Abstract:
A particle accelerator system for producing a charged particle beam having pulses of charged particles that have different energy levels from pulse to pulse. The system enables independent adjustment of the RF power delivered to first and second accelerating sections thereof without adjustment of the RF power generated by an RF source. Such independent adjustment enables the RF power provided to the first accelerating section to be maintained at a level appropriate for optimal particle capturing therein and for producing a tightly bunched beam of particles having different energy levels from pulse to pulse, while enabling the RF power provided to the second accelerating section to be varied in order to vary the energy levels of the charged particles of the charged particle beam from pulse to pulse.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of priority to and is a continuation of U.S. nonprovisional patent application Ser. No. 10/529,276 now U.S. Pat. No. 7,208,889 entitled “Particle Accelerator Having Wide Energy Control Range” filed on Mar. 25, 2005, which is a national phase patent application under 35 U.S.C. §371 of international patent application Ser. No. PCT/US03/030548 entitled “Particle Accelerator Having Wide Energy Control Range” filed on Sep. 29, 2003, which is based on and claims the benefit of priority to U.S. provisional patent application Ser. No. 60/414,132 entitled “Wide Energy Control Range Particle Accelerator” filed on Sep. 27, 2002, now expired. 
    
    
     FIELD OF THE INVENTION 
     The invention relates, generally, to the field of charged particle accelerators, and, more specifically, to charged particle accelerators capable of producing pulses of charged particles having different energy levels. 
     BACKGROUND OF THE INVENTION 
     In recent years, the proliferation of international terrorism has spurred concerns over the contents of cargo containers which are received from foreign countries by land or sea as such cargo containers may include explosives, weapons of mass destruction, or other items that may be harmful to individuals and/or property. Existing inspection systems utilize high energy X-rays to produce visual images of the contents of cargo containers. The high energy X-rays are, typically, obtained by generating a beam of highly energized electrons with a standing wave linear accelerator and directing the beam at a conversion target that transforms the electrons into high energy X-rays. The cargo containers are then exposed to the high energy X-rays and data is collected by detectors positioned behind the cargo containers after the high energy X-rays pass through the items in the cargo containers. However, the collected data is inadequate to identify or discriminate between different materials present in the cargo containers and, hence, such inspection systems provide only visual images of the contents of cargo containers. 
     To identify and discriminate between different materials in the cargo, containers, it is necessary to expose the cargo containers to high energy X-rays having different energy spectra and to appropriately evaluate data collected during such exposure. The generation of such high energy X-rays may be accomplished in a manner similar to that employed for the generation of high energy X-rays having a single energy spectra. That is, a beam of highly energized electrons may be obtained by generating a beam of highly energized electrons having different energy spectra and directing the beam at a conversion target to produce the high energy X-rays having different energy spectra. Unfortunately, the generation of such a beam of highly energized electrons having different energy spectra has proven to be problematic. 
     A number of approaches have been attempted in the past to vary the energy of a beam of electrons emerging from a particle accelerator to produce a beam of electrons having different energy spectra. In a first approach, the radio frequency (RF) power supplied to the accelerating cavities of a standing wave linear accelerator from the accelerator&#39;s RF power source is varied through use of an attenuator located in the waveguide connecting the RF power source to the accelerating cavities, thereby varying the amplitude of the accelerating field in the cavities and varying the energy level of the accelerator&#39;s output beam of electrons. However, varying the RF power in this manner causes the beam produced by the accelerator to have a large energy spread, and consequently, the efficiency of the particle accelerator is decreased. 
     In a second approach, the energy of the beam of electrons produced by a standing wave linear accelerator is regulated by varying the RF power supplied to the accelerator without the use of an attenuator. Such accelerator has two accelerating sections and a 3 dB waveguide hybrid junction which delivers equal RF power to each accelerating section. The accelerator, however, suffers from the same disadvantages as suffered by the accelerator of the first approach described above. The decrease in the RF power supplied to the accelerating sections directly causes the resulting electron beam to have a lower energy. The decrease in the RF power supplied to the first accelerating section weakens the accelerating field in the first accelerating section, thereby reducing the number of electrons that are captured and tightly bunched. Due at least in part to the weakened accelerating electric field, there is a decrease in the overall efficiency of the accelerator. 
     According to a third approach, RF power is supplied to the traveling wave accelerating section of a particle accelerator having a traveling wave accelerating section coupled to a standing wave accelerating section with an attenuator and variable phase shifter interposed therebetween. The RF power travels through the traveling wave accelerating section and creates an accelerating field therein. Before entering the standing wave accelerating section, the residual RF power from the traveling wave accelerating section is attenuated by the attenuator, thereby reducing the amplitude of the accelerating field in the standing wave accelerating section. The variable phase shifter may also vary the phase of the residual RF power and, hence, the phase of the accelerating field in the standing wave accelerating section. By controlling both amplitude and phase of the accelerating field in the standing wave accelerating section, the electron energy of the beam exiting the particle accelerator is controlled. Unfortunately, this approach is also inadequate because of the resulting ungrounded electromagnetic energy loss in the attenuator at amplitude control and in the standing wave accelerating section at phase control. 
     Two other approaches involve the mechanical adjustment of the magnetic field in a coupling cavity. In the first mechanical adjustment approach, a rod is inserted into one external coupling cavity of a side-coupled biperiodic accelerating structure with external coupling cavities. Insertion of the rod into the external coupling cavity changes the mode of oscillation therein. When the mode of oscillation in the coupling cavity is changed, an additional phase shift of one hundred eighty degrees results in a phase difference between the accelerating fields of two of the adjacent accelerating cavities. As a consequence, charged particles are accelerated near the beginning of the accelerating structure and decelerated near the end of the accelerating structure. 
     In the second mechanical adjustment approach, one of the coupling cavities of a side-coupled biperiodic accelerating structure is constructed such that it may be made asymmetrical by a mechanical adjustment. In this approach, two rods are inserted at opposite sides of the coupling cavity. By asymmetrically inserting the rods, the oscillation mode and the frequency remain unchanged in the coupling cavity, but the magnetic field distribution increases on the side in which the rod is inserted more, and thus, the coupling coefficient to the adjacent accelerating cavity is greater at such side. Although adjustment of the rods enables the output particle energy to be varied, the mechanical process by which the rods are adjusted is extremely slow and is inadequate for applications that require an output beam of electrons that must be rapidly varied between energy levels. Moreover, there is an inherent risk of sparking during sliding of the rods within the cavity. 
     Therefore, there exists in the industry, a need for a particle accelerator which is operable to produce particle beams with different energy levels over a wide range of energy levels such that the beam energy level may be changed rapidly between one energy level and another, that makes maximal use of electromagnetic power to accelerate charged particles, and that addresses these and other problems or difficulties which exist now or in the future. 
     SUMMARY OF THE INVENTION 
     Broadly described, the present invention comprises a particle accelerator system, including apparatuses and methods, for producing a charged particle beam having pulses of charged particles that have different energy levels from pulse to pulse. More particularly, the present invention comprises a particle accelerator system, including apparatuses and methods, for producing a charged particle beam having pulses of charged particles that have different energy levels from pulse to pulse by independently adjusting the amount of RF power delivered to first and second accelerating sections thereof without adjusting the amount of RF power generated by an RF source thereof. Such independent adjustment of the delivery of RF power enables the amount of RF power provided to the first accelerating section to be maintained at an appropriate level for optimal electron capturing therein and for producing a tightly bunched beam of electrons having different energy levels from pulse to pulse, while enabling the amount of RF power provided to the second accelerating section to be varied in order to vary the energy levels of the charged particles of the charged particle beam from pulse to pulse. 
