RU2513034C2 - Method for induction electron acceleration - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to acceleration techniques and can be used in making induction cyclic accelerators for industrial purposes, e.g. for modifying and producing new materials, sterilising medical instruments and food products, disinfecting medical wastes and other wastes, cleaning industrial flue gases from hazardous SO_x and NO_x oxides. The disclosed method involves achieving given final energy (≤10 MeV) using a rectangular wave of accelerating induction voltage and a triangular wave of the guiding magnetic field. In order to keep the radius of the equilibrium orbit constant during acceleration, special relationships between amplitude-time characteristics of magnetic induction on the orbit and induced accelerating voltage are satisfied. In order to realise strong focusing, a magnetic field with a large alternating gradient is formed on the orbit.

EFFECT: high average power of a beam of accelerated charged particles, reduced size and weight of the induced cyclic accelerator of electrons, simple power supply system of the induction accelerating system, low cost of the accelerator.

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Description

The invention relates to accelerator technology and can be used to create induction cyclic accelerators for industrial use, for example, for the modification and production of new materials, sterilization of medical instruments and food products, disinfection of medical and other wastes, purification of industrial gases from harmful SO _x and NO _x oxides.

Known electron accelerators for industrial technologies such as ELV [1]. These are direct action accelerators in which an accelerating electric field is created by the difference of constant potentials between the cathode and the anode electrode. To remove the beam from the accelerator, the anode must be at ground potential, therefore, in direct-acting accelerators, the cathode is at a voltage equal to the energy of accelerated electrons. At an energy of 2.5 MeV, the voltage at the cathode will be 2.5 MB, and the design of the direct-action accelerator should provide electrical insulation of the cathode for a constant voltage equal to the maximum allowable energy. This determines the large size of direct-acting accelerators (height over 4 m).

In high-frequency accelerators (which include ILU-type accelerators), an alternating high-frequency (HF) electric field is used to accelerate electrons, so the question of ensuring electrical insulation is easier to solve. In ILU-type accelerators, electrons are accelerated in the gap of a high-quality high-frequency resonator. The resonator is excited by the RF generator through a communication loop, and the RF circuit acts as a step-up transformer.

Accelerators of the ILU type [2-4] are single-resonator machines operating in the standing half-wave mode. The operating frequencies of the ILU accelerators are in the meter range of radio waves - 118 MHz (ILU-6 and ILU-10) and 180 MHz (ILU-8). The length of the accelerating gap of the ILU-8 accelerator is 3.6 cm, ILU-6 is 16 cm, ILU-10 is 26 cm. The accelerating gap of these machines is shorter than the wavelength in vacuum, therefore, during acceleration, the electrons acquired energy almost equal to the maximum voltage on the resonator. ILU accelerators use a triode electron gun (with a control electrode) located immediately in front of the accelerating gap.

Using the control voltage on the electron gun allows you to quickly adjust the beam current and reduces the phase angle of injection, which significantly reduces the spread of electron energy in the beam.

Accelerators of the ILU type have their advantages and disadvantages with respect to the most common type of accelerators, direct-acting accelerators, which include ELV-type accelerators produced by INP. ILU accelerators are impulse machines. Their dimensions are smaller (height 2-2.4 m), and the energy of accelerated electrons is greater (1-5 MeV) than that of ELV accelerators. They do not need a tank with compressed sulfur hexafluoride SF ₆ gas for insulation of high-voltage parts of the accelerator. In the ILU-10 accelerator, an RF voltage with an adjustable phase shift relative to the accelerating voltage is applied to the triode electron gun, which changes the phase angle of injection and reduces the spread of electron energies in the beam.

The disadvantages of ILU accelerators include: a relatively low coefficient of conversion of electric power consumed from the network into beam power, and the maximum accelerator power (up to 50 kW) is limited by the power of the generated generator lamps.

Unlike linear ELV and ILU accelerators, cyclic accelerators do not have high-voltage accelerating systems with a voltage of the order of 1-5 MB. Electrons acquire the required energy by repeatedly passing the accelerating gap with an average voltage [5, 6]. For radiation technologies used in industry, accelerated electron beams with an energy of 0.5-10 MeV are required. Cyclic accelerators in this energy range are much more compact and cheaper than direct-acting accelerators and microwave accelerators.

Induction cyclic accelerators [5, 6] and the criteria proposed in these works have a small mass of magnetic material and do not have tunable resonant accelerating structures, but they are designed for induction acceleration of light particles - electrons, which quickly gain speed at first revolutions, and the main The acceleration process is carried out at a particle velocity close to the speed of light. The period of electron revolution in the range of required energies is τ <10 ns, which complicates the formation of accelerating pulses of duration τ / 2 and fronts of the order of ≤10 ^-9 s.

