Patent Publication Number: US-9412474-B2

Title: Method and apparatus for compressing plasma to a high energy state

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a Divisional Application claiming the benefit of co-pending application Ser. No. 12/932,641 filed on Mar. 1, 2011. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to the field of plasma physics. More particularly, the invention concerns a method and apparatus for compressing plasma to a high energy state. 
     2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98 
     By way of brief background, in 1942, Enrico Fermi began discussing the idea of joining light nuclei by nuclear fusion to generate a large source of energy. He suggested burning deuterium, an abundant stable-isotope of hydrogen. 
     Today, the two primary approaches to the problem of achieving fusion power production have been Magnetic Confinement (MCF) and Laser Inertial Confinement (ICF) demonstration devices, such as the International Thermonuclear Experimental Reactor (ITER) tokamak that uses MCF or the National Ignition Facility (NIF) that uses ICF. These plasma experiments scale to very large sizes, measuring double-digit meters across. 
     Reactors based on these approaches scale to even larger sizes because they occupy either extreme of the density conditions necessary to fulfill the Lawson criterion for simultaneously achieving an energetic plasma for sufficient duration. MCF attempts to sustain a low-density 10 20  m −3  plasma for a long duration of about 2 to 4 seconds, using external magnetic fields, but suffers from plasma instabilities. ICF attempts to hold a high-density 10 28  m −3  plasma for nanoseconds. Magnetized Target Fusion (MTF) mitigates the problems encountered at either extreme by sustaining a medium-density 10 24  m −3  plasma for only several milliseconds, while simultaneously reducing the minimum reactor size and cost as compared to MCF or ICF. 
     Los Alamos National Laboratory (LANL) began early research into MTF, but became hampered by the impetus to scale their experiments to use the nearby Shiva Star capacitor bank as a power source, instead of scaling by best available theory and experiment. The Shiva Star facility is located at Kirtland Air Force Base in Albuquerque, N. Mex. They did not optimize their proof-of-principle design based on physics, but rather on their power supply limitations. Another weakness in their approach was the use of a theta pinch, instead of a more efficient antenna method to form a Compact Torus (CT) plasma structure. Lastly, they adhere to a non-reusable compression method (an aluminum can crusher), for single-shot experimentation. 
     A Canadian company improved upon this earlier implementation and attempted a smaller-scale MTF approach, one with lower input energy needs. However, this approach introduced high-atomic-number impurities (such as lead) that quench the plasma by radiation losses before ignition occurs. Controlling the timing of the acoustic-compression method of this company is also problematic. 
     The California Institute of Technology and Lawrence Livermore National Laboratory (LLNL) focused on injecting a compact torus (CT) into a tokamak, to sustain the latter. Their prototype ‘Compact Torus Accelerator’ experiment showed that it was possible to both translate and compress a compact torus plasma structure by moving it relative to a tapered wall. However, they also experienced impurity problems (iron from steel electrodes) and did not attempt to extend their initial achievement to a curved geometry, such as a spiral. 
     The University of Washington Plasma Physics Laboratory has long advocated cleanliness requirements to avoid plasma impurities. They also utilize newer and more efficient methods to form and accelerate compact toroids. However, the pure research of the University is not focused on advanced plasma compression for MTF and the University has not attempted to translate a CT along a curved wall made of beryllium or lithium-silicon, which are much lower-Z materials than their walls (made of silicon dioxide). 
     Prior art compact toroid compression mechanisms, include, but are not limited to the following:
     a. Explosive (liner technology)—For example the Los Alamos/Shiva Star and like projects. Such mechanisms are not reusable, require high input energy requirements and necessitate large system size.   b. Pneumatic (gas injection)—Such mechanisms typically exhibit pressure instabilities and are generally too slow for large plasmas.   c. Hydraulic (hydro-forming wall)—For example, the Canadian ‘General Fusion’ MTF concept. Such mechanisms, which require sub-microsecond-precision timing, require highly complex control systems. Also, the liquid walls of such mechanisms add high-atomic-number contaminants to the plasma that significantly increase radiation loss rates from the plasma.   d. Mechanical (piston)—For example, the Canadian ‘General Fusion’ concept. Such mechanisms, which require repetitive sub-microsecond timing, require highly complex control systems.   e. Electrical (relay-piston)—For example, the Canadian ‘General Fusion’ concept. Such mechanisms, which require repetitive sub-microsecond timing require highly complex control systems.   f. Magnetic (coil-current spike)—This mechanism has been tried in connection with many research programs, from the early TRISOPS (experiment at the University of Florida) to the University of Washington Plasma Physics Laboratory&#39;s latest CT devices. Such mechanisms require good timing, a large energy input, and may induce a plasma instability.   

