WO2020242511A1 - Procédé et système de synchronisation d'injections de faisceaux d'électrons dans un système d'inspection de chargement à rayons x multi-énergie - Google Patents

Procédé et système de synchronisation d'injections de faisceaux d'électrons dans un système d'inspection de chargement à rayons x multi-énergie Download PDF

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WO2020242511A1
WO2020242511A1 PCT/US2019/048483 US2019048483W WO2020242511A1 WO 2020242511 A1 WO2020242511 A1 WO 2020242511A1 US 2019048483 W US2019048483 W US 2019048483W WO 2020242511 A1 WO2020242511 A1 WO 2020242511A1
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pulse
sub
duration
energy
electrons
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PCT/US2019/048483
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English (en)
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Aleksandr Saverskiy
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American Science And Engineering, Inc.
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Priority claimed from US16/442,256 external-priority patent/US20200163199A1/en
Application filed by American Science And Engineering, Inc. filed Critical American Science And Engineering, Inc.
Priority to CN201980096970.7A priority Critical patent/CN113875316B/zh
Publication of WO2020242511A1 publication Critical patent/WO2020242511A1/fr

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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H9/00—Linear accelerators
    • H05H9/04—Standing-wave linear accelerators
    • H05H9/048—Lepton LINACS
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V5/00—Prospecting or detecting by the use of ionising radiation, e.g. of natural or induced radioactivity
    • G01V5/20—Detecting prohibited goods, e.g. weapons, explosives, hazardous substances, contraband or smuggled objects
    • G01V5/22—Active interrogation, i.e. by irradiating objects or goods using external radiation sources, e.g. using gamma rays or cosmic rays
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J35/00—X-ray tubes
    • H01J35/02—Details
    • H01J35/14—Arrangements for concentrating, focusing, or directing the cathode ray
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05G—X-RAY TECHNIQUE
    • H05G1/00—X-ray apparatus involving X-ray tubes; Circuits therefor
    • H05G1/08—Electrical details
    • H05G1/26—Measuring, controlling or protecting
    • H05G1/30—Controlling
    • H05G1/38—Exposure time
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05G—X-RAY TECHNIQUE
    • H05G1/00—X-ray apparatus involving X-ray tubes; Circuits therefor
    • H05G1/08—Electrical details
    • H05G1/58—Switching arrangements for changing-over from one mode of operation to another, e.g. from radioscopy to radiography, from radioscopy to irradiation or from one tube voltage to another
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H7/00—Details of devices of the types covered by groups H05H9/00, H05H11/00, H05H13/00
    • H05H7/02—Circuits or systems for supplying or feeding radio-frequency energy
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H7/00—Details of devices of the types covered by groups H05H9/00, H05H11/00, H05H13/00
    • H05H7/02—Circuits or systems for supplying or feeding radio-frequency energy
    • H05H2007/027—Microwave systems
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H2277/00—Applications of particle accelerators
    • H05H2277/14—Portable devices
    • H05H2277/1405—Detection systems, e.g. for safety

Definitions

  • the invention relates generally to systems and methods for inspection of cargo using penetrating radiation, and, more specifically to systems and methods for material discrimination on the basis of varying both the energy and the flux of incident radiation during the course of a single pulse.
  • An inspection system for cargo and containers screening typically employs an electron accelerator capable of interlaced dual energy operation, and differential transmission of X-rays characterized by distinct energy spectra can be used to distinguish among intervening materials of different atomic numbers.
  • the term“interlaced energies,” as employed herein, denotes the use of a stream of X-ray pulses wherein successive pulses are characterized by distinct energy spectra.
  • interlaced energy inspection for material discrimination is well known, with processing techniques surveyed, for example, by Ogorodnikov et ah, Processing of interlaced images in 4-10 MeV dual energy customs system for material recognition, Phys. Rev.
  • a Bremsstrahlung spectrum is characterized by its endpoint energy, defined by the energy of electrons impinging upon an X-ray target in order to generate the X-rays. Attenuation by an inspected object of transmitted radiation for two (or, on some occasions, more) distinct energies provides the input data for identifying the type of material being inspected.
  • FIG. 1 depicts a cargo inspection system employing such a technique.
  • a fan-shaped beam 12 of penetrating radiation, emitted by a source 14, is detected by elements 18 of a detector array 16 distal to a target object, here truck 10, is used to produce images of the target object.
  • Detector elements 18 produce corresponding detector signals processed by processor 19 to provide information relative to the material composition of the cargo and images of its spatial distribution.
  • the thickness of material to be penetrated by the X-rays may exceed 300 mm of steel equivalent in some cases.
  • inspection systems typically use X-rays with a maximum energy of several MeV, currently up to about 9 MeV.
  • X-rays in excess of 1 MeV are frequently referred to as hard X-rays or high-energy X-rays.
  • Information (such as mass absorption coefficient, effective atomic number Z eff , electron density, or the spatial distribution of any of the foregoing, etc.) with respect to the material composition of the contents of objects may be obtained on the basis of the interaction of X-rays with the material, and, more particularly, by illuminating the material with X-ray beams having energy spectra with more than one distinct energy endpoint (peak energy), or by employing energy discriminating detectors. Dual energy methods of material discrimination are widely used in X-ray inspection systems for security control of hand luggage in customs and other security checkpoints.
  • Dual (and, more generally, multiple-) energy methods have been extended to high-energy inspection systems for cargo containers, where material discrimination is less effective due to the weaker Z-dependence of the dominant interaction.
  • X-ray transmission data of an inspected object are obtained for both energies, and processed by computer, whereupon a resulting image is displayed on a monitor, typically in a special color palette that facilitates visual identification of contraband or hazardous materials. More particularly, special computer software may identify various materials and artificial colors may be assigned to various values of Z eff.
  • a typical energy range for the inspection of smaller objects is below 0.5 MeV, taking advantage of the strong Z-dependence of the X-ray attenuation coefficient due to the prevalence of the photoelectric interaction (characterized by a cross-section, ⁇ Z 4 -Z 5 ) at lower energies.
  • X-ray interaction is dominated by the Compton effect with its weak dependence of attenuation coefficient (mass absorption) on the atomic number: p c ⁇ Z/A (which is approximately constant and equal to 0.5), where Z denotes atomic number, and A denotes atomic mass, which is to say that the mass absorption coefficient is largely Z-insensitive in the energy regime dominated by Compton scatter.
  • a preferred method for material discrimination entails variation of the pulse energy during the course of each single pulse, as described in detail in U.S. Pat. No. 8,457,274 (“Arodzero '274”, issued Jun. 4, 2013), which is incorporated herein by reference.
  • Leo Szilard conceived of the linear accelerator (linac) in 1928, while a professor at the University of Berlin.
  • a linac was also constructed independently by Rolf Wi deroe, then an engineering graduate-student under Walter Rogowski at Aachen, at about the same time. Electrons accelerated by a linear accelerator were first used to generate X-rays at Stanford in the mid-1950's.
  • the maximum pulse repetition frequency (PRF) that a linac-based X-ray source can provide is limited by the RF source.
  • the RF source typically, a magnetron or a klystron
  • P a v , m a x and pulsed P p,ma x power are limitations on maximum average P a v , m a x and pulsed P p,ma x power. These two parameters define the maximum duty factor d ma x, which also can be expressed in terms of PRF (f) and pulse duration l P :
  • the maximum available frequency can be estimated from the equation
  • single-energy pulse rate may be achieved on an interlaced energy basis.
  • b is the coupling coefficient between an RF power feed waveguide 222 (shown in FIG. 2) and an accelerating structure 22 (shown in FIG. 2, also referred to herein as an“accelerating cavity structure”)
  • r is the shunt impedance of the accelerating structure 22
  • L is the length of the accelerating structure 22
  • P is the power dissipated in the accelerating structure 22
  • t is the decay time constant of the accelerating structure 22. (Thus, both numerator and denominator of the logarithmic argument have units of voltage.)