     According to a first embodiment, the particle accelerator system includes an RF drive system having an RF source coupled to an amplifier and a phase shifter so as to enable adjustment of the accelerating field created in an accelerating section without adjusting the power output from the RF source. The ratio of the amplitudes of the RF waves provided to the accelerating sections is regulated by shifting the phase of the RF waves delivered to the second accelerating section relative to the phase of the RF waves of the first accelerating section with a phase shifter. Because the magnitude, or strength, of the accelerating fields in the accelerating sections depends on the RF power provided, respectively, to each of the accelerating sections and because the RF power provided to each of the accelerating sections is based on the amplitudes of the RF waves provided thereto, shifting the phase of the RF waves for the second accelerating section enables changing of the RF power provided to the second accelerating section and of the magnitude of the accelerating field of the second accelerating section relative to the magnitude of the accelerating field of the first accelerating section. 
     In a first mode of operation of the first embodiment, the particle accelerator system includes a conventional phase shifter that is tuned prior to operation of the particle accelerating system to always perform a fixed phase shift on received RF waves. However, in a second mode of operation, the phase shifter comprises a high-speed phase shifter of a plurality of high-speed phase shifters that are capable of shifting the phase of received RF waves between at least two phases and between successive pulses of charged particles. 
     According to a second embodiment, a high-speed phase shifter interposed and connected to two 3 dB waveguide hybrid junctions functions as a variable phase shifter so as to regulate the ratio of RF power supplied to first and second accelerating sections without varying the power output from the RF source. In a high energy mode of operation (i.e., in which charged particles having a high energy level are produced), the phase of the RF waves provided to the second accelerating section is selected such that the accelerating fields in the accelerating sections are substantially equal. However, in a low energy mode of operation (i.e., in which charged particles having a low energy level are produced), the phase of the RF waves provided to the second accelerating section is changed to increase the portion of RF source power that is distributed to the first accelerating section. Simultaneously, to compensate for the increased power delivered to the first accelerating section, the injection current is increased so that strength of the accelerating field in the first accelerating section equals the strength of the accelerating field in the first accelerating section in the high energy mode. As a consequence, the incremental change in the energy level of the charged particles in the first accelerating section in both low and high energy modes is substantially the same. 
     The RF power supplied to the second accelerating section in low energy mode is significantly lower than the RF power supplied to the second accelerating section in the high energy mode. Because the RF power supplied to the second accelerating section is decreased in the low energy mode and because the injection current is increased in the low energy mode, the energy provided to the second accelerating section is lower and, hence, the strength of the accelerating field in the second accelerating section is lower than in high energy mode. As a consequence, the incremental energy increase in the energy level of the charged particles in the second accelerating section in low energy mode is substantially lower than the incremental energy increase in the energy level of the charged particles in the second accelerating section in high energy mode. 
     Other advantages and benefits of the present invention will become apparent upon reading and understanding the present specification when taken in conjunction with the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  displays a schematic block diagram representation of a particle accelerator system in accordance with a first embodiment of the present invention. 
         FIG. 2  displays a schematic block diagram representation of a first form of a high-speed phase shifter, which is employable as a phase shifter in accordance with the first and second embodiments of the present invention. 
         FIG. 3A  displays a schematic cross-sectional view of a second form of a high-speed phase shifter, which is employable as a phase shifter in accordance with the first and second embodiments of the present invention. 
         FIG. 3B  displays a schematic partial cross-sectional view of the second form of a high-speed phase shifter taken along lines  3 B- 3 B of  FIG. 3A . 
         FIG. 3C  displays a schematic partial cross-sectional view of the second form of a high-speed phase shifter taken along lines  3 C- 3 C of  FIG. 3A . 
         FIG. 3D  displays a schematic partial cross-sectional view of the second form of a high-speed phase shifter taken along lines  3 D- 3 D of  FIG. 3A . 
         FIG. 3E  displays a schematic partial cross-sectional view of the second form of a high-speed phase shifter taken along lines  3 E- 3 E of  FIG. 3A . 
         FIG. 4  displays a graphical illustration of the relationship between the phase angle, φ, of RF waves output by a high-speed phase shifter and the azimuth angle, θ, of rotary reflectors thereof. 
         FIG. 5  displays a schematic cross-sectional view of a third form of a high-speed phase shifter taken perpendicular to a longitudinal axis thereof, which is employable as a phase shifter in accordance with the first and second embodiments of the present invention. 
         FIG. 6A  displays a schematic cross-sectional view of a fourth form of a high-speed phase shifter taken perpendicular to a longitudinal axis thereof, which is employable as a phase shifter in accordance with the first and second embodiments of the present invention. 
         FIG. 6B  displays a schematic cross-sectional view of the fourth form of a high-speed phase shifter taken along lines  6 B- 6 B of  FIG. 6A . 
         FIG. 6C  displays a schematic cross-sectional view of the fourth form of a high-speed phase shifter taken along lines  6 C- 6 C of  FIG. 6A . 
         FIG. 7  displays a schematic block diagram representation of a particle accelerator system in accordance with a second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings in which like numerals represent like elements or steps throughout the several views,  FIG. 1  displays a schematic block diagram representation of a particle accelerator system  100  in accordance with a first embodiment of the present invention. The particle accelerator system  100  comprises a first accelerating section  102 , a second accelerating section  104 , an RF drive subsystem  106 , and an injector  108 . Preferably, the first and second accelerating sections  102 ,  104  comprise standing-wave accelerating sections  102 ,  104  having a biperiodic accelerating structure which are operable to accelerate charged particles through the transfer of energy from RF power provided to the accelerating sections  102 ,  104  by the RF drive subsystem  106 . 
     The first accelerating section  102  has a first end  110  and a second end  112 . The injector  108  is positioned proximate the first end  110  of the first accelerating section  102  and is connected to an input port  114  of the first accelerating section  102 . The injector  108  is operable to generate charged particles and to emit them in a pulsed mode of operation as pulses of charged particles, into the first accelerating section  102  through input port  114 . Preferably, the charged particles comprise electrons. The first accelerating section  102  defines an oblong-shaped slot  116  which couples the first accelerating section  102  to a feeder waveguide  118  of the RF drive subsystem  106  to enable RF power to propagate from the feeder waveguide  118  into and through the first accelerating section  102 . 
     Similar to the first accelerating section  102 , the second accelerating section  104  has a first end  120  and a second end  122 . The second accelerating section  104  is connected to the first accelerating section  102  to enable charged particles to travel between the first and second accelerating sections  102 ,  104 . The second accelerating section  104  includes an output port  124  located at the second end  122  of the second accelerating section  104 . A longitudinal axis  125  of the particle accelerator system  100  extends between, and is defined by, the input port  114  and the output port  124  thereof. The output port  124  is adapted to direct a beam of charged particles from the second accelerating section  104  (and, hence, from the particle accelerator system  100 ) toward a desired target or other object. The second accelerating section  104  defines an oblong-shaped slot  126  which couples the second accelerating section  104  to a feeder waveguide  128  of the RF drive subsystem  106  to allow RF power to propagate from the feeder waveguide  128  into and through the second accelerating section  104 . 
     The RF drive subsystem  106  comprises a radio frequency (RF) source  130 , a first amplifier  132 , a second amplifier  136 , and a phase shifter  134 . The RF source  130  is operable to generate RF power in the form of pulses of RF waves, having an appropriate frequency, power level, and pulse repetition rate, in a pulsed mode of operation synchronized with the emission of charged particles by injector  108  and to output such RF power via output coaxial lines  142 ,  146 . Preferably, the RF source  130  comprises an RF generator such as a solid state microwave generator which generates 400 W of RF power in the form of pulses of RF waves having a frequency of 2.8 GHz and a pulse repetition rate of 500 Hz. 
