Abstract:
Provided herein is a fusion energy extraction circuit (FEEC) device having a grid-tied bidirectional converter and a resonant converter. The resonant converter can include an inverse cyclotron converter with two or more or quadruple plates and a plurality of circuit switches. The bidirectional converter can include a three-phase grid-tied converter. The FEEC device is capable of decelerating plasma particle beams, thereby extracting the energy from the deceleration, converting the extracted energy to electric energy, and sending the electric energy to a power grid.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates generally to electric circuits and, more particularly, to an electric circuit that facilitates the extraction of energy from charged particles as a result of a controlled fusion reaction and sends the energy to the power grid with a unity power factor, leading power factor, or lagging power factor on demand. 
       BACKGROUND INFORMATION 
       [0002]    Controlled fusion power generation will open the door to abundant and clean energy sources. This topic has attracted significant research efforts in the United States and the world. The reported approaches are typically based on conversion of fusion energy to thermal energy then to electric energy. 
         [0003]    In an alternative approach described in U.S. Pat. No. 6,611,106 (the &#39;106 patent), entitled “Controlled fusion in a field reversed configuration and direct energy conversion,” which is incorporated herein by reference, controlled fusion energy, carried by charged particle beams in the form of momentum, can be converted directly to electricity by decelerating the charged particles using a quadropole inverse cyclotron converter (ICC). Thus, higher energy conversion is expected. A key technology is needed that extracts the energy from the ICC and injects it to the utility grid. 
         [0004]    Accordingly, it would be desirable to provide a power electronic circuit used to decelerate the plasma particles, extract the energy from the deceleration action, convert the plasma energy directly to electric energy and send the electricity to the power grid. 
       SUMMARY 
       [0005]    The exemplary embodiments of a fusion energy extraction circuit (FEEC) device described herein represent only a few examples of the many possible implementations of the FEEC device and are in no way intended to limit the subject matter of the present description. 
         [0006]    In one embodiment, the FEEC device preferably comprises a grid-tied bidirectional converter component and a resonant converter component. The bidirectional converter component can implement leading phase, lagging phase, or unity power factor grid-tied converters for different purposes. 
         [0007]    The resonant converter preferably comprises an inverse cyclotron converter (ICC), an inductor, and a plurality of circuit switches forming a bridge that chops the dc voltage to a pulse waveform. The ICC is preferably configured with two or more or quadrupole plates that function as a capacitor together with an inductor to act as a resonant tank. The plates are preferably elongate with an arcuate cross-section forming an elongate annular cylindrical chamber with axially extending elongate gaps formed between the plates. 
         [0008]    During start up of the FEEC device, energy flows from the utility grid via the grid-tied bidirectional converter component to the resonant converter. This establishes the resonance and excites the quadrupole electric field formed across the gaps between the plates. During power generation or energy extraction, charged particles of charge particle beams from, e.g., a fusion process are decelerated by the quadrupole electric field as the particle beams travel through the ICC. Also during power generation, lost energy will be collected by the quadrupole plates of the ICC in the form of an image current. The image current will then flow through the resonant converter and the grid-tied bidirectional converter component to the utility grid. 
         [0009]    The grid-tied converter functions as an ac/dc rectifier during start up time and as a dc/ac grid-tied inverter during power generation. In both cases, the grid-tied converter will operate with unity power factor, leading power factor, or lagging power factor to provide active power and reactive power (VAR) on demand. 
         [0010]    To realize electric field excitation and energy extraction, the resonant frequency and voltage of the resonant converter are preferably precisely controlled. The frequency in this case is fixed at slightly above the resonant frequency of the resonant tank, while the voltage control can be achieved by switching pattern modulation and feedback regulation. Two modulation methods, phase shift modulation (PSM) and pulse-width modulation (PWM), are capable of providing voltage control. Feedback regulation is achieved by comparing the sensed resonant voltage with a reference, while its error is used to modulate the phase or the pulse-width of the switches in the resonant converter. With this modulation, automatic bidirectional energy flow according to the operation mode is guaranteed. 
         [0011]    In an alternative embodiment of FEEC device, resonant conductor can implement multiple ferrite inductors connected in series to optimize the FEEC device operation. The series-connected resonant inductors have several advantages over a single resonant inductor. 
         [0012]    Feedback regulation is achieved by comparing the sensed resonant voltage with a reference, while its error is used to modulate the phase or the pulse-width of the plurality of switches in the resonant converter. 
         [0013]    In another exemplary embodiment, a feedback control loop of the resonant converter can be utilized to facilitate automatic bidirectional power flow. The feedback control loop is composed of a resonant voltage sensing circuit, an error compensator, and a PWM or PSM pulse generator. 
         [0014]    Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. As mentioned above, it is also intended that the invention not be limited to the details of the example embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0015]    The details of the invention, including fabrication, structure and operation, may be gleaned in part by study of the accompanying figures, in which like reference numerals refer to like parts. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, all illustrations are intended to convey concepts, where relative sizes, shapes and other detailed attributes may be illustrated schematically rather than literally or precisely. 