As a prototype, choose the method [6]. This method consists in creating a magnetic field increasing in time with an average value of magnetic induction, much smaller than the magnetic field induction in orbit, forming an alternating magnetic field gradient in orbit with a field index much larger than unity (strong focusing), and charged particles; accelerate charged particles by pulses of an induction electric field and output accelerated particles. The disadvantages of the prototype indicated earlier.

The technical result of the invention is to increase the average power of the accelerated beam, as well as reducing the weight and dimensions of the accelerator by decreasing the orbit perimeter and shortening the cycle period, simplifying and cheapening the accelerating system, reducing the cost of the accelerator and increasing the range of adjustment of the energy of accelerated electrons.

The method of induction acceleration of electrons is that they form a magnetic field that grows in time with an average value much smaller than the magnetic field in orbit; form an alternating magnetic field gradient in orbit with a field index much greater than unity (strong focusing); inject electrons into it; electrons accelerate with pulses of an induction electric field and output accelerated electrons, to accelerate electrons, they form a triangular waveform of the leading magnetic field and a rectangular waveform of the induction accelerating electric field, the duration of the accelerating part of the wave is equal to the duration of the linear growth of magnetic induction in equilibrium orbit, which corresponds to the duration of the acceleration process wherein the change in the flux of magnetic induction ΔФ in the inductors of the accelerating system is selected from the relation:

, $$\Delta F=\frac{\mathrm{one}}{e}\Delta PL=\Delta B_{ind}S$$

,

where ΔP = PP ₀ is the increase in the electron momentum during the acceleration (P ₀ is the electron momentum of the injection, P is the electron momentum at the end of the acceleration process), L is the perimeter of the electron orbit, ΔB _ind ≤2B _S is the range of variation of the induction in the accelerating inductors in the process acceleration, B _S is the induction saturation induction, S = Δrl is the total cross section of all the inductors of the accelerating section (Δr is the radial size of the inductors, / is the length of the induction section), e is the electron charge, and the value of the accelerating voltage is selected from the relation:

ΔB _ind S = V _acc T,

where V _acc is the total voltage of the accelerating inductors, T is the duration of the accelerating pulse.

The distinguishing features of the claimed method is the following: to accelerate electrons, a triangular waveform of the leading magnetic field and a rectangular waveform of the induction accelerating electric field are formed, the duration of the accelerating part of the wave equal to the duration of the linear growth of magnetic induction in equilibrium orbit, which corresponds to the duration of the acceleration process, the change in the flux of magnetic induction ΔF in the inductors of the accelerating system is chosen from the relation

, $$\Delta F=\frac{\mathrm{one}}{e}\Delta PL=\Delta B_{ind}S$$

,

where ΔP = PP ₀ is the increase in the electron momentum during acceleration (P ₀ is the electron momentum of injection, P is the electron momentum at the end of the acceleration process), L is the perimeter of the electron orbit, ΔB _ind ≤2B _S is the range of variation of induction in accelerating inductors, B _S is the induction saturation induction, S = Δrl is the total cross section of all the inductors of the accelerating section (Δr is the radial size of the inductors, l is the length of the induction section), e is the electron charge, and the value of the accelerating voltage is selected from the relation:

ΔB _ind S = V _acc T,

where V _acc is the total voltage of the accelerating inductors, T is the duration of the accelerating pulse.

The technical result of the invention using this method is: reducing the weight and dimensions of the accelerator by reducing the perimeter of the orbit and shortening the cycle period; simplification and cheapening of the accelerating system, reducing the cost of the accelerator and increasing the range of adjustment of the energy of accelerated electrons. This is achieved by the fact that the combination of all the essential features of the formula makes it possible to accelerate electrons from injection energy to a given final energy, not by a series of nanosecond pulses of an accelerating induction system, the number of which is equal to the number of acceleration cycles (the number of electron revolutions during acceleration), and the duration of each accelerating pulse (less or equal to half the electron revolution period τ ₀ ≤10 ^-9 s), and with a single pulse of a square wave with a duration equal to the acceleration process τ≈10 ^-7 -10 ^-6 s.

Such an acceleration method makes it possible to minimize the electron revolution period, which leads to an increase in the average beam power, a decrease in the orbit perimeter, a decrease in the accelerator dimensions, its weight and cost, and a significant simplification and cheapening of the system for generating accelerating voltage pulses.

The electron energy at the output of the accelerator is adjusted by changing the parameter T of the waves of magnetic induction of the accelerating voltage.

In addition, the use of an induction acceleration method for accelerating electrons in an increasing magnetic field with an average magnetic field much smaller than the magnetic field in orbit and with an alternating magnetic field gradient in orbit (strong focusing), allows you to further increase the beam intensity and reduce the weight and cost of the electron accelerator .

