US3846668A

US3846668A - Plasma generating device

Info

Publication number: US3846668A
Application number: US00334824A
Authority: US
Inventors: K Ehlers; W Kunkel
Original assignee: US Atomic Energy Commission (AEC)
Current assignee: US Atomic Energy Commission (AEC)
Priority date: 1973-02-22
Filing date: 1973-02-22
Publication date: 1974-11-05
Anticipated expiration: 1991-11-05

Abstract

An improved high current plasma generating device generally comprised of an annular shaped anode means disposed in radially outward and circumjacent spaced relation to a plurality of electron emitter elements so as to cause a gaseous medium upon introduction into the discharge chamber of the device to be progressively formed into a more useful and homogeneous plasma of substantially uniform ion current density in transverse section for enhancing the fueling of a thermonuclear reactor.

Description

United States Patent 1191 [11] 3,846,668 Ehlers et al. Nov. 5, 1974 [5 PLASMA GENERATING DEVICE 3,614,440 10/1971 Carr 315/111 Inventors: Kenneth w. Ehlers Alamo; wulf B. 3,760,225 9/1973 Ehlers et a1 313/63 KklBkl,bthfCl'f. er 6 ey O o al Primary ExaminerRonald L. W1bert Asslgneei The Umted States of America as Assistant Examiner-Richard A. Rosenberger p y the f q States Attorney, Agent, or FirmJohn A. Horan; Frederick Atom c Energy Commission, Robertson Washmgton, DC.

[22] Filed: Feb. 22, 1973 57 ABSTRACT [2]] Appl- N05 334,824 An improved high current plasma generating device generally comprised of an annular shaped anode 521 11.5. cu 315/111, 250/423, 313/63, means disPosed in radially Outward and Circumjacem 3 2 spaced relation to a plurality of electron emitter ele- 511 Int. Cl 1101 7/24, 110511 1/00 mems so as to cause a gaseous medium p introduc- [58] Field of Search 313/63 230- 315/111- tion into the discharge Chamber of the device to be 56 progressively formed into a more useful and homogeneous plasma of substantially uniform ion current den- 56] References Cited sity in transverse section for enhancing the fueling of a UNITED STATES PATENTS thermonuclear reactor. 3,345,820 10/1967 Dryden 315/111 6 Claims, 2 Drawing Figures MASTER CONTROL PATENTEDnnv 5|974 mm m 2 3L846668 MHSTER EiEl- PLASMA GENERATING DEVICE Reference is made to the copending pat. application entitled, High Current Ion Source by Kenneth W. Ehlers et al, filed June 6, 1972, and having S.N. 260,236, now US. Pat. No. 3,760,225, issued Sept. 18, 1973.

BACKGROUND OF THE INVENTION The invention was conceived or made in the course of Contract No. W-7405-ENG-48 with the United States Atomic Energy Commission.

This invention'relates to a plasma generating device. More particularly, it relates to an improved high current plasma generating device for producing a stable and quiescent plasma of substantially uniform ion current density. I

In the past various plasma generating devices have been designed as exemplified by two US. Pat. Nos. 2,785,31 l to Lawrence and 2,902,614 to Baker and the aforementioned copending US. application. Prior ion producing devices were incapable of generating plasmas that would satisfactorily meet the overall fuel requirements for a thermonuclear reactor without encountering various difficulties such as nonhomogeneity of an ion beam as it was extracted from the plasma generating device, excessive optical convergence or divergence of the extracted ion, etc.

This invention relates to an improved plasma generating device generally comprised of a plurality of electron emitter filaments and an annular shaped anode disposed in outwardly spaced and circumjacent relation to the plurality of emitter elements so as to cause a gaseous medium upon introduction into the discharge chamber of the device to be progressively formed into a homogeneous plasma for effecting fueling of the thermonuclear reactor with minimal difficulties.

Accordingly, it is an object of the present invention to provide an improved plasma forming device that will effect the production of a plasma having a stable and substantially uniform ion current density in transverse section upon operating the present device at are currents up to and on the order of I000 amperes.

Another object of the instant invention is to provide an improved plasma forming device having an annularshaped anode surface area for minimizing among other things the adverse effects of an anode sheath build-up having the tendency to cause accelerated wear and overheating of the instant device.

