US3005924A - Cold cathode hydrogen thyratron - Google Patents

Description

Oct. 24, 1961 ca. RIEILLY ETAL 3,005,924

cow CATHODE HYDROGEN THYRATRON Filed May 29, 1959 FIG. I

ARTHUR G. REILLY JOSEPH W. ESPOSITO INVENTORS ATTORNEYS United St t Paitented Oct. 24, 1961 3,005,924 COLD CATHODE HYDROGEN THYRATRON Arthur G. Reilly, Flor-ham Park, and Joseph W. Esposito, Morris Plains, N.J., assignors to Tung-Sol Electric Inc., a corporation of Delaware Filed May 29, 1959, Ser. No. 816,837 7 Claims. (Cl. 313-.-185) This invention relates to a gaseous discharge device having a cold cathode with a coating on the cathode surface which provides fast starting and a low cathode potential drop. It has particular reference to the design and position of batfies which cooperate with the cold cathode surface.

Cold cathode gaseous discharge devices have been manufactured for operation with low voltages and low currents. Such tubes have been used as indicator lamps, gates, and switching tubes. In order to use gaseous discharge devices in circuits which transmit considerable power, a hot cathode has always been employed because of the additional efficiency obtained by reducing the cathode voltage drop and by providing ,a source of electrons always ready for a grid firing potential. The present invention uses a cold cathode and thereby eliminates one of the sources of heat within the cathode space. The cathode is coated with a thin layer of magnesium oxide mixture which lowers the cathode voltage drop and permits fast gas ionization.

One of the objects of this invention is to provide an improved cold cathode thyratron which avoids one or more of the disadvantages and limitations of prior art arrangements.

Another object of the invention is to reduce the operating temperature of the. tube by eliminating the heater usuall necessary in power thyratrons.

Another object of the invention is to insure fast starting of the cathode-anode current after the grid firing voltage has been applied.

Another object of the invention is to reduce the cost of gaseous discharge devices by eliminating the cathode heaters.

Another object of the invention is to increase the efficiency of operation of gaseous discharge devices by eliminating the electrical power necessary to heat the cathode.

Another object of the invention is to reduce the grid firing potential necessary to start anode-cathode conduction. This is done by means of a cathode coating and the design of a baflie connected to the cathode.

The invention comprises a cathode, an anode, and a control electrode positioned within a sealed envelope which is filled with ionizable gas at a reduced pressure. The cathode includes a metallic cup having a coating of magnesium oxide on one of its inner surfaces. Secured to the cup is a solid bafile which is positioned adjacent to the magnesium oxide surface. The control electrode includes a grid member adjacent to the anode in the space between the anode and cathode.

For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawing.

FIG. 1 is a side view of the discharge device, with some parts in section, showing the electrodes within the envelope.

FIG. 2 is a cross sectional view of the device shown in FIG. 1 and is taken along line 2-2 of that figure.

FIG. 3 is another cross sectional view of the device shown in FIG. 1 and is taken along line 3-3 of that figure.

FIG. 4 is a cross sectional view showing the cathode bafiie and is taken along line 4-4 of FIG. 1.

V Referringnow to the figures, the discharge device includes an envelope having a base 11 at one end thereof with connecting pins 12 for connection to an external The cathode cup 18 is supported by three lead-in conductors 22 which are welded to the lowerinside rim of the cathode;

The control or firing electrode 23 is supported by a cylindrical member 24 which isaxially aligned with the tubular envelope. The portion of the control electrode adjacent to the anode is formed'with a plurality of radial openings 25. However, any type of opening may be used in this portion of the firing electrode and it may consist of a flat plate with a plurality of holes or a wire screen. The grid or firing electrode 23 is secured to a portion of the reentrant envelope 26 by a clamp 27 and the grid electrode is joined to lead-in conductor 28 by means of a conducting strap 30. In order to insure correct spacing between the lower part of the grid electrode and the top rim of the anode, three wheels 31, made of insulating material, are mounted around the periphery of the oathode brim and space this electrode from cylinder 24. This design insures proper insulation and also contributes to the ease of assembly. It is an important feature of this design to .provide a bafile between the electron emitting coating 21 and the cut-out portions 25 of the grid 23. Such a baffle may be flat but it has been found more efficient to use a coneshaped member 32 as shown in the drawing. Discharge devices of this type are generally used in circuits which apply at least 25,000 volts between the anode and cathode and in order to prevent a premature discharge, bafiies must be constructed between the control electrode and the cathode surface. One of these baffles 33 is connected to the control electrode and contains a central hole through which the discharge must pass. It will be noted that the openings 25 in the control electrode are effectively shielded by baflle 33 from the field which normally exists between the anode and cathode.