  • t is the decay time constant of the accelerating structure 22.
  • the coupling coefficient (b ) of the accelerating structure 220 (also referred to as an“accelerating resonator,” or a“resonator,” or “RF accelerating structure”) to the external circuit (feeding waveguide 222) depends on the current accelerated in (and interacting with) the resonator 220.
  • the presence of current decreases the coupling coefficient that is measured through VSWR (voltage standing wave ratio), and the phase of the reflected signal from the resonator 220.
  • the optimum coupling coefficient bo is a value that allows the resonator 220 to be matched with an external waveguide 222 at the accelerating current I.
  • the coupling coefficient b is equal to /3 ⁇ 4, the coupling is referred to herein as“optimal.”
  • An exact calculation of the optimum bo may be found by reference to Sobenin et ah, Electrodynamic Characteristics of Accelerating Cavities (Eng. trans.), CRC Press, particularly at p. 121 (Eqn. 4.49), (1999), Collin, Foundations for Microwave Engineering, McGraw-Hill, (1st ed., 1992), and Gao. Analytical formula for the coupling coefficient b of a cavity waveguide coupling system, Physics Research A, vol. 309, pp. 5-10 (1991), all of which are incorporated herein by reference.
  • the resonator 220 In practice of designing accelerating systems the resonator 220 must be over-coupled (coupling coefficient b € >1, al so b 3 bo) for all values of accelerating current (7) and RF-power ( P ) considered for operation. Otherwise, operation of accelerating structure 22 becomes unstable.
  • waveguides are designed to be close to the optimum coupling, while there are cases when waveguide is designed for broad area of applications and is noticeably over-coupled when it operates at“low-current” applications.
  • Embodiments of the present specification provide improvements over traditional interlaced systems of material discrimination with dynamic dose control employed.
  • US Patent no. 8,054,937 titled“Systems and methods for using an intensity-modulated X-ray source”, assigned to the applicant, and incorporated herein by reference, describes embodiments of a traditional system of material discrimination with dynamic dose control.
  • Material discrimination is frequently achieved by applying dual/multi-energy method; with interlacing pulses of different energy; or by forming dual/multi -energy structure within single microwave pulses.
  • Dynamic dose control is typically achieved by independently varying pulse duration of each energy spectrum component. There is a need for successful operation of such a system (with material discrimination and dynamic dose control) that the energy spectrum of each energy component must be constant while dose is varying due to change of the pulse duration within the range of defined values (from minimum to maximum).
  • US Patent No. 9,867,271 titled “Source for intra-pulse multi-energy X-ray cargo inspection”, assigned to the applicant, and related to the present specification, describes the method of forming the beams satisfied to these conditions by injecting the beams with specific timing delays.
  • One of the key assumptions of the method is in matching system for optimal coupling at the Low Energy/First (highest) beam current.
  • Methods for material discrimination are provided on the basis of varying both the energy and the flux of incident radiation during the course of a single pulse.
  • a beam of electrons is generated with an electron gun and modulated prior to injection into an accelerating structure to achieve at least a first and specified beam current amplitude over the course of respective beam current temporal profiles.
  • a radio frequency field is applied to the accelerating structure with a specified RF field amplitude and a specified RF temporal profile.
  • the first and second specified beam current amplitudes are injected serially, each after a specified delay, in such a manner as to achieve at least two distinct endpoint energies of electrons accelerated within the accelerating structure during a course of a single RF-pulse.
  • the beam of electrons is accelerated by the radio frequency field within the accelerating structure to produce accelerated electrons which impinge upon a target for generating Bremsstrahlung X-rays.
  • There is a further need to address practical aspects of forming X-ray beam that may simultaneously support material discrimination and dynamic dose control functions.
  • the present specification discloses a method for generating a multiple- energy X-ray pulse using an accelerating structure comprising a standing wave resonator, the method comprising: generating a beam of electrons with an electron gun; modulating the beam of electrons prior to injection into the accelerating structure, wherein modulating the beam of electrons produces at least 1) a first beam current amplitude and a first beam current temporal profile and 2) a second beam current amplitude and a second beam current temporal profile and wherein the beam of electrons is characterized by an electron beam pulse duration; applying to the accelerating structure a radio frequency field, wherein the radio frequency field is defined by RF field amplitude, a specified temporal profile, and an RF pulse duration; determining a temporal profile of an amount of power reflected from the accelerating structure; determining a first delay and a second delay, wherein each of the first delay and second delay is determined based, at least in part, on the temporal profile of the amount of power reflected from the accelerating structure; inject
  • the method further comprises optimizing a coupling coefficient for the accelerating structure, wherein the coupling coefficient is optimized to achieve greater than critical coupling at any beam current.
  • the injecting of the modulated beam of electrons at the first beam current amplitude and then at the second beam current amplitude occurs over a single RF pulse.
  • the injecting of the modulated beam of electrons is performed at a time that is based, at least in part, on achieving, during the first sub-pulse, a minimized deviation of energy level relative to the first steady state energy level and on achieving, during the second sub-pulse, a minimized deviation of energy level relative to the second steady state energy level.
  • a duration of the first sub-pulse is different from a duration of the second sub pulse.
  • at least one of a duration of the first sub-pulse or a duration of the second sub pulse is variable, wherein a minimum duration of any sub-pulse may be zero, and wherein a maximum duration of the first sub-pulse or a maximum duration of the second sub-pulse is defined by a function of the RF pulse duration, a time for the injecting of the modulated beam of electrons, and durations of one or more other sub-pulses.
  • the injecting of the modulated beam of electrons is performed at a time that is based, at least in part, on achieving, during the first sub-pulse, a minimized deviation of power magnitude reflected from the accelerating structure relative to a first steady state level of reflected power magnitude and on achieving, during the second sub-pulse, a minimized deviation of power magnitude reflected from the accelerating structure relative to a second steady state level of reflected power magnitude.
  • a duration of the first sub-pulse is different from a duration of the second sub pulse.
  • at least one of a duration of the first sub-pulse or a duration of the second sub pulse is variable, wherein a minimum duration of any sub-pulse may be zero, and wherein a maximum duration of the first sub-pulse or a maximum duration of the second sub-pulse is defined by a function of the RF pulse duration, a time for the injecting of the modulated beam of electrons, and durations of one or more other sub-pulses.
  • the injecting of the modulated beam of electrons is performed at a time that is based, at least in part, on achieving, during the first sub-pulse, a minimized deviation of a normalized X-ray beam intensity, on the pulse duration, for the first sub-pulse relative to an X- ray beam intensity corresponding to the steady state energy level of the first sub-pulse and on achieving, during the second sub-pulse, a minimized deviation of a normalized X-ray beam intensity, on the pulse duration, for the second sub-pulse relative to an X-ray beam intensity corresponding to the steady state energy level of the second sub-pulse.
  • a duration of the first sub-pulse is different from a duration of the second sub pulse.
  • at least one of a duration of the first sub-pulse or a duration of the second sub pulse is variable, wherein a minimum duration of any sub-pulse may be zero, and wherein a maximum duration of the first sub-pulse or a maximum duration of the second sub-pulse is defined by a function of the RF pulse duration, a time for the injecting of the modulated beam of electrons, and durations of one or more other sub-pulses.
  • the present specification discloses a system for generating a multiple- energy X-ray pulse, the system comprising: an electron gun configured to generate a beam of electrons; a standing wave resonator; an RF source configured to apply a radio frequency field to the standing wave resonator, wherein the radio frequency field is characterized by a RF-field amplitude, a specified temporal profile, and a RF pulse duration and wherein the standing wave resonator is configured to receive and accelerate the beam of electrons with the radio frequency field to produce accelerated electrons; at least one detector configured to generate data indicative of a temporal profile of an amount of power reflected from the accelerating structure and to generate values indicative of amounts of reflected power; a controller configured to 1) receive the values indicative of the amounts of reflected power from the at least one detector, 2) determine the temporal profile of the amount of reflected power, 3) determine a first delay and a second delay, wherein each of the first delay and second delay is determined based, at least in part, on the temporal
  • the at least one detector comprises a directional coupler and microwave detector.
