RU2556038C1 - Pulse generator of neutrons - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: proposed generator consists of pulsed HV voltage source and vacuum chamber including anode and cathode. Anode is composed of a hollow toroidal azimuthal-symmetric structure of two ring-shape plates with outer radius R and inner radius r spaced apart by distance l. At least n pulse heavy hydrogen isotope ion sources are arranged there between where n is not smaller than 3, source height and width being h and f. Cathode is arranged inside anode and aligned therewith and consists of two cylindrical d-diameter magnetic elements arranged in symmetry about anode and space by distance L with lengthwise magnetization to induction of 0.3 < B < 0.6 Tl. Outlets of heavy hydrogen isotope ion sources are directed toward anode axis while sizes R, r, l, L, h, f, d satisfy the preset ratios.

EFFECT: longer life owing to longer life of neutron-forming target.

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Description

The invention relates to the field of applied nuclear physics, in particular, to devices for generating pulsed neutron fluxes intended for use in applied problems of science and technology, for example, for geophysical applications.

Known pulsed neutron generator (GII), containing a neutron tube with a laser-plasma source of deuterons and an accelerating electrode system, a high voltage transformer and capacitor [1]. When laser radiation acts on a target covered by an anode electrode and a high voltage pulse is applied to the electrodes of a neutron tube, deuterons accelerated from the generated laser plasma interact with a neutron-forming target at the cathode, where a fast neutron flux is formed as a result of nuclear fusion reactions. The synchronization between the accelerating voltage pulse and the laser pulse acting on the target is ensured by the fact that the high-voltage block contains a laser spark gap located in front of the tube on the optical axis of the system — a switching element that is triggered by the laser pulse. When operating in the frequency mode on such a device, a neutron flux of up to 10 ¹⁰ neutrons / second can be obtained. However, the inevitable presence of a statistical spread in the response time of the laser spark gap with respect to the processes of plasma formation and expansion on the laser target limits the accuracy of synchronization and affects the stability of the neutron yield. In addition, the presence of a laser spark gap in the specified IIG complicates the design and reduces the manufacturability of application in applied problems.

This drawback is deprived of a pulsed neutron generator containing a neutron tube with an anode electrode covering a laser target, a high-voltage transformer and a capacitor, while the laser target is connected to the anode electrode through the primary winding of the transformer and the capacitor so that together they form a serial circuit [2]. This device eliminates the need for a laser spark gap, since the switching of the elements of the serial circuit occurs automatically through the space between the laser target and the anode when it is filled with laser plasma. Due to this, an increase in the stability of the neutron generator and simplification of the design is achieved. However, the implementation of a small-sized version of such a GII, in particular, for the needs of nuclear geophysics, is fraught with a number of difficulties. The presence of a high voltage pulse at the cathode complicates the design of the generator, since it requires reliable isolation of the cathode with the neutron-forming target from the GIN elements under the ground potential. In turn, this increases the dimensions of the neutron tube, removes the neutron-forming target from the irradiated samples, and complicates the use of magnetic isolation methods, thereby limiting the increase in the efficiency and manufacturability of the generator.

This drawback is deprived of a pulsed neutron generator [3], containing a neutron tube with an anode electrode covering a laser target, a high-voltage transformer and a capacitor, a laser target is connected to the anode electrode through the secondary and primary windings of the transformer and capacitor. The secondary winding of the transformer is made in the form of a two-wire line, the input of which is connected to the capacitor and the primary winding, and the output to the anode electrode and the laser target. Such a series connection of elements forms a discharge circuit, the switching of which is carried out through the gap between the laser target and the anode when it is filled with laser plasma. As a result, a high-voltage accelerating voltage pulse is formed on the anode electrode relative to the cathode, which in this case can be grounded.

Thus, the generator does not require the use of high-voltage electrical insulation of a neutron-forming target. However, there is a low resource of using a solid-state neutron-forming target located on the surface of the cathode and degrading from heating during bombardment by accelerated deuterons.

