Inertial Electrostatic Confinement Fusion Research Articles

Radiation shielding for inertial electrostatic confinement fusion system utilizing concrete and water

In this investigation, the impact of water thickness and various types of concrete materials, each characterized by different densities and elemental compositions, is examined for their role in shielding a radiation generator based on Inertial Electrostatic Confinement Fusion (IECF) device. The study focuses on assessing several vital parameters, including the effective removal cross-section (∑Rt) for fast neutrons, total mass attenuation coefficients (μmt), linear attenuation coefficients (μl), half-value layer (HVL), and mean free path (MFP) for X-rays across different concrete types. Different water thicknesses around the IECF chamber, ranging from 0.5 to 10.0 cm, are investigated, and five concrete types are evaluated: Ilmenite-magnetite Concrete (IMC), Ordinary Concrete-1 (OC1), Barite-containing Concrete (BC), Ordinary Concrete-2 (OC2), and Serpentine-containing Concrete (SC). The results indicate that, among these materials, SC requires the least thickness to attenuate 2.45 MeV generated from IECF to 1/100th of its initial intensity across varying water thicknesses (6.5 cm in case of 5 cm water thickness). The values of μmt, HVL, and MFP are also calculated for different water thicknesses and X-ray energies (ranging from 0.2 to 3.0 MeV). These calculations highlight BC as the material requiring the least thickness to attenuate X-rays to 1/100th of their initial intensity. Moreover, neutron dose rate measurements are conducted on a commercial IECF system shielded with 50 cm of water and operated at a neutron intensity of 105 ns−1, which was ∼12 nSv/h on average, approximately 0.002% of the initial intensity. This underscores the efficacy of water shielding in attenuating the outcomes of IECF.

A systematic approach to the modelling and comparison of the geometries of spherical electrodes in inertial electrostatic confinement fusion devices

Inertial electrostatic confinement fusion (IECF) devices often use two concentric spherical electrodes to converge ions in a plasma electrostatically. Using a highly transparent inner cathode, the ions can move through the cathode and collide at the center to undergo fusion reactions. This is a simple method to build a neutron source. Past research has focused chiefly on cathode “grids” manufactured by joining metal wire loops or disc-shaped elements via spot welding. There are two common geometries: “Globe” grids with a distinct latitude-longitude structure and “symmetric” grids with even-sized triangular-shaped apertures. Recent advances in additive manufacturing have opened the way to manufacturing a third class of grids in which the apertures are evenly distributed over the grid surface and have either circular or polygonal shaped apertures - here called “regular” grids. These three types are analyzed and compared based on a set of metrics, including transparency, homogeneity of aperture size, and the regularity of aperture distribution. It is shown that every type of grid comes with different advantages and disadvantages. The analysis focuses on grid geometries with 6 to 120 apertures.

Investigating the effect of changing parameters in the IEC device in comparative study

Kinetic simulations have been performed on an Inertial Electrostatic Confinement Fusion (IECF) device. These simulations were performed using the particle-in-cell (PIC) method to analyze the behavior of ions in an IEC device and the effects of some parameters on the Confinement Time (CT). CT is an essential factor that significantly contributes to the IEC's performance as a nuclear fusion device. Using the PIC method, the geometry of a two-grided device with variable grid radius, the number of cathode grid rings, variable pressure and different dielectric thickness for the feed stalk was simulated. In this research, with the development of previous works, the interaction of particles was simulated and compared with previous results. The simulation results are in good agreement with the previous results. In these simulations, it was found that with the increase of the dielectric thickness of the feed stalk, the electric field was weakened and as a result, the confinement time was reduced. On the other hand, with the increase of the cathode radius, the confinement time increased. Using the results, an IEC device can be designed with higher efficiency and more optimal CT for ions.

