A kind of compact D-D neutron generator
Technical field
The present invention relates to a kind of neutron generator, particularly a kind of compact D-D generator being applicable to neutron activation analysis or neutron photography use.
Background technology
High current deuterium deuterium (D-D) and deuterium tritium (D-T) fusion reaction accelerator neutron generator are important monoenergetic neutrons (abbreviation neutron generator), can be widely used in the various aspects such as Nuclear Data measurement, nuclear fusion stack basic research, military project basic research, fast neutron application technology.The feature of D-D and D-T fusion reaction is, under lower D beam energy, have larger reaction cross-section, namely available low energy accelerator accelerates D ion beam, bombards deuterium titanium (TiD) target or tritium titanium (TiT) target generation deuterium deuterium (D-D) or deuterium tritium (D-T) fusion reaction and produces strong fast neutron.
At present, D-D and D-T neutron generator has two developing direction, one is utilize voltage-multiplying type accelerator that the D ion beam of about tens mA is accelerated to 300-400keV energy, bombardment High Rotation Speed water-cooled deuterium titanium (TiD) target or tritium titanium (TiT) target, produce high current fast neutron, D-D and D-T reacts fast neutron yield can reach 1-5 × 10 respectively
10s
-1with 1-5 × 10
12s
-1magnitude.This high intensity proton beam volume is comparatively large, cannot be used for the miniaturized packaged type neutron such as neutron activation analysis, neutron photography application technology device, be mainly used in R&D units, to carry out the basic research in the fields such as Nuclear Data measurement, nuclear fusion stack and military project; Another developing direction is miniaturized sealing neutron tube, and its working method is, by the D beam acceleration of 0.1-0.2mA to 100-120keV energy, bombardment deuterium titanium (TiD) target or tritium titanium (TiT) target, itself D-D and D-T reacts fast neutron yield and is generally greater than 10
7s
-1with 10
9s
-1magnitude, its advantage is that volume is small, and shortcoming is that neutron yield is difficult to further improve, and meanwhile, sealing neutron tube is disposal vacuum potted component, and target exhausts rear whole sealing neutron and will scrap, and useful life is short, and cost is high.At present, the domestic neutron tube life-span can only reach hundreds of hour, and the international neutron tube life-span can reach thousands of hours.
In addition, comparatively speaking, although D-T neutron tube neutron yield is high, use radgas tritium, its environmental safety is poor, and D-D neutron tube does not use radgas tritium, has higher environmental safety, but D-D neutron tube 10
7s
-1neutron yield index on the low side, well cannot meet the requirement of miniaturized packaged type neutron application technology device.
Now the neutron generator of existing various ways discloses and has applied for patent.Such as: 1, Chinese patent CN102548181A[Shen Qing Publication day: on July 4th, 2012] disclose a small-diameter radio-frequency drive deuterium-deuterium neutron pipe, be characterized in that volume is very little, be particularly useful for neutron well logging application.Although this neutron tube DD neutron yield can reach 1 × 10
8s
-1magnitude, but owing to taking disposal vacuum hermetically-sealed construction, can only entirety scrap after the target lifetime arrival of 1000 hours, industrial activation analysis and other neutron application technologies online cannot be met to the requirement in useful life.2, Chinese patent CN102548181A[Shen Qing Publication day: on December 24th, 2012] disclose a small-sized high yield deuterium deuterium neutron generator, this patent gives 4 embodiments: 1) D beam energy 100keV, the strong 100mA of D line, adopts pure titanium target, beam power 10kw on target; 2) the D line in scheme 1 is brought up to 400mA by force, adopt ceramic target, beam power 40kw on target; 3) the strong 1000mA of D beam energy 200keV, D line, adopts pure titanium target, beam power 200kw on target; 4) change the titanium target in scheme 3 into ceramic target, line brings up to 4000mA, beam power 8000kw on target.Above four kinds of embodiments theoretically, can realize DD neutron yield and be greater than 10
11s
-1, even can reach 10
12s