     The first amplifier  132  is connected to the RF source  130  by coaxial line  142  and is adapted to receive RF power generated and output by RF source  130  via coaxial line  142 . The first amplifier  132  is operable to amplify the received RF power, to preferably, 2.5 MW and to deliver the amplified RF power to the first accelerating section  102  through feeder waveguide  118  and oblong-shaped slot  116  so as to create an accelerating field (i.e., the strength or magnitude of which is determined by the amplified RF power) in the first accelerating section  102  of particle accelerator system  100 . Preferably, amplifier  132  comprises a klystron. It should be understood that the scope of the present invention includes other forms of amplifiers or other appropriate devices for amplifying RF power. 
     The second amplifier  136  is connected to the RF source  130  by coaxial line  146  and is adapted to receive RF power generated and output by RF source  130  via coaxial line  146 . The second amplifier  136  is operable to amplify the received RF power, to preferably 2.5 MW, and to deliver the amplified RF power to the phase shifter  134  via waveguide  150 . Preferably, the second amplifier  136  includes a klystron. It should be understood that the scope of the invention includes other forms of amplifiers or other appropriate devices for amplifying RF power. 
     The phase shifter  134  is connected to the second accelerating section  104  by waveguide  128 . Phase shifter  134  is operable to receive RF power amplified by the second amplifier  136 , to change the phase of the RF waves thereof, and to supply the phase shifted RF power to the second accelerating section  104  via connected waveguide  128 . In a first mode of operation described below, the phase shifter  134  comprises a conventional phase shifter that is tuned prior to operation of the particle accelerating system  100  to always shift the phase of the received RF waves of the pulses of RF waves to a single fixed phase. However, in a second mode of operation described below, the phase shifter  134  comprises a high-speed phase shifter such as, for example, one of the phase shifters  200 ,  300 ,  500 ,  600  illustrated in  FIGS. 2 ,  3 ,  5 , and  6  described below, which are capable of shifting the phase of the RF waves of the pulses of received RF waves to one of at least two phases and to do so in synchronization with pulses of charged particles emitted by injector  108 . 
     It should be noted that the strength, or magnitude, of the accelerating field in the first and second accelerating sections  102 ,  104  depends on the RF power provided thereto. It should also be noted that the provided RF power depends on the amplitudes of the RF waves of the pulses of RF waves. Therefore, changing the gain of the second amplifier  136  and, hence, the RF power supplied to the second accelerating section  104  relative to the first accelerating section  102 , changes the strength of the accelerating field in the second accelerating section  104 , relative to the first accelerating section  102 . As a consequence, the incremental energy added to the charged particles in the second accelerating section  104  relative to the first accelerating section  102  is also changed. 
     In a first method of operation, the injector  108  of the particle accelerating system  100  generates and emits charged particles (preferably, electrons) into the first accelerating section  102 . Concurrently, the RF source  130  of the RF drive subsystem  106  generates RF power in a pulsed mode of operation synchronized with the emission of charged particles by injector  108  and outputs such RF power, including pulses of RF waves, to the first amplifier  132  via coaxial line  142 . The first amplifier  132  receives the generated RF power output by RF source  130  and amplifies the received RF power to a desired power level (preferably, 2.5 MW). The first amplifier  132  then delivers the amplified RF power to the first accelerating section  102  via feeder waveguide  118  and through oblong-shaped slot  116 . The amplified RF power creates an accelerating field in the first accelerating section  102  of particle accelerator system  100 . 
     As the RF source  130  generates and delivers RF power to the first amplifier  132 , the RF source  130  concurrently generates and delivers RF power to the second amplifier  136  via coaxial line  146 . The second amplifier  136  amplifies the received RF power and delivers the amplified RF power to the phase shifter  134  via waveguide  150 . In this first method of operation, the phase shifter  134  comprises a conventional phase shifter that performs a predetermined and fixed phase shift to the RF waves of the received pulses of RF waves. The phase shifted RF power exits phase shifter  134 , via waveguide  128 , and is received by the second accelerating section  104  through oblong-shaped slot  126 . The phase shifter  134  delivers the amplified and phase shifted RF power through waveguide  128  and oblong-shaped slot  126  to the second accelerating section  104 , and the received RF power creates an accelerating field in the second accelerating section  104 . 
     Alternatively, the phase shifter  134  may be connected between RF source  130  and the second amplifier  136 . In such case, the phase shifter  134  is connected via a coaxial line rather than a rectangular waveguide. 
     In the first method of operation, the particle accelerating system  100  alternately operates in a high energy mode and a low energy mode to produce and output charged particle pulses having energy levels which alternate between high energy and low energy levels. When operating in the high energy mode, the phase of the RF power as adjusted by phase shifter  134  is selected so that the strength of the accelerating field created in the second accelerating section  104  is maximized with the result being that the charged particles receive a maximum incremental increase in energy as they are accelerated by the second accelerating section  104 . 
     When operating in the low energy mode, the first amplifier  132  is adjusted such that the generated RF power delivered to the first accelerating section  102  by first amplifier  132  is amplified more than the generated RF power delivered to the first accelerating section  102  by the first amplifier  132  when operating in the high energy mode. Concurrently, the rate at which the injector  108  emits particles into the first accelerating section  102 , or in other words, the particle injection current, is increased in order to maintain the strength of the accelerating field of the first accelerating section  102  at the same strength as when operating in the high energy mode. Additionally, the second amplifier  136  is adjusted such that the RF power delivered by the RF source  130  to the phase shifter  134  and then to the second accelerating section  104  is less than the phase shifted RF power delivered by the second amplifier  136  to the second accelerating section  104  during operation in the high energy mode. 
     Through use of the first method of operation, the strength of the accelerating field created in the first accelerating section  102  is substantially identical in both the high and low energy modes. Thus, the quality and efficiency of particle bunching and capturing that occurs in the first accelerating section  102  remains substantially the same in both high and low energy modes. However, in the second accelerating section  104 , the incremental change in the amount of energy each charged particle receives in the low energy mode is significantly lower than the incremental change in the amount of energy each charged particle receives in the high energy mode. This result occurs because in the low energy mode, the RF power delivered to the second accelerating section  104  is reduced as compared to the RF power delivered to the second accelerating section  104  in the high energy mode in order to compensate for the increased particle injection current. Because the charged particle energy decrease in the low energy mode accompanies a beam current increase, the beam power levels in the high and low energy modes are substantially equal to one another, which has typically been required for precise bremsstrahlung registration by detectors in cargo container inspection systems. Thus, through use of the first method of operation, the particle accelerating system  100  enables rapid alternation between high and low energy modes for successive pulses of synchronized RF waves and injected particles. 
     In the second method of operation of the first embodiment, the particle accelerating system  100  alternately operates in a high energy mode and a low energy mode to produce and output pulses of charged particles which alternately have a high energy level and a low energy level. In both the high and low energy modes, the RF power amplification provided by amplifiers  132 ,  136  remains constant. That is, the amount by which the amplifiers  132 ,  136  amplify the received RF power remains identical in both the high and the low energy modes. Moreover, the particle injection current also remains constant in both the high and the low energy mode. However, phase shifter  134  shifts the phase of the generated RF power (i.e., the phase of the RF waves present in the RF wave pulses) provided thereto alternately between two phases and does so in synchronization with and for alternating pulses of charged particles emitted by injector  108 . To do so quickly and in synchronization with pulses, the phase shifter  134  comprises one of the high-speed phase shifters  200 ,  300 ,  500 ,  600  illustrated in  FIGS. 2 ,  3 ,  5 , and  6  described below and operates in accordance with the corresponding method of operation thereof. In this second method of operation, the difference in the resulting beam power level is greater between pulses than it is using the first method of operation. However, even though there is a greater differential between the energy levels of alternating pulses of charged particles in the output beam, the differential may be acceptable if the particle accelerator system  100  is used in a cargo container inspection system with a detector having a sufficient dynamic range for bremsstrahlung detection. 
