EA042810B1 - PULSE NEUTRON GENERATOR - Google Patents

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 and x-ray generators.

Known downhole pulsed neutron generator containing a vacuum neutron tube with a power supply circuit for an ion source of a vacuum neutron tube and an accelerating pulse formation circuit, consisting of two high-voltage transformers, a storage capacitor, a neutron tube ion source capacitor and a charging inductor, placed in a sealed housing in which all the elements of the vacuum neutron tube power supply circuit are made in the form of bodies of revolution with central holes, they are mechanically and electrically connected to each other by means of threaded electrical contacts with central holes, and with a vacuum neutron tube - through cup-shaped threaded bushings with central and side holes mounted on the target and the anode of the vacuum neutron tube, the vacuum neutron tube and the power supply circuit are placed in a hollow thin-walled cylinder with an outer diameter smaller than the inner diameter of the hermetic case, an outer cavity filled with a liquid dielectric is formed between the outer wall of the thin-walled cylinder and the inner wall of the hermetic case, which communicates with the inner cavity , formed by central holes in the cooled elements of the vacuum neutron tube power circuit. Patent of the Russian Federation No. 2368024, IPC G21G 4/02, 09/20/2009.

The disadvantage of this generator is the limited service life of the 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 tube ion source and a short tube life.

A pulsed neutron generator based on a vacuum neutron tube is known, containing in a metal case filled with a liquid dielectric, a neutron tube with a power supply circuit for its ion source and an accelerating voltage pulse shaper made according to a bipolar power supply circuit, a storage capacitor, a bias resistance. USSR author's certificate No. 708939, IPC H05G1 / 00, 04/30/1994.

In this generator, there is a system for suppressing secondary electron emission in the form of a grid electrode on a neutron tube and a bias resistance located at the end of the target electrode, however, in a well-known generator, the bias resistance is wound on a separate frame of insulating material and is an independent structural element, which requires space to accommodate.

In addition, during long-term operation of the generator and the development of the resource, the ion source of the neutron tube sometimes fails. The resistance of the neutron tube in this mode is hundreds of megohms, and in this case an idle mode of the high-voltage transformer occurs, and the voltage on its secondary winding reaches a value from 200 to 220 kV.

To exclude electrical breakdown, it is necessary to strengthen the insulation, which increases the overall weight characteristics of the generator.

A pulsed neutron generator is known, containing placed in a metal case filled with a liquid dielectric, a vacuum neutron tube with an ion source power supply circuit and an accelerating voltage pulse generation 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 a closed 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 H05H 3/06, 10/05/2017. This technical solution is accepted as a prototype.

The prototype has a large size, length. The generator uses a vacuum neutron tube containing a target assembly placed in a hermetically sealed glass case and a controlled 3-electrode ion 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.

A more negative potential with respect to the target is applied to the grid electrode using a bias resistance wound on a separate frame of insulating material, which ensures suppression of secondary electron emission.

To exclude the idle mode of the high-voltage transformer (the voltage on its secondary winding reaches a value from 200 to 220 kV), when the neutron tube fails, the prototype uses an additional high-voltage winding wound on one of the rods of the high-voltage transformer, which acts as a load resistance. However, in the known generator, the bias resistance and the load resistance are wound with a PEVNKh wire and are independent structural elements that require an additional

- 1 042810 volume, increasing the size and weight of the neutron generator.

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

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

The technical result is achieved by the fact that in a pulsed neutron generator containing placed in a metal case filled with a liquid dielectric, a vacuum neutron tube with an ion source power supply circuit and an 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 a closed magnetic circuit, the output of which is connected to a cup-shaped screen, and a vacuum neutron tube located in it, the vacuum-tight casing of the neutron tube is made in the form of the first and second hollow cylinders made of ceramic material with volumetric electrical resistance, the value of which is determined load resistance for the first hollow cylinder, and a bias resistance for the second hollow cylinder, while the first hollow cylinder is vacuum-hermetically connected to the anode and grid electrodes of the neutron tube, and the second hollow cylinder is connected to the grid and target electrodes, and have with them electrical and thermal contact.

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

- metal case of the generator;

- neutron tube;

- impulse high-voltage transformer;

- storage capacitor;

- tube ion source capacitor;

- throttle;

- the first hollow cylinder;

- the second hollow cylinder;

- target electrode of the neutron tube;

- grid electrode of the neutron tube;

- anode electrode of the neutron tube;

- cathode electrode of the neutron tube;

- ignition electrode of the neutron tube;

- spring contact;

- heat-conducting insulator;

- electric screen;

- temperature compensator;

- high-voltage bushing insulator.

