US3334257A - Coaxial cathode-anode electron tube with channel-shaped control grids for the beaming structure - Google Patents

Description

Aug. 1, 1967 D. DOOLITTLE ETAL 3,334,257 COAXIAL CATHODE-ANODE ELECTRON TUBE WITH CHANNEL-SHAPED CONTROL GRIDS FOR THE BEAMING STRUCTURE Filed Jan. 4, 1966 Howard D. Dooliiiie Helmui' Longer,

INVENTORS' 7 United States Patent 3,334,257 COAXlAL CATHODE-ANODE ELECTRON TUBE WITH CHANNEL-SHAPED CONTROL GRIDS FOR THE BEAMING STRUCTURE Howard D. Doolittle and Helmut Langer, Stamford, Conn., assignors to the United States of America as represented by the Secretary of the Army Filed Jan. 4, 1966, Ser. No. 518,748 3 Claims. (Cl. 313-69) This invention relates to improvements in beam focusing electron tubes and has particular reference to pulse beamed tubes having a novel electrode structure.

The present invention is directed to means for modifying the electric field in the cathode anode space in order to increase the electron flow from the cathode, without an increase in the positive potentials applied to the control grid and anode during the concluding cycle; still at high current flow from the cathode, the part which will result in current to the control-grid is still kept at a minimum so that the emitting electron beaming structure will supply high cathode current densities with lower tube drive requirements.

It has previously been proposed in US. Patent No. 2,932,754, issued to J. H. O. Harries et al., Apr. 12, 1960, to modify the shape of the electric field in the cathodeanode space whereby the electron trajectories which were previously turned back toward the control grid are instead caused to be directed toward the anode. This is accomplished by providing the screen grid wires with radially extending fin-like cross-sectional shapes which not only direct the electrons from the cathode to the anode in the desired manner but also maintain a high value of mu and reduce the screen grid to anode capacity. This invention further enhances the quantity of electrons available at the anode by placing novel channel shaped control grid electrodes along with the previously disclosed fin shaped screening grid in the cathode-anode space whereby a stronger and more uniform field is introduced in front of the cathode slot and has a more pronounced beaming effect on the electron stream from the cathode.

It is, therefore, an object of this invention to provide an electron tube with a predetermined shaped control grid which introduces a stronger and more uniform field in front of the cathode slot.

Another object of this invention is to provide a modification of especially the cathode-grid field of an electron tube to give a more pronounced beaming effect on the electron stream from the cathode.

Another object of this invention is to provide a more eflicient beamed triode having an amplification factor which is substantially doubled thus requiring less negative cut-off voltage during the non-conductive cycle.

A further object is to provide a more efficient beamed triode which requires lower total drive power requirements during the conducting cycle.

Other objects and advantages of the invention will become apparent from the following description taken in connection with the accompanying drawings, wherein:

FIGURE 1 is a horizontal sectional view of a typical beamed triode with modifications according to the present invention.

3,334,257 Patented Aug. 1 1 967 The electrode structures embodying the present invention include a cathode structure 5, a control grid structure 7, a screen grid structure 9 and an anode structure 11, all of which are coaxial structures mounted one within another as shown and suitably supported so as to maintain their respective predetermined space relations.

The cathode structure embodies a hollow cylindrical cathode 13 within which is located a heating coil or filament 15. The filament 15 is suitably connected to a source of electrical energy whereby it will radiantly heat the cathode 13 for liberation of electrons, as will be described.

' The outer surface of the cathode 13 is provided with a FIGURE 2 is an enlarged fragmentary horizontal secv plurality of longitudinal grooves 17 which are spaced substantially equidistant apart throughout the circumference of the cathode. The side walls 19 of the grooves 17 extend substantially radially with respect to the longitudinal axis of the cathode, and the bottoms of the grooves 17 are preferably slightly concave, being curved in a trans verse direction as shown in FIGURE 2. Deposited upon the bottom of each groove 17 is a layer 21 of a selected electron emissive material such as one of the oxides com-- monly used for this purpose in the electron tube industry. When the cathode is heated and a relatively high suitable potential applied in the normal manner across the tube, electrons are emitted by the material 21 and are caused to flow in a direction toward the anode.

Opposite each land 23 between the respective grooves 17 is located a respective channel shaped member 25 of the control grid 7. The channels 25 extend parallel to the cathode and to each other and in predetermined spaced relation thereto, and are generally U-shaped in crosssection having a width consistant with the widths of the lands 23 such that the channels 25 are as close to the sides of the electron beams emanating from the emissive material 21 in grooves 17 as is compatible with non-interception of the beams by the control grid.

' Radially spaced outwardly of each of the control grid channels 25 is a respective screen grid member or wire 27, the wires 27 being located in predetermined spaced relations to both the anode 11 and control grid channels 25.

