CN105407621B - A kind of compact D D accelerators for neutron production - Google Patents

Abstract

The invention discloses a compact D-D generator suitable for neutron activation analysis or neutron photography. The invention includes: a vacuum cavity, an ion source system, a beam extraction acceleration system, a target system, a high-voltage feed-in system and a vacuum pump system, wherein the ion beam generated by the ion source is extracted, accelerated and combined with the deuterium target on the target system The D-D fusion nuclear reaction releases neutrons, and the two ends of the vacuum chamber are respectively connected with the ion source system, the beam extraction acceleration system, the target system, and the high-voltage feed-in system by the ion source anode flange and the second flange, and the vacuum The cavity is sealed with the anode flange of the ion source and the flange of the high-voltage feeding system through an "O" ring. The ion source is a dual plasma source, and D gas is passed through it. The neutron yield of the present invention can be greater than 1×10 ⁸ s ^‑1 level, and the system such as ion source or target sheet and other internal components can be replaced very conveniently, and the cost of use is greatly reduced at the same time.

Description

A Compact D-D Neutron Generator

technical field

The invention relates to a neutron generator, in particular to a compact D-D generator suitable for neutron activation analysis or neutron photography.

Background technique

Intensive deuterium-deuterium (D-D) and deuterium-tritium (D-T) fusion reaction accelerator neutron source is an important single-energy neutron source (neutron generator for short), which can be widely used in nuclear data measurement, nuclear fusion reactor basic research, military industry Basic research, fast neutron application technology and other aspects. The characteristics of D-D and D-T fusion reactions are that at lower D beam energy, there is a larger reaction cross section, that is, a low-energy accelerator can be used to accelerate D ion beams to bombard deuterium titanium (TiD) targets or tritium titanium (TiT) targets. Deuterium-deuterium (D-D) or deuterium-tritium (D-T) fusion reactions produce intense fast neutrons.

At present, there are two development directions for DD and DT neutron generators. One is to use a pressure doubler accelerator to accelerate a D ion beam of about tens of mA to 300-400keV energy, and bombard a high-speed rotating water-cooled deuterium-titanium (TiD) target or tritium Titanium (TiT) target produces intense fast neutrons, and the yields of fast neutrons for DD and DT reactions can reach the order of 1-5×10 ¹⁰ s ^-1 and 1-5×10 ¹² s ^-1 respectively. This high-current neutron generator has a large volume and cannot be used for neutron activation analysis, neutron photography and other miniaturized mobile neutron application technology devices. It is mainly used in scientific research laboratories to carry out nuclear data measurement and nuclear fusion. Basic research in reactor and military fields; another development direction is miniaturized sealed neutron tube, which works by accelerating 0.1-0.2mA D beam to 100-120keV energy and bombarding deuterium-titanium (TiD) target Or tritium titanium (TiT) target, its DD and DT reaction fast neutron yield is generally greater than 10 ⁷ s ^-1 and 10 ⁹ s ^-1 magnitude, its advantage is small size, the disadvantage is that the neutron yield is difficult to further increase, At the same time, the sealed neutron tube is a one-time vacuum sealing element, and the whole sealed neutron will be scrapped after the target material is exhausted, the service life is short, and the cost is high. At present, the life of neutron tubes in China can only reach several hundred hours, while the life of neutron tubes in the world can reach thousands of hours.

In addition, in comparison, although the DT neutron tube has a high neutron yield, it uses the radioactive tritium gas, which has poor environmental safety. The DD neutron tube does not use the radioactive tritium gas, which has higher environmental safety. The neutron yield index of the neutron tube 10 ⁷ s ^-1 is low, which cannot well meet the requirements of miniaturized and movable neutron application technology devices.

