Abstract:
A device, method and system for generating a plasma is disclosed wherein an electrical arc is established and the movement of the electrical arc is selectively controlled. In one example, modular units are coupled to one another to collectively define a chamber. Each modular unit may include an electrode and a cathode spaced apart and configured to generate an arc therebetween. A device, such as a magnetic or electromagnetic device, may be used to selectively control the movement of the arc about a longitudinal axis of the chamber. The arcs of individual modules may be individually controlled so as to exhibit similar or dissimilar motions about the longitudinal axis of the chamber. In another embodiment, an inlet structure may be used to selectively define the flow path of matter introduced into the chamber such that it travels in a substantially circular or helical path within the chamber.

Description:
STATEMENT OF GOVERNMENT RIGHTS 
   This invention was made with government support under Contract No. DE-AC07-051D14517 awarded by the United States Department of Energy. The government has certain rights in this invention. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to plasma arc reactors and systems and, more particularly, to a modular plasma arc reactor and system as well as related methods of creating a plasma arc. 
   2. State of the Art 
   Plasma is generally defined as a collection of charged particles containing about equal numbers of positive ions and electrons and exhibiting some properties of a gas but differing from a gas in being a good conductor of electricity and in being affected by a magnetic field. A plasma may be generated, for example, by passing a gas through an electric arc. The electric arc will rapidly heat the gas by resistive and radiative heating to very high temperatures within microseconds of the gas passing through the arc. Essentially any gas may be used to produce a plasma in such a manner. Thus, inert or neutral gasses (e.g., argon, helium, neon or nitrogen) may be used, reductive gasses (e.g., hydrogen, methane, ammonia or carbon monoxide) may be used, or oxidative gasses (e.g., oxygen, water vapor, chlorine, or carbon dioxide) may be used depending on the process in which the plasma is to be utilized. 
   Plasma generators, including those used in conjunction with, for example, plasma torches, plasma jets and plasma arc reactors, generally create an electric discharge in a working gas to create the plasma. Plasma generators have been formed as direct current (DC) generators, alternating current (AC) plasma generators, as radio frequency (RF) plasma generators and as microwave (MW) plasma generators. Plasmas generated with RF or MW sources may be referred to as inductively coupled plasmas. In one example of an RF-type plasma generator, the generator includes an RF source and an induction coil surrounding a working gas. The RF signal sent from the source to the induction coil results in the ionization of the working gas by induction coupling to produce a plasma. In contrast, DC- and AC-type generators may include two or more electrodes (e.g., an anode and cathode) with a voltage differential defined therebetween. An arc may be formed between the electrodes to heat and ionize the surrounding gas such that the gas obtains a plasma state. The resulting plasma, regardless of how it was produced, may then be used for a specified process application. 
   For example, plasma jets may be used for the precise cutting or shaping of a component; plasma torches may be used in forming a material coating on a substrate or other component; and plasma reactors may be used for the high-temperature heating of material compounds to accommodate the chemical or material processing thereof. Such chemical and material processing may include the reduction and decomposition of hazardous materials. In other applications plasma reactors have been utilized to assist in the extraction of a desired material, such as a metal or metal alloy, from a compound which contains the desired material. 
   Exemplary processes which utilize plasma-type reactors are disclosed in U.S. Pat. Nos. 5,935,293 and RE37,853, both issued to Detering et al. and assigned to the assignee of the present invention, the disclosures of which are incorporated by reference herein in their entireties. The processes set forth in the Detering patents include the heating of one or more reactants by means of, for example, a plasma torch to form from the reactants a thermodynamically stable high temperature stream containing a desired end product. The gaseous stream is rapidly quenched, such as by expansion of the gas, in order to obtain the desired end products without experiencing back reactions within the gaseous stream. In one embodiment, the desired end product may include acetylene and the reactants may include methane and hydrogen. In another embodiment, the desired end product may include a metal, metal oxide or metal alloy and the reactant may include a specified metallic compound. However, as recognized by the Detering patents, gases and liquids are the preferred forms of reactants since solids tend to vaporize too slowly for chemical reactions to occur in the rapidly flowing plasma gas before the gas cools. If solids are used in plasma chemical processes, such solids ideally have high vapor pressures at relatively low temperatures. These type of solids, however, are severely limited. Of course, such processes are merely examples and numerous other types of processes may be carried out using plasma technologies. 
   As noted above, process applications utilizing plasma generators are often specialized and, therefore, the associated plasma jets, torches and/or reactors need to be designed and configured according to highly specific criteria. Such specialized designs often result in a device that is limited in its usefulness. In other words, a plasma generator that is configured to process a specific type of material using a specified working gas to form the plasma is not necessarily suitable for use in other processes wherein a different working gas may be required, wherein the plasma is required to exhibit a substantially different temperature or wherein a larger or smaller volume of plasma is desired to be produced. 