  • the controller is configured to inject the beam of electrons at the first beam current amplitude after the first delay to achieve the first sub-pulse and then at the second beam current amplitude after the second delay to achieve the second sub-pulse over a single RF pulse.
  • the controller is configured to inject the beam of electrons at a time that is based, at least in part, on achieving, during the first sub-pulse, a minimized deviation of energy level relative to the first steady state energy level and on achieving, during the second sub-pulse, a minimized deviation of energy level relative to the second steady state energy level.
  • a duration of the first sub-pulse is different from a duration of the second sub pulse.
  • at least one of a duration of the first sub-pulse or a duration of the second sub pulse is variable, wherein a minimum duration of any sub-pulse may be zero, and wherein a maximum duration of the first sub-pulse or a maximum duration of the second sub-pulse is defined by a function of the RF pulse duration, a time for injecting the beam of electrons, and durations of one or more other sub-pulses.
  • the controller is configured to inject the beam of electrons at a time that is based, at least in part, on achieving, during the first sub-pulse, a minimized deviation of power magnitude reflected from the standing wave resonator relative to a first steady state level of reflected power magnitude and on achieving, during the second sub-pulse, a minimized deviation of power magnitude reflected from the standing wave resonator relative to a second steady state level of reflected power magnitude.
  • a duration of the first sub-pulse is different from a duration of the second sub pulse.
  • at least one of a duration of the first sub-pulse or a duration of the second sub pulse is variable, wherein a minimum duration of any sub-pulse may be zero, and wherein a maximum duration of the first sub-pulse or a maximum duration of the second sub-pulse is defined by a function of the RF pulse duration, a time for injecting of the beam of electrons, and durations of one or more other sub-pulses.
  • the controller is configured to inject the beam of electrons at a time that is based, at least in part, on achieving, during the first sub-pulse, a minimized deviation of a normalized X-ray beam intensity, on the pulse duration, for the first sub-pulse relative to an X- ray beam intensity corresponding to the steady state energy level of the first sub-pulse and on achieving, during the second sub-pulse, a minimized deviation of a normalized X-ray beam intensity, on the pulse duration, for the second sub-pulse relative to an X-ray beam intensity corresponding to the steady state energy level of the second sub-pulse.
  • a duration of the first sub-pulse is different from a duration of the second sub pulse.
  • at least one of a duration of the first sub-pulse or a duration of the second sub pulse is variable, wherein a minimum duration of any sub-pulse may be zero, and wherein a maximum duration of the first sub-pulse or a maximum duration of the second sub-pulse is defined by a function of the RF pulse duration, a time for injecting of the beam of electrons, and durations of one or more other sub-pulses.
  • FIG. 1 illustrates a typical high-energy transmission X-ray inspection system, in accordance with some embodiments of the present specification
  • FIG. 2 illustrates a block diagram of an X-ray source employing an accelerating structure and modulated within a microwave pulse injection current and RF excitation, in accordance with some embodiments of the present specification
  • FIG. 3 illustrates dependence of energy and current within a microwave pulse, in accordance with some embodiments of the present specification
  • FIG. 4 illustrates a block diagram of an X-ray source employing a standing wave accelerating structure with modulated within a microwave pulse injection current and RF excitation, in accordance with some embodiments of the present specification
  • FIG. 5 illustrates a linac implementation with a dual-energy pulse created by applying the I I and I H currents with optimal delays, in accordance with an embodiment of the present specification
  • FIG. 6 illustrates a block diagram of an X-ray source employing an accelerating structure and modulated within a microwave pulse injection current and RF excitation, in accordance with some embodiments of the present specification
  • FIG. 7 illustrates waveform of reflected power from over-coupled microwave cavity and no accelerated beam current present, which may be detected by a detector, in accordance with some embodiments of the present specification
  • FIG. 8 is a graph illustrating a reflected power waveform obtained with a low energy and a high energy injection currents consecutively injected to form a dual energy beam, in accordance with some embodiments of the present specification
  • FIG. 9 is a graph illustrating an exemplary reflected power waveforms obtained from an industrial linac when a beam current injection pulse is injected at an optimal time
  • FIG. 10A is a graph illustrating an exemplary reflected power waveform when a beam current injection pulse is injected later than an optimal time (over-shoot);
  • FIG. 10B is another graph illustrating an exemplary reflected power waveform when a beam current injection pulse is injected earlier than an optimal time (under- shoot);
  • FIG. 11 is a graph illustrating an exemplary set of measurements of normalized on pulse width X-ray beam intensity ( D ) on y-axis and pulse width duration (!,,) on x-axis;
  • FIG. 12A illustrates an exemplary waveform for an intra-pulse dual energy structure, when a second (high energy) beam pulse is injected later than an optimal time (high-energy over shoot) in accordance with some embodiments of the present specification;
  • FIG. 12B illustrates an exemplary waveform for an intra-pulse dual energy structure, when a second (high energy) beam pulse is injected at an optimal time in accordance with some embodiments of the present specification
  • FIG. 13 is an exemplary flow chart illustrating a method of intra-pulse tuning, in accordance with some embodiments of the present specification
  • FIG. 14 is a graph illustrating a beam energy profile in an area around an optimum injection delay, in accordance with some embodiments of the present specification.
  • FIG. 15 is a flow chart illustrating an exemplary process for assessing an acceptable range of parameters and refining the requirements for dual-energy discrimination with dynamic dose control, in accordance with some embodiments of the present specification
  • FIG. 16 is a graph illustrating a plot of average per pulse relative energy deviation from steady state value against pulse duration and injection time error, typical for low energy, in accordance with some embodiments of the present specification
  • FIG. 17 is a graph illustrating a plot of average per pulse relative energy deviation from steady state value against pulse duration and injection time error, typical for low energy, in accordance with some embodiments of the present specification
  • FIG. 18 is an exemplary graph illustrating how to choose acceptable range of parameters for use in material discrimination with dynamic dose control, in accordance with some embodiments of the present specification.
  • FIG. 19 is a flow chart illustrating an exemplary process of generating a multiple-energy X-ray pulse, in accordance with some embodiments of the present specification.
  • each of the words “comprise” “include” and “have”, and forms thereof, are not necessarily limited to members in a list with which the words may be associated. It should be noted herein that any feature or component described in association with a specific embodiment may be used and implemented with any other embodiment unless clearly indicated otherwise.
  • multiple-energy shall refer to an X-ray inspection modality in which differential transmission through a medium by X-rays of distinct spectral composition is used to characterize the medium.
  • pulse duration refers to the duration of time that RF excitation is applied to a linac accelerating structure.
  • breaking point of a current pulse of duration tn+tn is defined to be the value of ti/t H , where h . and In refer, respectively, to durations of the current pulse during which an electron beam emitted from an accelerating structure is characterized by low- and high-energies, respectively.
  • any pair of sub-pulses may be characterized by a breaking point that is defined as the value of h . tin where h . and in refer, respectively, to durations of current sub-pulses.
  • a breaking point of a set of current pulses or sub-pulses shall be said to be“dynamically variable” if the breaking point is adapted to be varied from one pair of current pulses or sub pulses to another pair of current pulses or sub-pulses.
  • an end point of a pulse may also be characterized as“dynamically variable” if the end point is adapted to be varied from one current pulse to another current pulse.
  • current level refers to an average flux of electrons incident upon the target, expressed in milliAmperes (mA), and averaged over a specified duration of time. Unless otherwise indicated, the specified duration over which an average is taken is the duration of a pulse.
  • current amplitude refers to a value of an instantaneous flux of electrons incident upon the target, expressed in mA.
  • onset delay refers to a period between application of an RF field to an accelerating structure and injection of a pulse or sub-pulse of electron current into the accelerating structure. Where there are multiple sub-pulses of electron current, then the cumulative onset delays of the respective sub-pulses make up a sum of onset delays.
