RU2610712C1 - Method for generation of deceleration radiation with pulse-by-pulse energy switching and radiation source for implementation thereof - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention is a method for deceleration radiation generation with pulse-by-pulse energy switching and a source for implementation thereof with independent regulation of the radiation dose for each type of energy. The source is based on an accelerating structure with a standing wave, supplied by multibeam klystron. Pulse-by-pulse energy switching of an accelerated electron beam energy between the two values is achieved by switching of the high voltage pulse amplitude, that supplies the klystron from pulse to pulse. At that, the input RF klystron power pulses for low and high energy have the same amplitude and are genrated at the same frequency which varies in accordance with variation of the resonance frequency of the accelerating structure. The required dose power is provided by switching from electron gun control electrode voltage pulse to pulse.

EFFECT: increased service life of the klystron, increased stability of the accelerated beam parameters for each energy type and reduced energy consumption of particle accelerator.

21 cl, 4 dwg

Description

FIELD OF THE INVENTION

The invention relates to the field of physics of charged particle beams and accelerator technology and, more specifically, to a method for generating bremsstrahlung with pulse-by-pulse switching of energy and a radiation source for its implementation with independent control of the dose rate for each energy.

State of the art

One of the areas of intensive development of accelerator technology is associated with the creation of radiation sources based on linear electron accelerators with pulse-by-pulse switching of the energy and current of the accelerated beam, which are especially necessary in customs inspection complexes. The use of a radiation source in inspection complexes with switching energy from pulse to pulse between two or more values makes it possible to evaluate materials in the inspected object, to separate them according to the organic-inorganic criterion, and also to recognize groups of materials by the effective atomic number. Borders, ports, critical infrastructure in various countries of the world are actively equipped with such complexes.

The prior art method for generating bremsstrahlung with pulse-by-pulse switching of energy and a radiation source for implementing this method of generating radiation are described in patent RU 2452143 (C2), published May 27, 2012, most of which are also the authors of the present invention.

The specified known method of generating bremsstrahlung with pulse-by-pulse switching of energy is:

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 high-frequency power pulses to the resonators of the same particle accelerator in the form of pairs closely spaced in time;

feeding the klystron and cathode of the electron gun with a first electric power identical for the first input high-frequency power and for the second input high-frequency power;

sequentially supplying the control electrode of the electron gun with a second and third electric power different from the first electric power;

injecting the first and second electron beams into the accelerator cavities, 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 a first energy and a second energy different from the first energy, based at least in part on the first and second high-frequency power pulses; 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,

moreover, the regulation of energy from pulse to pulse is carried out by adjusting the level of the accelerating field by changing the level of output power of the high-frequency source simultaneously with the regulation of the levels of the first and second currents of the electron beam;

at low and high energy levels, the accelerator operates at the same frequency;

in the first cell of the accelerating structure, modulation of the speed of the continuous electron beam from the electron gun is carried out, acceleration, focusing and further grouping of the stream partially grouped into bunches is carried out in the second cell;

the high-frequency voltage U _g (accelerating field level) at the gap of the first cell is selected from the condition of ensuring 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 electric power supply of the klystron and the cathode of the electron gun and n = 1, 2, 3, ...;

the level of the accelerating field of the third cell is equal to the level of the accelerating field 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.

A known radiation source for implementing the above method of generating bremsstrahlung includes:

accelerating structure with a standing wave to accelerate electrons;

a three-electrode electron gun containing a cathode, anode and a control electrode, 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;

a high-voltage power system containing an electric voltage source of an electron gun control electrode, providing pulse-by-pulse switching of the electron gun beam current, and an electric power source (modulator) of a high-frequency power source;

a high-frequency power system containing a pulsed multipath amplification klystron for selectively supplying the accelerator with at least first and second high-frequency energy pulses, and a pathogen supplying a high-frequency power to the klystron and configured to switch the supplied power between two preset values, from pulse to pulse of the accelerator , at the same frequency of generated oscillations for both energy values;

an accelerator controller including a frequency controller; and

cooling system.

The indicated known method of generating bremsstrahlung with pulse-by-pulse switching of energy and a radiation source for its implementation have a number of advantages over analogues described in patent RU 2452143 (C2). A well-known source based on an accelerating structure with a standing wave fed by a compact multi-beam klystron with a low beam voltage and focusing by permanent magnets has local radiation protection and provides for each energy a small beam diameter on the braking target, a high percentage of particles trapped in the acceleration mode, and a small the width of the energy spectrum. Moreover, the pulse-by-pulse switching of the energy of an accelerated electron beam between two values at the same frequency is achieved by switching the input klystron power from pulse to pulse and, therefore, the output power of the klystron and field amplitude in the accelerating structure. Whereas the required dose rate is provided by switching from pulse to voltage pulse of the control electrode of the electron gun and, therefore, the magnitude of the beam current injected into the accelerating structure. Thus, the known solutions make it possible to simplify and reduce the size of the radiation source with pulse-by-pulse switching of energy, while increasing the reliability of its operation.

