US2595716A - Gaseous discharge device - Google Patents

Description

May 6, 1952 c. G. SMITH GASEOUS DISCHARGE DEVICE Filed Jan. 10, 1950 new LOAD

/h/\/A/TO R 0mm. ES 0. SMITH HTTOIg /EY Patented May 6, 1952 A UNITED STATES PATENT OFFECE GASEOUS DISCHARGE DEVICE Application January 10, 1950, Serial No. 137,685

6 Claims.

This invention relates to apparatus utilizing electron discharges through gaseous media for rectifying purposes, and more particularly discloses means whereby flash back from the anode to the cathode may be eliminated.

One of the major defects in gaseous discharge rectifiers is the occasional flash back on the inverse portion of the alternating current cycle. In this portion, the anode is negative and the cathode positive and electrons flow from the anode to the cathode. The results of the flash back are temporary failure of the rectified output and possible permanent injury of the discharge device.

A major factor which influences flash back is the condition of the gaseous medium between the cathode and the anode. If this gas is ionized, a flash back will readily occur. Moreover, it has been discovered that a recently ionized gaseous medium, such as, for example, mercury vapor, has a property which will be termed persistent excitation. While this persistent excitation comprises, in part, residual ions in the gaseous medium which have not as yet recombined, the major portion of the persistent excitation has been found to consist of a state of excitation of the gas which contains considerably more energy than the mere energy of ionization. While the exact nature of this increased excitation is not completely understood, it has been measured by measuring the amount of light given off by vapor through which a discharge has passed and comparing the energy of the light with the energy existing in the ionized gas due to merely the ionization thereof. It was found that the amount of light energy given off by the gas was greatly in excess of the energy required to merely ionize the gas. For these reasons, previous attempts to eliminate flash back, by shields between the anode structures or by restricting the passage through which the discharge passes such that the discharge medium will be in close proximity to a bounding wall thereby facilitating the recombination of the ions of the medium, have not been entirely successful.

This invention discloses a structure whereby the gaseous medium through which the discharge passes is continuously being changed and replaced such that those portions of the gaseous medium which have become persistently excited are removed to a point in the space discharge device which is remote from the normal discharge path between the anode and the cathode, said excited portions of the discharge medium being replaced by fresh unexcited gaseous media.

2 In particular, this invention provides a liquid pool cathode of the mercury type having a portion thereof in heat transferring relation to the anode structure whereby heat from the anode is transferred to the liquid mercury causing continuous vaporization thereof. The vaporized mercury blasts through the area surrounding the anode structure and particularly through the discharge path between the anode and the cathode thereby continuously removing mercury vapor in the discharge path which was persistently excited by previous discharges. The persistently excited vapor is thus removed to a point remote from the discharge path between the anode and the cathode where it gradually loses its persistent excitation by radiation and other means, and eventually condenses and returns to the liquid cathode pool.

In addition, this invention provides means whereby the are spot may be confined to a relatively small area on the cathode surface thus making the discharge device stable during operation at small currents. To effect this, a shield is positioned in the mercury pool rising slightly thereabove. An arc spot developed on the cathode pool by an igniter electrode will, upon developing into an are between the cathode pool and the anode, move toward the shield in the presence of a suitable magnetic field, and upon reaching the shield will tend to anchor itself thereto, thereby tending to keep the discharge distance between the cathode are spot and the anode relatively constant. In addition, the anchoring of the arc spot prevents the are spot from wandering into the immediate vicinity of the anode structure thereby preventing spattering of the anode structure with mercury particles from the are spot. This, in turn, eliminates one cause of flash back wherein globules of mercury on the anode act as cathodes.

Other advantages and features of the invention will become more apparent as the description thereof progresses, reference being had to the accompanying drawing, wherein:

Fig. 1 illustrates a longitudinal, cross-sectional view of a device embodying principles of this invention taken along line 1-! of Fig. 2; and

Fig. 2 illustrates a transverse, cr0ss-sectional view of the device shown in Fig. 1 taken along line 2-2 of Fig. 1.

Referring now to the drawing, there is shown a metallic envelope 10 which is cylindrical in form and has its upper and lower ends closed by metallic plates II and 12, respectively. Resting on lower plate I2 is a pool of mercury 13 which acts as the cathode of the device. Extending up from end plate I2 through mercury pool I3 is a pair of tubular shield members I4 and I5 which may be made of any desired conducting material, such as, for example, molybdenum, nickel or tungsten. Inside shields I4 and I5, respectively, and coaxial therewith, are anode members I6 and I1. Anode members I6 and I! are each supported by a pair of supporting rods I8 and I9, respectively, which extend upward through the end of the shield members I4 and I5 and are insulatedly supported in insulating seal members 23 and 2I, respectively, in upper end member II. Surrounding each pair of support members I8 and I9 are cup- shaped shield members 22 and 23 which comprise cylinders having their upper ends closed by plates which are connected, as by welding, to support members I8 and I9. The shield members 22 and 23 extend for a short distance above shield members I4 and I5 and are slightly spaced therefrom. Thus, it may be seen that the anode structures [6 and I! are insulatedly supported with respect to the cathode pool I3.

