RU2452143C2 - Method of generating deceleration radiation with pulse-by-pulse energy switching and radiation source for realising said method - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention is a method of generating deceleration radiation with pulse-by-pulse energy switching and a radiation source for an inspection system with a pulse-by-pulse energy switching system between two controlled values, with independent control of the dose rate for each energy. The source has local radiation protection, provides for each energy small beam diameter on the deceleration target, high percentage of particles captured in the acceleration mode and small width of the energy spectrum. The source is based on an accelerating structure with a standing wave, which is powered by a compact multibeam klystron with low beam voltage and focused by permanent magnets. Pulse-by-pulse switching of the value of the energy of the accelerated electron beam between two values at the same frequency is achieved by switching the value of input power of the klystron from pulse to pulse and, consequently, the output power of the klystron and amplitude of the field in the accelerating structure. The required dose rate is ensured by switching from pulse to pulse voltage of the control electrode of the electron gun and, consequently, the value of the current of the beam injected into the accelerating structure.

EFFECT: simple system, reduced dimensions and high reliability of the radiation source.

20 cl, 5 dwg

Description

The invention relates to the field of physics of charged particle beams and accelerator technology, in particular to the technology of electron acceleration in a pulsed linear accelerator with adjustable beam energy, more specifically, to a method for generating bremsstrahlung with pulse-by-pulse energy switching and to the design of a linear electron accelerator designed for inspection complexes.

Pulse linear electron accelerators are widely used in customs inspection complexes designed to control the contents of heavy containers. The accelerated electron beam is focused on the braking target mounted at the output of the accelerating structure, the generated bremsstrahlung is collimated, part of the radiation that has passed through the inspected object is detected by a line of detectors. Based on the signals of the detectors, the image of the object content is reconstructed.

Inspection complexes based on electron accelerators with pulse-by-pulse switching of the energy and current of the accelerated beam have been intensively developing in the last decade. The need for bremsstrahlung sources with energy switched from pulse to pulse between two or more values is due to the possibility of using them to evaluate the elemental composition of the inspected object and, therefore, to detect certain, for example, fissile, materials [Ogorodnikov, S .; Petrunin, V. (2002). "Processing of interlaced images in 4-10 MeV dual energy customs system for material recognition." Physical Review Special Topics - Accelerators and Beams 5 (104701)].

Almost all active accelerators for inspection systems, in particular the most widely used accelerators from Varian Medical Systems Inc., (USA, Whittum, DH, Trail, ME, Meddaugh, GE, State of the art in medical and industrial linear-accelerator systems, Vacuum Electronics Conference, 2008. IVEC 2008. IEEE International, Publication Date: 22-24 April 2008, p. 8-11) and Nuctech accelerators (China, Ch.Tang, H. Chen, Y. Liu, X. Wang, Low -Energy Linacs and their Applications in Tsinghua University, Proceedings of LINAC 2006, Knoxville, Tennessee USA, p. 256-258), are built using a magnetron as a source of microwave power, which allows to satisfy a number of important requirements for such accelerators - compact st, mobility and relatively low cost.

Important requirements for the accelerator for the inspection complex, including the accelerator with pulse-by-pulse switching of energy, along with compactness and low weight are a low radiation background outside the working area, a small beam size on the braking target, high stability of the beam energy and dose rate, and the ability to control power doses are independent for each energy.

When implementing a linear electron accelerator with pulse-switching energy, a number of specific problems arise due to the need to change the increase in particle energy along the entire length of the accelerating structure or in its part. In particular, the following problems arise.

1. When changing the energy of the accelerated beam by a pulse by changing the level of the accelerating field in a linear accelerator, in which a magnetron is used as a high-frequency energy source, it is necessary to change the level of high-frequency power generated by it, which is achieved by a pulse-by-pulse change in the amplitude of the high voltage pulse supplied to the magnetron cathode. When the amplitude of the high-voltage pulse changes, the frequency of the oscillations generated by the magnetron changes, which requires special measures to compensate for the mismatch of the frequency of the high-frequency signal and the resonant frequency of the accelerating structure. In addition, if, together with the switching of the amplitude of the high-voltage pulse, pulse-by-layer switching of the magnetron magnetic field is not carried out, the latter operates in a non-optimal mode with a significantly narrowed switching range of high-frequency power and, consequently, the energy of the accelerated beam, which negatively affects the sensitivity of the detection method of substances.

2. In case of pulse-by-pulse change in the energy of the accelerated beam due to a change in the level of the accelerating field in a linear accelerator, in which a klystron is used as a source of high-frequency energy, a change in the level of the high-frequency power amplified by it is achieved by a pulse change in the amplitude of a low-power high-frequency input signal with a constant frequency at a constant amplitude high voltage pulse supplied to the klystron cathode. Compared to a magnetron, this provides a wider range of energy switching, greater stability of the accelerated beam energy and the dose rate of bremsstrahlung. However, the single-beam klystrons currently used have large dimensions and mass due to the focusing solenoid, operate at high voltage, requiring oil isolation, which significantly increases the size and cost of electron accelerators created on their basis.