       FIG. 2  displays a schematic block diagram representation of a first form of a high-speed phase shifter  200 , which is employable as a phase shifter  134  in accordance with the first embodiment of the present invention. High-speed phase shifter  200  comprises a 3 dB waveguide hybrid junction  202 , two waveguide dischargers  204 ,  206 , and two waveguide shorting devices  208 ,  210 . The 3 dB waveguide hybrid junction  202  includes an input waveguide  212  that is connectable to an external waveguide for the receipt of pulses of input RF waves therefrom. The 3 dB waveguide hybrid junction  202  also includes first, second and third output waveguides  214 ,  216 ,  218  with the third output waveguide  218  being connectable to an external waveguide for the output of pulses of phase shifted RF waves produced by the high-speed phase shifter  200 . The first and second output waveguides  214 ,  216  are connected to respective waveguide dischargers  204 ,  206 . Waveguide shorting devices  208 ,  210  are connected, respectively, at the ends of the waveguide dischargers  204 ,  206  and are substantially perpendicular to the longitudinal axes of the first and second output waveguides  214 ,  216  of the 3 dB waveguide hybrid junction  202 . The waveguide shorting devices  208 ,  210  create, or define, a shorting plane  222  extending therethrough which, as illustrated in  FIG. 2 , is located at a distance, D 2 , from the first and second output waveguides  214 ,  216  of the 3 dB waveguide hybrid junction  202  and is substantially perpendicular to the longitudinal axes thereof. 
     The waveguide dischargers  204 ,  206  are operable and switchable between a first state and a second state. In the first state, the waveguide dischargers  204 ,  206  emit an electrical discharge that creates, or defines, an effective shorting plane  220  which, as illustrated in  FIG. 2 , is located at a distance, D 1 , from the first and second output waveguides  214 ,  216  of the 3 dB waveguide hybrid junction  202  and is substantially perpendicular to the longitudinal axis thereof. In the second state, the waveguide dischargers  204 ,  206  do not emit an electrical discharge  204 ,  206  and, hence, no effective shorting plane  220  is created or defined by the waveguide dischargers  204 ,  206 . 
     In operation, the phase angle, φ, of the phase shifted RF waves of a pulse of phase shifted RF waves output by the high-speed phase shifter  200  depends on the distance, D, between the first and second output waveguides  214 ,  216  of the 3 dB waveguide hybrid junction  202  and the particular shorting plane  220 ,  222  used by phase shifter  200 . Therefore, by alternately switching the waveguide dischargers  204 ,  206  on and off between the first and second states thereof at a rate substantially equal to the rate at which pulses of RF waves are received by the input waveguide  212 , one of shorting plane  220  or effective shorting plane  222  is selected for use to change the phase angle, φ, of the received RF waves. Thus, when the waveguide dischargers  204 ,  206  are switched-on and are in their first state, effective shorting plane  220  is used by phase shifter  200  to change the phase of the received RF waves with the phase angle, φ, of the output phase shifted RF waves being determined by distance D 1 . When the waveguide dischargers  204 ,  206  are switched-off and are in their second state, shorting plane  222  is selected for use to change the phase of the received RF waves with the phase angle, φ, of the output phase shifted RF waves being determined by distance D 2 . By alternately switching the waveguide dischargers  204 ,  206  between their first and second states, the phase angle, φ, of the output phase shifted RF waves in each output pulse of output phase shifted RF waves alternately switches between a first phase angle, φ 1 , and a second phase angle, φ 2 . Because the waveguide dischargers  204 ,  206  are switchable alternately between the first and second states thereof at a rate substantially equal to and synchronized with the rate at which pulses of charged particles are emitted by injector  108  and pulses of RF waves are received by input waveguide  212 , the high-speed phase shifter  200  is operable to produce pulses of output phase shifted RF waves having a desired phase angle, φ, at a rate required by the particle accelerator system  100  for changing of the accelerating field of the second accelerating section  104  thereof according to whether a high energy pulse of charged particles or a low energy pulse of charged particles is presently being generated by the particle accelerator system  100  (i.e., according to whether the particle accelerator system  100  is operating in a high energy mode or in a low energy mode). 
       FIG. 3A  displays a schematic cross-sectional view of a second form of a high-speed phase shifter  300 , which is employable as a phase shifter  134  in accordance with the first embodiment of the present invention. High-speed phase shifter  300  comprises a 3 dB waveguide hybrid junction  302 , a rotatable shaft  304  which defines a longitudinal axis  306 , and two asymmetric rotary reflectors  308 ,  310  (which are, essentially, shorting devices) secured to the rotatable shaft  302  for rotation with the rotatable shaft  302  about the longitudinal axis  306  at an appropriate rate. Preferably, the rotary reflectors  308 ,  310  are constructed of a dielectric material. The 3 dB waveguide hybrid junction  302  includes an input waveguide  312  that is connectable to an external waveguide for the receipt of pulses of input RF waves therefrom. The 3 dB waveguide hybrid junction  302  also includes first, second and third output waveguides  314 ,  316 ,  318  with the third output waveguide  318  being connectable to an external waveguide for the output of pulses of phase shifted RF waves produced by the high-speed phase shifter  300 . 
     The first and second output waveguides  314 ,  316  of the 3 dB waveguide hybrid junction  302  have, preferably, a rectangular cross-sectional shape and have respective narrow sides  320 A,  320 B,  322 A,  322 B and respective wide sides  324 A,  324 B,  326 A,  326 B (see  FIGS. 3A ,  3 B,  3 C). Preferably, the first and second output waveguides  314 ,  316  share a common wall therebetween which forms their respective narrow sides  320 B,  322 B. Reference planes  342 ,  344  are defined, preferably, as being perpendicular (see  FIGS. 3B and 3C ) to respective wide sides  324 A,  324 B,  326 A,  326 B and extending through longitudinal axis  306 . 
     Rotatable shaft  304 , preferably, extends between and through narrow sides  320 A,  320 B,  322 A,  322 B of the first and second output waveguides  314 ,  316  of 3 dB waveguide hybrid junction  302 . The rotary reflectors  308 ,  310  are, preferably, secured to the rotatable shaft  304  such that rotary reflector  308  is positioned for rotation within the first output waveguide  314  and rotary reflector  310  is positioned for rotation within the second output waveguide  316 . The rotary reflectors  308 ,  310 , preferably, comprise rectangular-shaped plates having rectangular-shaped cross-sections with a longitudinally-extending hole  328  defined therethrough for receipt of rotatable shaft  304  and are, preferably, manufactured from copper or another appropriate material. The dimensions of the rotary reflectors  308 ,  310  are selected to enable the rotary reflectors  308 ,  310  to be freely rotated, respectively, within the first and second output waveguides  314 ,  316  about longitudinal axis  306  upon rotation of rotatable shaft  304 . It should be understood that the scope of the present invention comprises rotary reflectors  308 ,  310  of different forms having different shaped cross-sections and rotary reflectors  308 ,  310  that are manufactured wholly, or in part, from different materials. 