The technical result of the inventive pulsed neutron generator is to increase the resource of the entire device by increasing the resource of the neutron-forming target, since the neutron-forming target is the place of neutron formation in the volume between the parts of the cathode, where accelerated deuterons move towards each other, and the solid-state neutron-forming target degrades from heating the cathode surface is absent. At the same time, the energy price of the generated neutrons decreases in a pulsed neutron generator.

This result is achieved by the fact that in the known pulsed neutron generator, consisting of a pulsed high-voltage voltage source and a vacuum chamber containing a cathode and anode, the anode is made in the form of a hollow toroidal azimuthally symmetric design of two plates of a ring configuration with an outer radius R and an inner radius r located at a distance l from each other, between which n is located, where n is at least 3, of pulsed ion sources of heavy hydrogen isotopes of each height h and width f, while inside the anode with based on it is a cathode consisting of two cylindrical magnetic elements symmetrically located relative to the anode with a diameter of d and spaced from each other at a distance L with longitudinal magnetization up to induction of 0.3 <B <0.6 T, and the output openings of the sources of ions of heavy hydrogen isotopes are directed to the axis of the anode, and the sizes R, r, l, L, h, f, d satisfy the following relationships:

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регулирует непопадание пучка дейтронов (тяжелых изотопов водорода) на катод и, одновременно, хорошее заполнение области генерации нейтронов между цилиндрическими магнитными элементами; второе и третье соотношения

регулируют равномерное заполнение дейтронами выходного отверстия источника дейтронов на аноде; четвертое соотношение

регулирует сверху условия вакуумной электроизоляции между анодом и катодом, а снизу - условие достаточности напряженности ускоряющего дейтроны электрического поля в области между анодом и катодом. А количество импульсных источников ионов тяжелых изотопов водорода n (n>3) установлено экспериментальным путем исходя из критерия равномерного распределения ионов тяжелых изотопов водорода на выходе из анода.The above ratios are explained as follows: first ratio

regulates the non-penetration of a deuteron beam (heavy hydrogen isotopes) to the cathode and, at the same time, good filling of the neutron generation region between cylindrical magnetic elements; second and third ratios

regulate the uniform filling by deuterons of the outlet hole of the deuteron source at the anode; fourth ratio

it regulates above the conditions of vacuum electrical insulation between the anode and cathode, and below it regulates the sufficiency of the electric field accelerating deuterons in the region between the anode and cathode. And the number of pulsed sources of heavy hydrogen isotope ions n (n> 3) was established experimentally based on the criterion for a uniform distribution of heavy hydrogen isotope ions at the output of the anode.

An example of a specific implementation of the device is illustrated in Fig.1 and Fig.2. Figure 1 presents the layout of the main elements of a pulsed neutron generator: 1 - anode; 2 - sources of ions of heavy hydrogen isotopes; 3 - cathode, which consists of two coaxial cylindrical magnetic elements; 4 - GIN; 5 - place of neutron generation in colliding beams of heavy hydrogen isotopes; 6 - two plates of the anode ring configuration; l is the distance between the annular plates of the anode; R is the outer radius of the annular plates of the anode; r is the inner radius of the annular plates of the anode; h is the height of the deuteron source; f is the width of deuteron sources; d is the diameter of the cylindrical magnetic elements; L is the distance between the cylindrical magnetic elements.

Figure 2 presents a section aa Figure 1, which shows the layout of the elements of a pulsed neutron generator: 1 - anode; 2 - sources of ions of heavy hydrogen isotopes; 6 - two plates of the anode ring configuration.

Permanent magnets, for example, of NdFeB, are used in the design of a pulsed neutron generator, which provide the required magnetic field induction in the proposed geometry in the range of 0.3 <V <0.6 T. The lower limit is determined by the beginning of the action of the magnetic isolation of electrons between the anode and cathode, the upper limit is determined by the possibility of magnetic elements and the absence of the need for a larger magnetic field induction.