List of drawings

Figure 1 - diagram of the accelerator.

Figure 2 is a diagram of C-shaped cores with an alternating gradient.

Figure 3 - waveform of magnetic induction in equilibrium orbit.

4 is a diagram of the O-shaped cores of the induction accelerating section.

Figure 5 - amplitude-time characteristics of magnetic induction in equilibrium orbit (a) and accelerating voltage on the turns of O-shaped cores (inductors) (b).

Figure 1 shows a diagram of a device that implements the proposed method, where

1) C-shaped electromagnets of the leading magnetic field system with an alternating gradient, 2) O-shaped cores of an induction accelerating system consisting of a series of inductors, 3) an injection and extraction system for the ion beam.

The method works as follows: A beam of charged particles (electrons) is brought into equilibrium orbit, the beam particles are held in equilibrium by the magnetic field of C-shaped electromagnets (1), accelerated by the electric field induced by O-shaped ferromagnetic cores (inductors) (2), and when the required energy is reached, it is removed from the accelerator.

To implement the proposed method of acceleration, an increasing magnetic field in time in orbit is formed by C-shaped electromagnets with high field gradients n >> 1 and n << - 1. The combination of two types of C-shaped cores allows for rigid focusing of ions.

Figure 2 presents a diagram of the C-shaped cores of electromagnets with an alternating gradient. Electromagnets form a triangular waveform of a magnetic field.

The waveform of magnetic induction B ₀ in orbit is shown in figure 3, where T is the duration of the growing part of the wave of induction, corresponding to the duration of the acceleration process.

Particles moving in an equilibrium orbit are accelerated by an electric field induced by O-shaped ferromagnetic cores (inductors), which are located in straight sections of the accelerator.

Figure 4 shows a diagram of the O-shaped cores of an induction accelerating system: 1) ferromagnetic cores of inductors, 2) turns of excitation, 3) field lines of the induced electric field. In order for the radius of the equilibrium orbit to remain constant during acceleration, it is necessary to fulfill the well-known constancy condition in the process of acceleration of the relation

P _(t) / eB _(t) = const,

where P _(t) and B _(t) is the ion momentum and the magnetic field induction in orbit during acceleration, e is the electron charge.

This condition is fulfilled when the total voltage induced by O-shaped cores is equal to:

V _acc = R ₀ LdB / dt,

where R ₀ is the radius of the equilibrium orbit, L is the total perimeter of the orbit, taking into account the straight sections.

The amplitude-time characteristics of magnetic induction in orbit and accelerating voltage on the turns of O-shaped cores (inductors) are shown in Figure 5:

a) The waveform of the magnetic field induction in the equilibrium orbit B _{0 (t)} ,

b) The waveform of the induction accelerating voltage of the inductors V _{acc (t)} .

The pulse duration of the accelerating voltage V _{acc (t)} is equal to the duration of the linear growth of magnetic induction in the equilibrium orbit B _{0 (t)} , which corresponds to the duration of the electron acceleration process.

The positive part of the pulse accelerates the ions, and the negative part magnetizes the O-shaped cores and returns them to their original state. Such an acceleration mode is possible if a change in the total flux of magnetic induction in the inductors of the accelerating section ΔФ = ΔB _ind S and a change in the electron momentum ΔР = Р-P ₀ are dependent on:

, $$\Delta F=\frac{\mathrm{one}}{e}\Delta PL$$

,

and the total voltage of the induction section

V _acc = ΔФ / T

where ΔB _ind ≤2B _S is the change in induction, B _S is the saturation induction, S is the total cross section of the cores of the inductors, L is the total perimeter length taking into account the straight sections, P = mcβγ and P ₀ are the final and initial electron momenta, T is the duration of the process accelerations, c is the speed of light, β and γ are the relative speed and relativistic factor of electrons.

The formation of a magnetic field in the gaps of C-shaped electromagnets with a large radial gradient and the focusing of ions by an alternating field gradient (strong focusing) makes it possible to increase the number of electrons accelerated in one acceleration cycle. A large indicator of the magnetic field reduces the amplitude of betatron oscillations and allows you to reduce the size of the vacuum chamber, to reduce the size, weight and cost of C-shaped magnets.

As an example, we consider the main parameters of an electron accelerator with an energy of 10 MeV. At an energy of 10 MeV, the relativistic electron factor is γ = 20.6, and their relative velocity is β≅1.0. When the amplitude of the magnetic induction of the leading magnetic field B _max = 0.1 T, the radius of the equilibrium orbit R ₀ is equal to:

R ₀ = P _max / eB _max = mc ² γβ / ecB _max = 0.33 L,

where P _max is the maximum electron momentum, e is the electron charge, m is the mass of the electron, c is the speed of light, β = ν / c is the relative velocity of protons, B _max is the maximum amplitude of the magnetic induction of the field.

