US2813209A

US2813209A - Electron beam tube

Info

Publication number: US2813209A
Application number: US459409A
Authority: US
Inventors: Robert E Byram; Jr Arthur P Sweet
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1954-09-30
Filing date: 1954-09-30
Publication date: 1957-11-12
Anticipated expiration: 1974-11-12

Description

Nov. 12, 1957 R. E. BYRAM ETAL 2,813,209

ELECTRON BEAM TUBE Filed Sept. 30, 1954 /i 1 If I L/ I /7 I"| I I I 1,.

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United States Patent Ofilice 2313209 Patented Nov. 12, 1957 ELECTRON BEAM TUBE Robert E. Byram and Arthur P. Sweet, Jr., Lancaster,

Pa., assignors to Radio Corporation of America, a corporation of Delaware This invention relates to an electron beam tube and more particularly to an anode structure for an electron beam'tube having the anode thereof sealed to an end of the tube. The invention provides an elongated electron tube which has beam forming means at one end thereof. A tubular anode, having a target plate therein adapted to withstand heating to incandescence by bombardment of an electron beam, is sealed into the tube envelope at the other end of the tube. The anode of the invention provides sufficient thermal insulation between the target plate and the anode-envelope seal to prevent excessive seal temperatures. Such a tube is particularly adapted to be operated at a relatively high anode potential. The anode structure described is illustrated but not claimed in copending application Serial No. 456,215 filed September 15, 1954, of R. D. Reichert and assigned to the same assignee as the present invention.

In certain types of electron tubes, for example in high voltage rectifiers or shunt regulator triodes, it is advantageous to support the anode from the envelope at an end of the tube remote from the other electrodes for insulation purposes. It is also desirable to reduce the voltage gradient at the more negative portions of the tube to reduce cold emission problems. This reduction in voltage gradient can best be accomplished by employing beam forming means to provide an electron beam directed at the anode. When it is also necessary to dissipate a relatively large amount of energy at the anode, and the energy is concentrated at a relatively small region in the anode, a problem of heat dissipation arises. The

relatively high anode voltages also give rise to hard X-ray radiation which may constitute a health hazard.

One way of obtaining anode heat dissipation and of reducing relatively high anode temperatures is by increasing the anode area. However, if the heating occurs at a relatively small area of the anode it is also necessary to increase the mass of the anode to conduct heat to the larger radiating area. A relatively massive anode is objectionable in the tube described as it puts a strain on the anode-envelope seal and on the envelope of the tube. An anode capable of a relatively high thermal dissipation by the means of increased anode mass and area requires relatively heavy supports. The increased anode mass renders the seal vulnerable to cracking due to strains placed on it by the inertia of the anode during the normal handling of the tube.

Accordingly, it is an object of the invention to provide an improved electron beam tube having an anode with a portion thereof adapted to be operated at a relatively high temperature.

It is another object of the invention to provide an electron beam tube having an improved anode which is sealed to the tube envelope at one end thereof and which is adapted to receive a relatively dense, high velocity electron beam at a target plate therein without substantially heating the tube envelope at the sealed end.

It is a further object of the invention to provide an improved electron beam tube adapted to be operated at relatively high anode voltages without producing hard X-ray radiation outside the tube.

The invention provides an improved electron tube having beam forming means at oneend of the tube and adjacent a base thereof. An anode is sealed through the envelope at the other end. The beam forming means may comprise a cathode and means for forming an electron lens to shape a stream of electrons, accelerated from the cathode to the anode, into a relatively narrow beam. The anode, which is spaced along the path of the electron beam from the beam forming means, has a tubular member around the axis defined by the beam and a target plate within a portion ofthe member intermediate the ends thereof. Thus the target plate is positioned in the path of the electron beam. The target plate intercepts the electron beam so that the beam dissipates substantially all of its energy at that plate. The beam raises the plate, and the portions of the member adjacent to the plate, to incandescence. The tubular member has about two-thirds of its length disposed between the target plate and the end of the tube through which the anode is sealed. The portion of the member remote from the beam forming means provides a support of low thermal conductivity such that the portion of the anode adjacent to the anode-envelope seal remains at a relatively low temperature. The portion of the member adjacent to the beam forming means acts as a shield to prevent the X-rays generated at the target plate from passing outside the tube.