   In view of the shortcomings in the art, it would be advantageous to provide a plasma generator and associated system that provides improved flexibility regarding the types of applications in which the plasma generator may be utilized. For example, it would be advantageous to provide a plasma generator and associated system that produces an improved arc and associated plasma column or volume wherein the arc and plasma volume may be easily adjusted and defined so as to provide a plasma with optimized characteristics and parameters according to an intended process for which the plasma is being generated. 
   BRIEF SUMMARY OF THE INVENTION 
   In accordance with one aspect of the invention an apparatus for generating a plasma is provided. The apparatus includes a chamber having an inlet and an outlet. A first electrode pair, comprising an anode and a cathode, is configured to provide a first electrical arc proximate the inlet of the chamber. A second electrode pair, also comprising an anode and a cathode, is configured to provide a second electrical arc within the chamber such that the second electrical arc extends between an arc endpoint on the cathode and an arc endpoint on the anode. A device is configured to selectively move a circumferential location of at least a portion of the second electrical arc within the chamber relative to a longitudinal axis of the chamber. In one embodiment, the device may include one or more electrical coils configured to generate a selectively controlled magnetic field so as to induce movement in the second electrical arc. 
   In accordance with another aspect of the present invention, another plasma generating apparatus is provided. The apparatus includes a plurality of interconnected modules cooperatively defining a chamber. Each module of the plurality of interconnected modules includes at least one device configured to generate an electrical arc within the chamber, and at least one device configured to generate a magnetic field within the chamber, the magnetic field being configured to selectively displace (e.g., rotate) at least a portion of the electrical arc within the chamber. 
   In accordance with a further aspect of the present invention, a method of generating a plasma is provided. The method includes providing an anode and a cathode, the cathode being positioned proximate the anode, and introducing matter to a region between the anode and the cathode. A voltage is applied between the first electrode and the second electrode and an electrical arc is established that extends between an arc endpoint on the anode and an arc endpoint on the cathode. At least one magnetic field is generated in at least one region through which at least a portion of the electrical arc passes the at least one magnetic field is selectively controlled so as to selectively move a circumferential location of at least one of the arc endpoint on the anode and the arc endpoint on the cathode about a longitudinal axis of the chamber. 
   In accordance with yet another aspect of the present invention, another method is provided of generating a plasma. The method includes providing a chamber comprising a plurality of interconnected modules to collectively define a chamber. Each module includes an electrode pair, including a cathode and an anode, and each module further includes at least one device configured to generate at least one selectively controllable magnetic field in at least one region through which the associated module&#39;s electrical arc is intended to pass through. A voltage is applied between the anode and the cathode of the electrode pair of each module so as to establish an electrical arc between an arc endpoint on a surface of its associated cathode and an arc endpoint on a surface of its associated anode. The at least one magnetic field of each module is selectively controlled so as to selectively move the circumferential location of at least one of the arc endpoint on the surface of the associated cathode and the arc endpoint on the surface of the associated anode. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     While the specification concludes with claims particularly pointing out and distinctly claiming that which is regarded as the present invention, various advantages of the invention may be more readily ascertained from the following description of the various embodiments of the invention when read in conjunction with the accompanying drawings in which: 
       FIG. 1  is a cross-sectional view of a module that may be used as part of a plasma generating apparatus in accordance with an embodiment of the present invention; 
       FIGS. 2A and 2B  are cross-sectional views of a portion of the module shown in  FIG. 1 , taken along section line  2 - 2  therein, which are used in illustrating certain principles of operation of the module; 
       FIG. 3  is a cross-sectional view of a plasma generating apparatus in accordance with an embodiment of the present invention; 
       FIG. 4  is a plan view of a component that may be used in a plasma generating apparatus in accordance with an embodiment of the present invention; 
       FIG. 5  is a side view of another component that may be used in a plasma generating apparatus in accordance with another embodiment of the present invention; and 
       FIG. 6  is a cross-sectional view of another plasma generating apparatus in accordance with another embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The illustrations presented herein are not meant to be actual views of any particular plasma generating apparatus or device but are merely idealized representations, which are employed to describe various embodiments of the present invention. It is noted that elements which are common between figures may retain the same numerical designation. 
   The term “module,” as used herein, means any structure that is configured to be attached to another structure to provide an apparatus including the two structures, the function, capability or method of operation of the apparatus being easily modified by adding, removing, or changing the structures. 
   Referring to  FIG. 1 , a module  10  that may be used as a plasma generating apparatus (or as a component part of a plasma generating apparatus) is shown in accordance with one embodiment of the presently disclosed invention. The module  10  includes an electrode pair comprising an anode  12  and a cathode  18 . The electrode pair is configured to provide an electrical arc between the anode  12  and the cathode  18  as discussed in further detail below. The module  10  may also include a first endplate  24 , a second endplate  26 , and an arc-enclosing structure  30 . 