At the same time, in these known solutions, significant shortcomings were identified, consisting in the method for regulating (switching) the energy of the accelerated beam between two values realized here. As noted above, in known solutions, the accelerated beam energy is controlled by adjusting the level of the high-frequency output of the klystron supplied to the accelerating structure by sequentially supplying the klystron with the first high-frequency input power and a second high-frequency input power different from the first high-frequency input power. In this case, the first electric power supplied to the klystron and cathode of the electron gun from the energy source (modulator) is the same for both the first high-frequency input power and the second high-frequency input power.

The essence of these disadvantages is as follows. Firstly, the electrical power of the klystron, i.e. the first electric power, the same for both energies of the accelerated electron beam, is selected so as to obtain the highest output high-frequency klystron power required to accelerate the electron beam to a higher energy from the two energies of the accelerated beam. At the same time, the indicated first electric power turns out to be excessive for less energy of the accelerated beam and the unspent part of the electric energy is uselessly dissipated in the klystron collector, which leads both to excessive energy consumption and to a decrease in the life of the klystron due to excessive selection of the cathode current and excessive heat load collector. In this mode of operation, the working point of the klystron for the lower energy, of the two energies of the accelerated beam, is located on a linear portion of its amplitude characteristic, characterized by a strong dependence of the output high-frequency power of the klystron on the input high-frequency power, as can be seen in FIG. 1. The latter circumstance reduces the stability of the energy of the accelerated beam and the dose rate of the generated bremsstrahlung for a low-energy pulse.

Secondly, the supply to the cathode of the electron gun of pulses of an unchanged first electric power means that the high voltage value U ₀ of the cathode supply of the electron gun in the formula for optimal particle grouping by the first accelerating cell

is unchanged to obtain both the first and second levels of the accelerating field (for the first and second energies of the accelerated beam), while the magnitude of the high-frequency voltage U _g at the gap of the first cell changes. Thus, the conditions for optimal grouping are not satisfied in the known solutions for either the first, the second, or both energies of the accelerated beam.

The need to address the above disadvantages of the solutions of the prior art formed the basis for the creation of this group of inventions. Moreover, the method for generating bremsstrahlung with pulse-by-pulse switching of energy and the radiation source for its implementation, known from patent RU 2452143 (C2), are the closest analogues of the claimed inventions and are selected as their prototypes.

Disclosure of invention

The present invention was the creation of a method for generating bremsstrahlung with pulse-by-pulse switching of energy and a radiation source for its implementation on the basis of a new method of regulating (switching) the energy of an accelerated electron beam between two values, eliminating the disadvantages of the prior art. Namely, the object of the present invention was to provide a method for controlling (switching) the energy of an accelerated beam between two values, ensuring that the klystron operating mode is optimal for each energy value and, thus, increasing the stability of parameters of accelerated electron beams for each energy value.

The technical result achieved by the implementation of the invention is to increase the life of the klystron, increasing the stability of the parameters of the accelerated electron beam for each energy and reducing the energy consumption of the particle accelerator.

The problem stated in the invention is solved due to the fact that the pulse-by-pulse switching of the energy of an accelerated electron beam between two values is carried out by switching the amplitude of a high voltage pulse supplying a klystron from pulse to pulse. In this case, the pulses of the input high-frequency power of the klystron for low and high energy are generated at the same frequency, changing in accordance with the change in the resonant frequency of the accelerating structure, and the required dose rate of bremsstrahlung is provided by switching from the pulse to the voltage pulse of the control electrode of the electron gun.

The proposed new method of pulse-by-pulse switching the energy of an accelerated electron beam between two values by switching the amplitude of a high-voltage pulse supplying a klystron allows the klystron to operate in the optimal mode for both of these energy values. Thus, the klystron operating point for both energy values is located in the region of the maximum amplitude characteristic of the klystron, as shown in FIG. 2, which increases the stability of the energy of the accelerated beam and the radiation dose rate at both energy values. The choice of the optimal electric power of the klystron power supply for both energy values allows reducing energy costs, eliminating the problem of supplying an excess part of the power supply to the klystron for a lower value of the accelerated beam energy, its dissipation in the klystron collector and a corresponding decrease in the life of the klystron. In addition, the present invention provides the fulfillment of conditions for optimal grouping of particles by the first accelerating cell of the accelerator for both values of the energy of the accelerated electron beam. Thus, the totality of the features of the invention in each of the options for its implementation, disclosed below and presented in the claims, provides a solution to the problem and the achievement of the claimed technical result.