If the total perimeter of the orbit, taking into account the straight sections, is L≈2.4 m, then the period of revolution of the accelerated protons will be τ _min ≈8 · 10 ^-9 s, and the required change in the flux of magnetic induction will be:

$$\Delta F=\frac{\mathrm{one}}{e}\Delta PL=\frac{m{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="00000007.png"\; state="\{\{state\}\}">c</figure-callout>}}^2\gamma \beta }{ec}=0.08Tl\cdot {\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="00000007.png"\; state="\{\{state\}\}">m</figure-callout>}}^2$$

With the duration of the acceleration cycle T = 1 μs, the amplitude of the accelerating voltage is V _acc = ΔФ / T = 80 kV. With a radial section size of the inductors of the accelerating section equal to Δr = 0.2 m, the length of the section of the inductors will be l = 0.4 m.If the radial size of each inductor is ≈ 0.01 m, then 40 inductors with a voltage on the exciting inductors V _ind = 2 kV will be required. If necessary, the voltage V _ind can be reduced by increasing the duration of the acceleration cycle T. For the formation of a square wave of accelerating voltage, it is possible to use transistor key circuits. Transistor DC voltage converters in speakers have high reliability, durability and efficiency. In [7], the implementation of a 1.6 MW converter with a switching frequency of 150 kHz was reported. There are transistor switches with a switching frequency of up to 30 MHz and a power of up to 1.8 kW [8]. The rapid progress in the field of semiconductor switches allows us to hope that powerful power systems for induction particle accelerators with a high repetition rate of cycles will be developed in the near future.

Bibliography

1. Salimov R.A., Cherepkov V.G., Golubenko J.I. et al. DC high power electron accelerators of ELV-series: status, development, applications // Radiation Physics and Chemistry. 2000. No57. P. 661-665.

2. Auslender V. L. ILU-type electron accelerator for industrial technologies // Nuclear Instruments and Methods in Physical Research. 1994. No. B 89. P.46-48.

3. Auslander V.L., Bezuglov V.V., Bryazgin A.A. et al. Electron accelerators of the ILU series and their use in radiation-technological processes // Vopr. atomic science and technology. Series: Technical Physics and Automation. 2004. Iss. 58. S.78-85.

4. Auslander V.L., Bryazgin A.A., Voronin L.A. et al. Electron accelerators of the ILU series and their application in industry and medicine // Collection of reports of the Eleventh International Meeting on the Use of Charged Particle Accelerators in Industry and Medicine. SPb., 2005. S.78-81.

5. G. V. Dolbilov, “The Compact Iduction Circular Accelerator for Radiation Technologies”, Proceedings of APAC 2007, Raja Ramanna Center for Advanced Technology (RRCAT), Indore, India, p. P. 628-629.

6. G.V.Dolbilov, “Method of induction acceleration of charged particles”, Patent for invention No. 2359434, July 05, 2007

7. H. Matthes, R. Jurgens, “1.6 MW 150 kHz Series Resonant Circuit Converter incorporating IGBT Device for welding Applikation”, International Heating Seminar, Padova, p.25-31.

8 Hammad Abo Zied, Peter Mutschler, Guido Bachmann, “A Modulator IGBT Converter System for High Frequency Induction Heating Application”, PCIM 2002, 14-16.05, Nurenberg.

Claims (1)

The method of induction acceleration of electrons, which consists in the fact that they form an increasing magnetic field in time with an average value much less than the magnetic field in orbit; form an alternating magnetic field gradient in orbit with a field index much larger than unity (strong focusing); inject electrons into it; accelerate electrons by pulses of an induction electric field and output accelerated electrons, characterized in that for the acceleration of electrons form a triangular waveform of the leading magnetic field and a rectangular waveform of the induction accelerating electric field, the duration of the accelerating part of the wave is equal to the duration of the linear growth of magnetic induction in equilibrium orbit, which corresponds to the duration of the acceleration process, while changing the flux of magnetic induction ΔF in the inductors of the accelerating system selects shouting from the ratio:

,
where ΔP = Р-P ₀ is the increase in the momentum of electrons during acceleration (P ₀ is the momentum of injection electrons, P is the momentum of electrons at the end of the acceleration process), L is the perimeter of the orbit of electrons, ΔB _ind ≤2B _S is the range of variation of induction in accelerating inductors , B _S is the induction saturation induction, S = Δrl is the total cross section of all the inductors of the accelerating section (Δr is the radial size of the inductors, l is the length of the induction section), e is the electron charge, and the value of the accelerating voltage is selected from the relation:
ΔB _ind S = V _acc T,
where V _acc is the total voltage of the accelerating inductors, T is the duration of the accelerating pulse.

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