  • the term “Bremsstrahlung” may be used to denote X-ray emission produced through impingement of high-energy electrons onto a metallic target, and, additionally, the physical process involved in that phenomenology.
  • steady state in general, refers to a period of substantially constant or unvarying condition, such as, for a given wave or signal, preceding or subsequent values, over a predefined period, that are within ⁇ n% of each other.
  • a steady state condition often follows a period of substantially changing or varying condition, such as, for a given wave or signal, preceding or subsequent values, within a predefined period, that are in excess of ⁇ n% of each other.
  • the n value depends on specifics of applications and can typically vary from 10% or more to 1% or less.
  • the first process - exponential approach to“steady state” value - is described by separately first or separately second term of equation (10). Mathematically, it takes an infinite time to reach steady state value. Technically, it takes t ⁇ 2.3 t to reach 90% or t ⁇ 4.6 t to reach 99% of the steady state value.
  • the second process is described by equation (10) as a whole.
  • Two exponential processes (first term and second term of equation (10)) characterized by the same timing constant t but different amplitude with opposite sign. There is unique time ho when resulting sum of two exponents become time-independent and, mathematically, reaches“steady state” value described by equation (11) precisely at time ho.
  • Various embodiments of the invention described herein employ variation of the spectral content of an X-ray pulse during the course of the pulse to discriminate differences in X-ray transmission of a medium in different energy regimes.
  • Approaches taught in accordance with the present invention are particularly advantageous in cases where high speed of scanning is required, such as train or high-throughput scanners.
  • a novel apparatus and novel methods are provided that may advantageously create a pulse profile of a multi-energy beam in such a manner that would improve material discrimination while preserving the highest possible scanning speed and allow optimizing dose to cargo and environment. Additionally, embodiments of the present specification provide methods of fine adjustment of optimal delay for low and high energy pulses for single energy, interlaced or intra-pulse operation.
  • a novel source of penetrating radiation designated generally by numeral 20, in accordance with an embodiment of the present invention, is now described with reference to FIG. 2.
  • Used in conjunction with linac 21 are an X-ray target 24, an RF-source 25, an RF-source modulator 26, an RF isolator 27 and an electron gun modulator 28.
  • An RF-circuit 29, comprising RF-source 25 and RF-source modulator 26, provides a constant level of microwave power 250 within pulse duration / RF .
  • Electron gun 23, driven by e-gun modulator 28, provides an accelerated electron beam 220 characterized by a two-level injection current pulse 210 (also referred to herein as“the pulse”) into accelerating structure 22 with a total duration t p ⁇ tRF.
  • Injection current pulse 210 may also be referred to herein as “injection current,” and its amplitude, which, as defined above, corresponds to its instantaneous value of electron flux in mA, denoted h and I H .
  • the first portion 212 of the pulse 210 characterized by a higher amplitude of the injection current , due to higher beam loading creates a low energy portion of the beam pulse, where the low energy portion is designated by W L .
  • W L refers both to the low energy portion of the pulse, and to the value of the instantaneous endpoint energy characterizing the low energy portion of the pulse. The same applies, mutatis mutandis, to W H , the high energy portion of the pulse.
  • the second portion 214 of the injection current pulse with lower amplitude I H produces a high energy portion of the beam pulse W H .
  • the “breaking point” of the pulse which, as defined above, has the specialized meaning of the value of ti/tH, may be variable, within the scope of the present invention, thereby enabling dynamic control of the dose of emitted X-rays to cargo and environment.
  • the breaking point may advantageously be varied from pulse to pulse, rendering it a dynamically variable breaking point.
  • FIG. 3 where dependence of energy and current within a microwave pulse is depicted.
  • Dashed line 32 shows the accelerated beam current
  • solid line 34 represents the beam energy.
  • Dotted line 30 shows energy dependence at constant current I H , as previously discussed.
  • WL(O.-I.5) PS 3.9 MeV
  • WH(I.8-3.3) S 5.8 MeV.
  • “energy level” refers to an average per sub-pulse duration electron beam energy.
  • An appropriate reference to the end-point energy of an ensemble of photons, distributed in energy according to an essentially Bremsstrahlung spectrum of photon energies can be made based on the electron beam energy spectrum.
  • Optimizing coupling coefficient bo of the accelerating structure for the parameters of the single energy beam is known in the art and has been described in the Background Section above.
  • the accelerating structure 22 is over-coupled (coupling coefficient /f /, also h > bo) for all values of accelerating current (7) and RF -power ( P ) considered for operation.
  • a linac 41 is shown that is similar to the linac 21 shown in FIG. 2.
  • the accelerating system 20 is based on a standing wave structure 42 (otherwise referred to herein as a “standing wave resonator”), the distinction of which with respect to a traveling wave structure has been laid out by Miller (1986).
  • the coupling coefficient bo is chosen to be optimal at the current , using the algorithm that was laid out in detail above.
  • the value of h is chosen to provide energy W L , and this energy value W L remains constant over an entire sub-pulse duration if h is applied with delay hi with respect to the beginning of the RF pulse.
  • Low energy current delay hi is defined by equation (4) above. At the end of the low energy pulse (after / /.
  • I H is chosen to provide W H , and this energy level remains constant if I H current is applied with delay t bH counting from the end of low energy pulse / /..
  • the high energy pulse delay is defined by equation:
  • the ri, point may be allowed to vary, thereby allowing the ratio ti/tn (defined herein as the“breaking point”) to be varied, and thus advantageously providing for dynamic control of the X-ray dose to cargo and environment.
  • the average current during the lower energy portion of the pulse will be referred to herein as the low energy current, and, mutatis mutandis, the average current during the higher energy portion of the pulse will be referred to herein as the high energy current.
  • the energies within each portion of the pulse will remain constant as long as the“low energy” current begins to be applied after a delay of fez, and as long as the“high energy” current is applied with a delay of t bH.
  • the constancy of energy within each of the low energy and high energy portions of the pulse is beneficial for material discrimination: the energy spectrum of X- ray beam remains constant hence no additional calibration point(s) is required.
  • parameters such as bo, r, L, P H , P L , I H , h are not known with enough accuracy to guarantee necessary constant value of the beam energy for both low and high energy level. Adjustments to optimal delay values are required if energy spectrum changes while dynamically changing pulse duration of the beam.
  • the adjustments can be performed based on parameters that are typically available for monitoring for most of accelerators. Such adjustments can be performed based on assessment of parameters that are typically used for monitoring particle accelerators and beams performance.
  • Such parameters for example are: instant value of electron beam energy, average energy per pulse (sub-pulse), instant value of the RF-Power reflected from the accelerating cavity with single or multiple current pulses injected, and X-ray beam intensity integrated over the pulse or sub-pulse duration.
  • Linear electron accelerator for applied applications typically do not have sophisticated equipment for direct monitoring of beam energy, energy spectrum of the beam, or even electron beam output.
  • adjustments to optimal delay values may be performed based on an analysis of reflected power waveform and consequently iteratively adjusting injection delay ( tbi and //, // ). The exemplary embodiments of adjusting the injection delay are described further in a subsequent section.
  • Information pertaining waveform of the power reflected from accelerating structure is commonly available for most RF accelerators. Additionally, an analysis of normalized intensity dependence vs. pulse duration may be performed followed by fine re adjusting of the injection delay. X-ray beam intensity measurements are also typically available for linacs with X-ray output.
  • the injection of electron beam pulses is timed, by applying predefined delays, in order to achieve a first sub-pulse, at a first beam current amplitude, and a second sub-pulse, at a second beam current amplitude, that are different and have minimized deviations relative to predefined steady state energy levels.
  • a system that determines the required pulse delays and achieves the optimized injection of electron beam pulses is shown, comprising an exemplary linac system 600 with intra-pulse operation and a directional coupler 602 for extracting reflected power waveform.