More specifically, the objective of the invention is solved by a new method for generating bremsstrahlung with pulse-by-pulse switching of energy, which consists in:

sequentially supplying the first and second pulses of the input high-frequency power from the pathogen to the klystron fed by electric power from the high-voltage power system;

the klystron sequentially amplifies the first and second pulses of the input high-frequency power to obtain the first and second pulses of the output high-frequency power;

sequential transmission of the first and second pulses of the high-frequency output of the klystron to the resonators of the same particle accelerator in the form of pairs of pulses closely spaced in time;

serial power, using the high-voltage power supply system, the control electrode of the accelerator’s electron gun, the first and second electric power of the control electrode, different from the electric power of the klystron, while the cathode of the electron gun is supplied with electric power of the klystron;

injection into the resonator of the accelerator of the first and second electron beams based at least in part on the first and second electric power supply of the control electrode;

sequentially accelerating injected electron beams by an accelerator operating at the same frequency 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 the high-frequency output power of the klystron; and

successive collisions of the first and second currents of accelerated electron beams with a stop target to generate radiation pulses having first and second different energies and first and second dose rates;

moreover, the modulation of the speed of the continuous electron stream from the electron gun of the accelerator 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, the high-frequency voltage U _g (level of the accelerating field) at the gap of the first cell is selected from the condition of the maximum amplitude of the first harmonic of the electron beam current in the center of the gap of the second cell

where U ₀ is the voltage of the electric power supply of the klystron and the cathode of the electron gun and n = 1, 2, 3, ...;

the level of the accelerating field of the third cell is equal to the level of the accelerating field of subsequent cells; and

the frequency of the input high-frequency power signal from the pathogen is controlled using a frequency controller based on data on the accelerator operating mode and coolant temperature,

and characterized in that

the voltage of the electric power supply of the klystron and the cathode of the electron gun (U ₀ ) is switched from pulse to pulse between the first value supplied to the klystron simultaneously with the first pulse of the input high-frequency power and the second value supplied to the klystron simultaneously with the second pulse of the input high-frequency power;

moreover, the indicated first and second values of the voltage of the electric power supply of the klystron and the cathode (U ₀ ) are selected so that for given first and second energies of the generated radiation pulses, the operating point of the klystron is in the region of the maximum amplitude characteristic for both the first and second energies accelerated electron beams, and the voltage at the gap of the first accelerating cell U _{g is} additionally chosen so that the ratio U ₀ / U _g remains essentially constant.

In a preferred embodiment, switching the voltage of the electric power supply of the klystron and the cathode of the electron gun from pulse to pulse is carried out by applying to the klystron and cathode pairs of closely spaced high-voltage pulses of different amplitudes obtained using a modulator and one high-voltage source of electric voltage. In this case, the necessary ratio of the amplitudes of the pulses in these pairs can be obtained by adjusting the time interval between the pulses, which determines the degree of compensation of the discharge of the storage capacitors by a high-voltage source of electrical voltage.

In another embodiment, switching the voltage of the electric power supply of the klystron and the cathode of the electron gun from pulse to pulse is carried out by applying to the klystron and cathode pairs of closely spaced high-voltage pulses of various amplitudes obtained using a modulator and two high-voltage sources of electric voltage. Accordingly, to ensure the necessary ratio of the amplitudes of the pulses in these pairs, the voltage at the sources is adjusted.

In addition, the task of the invention is solved by a new source for implementing the described method for generating bremsstrahlung. The specified source contains:

particle accelerator containing an accelerating structure with a standing wave to accelerate electrons;

a three-electrode electron gun at the input of the accelerating structure, comprising a cathode, anode, and a control electrode and configured to switch the current of the electron beam from pulse to pulse between two predetermined values;

a brake target for generating radiation located at the output of the accelerating structure;

a high-voltage power system comprising at least one electric voltage source and a modulator for selectively supplying the klystron and cathode of the electron gun with an electric power supply of the klystron, and selectively supplying the control electrode of the electron gun of the accelerator with the first and second electric power supply of the control electrode other than the electric klystron power supply;

a high-frequency power system containing a pulsed multipath amplification klystron for selectively supplying the accelerator with at least first and second pulses of the output high-frequency power, and a pathogen for supplying at least the first and second pulses of the input high-frequency power to the klystron at the same frequency of generated oscillations;

an accelerator controller comprising a frequency controller for controlling the frequency of the input high-frequency power from the pathogen based on data on the accelerator operating mode and coolant temperature; and

cooling system

and differs in that

the exciter of the high-frequency power system is configured to supply the first and second pulses of the input high-frequency power with the same power level to the klystron;

and the fact that the high-voltage power system is configured to switch from a pulse to a voltage pulse of the electric power supply of the klystron and the cathode of the electron gun between the first value supplied to the klystron simultaneously with the first pulse of the input high-frequency power and the second value supplied to the klystron simultaneously with the second pulse input high-frequency power.