           [0016]      FIG. 1  is a schematic of a fusion energy extraction circuit (FEEC). 
           [0017]      FIG. 2  is a schematic of a resonant converter circuit with equivalent image current source. 
           [0018]      FIG. 3  is a graph showing a Bode plot of the parallel resonant tank. 
           [0019]      FIG. 4  is a graph showing Pulse Width Modulation method illustration. 
           [0020]      FIG. 5  is a graph showing a mechanism of Pulse Width Modulation generation. 
           [0021]      FIG. 6  is a graph providing a Phase Shift Modulation illustration. 
           [0022]      FIG. 7  is a schematic of a Phase Shift Modulation generation circuit. 
           [0023]      FIG. 8  is a schematic of a feedback loop of the fusion energy extraction circuit. 
           [0024]      FIG. 9  is a schematic of a resonant voltage sensing circuit. 
           [0025]      FIG. 10  is a graph depicting a simulation result for the dynamic waveform of the power flow responding to the particle been injection. 
           [0026]      FIG. 11  is a graph depicting experimental results of the resonant voltage at the capacitor (emulating the quadruple plates). 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    The systems and methods described herein are directed to a direct fusion energy extraction. 
         [0028]      FIG. 1  is a block diagram depicting a preferred embodiment of the fusion energy extraction circuit (FEEC) device  100 . FEEC device  100  is composed of a grid-tied bidirectional converter component  110  and a resonant converter  120 . In a preferred embodiment of the FEEC device  100  in  FIG. 1 , the bidirectional converter component  110  implements a three-phase grid-tied converter  112 . However, it is appreciated that the bidirectional converter component  110  can implement different factor phase grid-tied converters for different purposes. For example, a single-phase grid-tied converter (not shown) can be implemented for lower power applications. 
         [0029]    In a preferred embodiment of the FEEC device  100 , the resonant converter  120  comprises an inverse cyclotron converter (ICC)  122  and a plurality of switches S 1 -S 4 . ICC  122 , which is described in greater detail in the &#39;106 patent (which is incorporated herein by reference), is preferably configured with a plurality of plates  124  shown in this instance in a quadrupole configuration. The quadrupole plates  124  of the ICC  122  function as a capacitor and together with an inductor L form a resonant tank  130 , which will be described in greater detail below. The plates  124  are preferably elongate with an arcuate cross-section forming an elongate annular cylindrical chamber with axially extending elongate gaps formed between the plates. When current is applied to the plate a multi-pole electric field is formed across the gaps between the plates. 
         [0030]    During device start up, energy flows from the utility grid  114  via the grid-tied bidirectional converter component  110  to the resonant converter  120  to establish the resonance and excite the quadrupole electric field of the resonant converter  120 . During power generation/energy extraction, charged particles beams from, such as, e.g., a fusion process, travel through the ICC  122  and decelerated by the quadrupole electric field formed across the gaps between the plates  124  of the ICC  122 . Also during generation/extraction, lost energy will be collected by the quadrupole plates  122  in the form of image current i s . The image current i s  will then flow through the resonant converter  120  and the grid-tied bidirectional converter component  110  to the grid  114 . The grid-tied converter  110  functions as an ac/dc rectifier during start up time and as a dc/ac grid-tied inverter during generation time. In both cases, the grid-tied converter  110  will operate with unity power factor, leading power factor, or lagging power factor to provide active power and reactive power (VAR) on demand. 
         [0031]    In order for the resonant converter  120  to realize electric field excitation and energy extraction, it is preferably that the resonant frequency and voltage be precisely controlled. The frequency in this case is fixed at slightly above the resonant frequency of the resonant tank  130  to ensure zero voltage soft-switching, while the voltage control can be achieved by switching pattern modulation and feedback regulation. Two modulation methods, phase shift modulation (PSM) and pulse-width modulation (PWM) are examined below. Both are capable of the task of voltage control; however, the PSM method yields a wider operation range for dynamic maneuver. Feedback regulation is achieved by comparing the sensed resonant voltage with a reference, while its error is used to modulate the phase or the pulse-width of the switches S 1 -S 4  in the resonant converter  120 . With this modulation, automatic bidirectional energy flow according to the operation mode is guaranteed. 
         [0032]      FIG. 2  is a schematic diagram depicting an exemplary embodiment of the resonant converter  120 , where the dc voltage v dc  is provided by the grid-tied bidirectional converter  110  (v dc  is also illustrated in  FIG. 1 ). Here, the resonant converter  120  includes a plurality of switches S 1 , S 2 , S 3 , and S 4 . The switches S 1 , S 2 , S 3 , and S 4  form a bridge that chops the dc voltage v dc  to a pulse waveform v AB  across AB at a switching frequency f s , which is much higher than the frequency of the power grid  114 . A capacitor C represents the quadrupole plates  124  of the ICC  122 . As indicated above, the capacitor C and the inductor L form the resonant tank  130 . Only the fundamental of v AB  will pass the resonant tank  130 , where it gains H(s), and will appear across the quadrupole plates  122  as a sinusoidal waveform v s . The current source i s  represents the corrected image current when the charged particles are decelerated, and the resistor R c  represents the heat and radiation losses from the charged particles. 
         [0033]    The gain H(s) of the resonant tank is: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         
                           H 
                            