   The arc-enclosing structure  30  may be configured to at least partially enclose a defined volume through which an electrical arc extending between the anode  12  and the cathode  18  passes. The arc-enclosing structure  30  may include, for example, a first cylindrical tube  32 , a second cylindrical tube  34  having a diameter larger than a diameter of the first cylindrical tube  32 , at least two rods or posts  36 , two connecting disks  38 , and compression plates  40 . The first cylindrical tube  32 , the second cylindrical tube  34 , and the posts  36  may all be secured and connected to the connecting disks  38 . It is noted that all of such described components are not necessary to the function of the module  10 , and that some of the components may be integrally formed. For example, the compression plates  40  may be eliminated or otherwise integrated into other components. Additionally, the module  10  may include other components not specifically shown. For example, O-rings or other seal members may be disposed between various interfacing surfaces of the individual components. In a more specific example, O-rings or other seal members may be disposed at a location adjacent the inner diameter of the compression plates  40  at the location where they abut the first cylindrical tube  32  or at other similar interfacing locations. 
   The first cylindrical tube  32  and the second cylindrical tube  34  may each comprise an electrically insulating refractory material such as, for example, quartz. The first cylindrical tube  32  may be positioned within the second cylindrical tube  34  so as to define a generally annular space  35  therebetween. A fluid passageway  39  may be defined in each of the connecting disks  38  and be arranged in communication with the annular space  35 . One fluid passageway  39  may be configured as a fluid inlet and one fluid passageway  39  may be configured as a fluid outlet to the annular space  35 . A fluid (not shown), such as water or some other coolant, may be circulated through one fluid passageway  39 , through the annular space  35 , and out of the second fluid passageway  39  so as to transfer heat from the arc-enclosing structure including the first cylindrical tube  32 . 
   The posts  36  may be used to provide added structural support to the arc-enclosing structure  30 . The posts  36  may be formed from, for example, a polymer material such as a phenolic material. While not shown, rods or other structural components may be used to couple the various components together. For example, a threaded rod may extend between the first and second end plates  24  and  26  and through appropriately sized and located openings  42  formed therein. Thus, in one embodiment, such rods may be used to compress the first and second endplates  24  and  26  toward one another to hold the other components of the module  10  in their desired positions. In other embodiments, the openings  42  may be used to couple the module  10  with other modules or other associated components. 
   Still referring to  FIG. 1 , the anode  12  and the cathode  18  each may have a substantially annular shape, and together with the arc-enclosing structure  30  may define a substantially cylindrical aperture or bore  44  extending through the module  10  and centered about a longitudinal axis  48 . As used herein, the term “substantially annular” means of, relating to, or forming any three-dimensional structure having an interior void or aperture extending through the structure from a first side of the structure to a second side of the structure. The interior void or aperture may be of any shape including, but not limited to, circular, oval, triangular, rectangular, etc., and may have a complex curved shape. By way of example and not limitation, substantially annular shapes include any prismatic shape (polyhedrons with two polygonal faces lying in parallel planes and with the other faces parallelograms) in which an interior void or aperture extends between two polygonal faces of the prismatic shape that are disposed in parallel planes, such as, for example, hollow cylindrical shapes. 
   The first endplate  24  and the second endplate  26  each may also have an interior void or aperture extending therethrough. 
   The anode  12  and the cathode  18  are configured to provide an electrical arc that extends through the bore  44  from an electrical arc endpoint on the anode  12  to an electrical arc endpoint on the cathode  18 . By way of example and not limitation, the anode  12  may include a substantially circular edge  14  defined by the intersection between a first surface  15  and a second surface  16  of the anode  12  such that the circular edge  14  is the radially innermost surface of the anode  12 . Similarly, the cathode  18  may include a substantially circular edge  20  defined by the intersection between a first surface  21  and a second surface  22  of the cathode  18 . The arc endpoint on the anode  12  may be located on the circular edge  14 , and the arc endpoint on the cathode  18  may be located on the circular edge  20 . Of course other configurations of the anode  12  and cathode  18  may be used as will be appreciated by those of ordinary skill in the art. 
   An electrical power source  50 A may be provided and configured to apply a voltage between the anode  12  and the cathode  18 . If the magnitude of the voltage between the anode  12  and the cathode  18  reaches a critical point, an electrical arc (not shown) may be generated and caused to extend between the anode  12  and the cathode  18 . The magnitude of this critical-point voltage may be reduced by providing charged ions within the bore  44  between the anode  12  and the cathode  18  thereby reducing the resistivity between the anode  12  and cathode  18 . In this manner, the anode  12 , the cathode  18 , and the electrical power source  50 A provide a device configured to generate an electrical arc within the module  10 . By way of example and not limitation, the power source may include a direct current (DC) power source configured to provide a voltage in a range extending from about 70 volts to about 80 volts and a current in a range from about 90 amps to about 110 amps between the anode  12  and the cathode  18 . 