The pulsed neutron generator is made according to the scheme of switching on a neutron tube with a grounded target. The generator includes a metal case 1, a neutron tube 2, a high-voltage part of its power circuit, which provides an accelerating voltage, with a high-voltage transformer 3 on a closed metal core, a storage capacitor 4, an ion source capacitor 5, a choke 6. The body of the neutron tube is a vacuum-tight shell , made in the form of two hollow cylinders 7 and 8 of the same diameter but different lengths, interconnected by a grid electrode 10. At the end of the first cylinder 7 of the housing, using the anode electrode 11, the ion-optical system of the ion source is fixed, containing coaxially located anode, cathode and ignition . At the end of the second cylinder 8 of the housing, the target is fixed with the help of the target electrode 9.

Connections of ceramic hollow cylinders 7 and 8 with metal electrodes are made by metal-ceramic sealed junctions and have electrical and thermal contact with them. The first hollow cylinder 7 and the second hollow cylinder 8 are made of a special ceramic material with bulk electrical resistance, the value of which is determined by the load resistance and bias resistance.

Special ceramics with the required volumetric electrical resistance can be obtained by ceramic technology, by hot pressing from powder. The required resistance depends on the composition of the powder, the pressing technology and the firing temperature. In addition, hollow cylinders can be made of ceramic material with the required resistance in other ways, for example, from semiconductor ceramics or by applying a resistive layer.

According to the scheme with a grounded target node, the grid electrode 10 of the neutron tube is connected to the metal case 1 by means of a spring contact 14, and the target electrode 9 is isolated from the case by a heat-conducting insulator 15.

To ensure electrical strength and improve heat transfer from internal energy sources to the external environment, the sealed metal case 1 is filled with liquid dielectric TKp, which has good dielectric properties. To compensate for temperature changes in volume

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Claims (1)

liquid dielectric, a compensator 17 is installed. To equalize the electric fields, a screen 16 is installed on the anode electrode of the ion source. External power and start pulses are supplied through ceramic bushings 18. The emitter unit works as follows. When the switching element (not shown in the drawing) is triggered, the storage capacitor 5 is discharged through the primary windings of the transformer 3. A voltage pulse of negative polarity 100-150 kV with a duration of 3-4 μs is formed on the secondary winding, which is fed through the spring contacts 14 to the grid electrode 10 of the neutron tubes. With a delay of 0.8 μs, an ion source ignition pulse is formed, which forms a discharge of capacitors 5 through the anode 11 and cathode 12 of the ion source. The resulting deuterium ions bombard the target M of the neutron tube 2. As a result of the reaction 1H ² ' + 1H ³ ^ ₂ He ⁴ + n, neutrons with an energy of 14 MeV and secondary electrons are formed on the target. When current flows through the accelerating gap on ceramic cylinder 8, as a result of the presence of an electrical bias resistance (from 800 Ohm to 5 kOhm), a potential difference arises in it, which locks the secondary electrons formed during the bombardment of the neutron tube target M with deuterium ions, which makes it possible to reduce the parasitic tube current and thereby increase its service life without the need to manufacture bias resistance, as in the prototype. When the generator is operating in normal mode, the electrical resistance of the hollow cylinder 7 - load does not affect the formation of the accelerating voltage, since the secondary winding has an order of magnitude lower resistance. When the generator is operating at a time when the ion source of the neutron tube does not operate, the idle mode of the high-voltage transformer does not occur, since the secondary winding is automatically connected to the load electrical resistance of the hollow cylinder 7, i.e. to a load of 25 to 30 kΩ, which leads to voltage stabilization on the secondary winding of the high-voltage transformer, stabilization of the neutron output and an increase in the service life of the generator without the need to manufacture load resistance, as in the prototype. Thus, the result of the invention is to reduce the size and weight of the neutron generator due to the absence of load resistance and displacement resistance, as independent structural elements, the functions of which are performed by the hollow cylinder 7 and the hollow cylinder 8 of the neutron tube body, made of ceramic material with the necessary volumetric electrical resistance. . In this case, the resulting free volume, which in the prototype was occupied by a core with a load resistance and a frame with a bias resistance, can be used to reduce the size and weight of the neutron generator. In addition, the reliability of the proposed generator should be higher than that of the prototype, since the number of contacted elements of the electrical circuit has decreased. CLAIM A pulsed neutron generator containing, placed in a metal case filled with a liquid dielectric, a vacuum neutron tube with an ion source power supply circuit and an accelerating voltage pulse generation 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 a closed magnetic core, 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 is made in the form of the first and second hollow cylinders made of ceramic material with volumetric electrical resistance, the value of which is determined by the load resistance for of the first hollow cylinder, and a bias resistance for the second hollow cylinder, wherein the first hollow cylinder is vacuum-hermetically connected to the anode and grid electrodes of the neutron tube, and the second hollow cylinder is connected to the grid and target electrodes, and have electrical and thermal contact with them. -