US1287265A - Electrical discharge device. - Google Patents

Description

S. DUSHMAN. ELECTRICAL D\SCHARGE DEVICE. APPLICATION HLED FEB. 20, 1915.

1,987,265. Patented Dec. 10, 1.918.

2 SHEET$$HEET 1.

Fig.

Inventor: Saul Bushman,

by His DIiorneg.

Witnesses S. DUSHMAN. ELECTRiCAL DISCHARGE DEVlCE. APPLICATION FILED FEB. 20. 1915.

1 281265: 7 Patented Dec. 10, 1918.

2 SHEETSSHEET 2- lnventor Saul Bushman,

His DTttorneg Witnesses:

SAUL DUSHMAN, OF SCOIIA,

NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY,

A CORPORATION OF NEW YORK.

ELECTRICAE DISCHARGE DEVICE.

Specification of Letters Patent.

Patented Dec. 10, 1918.

Application filed February 20, 1915. Serial No. 9,533.

To all 'lUhOII'L it may concern:

Be it known that I, SAUL Dusnemx, a subject of the King of Great Britain, residing at Scotia, county of Schenectady, State of New York, have invented certain new and useful Improvements in Electrical D ischarge Devices. of which the following is a. specification.

The present invention relates to the construction of devices having a cathode operating at incandescence and one of its main objects is to prevent injury to or dlstortlon of the cathode when subjected to static strains.

My invention relates particularly to the operation of electrical discharge devices comprising an electron emitting cathode, such, for example, as a filament of refractory metal, operating at incandescence a vacuum so high that evidences of positive ionization are substantially absent even at exceedingly high voltages.

In accordance with my invention the anode in a discharge device containing a cathode to be operated at incandescence is located on opposite sides of the cathode or symmetrically about the cathode thereby avoiding unequal static strains liable to distort or injure the cathode.

This feature and other novel features of my invention will be pointed out with greater particularity in the appended claims. For a more complete understanding of my invention reference may be had to the following description taken in connection with the accompanying drawings.

Figures 1 and 2 illustrate devices suitable particularly for handling currents of moderately high voltages; Fig. 3 illustrates in perspective a device operable to transmit currents up to about 50,000 volts, and Fig. i illustrates in perspective a device suitable for operation with the voltages.

Fig. 1 illustrates a device suitable particularly for voltages up to about 10,000 volts and currents up to about one-half to threefourths amperes. The envelop 1 consists of glass, such, for example, as the so-called low expansion glass, which is a sodium-magnesium boro-silicate. The cathode 2 consists of a tungsten wire attached to tungsten conductors 3, 1, the conductor 3 being coiled highest commercial for part of its length to the shape of a spiral 5 to give a tension to the filament to hold it in position. The leading-in conductors 4 and 6 are sealed directly into the wall of the envelop. The anode 7 consists of a tube of tungsten spaced symmetrically around the cathode. It is supported by the rods 8, 9, which may consist of tungsten or molybdenum to enable them to be sealed directly into the tubular envelop arms or extensions 10 and 11. The rods 8. 9 are attached by means of molybdenum rivets 8, 9 to the tube 7. Vibration of the rods 8 and 9 is prevented by-anchors 12. 13, consisting of molybdenum.

The envelop is given a preliminary exhaust and bakeout according to the best incandescent lamp exhaust practice, the last stages of evacuation being preferably carried out by means of a Gaede molecular pump. \Vhen the space within the envelop has been exhausted to a pressure of approximately .000001 millimeters, the cathode is heated to incandescence by suitable current and a moderate potential, for example, about 2000 to 3000 volts is applied between the cathode 2 and the anode 7, producing an electron discharge across the v'acuous space and thereby disengaging gas from the anode. The evacuation through the tube 14 is meanwhile continued to remove this gas. Care should be exercised to discontinue the electron discharge when the liberation of the gas becomes great enough to cause the appearance of a blue glow in the tube as this indicates positive ionization, which if continued will harmfully affect the cathode filament. As the evacuation continues the impressed potential may be progressively increased, thereby raising the temperature of the anode and continuing the liberation of gas. The process is continued with a step by step of increase in the discharge voltage andcontinuous pumping until the impressed voltage has exceeded the voltage at which the device is to be operated. This exhaust process is described in an application filed by Irving Langmuir on October 16, 1913 Serial No. 795,610. The exhaust tube finally is sealed oil when no more gas is evolved and the residual gas pressure'is about .001 of a micron or less. When thus prepared the device may be used for recticurrent or any other desired purpose. he exchange of energy between anode and cathode occurs as a substantially pure electron discharge without any accompanying evidences of positive ionization, such as fiuoresence of the tube walls, blue low, or electrical disintegration of the cat ode. The current will var above a certain minimum potential of a few volts directly with the 3/2 power of the impressed voltage np to a certain maxiuunn voltage, depending on the temperature of the cathode, when a further increase in voltage produces substantially no change in current. The axial location of the cathode filament within the tubular anode equalizes the static strains caused by the relatively high potential between these electrodes so that no distortion, short-circuit or injury to the cathode will occur.