   The module  10  may also include at least one device configured to generate a magnetic field in a desired region within the module  10 . The magnetic field may be selectively controlled to move the location of at least a portion of an electrical arc within the module  10 . For example, the module  10  may include an electrically conductive wire wound in a coil  54 A. The coil  54 A may surround at least a portion of the module  10 . In one particular embodiment, the coil  54 A may surround at least a portion of the module  10  proximate the cathode  18 . The module  10  may include an additional electrically conductive wire wound in a coil  54 B that surrounds a portion of the module  10  such as, for example, at a location proximate the anode  12 . An electrical power source  50 B may be provided and configured to pass electrical current through the electrically conductive wire of the coil  54 A, and an electrical power source  50 C may be provided and configured to pass electrical current through the electrically conductive wire of the coil  54 B. In another embodiment, a single electrical power source could be provided and configured to pass electrical current through both coils  54 A and  54 B. 
   As an electrical current is passed through the coils  54 A and  54 B, a magnetic field of a desired strength may be generated in a desired region within the module  10  depending on the configuration of the coils and the strength of current flowing therethrough. In one example, a magnetic field may be generated in a region located within the module  10  between the arc endpoint on the anode  12  and the arc endpoint on the cathode  18 . The magnetic field produced by such coils may be used advantageously to influence one or more characteristics of the generated arc as will be discussed in greater detail hereinbelow. 
   An electrical arc comprises a flow of electrons, each electron having a negative charge by definition. When an electrical arc is generated in the module  10 , the negatively charged electrons may travel through the bore  44  from the cathode  18  to the anode  12  (e.g., from the arc end point of the cathode  18  to the arc endpoint of the anode  12 ). 
     FIG. 2A  is a cross-sectional view of the cathode  18  as taken along section line  2 - 2  of  FIG. 1 . Referring to  FIG. 2A  in conjunction with  FIG. 1 , four electrons (represented by circles with a “−”, or a negative charge) are illustrated at various positions within the bore  44  of the module  10  proximate the cathode  18 . When electrical current is passed through the electrically conductive wire of the coil  54 A proximate the cathode  18  in the counter-clockwise direction (i.e., when looking through the bore  44  from the first endplate  24  toward the second endplate  26 ), a magnetic field may be generated in the bore  44 . At least a component of the magnetic field within the bore  44  in the plane of  FIG. 2A  may be directed inwardly toward the longitudinal axis  48  as represented by the magnetic field vectors B. If the electrons are moving through the bore  44  in a direction extending from the first endplate  24  to the second endplate, the current velocity vector of each electron extends vertically into the plane of  FIG. 2A . According to the Lorentz force law, F=qVXB, where q is the charge on a moving particle, V is the velocity vector of the moving particle, B is the magnetic field vector through which the particle is moving, and F is the force vector representing the force acting on the moving particle. Thus, according to the Lorentz force law, the negatively charged electrons flowing in the defined direction through the defined magnetic field may experience a force in the directions represented by the force vectors F 1  shown in  FIG. 2A . 
   The forces F 1  may cause at least a portion of the electrical arc extending between the anode  12  and the cathode  18  to move in a substantially clockwise circular motion within the bore of the module as represented by the directional arrow  58 . For example, these forces may cause the circumferential location of the arc endpoint to move along the edge  20  of the cathode  18  in a substantially clockwise circular motion within the bore  44  of the module  10 . 
   Positively charged ions flowing in the same direction as the electrons through the magnetic field may experience a force in an opposite direction to those represented by the force vectors F 1  in  FIG. 2A . As a result, such positive ions may move in a substantially opposite direction within the bore  44  relative to the negatively charged electrons thereby providing a potentially turbulent mixing effect within the bore  44  of the module  10 . 
   Referring now to  FIG. 2B  in conjunction with  FIG. 1 , the electrons are shown as being subjected to oppositely directed forces represented by the force vectors F 2  within the bore  44 . This may occur as a result of at least two different factors or inputs. First, the direction of current flow provided by the electrical power source  50 B through the coil  54 A proximate the cathode  18  may be reversed such that current flows through the coil  54 A in a clockwise direction (when looking through the bore  44  from the first endplate  24  toward the second endplate  26 ). Reversing the direction of current flow through the coil  54  also reverses the direction of the magnetic field vectors B (compared to that which is shown in  FIG. 2A ), such that the magnetic field vectors B extend in a radial direction outwardly from the longitudinal axis  48  toward the cathode  18 . Reversing the direction of the magnetic field vectors B results in the direction of the forces being reversed (assuming all other variables remain constant), as predicted by the Lorentz force law. 