     BRIEF SUMMARY OF THE INVENTION 
     The thrust of the present invention is to provide a compact toroid plasma structure compression assembly that is superior to and overcomes the problems associated with the various mechanisms described in the preceding paragraphs. More particularly, through analysis of the disadvantages of the aforementioned prior approaches, it has been possible to derive a unique set of design features that yield a novel approach with a distinct advantage. The details of these novel design features will be described further in the specification that follows. 
     With the foregoing in mind, it is an object of the present invention to provide a compressor assembly of novel design within which a plasma can be efficiently compressed to a high energy state. 
     More particularly, it is an object of the invention to provide a compressor assembly of the aforementioned character, which includes an elongated spiral passageway within which a compact toroid (CT) plasma structure can be efficiently compressed to a high-energy state by compressing the CT using its own momentum against the wall of the spiral passageway in a manner to induce heating by conservation of energy. 
     Another object of the invention is to provide a compressor assembly of the character described in the preceding paragraph, which includes a burn chamber that is in communication with the spiral passageway and into which the compressed CT is introduced following its compression. 
     Another object of the invention is to provide a burn chamber of the character described in the preceding paragraph, in which a magnetic sensor is embedded in the burn chamber for measuring the magnetic field vector versus time. 
     Another object of the invention is to provide a compressor assembly of the character described in the preceding paragraph, in which the burn chamber comprises a toroidal ring of constant cross-section, having at least one entrance port for receiving the compressed CT and having a multiplicity of smaller exhaust ports. 
     Another object of the invention is to provide a method for compressing a CT to a high-energy state using a compressor having an elongated spiral passageway by injecting the CT into the spiral passageway in a manner to avoid ricochet of the CT along the walls of the passageway. More particularly, in accordance with the method of the invention, ricochet is avoided by ensuring that the bulk axial kinetic energy of the CT at the point of injection is greater than the design “target” thermal energy sought to be achieved at the end of compression. 
     Another object of the invention is to provide a method of the character described in the preceding paragraph in which thermal conduction losses and particle diffusion losses are avoided by embedding a large magnetic field within the CT during formation, prior to launching the CT into the elongated spiral passageway. A highly magnetized CT impedes both thermal conduction losses and particle diffusion losses perpendicular to the embedded magnetic field lines. 
     Another object of the invention is to provide a method of the character described in the preceding paragraphs, in which thermal conduction losses and particle diffusion losses are avoided by applying a plasma-impurity impeding coating to the walls of the elongated spiral passageway. Examples of these coatings include low atomic number materials, such as beryllium or lithium-silicon. 
     Another object of the invention is to provide a method of the character described in the preceding paragraphs in which, following compression of the CT to the design “target” thermal energy, the CT is introduced into a burn chamber comprising a toroidal ring of constant cross-section having at least one entrance port for the compressed CT and having a multiplicity of smaller exhaust ports. 
     Another object of the invention is to provide a method of the character described in which, following compression of the CT to the design “target” thermal energy, the CT is introduced into a burn chamber and after the burn is complete, the compressed CT is caused to dissipate into a neutral gas, which is pumped out of the burn chamber by means of a suitable vacuum pump. 
     The forgoing as well as other objectives of the invention will be achieved by the apparatus illustrated in the attached drawings and described in the specification which follows. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a generally perspective view of one form of the apparatus of the invention for compressing plasma to a high energy state. 
         FIG. 2  is a generally perspective exploded view of one form of the plasma compressor of the apparatus showing the plasma structure to be compressed in position to be introduced into the plasma compressor. 
         FIG. 3  is a generally perspective exploded view of the plasma compressor illustrated in  FIG. 2 . 
         FIG. 4  is a longitudinal, cross-sectional view of the plasma compressor. 
         FIG. 4A  is a cross-sectional view taken along lines  4 A- 4 A of  FIG. 4 . 