In a preferred embodiment, said high-voltage power supply system comprises a modulator and at least one high-voltage source of electrical voltage, configured to form pairs of closely spaced high voltage pulses of various amplitudes and to control the time interval between these pulses to provide the necessary ratio of pulse amplitudes in pairs.

In another embodiment, the high-voltage power system comprises a modulator and at least two high-voltage sources of electrical voltage, configured to form pairs of closely spaced high-voltage pulses of various amplitudes. Said modulator is preferably a solid state modulator.

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

Additionally, in this embodiment, the distance L _g between the gap centers of the first and second cells of the accelerating structure is determined by the ratio

where β ₀ = ν ₀ / c, ν ₀ is the velocity of the electron flux 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 and n = 1, 2, 3, ...

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

According to various embodiments, the brake target can be mounted on a small diameter electron wire, and an ionization chamber can be installed after it. An electron gun, an accelerating structure with a magnetic screen, a brake target, and an ionization chamber are preferably mounted inside a local radiation shield, which can be provided with a slot. In the accelerating structure, a communication loop can be established.

Also in a preferred embodiment, the electron gun, 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 mounted in a waveguide through which high-frequency power is supplied to the accelerating structure. In this case, to maintain a high vacuum level in the indicated vacuum volume during the life of the accelerator, a getter pump can be 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.

Alternatively or additionally, an electric discharge pump may be installed on the waveguide, the current value of which is determined by the level of vacuum in the indicated volume, which can be connected to the indicated vacuum volume through slots in the narrow wall of the waveguide.

Brief Description of the Drawings

The advantages of the present invention are disclosed below in the detailed description of preferred embodiments with reference to the accompanying drawings, in which:

- in FIG. 1 shows the dependence of the output high-frequency power of the klystron on the input high-frequency power at a constant amplitude of the high voltage pulse supplying the klystron;

- in FIG. 2 illustrates a change in the dependence of the output high-frequency power of the klystron on the input high-frequency power when changing the amplitude of the high voltage pulse supplying the klystron;

- in FIG. 3 is a block diagram of a radiation source according to a preferred embodiment of the invention; and

- in FIG. 4 is a timing diagram of an operation of a radiation source according to an embodiment of the invention.

The implementation of the invention

The following describes a preferred embodiment of the invention in a radiation source based on a compact electron accelerator for inspection complexes with pulse-by-pulse switching of the energy of bremsstrahlung between two adjustable values and independent regulation of the dose rate for each energy value, the block diagram of which is shown in FIG. 3. Most of the components of the described radiation source are similar or essentially similar to those in the radiation source of the prototype, therefore, for brevity, such components are described in abbreviated form, at the functional level.

As shown in FIG. 3, the radiation source comprises a particle accelerator 1, a high-frequency power system 2, a high-voltage power system 3, a cooling system 4, an accelerator controller 5, and a control console 6.

The particle accelerator 1 includes a three-electrode electron gun 7 with a cathode 8, an anode, and a control electrode 9 connected through a ceramic insulator with an accelerating structure 10 with a standing wave. The accelerating structure 10 is configured to accelerate the electron beam 11 from the electron gun 7 to a certain final energy and focus the accelerated beam on the brake target 12 to generate bremsstrahlung 14.

As shown in FIG. 3, the brake target 12 is located at the end of the electron path 13 installed at the output of the accelerating structure 10 and having a small diameter substantially smaller than the diameter of the accelerating structure 10, which allows reducing the size and weight of the radiation protection 17 of the accelerator 1. The accelerated beam 11 hits the center of the brake target 12 provided with a magnetic screen 15 located around the electron gun 2 and the accelerating structure 10, which reduces the stray magnetic fields in the electron gun 7 and the accelerating structure 10 to a level not exceeding the level of the mag Earth’s filament field. Additionally, correction coils 16 can be placed over the accelerating structure 10 to adjust the position of the beam 11 on the brake target 12. To control the dose rate of the bremsstrahlung after the braking target 12, an ionization chamber 19 is installed. The level of bremsstrahlung in the entire area around the braking target 12 except for the working one the zone is reduced to a set value using radiation protection 17. The formation of the spatial distribution of the bremsstrahlung 14 in the working area is carried out using Jesi 18 Radiation Protection 17.