A linear electron accelerator is known, which can operate in a pulse-by-pulse energy switching mode (RU 2282955 C2), comprising an electron source, a microwave generator, power and control devices, an accelerating system that contains a grouping section with a standing wave and an accelerating section with a traveling wave, each which contains connected cells with tubes on the axis for the drift of the beam of accelerated electrons and windows on the periphery for electromagnetic coupling, while the accelerator contains a high frequency input device hydrochloric power connected to the first cell along the beam accelerating section bordering the last cell of the grouping section, and microwave power output device, connected to the last cell of the accelerating section.

Pulse-based energy regulation is carried out by changing the current of accelerated particles, which, presumably, should not affect the amplitude of the accelerating field in the grouping part of the accelerating system and, due to the load of the beam current, reduce the energy gain in the accelerating part.

The main disadvantage of the proposed option of pulse-by-pulse regulation of the beam energy is the interconnection of the dose rate and the beam energy, which does not allow for independent regulation of the dose rate for each energy level separately.

There is also known a linear electron accelerator circuit with pulse-switching energy (US 7,208,889 B2), containing:

- a power source generating electromagnetic waves;

- an injector producing pulses of charged particles;

- the first accelerating section, adapted to receive these pulses of charged particles, to obtain the specified electromagnetic waves and to transfer their energy to the indicated momenta of the particles;

- a second accelerating section adapted to receive said impulses of charged particles from said first section and to transfer energy to said impulses of charged particles;

- a phase shifter installed between the specified power source and the specified second accelerating section, adapted to alternately change the phase of these electromagnetic waves and for delivering these electromagnetic waves to the specified second accelerating section in the desired phase.

It is known that dividing the accelerating structure into two sections with separate high-frequency paths significantly complicates the microwave power supply system and the vacuum system, requires a complex control system and frequency adjustment of each of the sections.

Known electron accelerator for generating high-energy bremsstrahlung with pulse-by-pulse switching of the energy of bremsstrahlung between two values and with independent regulation of the dose rate for each energy value, including a source of bremsstrahlung, a high-frequency power system, a modulator of the control electrode of an electron gun, providing pulse-by-pulse switching of the electron gun beam current ; high-voltage power system, cooling system, accelerator controller, control console and brake target (US 7,130,371 B2). In this device, the bremsstrahlung source comprises an injector adapted to generate an electron beam from a first voltage pulse or a second voltage pulse and transmit it to an accelerating section adapted to generate and accelerate pulses of an electron beam by means of pulses of an electromagnetic signal.

The high-frequency power system includes at least two master oscillators adapted to produce pulses of a first electromagnetic signal of a first frequency and pulses of a second electromagnetic signal of a second frequency; a switch adapted to transmit the indicated pulses of the electromagnetic signal of the first frequency or the indicated pulses of the electromagnetic signal of the second frequency, the pathogen and the amplifier is a klystron for amplifying the amplitude of these pulses of the electromagnetic signal.

The high-voltage power system comprises a modulator of said amplifier, an injector modulator adapted to generate said first voltage pulse of a first amplitude and said second voltage pulse of a second amplitude, and a synchronization device of said injector modulator and amplifier modulator. The radiation spectrum of the known accelerator is suitable for identifying various materials.

US 7,130,371 B2 also protects the method underlying this device.

The indicated device and method allow switching the energy level of the accelerated beam and the current value of the accelerated beam from pulse to pulse. The method of switching energy in the specified device is based on the dependence of the phase velocity of the electromagnetic wave in an accelerating structure with a traveling wave on the frequency of the electromagnetic signal. As the frequency of the electromagnetic signal increases, the phase velocity of the electromagnetic wave and, therefore, the energy of the accelerated beam decrease.

The method for switching the accelerated beam current is based on the dependence of the injector current (three-electrode electron gun) on the voltage at the control electrode. As the voltage at the control electrode increases, the beam current of the injected and accelerated beam increases.

Thus, switching from pulse to pulse at the same time the frequency of the master oscillator and the voltage at the control electrode, it is possible to provide pulse-by-pulse switching of the upper limit of the radiation energy generated by the accelerated electron beam on the braking target, and to provide the dose rate of this radiation required for this energy. Fundamental for this method is the use of an accelerating structure on a traveling wave and a klystron as an amplifier of a high-frequency signal.

The disadvantages of the device and method described in US 7,130,371 B2 are as follows. The use of an accelerating structure on a traveling wave excludes the possibility of creating a compact accelerator, since it is known that to achieve the same energy of the accelerated beam at the same power of the microwave source (klystron, magnetron) the length of the accelerating structure on the traveling wave should be approximately twice the length of the accelerating structure with a standing wave . In addition, an accelerating structure on a traveling wave requires the installation of a solenoid that is bulky and consumes a lot of power over its initial part to hold and focus the beam. Since the magnitude of the solenoid field cannot switch from pulse to pulse, these devices and methods do not allow obtaining an equally well focused beam at high and low energies.

