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Publication numberUS3783227 A
Publication typeGrant
Publication dateJan 1, 1974
Filing dateApr 15, 1971
Priority dateApr 15, 1971
Publication numberUS 3783227 A, US 3783227A, US-A-3783227, US3783227 A, US3783227A
InventorsAitken M
Original AssigneeAitken M
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Fully energized plasma jet
US 3783227 A
Abstract
Apparatus and method for generating a more efficient, fully energized plasma are disclosed. The gas is introduced into an enclosed channel where it is subjected to an electromagnetic field. The field is adjusted to energize the gas close to its ionization potential. The energized gas is then passed through a nozzle and into and through a high voltage electrical arc where it is converted to a plasma. In another embodiment, the gas passing through the nozzle is first subjected to a high voltage electrical field where it is further energized prior to being subjected to an electric arc and thus converted to a plasma.
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United States Patent 1 [111 3,783,227 Aitken Jan. 1, 1974 FULLY ENERGIZED PLASMA JET Primary ExaminerC. L. Albritton Assistant ExaminerGale R. Peterson [76] lnvemor' :22 :13: g fgf g Att0rneyBrumbaugh, Graves, Donohue & Raymond [22] Filed: Apr. 15, 1971 Appl. No.: 134,315

POWER SOURCE 5 7 ABSTRACT Apparatus and method for generating a more efficient, fully energized plasma are disclosed. The gas is introduced into an enclosed channel where it is subjected to an electromagnetic field. The field is adjusted to energize the gas lose to its ionization potential. The energized gas is then passed through a nozzle and into and through a high voltage electrical are where it is converted to a plasma. In another embodiment, the gas passing through the nozzle is first subjected to a high voltage electrical field where it is further energized prior to being subjected to an electric arc and thus converted to a plasma.

24 Claims, 4 Drawing Figures COOLING LIQUID POWER SOURCE GAS SHEUIBF 4 PATENTEDJAH 1 I974 POWER SOURCE COOLING LIQUID INVENTOR MICHAEL D. AITKEN hi5 ATTORNEYS.

PATENTEDJAH 1 1974 3783.227

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F =Q l 314m Z6 Z6 22 INVENTOR;

GAS MICHAEL D. AITKEN h is ATTORNEYS.

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PATENIEDJAH 1 m4 3783.227 saw u m a POWER SOURCE COOLING LIQUID POWER SOURCE I NVE/YTOR. Z2 T MICHAEL D. AITKEN his ATTORNEYS.

FULLY ENERGIZED PLASMA JET BACKGROUND OF THE INVENTION A plasma is an ionized gas containing an approximately equal number of positive and negative free charges (positive ions and electrons). It is generated by energizing a gas until the bond between an atom and an electron is broken. The free electrons collide with one another, with ions, and with neutral atoms. These collisions generate radiant energy and raise the temperature of the gas into the range of 1,000" to 20,000C. In some applications, temperatures in the millions of degrees are achieved.

The energy and high temperatures produced by plasmas have caused them to be applied to many various uses, such as for electromagnetic propulsion engines, spray coating systems, thermionic convertors, torches, and the like.

A specialized application of a plasma comprises its use in plasma jets and plasma torches. These devices and systems are commercially used for materialcoating, cutting, drilling, welding, and the like. These devices and systems, however, have the disadvantages that they consume large amounts of gas and are relatively inefficient. Plasma arc drills, for example, typically have an electrical efficiency of only 70 percent and consume gas at the rate of 7,000 standard liters per hour; Maurer, Novel Drilling Techniques (Pergamon Press 1968). Also, the rate of cutting and drilling by plasma are devices is significantly lower than conventional mechanical techniques. For long term operation, in particular, these disadvantages are substantial.

SUMMARY OF THE INVENTION The present invention overcomes many of the practical disadvantages of plasma apparatus as it provides a more efficient system and apparatus for producing and using a plasma. The gas is introduced into an activation chamber where it is subjected to an electromagnetic field and excited to a high energy level close to its ionization potential. The gas then is passed through a nozzle and flowed through an electric are maintained between a plurality of electrodes whereby the gas is ionized, ignited, and converted to a plasma. The electromagnetic excitation utilizes the nuclear magnetic resonance of the gas and achieves maximum use of the energy of the gas.