The anode 11 is a hollow cylindrical body of copper which encloses the grids and cathode and forms in itself a large portion of the tube envelope.

The several electrodes are all supplied with various potentials by conductive means clearly shown and described in the above mentioned US. Patent to Harries et al. The tube is adapted to be operated by impressing the desired potential between the anode and cathode, applying a relatively high positive potential to the control grid, and applying to the screen grid a zero potential with respect to the cathode. Therefore, electrons emitted by the material 21 in the cathode grooves 17 will be focused, under the influence of the side walls 19 of the grooves, toward the anode 11. The control grid channels 25, located just out of the direct trajectories of the electrons, will not normally intercept the electrons. The curvature of the emitting surface also aids in properly focusing the electron beam because of the fact that electrons leave an emitting surface substantially normal to the surface at the point of emission.

In this type of tube structure, the positive control grid normally will not intercept any primary electrons until they have travelled past this grid and have reversed their directions and been trapped, therefore the fin-like shaped screen grid 9 is used and spaced between in the cathodeanode spacing as proposed previously by the above mentioned patent to Harries et al. to prevent the reversal of many of the electron trajectories.

It has been found that the control grid can be modified to have a generally U-shaped cross section which in turn provides modification of especially the cathode-grid field.

This modification introduces a stronger and more uniform field in front of the cathode slot and has a more pronounced beaming effect on the electron stream from the cathode. Using the channel shaped control grid electrode, the maximum positive potential, which will accelerate the electron beam from the cathode is by at least 12% higher at a given drive potential than using the conventional round electrode. The electron delay potential in the screen grid-anode region is by at least 5% lower using a channel shaped electrode grid than when using a round control grid electrode. The amplification factor mu of this structure is substantially doubled, which requires less negative cut-off voltage during the non-conductive cycle and lowers the total drive power requirements during the conducting cycle.

The dimensions and spacing of the particular elements are substantially the same as that disclosed in Harries et al. with the exception of the control grid channels which are approximately .070" to .100 wide and .060" deep radially.

While the invention has been described with reference to a preferred embodiment thereof, it will be apparent that various modifications and other embodiments thereof will occur to those skilled in the art in light of the present disclosure. Accordingly, it is desired that the scope of this invention be limited only by the appended claims.

What is claimed is:

1. In an electron tube, electrode beaming structures comprising a hollow anode, a cylindrical cathode coaxial within the anode, said cathode having on its outer surface a plurality of alternately located electron emitting and non-emitting areas having lands therebetween and means for focusing electrons from the emitting areas into beams directed toward the anode, said cathode and anode being operable at different known potentials, a screen grid means located in predetermined spaced relation between said anode and said cathode, and a control grid means located in predetermined spaced relation between said screen grid means and said cathode, said control grid means comprised of channel shaped members disposed adjacent to the non-emitting areas of said cathode and being operated at relatively high positive potentials.

2. In an electron tube as set forth in claim 1, said screen grid means comprised of members radially aligned with said control grid channels, said members being adapted to be maintained during operation of said tube at substantially cathode potential, said members being ribbonlike in shape to form electric fields therearound which aid electron flow to said anode and prevents substantial trapping of electrons between grids.

3. In an electron tube as set forth in claim 2 wherein said lands are no wider than said channel shaped members of said control grid means.

No references cited.

JAMES W. LAWRENCE, Primary Examiner.

V. LAFRANCHI, Assistant Examiner.

Claims (1)

1. IN AN ELECTRON TUBE, ELECTRODE BEAMING STRUCTURES COMPRISING A HOLLOW ANODE, A CYLINDRICAL CATHODE COAXIAL WITHIN THE ANODE, SAID CATHODE HAVING ON ITS OUTER SURFACE A PLURALITY OF ALTERNATELY LOCATED ELECTRON EMITTING AND NON-EMITTING AREAS HAVING LANDS THEREBETWEEN AND MEANS FOR FOCUSING ELECTRONS FROM THE EMITTING AREAS INTO BEAMS DIRECTED TOWARD THE ANODE, SAID CATHODE AND ANODE BEING OPERABLE AT DIFFERENT KNOWN POTENTIALS, A SCREEN GRID MEANS LOCATED IN PREDETERMINED SPACED RELATION BETWEEN SAID ANODE AND SAID CATHODE, AND A CONTROL GRID MEANS LOCATED IN PREDETERMINED SPACED RELATION BETWEEN SAID SCREEN GRID MEANS AND SAID CATHODE, SAID CONTROL GRID MEANS COMPRISED OF CHANNEL SHAPED MEMBERS DISPOSED ADJACENT TO THE NON-EMITTING AREAS OF SAID CATHODE AND BEING OPERATED AT RELATIVELY HIGH POSITIVE POTENTIALS.

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