The closest prototype of the proposed method is a method for generating bremsstrahlung with pulse switching energy (US 2010/003856311), which consists in:

- sequentially supplying the first input high-frequency power and the second input high-frequency power klystron, while the second input high-frequency power is different from the first;

- sequential amplification by the klystron of the first high-frequency pulses having a first power, and second high-frequency pulses having a second power different from the first power;

- sequential transmission of the first and second pulses of high-frequency power to the resonators of the same particle accelerator;

- feeding the klystron with the first electric power;

- sequential power supply of the electron gun of the second and third electric power, different from the first electric power;

- the creation and injection of the first and second electron beams into the resonators of the accelerator, while the first and second beams are based, at least in part, on electric powers other than the first electric power;

- sequential acceleration of the injected electrons to the first energy and a second energy different from the first energy, based at least in part on the first and second pulses of high-frequency power;

- sequential collision of the first and second currents of accelerated particles with a brake target to generate radiation having first and second different energies and first and second different corresponding dose rates.

The closest prototype of the proposed device is a radiation source (US 2010/003856311), including:

- an accelerating structure for accelerating electrons;

- an electron gun with the ability to switch the magnitude of the beam current from pulse to pulse between two preset values;

- a brake target located at the output of the accelerator, hit of accelerated electrons to which causes the generation of radiation;

- high voltage power system;

- a high-frequency power system containing a klystron for selectively supplying the accelerator with at least first and second high-frequency energy pulses having first and second different frequencies and an exciter supplying high-frequency power to the klystron;

- accelerator controller, including a frequency controller;

- cooling system.

In the main embodiment of the known method and device, a magnetron is used, the frequency of the generated oscillations of which can vary from pulse to pulse due to changes in the voltage of the supplying electric power, to ensure the accuracy of the frequency setting, control and correction devices are used. This principle of operation of the device is automatically transferred to a variant of the circuit with a klystron as a power source, which makes it inoperative without additional clarifications. The design of the klystron is not described.

The disadvantages of the known method of generation and radiation source are the need to switch the frequency of the RF power source or the use of two sources with different frequencies, which complicates the system and reduces its reliability, and the use of a conventional klystron is accompanied by the use of a solenoid and a high voltage power source with a voltage of over 100 kV with the corresponding an increase in the mass and dimensions of the device.

The technical result of the proposed utility model is to simplify the system, reduce its dimensions and increase the reliability of the radiation source for inspection systems with pulse-by-pulse switching of the bremsstrahlung energy level between two values and with independent dose rate control for each energy value.

The specified technical result is provided due to the fact that in the method of generating bremsstrahlung with pulse-by-pulse switching of energy, which consists in sequentially supplying the first input high-frequency power and the second input high-frequency power klystron, the second input high-frequency power being different from the first sequential klystron amplification of the first high-frequency pulses, having a first power and second high-frequency pulses having a second power different from the first power and, sequentially transmitting the first and second pulses of high-frequency power to the resonators of the same particle accelerator, feeding the klystron with the first electric power, sequentially supplying the control electrode of the electron gun with the second and third electric power, different from the first electric power, creating and injecting the first and second electron beams in the resonators of the accelerator, while the first and second beams are based, at least in part, on the second and third electric powers other than the first electrical power, sequentially accelerating the injected electrons to the first energy and a second energy different from the first energy, based at least in part on the first and second pulses of high-frequency power and the sequential collision of the first and second beams of accelerated particles with a stop target to generate radiation, having the first and second different energies and the first and second different corresponding dose rates, the transmission of the first and second pulses of high-frequency power to the resonators of one of the same accelerator is carried out in the form of pairs closely spaced in time, energy is regulated from pulse to pulse by adjusting the level of the accelerating field by changing the level of the output power of the RF source simultaneously with the regulation of the levels of the first and second currents of the electron beam, while at low, and at high energy levels, the accelerator operates at the same frequency, the first high-frequency pulse of a pulsed multipath klystron is aligned in time with the first current pulse electron beam, and the second power pulse is combined with the second current pulse, the first electric power supplied to the klystron and cathode of the electron gun from the energy source is the same for the first high-frequency input power and for the second high-frequency input power, the second electron power is supplied to the control electrode of the electron gun in series and a third electric power different from the first electric power supplied to the klystron and cathode of the electron gun, modulation the speed of the continuous electron flow from the electron gun is carried out in the first cell of the accelerating structure, in the second cell the flow is partially grouped into bunches, accelerated, focused and further grouped, the high-frequency voltage U _g (level of the accelerating field) at the gap of the first cell is selected to ensure maximum amplitude the first harmonic of the beam current in the center of the gap of the second cell

where: U ₀ is the voltage of the electron source,

n = 1, 2, 3 ...;

the level of the accelerating field of the third cell is equal to the field level of subsequent cells, and the frequency controller controls the frequency of the microwave signal generated by the synthesizer, which is part of the pathogen, based on data on the mode of operation of the accelerator and the temperature of the coolant.

