RU2773038C1 - Pulse neutron generator - Google Patents

Abstract

FIELD: pulsed neutron generators.

SUBSTANCE: invention relates to a pulsed neutron generator. The generator contains a vacuum neutron tube with its power supply circuit and with the accelerating voltage pulse formation circuit, which includes a storage capacitor, a charging inductor, a high-voltage transformer with a multi-row secondary winding made on a magnetic circuit, placed in a metal case filled with a dielectric. The output of the winding is connected to a bowl-shaped screen and a vacuum neutron tube located in it. The vacuum-tight body of the neutron tube has a target electrode located at the end, on the inner side of which there is an electrically conductive cylinder with a screening grid of high transparency. On the outer side of the target electrode, an annular permanent magnet of two half-rings of different poles is located coaxially, forming a magnetic field transverse with respect to the tube axis.

EFFECT: reduction in dimensions and weight while increasing the reliability of the operation of a pulsed neutron generator.

1 cl, 1 dwg

Description

The invention relates to the field of physical instrumentation, in particular to sources of neutron radiation, and is intended for use in the development of neutron generators.

Known downhole pulsed neutron generator containing placed in a metal case vacuum neutron tube with elements of the electrical circuit of its power supply, as well as elements of the accelerating voltage pulse formation circuit, including a storage capacitor, a high-voltage transformer with a multi-row secondary winding made on a magnetic circuit, the output of which is connected to cup-shaped screen and a vacuum neutron tube located in it. Patent of the Russian Federation No. 2368024, IPC G21G 4/02, 09/20/2009.

The disadvantage of this generator is the limited lifetime of the neutron tube due to the lack of an antidynatron grid, i.e. systems for suppressing secondary electron emission resulting from the bombardment of the tube target with deuterium ions. The consequence of this is a rapid failure of the ion source of the tube and a short service life of the neutron generator.

Known pulsed neutron generator containing placed in a metal case filled with a liquid dielectric, a vacuum neutron tube with its power circuit and the accelerating voltage pulse formation circuit, including a storage capacitor, a bias resistance, a choke, a load resistance, a high-voltage transformer with a multi-row secondary winding, made on magnetic circuit, the output of which is connected to a bowl-shaped screen and a vacuum neutron tube located in it. RF patent No. 174178, IPC H05N 3/06, 10/05/2017. This technical solution is taken as a prototype.

This generator has a system for suppressing secondary electron emission, which provides a blocking potential of negative polarity with respect to the target using a highly transparent electrically conductive grid. This potential is created on the grid due to the tube current flowing in the accelerating gap. That part of the current that falls on the grid electrode creates on it the so-called "bias voltage" relative to the target with the help of a resistive bias resistance, which is included in the circuit between the target and the grid electrode. The bias voltage is several kilovolts and is achieved by selecting a resistor, usually located outside the neutron tube. In addition to the difficulty of selecting the optimal resistance value, the disadvantage of using bias resistance is a decrease in the effective value of the accelerating voltage in the interelectrode gap "ion injector - target". This is due to the fact that the negative voltage on the grid electrode with respect to the target, after the deuterium ions pass through the grid electrode, begins to exert a retarding effect on it in relation to the target on positively charged ions.

This generator uses a vacuum neutron tube containing a target assembly placed in a hermetically sealed glass case and a controlled 3-electrode spark source, which consists of an annular anode, a cathode, and an igniting electrode.

The body of the neutron tube is a vacuum-tight shell of two glass cylinders connected to each other by a glass-to-metal junction using a grid electrode. A target assembly is fixed at one end of the shell, and a controlled 3-electrode spark source is fixed at the other. The grid electrode is made in the form of a V-shaped ring made of kovar vacuum-hermetically soldered on both sides with glass cylinders. The implementation of four glass-to-metal junctions significantly complicates the design of the neutron tube, leads to an increase in its length, a possible axial displacement of the two housing cylinders relative to each other. In addition, junctions of glass with a kovar in the region of high electric field strengths can be an additional source of "corona discharges" that can lead to a through breakdown of glass if there are even minor air inclusions in it in the form of "bubbles". To neutralize this phenomenon, it is necessary to install a special metal screen in the form of a cylinder with an edge radius of 1-2 mm.

The bias resistance is wound on a separate insulating frame with high resistivity wire and is an independent structural element that requires additional volume to accommodate.

The objective of the invention is to increase the reliability of the neutron generator, reduce the size and weight.

The technical result of the invention is to reduce the size, weight, increase the reliability of the pulsed neutron generator.

The technical result is achieved by the fact that a pulse neutron generator containing placed in a metal case filled with a dielectric, a vacuum neutron tube with its power supply circuit and with an accelerating voltage pulse formation circuit, including a storage capacitor, a charging inductor, a high-voltage transformer with a multi-row secondary winding, made on magnetic core, the output of which is connected to a bowl-shaped screen and a vacuum neutron tube located in it, the vacuum-tight body of the neutron tube has a target electrode located at the end, on the inside of which there is an electrically conductive cylinder with a high-transparency screening grid mechanically and electrically connected to it, and with On the outer side of the target electrode, an annular permanent magnet of two half-rings of different poles is located coaxially, forming a magnetic field transverse with respect to the axis of the tube.