         FIG. 5  is a generally perspective exploded view of the burn chamber of the plasma compressor illustrating the plasma in its compressed state. 
         FIG. 6  is a generally perspective exploded view of an alternate form of the plasma compressor of the apparatus showing the plasma to be compressed in position to be introduced into the plasma compressor. 
         FIG. 7  is a generally perspective exploded view of the plasma compressor illustrated in  FIG. 6 . 
         FIG. 8  is a longitudinal, cross-sectional view of the plasma compressor shown in  FIG. 6 . 
         FIG. 9  is a generally perspective exploded view of the burn chamber of the plasma compressor of this latest form of the invention illustrating the plasma in its compressed state. 
         FIG. 10  is a list of loss equations for electrons. 
         FIG. 11  is a list of loss equations for ions. 
         FIG. 12  is a list of loss equations for particle transfer. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
                            DEFINITIONS       As used herein, the following symbols        have the following meanings:                             Symbol   Meaning                       a 0     Bohr radius           a 12     ½ for single reactant,                otherwise 1           A s     plasma surface area           A w     wall surface area           B   magnetic flux density           c   speed of light           D   deuterium           D e     electron particle diffusivity           e 0     elementary charge           E 0     incoming ion energy for               sputtering           E 2     electron allowed energy               states           E H     hydrogen ground state                energy           E th     sputtering threshold energy           g fb     free-bound gaunt factor           g ff     free-free gaunt factor           h   Planck constant           H   hydrogen           He   helium           j e     electron sheath current to               wall           k   Boltzmann constant           K L     total transparency factor           Kn 2     2nd-order Bessel function           L i     ion inertial length           m e     electron mass           m i     ion mass           m P     product ion mass           n   neutron, or principal               quantum no.           n 1 , n 2     respective reactant densities           n e     electron density           n gas     neutral gas density           n i     ion density           n P     reactant ion particle density           N a     ion density * fractional                ionization           NZ   reactant ion density *               charge/mass           q   absolute sputtering yield           Q P     reaction product energy           r   radius           r 0     field null radius           r ci     ion cyclotron radius           r e     classical electron radius           r i     ion radius           r w     wall radius           R y     Rydberg energy           S nKRC     stopping power for KrC               potential           t   time step duration           T   tritium           T e     electron temperature           T i     ion temperature           T p     transient radial temp. profile           v d     ion velocity distribution           v i     ion most-probable thermal               speed           v P     reaction product ion velocity           V   plasma volume           W P     variable of integration for               energy           Z   average ion charge in plasma           Z P     ion product charge           α   fine-structure constant           β e     thermoelectric coefficient           γ   ratio of specific heats           Δr   plasma effective thickness           ε   reduced energy for               sputtering           ε 0     electric permittivity of free               space           H   product particles fraction               that stay           θ   variable of integration for               time           κ ew     electron-wall thermal               conductivity           κ iw     ion-wall thermal               conductivity           λ   sputtering decrease at low               energy           Λ e     plasma parameter for               electrons           Λ i     plasma parameter for ions           μ   sputtering decrease fit               parameter           μ 0     magnetic permeability free               space           π   geometric pi           σ cs     beam reaction cross-section           σ m     momentum transfer cross-               section           σ ∥     electric conductivity parallel               B           &lt;σv&gt;   integrated reaction cross-               section           τ ie     ion-electron equilibration               time           T   time that lost product               particles stay           φ   radial particle profile in time           X e     electrons to products               velocity ratio           X i     ions to products velocity               ratio           Ψ   magnetic flux radial profile               in time                        
Fusion
 
     The process by which two light nuclei combine to form a heavier one. The fusion process releases a tremendous amount of energy in the form of fast moving particles. Because atomic nuclei are positively charged—due to the protons contained therein—there is a repulsive electrostatic, or Coulomb, force between them. For two nuclei to fuse, this repulsive barrier must be overcome, which occurs when two nuclei are brought close enough together where the short-range nuclear forces become strong enough to overcome the Coulomb force and fuse the nuclei. The energy necessary for the nuclei to overcome the Coulomb barrier is provided by their thermal energies, which must be very high. For example, the fusion rate can be appreciable if the temperature is at least of the order on 10 keV—corresponding roughly to 100 million degrees Kelvin. The rate of a fusion reaction is a function of the temperature, and it is characterized by a quantity called reactivity. The reactivity of a D-T reaction, for example, has a broad peak between 30 keV and 100 keV. 