In another embodiment, a high voltage electric field is maintained across a series of electrodes positioned in the flow stream between the nozzle and the electric arc whereby the gas is further energized prior to being converted to a plasma.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 illustrates a plasma apparatus in accordance with the present invention;

FIG. 2 is a partial longitudinal section of the apparatus shown in FIG. 1;

FIG. 3 illustrates another embodiment of a plasma apparatus in accordance with the present invention; and

FIG. 4 is a partial longitudinal section of the apparatus shown in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A plasma jet apparatus in accordance with the present invention is shown in FIGS. 1 and 2. A tube (channel means) 10 is provided to enclose and energize a gas. The tube 10 is cylindrical and hollow, the central chamber indicated by numeral 1 1. The interior portion of the tube 10 is molded or machined so that the end portions 11' a"d ll" of chamber 11 are slightly larger than the center portion. In this manner, ledges l2 and 12 are formed.

The tube 10 can be made of any non-conductive material with gooti mechanical strength, such as ceramic or a plastic, but preferably is made of Teflon. The hightemperature properties of Teflon make it especially preferable forthe inventive apparatus where temperatures on the order of l,0O0 to 20,000C are typically produced. If a material with poor thermal properties is utilized, then a liquid cooled jacket or chamber (not shown) preferably is positioned around tube 10.

A pair of electrodes 13 and 14 either rest on or are supported by the ledges 12 and 12'. As shown in FIGS. 1 and 2, electrode 13 rests on ledge 12 and electrode 14 is supported by ledge 12'. The electrodes 13 and 14 preferably are made of fine steel wire mesh, but can be made of any conductive material. A matrix of strips of conductive material also could be utilized as long as electrode 13 is adapted to allow the gas introduced into chamber 11 to pass freely through it.

One or both of the electrodes 13 and 14 are preferably movable or adjustable in the tube 10. This feature allows the electromagnetic field transmitter 15 (discussed below) to be turned to resonance between the two electrodes 13 and 14. The electrodes are made adjustable by means of a plurality of annular rings 16, 17 and 18. The rings 16, 17 and 18 are adapted to slide easily within the end portions 11 and 11" of chamber 11 and to rest against ledges l2 and 12'. The rings can be of any height and it is understood that any number of rings can be provided; three rings 16, 17 and H8 are shown only for illustrative purposes. Referring to FIG. 2, it is clear that electrode 14 can be positioned anywhere along the length L of the chamber 11" depending on the positioning of the rings and their height and number. It is also understood that chambers 11' and 11" can be of any length to facilitate adjustment of electrodes 13 and 14 over a wide range of locations.

The rings l6, l7 and 18 must be non-conductive as they also insulate electrodes 13 and 14 from other parts of the apparatus. Preferably, the rings are made of Teflon.

A removable cap 20 is positioned on one end of the tube 10. The cap 20 facilitates easy adjustment of electrode l4 and can be made removable in any conventional manner, such as by screws, latches or the like, but preferably is threaded and thus screwed into the end of chamber 11''. The cap 20 can be made of any material, but preferably is non-conductive and similar in material to the tube 10.

Contained in the cap 20 is an aperture or gas inlet 21 to facilitate introduction of a gas into chamber ll 1. The inlet 21 is provided with connector means 22 to securely and detachably fasten a gas conductor 23 to the tube 10 for operation. A threaded cylinder 22 is illustrated in FIGS. 1 and 2, but any standard connector means can be utilized. Also, it is understood that the gas inlet 21 does not necessarily have to be positioned in the cap 20. The inlet 21 also could be placed on the side of the tube 10.

Attached to electrodes 13 and 14 is an electromagnetic field source (transmitter) 15. The source 15 is connected to the tube and the electrodes 13 and 14 by any conventional means; male plugs 25 and 26 and conductors 27 and 28, respectively, are shown in FIGS. l-4. Plugs 25 and 26 fit within female inlets 25' and 26, respectively, so that tip portions 29 and 30 come in electrical contact with the electrodes 13 and 14, respectively. If the electrodes 13 and 14 are made adjustable, then additional electrodes are positioned along the walls of the chambers 11 and 11", respectively. In FIGS. 1 and 2, for example, chamber 11" is machined with channel 32 along the side thereof and electrode 31 is positioned therein. Electrode 31 provides the necessary contact between the electrode 14 and the tip portion 30.

Preferably the source comprises a high frequency wave source operating within the range of l-45 megacycles. The source 15, however, can be any power source capable of establishing an alternating current or wave field in chamber 11. For example, the source 15 can be an ultrahigh frequency or microwave power source, a laser light source, an electromagnetic or permanent magnetic power source, a radioactive source, or merely a high voltage ionization source. The invention utilizes the phenomenon of the nuclear magnetic resonance of the atoms forming the gas in chamber 11. The gas atoms, when subjected to the field between electrodes 13 and 14 will absorb (or be pumped with) energy and, thereby, have more energy to release when subsequently converted to a plasma.