   Secondly, the electrons may be subjected to oppositely directed forces, such as is represented by the vectors F 2  shown in  FIG. 2B , by reversing the polarity of the power source  50 A connected between the anode  12  and the cathode  18  (which essentially reverses the positions of the anode  12  and the cathode  18  within the module  10 ). Since electrons flow from the cathode  18  to the anode  12 , reversing the polarity of the power source  50  causes the direction of the flowing electrons within the electrical arc to change such that the electrons are flowing vertically out from the plane of  FIGS. 2A and 2B . In other words, reversing the polarity of the electrical power source  50 A may reverse the direction of the velocity vector V in the Lorentz force law. Reversing the velocity vector, such that the velocity vector of each electron extends vertically out from the plane of  FIG. 2B  (or generally in the direction extending from the second end plate  26  to the first end plate  24 ), will also reverse the direction of the forces (assuming all other variables remain constant) as compared to those depicted in  FIG. 2A , as predicted by the Lorentz force law. 
   The forces F 2  depicted in  FIG. 2A  may cause at least a portion of the electrical arc extending between the anode  12  and the cathode  18  to move in a substantially counter-clockwise circular motion within the bore  44  of the module  10  as represented by the directional arrow  60 . For example, these forces may cause the circumferential location of the arc endpoint to move along the edge  20  of the cathode  18  in a substantially counter-clockwise circular motion within the bore  44  of the module  10 . 
   Additional magnetic fields may be provided within the module  10  proximate the anode  12  using the coil  54 B and the electrical power source  50 C in a substantially similar manner to that previously described in relation to the electrically conductive wire  54 A and the electrical power source  50 B. By selectively controlling the magnetic fields within the module  10  produced by the electrically conductive coils  54 A and  54 B, the circumferential location of the arc endpoint on the anode  12  and the circumferential location of the arc endpoint on the cathode  18  may be made to move concurrently in the same circular direction about the axis  48  within the module  10 . In another embodiment, the circumferential location of the arc endpoint on the anode  12  and the circumferential location of the arc endpoint on the cathode  18  may be made to move in opposite circular directions about the axis  48  by selectively controlling the magnetic fields within the module  10 . 
   Using the principles discussed in the preceding paragraphs, the voltage between the anode  12  and the cathode  18 , the current passing through the coil  54 B proximate the anode  12 , and the current passing through the coil  54 A proximate the cathode  18  may each be selectively controlled to selectively manipulate the location and movements of the electrical arc extending between the anode  12  and the cathode  18 . 
   In accordance with one aspect of the present invention, a plasma generating apparatus may include one or more modules such as, for example, the module  10  shown and described with respect to  FIG. 1 . 
   For example, referring to  FIG. 3 , a plasma generating apparatus  70  is shown in accordance with one embodiment of the present invention that includes the module  10  previously described herein in relation to  FIG. 1  and which may further include an arc-generating device  72  attached to the module  10 . The arc-generating device  72  includes an additional electrode pair comprising an anode  74  and a cathode  76 . By way of example and not limitation, the cathode  76  may exhibit a substantially solid, cylindrical shape, and the anode  74  may exhibit a substantially annular shape defining an aperture extending therethrough. The anode  74  may have a generally hollow, cylindrical shape with a generally tapered surface at one end thereof so as to maintain a substantially conformally spaced relationship with the cathode  76 . The cathode  76  may be at least partially positioned within the anode  74 . 
   The plasma generating apparatus  70  may include an additional electrical power source  50 D that is configured to provide a voltage between the anode  74  and the cathode  76  of the arc-generating device  72 . If the magnitude of a voltage applied between the anode  74  and the cathode  76  reaches a critical point, an electrical arc (not shown) extending between the anode  74  and the cathode  76  may be generated. The distance separating the anode  74  and the cathode  76  of the arc-generating device  72  may be significantly less than the distance separating the anode  12  and the cathode  18  of the module  10 . Therefore, the magnitude of the voltage required to generate an electrical arc between the anode  74  and the cathode  76  of this arc-generating device  72  may be significantly lower than the magnitude of the voltage required to generate an electrical arc between the anode  12  and the cathode  18  of the module  10 . In one embodiment, the arc-generating device  72  may include a commercially available plasma torch. 
   The electrical arc generated between the anode  74  and the cathode  76  may be referred to as an “ignition arc” in the sense that the electrical arc may be subsequently used to facilitate ignition of an electrical arc extending between the anode  12  and the cathode  18  of the module  10 . Matter, such as a plasma gas, may be passed through an inlet  78  which may include the space  82  between the anode  74  and the cathode  76 . The ignition arc extending between the anode  74  and the cathode  76  may generate a plasma that includes charged ions and electrons originating from atoms or molecules of the matter passing through the space  82  proximate the ignition arc. These charged ions and electrons may flow through the bore  44  to regions between the anode  12  and the cathode  18 . The presence of the charged ions and electrons between the anode  12  and the cathode  18  may lower the magnitude of the voltage required to generate an electrical arc therebetween, as previously discussed herein. 
   Once an electrical arc is established between the anode  12  and the cathode  18  of the module  10 , the location of the electrical arc within the bore  44  may be selectively manipulate by controlling the current flow through the coils  54 A and  54 B to generate one or more magnetic fields within the bore  44  as previously discussed. The currents passed through the coils  54 A and  54 B may be selectively controlled so as to optimize the density of the charged species in the plasma and the distribution of the plasma within a chamber  90  of the plasma generating apparatus  70 . 