In addition, the first electrons are injected into the accelerator resonators at the first beam current, while the first RF power pulses are transmitted to the accelerator, and the second electrons are injected into the accelerator cavities at the second beam current, different from the first beam current, while pulses of the second RF power are transmitted to the accelerator.

In this case, the first electric power, the second electric power and the third electric power are supplied from one source of electric power.

Another aspect of the invention is a radiation source, including an accelerating structure for accelerating electrons, an electron gun with the ability to switch the beam current from pulse to pulse between two preset values, a brake target located at the accelerator output, a high-voltage power system, and a high-frequency power system containing a klystron to selectively supply the accelerator with at least the first and second pulses of high-frequency energy and a pathogen, supplying high-frequency power to the klystron, the accelerator controller, including the frequency controller, and the cooling system, the electron gun is made of a three-electrode and contains a cathode, anode and a control electrode, the source of high-frequency energy is a pulsed multipath amplification klystron, the exciter is equipped with the ability to switch the power of the input high-frequency signal supplied to the input klystron, between two preset values from pulse to pulse of the accelerator at the same frequency proxy oscillations for both said high voltage power system energy values comprises a source of electric voltage of the control electrode of the electron gun, providing poimpulsnoe switching beam electron gun current and the source of electrical power (modulator) a source of RF power, the accelerating structure is a structure with a standing wave.

In addition, the accelerating structure contains a first (grouping) cell with a low level of the accelerating field, a second cell (accelerating and focusing) with a high field level, a third and subsequent (accelerating and focusing) cells with the highest level of the accelerating field, and the distance between the centers of the gaps of the first and the second cell ensures that the center of the accelerated bunch gets into the maximum of the accelerating field of the second cell with a phase shift between the cells of 180 °.

The distance L _g between the centers of the gaps of the first and second cells is determined by the ratio

where: β ₀ = ν ₀ / s,

ν ₀ - the value of the velocity of the electron beam at the entrance to the grouping cell,

λ is the wavelength of the microwave field of the source of high-frequency power in free space,

c is the speed of light

n = 1, 2, 3 ...

In addition, the klystron focusing system is made with permanent magnets, the specified pathogen consists of a synthesizer, a solid-state microwave amplifier and an electronic attenuator on p-i-n diodes, and the specified accelerating structure and the indicated electron gun are placed in a magnetic screen.

In addition, the brake target is mounted on a small diameter electron wire, an ionization chamber is installed after the brake target, the indicated electron gun, an accelerating structure with a magnetic screen, a brake target and an ionization chamber are installed inside the local radiation protection in which the slot is located.

In addition, a coupling loop is installed in the wall of the accelerating structure, these electron guns, the accelerating structure, and the electron wire with the brake target form a single vacuum volume isolated from the atmosphere by means of a high-frequency vacuum window installed in the waveguide, through which high-frequency power enters the specified accelerating structure, a getter pump is installed on the specified waveguide, which does not require a power source and is connected to the indicated volume through slots in the narrow waveguide wall, as well as ktrorazryadny pump, whose current value is determined by the level of vacuum in said screen coupled to said vacuum volume through slots in the narrow wall of said waveguide.

In addition, the modulator is configured to supply the klystron and the electron gun with the first electric power to generate both high-frequency power pulses by the klystron and to supply the accelerating structure with electron beams with both currents, the modulator being a solid-state modulator. In addition, the device may contain an electric power source separate from the modulator, attached to the control electrode of the electron gun with the ability to selectively apply at least the second and third different voltages to the control electrode.

The device and operation of the accelerator are illustrated in figures 1-4.

Figure 1 presents a block diagram of the proposed accelerator.

Figure 2 presents the timing diagram of the accelerator.

Figure 3 presents a photograph of a General view of the accelerator.

Figure 4 presents the energy spectrum of the accelerated beam in the mode of pulse-switching energy.

Figure 5 presents the pulse images of the beam in the energy switching mode and a scale grid with a pitch of 1 mm.

The invention is a compact electron accelerator for inspection systems with pulse-by-pulse switching of the energy level of bremsstrahlung between two adjustable values with independent regulation of the dose rate for each energy.

The accelerator contains a radiation source 1, a high-frequency power system 2, a high-voltage power system 3, a cooling system 4, an accelerator controller 5, a control console 6.

The specified radiation source includes an electron gun 7 with a cathode 8 and a control electrode 9, connected through a ceramic insulator to an accelerating structure 10 with a standing wave, designed to accelerate the electron beam 11 from the specified electron gun 2 to various final energy and focus it on the brake target 12, installed on the electric wire 13 and designed to generate bremsstrahlung 14.

The specified electron gun 7 and the specified accelerating structure 10 are surrounded by a magnetic shield 15. On top of the structure 10, correction coils 16 can be placed if necessary. These electron gun 7, the accelerating structure 10, the correcting coils 16 and the magnetic screen 15 are surrounded by radiation protection 17, in which a slot 18 for forming a spatial distribution of said bremsstrahlung. The ionization chamber 19 is installed after the indicated brake target 12. In one of the accelerating cells of the structure 10, a communication loop 20 (high-frequency antenna) is installed.