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, and a third and subsequent cells (accelerating and focusing) with the highest level of the accelerating field. In one of the accelerating cells of structure 10, a communication loop 20, preferably a high-frequency antenna, is installed to control the level of high-frequency losses in the walls of the accelerating structure 10 and, therefore, to control the level of the accelerating field and the energy of the accelerated electron beam. 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 shift between the cells is 180 °.

In particular, the distance L _g between the centers of the gaps of the first and second cells can be determined by the following relation:

where β ₀ = ν ₀ / c, ν ₀ is the velocity of the electron flux 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 and n = 1, 2, 3, ...

The main element of the high-frequency power supply system 2 is a pulsed multipath amplification klystron 25, which provides the excitation of the microwave field of the accelerating structure 10 by selectively supplying it with at least the first and second pulses of the output high-frequency power of the klystron. The pathogen 27, in turn, is designed to supply at least the first and second pulses of the input high-frequency power to the klystron 25, which have the same amplitude and the same oscillation frequency. In addition, the high-frequency power supply system 2 contains a waveguide 21 with a pumping system 22 and a dividing vacuum window 23, placed between the accelerating structure 10 and the waveguide 24 connected to the klystron 25 through a ferrite decoupling device 26, an insulating gas supply system 28 and a discharge sensor 29.

The klystron 25 preferably operates with a low supply voltage through the use of a multi-beam design and is compact due to the use of a permanent magnet focusing system. Also, the klystron 25 is characterized by a large gain, which allows the use of a pathogen 27 with a relatively low output power, which provides the ability to maintain high stability of the frequency of the output signal. The value of the high-frequency output of the klystron 25 is switched from pulse to pulse with the desired repetition rate, as described below. Pathogen 27 preferably consists of a synthesizer, a solid state microwave amplifier, and an electronic attenuator with p-i-n diodes.

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 installed between waveguides 21 and 24, through which pulses of the high-frequency output power of the klystron 25 enter the accelerating structure 10. To maintain a high level of vacuum in the vacuum volume, a getter pump is installed on waveguide 21, which does not require a power source and pumps out the specified volume through slots in a narrow Tenke waveguide 21. To control the vacuum level and generating a blocking signal to the deterioration of vacuum waveguide 21 is also mounted electric discharge pump connected to the vacuum volume through slots in the narrow wall. Together, getter and electric discharge pumps constitute a pumping system 22 supporting a working vacuum in the indicated vacuum volume, the vacuum volume being pumped out mainly by a getter pump, while the electric discharge pump is used to control the vacuum level. This allows you to quickly enter the radiation source 1 in the operating mode after long-term storage, guarantees stability of parameters and reliability.

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

The cooling of the accelerating structure 10, the brake target 12, the modulator 30 and the klystron 25 is carried out by a liquid with a constant temperature coming from the cooling device 32 of the cooling system 4. The temperature and flow rate of the liquid at the input and output of the accelerating structure 10 is controlled using a system of temperature and liquid flow sensors 33.

The high-voltage power supply system 3 contains a high-voltage modulator 30 for supplying the klystron 25 and the cathode 8 of the electron gun 7, as well as an electric power source 31 for supplying the control electrode 9 of the electron gun 7. In addition, in various embodiments, the modulator 30 is supplemented with one or two high-voltage sources electrical voltage (not shown in the drawings).

The modulator 30, using at least one high-voltage source of electric voltage, generates a signal of electric power supply of the klystron 25 and the cathode 8 of the electron gun in the form of a pair of closely spaced high-voltage pulses with different amplitudes. Thus, the high-voltage power supply system 3 provides for switching the voltage of the electric power supply of the klystron 28 and the cathode 8 of the electron gun 7 from pulse to pulse between the first and second values corresponding to the amplitudes of these high voltage pair pulses.

In a preferred embodiment of the invention, said pairs of high voltage pulses are obtained using a modulator 30 and one high voltage source of electrical voltage. In this case, the necessary ratio of the amplitudes of the pulses is obtained by adjusting the time interval between pulses in pairs, which determines the degree of compensation of the discharge of the storage capacitors by a high-voltage source of electrical voltage.

In another embodiment, said pairs of high voltage pulses are obtained using a modulator 30 and two high voltage sources of electrical voltage, the voltage values of which are adjusted to provide the necessary ratio of the amplitudes of the pulses in these pairs. Both of these options for implementation equally provide the achievement of the advantages of the claimed invention.

The electric power source 31 provides serial power to the control electrode 9 of the electron gun 7 of the first and second electric power supply to the control electrode, thus ensuring switching of the voltage value on the control electrode 9 and, accordingly, pulse-switching the current value of the electron beam 11.

