VNIIA neutron generators for thermonuclear research

VNIIA neutron generators for

thermonuclear research

The All-Russian Research Institute of Automatics named after N.L. Dukhov

Yevgeni P. Bogolubov, Valentin I. Ryzhkov, Sergey V. Syromukov


All-Russian Research Institute of Automatics named after N.L. Dukhov (VNIIA) is one of the leading institutions governed

by Federal Agency of Atomic Energy.One of the basic activity lines in the institute is the development and manufacture of neutron generators using sealed accelerating tubes.All produced by VNIIA generators may be divided into three types depending upon physical principles underlying their operation.

1. Generators using vacuum tubes2. Generators using gas-filled tubes3. Generators using "plasma focus" chambers

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Applications.1. Hazard material control and detection (nuclear

materials, explosives, toxic agents, drugs)2. Oil&gas field logging3. Neutron radiography and tomography4. Scientific research including solar system planet study5. Oncological patient radiotherapyVNIIA is the only firm in the world manufacturing such

variety of generator types having so wide spectrum of specifications and parameters. You may familiarize with products of VNIIA on website: www.vniia.ru .

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VNIIA serially produces generators having flux up to 1010 n/s. Urgent thermonuclear problem, radiotherapy, neutron radiography gave impetus for the development of neutron generators having 1010 - 1011 n/s flux.

The basic part of generator is sealed accelerating tube; just the tube defines generator parameters. Typical circuit for gas-filled neutron tube is shown in Fig.1.

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Figure 1. Gas-filled neutron tube circuit

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Sealed neutron tube contains ion source, accelerating electrode system, and target combined in hermetic sealed housing. Tube volume includes getter containing bound deuterium and tritium. While operation at heating getter deuterium and tritium release in tube volume and are ionized in ion source. Produced ions are formed in beam and accelerated between tube electrodes. Accelerated ions bombard target saturated with deuterium and tritium, and neutrons produce as a result of thermonuclear reactions.

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Gas-filled tubes use self-saturating neutron target. Such targets are saturated by deuterium and tritium while bombarding by ion beam within all tube operation time. This method allows appreciable increase of gas-filled tube life time in comparison with vacuum tubes. Tube has antidynatron electrode (suppressor) providing suppression of secondary electron current from target.

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Sealed tubes in powerful neutron generators are normally counted for 150-250 kV at ion current 3-5 mA. Such parameters provide neutron flux (0,5-1)x1011 n/s.Due to thermonuclear reactions 3H(d,n)4He or 2H(d,n)3He used in generators for neutron production the generators may be successfully used for thermonuclear facilities neutron field simulation.Portable neutron generators with sealed accelerating tubes are the most perspective for the purposes. The peculiarity of such generators is complete safety when switched off, simple operation, small sizes, and operation at any position of neutron unit.

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Simulation of thermonuclear facility neutron fields requires minimum distortion of neutron spectrum from tube target and distortion in neutron emission isotropy. For generator these requirements mean decrease of material quantity near target. This especially relates to materials with high coefficient of fast neutron scattering. For solving the task we used powering circuit for tube with grounded target in the developed generators for thermonuclear research. In such generators tube's ion source is under high potential inside hermetic housing of neutron unit filled with high-voltage dielectric; neutron-emitting target is grounded and jutted out of housing.

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Figure 2. Neutron unit of generator with grounded target

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Figure 2 shows neutron unit of generator with grounded target. Tube's target juts out neutron unit at about 50 mm. Target is heated by ion beam. Therefore target is cooled with water. Water film thickness near target is about 1 mm. High-voltage dielectric thermal compensator is positioned by neutron unit side opposite to tube.

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Some thermonuclear research using neutron generator should be performed within many tens hours. Generator and radiation detectors will be placed at rather distance from each other; materials effectively absorbing neutron emission will be placed between them. This stipulates more high requirements to neutron output and life time of sealed tube. Generator should provide neutron flux of about 1011 n/s and life time of sealed tube should be at least 100 hours.

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In some studies neutron unit will be placed inside thermonuclear facilities. This requires minimizing dimensions of generator's emitting module – neutron unit. It is necessary to provide transportability, possible displacement of neutron unit in thermonuclear facility volume.

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The next requirement is the possibility to obtain 2,5 MeV neutrons from the 2H(d,n)3He reaction. This requirement is realized by use of sealed tube filled with deuterium. D-D neutron output is about 100 times less than d-t neutron output because of difference in sections.

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VNIIA is currently developing the ING-14 and ING-24 neutron generators intended for simulation of thermonuclear facilities neutron field.

The ING-14 generator has flux up to 5x1010 n/s. Its development is now at final stage. Both generators are intended for continuous operation within many hours without interruption. They have grounded targets, placed beyond neutron units that, as shown above, decreases distortion of neutron spectrum and radiation isotropy. Generators contain neutron unit, power supply unit, and cable kit.

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The ING-14 generator uses the GNT5-67 sealed tube shown in Fig.3. The tube has ion source with cold cathode and permanent magnet. Housing of the tube is metal-glass. Tube is mounted on ING-14 neutron unit flange so that source and metal-glass housing are inside unit and target juts out unit at about 5 cm. ING-14 neutron unit photo is presented in Fig.4.

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GNT5-67 sealed neutron tube

Neutron energy 14 MeV

Neutron flux 5х1010n/s

Figure 3

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ING-14 neutron generator with GNT5-67 sealed tube


Neutron flux 5х1010n/s


Figure 4.

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The ING-24 neutron generator is designed for 1011 n/s; the generator contains metal-ceramic tube GNT1-100; photo of this tube is presented in Fig.5. This tube is also mounted on ING-24 neutron unit flange having rather large dimensions and appearance analogous to ING-14. Target of GNT1-100 tube juts out flange sizes at 5 cm too.

ING-14 and ING-24 specifications are presented in the Table 1.

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The GNT1-100 neutron tube


Neutron flux 1011n/s

Figure 5.

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Parameter ING-14 ING-24 Neutron flux, n/s 0,5х1011 1х1011

Target Grounded Grounded

Tube life time, hours 300 200

Accelerating voltage, kV 150 270

Emission mode steady steady

Power supply 220 V, 50-60 Hz 220 V, 50-60 Hz

Operation mode continuous continuous

Neutron unit dimensions, mm 240х620 280х700

Power supply dimensions, mm 465х430х155 465х430х300

Specifications of VNIIA neutron generators for thermonuclear research

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Thus VNIIA has scientific-technical, design, technological and production base for development and manufacture of a wide class of neutron generators, in that number, generators for thermonuclear facilities neutron fields simulation.

VNIIA is interested in developing science&technical co-operation in both delivery of generators designed for thermonuclear research and joint development of generators and equipment on their base.

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Documents

VNIIA neutron generators for thermonuclear research