     As illustrated in the schematic partial cross-sectional views of  FIGS. 3B and 3C  respectively taken along lines  3 B- 3 B and  3 C- 3 C of  FIG. 3A , the rotary reflectors  308 ,  310  have respective long sides  330 A,  330 B,  332 A,  332 B and respective short sides  334 A,  334 B,  336 A,  336 B. The rotary reflectors  308 ,  310  are, preferably, positioned about rotatable shaft  304  at the same angular orientation relative thereto such that rotary reflector  310  is hidden behind rotary reflector  308  in  FIGS. 3B and 3C  and such that the long sides  330 A,  330 B of rotary reflector  308  are coplanar with the long sides  332 A,  332 B of rotary reflector  310  and the short sides  334 A,  334 B of rotary reflector  308  are coplanar with the short sides  336 A,  336 B of rotary reflector  310 . Respective reference planes  338 ,  340  are defined as extending through longitudinal axis  306  and being parallel, respectively, to long sides  330 A,  330 B,  332 A,  332 B of the rotary reflectors  308 ,  310 . It should be understood that the scope of the present invention comprises rotary reflectors  308 ,  310  which are positioned about rotatable shaft  308  at different angular orientations relative thereto. 
     The rotary reflectors  308 ,  310  are, preferably, positionable in a plurality of positions relative to the first and second output waveguides  314 ,  316  of the 3 dB waveguide hybrid junction  302  by rotation of the rotatable shaft  304 . In a first exemplary position illustrated in  FIGS. 3B and 3C , planes  338 ,  340  of the rotary reflectors  308 ,  310  define an azimuth angle, θ 1 , relative to planes  342 ,  344  of the first and second output waveguides  314 ,  316  which measures zero (i.e., planes  338 ,  340 ,  342 ,  344  are all coplanar). In a second exemplary position illustrated in the schematic partial cross-sectional views of  FIGS. 3D and 3E  respectively taken along lines  3 D- 3 D and  3 E- 3 E of  FIG. 3A , planes  338 ,  340  of the rotary reflectors  308 ,  310  define an azimuth angle, θ 2 , relative to planes  342 ,  344  of the first and second output waveguides  314 ,  316  which measures ninety degrees (i.e., planes  338 ,  340  are, respectively, perpendicular to planes  342 ,  344 ). 
     In operation, the phase angle, φ, of the phase shifted RF waves of a pulse of phase shifted RF waves output by the high-speed phase shifter  300  depends on the orientation of the rotary reflectors  308 ,  310  relative to the first and second output waveguides  314 ,  316  of the 3 dB waveguide hybrid junction  302  (and, hence, on their&#39;azimuth angle, θ, relative to planes  342 ,  344  of the first and second output waveguides  314 ,  316  of the 3 dB waveguide hybrid junction  302 ). Therefore, by rotating the rotary reflectors  308 ,  310  between desired positions thereof (and, hence, between different azimuth angles θ) at a rate substantially equal to the rate at which pulses of RF waves are received by the input waveguide  312 , the phase angle, φ, of the phase shifted RF waves of a pulse of phase shifted RF waves output by the high-speed phase shifter  300  is changed accordingly. 
       FIG. 4  displays a graphical illustration of this relationship between the phase angle, φ, of the phase shifted RF waves of a pulse of phase shifted RF waves output by the high-speed phase shifter  300  and the azimuth angle, θ, of the rotary reflectors  308 ,  310  relative to planes  342 ,  344  of the first and second output waveguides  314 ,  316 . As illustrated in  FIG. 4 , when the rotary reflectors  308 ,  310  are rotated into the first position described above to change the phase of the received RF waves, the phase angle, φ, of the phase shifted RF waves of a pulse of phase shifted RF waves output by the high-speed phase shifter  300  is at a maximum value. When the rotary reflectors  308 ,  310  are rotated into the second position described above to change the phase of the received RF waves, the phase angle, φ, of the phase shifted RF waves of a pulse of phase shifted RF waves output by the high-speed phase shifter  300  is a different phase angle, φ, which, in such case, is a minimum phase angle. Because the rotary reflectors  308 ,  310  are rotatable into a plurality of positions thereof at a rate substantially equal to and synchronized with the rate at which pulses of charged particles are emitted by injector  108  and pulses of RF waves are received by input waveguide  312 , the high-speed phase shifter  300  is operable to produce pulses of output phase shifted RF waves having a desired phase angle, φ, at a rate required by the particle accelerator system  100  for changing of the accelerating field of the second accelerating section  104  thereof according to whether a high energy pulse of charged particles or a low energy pulse of charged particles is presently being generated by the particle accelerator system  100  (i.e., according to whether the particle accelerator system  100  is operating in a high energy mode or in a low energy mode). 
     In accordance with the first embodiment of the present invention described herein, the rotary reflectors  308 ,  310  are rotated about longitudinal axis  306  at a rotation rate of 50 Hz. However, it should be understood that the scope of the present invention comprises a high-speed phase shifter  300  having rotary reflectors  308 ,  310  which are rotatable at different rotation rates to change the phase angle, φ, of the output phase shifted RF waves as appropriate. 
       FIG. 5  displays a schematic cross-sectional view of a third form of a high-speed phase shifter  500  taken perpendicular to a longitudinal axis thereof, which is employable as a phase shifter  134  in accordance with the first embodiment of the present invention. High-speed phase shifter  500  comprises a waveguide segment  502 , a ferrite element  504  positioned within the waveguide segment  502 , and an electromagnet  506  that is secured to the outside of the waveguide segment  502 . The waveguide segment  502  has a first end (not shown) that is connectable to an external waveguide for the receipt of pulses of input RF waves therefrom. The waveguide segment  502  also has a second end (not shown) that is connectable to an external waveguide for the output of pulses of phase shifted RF waves produced by the high-speed phase shifter  500 . Additionally, the waveguide segment  502  has wall  510  that defines the substantially rectangular cross-section thereof such that the waveguide segment  502  includes opposing wide sides  512 A,  512 B and opposing narrow sides  514 A,  514 B. 
     The electromagnet  506  is secured to the outside of waveguide segment  502  proximate narrow side  514 B and comprises a core  516  defining a hollow cavity  518  therein adjacent narrow side  514 B. The electromagnet  506  further comprises a first coil  520  and a second coil  522 . Coil  520  extends substantially around a portion of core  516  at a first end thereof. Coil  522  similarly extends substantially around a second portion of core  516  at a second end thereof. The first and second coils  520 ,  522  are operable to create a magnetic field in the ferrite element  504  which is located inside the waveguide segment  502  at a position adjacent an inner surface of wall  510  proximate to narrow side  514 B of the waveguide segment  502 . 
     In operation, the first and second coils  520 ,  522  are energized to create a magnetic field in the ferrite element  504 . The phase of the phase shifted RF waves of a pulse of phase shifted RF waves output by the high-speed phase shifter  500  is changed by altering the magnetic field created in the ferrite element  504  through appropriate energizing and/or de-energizing of the first and second coils  520 ,  522 . Because the magnetic field created in the ferrite element  502  by the first and second coils  520 ,  522  is changeable at a rate substantially equal to and synchronized with the rate at which pulses of charged particles are emitted by injector  108  and pulses of RF waves are received by waveguide segment  502 , the high-speed phase shifter  500  is operable to produce pulses of output phase shifted RF waves having a desired phase angle, φ, at a rate required by the particle accelerator system  100  for changing of the accelerating field of the second accelerating section  104  thereof according to whether a high energy pulse of charged particles or a low energy pulse of charged particles is presently being generated by the particle accelerator system  100  (i.e., according to whether the particle accelerator system  100  is operating in a high energy mode or in a low energy mode). 
       FIG. 6A  displays a schematic cross-sectional view of a fourth form of a high-speed phase shifter  600  taken perpendicular to a longitudinal axis thereof, which is employable as a phase shifter  134  in accordance with the first embodiment of the present invention. High-speed phase shifter  600  comprises a waveguide segment  602  and two rotary asymmetric reflectors  604 ,  606  (also sometimes referred to herein as “rotary reflectors  604 ,  606 ”). The waveguide segment  602  has a first end  608  (see  FIGS. 6B and 6C ) that is connectable to an external waveguide for the receipt of pulses of input RF waves therefrom. The waveguide segment  602  also has a second end  609  that is connectable to an external waveguide for the output of pulses of phase shifted RF waves produced by the high-speed phase shifter  600 . Additionally, the waveguide segment  602  has wall  612  that defines the substantially rectangular cross-section thereof such that the waveguide segment  602  includes opposing wide sides  614 A,  614 B and opposing narrow sides  616 A,  616 B. 