     Field-Reversed Configuration (FRC) 
     An example of a compact toroid plasma structure is a Field-Reversed Configuration which is formed in a cylindrical coil which produces an axial magnetic field. First, an axial bias field is applied, then the gas is pre-ionized, which “freezes in” the bias field, and finally the axial field is reversed. At the ends, reconnection of the bias field and the main field occurs, producing closed poloidal magnetic field lines. A review well known to those skilled in the art is found in “Field Reversed Configurations,” M. Tuszewski, Nuclear Fusion, Vol. 28, No. 11, (1988), pp. 2033-2092. 
     Compact Toroid 
     The FRC belongs to the family of compact toroids. “Compact” implies the absence of internal material structures (e.g. magnet coils) allowing plasma to extend to the geometric axis. “Toroid” implies a topology of closed donut-shaped magnetic surfaces. The FRC is differentiated from other compact toroids by the absence of an appreciable toroidal magnetic field within the plasma. 
     Prime-Mover Subsystem 
     As used herein, prime-mover subsystem means a system for converting fusion-generated ion and/or neutron thermal energy to electrical energy. The prime-mover subsystem may comprise a heat exchanger and may also comprise various types of selected direct-conversion subsystems of a character also well known by those skilled in the art. 
     The Apparatus of the Invention 
     Referring now to the drawings and particularly to  FIG. 1 , one form of the apparatus of the invention for compressing plasma to a high energy state is there shown and generally designated by the numeral  20 . This form of the apparatus comprises a compressor  22 , a vacuum pump subsystem  24  connected to the compressor by an outlet port  25  and a wall-cleaning subsystem that is operably associated with the compressor. The wall-cleaning subsystem here comprises heater blankets  26   a , such as those readily commercially available from BH Thermal Corporation of Columbus, Ohio and like sources, a glow discharge cleaning (GDC) system  26   b  such as a system that is readily commercially available from XEI Scientific, Inc. of Redwood City, Calif. and an ion gettering pump  26   c  of the character readily available from commercial sources such as SAES Getters USA of Colorado Springs, Colo. Apparatus  20  also includes a plasma source subsystem  28  that here comprises stator antenna coils with pre-ionization capability, such as those commercially available from sources such as Alpha Magnetics of Hayward, Calif., a gas pulse injection valve with fire control unit  30  of the character that is available from Parker Hannifin of Pine Brook, N.J., and a ejector coil subsystem  32  that is also available from Alpha Magnetics. The pre-ionization process is preferably powered by a radiofrequency generator of the character that can be obtained from T &amp; C Power Conversion of Rochester, N.Y. As will be discussed in greater detail in the paragraphs that follow, a prime-mover subsystem, which is generally designated in  FIG. 1  by the numeral  34 , must be operably associated with a compressor  22  to convert the fusion-generated ion and/or neutron thermal energy to electrical energy. Prime-mover  34  here comprises a heat exchanger of a character well understood by those skilled in the art. Attached to the heat exchanger is a steam turbine, which is, in turn, attached to an electrical generator (not separately shown in the drawings). The prime-mover subsystem can also comprise various types of selected direct-conversion subsystems of a character also well known by those skilled in the art. 
     A highly unique feature of the apparatus of the present invention is the previously identified compressor  22 , the details of construction of which are illustrated in  FIGS. 2 through 4  of the drawings. In the present form of the invention, the plasma compressor  22  comprises first and second sealably interconnected portions  36  and  38  that are constructed from a material selected from the group consisting of aluminum, steel, copper, silicon, magnesium, carbon-carbon composites, nickel super alloys, tungsten, or other refractory alloys (such as molybdenum, niobium or rhenium). Preferably, portions  36  and  38  are formed using a conventional computer numerically controlled (CNC) machine, or a conventional electrical discharge machine (EDM), or by casting methods. As best seen in  FIGS. 3 and 4  of the drawings, each of the portions  36  and  38  is provided with an elongate spiral passageway  40  having continuous wall  40   a . Each of the spiral passageways has an inlet  40   b  and an outlet  40   c  ( FIG. 3 ). Disposed proximate the center of the compressor  22  and in communication with the outlet of the spiral passageway is the important burn chamber  41 , the construction and operation of which will presently be described. 