A second bafile 34 is positioned parallel to baffle 33 and has an opening at its central portion which coincides with the opening in baffle 33. Bafile 34 is secured to the top rim of the cathode cup 18. The cone baffle 32 which is about mid-way between baffle 34 and the cathode 20 is secured to the rim of the cathode cup by two straps 35.

When the tube is put into operation the anode 17 may be raised to 30,000 volts above the cathode 20 without any gaseous discharge. This is due to the fact that the three bafiles 32, 33, and 34 efiectively shield the cathode and anode from the electric field between them. When the device is fired, the control electrode is raised to about 400 volts and this starts a discharge between the cathode coating 21 and the grid bafile 33, the discharge moving around the edges of battle 32. This preliminary discharge quickly forms a plasma in the entire space between the cathode and anode and conduction is established. After conduction between the anode and cathode has been started, the discharge can be cut off only by reducing the anode voltage to zero. This is done by a pulse forming network which is not shown in the drawing but is well known in the art.

Large hydrogen thyratrons of the type herein described generally use a hydrogen reservoir to adjust the pressure of the gas within the envelope and to replenish the gas during the life of the device. A hydrogen reservoir is not shown in the drawing because it forms no part of the present invention. Other gases such as xenon and krypton may be used as the ionizable gas filling.

The foregoing disclosure and drawings are merely illustrative of the principles of this invention and are not to be interpreted in a limiting sense. The only limita-, tions are to be determined from the scope of the appended claims.

What is claimed is:

l. A gaseous discharge device comprising: a sealed envelope containing an ionizable gas at reduced pressure, an anode, a control electrode, and a cathode; said control electrode including a perforate grid conductor mounted between the anode and the cathode; saidicathode including a metallic conductor coated with a layer of magnesium oxide and an imperforate baflle mounted adjacent to the cathode coating.

2. A gaseous discharge devicecomprising: a. sealed envelope containing an ioniza'ole gas at reduced pressure, an anode, a control electrode, and a cathode; said control electrode including a perforate metal grid mounted between the anode and thecathode; said cathode formed in the shape of a cup with its inside base portion coated with a layer of magnesium oxide and an imperforate bafiie mounted adjacent to the cathode coating.

3. A gaseous discharge device as set forth in claim 2 wherein said baflle is positioned effectively to shield the coated portion of the cathode from the electric field normally applied between the anode and cathode when the device is nonconducting.

4. A gaseous discharge device comprising: a sealed envelope containing an ionizable gas at reduced pressure, an anode, a control electrode, and a cathode; said control electrode including a perforate grid conductor mounted between the anode and the cathode; said cathode formed in the shape of a cup having an uncoated cylindrical wall and a base portion formed in the shape of a magnesium oxide.

5. A gaseous discharge device as set forth in claim 4 wherein a bafrle is mounted adjacent to the cathode and connected thereto.

6. A gaseous discharge device comprising: a sealed envelope containing hydrogen at a reduced pressure, an anode, a control electrode, and a cathode; said control electrode including a hat perforate grid conductor mounted between the anode and thecathode and adjacent to the anode, a bathe plate secured to the grid conductor having a single central hole; said cathode formed in the shape of a cup having an uncoated cylindrical wall and a base portion formed in the shape of a cone, said cone portion. having its apex directed toward the anode, a portion of the cone being coated with porous magnesium oxide.

7. A gaseous discharge device comprising: a sealed envelope containing an ionizable gas at reduced pressure, an anode, a control electrode, and a cathode; said control electrode including a flat perforate grid conductor mounted between the anode and the cathode and adjacent to the anode, a baffie plate secured to the grid conductor having a single central hole; said cathode formed in the shape of a cup having an uncoated cylindrical wall, a base portion coated with porous magnesium oxide, an upper baflle plate having a single central hole, and an intermediate solid baffle plate mounted within the cup overlying the coated portion of the cathode and shielding it from the electric field formed when voltage is applied between the anode and cathode. I

References Cited in the file of this patent UNITED STATE PATENTS 2,492,666 Sloan Dec. 27, 1949

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