A nozzle 40 and nozzle-holder 41 are also positioned within chamber 11. The nozzle 40 preferably comprises a relatively short, hollow cylinder and is positioned within the nozzle-holder 41. A set screw 42 secures the nozzle 40 in position. The nozzle 40 can be made either conductive or non-conductive, depending on the manner in which the apparatus is operated (as discussed below). If conductive, the nozzle can be made of any metal, such as copper; if non-conductive, the nozzle can be made of any non-conductive material, such as Teflon or boron nitride. With the embodiment shown in FIGS. 1 and 2, the nozzle 40 preferably is non-conductive. The nozzle-holder 41 is cylindrical in shape, adapted to fit within chamber 11 and preferably made of stainless steel or brass.

The nozzle-holder 41 is held in position in chamber 11 by an insulator ring 46 and a plate 47. The ring 46 is similar in construction and purpose to rings 16, 17 and 18; the plate 47 can be of any material with good mechanical strength, such as stainless steel, brass, a plastic, or the like. The ring 46 and plate 47 are, in turn, held in position by a threaded cap 50.

The cap 50 can be made of any material, such as steel or brass, and is liquid cooled. Cooling tubes 51 are provided in cap 50 for this purpose. The cooling liquid enters the tubes 51 by inlet 52 and leaves by another conduit (not shown). Connector means 53 is provided to securely and detachably fasten a liquid conductor 54 to the cap 50. The cooling liquid and cooling system can be any conventional type.

A plurality of electrodes 60 are positioned in channels 61 in cap 50 so that the tips 62 of the electrodes 60 converge in an area directly above the nozzle 40.

Four electrodes 60 are provided in the embodiments shown in the drawings, but it is understood that any number can be utilized. The electrodes 60 preferably are made of carbon or tungston and are secured in position by set screws 63, or by any other similar means. Layers of non-conductive or insulating material 64 are positioned in channels 61 to insulate the electrodes 60 from the cap 50. Releasable caps 65 connect the electrodes 60 to an electrical power source 43 by means of conductors 66 a d 67. The source 43 preferably generates direct current on the order of 10 to 30 volts and at 50 to 300 amperes.

Placed betwe n cap 50 and tube 10 when the cap 50 is screwed into position as shown in the drawings, is a heat shield 70. The heat shield is made of a metal, such as steel or brass, and is cooled by circulation of a cooling liquid through tubes 71 (FIG. 2). The cooling liquid enters through inlet 72 and exits through a second conduit (not shown). Releasable connector means 73 and cap means 74 are provided to connect the heat shield to a conventional system and supply of cooling liquid. Preferably, the cap 50 and heat shield 70 are cooled by means of a common cooling system.

he purpose of the heat shield is to protect the tube 10, the other portions of the apparatus, and the electrical and supply equipment (not shown), from the intense heat of the plasma jet. Thus, the heat shield 70 can be of any size and shape to satisfy the particular conditions of the operation in which the plasma jet is utilized. Where there is little or no reflected heat from the operation, the heat shield 70 may not be necessary.

In operation of the apparatus, the high frequency wave source 15 and the electrical power supply 43 are activated and a gas which must be at least slightly conductive is introduced through inlet 21 into chamber 1 1. As the gas passes between electrodes 13 and 14, it is energized by the high frequency wave source as close as possible to its ionization potential, i.e., to the highest energy level prior to ionization. For any known supply and mixture of gas, the precise frequency for the wave source 15 can be determined which will excite the gas atoms to such energy level and the distance between electrodes 13 and 14 and the precise setting for the power source 15 can be determined accordingly. For example, with a gas supply comprising approximately 50 percent by volume nitrogen, 30 percent helium, 10 percent argon and 10 percent butane, a frequency of 5.67 megacycles is preferred.

From the ionization chamber 1 1, the energized gas is forced at least by its own pressure through a nonconductive nozzle 40 and past the electrodes 60. The power source 43 generates an arc across the tips 62 of the electrodes 60. When the energized gas flows through the are, it is converted to a plasma and ignited. The resultant flame protrudes many inches from the cap 50 and its high intensity and temperature, on the order of 1,000 to 20,000C, makes it useful for many purposes.

With the inventive apparatus and system, the nuclear magnetic resonance of the gas atoms is utilized and a given amount of gas is energized more completely than in conventional plasma apparatus and systems. The attainment of more completely energized gas significantly decreases the amount of gas necessary for given plasma conditions and thus significantly increases the efficiency of the system.