While the invention is pointed out with particularity in the appended claims it may be best understood from the following detailed description and drawing. The embodiment described is presented solely for illustrative purposes and not by way of limitation.

The drawing shows a side elevation partly in section of an electron beam tube embodying the invention.

The electron beam tube 1 includes an elongated, evacuated envelope 2. Prongs 3 extend from a base 4 at one end of the envelope. The tube may be supported in a tube socket (not shown) by means of these prongs and some of the internal tube elements may be electrically connected to the socket by the prongs.

Beam forming means 5 are provided within the envelope 2 at the end thereof adjacent the base 4. The beam forming means may include a thermionic cathode 6 and an apertured shield cup 7 which encloses the cathode. The shield cup is adapted to be biased at substantially the same potential as the cathode so as to form an electron lens at the aperture 8 therein. A screen 9 may be stretched across the aperture 8 to form a grid across the electron lens for controlling the beam current. The electron lens thus focuses a stream of electrons from the cathode through the grid and in the form of a beam 10. The path of the beam extends into an anode 11 which is sealed to the end of the envelope remote from the base.

The anode 11 includes a tubular member 12 around the path of the beam 16. The tubular member is spaced along the beam path from the beam forming means 5 and is fixed to an anode lead cap 13 which extends through an anode-envelope seal 34-. The anode lead cap may be provided with a number of apertures 15 at a portion thereof within the envelope and adjacent the seal. These apertures serve to reduce the conduction of heat between material must be mechanically strong and have low vapor pressure at this temperature. Tantalum, which has a relatively low vapor pressure, has proven ideally suited for a target plate. Tantalum also exhibits gettering action at the aforementioned temperature so that the target plate itself getters gases released within the anode. The tubular anode member which supports the target plate is of a material, such as stainless steel, which exhibits a relatively high structural strength and which has a relatively high thermal resistivity suflicient to prevent heat from the target plate from being immediately conducted to the anode-envelope seal. During normal tube operation the portion of the tubular member adjacent the target plate is also heated to a relatively high temperature. Consequently, it is also desirable to provide a gettering action around the region of the outside of the member in registry with the target plate. A band 17 of getter material such as zirconium is provided around the member for that purpose.

It will be apparent from the foregoing description that a novel electron beam tube is provided which is particularly adapted to be used in relatively high voltage applications. A tube using the improved anode structure described is capable of relatively high heat dissipation with a relatively low anode mass.

What is claimed is:

1. An electron beam tube having an elongated envelope containing at one end thereof beam forming means for producing a focused electron beam along a beam axis, and sealed to the other end thereof an anode around said axis and spaced from said beam forming means, said anode including a tubular member having an open end thereof facing said beam forming means and being of a material characterized by a relatively high thermal resistivity, and a target plate within and across a portion of said member intermediate the ends thereof and disposed closer to said open end than to the other end of said member so that substantially all of the energy of said beam is dissipated at said plate, said plate being thermally insulated from said envelope to an extent sufficient to prevent overheating of said envelope and forming a shield for shielding said envelope from hard X-ray radiation produced by the bombardment of said plate by said beam.

2. An electron beam tube having an elongated envelope containing at one end thereof a cathode and lens forming means adjacent said cathode for providing an electron lens for producing a focused electron beam along a beam axis, an anode sealed to the other end of said envelope and having a portion thereof around said axis and spaced from said electron lens, said anode including a tubular member having an open end thereof adjacent said electron lens and being of a material characterized by a relatively high thermal resistivity, and a substantially cup-shaped target within and across a portion of said member and spaced from each of the ends of said memher a distance equal to at least about one-third of the distance represented by the length of said member, said cupshaped target having an open end thereof facing said electron lens whereby substantially all of the energy of said beam is dissipated within said target without overheating said other end of said envelope.