The essence of the invention is illustrated by the drawing, where:

1 - metal case of the block;

2 – neutron tube;

3 - pulse high-voltage transformer;

4 - storage capacitor;

5 – ion source capacitor;

6 - charging choke;

7 – body of the neutron tube;

8 – target electrode of the neutron tube;

9 – anode electrode of the neutron tube;

10 – cathode electrode of the ion source;

11 – ignition electrode of the ion source;

12 - electrically conductive cylinder;

13 - shielding mesh;

14 - target;

15 – ring-shaped permanent magnet;

16 - bowl-shaped screen;

17 - temperature compensator;

18 - high-voltage bushing.

The pulsed neutron generator is made according to the scheme of switching on a neutron tube with a grounded target assembly. The generator includes a metal case 1, a neutron tube 2, a high-voltage part of its power supply circuit, which provides an accelerating voltage, with a high-voltage transformer 3 on a metal core, a storage capacitor 4, an ion source capacitor 5, a charging inductor 6. The body of the neutron tube 7 is vacuum-tight a glass or ceramic cylinder connected on one side to the target electrode 8, and on the other side to the anode electrode 9 of an ion source containing coaxially located anode 9, cathode 10 and ignition 11. The body of the neutron tube 7 is made of glass or ceramic.

On the inner side of the target electrode, there is a hollow electrically conductive cylinder 12 with a screening grid 13 with high transparency, mechanically and electrically connected to it, as well as a target 14. On the outer side of the target electrode, an annular permanent magnet 15 is coaxially located from two half-rings of different poles, forming a transverse relative to the axis tube magnetic field.

The anode electrode 9 and the hollow electrically conductive cylinder 12 form a closed electrode-to-electrode system, which minimizes the ingress of plasma and electrical discharge products onto the inner surface of the tube body. Screen 16 is installed on the anode electrode of the ion source to equalize the electric fields.

To ensure electrical strength and improve heat transfer from internal energy sources to the external environment, the block is filled with a liquid dielectric having good electrical insulating properties. To compensate for the temperature change in the volume of the liquid dielectric, a thermal compensator 17 is installed.

External power and start pulses are fed through ceramic bushings 18.

The generator works as follows.

1Н2 + 1Н3 → 2Не4 + n образуются нейтроны с энергией 14 МэВ и вторичные электроны.When the switching element (not shown in the drawing) is triggered, the storage capacitor 4, charged up to several kV, is discharged through the primary winding of the transformer 3. A voltage pulse of positive polarity 100–150 kV with a duration of several μs is formed on the secondary winding, which is fed to the cathode electrode 10 of the neutron tube . When the “ignition” pulse of the ion source is applied, the capacitor of the ion source 5 is discharged through the anode 9 and cathode 10. As a result of the desorption of deuterium and its ionization under the action of an arc discharge, deuterium ions are formed, which bombard the target 14 of the neutron tube 2. On the target, as a result of the reaction

1H2 + 1H3 → 2He4 + n, neutrons with an energy of 14 MeV and secondary electrons are formed.

The current of secondary electrons is parasitic and leads to heating of the electrodes of the ion source, reducing the service life of the neutron tube.

The proposed method for suppressing the secondary emission of electrons from the target is associated with the creation of a magnetic field in the target region, the intensity vector of which is directed perpendicular to the trajectories of secondary electrons and the axis of the neutron tube. The secondary electrons knocked out of the target 14 fall into the equipotential volume formed by the electrically conductive cylinder 12 with the screening grid 13 and the target 14 and are returned by the magnetic field to the target, which prevents them from entering the acceleration gap. The advantage of this method over the prototype is that when using permanent magnets, there is no energy cost to suppress electrons and there is no decrease in the energy of ions in the process of their acceleration to the target, as is the case in the prototype.

The effectiveness of the proposed technical solution was verified as a result of comparative tests on the same vacuum neutron tubes. The experiment is verified by measuring the neutron yield by suppressing secondary electrons with a permanent magnet and by using an antidynatron grid and bias resistance. The results are identical within the measurement error.

Thanks to this technical solution, due to the absence of an antidynatron grid and a grid electrode on the neutron tube body, there is no need to manufacture the bias resistance as an independent structural element on a separate frame, as in the prototype, which leads to a simplification of the neutron tube design and a reduction in the weight of the generator. Due to the volume formed as a result of the exclusion of the displacement resistance on a separate frame, the dimensions of the generator are significantly reduced.

Also, the exclusion of the bias resistance from the design made it possible to improve the heat removal from the target of the tube, thus, the cooling of the target was significantly improved and the number of contacting elements of the electrical circuit was reduced, which led to an increase in the reliability of the generator compared to the prototype.

Claims (1)

A pulsed neutron generator containing, placed in a metal case filled with a dielectric, a vacuum neutron tube with its power supply circuit and with an accelerating voltage pulse generation circuit, including a storage capacitor, a charging inductor, a high-voltage transformer with a multi-row secondary winding made on a magnetic circuit, the output of which is connected to a bowl-shaped screen and a vacuum neutron tube located in it, characterized in that the vacuum-tight body of the neutron tube has a target electrode located at the end, on the inside of which there is an electrically conductive cylinder with a screening grid of high transparency mechanically and electrically connected to it, and on the outside The target electrode is coaxially arranged with an annular permanent magnet of two half-rings of different poles, which forms a magnetic field transverse with respect to the axis of the tube.

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