                           
                             ( 
                             s 
                             ) 
                           
                         
                         = 
                         
                           
                             
                               1 
                               sC 
                             
                             // 
                             
                               R 
                               C 
                             
                           
                           
                             
                               sL 
                               + 
                               
                                 1 
                                 sC 
                               
                             
                             // 
                             
                               R 
                               C 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           1 
                           
                             
                               
                                 s 
                                 2 
                               
                                
                               LC 
                             
                             + 
                             
                               s 
                                
                               
                                 L 
                                 
                                   R 
                                   C 
                                 
                               
                             
                             + 
                             1 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0034]    Therefore, the magnitude (voltage gain) is: 
         [0000]    
       
         
           
             
               
                 
                   
                      
                     
                       H 
                        
                       
                         ( 
                         jω 
                         ) 
                       
                     
                      
                   
                   = 
                   
                     1 
                     
                       
                         
                           
                             ( 
                             
                               1 
                               - 
                               
                                 
                                   ω 
                                   2 
                                 
                                  
                                 LC 
                               
                             
                             ) 
                           
                           2 
                         
                         + 
                         
                           
                             ( 
                             
                               
                                 ω 
                                  
                                 
                                     
                                 
                                  
                                 L 
                               
                               
                                 R 
                                 C 
                               
                             
                             ) 
                           
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0035]    The maximum amplitude frequency is ω m  at which frequency the output voltage has the maximum value: 
         [0000]    
       
         
           
             
               
                 
                   
                     ω 
                     m 
                   
                   = 
                   
                     
                       
                         1 
                         LC 
                       
                       - 
                       
                         
                           1 
                           2 
                         
                          
                         
                           
                             ( 
                             
                               1 
                               
                                 CR 
                                 C 
                               
                             
                             ) 
                           
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
         [0036]    For the FEEC device  100 , R C  is typically very large, thus: 
         [0000]    
       
         
           
             
               
                 
                   
                     ω 
                     m 
                   
                   = 
                   
                     
                       ω 
                       r 
                     
                     = 
                     
                       1 
                       
                         LC 
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
         [0037]      FIG. 3  illustrates a bode plot of the parallel resonant tank  130 . The maximum gain appears approximately at the resonant frequency ω r . Another important parameter for the resonant circuit is Quality Factor Q: 
         [0000]    
       
         
           
             
               