The accelerating structure 10 comprises a first (grouping) cell with a low level of the accelerating field, a second cell (accelerating and focusing) with a high field level, a third and subsequent (accelerating and focusing) cells with the highest level of the accelerating field, while the distance between the centers of the gaps of the first and the second cell ensures that the center of the accelerated bunch gets into the maximum of the accelerating field of the second cell with a phase shift between the cells of 180 °.

In one particular case, the distance L _g between the centers of the gaps of the first and second cells is determined by the relation

where: β ₀ = ν ₀ / c,

ν ₀ - the value of the velocity of the electron beam at the entrance to the grouping cell,

λ is the electromagnetic wavelength of the source of high-frequency power in free space,

c is the speed of light

n = 1, 2, 3 ...

The specified high-frequency power system contains a waveguide 21 with a pumping system 22 and a dividing vacuum window 23, placed between the accelerating structure 10 and the waveguide path 24 connected to the klystron 25 through a ferrite decoupling device 26, a pathogen 27, an insulating gas supply system 28 and a discharge sensor 29.

The pulse amplifying klystron 25, operating at a low voltage due to the use of a multi-beam design, is compact due to the use of a focusing system with permanent magnets and provides excitation of the microwave field of the accelerating structure 10. However, the possibility of using a low-voltage, therefore small-sized, modulator for the klystron can significantly reduce the size design even when creating a magnetic field by a solenoid.

The klystron 25 has a large gain, which allows the use of a pathogen 27 with a low output power, providing the ability to maintain high frequency stability; while the value of its output power can be switched from pulse to pulse with the desired repetition rate. As a source of high-frequency power for the accelerating structure, a small-sized multipath klystron can be used, similar, for example, to the KIU-147A klystron described in [Multy-beam klystrons with reverse permanent magnet focusing system as the universal rf power sources for the compact electron accelerators, IA Frejdovich, PVNevsky, VPSakharov et al., In Proceedings of RuPAC 2006, Novosibirsk, Russia, p. 100]. The klystron operates at low voltage, which allows the use of a small-sized modulator, electron beams are created using a multipath electron gun and pass them through the klystron resonators and drift tubes in a magnetic field created by permanent magnets. This design of the klystron allows, and together with devices to control the frequency of the pathogen, ensures the accuracy of matching the generated frequency with the resonant frequency of the accelerating structure with a sharp reduction in the mass and dimensions of the radiation source.

The specified high-voltage power system contains a high-voltage modulator 30 of the klystron and the cathode of the gun 7 and an electric power source 31 of the control electrode 9 of the gun 7.

The specified cooling system includes a cooling device 32 and a system of sensors 33 for measuring temperature and fluid flow.

The pulse current switching of the beam current is ensured by switching the voltage at the control electrode 9 of the electron gun 7 using the electric power source 31. The change in the final beam energy is achieved by changing the level of high-frequency power supplied to the input of the accelerating structure, the ratio of the maximum possible and minimum possible energies of the accelerated beam not less than two, and the beam diameter on the brake target in the entire range of energy changes is not more than 2 mm.

Pathogen 27 consists of a synthesizer, a solid-state microwave amplifier, and an electronic attenuator with p-i-n diodes. The attenuator is used to switch the output level of the pathogen from pulse to pulse. All of these devices are standard.

The communication loop 20 in one of the accelerating cells of the specified accelerating structure 10 is installed to control the level of high-frequency losses in the walls of the accelerating structure and, therefore, to control the level of the accelerating field and the energy of the accelerated beam.

To generate bremsstrahlung, a braking target 12 is used, which is located at the end of the electron line 13, which is installed at the output of the accelerating structure 10 and has a small diameter, which reduces the size and weight of radiation protection. The accelerated beam entering the center of the brake target 12 is provided with a magnetic screen 15 located around the electron gun 2 and the accelerating structure 10; to control the dose rate of bremsstrahlung after the brake target 12, an ionization chamber 19 is installed. To reduce the dose rate of spurious bremsstrahlung, an electron gun 2, an accelerating structure 10 with a magnetic shield 15, a brake target 12 and an ionization chamber 19 are installed inside the local radiation protection 17, which also provides formation of the required distribution of bremsstrahlung at the inspected object. The electron gun 2, the accelerating structure 10 and the electron wire 13 with the brake target 12 form a single vacuum volume isolated from the atmosphere by means of a high-frequency vacuum window 23 mounted between the waveguides 21 and 24, through which high-frequency power is supplied to the accelerating structure 10. To maintain a high level getter pump 22 is installed in the vacuum volume on the waveguide 21, which does not require a power source and pumps out the specified volume through the slots in the narrow wall of the waveguide 21. To control the level of vacuum and generation of blocking signals when the vacuum deteriorates, an electric discharge pump (not shown) is also installed on waveguide 21, connected to the vacuum volume through slots in a narrow wall.