  • a linac 61 includes a standing wave accelerating structure 62, and an electron gun 63 serving as an injector of electrons emitted by cathode 635. Further included are an X-ray target 64, an RF-source 65, an RF-source modulator 66, and an RF isolator 67.
  • the standing wave accelerating structure 62 is connected to the RF-source 65 with feeding waveguide 622 and characterized by coupling coefficient b V which is chosen to provide over-coupling conditions (b V > 1 ) of the accelerating structure in presence of the accelerating current with highest amplitude I max.
  • Further linac includes an electron gun modulator 68.
  • electron gun modulator 68 may also be referred to herein as a gun-controller 68 as it controls the injection of electron beam current.
  • An RF-circuit 69 comprising RF source modulator 66 and RF source 65, provides either a constant level of microwave power ( P ) 600a within pulse duration t RF or two-level (multi-level) microwave power function ⁇ P L , P H ) 600b for enhancing the energy difference between low-energy 614 and high-energy 642 sub-pulses.
  • the RF-circuit 69 may also be referred to herein as an RF-controller 69 as it controls the structure of microwave power feeding into accelerating structure 62.
  • Electron gun 63 driven by e-gun modulator 68, provides an electron beam characterized by a two-level injection current pulse 610 (also referred to herein as“the pulse”) into accelerating system 62 with a total duration t p ⁇ t RF .
  • Injection current pulse 610 may also be referred to herein as “injection current”, and its amplitude, which, as defined above, corresponds to its instantaneous value of electron flux in m A, denoted h and I H .
  • a first portion 612 of the pulse 610 characterized by a higher amplitude of the injection current , that due to higher beam loading creates a low-energy portion 641 of the beam pulse 640, where the low-energy portion is designated by W L .
  • W L refers both to the low energy portion of the pulse, and to the value of the instantaneous endpoint energy characterizing the low energy portion of the pulse. The same applies, mutatis mutandis, to W H , the high-energy portion of the pulse.
  • a second portion 614 of the injection current pulse with lower amplitude I H produces a high energy portion 642 of the beam pulse W H .
  • Sub-pulses duration h . and In may respectively refer to the duration of h and I H , and subsequently W L and W H .
  • the RF-circuit 69 provides a two-level pulse of microwave power 600b within pulse duration t RF , characterized by low-energy microwave power level P L and time duration of this level at least At+ri, and high-energy microwave power level P H with remaining time duration of RF-pulse t RF .
  • Electron gun modulator 68 provides electron beam characterized by a two-level injection current pulse with a total duration t p ⁇ t RF . The first pulse is characterized by a higher amplitude of the injection current h.
  • the high energy pulse WH can be created first by placing high energy microwave power level PH and appropriate injection current In at the beginning of the microwave pulse following low energy pulse WL that is created with appropriate microwave power level PL and injection current h. Therefore, in embodiments, the electron gun modulator 68 and RF-circuit 69 are configured to produce X-ray energy levels either in a descending or an ascending order.
  • RF-controller provides microwave power pulse of constant amplitude 600a
  • gun controller provides descending order of injection current 610 with amplitudes lH ⁇ h ⁇ Imax.
  • Gun-controller also generates low-energy sub-pulse optimal delay hi and high- energy sub-pulse optimal delay t bH in order to maintain constant amplitude of beam energy correspondently within low-energy sub-pulse 641 and high-energy sub-pulse 642.
  • the optimal delays hi and t bH for this case are defined by equations (7),
  • RF-controller provides microwave power pulse with two distinct power level with amplitudes PL ⁇ PH in ascending order 600b where low-energy sub-pulse PL has duration tbi+ti, gun controller provides descending order of injection current 610 with amplitudes l H ⁇ Ii ⁇ Ima x .
  • Gun-controller also generates low-energy sub-pulse optimal delay hi and high-energy sub-pulse optimal delay tbH_a in order to maintain constant amplitude of beam energy correspondently within low-energy sub-pulse 641 and high-energy sub-pulse 642.
  • the optimal delays hi and t bH for this case are defined by equations (8),
  • RF-controller provides microwave power pulse with two distinct power levels with amplitudes PH>PL in descending order where high-energy sub-pulse PH has duration tbii+hi
  • gun controller provides ascending order of injection current 610 with amplitudes l H ⁇ Ii ⁇ I max.
  • Gun-controller also generates first high-energy sub-pulse optimal delay t bH and second low-energy sub-pulse optimal delay t b L_ d in order to maintain constant amplitude of beam energy correspondently within low- energy and high-energy sub-pulses.
  • the optimal delays t bH and hi for this case are defined by equations (9),
  • electron gun modulator 68 further tunes the appropriate delay on the basis of an amount of power reflected from accelerating structure 62.
  • a directional coupler and microwave detector 602 are configured to determine an amount of power reflected from accelerating structure 62.
  • detector 602 operates in a region closed to a square low resulting in the signal proportional to the microwave power.
  • the objective to tune each delay is to maintain the amplitude of power reflected from accelerating structure 62 during accelerating beam current pulses h and/or I H within predefined deviation ranges of steady state values of reflected power correspondently for low and high energy pulse (or sub-pulse). Further, electron gun modulator 68 modifies the tuned delays ( hi , // >/.
  • an intra-pulse or a single-energy operation fine tuning of an injection point of a single high or low energy pulse may be achieved by first assessing an optimal delay for the high and low energy components assuming single beam pulse structure. This may be followed by analyzing the reflected power waveform shape and adjusting injection time for achieving acceptable level of beam energy deviation within injected beam pulse. This step may be performed for each energy component as a single energy beam pulse structure or an intra pulse dual-energy structure. Finally, normalized X-ray beam intensity distribution may be collected and analyzed. Fine adjustments to the injection time may be made accordingly.
  • FIG. 7 illustrates reflected power 704 from microwave cavity with no accelerated beam present, which may be detected by detector 602, in accordance with some embodiments of the present specification.
  • detector 602 operates in the region close to a square low resulting in a signal proportional to the microwave power.
  • the coupling coefficient is greater than one for any considered combination of microwave power P and accelerated current /, which means that the accelerating structure 62 is over-coupled for any considered mode of operation (low energy or high energy pulses).
  • a numerical value of the reflected power is represented by reflection coefficient (G) and Voltage Standing Wave Ratio ( V R).
  • VSWR for over-coupled cavity is also equal to the coupling coefficient /f and may be calculated from the reflected power waveform.
  • Accelerating current injected in the waveguide provides “additional matching” effectively reducing VSWR of accelerating cavity with current.
  • VSWR 1. The highest value of accelerating waveguide efficiency is reached at these parameters.
  • the reflected signal will remain constant during first beam pulse duration time (/ /. or ri / ) if delay is equal to the optimal delay defined by first equation in appropriate system of equations (7), (8) or (9).
  • the high-energy accelerating current I H for ascending order of energy levels or low- energy pulse (h) for descending order of energy levels may then be injected at the time of corresponding optimal delay t bH /t bH-a /t bL-d for the reflected signal to also remain constant during this beam pulse duration time ( tn or h) at pulse-specific value of VSWR.
  • FIG. 8 is a graph illustrating a simulated reflected power waveform 802 obtained with a low energy (/ /. ) 812 and a high energy (/ // ) 814 accelerated currents consecutively injected at optimum delays to form an intra-pulse dual-energy beam, in accordance with some embodiments of the present specification.
  • the field in the cavity remains constant over the beam duration time (/ /. ).
  • the high-energy accelerating current IH ⁇ II to be accelerated in the waveguide, is injected at the time of optimal delay t bH so that the reflected signal also remains constant during this beam duration time (hi) at the higher value of“high-energy” VSWR amplitude.
  • a“classical” reflected power waveform such as the ones illustrated in FIGS. 7 and 8, could be achieved with high restrictions on parameters such as but not limited to: RF-pulse shape such that it is perfectly square, presence of noise, and losses in the RF-line, among others.
  • RF-pulse shape such that it is perfectly square
  • noise such as but not limited to: RF-pulse shape
  • losses in the RF-line among others.