                 
                   Q 
                   = 
                   
                     
                       R 
                       C 
                     
                     
                       R 
                       0 
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
         [0038]    where R0 is the characteristic impedance of the resonant tank  130 : 
         [0000]    
       
         
           
             
               
                 
                   
                     R 
                     0 
                   
                   = 
                   
                     
                       L 
                       C 
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
         [0039]    Therefore: 
         [0000]    
       
         
           
             
               
                 
                   Q 
                   = 
                   
                     
                       R 
                       C 
                     
                     
                       
                         L 
                         C 
                       
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
         [0040]    From equation (7), it is noted that a larger R C  results in a higher Q and a steeper slope of change in voltage gain off the resonance. 
         [0041]    As mentioned above, the resonant converter  120  output voltage control can be achieved by switching pattern modulation and feedback regulation. Both phase shift modulation (PSM) and pulse-width modulation (PWM) are capable of the task of voltage control. 
         [0042]    Pulse Width Modulation (PWM): With PWM, the pulse widths of the switches S 1 , S 2 , S 3 , and S 4  in the two legs are adjusted. The resulted voltage difference is in a staircase shape whose fundamental component is adjustable by the pulse width. 
         [0043]      FIG. 4  shows the trigger pulse waveform for all the switches S 1 , S 2 , S 3 , and S 4  illustrated in  FIG. 2 . The on time of the switches S 1  and S 2  is adjusted between 0-50%. The switches S 4  and S 3  are complementary to the switches S 1  and S 2  respectively.  FIG. 4  also illustrates the voltage pulse waveform at nodes A (v A ) and B (v B ) of the circuit embodiment illustrated in  FIG. 2 . 
         [0044]    The fundamental of the bridge voltage v AB  (as illustrated in  FIG. 4 ) is expressed as follows: 
         [0000]    
       
         
           
             
               v 
               
                 AB 
                  
                 
                     
                 
                  
                 1 
               
             
             = 
             
               
                 
                   600 
                   π 
                 
                  
                 
                   sin 
                    
                   
                     ( 
                     
                       π 
                        
                       
                           
                       
                        
                       D 
                     
                     ) 
                   
                 
                  
                 
                   cos 
                    
                   
                     ( 
                     
                       
                         
                           
                             2 
                              
                             π 
                           
                           
                             T 
                             s 
                           
                         
                          
                         t 
                       
                       - 
                       
                         π 
                          
                         
                             
                         
                          
                         D 
                       
                     
                     ) 
                   
                 
                  
                 
                     
                 
                  
                 D 
               
               &lt; 
               0.5 
             
           
         
       
     
         [0045]    The appropriate trigger signals for all switches can be realized by a simple and frequently used circuit. 
         [0046]    As depicted in  FIG. 5 , two saw tooth waves  151  and  152 , whose phase shift equals T s /2, are compared with the same control signal V C . The duty ratio D equals the portion of time when V C  is greater than the magnitude of the saw tooth. The resulted two pulses are used to trigger the MOSFET switches S 1  and S 2  respectively. As mentioned above, the switches S 4  and S 3  are driven by the complementary signals of the switches S 1  and S 2  respectively. It is noted that the duty ratio D can only be varied between 0-50%. In a preferred embodiment, resonant converter  120  is configured with MOSFET switches S 1 -S 4 . It is appreciated that resonant converter  120  can be configured with a variety of circuit switches that would achieve the same result. 
         [0047]    Phase Shift Modulation (PSM): In PSM method, the output voltage of the resonant converter  120  is regulated by adjusting the phase difference between the trigger pulses to the switches of the two legs.  FIG. 6  illustrates the typical PSM waveforms of the switch network, where α is the phase shift between leg A and B. Note that the pulse width of the switches does not change. As α changes, the pulse width of the bridge voltage v AB  changes. Consequently, the fundamental component changes and the resonate voltage v s  is regulated. The fundamental of the bridge voltage v AB  is a function of α: 
         [0000]    
       
         
           
             
               v 
               AB 
             
             = 
             
               
                 
                   600 
                   π 
                 
                  
                 
                   cos 
                    
                   
                     ( 
                     
                       α 
                       2 
                     
                     ) 
                   
                 
                  