SUMMARY OF THE INSTANT INVENTION The present invention relates to an improved plasma generating device generally comprised of a plurality of electron emitter elements and a novel annular shaped anode disposed in radially outward and circumjacent spaced relation to the emitter elements for effecting ionization of a gaseous medium made-up of various selected atomic compositions into an ionized plasma of substantially uniform ion current density, such uniform ion density effecting formation of an improved fuel for a thermonuclear reactor.

IE E CR TI OF TEEQBAMNQS...

FIG. 1 is a schematic and sectional view in dotted and solid lines of a plasma generating device that incorporates a preferred embodiment of the instant invention; and

FIG. 2 is a graphic view of the radial profile of the ion current density of more than one plasma produced by the present inventive device.

With continued reference to the drawings they illustrate a preferred embodiment of an improved plasma generating device 10 for introducing and subjecting a given pulsed volume of a gaseous medium to a relatively high are current range so as to cause formation of the introduced gaseous medium into a pulse type plasma of substantially uniform ion current density the ions of which can be extracted for fueling a thermonuclear reactor in improved fashion. Although the instant device is preferably operated to produce a plasma in pulse-type fashion it is not intended to be limited thereto. Device 10 is generally comprised of a hollow cylindrical shaped vessel made up of uniquely interconnected elements so as to define a vacuum electron arc discharge and plasma forming chamber 14. A master control electric pulse and operating circuit 16 and a pressurized gaseous source 18 for timely supplying a selected amount of a gaseous medium to be ionized in chamber 14 are associated with device 10 in the manner shown in FIG. 1. An ion accel-decel extraction grid 20 is connected to the right or outlet end of decive 10 as illustrated in FIG. 1 for extracting and accelerating a plurality of ions from a plasma formed in chamber 14 to grid 20 while at the same time focussing the extracted and accelerated ions in the configuration of an ion beam of improved collimated shape from grid 20 to the containment zone of a thermonuclear reactor (not shown) such as, e.g., a 2X-ll type or Baseball type of thermonuclear reactor all during operation of device 10. As will become more fully apparent hereinafter because of the device creating a plasma of substantially uniform ion current density as well as forming a improved ion beam from the plasma created, a thermonuclear reactor can be fueled in a more efficient fashion.

In an advantageous embodiment of the present invention, device 10 is comprised of a vessel having an mused TifillPEBiEPJZEIIS paitgi spa ial y aligned intermediately disposed

annular ring elements

26 and 28. Since the inner annular surface 25 of ring 26 preferably serves as the anode of the present device, ring 26 is electrically connected to master control 16 by way of electric lead 27.

As indicated in FIG. 1, the inner opposed wall portions of end cap 22 and ring 26 and

rings

26 and 28, are provided with opposed and matching 0-ring receiving grooves. Upon inserting an 0-ring 29 in an 0-ring receiving groove of a given vessel element, e.g., ring 26 in conventional fashion, it is to be understood that the 0-ring has sufficient thickness such that upon assembling the

rings

26 and 28 and end cap 22 together to form the right vessel end of device 10, the opposed inner end faces of

rings

26 and 28 and ring 26 and end cap 22 are held in spaced relation to each other. At the same time an O-ring is inserted in a groove between rings 26 and- 28 and between end cap 22 and ring 26, the outer opposed and matching stepped and recessed portions of

rings

26 and 28 and ring 26 and end cap 22 are provided with an elastomeric seal ring 30 clampingly held therebetween in the manner shown in FIG. 1. Seal ring 30 is preferably composed of a suitable rade iszv rxmat nalharinsap tqrai e he t e i tance and dielectric properties.

In another advantageous embodiment of the present invention, vessel includes a plurality of thermionic electron emitter elements 36 mounted at the left end thereof in unique relation to anode ring 26. Each one of the emitter elements 36 is of corresponding hairpin or U-shaped configuration and is preferably composed of a suitable grade of refractory tungsten material of wire-like configuration that normally has a diameter on the order of a half millimeter.