  • a“classical” reflected power waveform can be achieved at low RF-power signals with“sharp” leading and rear fronts.
  • FIG. 9 is a graph illustrating reflected power waveforms corresponding to a beam current pulse 912 obtained from an industrial linac.
  • Reflected power waveform 902 shown in yellow line, corresponds to beam current pulse 912, shown in red line, which is injected at a time close to an optimal time delay, as described above.
  • Another reflected power waveform 904 (“unloaded”) shown in grey, corresponds to the same RF-pulse but for a scenario when there is no accelerated beam current pulse. Reflected power waveforms 902 and 904 coincide until the beam current pulse 912 is applied. Within the beam pulse duration reflected power waveform 902 deviates from“unloaded” waveform 904 and demonstrates constant amplitude level.
  • a reference line 903 on the waveform is shown to demonstrate a steady state value of the reflected power signal (for specific accelerating beam and the accelerating structure parameters P, I, L, r, b V ) and the signal deviation from the steady state level 903.
  • Both reflected power waveforms 902 and 904 are contaminated with some reflections and noise most visible at the leading edge of the beam current pulse 912. The area depicting the contamination is enclosed within a dotted circle 914.
  • Reflected power waveforms 902 and 904 are also skewed by long rear front of the magnetron pulse.
  • the portion of waveform 902 within the beam current pulse duration (“loaded” waveform) has technically achievable minimal deviation from reflected power steady state level 903.
  • Tuning accelerating beam to achieve constant level 903 of reflected power 902 within an accelerated beam current pulse 912 also helps achieve more constant level of accelerated current itself. Reflected power level that mirrors linac accelerating field and the accelerated beam current amplitude are interdependent, especially in a buncher-type structure (that typically is the case for industrial linacs). Constant accelerating field results in constant injection beam capturing therefore a more uniform accelerated beam current amplitude is observed on the front portion of the beam current pulse in FIG. 9, and following FIGS. 10A and 10B.
  • FIGS. 10A and 10B illustrate two examples of an inaccurate beam injection time.
  • FIG. 10A is a graph illustrating an exemplary reflected power waveform 1002a when an accelerated beam current pulse 1012a is injected later than an optimal time (“over-shoot”). Reflected power waveform 1002a associated with beam current pulse 1012a coincides with“unloaded” waveform 1004a until the beam pulse 1012a is applied. Subsequently, reflected power amplitude reduces, exponentially approaching a steady-state level 1003a that has the same value as in FIG. 9 and marked with the reference line 903.
  • amplitude of reflected power waveform 1002a is not constant: a leading portion of the waveform is above steady state value 1003 a and an initial point 1042a of the“loaded” portion of waveform, exceeds the steady state value 1003a by at least two times.
  • the amplitude of point 1042a is depicted with a reference line 1005a.
  • the electron beam is accelerated by high electric field at the beginning of the current pulse 1012a and gains higher energy.
  • the energy amplitude varies within the beam pulse 1012a duration. Energy spectrum as well as beam intensity spectrum varies with pulse duration of the beam (that is, intensity vs. pulse duration is not linear).
  • current pulse 1012a needs to be moved to the left to the point where reflected power amplitude is equal to steady state value 1003a, thus achieving constant level of reflected power 1002a and, therefore, constant amplitude of beam energy within the beam pulse 1012a.
  • FIG. 10B is another graph illustrating an exemplary reflected power waveform 1002b when accelerated beam current pulse 1012b is injected earlier than an optimal time (“under shoot”).
  • a leading portion of the reflected waveform 1002b within the beam pulse is below steady state value 1003b.
  • a value of leading portion 1042b of the“loaded” portion of waveform 1002b is at least two times less than steady state value 1003b.
  • beam current pulse 1012b needs to be moved to the right toward the point where reflected power amplitude is equal to the steady state value thus achieving constant level of reflected power within the beam pulse and therefore a constant amplitude of beam energy.
  • the reflected power waveform may be continuously monitored and analyzed in order to determine the extent of adjustment to the injection time of beam current pulses. Additionally, with each analysis, the beam current pulse injection time may be adjusted to an optimal level needed to achieve a constant level of reflected power within each injected pulse, or to maintain the amount of power reflected from the accelerating structure within a predefined deviation range, such as outlined in subsequent section“Controlling Beam Energy Stability”. The analysis and adjustment may be performed for each energy component both as a single energy beam pulse structure within an RF-pulse or dual (multi) energy beam structure within single RF-pulse (intra-pulse).
  • normalized X-ray beam intensity distribution information may be collected and analyzed in order to make further finer adjustments to the beam current pulse injection time.
  • the finer adjustment may be based on determining a timing required to maintain a normalized X-ray beam intensity in a predefined range, wherein the normalized X-ray beam intensity is a function of the X-ray beam intensity relative to the corresponding pulse width.
  • the normalized X-ray beam intensity within a pulse can be used for such measurements.
  • Intensity of X-ray beam (e.g. dose rate D ) is a function of both beam energy and current. It may be assumed that the beam current is constant within the pulse width t p , therefore measuring dependence of the normalized intensity D/t p vs. pulse width t p provides information on the energy stability when beam pulse duration changes.
  • FIG. 11 is a graph 1100 illustrating an exemplary set of measurements of normalized on pulse width X-ray beam intensity (D) 1105 on y-axis and pulse width (t p ) 1110 on x-axis.
  • the data were collected for a single energy beam, where a starting point of the beam pulse was maintain constant. Beam intensity was normalized on the pulse duration and then on the average value of all data points.
  • the normalized on the pulse width X-ray beam intensity ( D ) is higher (up to ⁇ 7%) for the lower pulse durations (t p ), implying that the energy amplitude of the accelerated beam is higher at the beginning of the pulse (as in example of FIG. 10A).
  • the beam injection time may need to be reduced (pulse shifted to the left) if magnitude of deviation is outside of an acceptable range that may be defined using methods outlined in a subsequent section in the present specification relating to“Controlling Beam Energy Stability”.
  • FIGS. 12A and 12B illustrate exemplary graphs for an intra-pulse dual energy structure, in accordance with some embodiments of the present specification.
  • “loaded” reflected power waveforms 1202a and 1202b are shown that correspond to a low energy beam current pulse 1212 and high energy beam current pulses 1214a and 1214b, respectively.
  • Low energy beam current pulse 1212 may be placed at an injection time found during a preliminary adjustment stated above for a single energy beam pulse structure in context of FIG. 9.
  • “Unloaded” reflected waveforms 1204 are also shown.
  • Loaded reflected power waveforms 1202a and 1202b demonstrate constant level of reflected power during the low energy beam current pulse 1212 with an amplitude that equals to a reflected power steady state value for low energy pulse.
  • the high energy beam current 1214a is placed with higher than optimum injection delay.“Loaded” reflected waveform 1202a exceeds high energy reflected power steady state level 1203, at the beginning 1242a of the high energy beam pulse.
  • the highest amplitude of reflected power within high energy beam pulse is depicted with a line 1205a and exceeds steady state level by approximately 10%. Referring to FIG.
  • injection time of high energy beam pulse has been reduced by ⁇ 0.2ps (pulse moved to the left) and the level of the reflected power waveform 1202b remains constant and equals to high energy steady state value during the high energy beam pulse 1214b as per the various embodiments of the present specification.
  • normalized X-ray beam intensity distribution vs. sub-pulse duration for high energy component may be collected and analyzed. Necessary adjustment to injection time may be made accordingly.
  • total intensity of the dual energy pulse can be measured while the low energy pulse time is fixed and equal to the value of one of the pulse durations taken in the course of preliminary low energy tuning.
  • the intensity of the high energy sub-pulse component may be calculated as a difference of the total intensity and the known intensity of a low energy sub-pulse and then normalized using the high energy sub-pulse duration.
