Discharge-type Fusion Neutron Source Research Articles

Employing of ZrCo as a fuel source in a discharge-type fusion neutron source operated in self-sufficient mode

A discharge-type fusion neutron source generates neutrons by fusion reactions of hydrogen isotope atoms. In order to operate the fusion device based on the deuterium–tritium (D–T) fusion reaction, the tritium inventory is required to be decreased. In the present work, a self-sufficient system was installed into the fusion device for reducing the amount of hydrogen isotope fuel gas. The fuel gas was supplied and recovered with an intermetallic compound ZrCo in a sealed chamber in this system. A deuterium–deuterium operation was maintained for more than 60 min with stable discharge voltages, and the temperature of the ZrCo bed was changed to improve the neutron production rate. Factors that influenced the pressure inside the chamber were determined and optimized. Gas analysis using a quadrupole mass spectrometer indicates a dilution of the deuterium fuel was caused by hydrogen isotope exchange between the supplied deuterium gas and the absorbed protium on the chamber and electrodes surface. This system's hydrogen isotope control method and the amount of fuel were proposed for a D–T operation.

Characteristics of Gas Mixture Supply/Pressure Control Using Non-Evaporable Getters in a Discharge-Type Fusion Neutron Source

The first tritium burning experiments of the discharge type fusion neutron source were conducted in January 2015, using a 93% deuterium and 7% tritium gas mixture. In order to conduct the experiment in a closed environment, a gas feed and exhaust system using non-evaporable getter material was prepared. This system was designed to minimize tritium usage and produce measurable changes in the neutron production rate on the basis of the dependence of the equilibrium pressure on getter temperature as included in the manufacturer’s data sheet. However, the present experiments revealed that the gas supply was insufficient and that the discharge duration was limited to about 2 minutes by the pressure drop during discharge.To determine the cause, verification experiments using hydrogen and deuterium gas were performed. It was found that the pressure variation with getter temperature could be mimicked by exploiting isotope effects and adjusting the hydrogen/deuterium concentration in the getter material according to the gas released into the vacuum chamber. Moreover, prolonged maintenance of a discharge was demonstrated by roughly tripling the amount of gas.The tritium concentration in the gas mixture, estimated on the basis of the present results, varied between 1.5% and 6.7% according to the assumptions used.

Neutron Beam Generation by the Cylindrical Fusion Neutron Source

We have investigated the neutron generation characteristics of discharge-type fusion neutron source by experiments and computer simulations for several years. The cylindrical inertial electro-static confinement device used for these studies has been considered to be a point source where neutrons emitted isotropic. The aspect ratio (length divided by diameter) of the device is 1∼2. For neutron applications, a beam shape where neutrons are emitted in a specific direction may be more convenient.In this paper we describe recent results of neutronic calculations for making a beam-type neutron source by increasing aspect ratio of the device and by locating reflecting material around the device. It is found that the increase of aspect ratio of 2∼5 does not strongly affect the neutron flux distribution, but that neutron fluxes in the axial direction becomes 2∼3 times larger than those without reflectors and more than 1 order stronger than the radial direction by adding reflector.

Research and Development of the Humanitarian Landmine Detection System by a Compact Fusion Neutron Source

A 5 year task is described on the research and development of the advanced humanitarian landmine detection system by using a compact discharge-type fusion neutron source called IECF (Inertial-Electrostatic Confinement fusion) device and 3 dual sensors made of BGO and NaI. With 107 D-D neutrons/s stably produced in steady-state mode, H-2.2 MeV, N-5.3, 10.8 MeV, gamma rays from (n, gamma) reaction with nitrogen atoms in the explosives are measured for two kinds of explosives (TNT, RDX), under the conditions of three different buried depths, and soil moistures. Final detection probabilities for arid soil are found to be 100 % in the present tests, i.e., depths not exceeding 15 cm, moisture content of 18.5 % or less, and 20-minute measurements. The neutron backscattering method is found also excellent.

Research and Development on Humanitarian Landmine Detection System by Use of a Compact D-D Fusion Neutron Source

Current results are described on the research and development of the advanced humanitarian landmine detection system by using a compact discharge-type fusion neutron source called IECF (Inertial-Electrostatic Confinement fusion) devices. With a 50 mm-thick water-jacketed IEC device (IEC20C) of 200 mm inner diameter can have produced 107 neutrons/s stably in CW mode for 80 kV and 80 mA. Ample 10.8 MeV σ-rays produced through (n,σ) reaction with nitrogen atoms in the melamine (C3H6N6) powder (explosive simulant) are clearly measured by a BGO-NaI-combined scintillation sensor with distinct difference in case of with/without melamine, indicating identification of the buried landmines feasible.

Research and development of a compact discharge-driven D–D fusion neutron source for explosive detection

Current results are described on the research and development of the advanced humanitarian landmine detection system by using a compact discharge-type fusion neutron source called IECF (Inertial-Electrostatic Confinement fusion) devices. With a 50mm-thick water-jacketed IEC device (IEC20C) of a 200mm inner diameter, it can produce 107neutrons/s stably in CW mode for 80kV and 80mA. Ample 10.8MeV γ-rays produced through (n,γ) reaction with nitrogen atoms in the melamine (C3H6N6) powder (explosive simulant) are clearly measured by a BGO-NaI-combined scintillation sensor with distinct difference in cases with and without melamine. This proves feasibility of the identification of the buried landmines.

Research and Development of Landmine Detection System by a Compact Fusion Neutron Source

Current results are described on the research and development of an advanced anti-personnel landmine detection system by using a compact discharge-type fusion neutron source called IECF (Inertial-Electrostatic Confinement Fusion). Landmines are to be identified through backscattering of neutrons, and specific-energy capture γ-rays by hydrogen and nitrogen atoms in the landmine explosives.For this purpose, improvements in the IECF were made by various methods to achieve a drastic enhancement of neutron yields of more than 108 n/s in pulsed operation. This required R&D on the power source, as well as analysis of envisaged detection systems with multi-sensors. The results suggest promising and practical features for humanitarian landmine detection, particularly, in Afghanistan.

Magnetron-Discharge-Based Ion Source for Improvement of an Inertial Electrostatic Confinement Fusion Device

A magnetron discharge as a built-in ion source have studied both experimentally and numerically for a compact discharge-type fusion neutron source called IECF (Inertial Electrostatic Confinement Fusion). With this magnetron discharge, ions are produced in the vicinity of the vacuum chamber (anode) at negative electric potential. Therefore, produced ions are expected to have nearly full energy corresponding to the applied voltage to the IECF cathode but slightly smaller energy preventing them from hitting the anode of the opposite end, eventually improving both fusion reaction rate and ion recirculation life. Also, the magnetron ion source was found to produce ample ion current for maintenance of the discharge. With the optimization of the configuration of the magnetron discharge, further improvement of the fusion reaction rate is found feasible.