   The plasma generating apparatus  70  may also include an inlet structure  86  disposed between the arc-generating device  72  and the module  10  defining an additional material inlet  96  into the chamber  90 . The inlet structure  86  may exhibit a substantially annular shape and may include an aperture or bore  88  extending therethrough that defines a space between the arc generating device  72  and the bore  44  of the module  10  and is also in communication with each. The chamber  90  of the plasma generating apparatus  70  is collectively defined by the bore  88  of the structure  86  and the bore  44  of the module  10 . 
   The inlet  96  may be formed as a passage through the body of the inlet structure  86  and may be configured to introduce material passing through the inlet  96  into the chamber  90  such that the material exhibits a generally circular or helical flow path within the chamber  90 .  FIG. 4  is a plan view of an embodiment of an inlet structure  86  in accordance with one embodiment of the present invention. As seen therein, the inlet structure  86  may include a substantially annular shaped disk or body  87 . The inlet  96  may include an elongated bore or passage through the body  87  that extends from a radially exterior surface  87 A to the radially interior surface  87 B that defines bore  88 . The elongated bore of the inlet  96  may be centered about a longitudinal axis  97  that does not intersect the longitudinal axis  48  of the module&#39;s bore  44  (which, in the presently described embodiment, is also coaxial with the longitudinal axis of the inlet structure&#39;s bore  88 ). As seen in  FIG. 4 , the inlet  96  may be configured to introduce material passing therethrough into the chamber  90  in an initial direction that is substantially tangential to the radially inner surface  87 B that defines the bore  88  of the inlet structure  86 . Such a configuration results in a generally circular or swirling flow path of the material introduced into the bore  88  in a clockwise direction within the chamber (when looking through the chamber  90  from the inlet toward the outlet thereof), as indicated by the directional arrow  98 . Of course, the inlet  96  may be configured to introduce material into the chamber  90  such that it exhibits a generally counter-clockwise swirling or circular flow path within the chamber  90  if so desired. 
     FIG. 5  illustrates another inlet structure  86 ′ that may be used in the plasma generating apparatus  70  according to another embodiment of the present invention. The inlet structure  86 ′ includes a passage or inlet  96 ′ into the chamber  90  of the plasma generating apparatus  70  and is generally configured similar to the inlet structure  86  described with respect to  FIG. 4 . However, the inlet structure  86 ′ is additionally configured to induce an initial longitudinal component (i.e., in a direction along the longitudinal axis  48 ) to the velocity vector of the material. The additional initial longitudinal velocity component results in a generally helical motion of the material as it is initially introduced into the chamber  90 . Thus, for example, the longitudinal axis  97 ′ about which the elongated bore of the inlet structure  86 ′ is centered, lies in a plane that is oriented at an angle  106  that is less than 90° relative to the longitudinal axis  48  of the bore  44  or chamber  90 . It is noted that used of either inlet structure  86  or  86 ′ results in a generally helical flow path of material introduced thereby and flowing through the chamber  90  of the plasma generating device  70 . This is due to the general flow path of material from the inlet structure  86 ,  86 ′ of the chamber  90  to the outlet of the chamber  90 . However, it can be seen that the inlet structures  86  and  86 ′ may be selectively configured to influence the downward or longitudinal component of the velocity vector of any material introduced thereby. Such selective configuration enables further tailoring of the residence time of a given material within the chamber  90  and, therefore, provides substantial flexibility in configuring a plasma generating device for a desired material process. 
   Referring again to  FIG. 3 , matter such as, for example, a gas or a liquid may be passed into the chamber  90  and caused to follow a desired flow path (e.g., a generally or substantially circular or helical flow path) by way of the additional inlet or passage  96  of the inlet structure  86 . Causing the matter within the chamber  90  to rotate in a generally circular or helical path may cause an electrical arc extending between the anode  12  and the cathode  18  of the module  10  to move in a generally circular path following the path of charged species within the bore  44 , even in the absence of any magnetic fields generated by the electrically conductive coils  54 A or  54 B. In this manner, the inlet  96  may be used to selectively move the location of at least a portion of the electrical arc within the bore  44 . Moving the electrical arc within the bore  44  may enhance the density of charged particles within the plasma and enhance the distribution of the plasma within the bore  44 . Thus, the density of charged particles within the plasma and the distribution of the plasma within the bore  44  may be optimized by selectively moving the electrical arc within the bore  44  in a manner that provides optimum conditions therein. 