When it is desired to transmit currents up to only about 1/10 of an ampere at voltages up to about 10,000 volts, a simpler form of apparatus may in some cases be employed as illustrated in Fig. 2. In this case the anode 15 is cup-shaped and the cathode 16, which is in the form of a short spiral, projects centrally into the cup-shaped anode. thereby likewise producing an equal distriution of static strains between the anode and cathode. The other parts of the apparatus are similar to the apparatus already described in connection with Fig. 1. The cathode terminal wires 17, 18 pass through a glass stem 19 sealed into an arm 53 of the envelop and are attached to a base 20 similar to an incandescent lamp base. The anode wire 21 passes through a stem 54 sealed into an oppositely located envelop arm 55 and is secured to a conductive cap 22.

In Fig. 3 is shown an apparatus suitable for passing currents of about one-half ampere at voltages up to about 50,000 volts. In this case the cathode 23 consists of a filamentary tungsten wire supported within a frame-work 24, which may consist of molybdenum or The plate-shaped anodes 25, 26 are located on opposite sides of the cathode, each being spaced a sub stantially equal distance from the cathode.

hese anodes are connected electrically in parallel, being supported by molybdenum rods 27, 28 attached to a molybdenum plate 29, which is in turn to a tube 30 of molybdenum or iron. This tube is inserted into a glass tube 31 fused to the tubular extension 32 of the envelop. The cathode filament 23 is connected to leading-in wires 33, 34, brought out to a threaded socket connection 35. One of the filament terminals, for example, terminal 34, is electrically connected to the frame 24, the other terminal 33 being insulated. The

spring 36 engaging fying alternating with the bight of the filament is likewise insulated from the frame connected mechanically by mica strips 37. The frame 24 is thus brought to the potential of one terminal of the filament. The filament frame is carried by a molybdenum stem 38 mechanically attached to a tube 39 consisting of molybdenum or iron. This tube is inserted into a tubular glass socket 40 of the envelop.

he evacuation and treatment of the an odes to drive out gases is similar to that already described in connection with Fig. 1. IVith the construction shown in Fig. 3 the device may be used to rectify currents up 50,000 volts without endangering the cathode by electrostatic attraction to the anodes as it is equally distant from the two anode plates.

In this construction the parts of the anode do not completely surround the cathode. For still higher voltages it is desirable that the anode should 'even more symmetrically surround the cathode which should be securely supported against electrostatic distortion.

A device suitable for operation with voltages up to about 100.000 volts is shown in Fig. 4 in which a short straight cathode filament 41 is centrally located within a cylindrical anode 42. The cathode at one end is connected to a tungsten wire 43 which for part of its length is coiled into a. spiral 44 to exert tension upon the cathode. This wire 43 is sealed directly into the envelop wall 45. The opposite end of the cathode 41 is attached to a support 46 consisting of a molybdenum wire bent back upon itself and attached to a plate 47, also preferably consisting of molybdenum. This plate 47 is carried by wires 48, 49. a so consisting of molybdenum. these in turn being fastened to another plate 50 of tungsten or molyb- The function of these plates or the perforation in plates 47 and 50 by clamps 52 insulated from the cathode bv mica or the like. The preparation of this device is similar to that already described in connection with the other figures.

During the evacuating treatment of these electron discharge devices, electrical disintegration of the cathode terminal is apt to occur, especially at the higher voltages. the treatment of the device shown in Fig. 4 at very high voltages, the shields 46 and 49 have been provided to protect the cathode seal.

In all cases the cathode against sagging or distortion not only by the symmetrical spacing of the anode. but also by tensional springs as shown in Figs.

is protecteding an inclosing 1, 3 and 4, or by the self-retaining character of the short, twisted filament as shown in Fig. 2.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. An electrical discharge device comprisenvelop, a cup-shaped anode, a filamentary cathode projecting into the mouth of said cup-shaped anode, and means for independently heating said cathode.

2. An electrical discharge device operable with high voltage currents comprising an inclosing evacuated envelop having outwardly extending oppositely located arms, a substantially cylindrical anode, an anode support sealed into an envelop arm, a cathode located within said anode near the axis of said anode, and a cathode support sealed into another envelop arm, said device being freed from gas to such degree that electron conduction may occur therein independently of gas ionization.

3. An electrical discharge device comprising an envelop having outwardly extending arms, a filamentary cathode, a current conveying conductor therefor sealed into one of said arms, an anode symmetrically located about said cathode, and a current-conveying conductor for said anode sealed into another of said envelop arms, the parts of said device and the space within said envelop being so completely deprived of gas that evidences of positive ionization are substantially absent during the operation of said device.

i. A rectifying device for high voltage alternating currents comprising an evacuated envelop, a filamentary cathode adapted to be heated independently, means for putting said filament under tension and an anode arranged in said envelop substantially symmetrically about said cathode, said device being freed from gas to such degree that electron conduction may occur therein independently of gas ionization.

A device for conducting high voltage alternating currents comprising an envelop, a cathode, means for causing electrons to be emitted by the cathode, an anode arranged in said envelop substantially symmetrically about said cathode, current conductors for said cathode and anode sealed into said envelop and shielding means located between the cathode conductor seal and the anode, said device being freed from gas to such degree that electron conduction may occur therein independently of gas ionization.

6. An electrical discharge device operable at high voltage currents comprising an inclosing envelop having outwardly extend ing oppositely located arms. a cup-shaped anode having a stem sealed into one of said arms, a filamentary cathode extending into said anode and leading-in conductors for said cathode sealed into another of said arms, said device being deprived of gas to such a degree that electron conduction may occur therein substantially independent of gas ionization.

In witness whereof I have hereunto set my hand this 18th day of February, 191:3.

SAUL DUSHMAN.

Witnesses WILLIAM C. WHITE, HELEN Onronn.

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