An inner chuck assembly includes an annular plate 38 and a series of plug-shaped molybdenum chucks 39 only one of the chucks 39 being shown for the sake of brevity in FIG. 1. Each one of the chucks 39 is threadably connected to one end face of plate 38 is equally spaced circumferential relation to the other chucks. An outer chuck assembly at the left end of device 10 includes an annular plate 40 and a series of plug-shaped molybdenum chucks 41 only one of the chucks 41 being shown for the sake of brevity in FIG. 1. For reasons apparent hereinafter chuck 41 has a longer length than chuck 39. As with chucks 39, each one of the chucks 41 is threadably connected to one end face of plate 40 in equally-spaced and circumferential relation to the other chucks 41.

Inner chuck plate 38 is provided with a series of apertures 42 interposed between the series of chucks 39 in equally spaced and circumferential relation to each other and the series of chucks 39. Each one of the apertures 42 in plate 38 freely receives a given chuck 41 upon assembly of

plates

38 and 40 together in the manner shown in FIG. 1. A spacer ring 44 is provided with a series of apertures 46 for freely receiving the outer ends of the alternate series of chucks 39 and 41 upon assembly of spacer ring 44 to previously assembled inner and

outer plates

38 and 40. As with

annular rings

26 and 28, an annular seal 48 of epoxy material is inserted between opposed faces of

plates

38 and 40 and plate 38 and ring 44 during assembly of

plates

38 and 40 and ring 44 as depicted in FIG. 1.

Prior to connection of spacer ring 44 to ring 28, the opposed ends of each one of the hairpin-shaped emitter elements 36 is appropriately connected to its respective chuck 39 or 41. Upon connecting each one of the emitter elements 36 to its respective chuck 39 or 41, ring 44 is connected to ring 28 whereby the series of circumferentially spaced emitter elements 36 extend longitudinally of vessel 10 in chamber 14 and are disposed radially inward of

vessel rings

26 and 28 in circumjacent spaced relation thereto.

Rings

28 and 44 are provided with opposed and matching grooves for receiving an O-ring 29 as well as opposed and matching stepped and recessed portions for receiving an annular seal 30. The particular manner, such as bolt nut assemblies, etc., for effecting connection of

plates

38 and 40,

rings

26, 28 and 44 and end cap 22 to form vessel 10 have not been shown for the sake of simplicity in FIG. 1. Electric leads 48' and 50 extend between

plates

38 and 40 and master control 16 thereby electrically connecting elements 36 in parallel fashion across master control 16.

A stem-shaped cap 52 closes off the left end of vessel 10 upon assembling cap 52 to ring 44. Prior to assembling cap 52 in the counterbored aperture of ring 44, an annular seal 54 of epoxy material is inserted between the opposed shoulders of the cap and ring 44.

Cap 52 and ring 44 as well as cap 22 and ring 28 are structural members only, defining wall and end portions of chamber 14, and are allowed to float electrically. It is to be understood that these metal elements of vessel 10 may, if it is desired, also be electrically connected to master control 16 for selectively applying a voltage to section 22, ring 28, etc. Such selective application of a voltage potential to ring 22, e.g., effectively minimizes the side capacitance effects that would otherwise normally occur during operation of device 10. Although master control 16 is schematically shown, it is believed that the various circuits for applying the proper voltages across emitter elements 36, anode ring 26, etc., are believed to be within the skill of an electric circuit designer.

A pressurized ionizable gas source 18 is interconnected to the fully-bored-through-stem portion of cap 52 by way of conduit 56. An electric lead 58 interconnects source 18 and master control 16 whereby a timely signal from the control triggers a valve (not shown) for transmitting a selected amount of ionizable gaseous medium from the source to the electron arc discharge vacuum chamber 14 of device 10 during operation of device 10. Depending upon the particular fuel requirements for a thermonuclear reactor, source 18 can be filled with various gaseous mediums such as hydrogen, deuterium, tritium and various admixtures thereof.

Another advantageous embodiment of the present invention, device 10 is comprised of an ion accel-decel extraction grid 20 for effecting extraction, acceleration and focussing of ions from a plasma formed in device 10 to the containment zone of a thermonuclear reactor (not shown). Grid 20 is comprised of an outer openended sleeve 60, the left flanged end of which is suitably connected to the apertured end cap 22 of device 10. The right flanged end of sleeve 60 (not shown) is connected to the fuel inlet port (also not shown) of a thermonuclear reactor. A grid assembly 62 is mounted within the interior of sleeve 60 and is preferably made up of a series of three parallel spaced grid elements 64, 66 and 68. Each grid element 64, 66 or 68 is separately connected to the master control by way of electric leads 70, 72 and 74. A given grid 64, 66 or 68 includes a series of longitudinally extending slots 76 across the width thereof disposed in axial alignment with respect to the series of slots of the other grid elements.