In order to allow the cathode pool I3 to flow into shield members I4 and 15, there is provided an aperture in each of the shield members I4 and I5 through which the liquid mercury can fiow. The apertures comprise round holes 24 and 25 in shield members I4 and I5, respectively, said holes being positioned half below and half above the surface of the mercury pool. The holes 24 and 25 are positioned in shields I4 and I5 so that they substantially face each other and face an igniter electrode 29 positioned between shield members I4 and I5. Igniter electrode 26 comprises a conducting member 21 extending through an insulating seal 28 in upper end plate IT. The lower end of conductor 21 has an igniting tip 29 attached thereto, said igniting tip being of any desired material, such as, for example, carborundum. Igniter electrode 26 is so position'ed that the end of igniting tip 29 extends below the surface of the mercury pool I3. When a suitable voltage is applied between the igniter electrode 26 and the cathode p001 I3, for example, 50 volts, by means of a battery 39 connected to igniter electrode 25 and through a control circuit (H which may be, for example, a switch to container I9 which contacts the mercury pool cathode I3, an incipient are spot will occur at the contact region of igniting tip 29 and the mercury pool I3.

In order to provide alternating current between the cathode pool I3 and the anode members l9 and [1, said anode members are connected through conductors I8 and I9, respectively, to the opposite ends of a high voltage transformer secondary winding 32 of a transformer 33. Winding 32 has a center tap which is connected through a load 34 to container IE3. The primary winding 35 of transformer 33 may be connected to any desired source of alternating current such as, for example, 220 volts, 60 cycles. When one of the anodes, for example, anode I6, is driven positive with respect to cathode I3 and an incipient are spot is occurring at the igniter electrode 26, electrons from the spot will be drawn to the anode, striking gaseous particles in their path, thereby creating ionization of said particles resulting in establishment of the arc.

In order to insure reliable initiation of the discharge between the anodes and the cathode poo-l, a pair of auxiliary electrodes 36 and 31 is positioned outside and adjacent shield members I4 and I5, respectively. Auxiliary electrodes 36 and 31 which may be of any desired metal, such as nickel or tungsten, extend upward through upper end plate I1 and are insulatedly supported therein by sealing members 38 and 39, respectively. Electrodes 36 and 31 are connected through current-limiting resistors 40 and 4| to the opposite ends of an auxiliary winding 42 on transformer 33, the center tap of which is connected to container I9. Transformer winding 42 is so phased with winding 32 that, as anode member I6 is driven positive, the auxiliary electrode outside shield member I4 surrounding anode member I3 will also be driven positive. The discharge is then initiated from the incipient are spot at igniting tip 29 to auxiliary electrode 36, and is then drawn over through hole 24 to anode member I6 for the main discharge. Once the main discharge has been initiated, the spot on the surface of mercury pool I3 has a tendency to wander from its point of initiation at igniting tip 29 over the surface of the pool and may even enter the shield member I4 through hole 24. To prevent this, a weak magnetic field, for example, on the order of 10 gauss, is produced parallel to the surface of mercury :pool I3. This magnetic field may be produced by any desired means, such as a permanent magnet 43 attached to the lower end plate I2 of container ID by screws 44. In order to more effectively direct the magnetic field produced by magnet 43, a pair of pole pieces 45 and 43 is inserted into container I9 adjacent the ends of magnet 43 and lie slightly below the surface of mercury pool I3. Magnet 43 and pole pieces 45 and 45 are so positioned that the magnetic field will lie substantially parallel to a line which perpendicularly intersects the axes of anode members I6 and II with the result that the are spot will be caused to move in a direction perpendicular to said line.

When low vapor pressures are used, for example, one millimeter or lower as in the present device, the direction of motion of the spot will be opposite to that which would be produced on an electron stream flowing to an anode by the presence of the magnetic field. With the polarity of magnet 43 such that the pole adjacent anode I6 is north and the pole adjacent anode I7 is south, the spot will move toward the back of the container I0. A shield member 47 is positioned in back of igniter electrode 26, said shield member being attached to the lower end plate I2 and extending slightly above the surface of the mercury pool. The arc spot moves toward the shield member 41 under the influence of the magnetic field, and, upon striking said shield member, anchors itself thereon. This prevents wandering of the arc spot around the inside of container I 0 on the surface of pool I3. When anode I1 is driven positive and anode I6 negative, a discharge is initiated from igniting tip 29 to auxiliary electrode 37 and then to anode I1 through hole 25. Successive discharges will occur as long as the control circuit 3| maintains a potential between igniter electrode 26 and mercury pool I3.