     Also forming a part of the compressor  22  is an inlet port component  42  and an inner ring  44  that is operably associated with the burn chamber  41 . Inlet port component  42  is in communication with the inlet of the spiral passageway  43  ( FIG. 4 ) that is formed when portions  36  and  38  are joined together in the manner illustrated in  FIG. 2  of the drawings by brazing, welding, diffusion bonding, or mechanical assembly (with bolts and seals). As illustrated in  FIG. 2 , spiral passageway  43  is of progressively decreasing diameter with the smallest diameter of the passageway being in communication with the burn chamber  41 . Both the inlet port component and the inner ring are also preferably formed from a material selected from the group consisting of aluminum, steel, copper, silicon, magnesium, carbon-carbon composites, tungsten, or other refractory alloys. 
     In order to avoid contamination of the plasma during the compression process, the wall of the elongated spiral passageway  40  of the compressor  22 , as well as all other internal surfaces of the compressor that are exposed to the plasma, must be provided with a coating “C” preferably comprising either lithium-silicon, beryllium, or diboride ceramic, all of which are electrically conductive and low atomic-number materials (see  FIGS. 3 and 4A ). With respect to the lithium-silicon coating, it is to be noted that because pure lithium metal reacts with water vapor in the air, it is necessary that it be strictly maintained under vacuum between the point of manufacture of the coating powder and its application to the internal walls of the compressor. For certain applications, an electrically-conductive diboride ceramic or similar composite coating that consists of low atomic-number elements, which sputter slowly, could also advantageously be used to coat the internal walls of the compressor. The various techniques for coating the interior walls of the compressor are well known to those skilled in the art. For beryllium coatings, these techniques are fully described in a work entitled  Beryllium Chemistry and Processing , Kenneth A. Walsh, Edgar E. Vidal, et al, ASM International (2009) (see particularly, Chapter 22, “Beryllium Coating Processes”, Alfred Goldberg, pp. 361-399). 
     Once machined and properly coated, the inlet port component  42 , the inner ring  44  and the inner walls of the compressor  22  that are exposed to the plasma are carefully cleaned and the various components of the compressor are joined together in the manner well understood by those skilled in the art, such as by brazing, welding, diffusion bonding, or mechanical assembly. 
     After further cleaning and leak checks, the compressor  22  is integrated with the other subsystems of the apparatus of the invention in the manner depicted in  FIG. 1  of the drawings. These subsystems include the previously described vacuum pump subsystem  24 , the wall-cleaning subsystem that comprises heater blankets  26   a , a glow discharge cleaning (GDC) system  26   b  and an ion gettering pump  26   c  and the plasma source subsystem  28 . After these various subsystems have been interconnected with the compressor and the completed system has been thoroughly tested, the prime-mover subsystem  34  is interconnected with the compressor  22  in the manner indicated in  FIG. 1  of the drawings. 
     Prior to operating the apparatus of the invention, it is desirable to include a variety of well-known diagnostic tools around the apparatus (not shown in the drawings), such as a high-speed x-ray camera for observing shots, along with a neutron diagnostic, plus Rogowski coils for timing the ejection speed of the CT through the input port, as well as the speed of the CT in the burn chamber  41 . 
     Before considering the methods of the invention an alternate embodiment of the compressor unit will be considered. This alternate form of the compression unit is illustrated in  FIGS. 6-9  of the drawings and is generally designated by the numeral  52 . This embodiment is similar in many respects to the embodiment shown in  FIGS. 1 through 5  and functions in a substantially identical manner. The primary difference between this latest embodiment of the invention and the previously described embodiment resides in the fact that the compressor is constructed from an electrically conductive, metallic alloy having a low atomic number, such as a beryllium alloy. More particularly, in this latest embodiment of the invention, portions  54  and  56  of the compressor unit  52  are formed from a block of beryllium alloy using a conventional computer numerically controlled (CNC) machine, or a conventional electrical discharge machine (EDM), or by casting method. As in the earlier described embodiment of the invention and as illustrated in  FIGS. 7 and 8  of the drawings, each of the portions  54  and  56  is provided with an elongated spiral passageway  58  having continuous wall  58   a . Each of the spiral passageways has an inlet  58   b  and an outlet  58   c  ( FIG. 7 ). 