                 
                   sin 
                    
                   
                     ( 
                     
                       
                         
                           2 
                            
                           π 
                         
                         
                           T 
                           s 
                         
                       
                        
                       t 
                     
                     ) 
                   
                 
                  
                 
                     
                 
                  
                 0 
               
               ≤ 
               α 
               ≤ 
               π 
             
           
         
       
     
         [0000]    It is clear that the phase shift a can control the amplitude of v AB . 
         [0048]      FIG. 7  illustrates one exemplary embodiment of a circuit capable of implementing an adjustable phase shift between v A  and v B . It is appreciated that many other circuit embodiments can achieve the same goal. For example, various digital circuits can be used for the purpose of implementing an adjustable phase shift. As illustrated in  FIG. 7 , a saw tooth wave  170  is used as a carrier to compare with two DC voltages—control signal v C  and fixed DC signal v fix . When the saw tooth wave  170  is compared with the control signal v C , the comparison results in a phase shift value. When the saw tooth wave  170  is compared with the fixed DC signal v fix , the comparison results in a clock signal for all the digital components in the control circuit. The frequency of the saw tooth is twice of the switching frequency which is divided by 2 after passing the D flip-flop. 
         [0049]    Resonant Inductor Implementation: In an alternative embodiment of the FEEC device  100 , resonant conductor  120  can implement multiple ferrite inductors connected in series to optimize the FEEC device  100  operation. The series-connected resonant inductors have several advantages over a single resonant inductor. First, the power loss can be reduced because each series-connected inductor can be realized by a small-size, high frequency ferrite core with low core loss and small flux swing. Second, it is possible to make each resonant inductor with a single layer structure, eliminating the need for high voltage isolation between layers. Furthermore, the parasitic capacitance and coupling inductance between layers is also eliminated. These parasitic capacitances and coupling inductances can have a serious effect on the resonant circuit  120  of the FEEC device  100 . Third, the single layer structure can provide an effective cooling solution for the resonant inductors without overheating the inner layers. Finally, the series-connected resonant inductors can be implemented by small-size ferrite cores, which are commercially available for high frequency power applications. 
         [0050]    Feedback Control Loop: As mentioned above, the output voltage control of resonant converter  120  can be achieved by switching pattern modulation and feedback regulation. The two modulation methods were described in detail above. Feedback regulation is achieved by comparing the sensed resonant voltage with a reference, while its error is used to modulate the phase or the pulse-width of the switches S 1 -S 4  in the resonant converter  120 . 
         [0051]      FIG. 8  illustrates an exemplary embodiment of a feedback control loop  180  of the resonant converter  120 . The feedback control loop  180  of the resonant converter  120  is a crucial element of the FEEC device  100  because it facilitates automatic bidirectional power flow. Feedback control loop  180  is composed of a resonant voltage sensing circuit  182 , an error compensator  184 , and a PWM or PSM pulse generator  186 . During the start up mode, the resonant voltage v s  is initially zero. This zero value of the resonant voltage v s  results in a large error and high output from the compensator  184  and the PWM or PSM pulse generator  186  will then produce a high duty ratio or small phase shift, respectively, to ramp up the resonant voltage v s . 
         [0052]    During the generation or extraction mode, charged particle beams will travel through the ICC  122  and are decelerated as they rotate through the quadrupole electric field formed across the gaps between the quadrupole plates  124 . The lost energy collected at the quadrupole plates  124  will be forced to flow into the resonant converter  120  by the feedback loop  180 . Similarly, the feedback loop  180  of the grid-tied bidirectional converter  110  will force the energy collected at the dc bus  181  to flow back to the power grid. 
         [0053]      FIG. 9  illustrates an exemplary embodiment of resonant voltage sensing circuit  182 . The input v 0  of resonant voltage sensing current is coupled to the resonant output terminal v s , whose resonant voltage modulates the photo diode current. The output of the resonant voltage sensing current (“v 0  feedback”) is coupled to the error compensator of the PWM or PSM controller with high voltage optic isolation. Therefore, variations in the resonant voltage can be optically transferred as the feedback signal for the control loop  180 . 
         [0054]    Benefits of this method include low cost, high voltage isolation, and simple implementation. Specifically, the AC input photocoupler with high voltage (HV) divider resistors imposes little effect on the resonant operation since the HV divider resistors have very high resistance. 