-1but beam power is too large on such scheme target, go to ensure the control to target temperature with the oil cooling mentioned in scheme, target lifetime will be very short, in addition, the antenna of radio frequency ion source that this scheme neutron occurs is in the outer section of neutron generator, and the frequency electromagnetic waves that antenna sends produces strong interference by the power supply of neutron generator and control element, can cause fluctuation of service.3, Chinese patent CN203748097U[authorized announcement date on July 3rd, 2014] disclose compact directional neutron generator scheme, be characterized under coaxial electric field is accelerated, bombard microscler directed target, produce high-throughout neutron at target axis direction, but the life-span is short suitable with neutron tube.4, Chinese patent CN203761670U[authorized announcement date on August 6th, 2014] disclose a kind of neutron generator scheme that adopts grid, be characterized in adopting grid effectively to suppress the anti-acceleration of secondary electron, yield is not high, and the life-span is short suitable with neutron tube.5, Chinese patent CN101978429B[authorized announcement date on April 29th, 2015] disclose a life-span long high efficiency neutron generator, this neutron generator have employed high frequency coil induction type radio frequency ion source, be characterized in that D particle beams monatomic ion is than high (about 80%), efficiency is high, but ionogenic quartz glass inner cavity surface is easily because ion sputtering forms metal film, affect frequency electromagnetic waves feed-in discharge cavity, need periodic cleaning to safeguard.Also there is a common deficiency in prior art, the scattering around device of namely produced neutron, causes the inconvenience in use, and the neutron energy of generation also can be made on the other hand to decay and be unfavorable for that it is applied.
Summary of the invention
The invention provides a kind of compact D-D neutron generator that overcome prior art deficiency, that be applicable to neutron activation analysis or neutron photography use.
Compact D-D neutron generator of the present invention comprises: vacuum cavity; Ion source system; Line draws accelerating system; Target system; High pressure feedthrough system and vacuum pump system; The ion beam current wherein produced by ion source is drawn, accelerate and with the deuteron target on target system, D-D fusion nucleus occurs to react and release neutron, it is characterized in that vacuum cavity is one section of tubular element, its two ends respectively with ion source anode flange and the second flange and ion source system and line draw accelerating system, target system, high pressure feedthrough system realize connecting.Vacuum cavity and realize vacuum seal respectively by the first and second "O"-rings between ion source anode flange and high pressure feedthrough system flange, is bled by vacuum pump system simultaneously and keeps being high vacuum in vacuum cavity.Described ion source is two plasma sources, and be connected with D gas in it and produce plasma by electric discharge, realize high plasma density by mechanical compress and magnetic compression, easily can draw the D ion beam current being greater than 2mA, the D monatomic ion ratio of its line is about 50%.
In the embodiment of a kind of compact D-D neutron generator of the present invention, the stainless steel manufacture of its vacuum cavity, its tube wall is provided with the pipeline being communicated with vacuum pump, and vacuum cavity ground connection; Described line is drawn accelerating system and is comprised: an extraction accelerating electrode be made up of stainless steel, by high pressure feedthrough system, negative high voltage is fed on extraction accelerating electrode, electric field is formed between ion source anode and extraction accelerating electrode, draw from ion source and accelerate D ion beam, D ion beam is through drawing accelerating electrode hole on target.
In the embodiment of a kind of compact D-D neutron generator of the present invention, it draws accelerating electrode is a tubular structure, offer one at the bottom of cylinder in the extraction accelerating electrode of tubular enter with ionogenic ion outgoing position opposite position for ion and act on the collimating aperture on target, target system is arranged in the extraction accelerating electrode of tubular, described target system comprises target holder, target sheet and target sheet mounting flange are formed, target sheet target sheet mounting flange and the 3rd " O " RunddichtringO are arranged on target holder, target holder is provided with the cooling bath be communicated with cooling pipe, cooling fluid well cools target sheet through cooling pipe and cooling bath.