     Also forming a part of the compressor  52  is an inlet port component  60 , outlet port component  61  and an inner ring  62 , the functions of which are substantially identical to the functions of inlet port  42  and the inner ring  44  of the previously described embodiment. Both the inlet port component and the inner ring are also preferably formed from a low atomic number, electrically conductive material, such as a beryllium alloy. Once machined, the inlet port component  60 , the inner ring  62  and portions  54  and  56  are carefully cleaned and connected together in the manner well understood by those skilled in the art, such as by brazing, welding, diffusion bonding, or mechanical assembly using bolts and seals. After portions  54  and  56  are fused together the elongated spiral passageways  58  formed in each of the portions cooperate to define a spiral passageway  63  ( FIG. 8 ). As illustrated in  FIG. 8 , spiral passageway  58  is of progressively decreasing diameter with the smallest diameter of the passageway being in communication with the burn chamber  65 . Disposed proximate the center of the compressor  52  and in communication with the outlet of the spiral passageway  63  is the important burn chamber  65  of this latest form of the invention, the construction and operation of which is substantially identical to the previously identified burn chamber  41 . 
     Other candidate materials for use in constructing the compression structure  52  include Carbon-Carbon composites and refractory metal alloys (both higher atomic number materials than Beryllium). 
     The use of the beryllium alloy material in constructing the compressor is somewhat less desirable than the use of the more common materials such as steel, copper, silicon, magnesium, tungsten or other refractory alloys, all of which absorb x-rays better than beryllium. Additionally, the use of these materials is considerably less hazardous and the materials combine the function of a vacuum structural wall and x-ray shielding wall into one component. 
     It is to be understood that a variety of gasses, including but not limited to: hydrogen, deuterium, deuterium-tritium mixtures, pure tritium, helium-3, diborane and mixtures thereof can be used with the compression apparatus of the invention. In the case that the compression apparatus is used to compress a deuterium-rich gas to ignition and/or “burn” conditions, a portion of the burn ash will contain the rare gas helium-3. This is because the helium-3 generated from the reacted deuterium has a slower initial speed than other generated particles, such as tritium, and thus more easily thermalizes in the plasma. However, its nuclear fusion reaction rate is also slower than the tritium-deuterium reaction rate, such that it is not consumed as fast as the thermalized tritium. As a result of this breeding process, the ash from deuterium reactions accumulates the rare stable isotope helium-3. 
     In order to collect the helium-3, a filtration system attached to the vacuum pumps will need to separate the isotopes in the exhaust. This apparatus is used to collect and purify the helium-3, as well as other exhaust products (such as tritium) that should not be vented to atmosphere from the pump exhaust. Additionally, hydrogen-1 (protons) and helium-4 could be obtained from the exhaust using an isotopic separating filtration system. 
     The first step in carrying out the method of the present invention is to form a compact torus (CT) plasma structure. One type of CT is the Field Reversed Configuration (FRC). An FRC is formed in a cylindrical coil which produces an axial magnetic field. First, an axial bias field is applied, then the gas is pre-ionized, which “freezes in” the bias field, and finally the axial field is reversed. At the ends, reconnection of the bias field and the main field occurs, producing closed field lines. 
     Following the formation of the CT, unlike the previously identified prior art methods which involve the use of compact toroid compression mechanisms, the CT, which is identified in the drawings by the numeral  68 , is launched at high speed into the inlet port component  42  of the plasma compressor of the invention. As will be discussed in greater detail in the paragraphs that follow, as the CT travels through the plasma compressor it is crushed against a low atomic number material wall of the elongated spiral by means of its own inertia, inducing heating by conservation of energy. The internal thermal energy of the CT increases as its kinetic energy decreases. 
     As the CT compresses against the walls of the spiral passageway  43 , the pressure force it exerts has a vector component in the opposite direction to its forward motion (unless the walls are of constant cross-section). Therefore, it is important that the bulk axial kinetic energy of the CT at the point of ejection be greater than the design “target” thermal energy at the end of compression, to avoid a ricochet effect along the walls. 
     The wall of the spiral passageway  43 , as well as the other walls of the plasma compressor into which the CT comes in contact, absorb a portion of the heat, the degree to which is significantly reduced by embedding a large magnetic field within the CT during formation, prior to ejection. A highly magnetized CT impedes both thermal conduction losses and particle diffusion losses from its core to the walls. 
