Inertial Electrostatic Confinement Fusion Research Articles

Inertial electrostatic confinement and DD fusion at interelectrode media of nanosecond vacuum discharge. PIC simulations and experiment

The generation of energetic ions and DD neutrons from microfusion at the interelectrode space of a low-energy nanosecond vacuum discharge has been demonstrated recently [1, 2]. However, the physics of fusion processes and some results regarding the neutron yield from the database accumulated were poorly understood. The present work presents a detailed particle-in-cell (PIC) simulation of the discharge experimental conditions using a fully electrodynamic code. The dynamics of all charge particles was reconstructed in time and anode–cathode (AC) space. The principal role of a virtual cathode (VC) and the corresponding single and double potential wells formed in the interelectrode space are recognized. The calculated depth of the quasistationary potential well (PW) of the VC is about 50–60 keV, and the D+ ions being trapped by this well accelerate up to energy values needed to provide collisional DD nuclear synthesis. The correlation between the calculated potential well structures (and dynamics) and the neutron yield observed is discussed. In particular, ions in the potential well undergo high-frequency (∼80 MHz) harmonic oscillations accompanied by a corresponding regime of oscillatory neutron yield. Both experiment and PIC simulations illustrate favorable scaling of the fusion power density for the chosen IECF scheme based on nanosecond vacuum discharge.

Neutron Source Based on a Counter-Deuterium Beam Linear IEC

A high-efficiency inertial electrostatic confinement (IEC) neutron generator consists of linear IEC fusion chamber and ionization chambers at both ends, connected by an externally applied magnetic field. A pair of deuterium beams is produced in the ionization chambers that are positively biased so as to accelerate deuterium ions along the magnetic field towards the reaction chamber. For the purpose of achieving high-efficiency, the counter-streaming beam column is focused to form a thin filament. Such a configuration must avoid beam-driven instabilities such as the two-beam instability and Weibel’s instability. The stability analysis is performed showing that these modes are stabilized by an externally applied magnetic field parallel to the ion beams. The required magnetic field is less than several of 0.1 Tesla. Thus highly efficient neutron generator is potentially possible with counter-streaming ion beams focused and stabilized by an external magnetic field. An example giving specifications for such a neutron generator is presented.

Development of Excited Helium Beam Injector for Electric Field Measurement by Laser-Induced Fluorescence Method

A 21S metastable helium atomic beam injector was studied for a beam probe of electric field diagnoses, which is applicable to high electric potential region in Inertial Electrostatic Confinement Fusion (IECF) plasmas where a solid probe can hardly be utilized. With deuterium background gas (∼0.1Pa) which is the minimum operation pressure of the IECF devices, the beam density was found to decrease ten times lower than beam density without background gas because of collisional effect. Also, plasma parameters in a-magnetron-discharge-based exciter were evaluated by means of Langmuir probe and emission spectroscopy. These results strongly imply a high excitation rate of ∼10-4 into 21S metastable state.

Neutron Production Rate of Inertial Electrostatic Confinement Fusion Device with Fusion Reaction on Surface of Electrodes

The neutron production rate (NPR) through fusion reaction on the surface of electrode(s) of an IECF (Inertial Electrostatic Confinement Fusion) device, which is expected to increase at low pressure, has been evaluated with a one dimensional simulation code and an experimental device. In the simulation, the NPR on the cathode and the anode has been evaluated individually as a function of pressure. The simulation results reveal that the NPR on the cathode increases at low pressure and that on the anodes increases at high pressure. In the experiment, titanium coated electrodes have been used in order to rise the adsorbed amount, and the results show same tendency along with the pressure as calculation results. And the maximum value increases 3 times by coating titanium.

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.

Comparison of Spherical and Cylindrical Cathode Geometries in Inertial Electrostatic Confinement Devices

The performance of a new Inertial Electrostatic Confinement (IEC) fusion device using a cylindrical anode and two different cathode geometries, spherical and cylindrical, was compared to an existing IEC device with two different sized configurations of spherical anodes and cathodes. Experimental data was generated at -30 to -150 kilovolts, 30 milliamps steady-state, and 0.3 Pascal of Deuterium (D) and/or Helium-3 (3He). The best neutron rate achieved by the new device in a D environment was 2.7x107 neutrons per second at 145 kV and 35 mA. In a D-3He environment, the best proton rate achieved was 2.0x107 protons per second at 130 kV and 30 mA. Both the D-D neutron rate and the D-3He proton rate were approximately 40% lower than the larger volume existing IEC device.