A kind of compact D-D neutron generator of the present invention, its high pressure feedthrough system comprises: its two ends with flange tubular ceramic High-Voltage Insulation component, for fixing extraction accelerating electrode and realize electrically connect the first flange, the second flange and high-tension cable, wherein: two end boss of tubular ceramic High-Voltage Insulation component and fixedly mounting with lap joint flange and screw respectively between the first flange and the second flange, vacuum seal is realized with the 4th " O " RunddichtringO between two end boss of tubular ceramic High-Voltage Insulation component and lap joint flange; The inner chamber of tubular ceramic High-Voltage Insulation component inserts high-tension cable; The outer rim of high-tension cable is provided with coolant duct, is filled with the dielectric as transformer oils between the inner chamber of tubular ceramic component and the gap of high-tension cable outer rim and cooling pipe, to realize the good High-Voltage Insulation performance in this region.
A kind of compact D-D neutron generator of the present invention, its coolant duct is the spiral pipe being around in high-tension cable outer rim that insulating material is made.
A kind of neutron generator of the present invention, is characterized in that cylindrical shape vacuum chamber body wall is respectively arranged with neutron output window with opposite position on the barrel of tubular line extraction accelerating electrode.
The present invention owing to adopting flange connect ion source and target system etc. on vacuum cavity, therefore can change easily the system such as ion source or target sheet and other in establish parts, so just can greatly facilitate it to apply, greatly reduce the cost of use simultaneously.
The present invention is owing to have employed two plasma source, and be communicated with D gas source by pipeline in it, this structure makes to avoid in prior art and is arranged in quartz glass chamber by ion source, causes its surface easily because ion sputtering forms the worn-out sick of metal film.
Offer one at the bottom of cylinder in the present invention in the extraction accelerating electrode of tubular structure enter with ionogenic ion outgoing position opposite position for ion and act on the collimating aperture on target, and target system is arranged in the extraction accelerating electrode of tubular, by target holder and target sheet mounting flange, target sheet is fixed, on target holder, be provided with the cooling bath be communicated with cooling pipe simultaneously, this structure achieves the good cooling to target sheet, use " O " RunddichtringO to realize sealing simultaneously, its structure is relatively simple, and the replacing of also more convenient target sheet.
By within high pressure feedthrough system tubular ceramic High-Voltage Insulation component in the present invention, and high-tension cable is set in the inside of this tubular ceramic High-Voltage Insulation component, in its one end, accelerating electrode is set, Ceramic high-pressure insulating component is very insoluble problem with connecting of metal in the prior art, the connection technique measure now adopted is welded with metalwork by pottery, its rate of finished products is low, and costly.The tubular ceramic High-Voltage Insulation component of its two ends with flange is have employed in the present invention, and realize connecting of ceramic component and metal parts with lap joint flange and screw, " O " RunddichtringO is adopted to realize the vacuum seal of point of attachment, its structure is very simple and have splendid connection and sealing effectiveness, solves the long-term unsolved technical barrier of prior art.
Coolant duct of the present invention is the two-layer spiral pipe being around in high-tension cable outer rim that insulating material is made, the present invention adopts spiral pipe to add the length of cooling fluid pipeline, can effectively increase cooling fluid resistance, adopt resistivity 20k Ω pure water as cooling fluid, less wire tension can be ensured, the defect of the cooling effect difference avoiding cooling fluid in prior art to use transformer oil to cause.
A kind of neutron generator of the present invention, is characterized in that cylindrical shape vacuum chamber body wall is respectively arranged with neutron output window with opposite position on the barrel of tubular line extraction accelerating electrode.Window is the stainless steel that 1mm is thick, effectively can reduce the interaction probability of window material and fast neutron, to reduce the impact on neutron spectrum and neutron flux.
Its contour length of embodiment 1000mm of a compact D-D neutron generator of the present invention, diameter of phi 300mm, D-D neutron yield can be greater than 1 × 10
8s
-1magnitude, makes a D-D neutron yield magnitude higher than D-D sealing neutron tube.