     Once compressed to the design “target” thermal energy, the compressed CT  68   a  enters a comparatively short transfer conduit  70 , which guides it away from the plane of symmetry of the compressor, and into the burn chamber  41 . As previously discussed, the burn chamber comprises a toroidal ring of constant cross-section, with a single entrance port for the compressed CT  68   a  ( FIGS. 3 and 7 ), and multiple smaller exhaust ports  72  ( FIG. 5 ) which are in communication with the vacuum system  24 . 
     After the burn is complete, the compressed CT  68   a  dissipates into neutral gas, which is pumped out through the main vacuum exit port  74 . Referring to  FIGS. 5 and 9  of the drawings, it is to be noted that the inner ring is provided with a circular hole  78 , which is adapted to receive an alignment gauge pin during assembly (not shown). After assembly, the alignment gauge pin is removed, leaving two through-holes that can be conveniently used for the insertion of diagnostic probes, such as a Rogowski coil loop. 
     A major advantage of the method of the present invention is that neutral beams are not necessary for heating the plasma, maintaining the compact toroid plasma thermal energy, or providing stability to the plasma structure. Another advantage of the method is that collapsible walls are not needed for compressing the plasma. Additionally, in practice, the compression apparatus of the invention can be used multiple times. 
     By way of background, in burning deuterium, which is an abundant stable-isotope of hydrogen, the reaction cycle consists of the following five equations:
 
 2 D+ 2 D→ 3 He (0.8 MeV)+ 0   1   n  (2.4 MeV)  Primary neutron-branch
 
 2 D+ 2 D→ 3 T (1.0 MeV)+ 1 H (3.0 MeV)  Primary proton-branch
 
 2 D+ 3 He→ 4 He (3.7 MeV)+ 1 H (14.7 MeV)  Secondary helion-branch
 
 2 D+ 3 T→ 4 He (3.5 MeV)+ 0   1   n  (14.0 MeV)  Secondary triton-branch
 
 3 T+ 3 T→ 4 He (3.8 MeV)+ 0   1   n  (3.8 MeV)+ 0   1   n  (3.8 MeV)  Tertiary triton-branch
 
     It is important to understand that in carrying out the method of the present invention, the wall of the spiral passageway, as well as any surface that the CT plasma structure comes in direct line-of-sight contact with, be clean, of low atomic number, and sputter slowly. These features will minimize losses due to impurities entering the plasma from the walls. In addition, it is beneficial for the walls to be electrically conductive, as this minimizes the loss due to synchrotron (cyclotron) radiation from the heated plasma by reflecting the emitted millimeter-wavelength light back into the plasma for re-absorption. This becomes apparent upon reviewing the fundamental equations governing the energy balance for the system. 
     The equation for the power gained by fusion reactions is:
 
Fusion Gain P f =a 12 n 1 n 2   σv   A.1
 
     The loss equations for electrons, ions, and particle transfer appear respectively in  FIGS. 10, 11 and 12  of the drawings with all variables being as defined in the previously set forth symbol definition table. 
     A key observation, based on these equations, as well as prior experiment literature, is that avoiding impurity-driven losses is a crucial requirement for maintaining a hot plasma. To accomplish this, it is essential that the plasma not come into contact with high atomic number (high Z) materials, such as steel. The end-result of impurities in the plasma is that the loss rates increase by orders of magnitude. There are multiple loss paths due to high-Z contamination. The volumetric radiation power loss mechanisms that increase most significantly with Z are Bremsstrahlung, Recombination, and Excitation Line. However, the average Z also influences thermal conduction losses and even thermalization rates. 
     Bremsstrahlung radiation is strongly affected by the average ion charge Z of the plasma, as the multi-pole non-relativistic equation A.2 ( FIG. 10 ) indicates. In addition to this equation, it is important to calculate both the dipole and relativistic versions of the Bremsstrahlung loss rate, as well as all the quantum-mechanical “gaunt factor” corrections for each ion species, before arriving at the dominant loss rate due to Bremsstrahlung radiation. Bremsstrahlung occurs in the x-ray spectrum and leaves the plasma. However, Bremsstrahlung is dominant only at high energy levels that are commensurate with burn conditions. For this reason, and the fact that the plasma is transparent to x-rays, Bremsstrahlung is usually the primary loss mechanism considered in simulation programs. At lower energy levels, which the plasma must pass through in order to get from a neutral-gas state to burn conditions, recombination and excitation line radiation dominate the plasma&#39;s radiative loss mechanisms. This is especially the case for high-impurity content plasma. 