Due to the arc discharges between anode members I6 and I! and the mercury pool I3, the anode structures I6 and I"! become elevated in temperature above other parts of the discharge device. These anode structures then radiate heat to the inner surface of shield members I4 and I5 and to that portion of the mercury pool which lies within the shield members I4 and I5. Heat radiated to the inner surface of shield members l4 and i5 is transferred by conduction tov the mercury pool in immediate contact with shield members [4 and I5. The net result is heating of the portions of the mercury pool inside shield members M and I5. Due to the low vapor pressure in the device, a relatively small amount of heating of these portions of the mercury pool produces rapid vaporization thereof. The vaporized mercury then blasts out through holes 24 and 25 with a small amount of the mercury vapor blowing out through the tops of shield members I4 and past cup-shaped shields 22 and 23. Since heat is being continuously transferred from the anodes I6 and I! between conduction periods as well as during conduction periods, the mercury within shield members it and I5 is being continuously vaporized and continuously blasts out through holes 24 and 25. As a result, vapor which was in the discharge path between the cathode and the anode during the discharge, and which thereby became ionized and persistently excited, is immediately removed from the path when the discharge ceases, thereby eliminating the unstable gas which would facilitate a flash back.

A convenient method of processing the discharge device after assembly thereof comprises evacuating the container I0, admitting a proper amount of mercury for the cathode, and then admitting a few millimeters, for example ten of pure hydrogen. An arc is then run from the anodes l6 and I1 to the mercury cathode. The mercury cathode is maintained positive with respect to anodes l6 and It so that said anodes become electron sources for the arc, and are thereby rapidly heated by ionic bombardment. This removes the oxides from the anodes l6 and i1, said oxides being reduced by the hydrogen to form water vapor which is then pumped out of the device.

It is to be clearly understood that other means for heating the vapor within the shield members I 4 and I5 could be used rather than radiation of heat from the anode. For example, electrical heating structures could be positioned inside shield members [4 and I5 in the mercury pool. Furthermore, the mercury pool need not necessarily be used as the cathode. Any desired cathode such as a solid or thermionically heated cathode could be used. In addition, the action of blasting the vapor out of the gaseous discharge path could be applied to other gaseous media than mercury. Also, the principle is not necessarily limited to operation with a pair of anode structures, but may be used with a single anode or more than two. The control circuit and voltage supply are shown here by way of example only, and any desired circuit could be used. Therefore, applicant does not wish to be limited to the particular details of the modification of the invention described herein, except as defined by the appended claims.

What is claimed is:

1. An electron discharge device comprising an envelope containing an ionizable gas, an anode, a liquid cathode, a discharge path between said anode and said cathode, and means for continuously displacing the portion of said gas adjacent said anode comprising means for continuously vaporizing a portion of said liquid cathode and means for directing gas vaporized from'said portion toward said anode substantially along said discharge path.

2. An electron discharge device comprising an envelope containing an anode, a liquid cathode, a heat-conductive shield substantially surrounding said anode in heat transferring relation therewith and extending into said cathode, and means for continuously vaporizing the portion of said liquid cathode inside said shield, whereby gas vaporized from said cathode continuously blasts through the discharge path between said anode and said cathode.

3. An electron discharge device comprising an envelope containing an ionizable medium, an anode, a liquid cathode, a metallic shield substantially surrounding said anode in substantial heat transferring relation therewith and extending into said cathode, said shield having an aperture therein and adapted to allow liquid from said cathode to pass therethrough, the heat from said shield continuously vaporizing the portion of said liquid cathode therein, whereby gas vaporized from said portion blasts outwardly through said aperture.

4. An electron discharge device comprising an envelope containing an ionizable medium, an anode, a liquid cathode, a shield substantially surrounding said anode and extending into said cathode, said shield having an aperture therein through which liquid from said cathode may pass, and an igniter electrode positioned outside said shield.

5. An electron discharge device comprising an envelope containing an ionizable medium, an anode, a liquid cathode, means for stabilizing the position of the discharge spot on said cathode comprising a magnetic field, and means for continuously forcing unexcited portions of said medium into the area adjacent said anode.

6. An electron discharge device comprising an envelope containing an ionizable medium, an anode, a liquid cathode, means for stabilizing the position of the discharge spot on said cathode comprising a magnetic field, and means for continuously forcing unexcited portions of said medium into the area adjacent said anode comprising means for continuously vaporizing a portion of said liquid cathode and means for directing gas vaporized from said portion toward said anode substantially along the discharge path between said cathode and said anode.

CHARLES G. SMITH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,179,929 Hansell Nov. 14, 1939 2,210,816 Miles Aug. 6, 1940 2,254,722 Aoki Sept. 2, 1941

Images