Since the inner annular anode surface 25 of ring 26 presents an extended anode surface area each one of the series of electrons emitted from the plurality of emitter elements 36 travels from its respective element to a certain surface portion of anode ring 26 without resulting in an excessive concentration of electrons about the anode ring during operation of the present device. It has been found that reducing the excessive concentration of electrons traveling from emitter elements 36 to anode ring 26 not only reduces the buildup of cathode spots adjacent to anode ring 26 but also effectively minimizes the build-up of an anode sheath or voltage gradient adjacent thereto. Reduction in the adverse effects of cathode spots and anode sheaths assures the formation of a homogeneous plasma as produced from a given pulse of gaseous medium introduced into vacuum chamber 14 when the instant device is operating. Moreover, in reducing the cathode spots the series of electrons in traveling from the plurality of emitters 36 to the anode surface 25 are incapable of forming magnetic fields, commonly known as theta fields, that produce instable plasma hash effects as indicated by the zig-zag dotted line waveform 68 in FIG.

Upon forming a plasma in chamber 14 of device 10, control 16 can apply selective voltage potentials across grids 64, 66 and 68. For instance grid 64 could have a voltage potential of +20 kilovolts, grid 66 a voltage potential of 5 kilovolts and grid 68 a ground potential. Since the uniquely shaped anode 26 of device effects formation of a substantially homogeneous plasma, for instance, a plasma formed from an H or D (hydrogen or deuterium) gaseous medium as indicated by the relatively flat H and D waveforms in FIG. 2 upon moving plasma ion current sensing probe 78 in FIG. 1, grid 64 will effect extraction and acceleration of ions from the plasma in the chamber 14 of device 10 to the interior of grid 20. At the same time grid will also be able to uniformly focus various portions of the extracted and accelerated ions of substantially uniform current density from chamber 14 of device 10 into a plurality of collimated ion beams 80 that are directed through their associated axially aligned slots of grids 64, 66 and 68 as indicated by dotted lines in FIG. 1. In the absence of device 10 forming a homogeneous plasma as aforedescribed, grid 20 would form an ion beam having convergent and/or divergent shapes 82 and 84 thereby resulting in loss of ions for fueling a thermonuclear reactor. Hence the instant device 10 provides minimal loss of ions thereby assuring a resultant ion beam of maximum density for fueling a thermonuclear reactor.

In an operative embodiment of device 10 the inner surface of anode ring 26 had a diameter on the order of 14 centimeters, a plurality of 20 filaments 36 had an average perimeter diameter on the order of 13.50 centimeters and the grid outlet opening of vessel 10 had a diameter on the order of 13 centimeters. In operating device 10 at pulse line voltages on the order of 40 to 300 volts and are voltages on the order of 35-100 volts, a stable deuterium plasma was formed having an ion current density of 0.5 amperes per square centimeter, with variations in current density on the order of 5.0 percent, when the arc current of device 10 was on the order of a 1000 amperes as depicted in FIG. 2.

Similarly, another plasma essentially composed of hydrogen ions had a homogeneous ion current density on the order of 0.3 amperes per square centimeter, with variations in density on the order of :5.0 percent, as indi cate d by the relatively flat waveform in FIG. 2 where the arc current of device 10 was on the order of 600 amperes.

In view of the foregoing embodiments of the instant invention modification may be made therein without departing from the present invention as covered by the appended claims, wherein:

What we claim is:

l. A high current plasma generating device comprising a vessel means having an evacuated electron arc discharge chamber therein, an electron emitter means being made up of a plurality of refractory metal filaments, each one of said plurality of metal filaments being individually mounted at one end of said vessel means so as to project longitudinally into the are discharge chamber and to be disposed in circumferentially spaced relation to each other as well as inwardly spaced relation to the surrounding outer peripheral wall of said vessel means, reservoir means for selectively introducing a predetermined amount of a gaseous medium to be ionized into the discharge chamber of said vessel means, and an annular shaped anode means provided in the outer wall of said vessel means in outwardly spaced and circumjacent relation to said plurality of electron emitter means for causing a series of electron arc discharges between said plurality of electron emitter means and said anode means so as to effect formation of the introduced amount of gaseous medium into a relatively stable and quiescent high current plasma of substantially uniform ion current density throughout its extent upon simultaneous electric energization of said anode means and said plurality of emitter means when said reservoir means admits a predetermined amount of gaseous medium into the discharge chamber.