The change in the final energy of the accelerated electron beam 11 is achieved by adjusting the level of the accelerating field in the accelerating structure 10 by changing the output high-frequency power of the klystron 25 by switching the voltage of the electric power supply of the klystron 25 from pulse to pulse, as described above. Preferably, the ratio of the maximum possible and minimum possible energies of the accelerated electron beam is at least two, and the diameter of the beam on the brake target 12 in the entire range of energy changes is not more than 2 mm.

The accelerator controller 5 synchronizes the operation of the systems of the particle accelerator 1 and the switching of the blocking signals between the systems is similar to the prototype. In particular, the accelerator controller 5 contains a frequency controller for controlling the frequency of the signal of the high-frequency output power of the pathogen 27 based on the data on the operation mode of the accelerator 1 and the coolant temperature received from the sensors 33. The control console 6 provides the setting of operating modes and monitoring the operation of the radiation source systems in the same way prototype.

The described radiation source is intended to implement a method of generating bremsstrahlung with pulse-by-pulse switching of energy according to the claimed invention. A timing diagram of the operation of this radiation source is shown in FIG. 4, where τ is the pulse duration, T ₁ is the distance between pulses in a pair of pulses, T ₂ is the distance between pairs of pulses. The functioning of this radiation source is largely similar to the radiation source of the prototype, therefore, is described below briefly, highlighting the distinctive features of the radiation generation method according to the present invention.

Shown in FIG. 4, the start and energy signals are generated by the controller 5 of the particle accelerator 1 to synchronize the operation of the radiation source and are supplied to the particle accelerator 1, the high-frequency power system 2 and the high-voltage power system 3, respectively.

When receiving energy signals and triggering in the high-voltage power supply system 3, the modulator 30 generates a signal of the electric power supply of the klystron 25 and the cathode 8 of the electron gun 7 in the form of a pair of high voltage pulses closely spaced in time, the amplitudes of which are set by the received energy signal. Thus, the switching of the voltage of electric power (U ₀ ) of the power supply of the klystron 25 and the cathode 8 of the electron gun 7 from pulse to pulse between the first and second values is ensured. In FIG. 4, the signal of the electric power supply of the klystron and the cathode of the electron gun is designated as “modulator pulse”.

Synchronously with this, the electric power source 31 generates the first and second pulses of the electric power supply of the control electrode 9 of the electron gun, different from the indicated pair pulses of the electric power supply of the klystron 25 and the cathode 8 of the electron gun 7. FIG. 4 pulses of electric power supply to the control electrode are designated as “voltage of the control electrode”.

In the high-frequency power supply system 2, in response to receiving energy and triggering signals, the exciter 27 generates, at the same frequency, the first and second pulses of the input high-frequency power of the klystron of the same amplitude, which are sequentially supplied by the klystron 25, fed, as described above, in pairs pulses of electric power from the modulator 30. In FIG. 4 pulses of the input high-frequency power of the klystron are designated as “input signal of the klystron”.

Thus, unlike the prototype, in the present invention, the input high-frequency power supplied to the klystron 25 remains unchanged in level, however, the voltage of the electric power supply of the klystron 25 changes from pulse to pulse. Accordingly, the klystron 25 sequentially amplifies the first and second pulses of the input high-frequency power with receiving the first and second pulses of the output high-frequency power of the klystron ("output signal of the klystron" in Fig. 4), the difference of the amplitudes of which is based on switching from imp lsa to pulse voltage klystron electric power supply 25 between the first value applied to the klystron 25 simultaneously with the first pulse of the input RF power, and the second value supplied to the klystron 25 while the second pulse of the input RF power. Further, the first and second pulses of the output high-frequency power of the klystron 25 are sequentially transmitted, through a ferrite decoupling device 26, a waveguide 24, a vacuum window 23 and a waveguide 21, to the resonators of the accelerating structure 10 in the form of pairs of pulses closely spaced in time, exciting the accelerating field in the structure 10. A small time delay between the indicated pulses (T ₁ in FIG. 4) can be, for example, 500 μs.

Simultaneously with the described operations, when receiving energy signals and triggering in the particle accelerator 1, the electron gun 7 forms the first and second electron beams and injects them into the resonators. The said first and second electron beams have different current levels, which are set by the amplitudes of the first and second pulses of the electric power supply of the control electrode supplied from the electric power source 31. The injected electron beams are sequentially accelerated to the first energy and the second energy different from the first energy based at least partially on the first and second pulses of the output high-frequency power of the klystron 25.