   Additionally, the passage or inlet  96  of the inlet structure  86  may be configured to swirl matter passing therethrough into the chamber  90  in a generally circular or helical flow path in a first direction about the longitudinal axis  48  of the chamber  90  of the plasma generating apparatus  70 , and the coils  54 A and  54 B may be configured to generate magnetic fields within the chamber  90  that cause at least a portion of the electrical arc to move in a generally circular motion in a second, opposite direction about the longitudinal axis  48  of the chamber  90 . For example, an electrical arc extending between an arc endpoint on the cathode  18  and an arc endpoint on the anode  12  may be selectively rotated about the longitudinal axis  48  in a clockwise direction within the chamber  90 , while the inlet  96  may be configured to induce a swirling flow path of the matter within the chamber  90  in a counter-clockwise direction within the chamber  90 . In such a configuration, turbulent flow of matter within the chamber  90  may be increased, which may enhance the mixing of the molecules, atoms, and ions within the chamber  90 . 
   In another embodiment, the inlet structure  86  and the coils  54 A and  54 B may be selectively configured such that the flow path of the material flowing through the chamber  90  is the same as (or concurrent with) the motion of the arc about the longitudinal axis  48 . 
   To use the plasma generating apparatus  70  to process or synthesize materials, raw materials may be passed from the inlet  78  of the arc-generating device  72 , the inlet  96  of the inlet structure  86 , or from both, through the chamber  90  to an outlet  79  of the plasma generating apparatus  70 . Other additional materials or chemicals, which may be used as catalysts, oxidizers, reducers or serve as a plasma gas, may also be passed through the chamber  90  from one or both of the inlets  78  to the outlet  79  of the plasma generating apparatus  70 . The electrical arc extending between the anode  12  and the cathode  18  may generate a plasma comprising reactive ions from at least one of the raw materials and the other materials or chemicals. The reactive ions may facilitate chemical transformations in the raw materials and chemical reactions between the raw materials and the other additional materials or chemicals. These chemical transformations and reactions may be used to process or synthesize a wide variety of materials or chemicals. In some embodiments, the plasma generating apparatus  70  may be used to conduct either oxidative or reductive chemical reactions in the plasma. In another example, the plasma generating apparatus  70  may be used to produce nanoparticles from larger, solid particles of raw materials. 
   The structure and configuration of the module  10  enables plasma generating apparatuses to be quickly and easily assembled and configured to process or synthesize particular materials by fastening and arranging a selected number of modules  10  together. For example, a selected number of modules  10  may be secured together in an end-to-end configuration to provide a plasma generating apparatus having desired properties and operating characteristics. 
   Referring to  FIG. 6 , a plasma generating apparatus  110  according to another embodiment of the present invention is shown. The plasma generating apparatus  110  includes the previously described plasma generating apparatus  70  shown in  FIG. 3  and an additional module  10 ′ (referred to as a second module  10 ′ for purposes of clarity) secured thereto. The second module  10 ′ may be substantially identical to the module  10  previously described herein (referred to subsequently herein as a “first module  10 ” for purposes of clarity), and may include, generally, an anode  12 ′, a cathode  18 ′, and a bore  44 ′. In this configuration, the plasma generating apparatus  110  includes a chamber comprising at least the bore  44  of the first module  10  and the bore  44 ′ of the second module  10 ′. The plasma generating apparatus  110  also may include an inlet  114  and an outlet  116  that are each in communication with the chamber. Furthermore, an additional inlet structure  86 ′ including an additional passage or inlet  96 ′ may be provided between the first module  10  and the second module  10 ′. 
   An electrical power source  50 E may be provided and configured to apply a voltage between the anode  12 ′ and the cathode  18 ′. As shown in  FIG. 6 , the polarity of the electrical power source  50 E may be oppositely directed relative to the electrical power source  50 A that is configured to provide a voltage between the anode  12  and the cathode  18  of the first module  10 , effectively switching the position of the anode  12 ′ and the cathode  18 ′ of the second module  10 ′ relative to the first module  10 . In another embodiment, the polarity of the power sources  50 A and  50 E may be the same. 
   An electrical power source  50 F may be provided and configured to pass electrical current through an electrically conductive wire forming a coil  54 A′ adjacent the anode  12 ′. Similarly, an electrical power source  50 G may be provided and configured to pass electrical current through an electrically conductive wire forming a coil  54 B′ adjacent the cathode  18 ′. The electrical power supplies  50 F and  50 G may be configured such that current flows in the same direction through the coil  54 A′ of the second module  10 ′ and the coil  54 A of the first module  10 , and such that current flows in the same direction through the coil  54 B′ of the second module  10 ′ and the coil  54 B of the first module  10 . In such a configuration, an electrical arc extending through the bore  44 ′ between an arc endpoint on the anode  12 ′ and an arc endpoint on the cathode  18 ′ of the module  10 ′ may be selectively moved, due to the magnetic fields imposed by the coils  54 A′ and  54 B′, in a circular motion about a longitudinal axis  118  of the chamber in a direction that is opposite to the direction of motion of an electrical arc extending through the bore  44  between an arc endpoint on the anode  12  and an arc endpoint on the cathode  18  of the first module  10 . 