2. A plasma generating device as set forth in claim 1 in which a given emitter means is of hairpin shaped configuration.

3. A plasma generating device as set forth in claim 1 in which a given emitter means is essentially composed of a refractory metal material such as a suitable grade of tungsten.

4. A plasma generating device as set forth in claim 1 wherein said vessel means has an outlet opening at the end opposing said one end where filaments are mounted and said plasma generating device includes means connected to said vessel means at said outlet opening for extracting and accelerating the ions of a plasma from the discharge chamber of said vessel means to the inlet port of a thermonuclear reactor while at the same time focusing the extracted and accelerated ions into the shape of a collimated ion beam for injection into the inlet port of a thermonuclear reactor.

-5. A plasma generating device as set forth in claim 1 in which said reservoir means includes a gaseous medium selected from the group of hydrogen, deuterium, tritium and various admixtures thereof.

6. In a high current plasma generating device made up of a vessel means and a plurality of electron emitter elements mounted at one end of said vessel means and disposed in the evacuated electron arc discharge chamber therein, each one of said elements being disposed in circumferentially spaced relation to each other and extending longitudinally into the chamber of said vessel means, a reservoir means for introducing a predetermined amount of a gaseous medium into the chamber of said vessel means, and an anode means disposed in electron arc discharge relation to said emitter means, the improvement comprising an annular shaped anode means provided in the outer peripheral wall of said vessel means and disposed in radially outward and circum- 5 5 jacent spaced relation to said plurality of emitter elements so as to cause an introduced amount of gaseous medium in the chamber to be formed into a relatively stable and quiescent high current plasma of substantially uniform ion current density throughout its extent upon simultaneous electric energization of said anode means and said plurality of emitter means when said reservoir means admits a predetermined amount of gaseous medium to be ionized into thedischarge chamber.

Claims

1. A high current plasma generating device comprising a vessel means having an evacuated electron arc discharge chamber therein, an electron emitter means being made up of a plurality of refractory metal filaments, each one of said plurality of metal filaments being individually mounted at one end of said vessel means so as to project longitudinally into the arc discharge chamber and to be disposed in circumferentially spaced relation to each other as well as inwardly spaced relation to the surrounding outer peripheral wall of said vessel means, reservoir means for selectively introducing a predetermined amount of a gaseous medium to be ionized into the discharge chamber of said vessel means, and an annular shaped anode means provided in the outer wall of said vessel means in outwardly spaced and circumjacent relation to said plurality of electron emitter means for causing a series of electron arc discharges between said plurality of electron emitter means and said anode means so as to effect formation of the introduced amount of gaseous medium into a relatively stable and quiescent high current plasma of substantially uniform ion current density throughout its extent upon simultaneous electric energization of said anode means and said plurality of emitter means when said reservoir means admits a predetermined amount of gaseous medium into the discharge chamber.

5. A plasma generating device as set forth in claim 1 in which said reservoir means includes a gaseous medium selected from the group of hydrogen, deuterium, tritium and Various admixtures thereof.

6. In a high current plasma generating device made up of a vessel means and a plurality of electron emitter elements mounted at one end of said vessel means and disposed in the evacuated electron arc discharge chamber therein, each one of said elements being disposed in circumferentially spaced relation to each other and extending longitudinally into the chamber of said vessel means, a reservoir means for introducing a predetermined amount of a gaseous medium into the chamber of said vessel means, and an anode means disposed in electron arc discharge relation to said emitter means, the improvement comprising an annular shaped anode means provided in the outer peripheral wall of said vessel means and disposed in radially outward and circumjacent spaced relation to said plurality of emitter elements so as to cause an introduced amount of gaseous medium in the chamber to be formed into a relatively stable and quiescent high current plasma of substantially uniform ion current density throughout its extent upon simultaneous electric energization of said anode means and said plurality of emitter means when said reservoir means admits a predetermined amount of gaseous medium to be ionized into the discharge chamber.