     Recombination radiation, governed by equation A.3 ( FIG. 10 ), is the loss most strongly affected by Z. As can be seen inside the integrand, recombination radiation is extremely sensitive to increases in Z. It can be orders of magnitude less than Bremsstrahlung for a pure hydrogenic plasma, but can rapidly exceed Bremsstrahlung at lower energy levels from even moderate impurity content. Thus, by controlling impurities, the recombination radiation loss mechanism can be minimized. Similarly, excitation line radiation in equation A.4 ( FIG. 10 ) is affected by Z. Although not as apparent from this top-level equation, the calculation of N a  utilizes a nonlinear function with Z as a directly dependant variable. 
     Recombination and line radiation are often over-looked in sizing calculations, as they are assumed to be negligible as compared to Bremsstrahlung. This is the case under certain circumstances, but it is important to include their equations in case impurities enter the plasma. Overall, it is always beneficial (loss-reducing) to minimize the average Z. This is best accomplished by keeping impurities out of the plasma by utilizing clean, low-Z walls that sputter at as low a rate as possible. 
     In a clean, but non-magnetized plasma, the dominant loss mechanism is usually thermal conduction to the walls (equations A.6 and A.8— FIGS. 10 and 11 ), followed by particle diffusion (equation A.15— FIG. 12 ). Increasing the ambient magnetic field parallel to the walls inhibits these losses, but it also gradually increases the loss from Synchrotron radiation (equation A.5— FIG. 10 ). From simulations, a compact torus (CT) plasma can sustain several hundred Tesla before Synchrotron radiation exceeds the Bremsstrahlung radiation loss rate. This is because the plasma is highly absorbent to the millimeter-wave spectrum emitted by Synchrotron radiation and electrically-conductive walls efficiently reflect Synchrotron radiation, as well as the fact that Synchrotron radiation is not affected by Z. 
     Other losses included in the tables are ion Bremsstrahlung (equation A.10— FIG. 11 ) and ion Synchrotron (equation A.11— FIG. 11 ) radiation, which are comparatively minor to their electron counterparts in quasi-neutral plasmas. Neutral drag (equation A.9— FIG. 11 ) is also a comparatively small loss, but its inclusion enables prediction of how high a vacuum is required to sustain a moving plasma with negligible drag loss. Similarly, simulating sputtering of impurities from the wall (equation A.16— FIG. 12 ) and tracking magnetic dissipation (equation A.7— FIG. 10 ) allow estimation of how many impurities a wall will impart to a transient plasma and how long its internal magnetic field will last, respectively. The remaining effects of ion-to-electron kinetic transfer collisions (equation A.12— FIG. 11 ), product energy ion apportionment (equation A.13— FIG. 11 ), product energy ion thermalization (equation A.14— FIG. 12 ), and particle thermalization (equation A.17— FIG. 11 ) are essential to accounting for the allotment of energy and particles coming from core burn dynamics. In effect, they determine not the burn rate, but rather how to apportion the fusion energy coming from the original gain equation A.1, given the state of the plasma as instigated by an external device. 
     Once the governing equations are accounted for, it is possible to perform an optimization of the parameters for the method of the invention. By way of example, for deuterium gas, a convenient diameter for the starting and ending CT is 137 and 19 millimeters, respectively. The initial embedded magnetic field is preferably on the order of 6±1 Tesla and the minimum initial plasma ion density is approximately 5×10 15  particles per cubic centimeter. For optimum performance, the ejection speed of the CT requires a minimum of 4.8×10 6  meters per second and the minimum amount of time required for compression is on the order of 2 microseconds. 
     Having now described the invention in detail in accordance with the requirements of the patent statutes, those skilled in this art will have no difficulty in making changes and modifications in the individual parts or their relative assembly in order to meet specific requirements or conditions. Such changes and modifications may be made without departing from the scope and spirit of the invention, as set forth in the following claims.