces influencing flow of electrons radially from said filaments to said anode.

' the envelope and having an annular open-ended cavity therein, an annular array of cathode filaments extending Within said cavity, decks supporting respective opposite ends of the filaments, a pair of annular grids extending into said cavity one on either side of said filament array, said grids each composed of U-shaped wires, the respective legs of which comprise parts of respective grids, the U-shaped wires each being disposed in a plane extending radially of the device, a deck supporting one of said grids, a ring supporting the other grid, means extending through said filament-supporting decks mounting the ring on the grid-supporting deck, terminals connected to said decks extending externally of said envelope, and an annular magnet enclosing said anode, the magnet having inner and outer walls defining an annular cavity within which the anode is suspended, the inner and outer walls of the magnet being pole pieces influencing flow of electrons radially from said filaments to said anode.

6. A high power electron discharge device comprising an envelope, an annular anode connected at one end to the envelope and having an annular open-ended cavity therein, an annular array of cathode filaments extending within said cavity, a pair of annular arrays of grid wires extending into said cavity one on either side of said filament array, terminals connected to said filaments and grid wires extending externally of said envelope, an annular magnet enclosing said anode, the magnet having inner and outer walls defining an annular cavity within which the anode is suspended, the inner and outer walls of the magnet being pole pieces influencing flow of electrons radially from said filaments to said anode, and means for cooling said anode comprising a jacket enclosing the sides and one end of said magnet in spaced relation therewith, inlet and outlet means connected to said jacket, and means for directing coolant from said inlet means through the magnet onto'the anode and thence along the outer surface of the magnet to the outlet means.

7. A high power electron discharge device comprising an envelope, an anode connected at one end to the envelope and having a cavity therein, an array of cathode filaments extending in a linear fashion Within said cavity, a pair of arrays of grid wires extending into said cavity one on either side of said filament array, terminals connected to said filaments and grid wires extending externally of said envelope, and a magnet enclosing said anode and defining a cavity within which the anode is suspended, opposed side walls of the magnet being pole pieces influencing flow of electrons transversely from said filaments to said anode.

8. A high power electron discharge device comprising an envelope, an anode connected at one end to the envelope and having a cavity therein, an array of cathode filaments extending within said cavity, a pair of arrays of grid wires extending in a linear faslr'on into said cavity one on either side of said filament array, a pair of substantially parallel filament-supporting decks, the filaments being connected at opposite ends to respective decks, terminal members extending from respective decks and from said grid wires externally of the envelope, and a magnet enclosing said anode and defining a cavity within which the anode is suspended, opposed side walls of the magnet being pole pieces influencing flow of electrons transversely from said filaments to said anode.

9. A device as set forth in claim 8 wherein one of said decks is rigid and the other is flexible, said flexible deck comprising means for maintaining the filaments stress free under conditions of varying temperature.

10. A high power electron discharge device comprising an envelope, an anode connected at one end to the envelope and having a cavity therein, an array of cathode filaments extending within said cavity, a pair of arrays of grid wires extending into said cavity one on either side of said filament array, terminals connected to said filaments and grid Wires extending externally of said envelope, said filaments comprising Wires formed substan tially in U-shapes and disposed in planes extending substantially in a predetermined configuration, said grid wires each defining a U-shaped configuration and each disposed in a plane substantially at right angles to the planes of the filament wires, and a magnet enclosing said anode and defining a cavity within which the anode is suspended, opposed side walls of the magnet being pole pieces infiuencing flow of electrons transversely from said filaments to said anode.

11. A high power electron discharge device comprising an envelope, an anode connected at one end to the envelope and having a cavity therein, an array of cathode filaments extending within said cavity, decks supporting respective opposite ends of the filaments, a pair of grids extending into said cavity one on either side of said filament array, said grids each composed of U-shaped wires, the respective legs of which comprise parts of respective grid elements, the U-shaped Wires each being disposed in a plane extending transversely of the filament array, a

deck supporting one end of said grids, a support for the other end of the grid, means extending through said filament-supporting decks mounting the support on the gridsupporting deck, terminals connected to said decks ex-. tending externally of said envelope, and a magnet enclosing said anode and defining a cavity within which the anode is suspended, opposed sides of the magnet being pole pieces influencing flow of electrons transversely from said filaments to said anode.

12. A high power electron discharge device comprising an envelope, an anode connected at one end to the envelope and having a cavity therein, an array of cathode filaments extending within said cavity, a pair of arrays of grid wires extending into said cavity one on either side of said filament array, terminals connected to said filaments and grid wires extending externally of said envelope, a magnet enclosing said anode and defining a cavity Within which the anode is suspended, opposed sides of the magnet being pole pieces influencing flow of electrons transversely from said filaments to said anode, and means for cooling said anode comprising a jacket enclosing the sides and one end of said magnet in spaced relation therewithin, inlet and outlet means connected to said jacket, and means for directing coolant from said inlet means through the magnet onto the anode and thence along the outer surface of the magnet to the outlet means.

References Cited UNITED STATES PATENTS l,714,405 5/1929 Smith 313l6l 2,332,977 10/ 1943 Skellet 3 13-162 2,496,003 1/1950 Eaves 313-246 2,810,849 10/ 1957 Agule 313-45 DAVID J. GALVIN, Primary Examiner.

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