Various forms of neutron generators have been published and patented. For example: 1. Chinese patent CN102548181A [Application publication date: July 4, 2012] discloses a small-diameter radio-frequency driven deuterium-deuterium neutron tube, which is characterized by a small volume and is especially suitable for neutron logging applications. Although the neutron yield of this neutron tube DD can reach the order of 1×10 ⁸ s ^-1 , due to the one-time vacuum sealing structure, it can only be scrapped as a whole after the target life of 1000 hours is reached, which cannot meet the requirements of industrial on-line activation analysis. And other neutron application technology requirements for service life. 2. Chinese patent CN102548181A [Application publication date: December 24, 2012] announced a small-scale high-yield deuterium-deuterium neutron generator. The patent gives 4 implementations: 1) D beam energy 100keV, D beam current The intensity is 100mA, using a pure titanium target, and the beam power on the target is 10kw; 2) The D beam intensity in Scheme 1 is increased to 400mA, using a ceramic target, and the beam power on the target is 40kw; 3) The energy of the D beam is 200keV, and the D beam The current intensity is 1000mA, the pure titanium target is used, and the beam current power on the target is 200kw; 4) The titanium target in scheme 3 is replaced by a ceramic target, the beam current is increased to 4000mA, and the beam current power on the target is 8000kw. Theoretically speaking, the above four implementation schemes can achieve DD neutron yield greater than 10 ¹¹ s ^-1 , even up to 10 ¹² s ^-1 , but the beam power on the target of the above scheme is too large, and the Oil cooling cannot guarantee the control of the target temperature, and the target life will be very short. In addition, the antenna of the high-frequency ion source for neutron generation in this scheme is located at the outer section of the neutron generator, and the high-frequency electromagnetic waves emitted by the antenna will have a negative impact on the neutrons. The power supply and control components of the generator produce strong interference, which will cause unstable operation. 3. Chinese patent CN203748097U [authorized announcement date July 3, 2014] announced the scheme of a small directional neutron generator, which is characterized by bombarding a long directional target under the acceleration of a coaxial electric field and generating high flux in the direction of the target axis neutrons, but their lifespan is as short as that of neutron tubes. 4. Chinese patent CN203761670U [authorized announcement date August 6, 2014] announced a neutron generator scheme using a grid, which is characterized in that the grid is used to effectively suppress the reverse acceleration of secondary electrons, and the output is not high , the short life is equivalent to that of neutron tubes. 5. Chinese patent CN101978429B [authorized announcement date April 29, 2015] announced a long-life and high-efficiency neutron generator. The neutron generator uses a high-frequency coil induction high-frequency ion source, which is characterized by D particles The monoatomic ion ratio of the beam is high (about 80%), and the efficiency is high, but the inner surface of the quartz glass cavity of the ion source is prone to form a metal film due to ion sputtering, which affects the high-frequency electromagnetic wave feeding into the discharge cavity, and requires regular cleaning and maintenance. There is also a common deficiency in the prior art, that is, the generated neutrons are scattered around the device, causing inconvenience in use, and on the other hand, the energy of the generated neutrons will be attenuated, which is not conducive to its application.

Contents of the invention

The invention provides a compact D-D neutron generator applicable to neutron activation analysis or neutron photography, which can overcome the deficiencies of the prior art.

The compact D-D neutron generator of the present invention comprises: a vacuum cavity; an ion source system; a beam extraction acceleration system; a target system; a high-voltage feed-in system and a vacuum pump system; And the D-D fusion nuclear reaction with the deuterium target on the target system releases neutrons. It is characterized in that the vacuum cavity is a section of tubular member, and its two ends are respectively accelerated by the ion source anode flange and the second flange and the ion source system and beam extraction. System, target system, and high-voltage feed-in system are connected. The vacuum chamber is vacuum sealed with the ion source anode flange and the high-voltage feeding system flange respectively through the first and second "O" rings, and the vacuum pump system is used to pump air to maintain a high vacuum in the vacuum chamber. The ion source is a double plasma source, which has D gas in it to generate plasma through discharge, realizes high plasma density through mechanical compression and magnetic compression, and can easily draw a D ion beam greater than 2mA. D monatomic ion ratio is about 50%.