Controller 5 synchronizes the operation of the accelerator systems and switches the blocking signals between the systems similarly to the prototype, but the frequency controller, receiving information from the sensors, adjusts, if necessary, the exciter that generates the signal at only one frequency, unlike the prototype. The management console 6 provides the installation of operating modes and monitoring the operation of the accelerator systems similarly to the prototype.

The timing diagram of the radiation source is shown in figure 2, where τ is the pulse duration, T ₁ - the distance between pulses in a pair of pulses, T ₂ - the distance between pairs of pulses. The functioning of the source is synchronized by the start and energy signals coming from the accelerator controller 5 (Fig. 1). The radiation source works as follows. The high voltage pulse generated by the modulator 30 upon arrival of the synchronization signal is supplied to the klystron 25 for sequential power supply of the klystron with the first electric power and to the cathode of the electron gun 8 for powering the gun with the first electric power, and from the electric power source 31 the high voltage pulse is supplied to the electronic control electrode guns 9 for sequentially supplying the control electrode with a second electric power and a third electric power different from the first electric power supplied to the klystron and cathode of the electron gun, providing conditions for the formation of a beam by an electron gun 7 and injection of the first and second electron beams into the accelerator resonators, while the first and second beams are based, at least in part, on the second and third electric powers, excellent from the first electric power, while the first electric power supplied to the klystron and cathode of the electron gun from the source of electric energy is the same for the first input high-frequency power and for the second input high-frequency power.

During the formation of the first and second electron beams, the electric power supplied to the klystron 25 remains unchanged.

As a result, an electron beam is formed at the output of the electron gun 7 with an energy equal to the voltage of the high-voltage modulator klystron 30, and with a current determined by the voltage of the electric power source 31 connected to the control electrode 9, which is input to the accelerating structure 10.

The klystron 25 sequentially supplies the first input high-frequency power and the second input high-frequency power from the pathogen 27, while the second input high-frequency power is different from the first, then the klystron sequentially amplifies the first high-frequency pulses having the first power, and the second high-frequency pulses having a second power other than first power, while the transmission of the first and second pulses of high-frequency power to the resonators of the same accelerator is carried out in the form of close p time-based pairs, for example, the time delay between pulses (T ₁ in FIG. 2) can be 500 μs.

In the process of amplification by a klystron of 25 different first and second high-frequency powers, the electric power supplied to it does not change.

The energy from pulse to pulse is controlled by adjusting the level of the accelerating field by changing the level of the output power of the RF source simultaneously with the regulation of the levels of the first and second currents of the electron beam, while the accelerator operates at the same and low energy levels frequency, the first high-frequency power pulse of the pulsed multipath klystron is time aligned with the first current pulse of the electron beam, and the second power pulse is combined with the second current pulse .

Then, through the ferrite decoupling device 26, the vacuum window 23 and the segments of the waveguide path 24, 21 sequentially transmit the first and second high-frequency power pulses to the input of the resonators of the accelerating structure 10 of the same particle accelerator, exciting an accelerating field in it.

The injected electrons are sequentially accelerated to a first energy and a second energy different from the first energy, based at least in part on the first and second pulses of high-frequency power. The modulation of the speed of the continuous electron beam from the electron gun is carried out in the first cell of the accelerating structure, in the second cell the stream partially grouped into bunches is accelerated, focused and further grouped, while the high-frequency voltage U _g (level of the accelerating field) in the gap of the first cell is selected from the condition the maximum amplitude of the first harmonic of the beam current in the center of the gap of the second cell

where: U ₀ is the voltage of the electron source,

n = 1, 2, 3 ...

The level of the accelerating field of the third cell is equal to the level of the field of subsequent cells.

The frequency controller controls the frequency of the microwave signal generated by the synthesizer, which is part of the pathogen, based on data on the mode of operation of the accelerator and the temperature of the coolant.

The specified electron beam of the electron gun 7, passing through the accelerating structure, interacts with the specified accelerating field, forms in clumps, focuses and accelerates to an energy whose value is determined by the level of the specified accelerating field. Then, the first and second beams of accelerated electrons sequentially collide with the stop target 12 mounted on the electron wire 13, resulting in the generation of stop radiation 14 having the first and second different energies and the first and second corresponding dose rates. By selecting the values of the second and third electric powers at the control electrode 9, close values of the dose rate are achieved at the first and second beam energies.

In one particular embodiment of the invention, the first electrons are injected into the accelerator resonators at the first beam current, while the first RF power pulses are transmitted to the accelerator, and the second electrons are injected into the accelerator resonators at the second beam current other than the first beam current, while while the pulses of the second RF power are transmitted to the accelerator.

In another particular embodiment of the method, consumers are supplied with first electric power, second electric power and third electric power from one electric power source.