  • FIG. 13 is an exemplary flow chart illustrating a method of intra-pulse tuning, in accordance with some embodiments of the present specification. Referring simultaneously to FIGS. 6 and 13, at 1302, electron gun 63, controlled by modulator 68, generates a beam of electrons within standing wave accelerating structure 62.
  • Electron gun 63 controlled by electron gun modulator 68 is configured, at 1304, to modulate the beam of electrons prior to injection into accelerating structure 62 to achieve at least a first beam current amplitude (h) and a first beam current temporal profile of duration U and injected at a first delay of fez,, and a second beam current amplitude (In) and a second beam current temporal profile of duration hi and injected after a second delay of t bH .
  • a descending sequence of beam current pulses is injected into accelerating structure 62 in order to generate an ascending sequence of energy beams correspondently W L and W H .
  • a reverse sequence may be adopted.
  • the first beam current amplitude (In) is injected to form a high energy beam pulse W H , followed by a second beam current amplitude (/ /. ) to form a low energy beam pulse W L .
  • RF source 65 applies a radio frequency field with an RF power amplitude (P) and an RF power temporal profile characterized by an RF pulse duration (tup) to accelerating structure 62.
  • P RF power amplitude
  • Tup RF pulse duration
  • the beam of electrons is accelerated within accelerating structure 62 with the RF field to produce accelerated electrons toward target 64 for generating X-rays.
  • an amount of RF- power reflected from the accelerating structure 62 is determined with the aid of directional coupler and microwave detector 602.
  • electron gun 63 controlled by electron gun modulator 68 injects the beam of electrons at the first beam current amplitude (IP) after first time delay and then at the second beam current amplitude (In) after a second time delay.
  • the time delay for each beam current pulse may be determined using the equations (7), (8) or (9).
  • the time delays are determined so as to maintain an energy deviation from a correspondent steady state energy level of less than a predefined amount, as described above. Additionally, the time delays are determined such that the amount of RF -power reflected from the accelerating structure 62 during each beam sub-pulse is maintained within a predefined deviation range of correspondent steady state reflected power levels.
  • the time delay is adjusted to ensure that a normalized X-ray beam intensity lies within a predefined range, wherein the normalized X-ray beam intensity is a function of the X- ray beam intensity relative to the corresponding beam pulse width (t ⁇ or hi).
  • the beam of electrons is accelerated with the RF field within accelerating structure 62 to produce accelerated beam with dual-energy structure within a single RF-pulse.
  • the accelerated electrons impinge upon target 64 for generating X-rays by Bremsstrahlung.
  • energy amplitudes within each portion of an RF-pulse will remain constant as long as a“low energy” current begins to be applied after a delay of t bL , and as long as a“high energy” current is applied with a delay of t bH.
  • the constancy of energy within each of the low energy and high energy portions of the pulse is beneficial for material discrimination while duration of sub-pulses fc and/or In are varied.
  • the energy spectrum of X-ray beam remains constant within each pulse hence no additional calibration point(s) is required.
  • Minimizing beam energy variation for each energy level is crucial in using dual/multi energy method of material discrimination, in accordance with the embodiments of the present specification.
  • W is electron beam energy
  • P is RF pulse power, necessary to provide acceleration energy level
  • R is effective shunt impedance
  • L is accelerating system length
  • b, bo are coupling, and optimal coupling coefficients of RF-cavity
  • t, t p are time starting from beginning of RF pulse, and duration of the RF-pulse
  • t b , ho, d are time, optimum time for accelerating current to be turned on (injected in accelerating system), and deviation from optimum time.
  • t is the exponent defined as
  • Beam energy relative deviation from steady state value can be calculated from the following equation:
  • FIG. 14 is a graph illustrating a plot of energy dependence versus time (pulse duration) according to equation (10) for four cases.
  • dotted line 1402 shows electrical field build-up without any current injected
  • green line 1404 shows energy of the beam injected at optimum time and constant level of beam energy with no dependence on time
  • red line 1406 shows the energy level for an early injection (“undershoot”) of the beam pulse
  • blue line 1408 shows energy level for a late injection (“overshoot”) of the beam pulse.
  • Average electron beam energy per pulse is used for deriving interdependence of beam energy variation and timing parameters of the beam.
  • the average energy deviation depends on three timing parameters: the value of optimum delay ho, the deviation from optimum delay d, and pulse duration t p .
  • the relative energy deviation is given by:
  • FIG. 15 is a flow chart illustrating an exemplary set of steps for assessing the requirements for dual-energy material discrimination with dynamic dose control.
  • an acceptable energy variation may be defined based on specifics of material discrimination method and hardware. In an embodiment, it is assumed that for successful material discrimination, the relative energy deviation should be within ⁇ 1%. Therefore, this requirement determines the range and interdependence of timing parameters sufficient to maintain the relative energy variation within requested limit (of 1%) while employing dynamic dose variation.
  • Optimum delay ho is“external” timing parameter to this task that is mainly defined by energy and current of correspondent dual-energy components. Relative energy deviation for two values of optimum delay (considered in an example for single-pulse operation) is illustrated in FIGS. 16 and 17 in the form of surface plots.
  • FIGS. 16 and 17 represents the deviation from optimum delay d and the vertical axis 1604/1704 represents the pulse duration t p.
  • Value of relative energy deviation is represented with colors in the FIGS. 16 and 17.
  • the regions in green color 1606 represent relative energy deviation of ⁇ 1%; the regions in yellow color 1608 represent relative energy deviation in a range of (1-2)%; and the regions in red color 1610 represent relative energy deviation of > 2%.
  • the regions in light green color 1706 represent relative energy deviation of ⁇ 0.5%; the regions in dark green color 1707 represent relative energy deviation of (0.5-1.0)%; region in yellow color 1708 represent relative energy deviation in a range of (1-1.5)%.
  • the performance of the material discrimination method is constrained by low energy component.
  • Minimum pulse width is limited by accuracy of adjusting and maintaining injection delay value.
  • the accuracy of adjustments (4) should not exceed approximately 20 ns.
  • the accuracy of timing adjustment (including timing jitter) constraints minimum pulse duration at chosen accuracy of energy deviation. High energy component requirements are less restrictive and do not impose additional challenges on dual energy material discrimination performance with dynamic dose variation.
  • step 1506 energy stability may be adjusted and controlled by adjusting and maintaining injection time within required boundaries, determined at step 1504.
  • step 1508 the actual performance of material discrimination may be verified for a given set of hardware and software against requirements for material discrimination and dose variation with further corrections of the acceptable beam energy variation range at step 1510 and reiterating requirements assessment process.
  • tools are used for the purpose of adjusting and controlling the energy stability.
  • the tools for direct measuring of the beam energy may be used to measure an instant or an average per pulse energy value, for the monitoring, correction or adjustment of energy deviation. Since average per pulse energy is chosen as primary parameter for defining the limitation on energy deviation, the accuracy of adjustments is linear to required deviation. The values and accuracy of adjustments (and required deviation) are defined by equations (12), (13), (14) and (15).
  • reflected power (Pn e fl) is used as a tool for monitoring microwave processes in standing wave cavity and adjusting necessary parameters. Reflected power is a relatively more sensitive parameter of measuring necessary adjustment since SP Refl ⁇ W 2 .
  • Pn e fl for monitoring and correcting energy deviation is that Pn e fl signal (waveform) provides a “live signal” of the RF-field in the accelerating cavity (including beam loading). This signal needs very little processing.
  • X-ray beam intensity ( D ) may be an even more relatively sensitive tool for adjustment/control of beam energy since 5D ⁇ W 11 .
  • FIG. 18 is an exemplary graph illustrating how to choose acceptable range of parameters for use in material discrimination with dynamic dose control, in accordance with some embodiments of the present specification.
  • Line 1808 illustrates an acceptable deviation value of reflected power ( P Reji £ 2%) and dose rate (SD ⁇ 2.7%) to maintain SW ⁇ 1%.
  • FIG. 19 is a flow chart illustrating an exemplary process of generating a multiple-energy X-ray pulse, in accordance with some embodiments of the present specification.