In the embodiment of a kind of compact D-D neutron generator of the present invention, its vacuum chamber body is made of stainless steel, and its pipe wall is provided with the pipeline that communicates with vacuum pump, and the vacuum chamber body is grounded; The system includes: an extraction acceleration electrode made of stainless steel, the negative high voltage is fed to the extraction acceleration electrode by the high voltage feed-in system, an electric field is formed between the ion source anode and the extraction acceleration electrode, and D is extracted from the ion source and accelerated. Ion beam, D The ion beam passes through the hole of the extraction accelerating electrode to the target.

In an embodiment of a compact D-D neutron generator of the present invention, the extraction accelerating electrode is a cylindrical structure, and the bottom of the cylindrical extraction accelerating electrode is provided at a position corresponding to the ion output position of the ion source. A collimating hole for ions to enter and act on the target. The target system is set in the cylindrical extraction acceleration electrode. The target system includes a target holder, a target sheet and a target mounting flange. The target sheet uses a target The plate mounting flange and the third "O" type sealing ring are installed on the target support, and the target support is provided with a cooling groove connected with the cooling pipe, and the cooling liquid cools the target plate well through the cooling pipe and the cooling groove.

A compact D-D neutron generator of the present invention, its high-voltage feed-in system includes: a tubular ceramic high-voltage insulating member with flanges at both ends, and a first flange for fixing the extraction accelerating electrode and realizing electrical connection , the second flange and the high-voltage cable, wherein: the flanges at both ends of the tubular ceramic high-voltage insulating component are fixed to the first flange and the second flange with loose flanges and screws respectively, and the two ends of the tubular ceramic high-voltage insulating component The fourth "O" type sealing ring is used to realize vacuum sealing between the end flange and the loop flange; the inner cavity of the tubular ceramic high-voltage insulating component is inserted into the high-voltage cable; the outer edge of the high-voltage cable is provided with a cooling liquid pipe, and the inner cavity of the tubular ceramic component The gap between the cavity and the outer edge of the high-voltage cable and the cooling pipe is filled with an insulating medium such as transformer oil to achieve good high-voltage insulation performance in this area.

In the compact D-D neutron generator of the present invention, the coolant pipe is a spiral pipe made of insulating material and wound around the outer edge of a high-voltage cable.

A neutron generator of the present invention is characterized in that neutron output windows are respectively arranged on the wall of the cylindrical vacuum chamber and at the corresponding positions on the wall of the cylindrical beam extraction accelerating electrode.

Since the present invention uses a flange to connect the ion source and the target system on the vacuum cavity, it is very convenient to replace the ion source or the target system and other internal components, which greatly facilitates its application and greatly reduces the cost. cost of use.

Due to the adoption of dual plasma sources in the present invention, which are communicated with the D gas source through pipelines, this structure avoids setting the ion source in the quartz glass chamber in the prior art, causing its surface to easily form metal due to ion sputtering. Membrane disease.

In the present invention, a collimation hole for ions to enter and act on the target is provided on the bottom of the cylinder in the extraction accelerating electrode of the cylindrical structure corresponding to the ion output position of the ion source, and the target system is arranged in the cylinder The target is fixed by the target support and the target mounting flange in the lead-out accelerating electrode, and a cooling groove connected with the cooling pipe is provided on the target support. This structure realizes good cooling of the target and at the same time The "O" type sealing ring realizes sealing, and its structure is relatively simple, and it is also more convenient to replace the target.

In the present invention, the high voltage is fed into the tubular ceramic high-voltage insulating member of the system, and a high-voltage cable is arranged inside the tubular ceramic high-voltage insulating member, and an accelerating electrode is arranged at one end thereof. In the prior art, the ceramic high-voltage insulating member and the metal Connection is a very difficult problem to solve, and the connection technology measure that adopts now is to weld ceramics and metal parts, and its yield rate is low, and cost is very high. In the present invention, a tubular ceramic high-voltage insulating member with flanges at both ends is used, and the connection between the ceramic part and the metal part is realized by a loose flange and screws, and an "O" type sealing ring is used to realize the vacuum sealing of the joint part. The structure is extremely simple and has excellent connection and sealing effect, which solves the technical problem that the prior art has not solved for a long time.