3. An electron beam tube having an elongated envelope containing at one end thereof beam forming means for producing an electron beam along a beam axis, an anode sealed to the other end of said envelope and having a portion thereof around said axis and spaced from said beam forming means, said anode including a substantially tubular member having an open end thereof adjacent said beam forming means and being of a material characterized by a relatively high thermal resistivity, and a substantially cup-shaped target within and across a portion of said member and spaced along said member from said other end of said envelope, said cup-shaped target having the open end thereof facing said beam forming means whereby substantially all of the energy of said beam is dissipated at said target, the distance between the end of said member adjacent said beam forming means and said target being about half the distance between the end of said member remote from said beam forming means and said target whereby said target is thermally insulated from said envelope to an extent sufficient to prevent overheating of said envelope.

4. An electron beam tube having an elongated envelope containing at one end thereof a cathode and lens forming means adjacent said cathode for providing an electron lens for producing a focused electron beam along a beam axis, an anode sealed to the other end of said envelope and having a tubular member around said axis and spaced along said axis from said lens forming means, said tubular member having an open end thereof adjacent said electron lens and being of a material characterized by a relatively high thermal resistivity, and a substantially cup-shaped target within and across a portion of said member and spaced along said member from said other end of said envelope, said cup-shaped target having an open end thereof facing said electron lens whereby substantially all of the energy of said beam is dissipated within said target without overheating said other end of said envelope and being of a material including tantalum so that said target effects a gettering action within said tube at portions thereof adapted to be heated to a relatively high temperature.

5. An electron beam tube having an elongated envelope containing at one end thereof beam forming means for producing a focused electron beam along a beam axis, an anode sealed to the other end of said envelope and having a portion thereof around said axis and spaced from said beam forming means, said anode including a tubular member having an open end thereof adjacent said beam forming means and being of a material characterized by a relatively high thermal resistivity, and a target plate within and across a portion of said member so that substantially all of the energy of said beam is dissipated at said plate, said plate being spaced along said member from said other end of said envelope whereby said plate is thermally insulated from said envelope to an extent sufficient to prevent overheating of said other end of said envelope and being of a material characterized by a relatively low vapor pressure and relatively good gettering properties at the temperature attained by said plate during normal tube operation whereby gases released within said envelope are absorbed by said plate.

6. An electron beam tube having an elongated envelope containing at one end thereof beam forming means for producing a focused electron beam along a beam axis, an anode sealed to the other end of said envelope and having a portion thereof around said axis and spaced from said beam forming means, said anode including a tubular member having an open end thereof adjacent said beam forming means and being of a material characterized by a relatively high thermal resistivity, a target plate within and across a portion of said member so that substantially all of the energy of said beam is dissipated at said plate, said plate being spaced along said member from said other end of said said envelope whereby said plate is thermally insulated from said envelope to an extent sufficient to prevent overheating of said other end of said envelope and being of a material characterized by relatively good gettering properties at the temperature attained by said plate during normal tube operation, and a getter band around said tubular member at a portion thereof in'reg-.

istry with said plate within said member, whereby gettering action is provided at the portions of the tube adapted to be heated to a relatively high temperature by the dissipation of the beam energy at said plate.

7. An electron beam tube including an envelope having beam forming means at one end thereof for producing a focused electron beam, a substantially tubular anode characterized by a relatively high thermal resistivity and sealed at one end thereof to the other end of said envelope, and a substantially cup-shaped target within and across a portion of said anode intermediate the ends thereof and in a position to receive said beam and disposed closer to the end of said anode adjacent to said beam forming means than to said one end of said anode, whereby substantially all of the energy of said beam is dissipated at said target without overheating said envelope.

References Cited in the file of this patent UNITED STATES PATENTS 2,223,908 Bull Dec. 3, 1940 2,269,845 Dailey Jan. 13, 1942 10 2,269,852 Hummel Jan. 13, 1942 2,412,998 Litton Dec. 24, 1946 2,558,357 Grimm June 26, 1951