     The rotary reflectors  604 ,  606  are located substantially adjacent to the inner surface of wall  612  proximate narrow side  616 B of the waveguide segment  602 . Preferably, the rotary reflectors  604 ,  606  are manufactured from a dielectric material or other material having similar properties. The rotary reflectors  604 ,  606  are secured to respective rotatable shafts  610 ,  611  having respective longitudinal axes  618 ,  620 . The rotatable shafts  610 ,  611  extend through wall  612  at the narrow side  616 B of the waveguide segment  602  and are operable for rotation at an appropriate rate and/or at appropriate times by a suitable drive system (not shown) such that when rotatable shafts  610 ,  611  are rotated about their respective longitudinal axes  618 ,  620 , the rotary reflectors  604 ,  606  are also rotated about longitudinal axes  618 ,  620 . Preferably, the rotatable shafts  610 ,  611  are rotated in unison, in the same angular direction, at the same rate, and/or at the same times, thereby causing the rotary reflectors  604 ,  606  to also be rotated in unison, in the same angular direction, at the same rate, and/or at the same times. 
     As illustrated in the schematic cross-sectional views of  FIGS. 6B and 6C  which are taken along lines  6 B- 6 B and  6 C- 6 C of  FIG. 6A , the first rotary reflector  604  is, preferably, located relative to the second reflector  606  such that the distance, D, between the respective longitudinal axes  618 ,  620  about which the rotary reflectors  604 ,  606  rotate is equal to one fourth of the waveguide segment&#39;s wavelength. By locating the first rotary reflector  604  relative to the second rotary reflector  606  at such a distance, D, reflections from the rotary reflectors  604 ,  606  are compensated for. As also illustrated in  FIGS. 6B and 6C , reference planes  622 ,  624  are defined as passing through the respective longitudinal axes  618 ,  620  of rotary reflectors  604 ,  606  and are oriented perpendicular to the wide sides  614 A,  614 B of waveguide segment  602  and parallel to the first and second ends  608 ,  610  thereof. 
     The rotary reflectors  604 ,  606 , preferably, comprise rectangular-shaped plates having rectangular-shaped cross-sections with holes  626 ,  628  extending therethrough for receipt of respective rotatable shafts  610 ,  611 . The dimensions of the rotary reflectors  604 ,  606  are selected to enable the rotary reflectors  604 ,  606  to be freely rotated adjacent to the inner surface of wall  612  proximate narrow side  616 B of the waveguide segment  602  upon rotation of rotatable shafts  610 ,  611 . It should be understood that the scope of the present invention comprises rotary reflectors  604 ,  606  of different forms having different shaped cross-sections and which are manufactured wholly, or in part, from different materials. 
     The rotary reflectors  604 ,  606 , as illustrated in  FIGS. 6B and 6C , have respective opposing long sides  630 A,  630 B,  632 A,  632 B and respective opposing short sides  634 A,  634 B,  636 A,  636 B. The rotary reflectors  604 ,  606  are, preferably, positioned about rotatable shafts  610 ,  611  at the same angular orientation relative thereto such that rotary reflector  604  is hidden behind rotary reflector  606  in  FIG. 6A . Reference planes  638 ,  640  extend through the respective longitudinal axes  618 ,  620  of rotatable shafts  610 ,  611  and are, respectively, parallel to the opposing long sides  630 A,  630 B,  632 A,  632 B of the rotary reflectors  604 ,  606 . It should be understood that the scope of the present invention comprises rotary reflectors  604 ,  606  which are positioned about rotatable shafts  610 ,  611  at different angular orientations relative thereto. 
     The rotary reflectors  604 ,  606  are, preferably, positionable in a plurality of positions relative to the waveguide segment  602  by rotation of the rotatable shafts  610 ,  611 . In a first exemplary position illustrated in  FIG. 6B , planes  638 ,  640  of the rotary reflectors  604 ,  606  define an azimuth angle, θ 1 , relative to planes  622 ,  624  of waveguide segment  602  which measures zero (i.e., planes  638 ,  640 ,  622 ,  624  are all coplanar). In a second exemplary position illustrated in  FIG. 6C , planes  638 ,  640  of the rotary reflectors  604 ,  606  define an azimuth angle, θ 2 , relative to planes  622 ,  624  of waveguide segment  602  which measures ninety degrees (i.e., planes  638 ,  640  are, respectively, perpendicular to planes  622 ,  624 ). 
     In operation, the phase angle, φ, of the phase shifted RF waves of a pulse of phase shifted RF waves output by the high-speed phase shifter  600  depends on the orientation of the rotary reflectors  604 ,  606  relative to the waveguide segment  602  (and, hence, on their azimuth angle, θ, relative to planes  622 ,  624  of waveguide segment  602 ). Therefore, by rotating the rotary reflectors  604 ,  606  between desired positions thereof (and, hence, between different azimuth angles θ) at a rate substantially equal to the rate at which pulses of RF waves are received by the waveguide segment  602 , the phase angle, φ, of the phase shifted RF waves of a pulse of phase shifted RF waves output by the high-speed phase shifter  600  is changed accordingly. 
     The relationship between the phase angle, φ, of the phase shifted RF waves of a pulse of phase shifted RF waves output by the high-speed phase shifter  600  and the azimuth angle, θ, of the rotary reflectors  604 ,  606  relative to planes  622 ,  624  of the waveguide segment  602  is substantially similar to that illustrated in  FIG. 4  and described above with respect to high-speed phase shifter  300 . As illustrated in  FIG. 4  and with respect to high-speed phase shifter  600 , when the rotary reflectors  604 ,  606  are rotated into the first position described above to change the phase of the received RF waves, the phase angle, φ, of the phase shifted RF waves of a pulse of phase shifted RF waves output by the high-speed phase shifter  600  is at a maximum value. When the rotary reflectors  604 ,  606  are rotated into the second position described above to change the phase of the received RF waves, the phase angle, φ, of the phase shifted RF waves of a pulse of phase shifted RF waves output by the high-speed phase shifter  600  is a different phase angle, φ, which, in such case, is a minimum phase angle. Because the rotary reflectors  604 ,  606  are rotatable into a plurality of positions thereof at a rate substantially equal to and synchronized with the rate at which pulses of charged particles are emitted by injector  108  and pulses of RF waves are received by waveguide segment  602 , the high-speed phase shifter  600  is operable to produce pulses of output phase shifted RF waves having a desired phase angle, φ, at a rate required by the particle accelerator system  100  for changing of the accelerating field of the second accelerating section  104  thereof according to whether a high energy pulse of charged particles or a low energy pulse of charged particles is presently being generated by the particle accelerator system  100  (i.e., according to whether the particle accelerator system  100  is operating in a high energy mode or in a low energy mode). 
     It should be understood that while high-speed phase shifter  600  has been described herein as comprising two rotary reflectors  604 ,  606 , it should be understood that the scope of the present invention comprises similar high-speed phase shifters having one or more rotary reflectors. It should be understood that while the rotary reflectors  604 ,  606  of high-speed phase shifter  600  are, generally, rotated in unison by respective rotatable shafts  610 ,  611  and oriented in the same position relative to respective reference planes  622 ,  624  at a particular time, the scope of the present invention comprises similar high-speed phase shifters having rotary reflectors which are not rotated in unison by respective rotatable shafts and/or which are not oriented in the same position relative to respective reference planes  622 ,  624  at such particular time. 