The cooling liquid pipe of the present invention is a two-layer spiral pipe made of insulating material around the outer edge of the high-voltage cable. The present invention uses the spiral pipe to increase the length of the cooling liquid pipe, which can effectively increase the resistance of the cooling liquid. Pure water with a rate of 20kΩ is used as the cooling liquid, which can ensure a small high-voltage leakage current, and avoid the defect of poor cooling effect caused by using transformer oil as the cooling liquid in the prior art.

A neutron generator of the present invention is characterized in that neutron output windows are respectively arranged on the wall of the cylindrical vacuum chamber and at the corresponding positions on the wall of the cylindrical beam extraction accelerating electrode. The window is made of stainless steel with a thickness of 1 mm, which can effectively reduce the probability of interaction between the window material and fast neutrons, so as to reduce the impact on the neutron energy spectrum and neutron flux.

The embodiment of a compact DD neutron generator of the present invention has an overall length of 1000 mm and a diameter of Φ300 mm, and the DD neutron yield can be greater than 1×10 ⁸ s ^-1 order of magnitude, so that the DD neutron yield is higher than that of the DD sealed neutron An order of magnitude higher.

Description of drawings

Accompanying drawing 1 is the schematic cross-sectional structure diagram of the present invention.

Accompanying drawing 2 is the partially enlarged schematic diagram of part A in the accompanying drawing 1.

Accompanying drawing 3 is the partially enlarged schematic diagram of part B in the accompanying drawing 1.

Accompanying drawing 4 is the equipotential surface distribution diagram of the electric field in the vacuum chamber of the present invention.

In the drawings: 1-ion source; 2-beam extraction accelerating electrode; 3-neutron output window; 4-target system; 5-tubular ceramic high-voltage insulating member; 8-cooling liquid inlet and outlet pipe; 9-inner cavity of tubular ceramic high-voltage insulating member 5; 10-vacuum flange; 11-vacuum pump; 12-loop flange; 13-cooling pipe; 14-vacuum cavity; 15-stainless steel Vacuum chamber shell; 16-target support; 17-target vacuum sealing flange; 18-target; 19-third vacuum seal "O" rubber ring; 20-first flange; 21-second method Lan; 22-the fourth vacuum seal "O"-shaped rubber ring, 23-the flanges located at both ends of the tubular ceramic high-voltage insulating member 5.

detailed description

The present invention is illustrated below with reference to the accompanying drawings and embodiments. All the following content is only to illustrate the relevant structures in the embodiments of the present invention, and should not be regarded as limiting the content of the present invention.