  • a beam of electrons is generated with an electron gun.
  • the beam of electrons is characterized by an electron beam pulse duration.
  • the generated beam of electrons is modulated to achieve at least a first beam current amplitude and a first beam current temporal profile and a second beam current amplitude and a second beam current temporal profile, prior to injection into an accelerating structure.
  • the accelerating structure comprises a standing wave resonator.
  • a coupling coefficient for the accelerating structure is optimized to achieve greater than critical coupling (fi c >l, also h > bo) at any beam current.
  • a radio frequency (RF) field is applied to the accelerating structure.
  • the RF field is defined by an RF field amplitude, a specified temporal profile, and an RF pulse duration.
  • a temporal profile of power reflected from the accelerating structure is determined.
  • a detector is used to determine the temporal profile of power reflected from the accelerating structure to generate values indicative of amounts of reflected power (Pn e fl) ⁇
  • the detector may include a directional coupler and a microwave detector.
  • a first delay and a second delay are determined for injecting the current pulses.
  • the delays are determined based, at least in part, on the temporal profile of the amount of power reflected from the accelerating structure. In some embodiments, methods described in context of FIG. 15 are used to determine the delays.
  • the modulated beam of electrons at the first beam current amplitude is injected after the first delay to achieve a first sub-pulse.
  • the second beam current pulse with the second beam current amplitude is injected after the second delay to achieve a second sub-pulse.
  • a controller is configured to perform the injection of modulated beam of electrons.
  • the beam current pulses are injected to achieve a first steady state energy level of electrons for the first sub-pulse and a second steady state energy level of electrons for the second sub-pulse, where the first and the second steady state energy levels are different.
  • the first and the second beam current pulses are injected within the occurrence of a single RF pulse.
  • injecting of the modulated beam of electrons is performed at a time that is based, at least in part, on achieving, during the first sub-pulse, a minimized deviation of energy level relative to the first energy steady state level and on achieving, during the second sub-pulse, a minimized deviation of energy level relative to the second energy steady state level.
  • a duration of the first sub-pulse is different from a duration of the second sub-pulse. Duration of either the first sub-pulse or the second sub pulse is variable. Minimum duration of any sub-pulse may be zero and the maximum duration may be defined by a function of the RF pulse duration, a time delays for the injecting of the modulated beams of electrons, and durations of one or more other sub-pulses.
  • the modulated beam of electrons is injected at a time that is based, at least in part, on achieving, during the first sub-pulse and during the second sub-pulse, a minimized deviation of reflected power (Pit c/i ) from the accelerating structure relative to a steady state level of reflected power magnitude during each sub-pulse.
  • the modulated beam of electrons is injected at a time that is based, at least in part, on achieving, during the first sub-pulse and during the second sub-pulse, a minimized deviation of a normalized on the pulse duration X-ray beam intensity for the first and second sub-pulses, respectively, relative to an X-ray beam intensity corresponding to the first/second sub-pulse steady state energy level.
  • the modulated beam of electrons is accelerated with the RF field within the accelerating structure to produce accelerated electrons.
  • the accelerated electrons impinge upon a target for generating X-rays by Bremsstrahlung.

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Abstract

Selon des modes de réalisation, la présente invention concerne un système et un procédé permettant de générer une impulsion de rayons X à énergie multiple. Un faisceau d'électrons est généré à l'aide d'un canon à électrons et modulés avant d'être injectés dans une structure d'accélération pour obtenir au moins une première et une seconde amplitudes de courant de faisceau spécifiques pendant la durée des profils temporels de courant de faisceau respectifs. Un champ de radiofréquence est appliqué à la structure d'accélération avec une amplitude de champ RE spécifique et un profil temporel RE spécifique. Les première et seconde amplitudes de courant de faisceau spécifiques sont injectées en série, chacune après un retard spécifié de manière à obtenir au moins deux énergies distinctes des électrons accélérés dans la structure d'accélération au cours d'une seule impulsion RF. Le faisceau d'électrons est accéléré par le champ radiofréquence dans la structure d'accélération afin de produire des électrons accélérés qui viennent heurter une cible pour générer des rayons X par effet Bremsstrahlung.
PCT/US2019/048483 2019-05-31 2019-08-28 Procédé et système de synchronisation d'injections de faisceaux d'électrons dans un système d'inspection de chargement à rayons x multi-énergie WO2020242511A1 (fr)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20120313555A1 (en) * 2009-07-08 2012-12-13 Ching-Hung Ho Interleaving multi-energy x-ray energy operation of a standing wave linear accelerator using electronic switches
US20140270086A1 (en) * 2013-03-14 2014-09-18 The Board Of Trustees Of The Leland Stanford Junior University Intra Pulse Multi-Energy Method and Apparatus Based on RF Linac and X-Ray Source
US20180368248A1 (en) * 2014-05-16 2018-12-20 American Science And Engineering, Inc. Source for Intra-Pulse Multi-Energy X-Ray Cargo Inspection

Family Cites Families (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20080211431A1 (en) * 2000-02-10 2008-09-04 American Science And Engineering, Inc. Pulse-to-Pulse-Switchable Multiple-Energy Linear Accelerators Based on Fast RF Power Switching
RU2246719C1 (ru) * 2003-07-04 2005-02-20 Общество с ограниченной ответственностью "Интроскан" Способ облучения конверсионной мишени импульсами тока ускоренных электронов и устройство для его реализации
US7110500B2 (en) * 2003-09-12 2006-09-19 Leek Paul H Multiple energy x-ray source and inspection apparatus employing same
US7492339B2 (en) * 2004-03-26 2009-02-17 E Ink Corporation Methods for driving bistable electro-optic displays
US7382861B2 (en) * 2005-06-02 2008-06-03 John M. J. Madey High efficiency monochromatic X-ray source using an optical undulator
CN1997256B (zh) * 2005-12-31 2010-08-25 清华大学 一种高低能x射线输出装置
CN101076218B (zh) * 2006-05-19 2011-05-11 清华大学 产生具有不同能量的x射线的设备、方法及材料识别系统
CN102440078A (zh) * 2008-08-11 2012-05-02 拉派斯坎实验室股份有限公司 使用强度调制的x射线源的系统及方法
US7792241B2 (en) * 2008-10-24 2010-09-07 General Electric Company System and method of fast KVP switching for dual energy CT
US8942351B2 (en) * 2010-10-01 2015-01-27 Accuray Incorporated Systems and methods for cargo scanning and radiotherapy using a traveling wave linear accelerator based X-ray source using pulse width to modulate pulse-to-pulse dosage
US9167681B2 (en) * 2010-10-01 2015-10-20 Accuray, Inc. Traveling wave linear accelerator based x-ray source using current to modulate pulse-to-pulse dosage
US9772427B2 (en) * 2013-11-14 2017-09-26 Tsinghua University Multiple-power multiple-dosage accelerators, rapid examination systems and rapid examination methods thereof
CN108450029B (zh) * 2015-11-09 2021-07-20 美国科学及工程股份有限公司 移动x射线扫描速度控制
KR101827726B1 (ko) * 2016-07-27 2018-02-12 이비테크(주) 멀티플 및 엑스선회절격자 선택형 위상차 엑스선 영상장치
US10641918B2 (en) * 2017-10-28 2020-05-05 Radiabeam Technologies, Llc Adaptive cargo inspection based on multi-energy betatron

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20120313555A1 (en) * 2009-07-08 2012-12-13 Ching-Hung Ho Interleaving multi-energy x-ray energy operation of a standing wave linear accelerator using electronic switches
US20140270086A1 (en) * 2013-03-14 2014-09-18 The Board Of Trustees Of The Leland Stanford Junior University Intra Pulse Multi-Energy Method and Apparatus Based on RF Linac and X-Ray Source
US20180368248A1 (en) * 2014-05-16 2018-12-20 American Science And Engineering, Inc. Source for Intra-Pulse Multi-Energy X-Ray Cargo Inspection

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