Development of a Time-Independent Particle-in-Cell Code for Simulating DC Discharges in Inertial Electrostatic Confinement Devices

A two-dimensional numerical code has been developed for simulating dc discharges in inertial electrostatic confinement (IEC) fusion devices. Unlike the existing IEC codes, the developed code is not based on Monte Carlo scheme by the use of random number nor time-domain particle-in-cell (PIC) method, aiming at a drastic reduction of computational efforts. It is based on a time-independent scheme, i.e. iterative calculations of particle-tracking and induced self-field, leading to a much faster convergence than the time-domain PIC scheme on steady-state self-consistent solutions. Also, a new scheme for atomic process treatment is proposed, which is completely free from the inherent difficulty of Monte Carlo method, i.e. requiring many particles for simulating rare events. Preliminary numerical result from the this code showed agreement with experimental helium discharge characteristics in an IEC device.

Spatial Distribution of D-D Neutrons from a Compact Water-Cooled Inertial Electrostatic Confinement Device

A new Inertial Electrostatic Confinement (IEC) fusion device has been manufactured as a compact neutron source. This device consists of double jacket chambers to provide sufficient water cooling, having the diameters of inner and outer chambers of, respectively, 20 cm and 30 cm. The effective water-cooling enabled the IEC device to operate at high cathode current of more than 80 mA. A target neutron yield of 1×107 has been achieved for cathode voltage of 80 kV and (cathode) current of 80 mA. The water jacket of a 5 cm width was designed as well to assure the sufficient reflection of 2.45 MeV D-D neutrons downward, where a thinner 1 cm thick water jacket is installed at the bottom. This non-uniformity of water jacket thickness resulted in increased neutron flux downward.

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.

Glow Discharge Characteristics in Relation to Anode Size in Inertial Electrostatic Confinement Fusion

An Inertial Electrostatic Confinement Fusion device is a very simple and safe neutron source that uses a glow discharge for deuterium-deuterium fusion. The discharge characteristics of the device were studied experimentally. The relationship between gas pressure and applied voltage was examined by light changes of the device's anode size. The gas pressure ranges in which the device was able to function effectively were differed. In the case of a larger anode (300 mm in diameter), the glow discharge occurred even under a relatively low pressure of 0.7 Pa and was very stable during a long period of neutron production. The characteristics of the gas pressure-neutron yield of different size anodes were also studied experimentally. At lower gas pressure, a greater neutron yield was obtained by a larger anode.

Confinement of ions in an inertial electrostatic confinement fusion (IECF) device and its influence on neutron production rate

Using a one-dimensional particle code, low pressure and large current discharge in an inertial electrostatic confinement fusion (IECF) device has been simulated, and confinement level of ions and the neutron yield through beam–beam fusion have been investigated. From the calculation of low-pressure operation, it is clear that the averaged life span of ions is extended but converges to a value corresponding to the geometrical transparency of the cathode. Calculation of large current discharge (injecting D 2 + current of 200 mA) can be carried out by applying the anode radius of 10 cm. The neutron yield through beam–beam reaction is insensitive to the pressure, but is higher than that through beam–background reaction at the pressure of 0.1 mPa or lower.

Inertial electrostatic confinement fusion device with an ion source using a magnetron discharge

An inertial electrostatic confinement (IEC) fusion device is studied for a compact fusion neutron/proton source using a built-in magnetron ion source. The addition of an ion source to the IEC fusion device enhances fusion reactions by allowing a lower operating gas pressure and by providing a beam-like ion energy distribution. Under lower gas pressures, charge exchange collisions are reduced, resulting in longer ion lifetime and thus enhanced ion re-circulation. The performance characteristics of this IEC fusion device found in the experiments were compared with the numerical calculations and found qualitatively in good agreement. An improvement in normalized neutron yield (defined as neutron yield divided by the product of grid current and operating gas pressure), more than a factor of two, has been observed compared with the conventional glow-discharge driven IEC fusion device.

Pulsed Operation of a Compact Fusion Neutron Source Using a High-Voltage Pulse Generator Developed for Landmine Detection

Preliminary experimental results of pulsed neutron source based on a discharge-type beam fusion called Inertial Electrostatic Confinement Fusion (IECF) for landmine detection are presented. In Japan, a research and development project for constructing an advanced anti-personnel landmine detection system by using IECF, which is effective not only for metal landmines but also for plastic ones, is now in progress. This project consists of some R&D topics, and one of them is R&D of a high-voltage pulse generator system specialized for landmine detection, which can be used in the severe environment such as that in the field in Afghanistan. Thus a prototype of the system for landmine detection was designed and fabricated in consideration of compactness, lightness, cooling performance, dustproof and robustness. By using this prototype pulse generator system, a conventional IECF device was operated as a preliminary experiment. As a result, it was confirmed that the suggested pulse generator system is suitable for landmine detection system, and the results follow the empirical law obtained by the previous experiments. The maximum neutron production rate of 2.0×108 n/s was obtained at a pulsed discharge of -51 kV, 7.3 A.