Accompanying drawing explanation
Accompanying drawing 1 is cross-sectional view of the present invention.
Accompanying drawing 2 is A position close-up schematic view in accompanying drawing 1.
Accompanying drawing 3 is B position close-up schematic view in accompanying drawing 1.
Accompanying drawing 4 is electric field equipotential surface distribution map in vacuum chamber of the present invention.
In accompanying drawing: 1-ion source; 2-line draws accelerating electrode; 3-neutron output window; 4-target system; 5-tubular ceramic High-Voltage Insulation component; 6-helical form coolant duct; 7-high-tension cable; 8-cooling fluid inlet/outlet pipe; The inner chamber of 9-tubular ceramic High-Voltage Insulation component 5; 10-vacuum flange; 11-vacuum pump; 12-lap joint flange; 13-cooling pipe; 14-vacuum cavity; 15-stainless-steel vacuum cavity shell; 16-target holder; 17-target sheet vacuum seal flange; 18-target sheet; 19-the 3rd vacuum seal " O " type rubber ring; 20-first flange; 21-second flange; 22-the 4th vacuum seal " O " type rubber ring, 23-is positioned at the flange at tubular ceramic High-Voltage Insulation component 5 two ends.
Embodiment
The present invention is below in conjunction with drawings and Examples explanation.Following all the elements are only and dependency structure in embodiments of the invention are described, and can not be considered as the restriction to content of the present invention.
Accompanying drawing 1 is the cross-sectional view of an embodiment of compact neutron generator of the present invention, wherein has an entirety to be columnar structured vacuum cavity 14, is communicated with vacuum pump 11 at vacuum cavity 14.Realize connecting with ionogenic at vacuum cavity 14 left end ion source anode flange, accelerating system, target system, the connecting of high pressure feedthrough system are drawn in the right-hand member realization of high pressure feedthrough system flange and line.In the present embodiment, ion source used is two plasma sources, and be wherein provided with the pipeline being communicated with deuterium source, described deuterium source can be deuterium bottle, and realizes the accurate control to air inflow by pressure-reducing valve and gas mass flow controller.The high pressure feedthrough system of the present embodiment comprises: its two ends with the tubular ceramic High-Voltage Insulation component 5 of flange 23, to draw the first flange 20, second flange 21 and high-tension cable 7 that accelerating electrode 2 also realizes electrically connecting for fixing line, and line draws accelerating electrode 2, target system, see accompanying drawing 3.Wherein: the two ends of tubular ceramic High-Voltage Insulation component 5 are respectively provided with flange 23, these two flanges 23 fixedly mount respectively with lap joint flange 21 and screw respectively and between the first flange 20 and the second flange, and described lap joint flange refers to the flange be made up of the flange body of at least two semicircles.Vacuum seal is realized with the 4th " O " RunddichtringO between two end boss 23 and lap joint flange of tubular ceramic High-Voltage Insulation component 5.High-tension cable 7 is inserted in the inner chamber 9 of tubular ceramic High-Voltage Insulation component 5, the outer rim of high-tension cable 7 is spiral helicine coolant duct 6, spiral helicine coolant duct 6 in the present embodiment is two-layer, its input and output go out pipe conducting with cooling fluid inlet pipe 8 and cooling fluid respectively, only showed cooling fluid inlet pipe 8 in accompanying drawing 1 and accompanying drawing 3, and do not indicate cooling fluid go out pipe.Dielectric is filled with between the internal chamber wall of tubular ceramic High-Voltage Insulation component 5 and the gap of high-tension cable outer rim and cooling pipe, what be filled with in the present embodiment is No. 25 transformer oil, and this measure ensure that high-tension cable and is in the good High-Voltage Insulation between the vacuum cavity 14 of earthing potential.In embodiment shown in accompanying drawing 1, it is a tubular structure that line draws accelerating electrode 2, cylinder bottom in the extraction accelerating electrode of tubular and offer one for ion with ionogenic ion outgoing position opposite position and enter and act on the collimating aperture on target, draws the first flange 20 that accelerating electrode 2 is electrically connected and flange 23, second flange 21 being positioned at tubular ceramic High-Voltage Insulation component 5 one end with line and the flange 23 that is positioned at tubular ceramic High-Voltage Insulation component 5 other end is interconnected respectively by lap joint flange 12.In the present embodiment, target system 4 is arranged in the cylindrical shell of line extraction accelerating electrode 2 of tubular.Described target system 2 comprising target holder 16, forming, see accompanying drawing 2 for installing the target sheet mounting flange 17 of target sheet, target sheet 18 and the 3rd " O " RunddichtringO 19.Below target sheet 18 be provided with the cooling bath be communicated with cooling pipe 13 between target holder 16, cooling pipe 13 then with helical form coolant duct 6 conducting.The outer wall of cylindrical shape vacuum cavity 14 is provided with neutron output window 3, the barrel of tubular line extraction accelerating electrode is also provided with neutron output window, see accompanying drawing 2 with window 3 relevant position.