Pulse-switched energy and dose rate of bremsstrahlung is as follows. The energy signal (figure 2) of the controller 5 for each pulse of the accelerator determines the power of the high-frequency signal generated by the pathogen, and thus determines the amplitude of the accelerating field in the accelerating structure 10, the energy of the accelerated beam 11 and the upper limit of the spectrum of bremsstrahlung 14. In addition, for each pulse of the accelerator, the energy signal of the controller 5 determines the voltage on the control electrode 9 and, thus, the magnitude of the current of the electron gun 7, the magnitude of the current of the accelerated beam 11 and dose rate of bremsstrahlung 14. The level of the accelerating field is monitored using an antenna 20 installed in one of the accelerating cells of the accelerating structure 10. The dose rate of the bremsstrahlung 14 is controlled using an ionization chamber 19 installed after the brake target 12.

To ensure that the accelerated electron beam 11 enters the center of the brake target 12, the parasitic magnetic fields in the electron gun 7 and the accelerating structure 10 are reduced to a level not exceeding the Earth’s magnetic field using a magnetic shield 15. The beam 11 can be adjusted to the brake target 12 using corrective coils 16.

The level of bremsstrahlung in the entire area around the brake target 12, with the exception of the working area, is reduced to a set value using radiation protection 17. To reduce the size and mass of radiation protection 17, the brake target 12 is mounted at the end of the electrical circuit 13 having a diameter substantially smaller than the diameter of the accelerating structure. The spatial distribution of the bremsstrahlung 14 in the working area is formed using the slot 18 in the radiation protection 17.

The working vacuum in a vacuum volume formed by an electron gun 7, an accelerating structure 10, a segment of a waveguide 21 with a vacuum window 23 and an electric wire 13 with a brake target 12, is supported by a vacuum system 22 consisting of getter and electric discharge pumps, and the evacuation of the indicated vacuum volume in the finished device carried out mainly by the specified getter pump, and the specified electric discharge pump is used to control the level of vacuum. This allows you to quickly enter the source into operating mode after prolonged storage, guarantees stability of parameters and reliable operation.

The cooling of the accelerating structure 10, the brake target 12, the high-voltage modulator 30 and the klystron 25 is carried out by a liquid with a constant temperature coming from the cooling device 32. The temperature and flow rate of the liquid at the inlet and outlet of the accelerating structure 10 is monitored using temperature and flow sensors 33.

To prevent high-frequency breakdowns, the indicated path 24 and the ferrite decoupling device 26 are filled with insulating gas using a gas supply system 28. In the event of a discharge on the vacuum window 23, in the waveguide path 24 or ferrite decoupling device 26, the discharge sensor 29 generates a blocking signal that disables the generation of high-frequency pathogen signal 27.

A general view of the radiation source is shown in FIG. 3. Figure 4 shows the results of measuring the energy spectrum of the accelerated beam using a magnetic spectrometer in the mode of pulse-switching energy. Figure 5 shows the pulse images of the beam in the energy switching mode obtained using a CCD camera, the operation of which was synchronized with the operation of the accelerator, also shows a large-scale grid, the step of which is 1 mm.

The industrial applicability of the claimed invention is guaranteed by the applicability of its constituent elements and assemblies in known structures with the provision of their properties and characteristics used in the present invention and is based on the test results of a prototype constructed in accordance with the above description.

Description of the proposed design is not published anywhere.

Claims (20)

1. A method of generating bremsstrahlung with pulse-by-pulse switching of energy, which consists in:
sequentially supplying the first input high-frequency power and the second input high-frequency power klystron, while the second input high-frequency power is different from the first;
the klystron sequentially amplifies the first high-frequency pulses having a first power and the second high-frequency pulses having a second power different from the first power;
sequential transmission of the first and second pulses of high-frequency power to the resonators of the same particle accelerator;
feeding the klystron with the first electric power;
sequentially supplying the control electrode of the electron gun with a second and third electric power different from the first electric power;
injection of the first and second electron beams into the accelerator resonators, wherein the first and second beams are based at least in part on the second and third electric powers other than the first electric power;
sequentially accelerating the injected electrons to the first energy and a second energy different from the first energy, based at least in part on the first and second pulses of high-frequency power; and
sequential collision of the first and second currents of accelerated particles with a brake target to generate radiation having first and second different energies and first and second different corresponding dose rates, characterized in that
first and second pulses of high-frequency power are transmitted to the resonators of the same accelerator in the form of pairs closely spaced in time;
energy from pulse to pulse is controlled by adjusting the level of the accelerating field by changing the level of the output power of the RF source simultaneously with the regulation of the levels of the first and second currents of the electron beam;
at the same time, both at low and at high energy levels, the accelerator operates at the same frequency;
the first high-frequency power pulse of the pulsed multipath klystron is aligned in time with the first current pulse of the electron beam, and the second power pulse is combined with the second current pulse;
the first electric power supplied to the klystron and cathode of the electron gun from the energy source is the same for the first input high-frequency power and for the second input high-frequency power;
serial power supply to the control electrode of the electron gun is carried out by a second electric power and a third electric power different from the first electric power supplied to the klystron and the cathode of the electron gun;
the modulation of the speed of the continuous electron flow from the electron gun is carried out in the first cell of the accelerating structure, in the second cell the stream partially grouped into bunches is accelerated, focused and further grouped, while the high-frequency voltage U _g (level of the accelerating field) at the gap of the first cell is selected from the condition the maximum amplitude of the first harmonic of the beam current in the center of the gap of the second cell