Accompanying drawing 1 is the schematic cross-sectional structure diagram of an embodiment of the compact neutron generator of the present invention, wherein there is a vacuum chamber 14 with a cylindrical structure as a whole, and the vacuum chamber 14 communicates with a vacuum pump 11 . At the left end of the vacuum chamber 14, the ion source anode flange is used to connect with the ion source, and the right end is connected to the beam extraction acceleration system, target system, and high-voltage feeding system with a high-voltage feeding system flange. In this embodiment, the ion source used is a dual plasma source, wherein a pipeline communicating with a deuterium gas source is provided, and the deuterium gas source can be a deuterium gas cylinder, and is realized by a pressure reducing valve and a gas mass flow controller. Precise control of air intake. The high-voltage feeding system of this embodiment includes: a tubular ceramic high-voltage insulating member 5 with flanges 23 at both ends, a first flange 20 and a second flange for fixing the beam extraction accelerating electrode 2 and realizing electrical connection. 21 and the high-voltage cable 7, as well as the beam extraction accelerating electrode 2 and the target system, see accompanying drawing 3. Wherein: the two ends of the tubular ceramic high-voltage insulating member 5 are respectively provided with flanges 23, and the two flanges 23 are respectively fixed and installed with the first flange 20 and the second flange with looper flanges 21 and screws. The looper flange mentioned above refers to a flange composed of at least two semicircular flange bodies. A fourth "O" type sealing ring is used to realize vacuum sealing between the flanges 23 at both ends of the tubular ceramic high-voltage insulating member 5 and the looper flange. A high-voltage cable 7 is inserted into the inner cavity 9 of the tubular ceramic high-voltage insulating member 5, and the outer edge of the high-voltage cable 7 is a spiral coolant pipeline 6. The spiral coolant pipeline 6 in this embodiment has two layers, and its input end The output end is connected with the coolant inlet pipe 8 and the coolant outlet pipe respectively, and only the coolant inlet pipe 8 is shown in the accompanying drawings 1 and 3, but the coolant outlet pipe is not shown. An insulating medium is filled between the inner cavity wall of the tubular ceramic high-voltage insulating member 5 and the outer edge of the high-voltage cable and the gap between the cooling pipe. In this embodiment, No. 25 transformer oil is filled. This measure ensures that the high-voltage cable and the grounding Good high-voltage insulation between the vacuum chambers 14 of the electric potential. In the embodiment shown in accompanying drawing 1, the beam current extraction accelerating electrode 2 is a cylindrical structure, and the bottom of the tube in the cylindrical extraction accelerating electrode is provided with a position corresponding to the ion output position of the ion source for ion entry. And act on the collimation hole on the target, the first flange 20 electrically connected with the beam extraction accelerating electrode 2 and the flange 23 at one end of the tubular ceramic high-voltage insulating member 5, the second flange 21 and the tubular ceramic high-voltage The flanges 23 at the other end of the insulating member 5 are respectively connected to each other through the loop flanges 12 . In this embodiment, the target system 4 is arranged in the cylinder of the cylindrical beam extraction accelerating electrode 2 . The target system 2 includes a target holder 16, a target mounting flange 17 for mounting a target, a target 18 and a third "O"-shaped sealing ring 19, see FIG. 2 . Between the target sheet 18 and the target holder 16, there is a cooling groove which communicates with the cooling pipeline 13, and the cooling pipeline 13 communicates with the helical cooling liquid pipeline 6. A neutron output window 3 is provided on the outer wall of the cylindrical vacuum cavity 14 , and a neutron output window is also provided at the corresponding position of the window 3 on the wall of the cylindrical beam extraction accelerating electrode, see FIG. 2 .

The structure composed of the tubular ceramic high-voltage insulating member 5 and the high-voltage cable 7 in the embodiment of the present invention feeds the -120kV high voltage into the beam extraction acceleration electrode 2, and forms an electric field between the ion source anode 1 and the extraction acceleration electrode 2, and the electric field Draws greater than 1mA from the ion source plasma. In this embodiment, dual plasma sources are used, and the plasma generated by the discharge can produce high-density plasma through mechanical compression and magnetic compression, and can easily draw D ion beams greater than 1 mA of D ion beam current. The D ion beam is accelerated to 120keV, The ion beam bombards on deuterium titanium (TiD) target 4, D-D fusion reaction occurs, and fast neutrons are released. In this embodiment, the stainless steel vacuum chamber shell 15 and the metal shell of the ion source 1 are both grounded, and the high voltage electric field is confined inside the neutron generator vacuum chamber 14 . The spiral cooling liquid pipe 6 is made of a nylon pipe with good high-voltage insulation performance, and is fixed outside the high-voltage cable. The cooling liquid is fed through the stainless steel joint 8, and passes through the nylon cooling pipe (6) and the stainless steel pipe (13). Reach the target system to realize the cooling of the target piece. The coolant is high-purity water with a resistivity greater than 20kΩ.cm, and its leakage current is not greater than 1mA. After the high-voltage cable is inserted into cavity 9, it is vacuumized and filled with No. 25 transformer oil to ensure good high-voltage insulation performance in this area.

In this embodiment, the neutron output window 3 is a thin flange made of stainless steel, with a diameter of 30mm and a window thickness of 1mm; The electrode aperture is 22mm, and the tubular ceramic high-voltage insulating member 5 is made of 95% ceramics, with a length of 250mm, an outer diameter of 110mm, and an inner diameter of 80mm. The target piece (18) used is made of molybdenum metal, with a diameter of Ф50mm and a thickness of 1mm. The central area is plated with a titanium film with a diameter of Ф50mm and a thickness of about 10um, which is used to absorb deuterium gas. Its dimensions are 1000mm in length and Φ300mm in diameter. In this embodiment, an air-cooled molecular pump with a pumping speed of 300L is used to pump air to ensure that the vacuum degree in the vacuum chamber (14) reaches a high vacuum of 1×10 ^-4 Pa. The molecular pump is equipped with a mechanical pump with a pumping speed of 3L. The pump acts as a backing pump.