   In other words, at least a portion of an electrical arc within the first module  10  may be moved in a first circular direction about the longitudinal axis  118  within the chamber of the plasma generating apparatus  110 , while at least a portion of an electrical arc within the second module  10 ′ may be moved in a second, opposite circular direction about the axis  118  within the chamber of the plasma generating apparatus  110 . It is noted that the same resulting motion of electrical arcs within the plasma generating apparatus  110  may be achieved by configuring the polarity of the electrical power source  50 E to be the same as the polarity of the electrical power source  50 A, while configuring the polarity of the electrical power source  50 F to be opposite to the polarity of the electrical power source  50 B, and also configuring the polarity of the electrical power source  50 G to be opposite to the polarity of the electrical power source  50 C. 
   In another embodiment, at least a portion of an electrical arc within the first module  10  may be induced to move in a circular direction about an axis within the chamber of the plasma generating apparatus  110 , and at least a portion of an electrical arc within the second module  10 ′ may be induced to moved in the same circular direction about the axis  118  within the chamber of the plasma generating apparatus  110 . Such may be accomplished by configuring the polarity of the electrical power source  50 E to be the same as the polarity of the electrical power source  50 A, configuring the polarity of the electrical power source  50 F to be the same as the polarity of the electrical power source  50 B, and configuring the polarity of the electrical power source  50 G to be the same as the polarity of the electrical power source  50 C. The same resulting motion of electrical arcs within the plasma generating apparatus  110  (i.e., both being induced to move in the same circular direction) may be achieved by configuring the polarity of the electrical power source  50 E to be opposite the polarity of the electrical power source  50 A, configuring the polarity of the electrical power source  50 F to be opposite the polarity of the electrical power source  50 B, and configuring the polarity of the electrical power source  50 G to be opposite the polarity of the electrical power source  50 C. 
   As previously described herein, the passage or inlet  96  of the inlet structure  86  may be configured to introduce matter passing through the inlet  96  into the bore  44  such that it swirls either a clockwise or a counter-clockwise direction within the chamber (when looking through the chamber from the inlet  114  toward the outlet  116 ). Similarly, the passage or inlet  96 ′ of the second inlet structure  86 ′ may be configured to introduce matter passing through the inlet  96  into the bore  44 ′ such that it swirls in either a clockwise or a counter-clockwise direction within the chamber. Moreover, the additional inlet  96  of the structure  86  and the additional inlet  96 ′ of the structure  86 ′ may be selectively configured to swirl matter passing through the inlets  96 ,  96 ′ in either the same (concurrent) direction about the axis  118  within the chamber or in opposite (countercurrent) directions about the axis  118  within the chamber. 
   It is noted, therefore, that the plasma generating apparatus  110  shown and described with respect to  FIG. 6  can be operated in at least sixteen different configurations or modes since the inlet structures  86  and  86 ′ can each be independently configured to swirl matter in either the clockwise or the counter-clockwise direction, the first module  10  can be configured to move at least a portion of its electrical arc in either the clockwise or the counter-clockwise direction, and the second module  10 ′ can be configured to move at least a portion of its electrical arc in either the clockwise or the counter-clockwise direction about the longitudinal axis  118 . As can be recognized, plasma generating apparatuses that embody teachings of the present invention may be operated in at least 2 N  different configurations or modes, where N is equal to the total number of modules and inlet structures that are configured to induce a swirling motion of the matter flowing through the chamber of the apparatus. 
   Individual modules of a plasma generating apparatus may be additionally selectively configured. For example, the power supplied by the electrical power source  50 E to the anode  12 ′ and the cathode  18 ′ of the module  10 ′ may be less than, equal to, or greater than the power supplied by the electrical power source  50 A to the anode  12  and the cathode  18  of the first module  10 . For example, the power supplied to the electrode pairs of each module may increase in the direction extending from the inlet  114  to the outlet  116  of the plasma generating apparatus  110 . In another embodiment, the power supplied to the electrode pairs of each module may decrease in the direction extending from the inlet  114  to the outlet  116  of the plasma generating apparatus  110 . In yet another embodiment, the power being supplied to each module may be substantially consistent. 
   The plasma generating apparatuses and devices described herein may be used to process or synthesize materials. Modular plasma generating devices that embody teachings of the present invention allow for plasma generating apparatuses and systems to be quickly and easily customized for processing or synthesizing particular materials. Furthermore, plasma generating apparatuses embodying teachings of the present invention as described herein may be used to provide large heating zones and resulting plasmas that are characterized by enhanced uniformity of temperature. Furthermore, an unlimited number of modular plasma generating devices may be assembled to provide plasma generating apparatuses of virtually unlimited lengths, thereby providing long residence times for materials within the chamber. The use of multiple modules in a plasma generating device enables residence times of materials within plasma to be more accurately controlled, which ultimately leads to greater stability and predictability in material reactions of a given process. 
   While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.