-120kV high pressure is fed into line and draws accelerating electrode 2 by the structure that the tubular ceramic High-Voltage Insulation component 5 of embodiments of the invention and high-tension cable 7 form, between ion source anode 1 and extraction accelerating electrode 2, form electric field, this electric field is drawn and is greater than 1mA from ion source plasma.Two plasma source is employed in this embodiment, the plasma that its electric discharge produces is by mechanical compress and magnetic compression, high-density plasma can be produced, easily can draw the D ion beam current being greater than 1mA. D ion beam and accelerate to 120keV, ion beam bombardment is on deuterium titanium (TiD) target 4, there is D-D fusion reaction, release fast neutron.The stainless-steel vacuum cavity shell 15 of this embodiment and the equal ground connection of metal shell of ion source 1, and high voltage electric field is confined to the inside of neutron generator vacuum cavity 14.Helical form coolant duct 6 nylon tube with good High-Voltage Insulation performance turns to helical form, be fixed on outside high-tension cable, cooling fluid is sent into by stainless joint 8, and arrives target system through nylon cooling pipe (6) and stainless steel pipes (13), realizes the cooling of target sheet.Cooling fluid adopts resistivity to be greater than the high purity water of 20k Ω .cm, and its leakage current is not more than 1mA.After high-tension cable inserts chamber 9, through vacuumizing and filling with No. 25 transformer oil, to ensure that this region is by good High-Voltage Insulation performance.
In the present embodiment, the thin flange that neutron output window 3 is made for stainless steel, diameter is 30mm, window thickness 1mm; Line is drawn accelerating electrode 2 and is processed by stainless steel, external diameter 106mm, internal diameter 100mm, long 245mm, draw accelerating electrode aperture 22mm, tubular ceramic High-Voltage Insulation component 5 is made up of 95% pottery, its length is 250mm, and external diameter 110mm is interior through 80mm, target sheet (18) used is made up of molybdenum, and diameter is Ф 50mm, and thickness is 1mm, central area plating diameter Ф 50mm thickness is about the titanium film of 10um, for adsorbing deuterium, its overall dimension is length 1000mm, diameter of phi 300mm.The present embodiment adopts the fast molecular pump for 300L of a typhoon cold-draw to bleed to ensure that the vacuum degree in vacuum chamber (14) reaches 1 × 10
-4the high vacuum of Pa, it is that the mechanical pump of 3L is as fore pump that molecular pump is furnished with a pumping speed.
Show through actual motion and test, the present embodiment can produce the fast neutron of 2.5MeV energy, and D-D neutron yield is greater than 1 × 10
8s
-1magnitude; Electric field equipotential surface distribution in its vacuum chamber 14 as shown in Figure 2, maximum field in chamber is not more than 45kV/cm, much smaller than the limit value of high vacuum breakdown electric field 100kV/cm, can stable operation be ensured, the high-voltage safety in laboratory and commercial Application scene can be guaranteed.