       FIG. 7  displays a schematic block diagram representation of a particle accelerator system  700  in accordance with a second embodiment of the present invention. The particle accelerator system  700  comprises a first accelerating section  702 , a second accelerating section  704 , an RF drive subsystem  706 , and an injector  708 . In the second embodiment, the first and second accelerating sections  702 ,  704  and the injector  708  are substantially similar to the first and second accelerating sections  102 ,  104  and the injector  108  of the first embodiment. 
     The first accelerating section  702  has a first end  710  and a second end  712 . The injector  708  is positioned proximate the first end  710  of the first accelerating section  702  and is connected to an input port  714  of the first accelerating section  702 . The injector  708  is operable to generate charged particles and to emit them in a pulsed mode of operation as pulses of charged particles, into the first accelerating section  702  through input port  714 . The rate at which the injector  708  emits pulses of charged particles may be increase or decreased as needed. The first accelerating section  702  defines an oblong-shaped slot  716  which couples the first accelerating section  702  to a feeder waveguide  718  of the RF drive subsystem  706  to enable RF power to propagate from the feeder waveguide  718  into and through the first accelerating section  702 . 
     Similar to the first accelerating section  702 , the second accelerating section  704  has a first end  720  and a second end  722 . The second accelerating section  704  is appropriately connected to the first accelerating section  702  to enable charged particles to travel between the first and second accelerating sections  702 ,  704 . The second accelerating section  704  includes an output port  724  located at the second end  722  of the second accelerating section  704 . A longitudinal axis  725  of the particle accelerating system  700  extends between, and is defined by, the input port  714  and the output port  724 . The output port  724  is adapted to direct a beam of charged particles from the second accelerating section  702  (and, hence, from the particle accelerator system  700 ) toward a desired target or other object. The second accelerating section  704  defines an oblong-shaped slot  726  which couples the second accelerating section  704  to a feeder waveguide  728  of the RF drive subsystem  706  to allow RF power to propagate from the feeder waveguide  728  into and through the second accelerating section  704 . 
     The RF drive subsystem  706  comprises an RF source  730 , an isolating device  732 , a first 3 dB waveguide hybrid junction  734 , a phase shifter  736 , and a second 3 dB waveguide hybrid junction  738 . The RF source  730  is operable to generate RF power in the form of pulses of RF waves, having an appropriate frequency, power level, and pulse repetition rate, using a pulsed mode of operation synchronized with the emission of charged particles by injector  708  and to output such RF power via connected waveguide  744 . Preferably, the RF source  730  includes a magnetron which generates 2.5 MW of RF power in the form of pulses of RF waves having a frequency of 2.8 GHz and a pulse repetition rate of 200 Hz. Also preferably, the RF source  730  may include a microwave generator, klystron, or other device for generating an appropriate level of RF power in the form of pulses of RF waves having an appropriate frequency and pulse repetition rate. 
     An isolating device  732  is connected to the RF source  730 , via waveguide  744 , for receiving RF power and pulses of RF waves generated and output by RF source  730 . The isolating device  732  is operable to prevent RF power from propagating back to and reentering RF source  730 , and thereby possibly damaging the RF source  730 . The isolating device  732  is connected to a waveguide load  750  via waveguide  752 . Waveguide load  750  is operable to dissipate reflected RF power received from connected waveguide  754 . Preferably, the isolating device  732  comprises a ferrite circulator or a ferrite isolator. It should be understood that the scope of the present invention includes other appropriate devices for isolating an RF source  730 . 
     Isolating device  732  is also connected to an input waveguide  754  of a first 3 dB waveguide hybrid junction  734  and is adapted to receive RF power in the form of pulses of RF waves supplied from the RF source  730  via the isolating device  732 . The first 3 dB waveguide hybrid junction  734  has an input waveguide  754  and three output waveguides  756 ,  758 ,  760 . Output waveguides  756 ,  758  are adapted to receive generated RF power from input waveguide  754  and to deliver it, respectively, to waveguide  764  of a second 3 dB waveguide hybrid junction  738  and phase shifter  736 . Output waveguide  760  connects to a matched waveguide load  762 . The matched waveguide load  762  is adapted to receive and dissipate reflected RF power. 
     Output waveguide  758 , as indicated above, connects to phase shifter  736 , which is substantially similar to the phase shifter  134  of the first embodiment and is, therefore, not described again in detail. Phase shifter  736  is capable of shifting the phase of the RF waves of a received pulse of RF waves between at least a first and a second phase and doing so in synchronization with pulses of charged particles emitted by injector  108 . Phase shifter  736 , preferably, comprises one of the high-speed phase shifters  200 ,  300 ,  500 ,  600  described with reference to  FIGS. 2 ,  3 ,  5 , and  6  below. It should be understood that the scope of this invention includes other appropriate devices capable of shifting the phase of the RF waves of a pulse of RF waves between first and second phases which are appropriate. 
     Output waveguide  756  connects to input waveguide  764  of second 3 dB waveguide hybrid junction  738 . The second 3 dB waveguide hybrid junction  738  has two input waveguides  764 ,  766  and two output waveguides  768 ,  770 . The second input waveguide  766  is connected to a waveguide of the phase shifter  736  and is adapted to receive a pulse of phase shifted RF waves from the phase shifter  736 . Output waveguide  768  connects to the input waveguides  764 ,  766  and is adapted to receive RF power in the form of pulses of RF waves from input waveguide  764  and RF power in the form of pulses of phase shifted RF waves from input waveguide  766  and to supply such RF power to the first accelerating section  702  through connected feeder waveguide  718  and oblong-shaped slot  116  thereof so as to create an accelerating field in the first accelerating section  702 . Similarly, output waveguide  770  connects to the input waveguides  764 ,  766  and is adapted to receive generated RF power in the form of pulses of RF waves from input waveguide  764  and RF power in the form of pulses of phase shifted RF waves from input waveguide  766  and to supply such RF power to the second accelerating section  704  through connected feeder waveguide  728  and oblong-shaped slot  726  thereof so as to create an accelerating field in the second accelerating section  704 . Together, the first 3 dB waveguide hybrid junction  734 , the phase shifter  736 , and the second 3 dB waveguide hybrid junction  738  function as a variable, directional coupler to regulate the ratio of the RF power supplied to the first and second accelerating sections  702 ,  704 . 
     In operation, the injector  708  of the particle accelerating system  700  generates and emits charged particles (preferably, electrons) into the first accelerating section  702  and, concurrently, the RF source  730  of the RF drive subsystem  706  generates RF power, in a pulsed mode of operation synchronized with the emission of charged particles by injector  708 , and outputs such RF power in the form of pulses of RF waves. The RF source  730  delivers such RF power to isolating device  732  via waveguide  744 . The isolating device  732  prevents the generated RF power from returning to the RF source  730 . Reflections of the RF power are directed by the isolating device  732 , via waveguide  752 , to the waveguide load  750 , where the RF power is dissipated. 
     From the isolating device  732 , the generated RF power enters the input waveguide  754  of the first 3 dB waveguide hybrid junction  734 . The first 3 dB waveguide hybrid junction  734  divides the RF power (preferably, in half) with a first portion of the generated RF power propagating through output waveguide  756  of the 3 dB waveguide hybrid junction  734  and into the first input waveguide  764  of the second 3 dB waveguide hybrid junction  738 . 
     A second portion of the generated RF power propagates through output waveguide  758  of the first 3 dB waveguide hybrid junction  734  and into phase shifter  736 . The phase of the RF waves in the pulses of RF waves is, preferably, changed by phase shifter  736  using the appropriate operating method of high-speed phase shifters  200 ,  300 ,  500 ,  600  employed as phase shifter  736 , as described in detail above. Alternatively, the phase of the RF waves in the pulses of RF waves of the generated RF power may be changed by other appropriate devices and methods. 