In more detail, the electron beam passing through the accelerating structure 10 interacts with the accelerating field created in it, forms into bunches, focuses and accelerates to an energy whose value is determined by the level of the accelerating field. The level of the accelerating field is determined by the pulses supplied to the accelerator 1 of the output high-frequency power of the klystron 25, regulated by switching the voltage of the electric power supply of the klystron, as described above. The first pulse of the output high-frequency power of the klystron 25 is aligned in time with the first pulse of the current of the electron beam of the electron gun 7, and the second pulse of the output high-frequency power of the klystron 25 is aligned with the second pulse of the current of the electron beam of the electron gun 7.

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 10, in the second cell the stream partially clustered into clusters is subjected to acceleration, focusing and further grouping, while the high-frequency voltage U _g (level of the accelerating field) in the gap of the first cell is selected from the condition ensuring 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 electric power supply of the klystron and the cathode of the electron gun and n = 1, 2, 3, ...

The level of the accelerating field of the third cell is equal to the field level of subsequent cells. At the same time, both at a low and a high energy level, the particle accelerator 1 operates at the same frequency, which is controlled by a frequency controller, by controlling the frequency of the input high-frequency power signal from the pathogen 27, as described above.

Accelerated first and second electron beams sequentially collide with the brake target 12 mounted on the electron wire 13, resulting in the generation of bremsstrahlung pulses 14 having the first and second different energies and the first and second corresponding dose rates.

The selection of the first and second electric power supply of the control electrode 9 and, accordingly, the current of the electron gun 7 provides essentially equal values of the dose rate of bremsstrahlung for both energies of the accelerated electron beam, as shown in FIG. four.

The selection of the first and second values of the voltage of the electric power (U ₀ ) of the power supply of the klystron 25 and the cathode 8 of the electron gun 7 is carried out in such a way that, for given radiation energies, the operating point of the klystron 25 is in the region of maximum amplitude characteristic for both values of the energy of the accelerated electron beam, for example, as shown in FIG. 2. The voltage at the gap of the first accelerating cell U _{g is} additionally chosen so that the ratio U ₀ / U _g remains substantially constant.

Thus, when implementing the method of generating bremsstrahlung according to the invention, the proposed radiation source provides pulse-by-pulse switching of the energy of accelerated electrons and the dose rate of bremsstrahlung, moreover, for both energy values, the optimal operation mode of the klystron and the fulfillment of the conditions for the optimal grouping of particles by the first accelerating cell of the accelerator are ensured.

You must understand that the above-described examples of embodiments of the invention, although they are preferred, do not limit the scope of the invention. After reviewing the present description, those skilled in the art can propose many changes and additions to the described embodiments, all of which fall within the scope of patent protection of the invention defined by the following claims.

Claims (48)

1. A method of generating bremsstrahlung with pulse-by-pulse switching of energy, which consists in: sequentially supplying the first and second pulses of the input high-frequency power from the pathogen to the klystron fed by electric power from the high-voltage power system; the klystron sequentially amplifies the first and second pulses of the input high-frequency power to obtain the first and second pulses of the output high-frequency power; sequential transmission of the first and second pulses of the high-frequency output of the klystron to the resonators of the same particle accelerator in the form of pairs of pulses closely spaced in time; serial power, using the high-voltage power supply system, the control electrode of the accelerator’s electron gun, the first and second electric power of the control electrode, different from the electric power of the klystron, while the cathode of the electron gun is supplied with electric power of the klystron; injection into the resonator of the accelerator of the first and second electron beams based at least in part on the first and second electric power supply of the control electrode; sequentially accelerating the injected electron beams by an accelerator operating at the same frequency 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 the high-frequency output power of the klystron; and successive collisions of the first and second currents of accelerated electron beams with a stop target to generate radiation pulses having first and second different energies and first and second dose rates; the modulation of the speed of the continuous electron flow from the electron gun of the accelerator 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, the high-frequency voltage U _g (level of the accelerating field) at the gap of the first cell is selected from the condition ensuring the maximum amplitude of the first harmonic of the electron beam current in the center of the gap of the second cell