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.

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.

The Production of 13N Using Beam-Target D-3He Fusion Reactions

The D-3He fusion reaction has been used to produce medical radioisotopes using the University of Wisconsin Inertial Electrostatic Confinement (IEC) Fusion Device. The high-energy 14.7 MeV proton generated from the reaction can activate materials for isotope production. The traditional IEC setup has been altered to generate medical isotopes using beam-target D-3He fusion. Beam target D-3He reactions in a thin-walled, water-cooled, stainless steel tube were used to create 13N, an isotope used in Positron Emission Tomography. At a maximum ion energy of 85 keV, 1.0 nCi of 13N was created as a proof of principle experiment. A scaled-up version of this concept may provide for a smaller, less expensive radioisotope generator for future commercial needs.

Optimizing Neutron Production Rates from D-D Fusion in an Inertial Electrostatic Confinement Device

Detection of explosives has been identified as a near term commercial opportunity for using a fusion plasma. Typical explosive compositions contain low Z material (C, N, O) which are not easily detected using conventional x-rays or metal detectors. However, 2.45 MeV neutrons produced in a D-D fusion reaction can be used for detection of explosives or other clandestine materials in suitcases, packages, or shipping containers.Steady-state D-D operation is possible using an Inertial Electrostatic Confinement (IEC) fusion device. The University of Wisconsin IEC device has produced D-D neutrons at 1.8 × 108 neutrons/second at a true cathode voltage of 166 kV and a meter current of 68 mA. These neutron production rates are approaching the levels required for the detection of explosives. In order to increase and optimize the neutron production rate in the IEC device, experiments were performed altering the cathode’s size (diameter), geometry, and material composition. Preliminary results indicate that significant differences in neutron production rates are not achieved by altering the geometry or material composition of the cathode. However, the neutron production rate was found to increase approximately 20% by doubling the cathode’s diameter from 10 cm to 20 cm. In addition, increasing the cathode voltage from 34 kV to 94 kV at a meter current of 30 mA increased the neutron production rate from 1.24 × 106 n/s to 2.83 × 107 n/s.

Numerical Study on Glow Discharge of IEC Fusion

An inertial electrostatic confinement (IEC) fusion device is possibly used for the neutron source that has the ability to produce the neutrons of 105-108/s by the glow discharge. It works more efficiently at the condition of the high voltage and the low pressure. It, however, is difficult to keep the continuous operation at the low-pressure because the glow discharge is apt to be unstable. We have made the three-dimensional Monte Carlo PIC code including atomic processes to investigate the glow discharge. The study reveals the spatial position where the ionization occurs and numerically reproduces the discharge called ’star mode’.

Optimal Position of Ion Source for High Performance of IEC

An inertial electrostatic confinement (IEC) fusion device is possibly used for portable neutron sources. R. L. Hirsh reported that D-D the neutrons of 1.8 × 108 n/s were produced. Recently, the similar amounts of fusion reactions are observed to occur in IEC devices In the most of IEC devices, since gas pressure is so high that the ions lose their energy by the frequent collisions with the neutral gas. The conditions of the high voltage and the low pressure are preferable because the energy of beam ions is kept very high and used for the fusion reaction more efficiently. It, however, is difficult to produce enough amounts of ions through a glow discharge at the low pressure. One of the solutions is to equip the ion source such as a magnetron near the anode. We have made three-dimensional orbit following code to evaluate the life of the ions produced near the anode surface. The code includes atomic collisions with background neutral gas and indicates the optimal positions to equip ion source which gives longer life of accelerated ions.

Fast Neutral Generation by Charge Exchange Reaction and Its Effect on Neutron Production Rate in Inertial Electrostatic Confinement Fusion Systems

Fast neutral generation by charge exchange reaction in inertial electrostatic confinement plasmas is studied by solving the Poisson equation and the Boltzmann equation for fast neutrals. Fusion reactions carried by the charge exchange fast neutrals become appreciable compared with ion-background fusion reaction. It is shown that the fusion reaction between fast neutral and background gas is sensitively affected by experimental parameters (grid voltage, background gas pressure) and ion distribution function.