, тем самым достигается высокий КПД использования энергии источника импульсного высоковольтного напряжения 4 и уменьшается энергетическая цена генерируемых нейтронов, так как энергия расходуется исключительно на ускорение ионов тяжелых изотопов водорода, а не электронов. Движущиеся на встречу дейтроны сталкиваются друг с другом, при этом происходит ядерная реакция синтеза с образованием нейтронов в месте 5.A pulsed neutron generator operates as follows. When switching on the pulsed sources of ions of heavy hydrogen isotopes 2 from the outlet of the source of heavy hydrogen isotopes 2 ions into the cavity of the anode 1, deuterons come out already in azimuth uniformly. At this moment, the source of the pulsed high-voltage voltage is turned on 4. Deuterons are accelerated in the direction of the axis of the anode and cathode to the neutron generation site 5. Passing through the axial line, accelerated deuterons are decelerated, moving again to the ring anode, then are accelerated again to the axis and repeat this trajectory several times. . The magnetic field of the magnetic elements impedes the movement of electrons generated at the cathode to the anode, since the Larmor radius of electrons in the selected magnetic field at cathodes 3 is much smaller $$r-\frac{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="00000010.png"\; state="\{\{state\}\}">d</figure-callout>}}{2}$$

Thus, a high efficiency of using the energy of a source of pulsed high-voltage voltage 4 is achieved and the energy price of the generated neutrons decreases, since the energy is spent solely on the acceleration of ions of heavy hydrogen isotopes, and not electrons. The deuterons moving towards the encounter collide with each other, and a nuclear fusion reaction occurs with the formation of neutrons in place 5.

Due to the fact that in the proposed pulsed neutron generator, neutrons are formed as a result of a nuclear reaction in the collision of accelerated deuterons that oscillate many times (up to 1000 times) relative to the axis of the structure and moving towards each other. Therefore, the degradation of a solid-state neutron-forming target at high fluxes of accelerated deuterons and, accordingly, a decrease in the neutron output of the generator, since such a target is generally absent in the proposed pulsed neutron generator, is excluded.

The proposed technical solution allows to increase the resource of the neutron-forming target while achieving high efficiency of using the energy of a high-voltage source.

This increases the manufacturability and efficiency of using the device in various applied problems of science and technology, for example, for geophysical applications, elemental analysis of substances using short-lived radionuclides, and testing of diagnostic tools for powerful pulsed installations for thermonuclear fusion.

Information sources

1. Bespalov D.F., Bykovsky Yu.A., Vergun I.I., Kozlovsky K.I., Kozyrev Yu.P., Leonov R.K., Simagin B.I., Tsybin A.S., Shikanov A.E. Pulsed neutron generator. A.S. USSR, No. 580725, cl. G21G 4/02. - Bull. No. 48, December 30, 1979.

2. Bakhurova L.A., Bespalov D.F., Vergun I.I., Mints A.Z., Pleshakova R.P., Ryabov E.V., Starinsky A.A., Shikanov A.E. Pulsed neutron generator. A.S. USSR, No. 971068, class H05H 1/00. - Bull. No. 48, December 30, 1986.

3. Patent - 135216 RF, IPC Н05Н 3/06. Pulsed neutron generator / Vovchenko E.D., Kozlovsky K.I., Ponomarenko A.G., Ponomarev D.D., Shvedova T.A., Shikanov A.E .; Federal State Autonomous Educational Institution of Higher Professional Education "National Research Nuclear University MEPhI" (NRNU MEPhI). - No. 2013127722/07, Application. 06/18/2013; Publ. 11/27/2013, Bull. No. 33.

Claims (1)

A pulsed neutron generator, consisting of a pulsed high-voltage voltage source and a vacuum chamber containing a cathode and anode, characterized in that the anode is made in the form of a hollow toroidal azimuthally symmetric design of two plates of a ring configuration with an external radius R and an internal radius r located at a distance l from each other, between which n, where n is at least 3, are located, of pulsed ion sources of heavy hydrogen isotopes of each height h and width f, while the cathode is located coaxially with it inside the anode consisting of two cylindrical magnetic elements symmetrically located relative to the anode with a diameter of d and spaced from each other at a distance L with longitudinal magnetization up to induction of 0.3 <B <0.6 T, and the output openings of the sources of ions of heavy hydrogen isotopes are directed to the axis of the anode, and the sizes R, r, l, L, h, f, d satisfy the following relationships:

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