Actual operation and testing show that this embodiment can generate fast neutrons with an energy of 2.5 MeV, and the DD neutron yield is greater than 1×10 ⁸ s ⁻¹ ; the electric field equipotential surface distribution in the vacuum cavity 14 is shown in the accompanying drawing As shown in 2, the maximum electric field in the cavity is not greater than 45kV/cm, which is far less than the limit value of 100kV/cm for high vacuum breakdown electric field, which can ensure stable operation and high-voltage safety in laboratories and industrial applications.

Claims (3)

1. A compact D-D neutron generator, comprising: a vacuum cavity; an ion source system; a beam extraction acceleration system; a target system; a high-voltage feeding system and a vacuum pump system; wherein the ion beam generated by the ion source is extracted , accelerate and undergo D-D fusion nuclear reaction with the deuterium target on the target system to release neutrons. The vacuum cavity is a section of tubular member, and its two ends are respectively connected with the ion source system and the beam extraction acceleration system by the ion source anode flange and the second flange. , the target system, and the high-voltage feed-in system are connected, and the vacuum chamber and the anode flange of the ion source and the flange of the high-voltage feed-in system are respectively vacuum-sealed through the first and second "O" rings, and the air is pumped by the vacuum pump system at the same time Maintain a high vacuum in the vacuum chamber, the ion source is a dual plasma source, and D gas is passed through it, the vacuum chamber is made of stainless steel, and the pipe wall is provided with a pipeline connected to the vacuum pump, and the vacuum chamber The body is grounded; the beam extraction acceleration system includes: an extraction acceleration electrode made of stainless steel, a negative high voltage is fed to the extraction acceleration electrode by a high-voltage feed-in system, and a beam is formed between the ion source anode and the extraction acceleration electrode. The electric field extracts and accelerates the D ion beam from the ion source, and the D ion beam passes through the hole of the extraction accelerating electrode to the target. The extraction acceleration electrode is a cylindrical structure, and the bottom of the cylindrical extraction acceleration electrode is connected to the ion source The corresponding position of the ion output position is provided with a collimation hole for ions to enter and act on the target. The target system is set in the cylindrical extraction acceleration electrode. The target system includes a target holder, a target sheet and a target sheet The mounting flange is composed of the target plate with the target plate mounting flange and the third "O" type sealing ring installed on the target support. The target support is provided with a cooling groove connected with the cooling pipe. The high-pressure feeding system includes: its two ends A tubular ceramic high-voltage insulating member with a flange, a first flange, a second flange, and a high-voltage cable for fixing the accelerating electrode and realizing electrical connection, wherein: the flanges at both ends of the tubular ceramic high-voltage insulating member are connected to the lead-out The flange of the accelerating electrode and the flange of the high-voltage feed-in system are respectively fixed and installed with loose flanges and screws, and the fourth "O"-shaped sealing ring is used to realize vacuum between the flanges at both ends of the tubular ceramic high-voltage insulating member and the loose flange. Sealing; the inner cavity of the tubular ceramic high-voltage insulating member is inserted into the high-voltage cable; the outer edge of the high-voltage cable is provided with a cooling liquid pipe, and the gap between the inner cavity of the tubular ceramic member and the outer edge of the high-voltage cable and the cooling pipe is filled with an insulating medium to achieve this. Good high voltage insulation performance in the area. 2. A kind of compact D-D neutron generator according to claim 1, characterized in that the coolant pipeline is a two-layer spiral pipeline made of insulating material that is wound around the outer edge of the high-voltage cable. 3. A kind of compact D-D neutron generator according to claim 2, it is characterized in that on the cylindrical vacuum cavity wall and on the cylindrical wall of the cylindrical beam current extraction accelerating electrode, corresponding positions are provided with neutrons respectively output window.