The amount of gas typically consumed by plasma jets can be on the order of 7,000 standard liters per hour. For a long term operation, such as for mining operations, the amount and cost of the gas will be substantial. Thus, the decrease in the amount of the gas necessary for operation of the present invention may make the difference between an economically successful or unsuccessful operation.

Moreover, energizing or electromagnetically activating the gas prior to converting it to a plasma means that less energy (and thus less power and expense) is required to subsequently convert it to a plasma. For example, with conventional plasma jets, power sources on the order of 100 volts and at 1,000 amperes are typically utilized, while, in the present apparatus and system, only -30 volts at 50 to 300 amperes are necessary.

Another embodiment of the invention is shown in FIGS. 3 and 4. The tube 10 and its contents, the heat shield 70 and the cap 50 and its parts are similar to those described with reference to FIGS. 1 and 2 although an adjustable screw 75 is provided in the wall of the tube 10 and power source 76 is substituted for source 43. Conductor 77 and cap means '78 connect source 76 to the screw 75. Thus, the screw 75 connects the nozzle-holder 41 to power source 76 and, when a conductive nozzle 40 is utilized, enables an electric field to be established between the nozzle 40 and the electrodes 60.

The source 76 preferably is a high voltage power source on the order of 10 to 10,000 volts alternating current and at l ampere, but can be any alternating current or wave source similar to those capable of being utilized for source in FIGS. l. and 2.

Also included in the embodiment illustrated in FIGS. 3 and 4 is a second set of electrodes 80 and 81. The electrodes 80 and 81 are preferably carbon or tungston rods and are connected by conductors 82 and 83 to an electrical power source 84. The power source 84 preferably is similar to the power source 43 described above and maintains an electric are between electrodes 80 and 81.

The electrodes 80 and 81 are maintained in holders 90 and 91, respectively, which preferably are nonconductive and cooled in a manner similar to the cooling of the heat shield 70 and the cap 50. If desired, layers of non-conductive or insulating material (not shown) similar to material 64 can be provided to insulate electrodes 80 and 81 from their holders 90 and 91. The holders 90 and 91 are supported on the heat shield 70 by supports 92 and 93, respectively.

In operation of this embodiment, a gas which is at least partially conductive is introduced into tube 10 through inlet 21 and electromagnetically activated by the power source 15 close to its ionization potential. The energized gas is then passed through conductive nozzle 40 and past electrodes 60. Because the energized gas is magnetic and the nozzle 40 is conductive, a current is induced in nozzle 40 and thus some of the energy of the gas is lost to the atmosphere and the apparatus. The field maintained between nozzle 40 and electrodes 60 by source 76 pumps the gas back to or above the energy level that it had achieved prior to entering the nozzle 40.

The energized gas subsequently passes through the are maintained between electrodes 80 and 81 where it is converted to a plasma. The characteristics of the plasma achieved by this embodiment are similar to the characteristics above described with reference to the plasma achieved by the apparatus of FIGS. 1 and 2.

The invention has been described with respect to particular embodiments, but it is understood that numerous modifications and changes may occur to those skilled in the art. Any such modifications and changes are included within the scope of the invention as defined by the following claims.

I claim: 1. A method of converting a gas to a plasma comprising flowing the gas in a channel means, electromagnetically exciting the gas in the channel means to energize it at least partially, passing the energized gas through a nozzle means,

and subjecting the energized gas to an electric arc whereby the gas is converted to a plasma. 2. The method of claim 1 wherein the gas is electromagnetically excited by a high frequency wave source.

3. The method of claim 1 wherein the gas is energized close to its ionization potential in the channel means.

4. A method of converting a gas to a plasma comprising flowing the gas in a channel means,

electromagnetically exciting the gas in the channel means to energize it at least partially,

flowing the energized gas through a nozzle means,

subjecting the energized gas to an electrical field downstream of the nozzle means to further energize the gas, and

converting the gas to a plasma by means of an electric are.

5. The method of claim 4 wherein the gas is electromagnetically excited by a high frequency wave source.

6. The method of claim 4 wherein the gas is energized close to its ionization potential at least in the channel means.

7. A plasma jet apparatus comprising enclosed channel means,

means for introducing a gas into the channel means,

a plurality of first electrodes disposed in the channel means,

an electromagnetic field source connected to the first electrodes to energize the gas in the channel means,

a nozzle in communication with the channel means,

a plurality of second electrodes in communication with the channel means and positioned downstream of the nozzle, and

a power source attached to the second electrodes whereby an electric arc is generated between the second electrodes and the gas is converted to a plasma as it flows past the second electrodes.