where U ₀ is the voltage of the electron source;
n = 1, 2, 3, ...;
the level of the accelerating field of the third cell is equal to the field level of subsequent cells;
the frequency controller controls the frequency of the microwave signal generated by the synthesizer, which is part of the pathogen, based on data on the mode of operation of the accelerator and the temperature of the coolant. 2. The method according to claim 1, characterized in that the first electrons are injected into the accelerator resonators at the first beam current, while the first RF power pulses are transmitted to the accelerator, and the second electrons are injected into the accelerator resonators at the second beam current, different from the first beam current, while pulses of the second RF power are transmitted to the accelerator. 3. The method according to claim 1, which consists in supplying a first electric power, a second electric power and a third electric power from a single electric power source. 4. A radiation source for implementing a method of generating radiation, including:
accelerating structure for accelerating electrons;
an electronic gun with the ability to switch the magnitude of the beam current from pulse to pulse between two preset values;
a brake target located at the output of the accelerator, hit of accelerated electrons on which causes the generation of radiation;
high voltage power system;
a high-frequency power system containing a klystron for selectively supplying the accelerator with at least first and second pulses of high-frequency energy and a pathogen supplying high-frequency power to the klystron,
an accelerator controller including a frequency controller;
cooling system, characterized in that
the electron gun is made of a three-electrode and contains a cathode, anode and a control electrode;
a source of high-frequency energy is a pulsed multipath amplification klystron;
the pathogen is equipped with the ability to switch the power of the input high-frequency signal supplied to the klystron input between two preset values from pulse to pulse of the accelerator, at the same frequency of generated oscillations for both energy values;
the specified high-voltage power system contains an electric voltage source of the control electrode of the electron gun, providing pulse-by-pulse switching of the electron gun beam current, and an electric power source (modulator) of the RF power source — the accelerating structure is made in the form of a standing wave structure. 5. The source according to claim 4, characterized in that the accelerating structure contains a first (grouping) cell with a low level of the accelerating field, a second cell (accelerating and focusing) with a high field level, a third and subsequent (accelerating and focusing) with the highest level accelerating field, while the distance between the centers of the gaps of the first and second cells ensures that the center of the accelerated bunch hits the maximum of the accelerating field of the second cell when the field phase between the cells is shifted 180 °. 6. The source according to claim 5, characterized in that the distance L _g between the centers of the gaps of the first and second cells is determined by the ratio

where β ₀ = ν ₀ / c;
ν ₀ is the value of the velocity of the electron beam at the entrance to the grouping cell;
λ is the electromagnetic wavelength of the high-frequency power source in free space;
c is the speed of light;
n = 1, 2, 3, ... 7. The source according to claim 4, characterized in that the klystron focusing system is made with permanent magnets. 8. The source according to claim 4, characterized in that said pathogen consists of a synthesizer, a solid-state microwave amplifier and an electronic attenuator with p-i-n diodes. 9. The source according to claim 4, characterized in that said accelerating structure and said electron gun are placed in a magnetic screen. 10. The source according to claim 4, characterized in that the brake target is mounted on a small diameter electric wire. 11. The source according to claim 4, characterized in that an ionization chamber is installed after said inhibitory target. 12. A source according to any one of claims 4, 9, 11, characterized in that said electron gun, said accelerating structure with said magnetic shield, said brake target and said ionization chamber are installed inside the local radiation protection. 13. The source according to p. 12, characterized in that in the specified local radiation protection is located slot. 14. The source according to claim 4, characterized in that a communication loop is installed in the wall of the accelerating structure. 15. The source according to claim 4, characterized in that said electron gun, said accelerating structure, and said electric wire with said brake target form a single vacuum volume isolated from the atmosphere by means of a high-frequency vacuum window installed in a waveguide through which high-frequency power is supplied to specified accelerating structure. 16. The source of claim 15, wherein in order to maintain a high level of vacuum in the indicated vacuum volume during the life of the accelerator, a getter pump is installed on the specified waveguide, which does not require a power source and is connected to the specified volume through slots in the narrow waveguide wall. 17. A source according to any one of paragraphs.15 and 16, characterized in that an electric discharge pump is installed on said waveguide, the current value of which is determined by the level of vacuum in said volume, connected to said vacuum volume through slots in the narrow wall of said waveguide. 18. The source according to claim 4, characterized in that the modulator is configured to power the klystron with first electric power to generate both high-frequency power pulses by the klystron. 19. The source according to claim 4, characterized in that it contains a source of electrical power, separate from the modulator, attached to the electron gun, with the ability to selectively apply at least the second and third different voltages to the control electrode of the electron gun. 20. The source according to p, characterized in that the modulator is a solid-state modulator.

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