, where U ₀ is the voltage of the electric power supply of the klystron and the cathode of the electron gun and n = 1, 2, 3, ...; the level of the accelerating field of the third cell is equal to the level of the accelerating field of subsequent cells; and the frequency of the input high-frequency power signal from the pathogen is controlled using a frequency controller based on data on the accelerator operating mode and coolant temperature, characterized in that the voltage of the electric power supply of the klystron and the cathode of the electron gun (U ₀ ) is switched from pulse to pulse between the first value supplied to the klystron simultaneously with the first pulse of the input high-frequency power and the second value supplied to the klystron simultaneously with the second pulse of the input high-frequency power; moreover, the indicated first and second values of the voltage of the electric power supply of the klystron and cathode (U ₀ ) are selected so that for given first and second energies of the generated radiation pulses, the klystron operating point is in the region of the maximum amplitude characteristic for both the first and second accelerated energies electron beams, and the voltage at the gap of the first accelerating cell U _{g is} additionally chosen so that the ratio U ₀ / U _g remains essentially constant. 2. The method according to p. 1, characterized in that the switching voltage of the electric power supply of the klystron and the cathode of the electron gun from pulse to pulse is carried out by applying to the klystron and cathode pairs of closely spaced high-voltage pulses of various amplitudes obtained using a modulator and one high-voltage a source of electrical voltage, and the required ratio of the amplitudes of the pulses in pairs is obtained by adjusting the time interval between these pulses and, which determines the degree of compensation of the discharge of storage capacitors by a high-voltage source of electrical voltage. 3. The method according to p. 1, characterized in that the switching voltage of the electric power supply of the klystron and the cathode of the electron gun from pulse to pulse is carried out by applying to the klystron and cathode pairs of closely spaced high-voltage pulses of different amplitudes obtained using a modulator and two high-voltage sources of electrical voltage, the voltage values on which are regulated to provide the necessary ratio of the amplitudes of the pulses in the specified pairs. 4. A radiation source for implementing the method of generating bremsstrahlung according to any one of paragraphs. 1-3, containing: particle accelerator containing an accelerating structure with a standing wave to accelerate electrons; a three-electrode electron gun at the input of the accelerating structure, comprising a cathode, anode, and a control electrode and configured to switch the current of the electron beam from pulse to pulse between two predetermined values; a brake target for generating radiation located at the output of the accelerating structure; a high-voltage power system comprising at least one electric voltage source and a modulator for selectively supplying the klystron and cathode of the electron gun with electric power of the klystron and selectively supplying the control electrode of the electron gun of the accelerator with the first and second electric power supply of the control electrode, different from the electric power of the klystron ; a high-frequency power system containing a pulsed multipath amplification klystron for selectively supplying the accelerator with at least the first and second pulses of the high-frequency output power, and a pathogen for supplying at least the first and second pulses of the high-frequency input power to the klystron at the same frequency of generated oscillations; an accelerator controller comprising a frequency controller for controlling the frequency of the input high-frequency power from the pathogen based on data on the accelerator operating mode and coolant temperature; and cooling system characterized in that the exciter of the high-frequency power system is configured to supply the first and second pulses of the input high-frequency power with the same power level to the klystron; and the fact that the high-voltage power system is configured to switch from a pulse to a voltage pulse of the electric power supply of the klystron and the cathode of the electron gun between the first value supplied to the klystron simultaneously with the first pulse of the input high-frequency power and the second value supplied to the klystron simultaneously with the second pulse input high-frequency power. 5. The source according to claim 4, characterized in that the high-voltage power supply system comprises a modulator and one high-voltage source of electrical voltage, configured to generate pairs of high-voltage pulses of close proximity in time of various amplitudes and to regulate the time interval between these pulses to provide the necessary ratio of pulse amplitudes in the specified pairs. 6. The source according to claim 4, characterized in that the high-voltage power system comprises a modulator and two high-voltage sources of electrical voltage, configured to form pairs of closely spaced high-voltage pulses of different amplitudes. 7. The source according to claim 4, characterized in that the accelerating structure 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) 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 °. 8. The source according to claim 7, 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 = v ₀ / c, v ₀ is 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, and n = 1, 2, 3, ... 9. A source according to claim 4, characterized in that the klystron focusing system is made with permanent magnets. 10. 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. 11. The source according to claim 4, characterized in that said accelerating structure and the electron gun are placed in a magnetic screen. 12. The source according to claim 4, characterized in that the said brake target is mounted on a small diameter electric wire. 13. A source according to claim 4 or 12, characterized in that an ionization chamber is installed after said inhibitory target. 14. The source according to claim 11, characterized in that said electron gun and accelerating structure with a magnetic screen are installed inside the local radiation protection. 15. The source according to claim 13, characterized in that said electron gun and accelerating structure with a brake target and an ionization chamber are installed inside the local radiation protection. 16. The source according to p. 14 or 15, characterized in that said local radiation protection is provided with a slot. 17. A source according to claim 4, characterized in that a communication loop is installed in said accelerating structure. 18. The source according to claim 12, characterized in that said electron gun, accelerating structure, and electronic conductor with a 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 the accelerating structure. 19. A source according to claim 18, characterized in that a getter pump is installed on said waveguide to maintain a high level of vacuum in the indicated vacuum volume, which does not require a power source and is connected to the specified volume through slots in the narrow waveguide wall. 20. A source according to claim 18 or 19, characterized in that an electric discharge pump is additionally 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. 21. The source according to claim 4, characterized in that said modulator is a solid-state modulator.

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