8. The apparatus of claim 7 wherein the nozzle is comprised of a non-conductive material.

9. The apparatus of claim 7 wherein the electromagnetic field source is a high frequency wave source.

10. The apparatus of claim 7 further comprising means to cool the second electrodes.

11. The apparatus of claim 7 further comprising a heat shield adjacent to the channel means, the heat shield having cooling means therein.

12. The apparatus of claim 7 wherein the electromagnetic field source is connected to the first electrodes by detachable connecting means.

13. The apparatus of claim 7 wherein the power source is connected to the second electrodes by detachable connecting means.

14. The apparatus of claim 7 wherein at least one of the first electrodes is adapted to be adjusted in the channel means.

15. The apparatus of claim 7 wherein the plurality of second electrodes are disposed in a cap means which is releasably connected to the channel means.

16. The apparatus of claim 9 wherein the high frequency wave source generates waves in the range of 1 to 45 megacycles.

17. The apparatus of claim 7 wherein the channel means comprises a tube of Teflon, the nozzle is comprised of carbon, and the second electrodes are comprised of tungston.

18. A plasma jet comprising enclosed means for introducing a gas into the channel means,

a plurality of first electrodes disposed in the channel means,

a first electromagnetic field source connected to the first electrodes to energize the gas in the channel means,

a nozzle in communication with the channel means,

a plurality of second electrodes in communication with the channel means and positioned downstream of the nozzle,

a second electromagnetic field source attached to the nozzle and the second electrodes whereby the gas is further energized as it flows through the nozzle and past the second electrodes,

a plurality of third electrodes in communication with the channel means and positioned downstream of the second electrodes, and

a power source attached to the third electrodes whereby an electric arc is generated between the third electrodes and the gas is converted to a plasma as it flows past the third electrodes.

19. The apparatus of claim 18 wherein the nozzle is comprised of a conductive material.

20. The apparatus of claim 18 wherein the first electromagnetic field source is a high frequency wave source.

21. The apparatus of claim 18 wherein the second electromagnetic field source is a high frequency wave source.

22. The apparatus of claim 18 further comprising means to cool the second and third electrodes.

23. The apparatus of claim 18 further comprising a heat shield adjacent to the channel means, the heat shield having cooling means therein.

24. The apparatus of claim 18 wherein at least one of the first electrodes is adapted to be adjusted in the channel means.

T572330 Q "UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION inye Michael D. Aitken j It is certified that error appears in the above-identified patent V ancfthat said Letters Patent are hereby corrected as shown beldwi Col. 7, line 17, after "jet" insert -apparatus--; and

Col. 7, line 18, after "enclosed" insert -.-channel means,.

Signed and s e aelQecl this 18th day of June- 19714.. I

(SEAL) Attest:

EDWARD MJLETCHER'JR; C. MARSHALL mum Attesting Officer Commissionerof Patents

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3140421 *Apr 17, 1962Jul 7, 1964Spongberg Richard MMultiphase thermal arc jet
US3280364 *Mar 5, 1963Oct 18, 1966Hitachi LtdHigh-frequency discharge plasma generator utilizing an auxiliary flame to start, maintain and stop the main flame
US3344256 *Oct 1, 1963Sep 26, 1967 Method for producing arcs
US3541297 *Dec 31, 1968Nov 17, 1970Soudure Autogene ElectHeating a reactive fluid to high temperature
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4009413 *Feb 27, 1975Feb 22, 1977Spectrametrics, IncorporatedPlasma jet device and method of operating same
US4035604 *Jul 21, 1975Jul 12, 1977Rolls-Royce (1971) LimitedMethods and apparatus for finishing articles
US5464667 *Aug 16, 1994Nov 7, 1995Minnesota Mining And Manufacturing CompanyJet plasma process and apparatus
US6203898Aug 29, 1997Mar 20, 20013M Innovatave Properties CompanyArticle comprising a substrate having a silicone coating
US6348237Jan 12, 2001Feb 19, 20023M Innovative Properties CompanyJet plasma process for deposition of coatings
US7189436Aug 2, 2004Mar 13, 20073M Innovative Properties CompanyFlash evaporation-plasma coating deposition method
Classifications
U.S. Classification219/121.36, 313/231.1
International ClassificationH05H1/26, B23K10/00
Cooperative ClassificationH05H1/26, B23K10/00
European ClassificationH05H1/26, B23K10/00