         [0055]    Simulation and Experiments:  FIG. 10  illustrates simulation results for various particle strengths. With the FEEC converter device  100 , illustrated in  FIG. 1 , direct fusion energy extraction is demonstrated by the simulation result shown in  FIG. 10 . The average DC link current I DC  values during the start up time and the generation time are illustrated corresponding to the intensity of particle beam injection, which is modeled by the image current source I s . In  FIG. 10 , charged particles were injected into the ICC  122  at 300 μs. When the charged particles are decelerated by the ICC  122 , the fusion energy is approximately proportional to the image current. In this simulation, the heat and radiation losses are modeled by the resistor R C  which is 1 MΩ. During the start up time, the average DC link current I DC  value is 117.5 mA that represents the circuit losses. After the image current is injected, I DC  value decreases due to the fusion energy input. For example, the DC link current I DC  value is reduced to 87.5 mA when a 3 mA image current is injected into the resonant converter  120 , which is a 5 W injection case. From  FIG. 10 , it is expected that when the fusion energy is between 15 W and 20 W, the average DC link current I DC  reaches zero (break even) and then is reduced to the negative value (power generation). 
         [0056]    The presented FEEC device  100  is capable of providing energy to the quadrupole plates  124  of the ICC  122  to start the deceleration process. When the image current is collected at the quadrupole plates  124 , the energy will be sent back to the power grid via the bidirectional grid-tied converter  110 . 
         [0057]      FIG. 11  illustrates an experimental waveform measured across the resonant capacitor C (illustrated in  FIG. 2 ). In this experiment, the resonant inductor L value is about 370 μH and the emulated capacitor value C of the quadrupole plates is 70 pF. The estimated resistor R C  of the heat and radiation losses is 2MΩ and the frequency of the image current is 1 MHz which is the same as the switching frequency of the resonant converter. With the closed loop control 180, 126V DC link voltage V DC  of the resonant converter can generate 3 kV, 1 MHz resonant voltage during the start up time shown in  FIG. 11 . 
         [0058]    The systems and methods provided herein are described for exemplary purposes only with regard to direct fusion energy extraction. However, one skilled in the art would readily appreciate that the systems and methods provided herein for extracting the kinetic energy of charged particles could be used for the recovery of energy in high current ion accelerators. As one of ordinary skill in the art is well aware, high power ion beams from high current ion accelerators are used in various commercial and academic research settings in science and engineering. All these applications are energy intensive. Today most of the energy is simply wasted. The energy extraction process described herein provides a means to recover such energy and reduce the energy consumption of such installations. To achieve this, the extraction design would simply be added at the end of the beam line past the target area. 
         [0059]    One skilled in the art would also readily appreciate that the systems and methods provided herein could be used in combination with other systems for the recovery and extraction of energy. PCT Application No. PCT/US2006/008251, entitled “Plasma Electric Generation System,” which is incorporated herein by reference, refers to an energy generator system used to provide direct space plasma propulsion. One skilled in the art would readily recognize that the energy extraction process described herein could facilitate energy recovery and extraction from the fusion energy stream when propulsion is not desired. 
         [0060]    One skilled in the art would also readily appreciate that the process for extracting the kinetic energy of charged particles could be used for efficiency enhancements in neutral beam accelerators. High power neutral atom beams from positive and/or negative ion sources are used for diagnostics or as energetic atom sources in different commercial and academic settings. In all these applications, the beam sources are characterized by efficiency constraints that arise from the fairly small charge-exchange cross-sections. To achieve pure neutral atom beams, all residual ions past the neutralizing cell are deflected and dumped. This waste energy is usually half of the plug power. Extraction systems of the type described herein can help to recover most of the energy of these “filtered” ions. 
         [0061]    In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. For example, the reader is to understand that the specific ordering and combination of process actions shown in the process flow diagrams described herein is merely illustrative, unless otherwise stated, and the invention can be performed using different or additional process actions, or a different combination or ordering of process actions. As another example, each feature of one embodiment can be mixed and matched with other features shown in other embodiments. Features and processes known to those of ordinary skill may similarly be incorporated as desired. Additionally and obviously, features may be added or subtracted as desired. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.