     The phase shifted RF power (i.e., in the form of pulses of phase shifted RF waves) then propagates through phase shifter  736  and into the second input waveguide  766  of the second 3 dB waveguide hybrid junction  738 . The phase shifted RF power is then divided by the second 3 dB waveguide hybrid junction  738 , into first and second portions of the phase shifted RF power with, preferably, the first portion of the phase shifted RF power (i.e., one-fourth of the generated RF power) propagating via output waveguide  768  into feeder waveguide  718 . Subsequently, the first portion of the phase shifted RF power propagates into and throughout the first accelerating section  702  via oblong-shaped slot  716 . The second portion of the phase shifted RF power (i.e., one-fourth of the generated RF power) propagates via output waveguide  770  into feeder waveguide  728 . Subsequently, the second portion of the phase shifted RF power propagates into and throughout the second accelerating section  704  via oblong-shaped slot  726 . 
     The generated RF power from waveguide  756  is then divided by the second 3 dB waveguide hybrid junction  738  into first and second portions of the generated RF power with, preferably, the first portion of the RF power (i.e., preferably, one-fourth of the generated RF power) propagating, via output waveguide  768 , into feeder waveguide  718 . Subsequently, the first portion of the RF power propagates into and throughout the first accelerating section  702  via oblong-shaped slot  716 . The second portion of the RF power (i.e., preferably, one-fourth of the generated RF power) propagates, via output waveguide  770 , into feeder waveguide  728 . Subsequently, the second portion of the RF power propagates into and throughout the first accelerating section  704  via oblong-shaped slot  726 . 
     Consequently, the RF waves having amplitudes corresponding to one-fourth of the generated power with and without phase shift propagate into and throughout each of the accelerating sections  702 ,  704 . Contemporaneously, the charged particles emitted into the first accelerating section  702  travel through the first accelerating section  702  while being accelerated by the accelerating field developed from the RF waves having amplitudes corresponding to one-fourth of the generated power with and without phase shift and formed into a charged particle beam. Upon reaching the second end  712  of the first accelerating section  702 , the charged particles of the charged particle beam travel into and through the second accelerating section  704  while being further accelerated by the accelerating field developed from the RF waves having amplitudes corresponding to one-fourth of the generated power with and without phase shift. The charged particles of the charged particle beam exit the particle accelerator system  700  via output port  724  located at the second end  722  thereof as pulses of bunched charged particles (preferably, electrons). 
     It should be noted that although the 3 dB waveguide hybrid junctions  734 ,  738  have been described as dividing the generated RF power equally between the output waveguides  756 ,  758  and  768 ,  770 , respectively, the 3 dB waveguide hybrid junctions  734 ,  738  are capable of dividing the RF power in any ratio. It should also be noted that the phase differential of the RF waves of the pulses of RF waves in output waveguides  768 ,  770  does not depend on the configuration of the phase shifter  736 . However, the amplitude of the RF waves in the pulses of RF waves depends on the phase shift performed by the phase shifter  736 . Additionally, it should be noted that the RF power in the output waveguides  768 ,  770  is proportional to the electromagnetic field amplitude, E, squared. At the output feeder waveguides  718 ,  728  of the second 3 dB waveguide hybrid junction  738 , the electromagnetic fields of the RF waves having amplitudes corresponding to one-fourth of the generated power with and without phase shift in the feeder waveguide  718  and the electromagnetic fields of the RF waves having amplitudes corresponding to one-fourth of the generated power with and without phase shift in the feeder waveguide  728  are summed vectorially by taking into account their the phase differentials. For example, in one extreme mode, if the phase shifter  736  is configured such that at the junction of the output feeder waveguides  718 ,  728  of the second 3 dB waveguide hybrid waveguide junction  738  the phases of the each of the RF waves having amplitudes corresponding to one-fourth of the generated power with and without phase shift in the feeder waveguide  718  and the electromagnetic fields of the RF waves having amplitudes corresponding to one-fourth of the generated power with and without phase shift in the feeder waveguide  728  coincide, the sum of the amplitudes of the RF waves is taken. Thus, the entire RF power propagates through output feeder waveguide  718  through oblong-shaped slot  716  and into the first accelerating section  702 , and none of the RF power enters the second accelerating section  704 . 
     To further illustrate this example, the following equation represents the electromagnetic field created in the waveguide at the input of first accelerating section  702 , “E” as defined by the relationship between the amplitudes of the electromagnetic fields in output feeder waveguides  718 ,  728  and the phase of the phase shifted RF wave:
 
 E =√{square root over ( E   1   2   +E   2   2 +2 ·E   1   ·E   2 ·COS φ)}
 
     where E 1  and E 2  are amplitudes of the electromagnetic fields of RF waves having amplitudes corresponding to one-fourth of the generated power with and without phase shift in the output feeder waveguides  718 ,  728  and φ is the phase shift between these RF waves. Where both 3 dB waveguide hybrid junctions  734 ,  738  divide the RF waves equally, E 1  equals E 2 . In this mode, where the RF waves are equally divided between the first and second accelerating sections  702 ,  704 , φ equals ninety degrees. However, in the extreme mode previously described above where the entire generated RF power is directed into the first accelerating section  702 , and no portion of the RF power is directed into the second accelerating section  704 , φ equals zero degrees. Thus, the change of the phase shift in the phase shifter  736  allows control of power division and delivery between the first accelerating section  702  and the second accelerating section  704  from (i) the entire RF power being delivered to the first accelerating section  702  and no RF power being delivered to the second accelerating section  704  to (ii) no RF power being delivered to the first accelerating section  702  and the entire RF power being delivered to the second accelerating section  704 . 
     Preferably, the particle accelerating system  700  alternately operates in two modes, a high energy mode and a low energy mode in which the high and low energy modes alternate between successive pulses such that the pulses generated and output by the particle accelerating system  700  alternatingly have high and low energy levels. In the high energy mode of operation, the phase shift of the RF power performed by phase shifter  736  is selected such that the accelerating fields created in the first and second accelerating sections  702 ,  704  are approximately equal in strength. 
     In the low energy mode of operation, the phase shift of the RF power performed by the phase shifter  736  is selected to increase the strength of the accelerating field created in the first accelerating section  702  relative to the strength of the accelerating field created in the second accelerating section  704 . To compensate for the increased strength of the accelerating field in the first accelerating section  702 , the rate at which the injector  708  emits charged particles into the first accelerating section  702  (i.e., the injector current) is increased. By increasing the current, the strength of the accelerating field created in the first accelerating section  702  in the low energy mode equals the strength of the accelerating field created in the first accelerating section  702  in the high energy mode. As a consequence, the incremental change in the energy level of each charged particle in the first accelerating section  702  is identical in both the high energy and the low energy modes. 
     However, in the low energy mode, the strength of the accelerating field in the second accelerating section  704  is reduced relative to the strength of the accelerating field in the second accelerating section  704  in the high energy mode. Thus, in the low energy mode, the incremental change in the energy level of the charged particles in the second accelerating section  704  is smaller relative to the incremental change in the energy level of the charged particles in the second accelerating section  704  in the high energy mode. 
     Whereas the present invention has been described in detail above with respect to exemplary embodiments thereof, it is understood that variations and modifications can be effected within the spirit and scope of the invention, as described herein before and as defined in the appended claims. The corresponding structures, materials, acts, and equivalents of all means-plus-function elements, if any, in the claims below are intended to include any structure, material, or acts for performing the functions in combination with other claimed elements as specifically claimed.