Effect of Positive Polarity in an Inertial Electrostatic Confinement Fusion Device: Electron Confinement, X-Ray Production, and Radiography

The conventional inertial electrostatic confinement fusion (IECF) operation is based on the application of high negative voltage to the central grid, which results in the production of neutrons due to the fusion of lighter ions. The device can also be used as an X-ray source by altering the polarity of the central grid. In this work, electron dynamics during the positive polarity of the central grid are studied using the object-oriented particle-in-cell code XOOPIC. The simulated trapped electron density inside the anode is found to be on the order of 1016 m when 10 kV is applied to the anode. The recirculatory characteristics of the electrons are also studied from the velocity distribution function. A scintillator-based photomultiplier tube is used to detect the produced X-ray. The X-ray-emitting zones of the device are investigated by pinhole imaging techniques. Last, the radiography of metallic as well as biological samples are reported in the later part of this paper. This study shows the utilization of the IECF device when the polarity of the central grid is reversed.

Assessment of Five Concrete Types as Candidate Shielding Materials for a Compact Radiation Source Based on the IECF

A radiation source based on the inertial electrostatic confinement fusion (IECF) system is being developed for multidisciplinary research applications. The radiation outputs from the IECF system are 2.45 MeV fast neutrons and the associated co-generated X-rays with an energy less than 3 MeV. A radiation shielding study has been performed on five types of concrete to define the most efficient material for the shielding design of the system. The proposed materials were ilmenite-magnetite concrete (IMC), ordinary concrete-1 (OC-1), barite-containing concrete (BC), ordinary concrete-2 (OC-2), and serpentine-containing concrete (SC). A numerical model was applied to determine the effective removal cross-section coefficients (∑Rt) for the fast neutrons and the total mass attenuation coefficients (µm), the half-value layer (HVL), the mean free path (MFP), the effective atomic number (Zeff), and effective electron density (Neff) for photons inside the materials. The model considered the radiation source energy and the material properties of the concrete types. The results revealed that the serpentine-containing concrete exhibited the highest ∑Rt with 12 cm of concrete thickness needed to attenuate an incident neutron flux to 1/100 of its initial value. In addition, the BC shows the highest µm with a 38 cm concrete thickness needed to attenuate the 3 MeV energy X-ray flux to 1/100 of its initial value. This study suggests that a 40 cm thickness of SC or BC adequately shields the radiation generated from an IECF system with a maximum particle production rate of up to 1 × 107 n/s.

Influence of electrodes' geometrical properties on the neutron production rate of a discharge fusion neutron source

Trapping ions, such as deuterium and tritium, inside a potential well to generate neutrons is a well-established technology through electric and magnetic fields via the inertial electrostatic confinement fusion (IECF) and the tokamak, respectively. In the IECF, the straightforward configuration is a concentric cathode connected to a negative bias, surrounded by a grounded anode that serves as a vacuum vessel. Theoretically, neutrons are generated inside the vessel through fusion between ions that are accelerated by applying several tens kV voltage and tens mA current. Many parameters affect the plasma conditions and fusion in the system, hence the neutron production rate (NPR). This study investigates the cathode transparency and the number of apertures effect on NPR. For this end, eleven cathodes were fabricated from stainless steel in three different groups with different transparency and number of apertures. NPRs were investigated as a function of the cathode transparency and number of apertures at low power operating mode ∼1 kW. Experimental results revealed that higher NPR was produced from lower grid transparency and vice versa; this behavior was explained through beam–surface fusion with grid surface. In addition, a higher NPR was generated from the grid with many apertures; this was attributed to the effect of the deuterium ionization improvement by the number of ionizing electrons through the grid channels.

Studies on ion flow dynamics in a disk-shaped inertial electrostatic confinement fusion device under the influence of a triple grid arrangement

The basic interest of studying the ion flow dynamics in a disk-shaped inertial electrostatic confinement fusion (IECF) device is to achieve an explicit condition where large fusion products are possible from such a portable device, and then, it can be used for a wide range of applications. We modified the existing IECF device by introducing two external grids along with the central grid and investigated the plasma properties using the Langmuir probe technique at different operating voltages in this new configuration of the device. By taking measurements of the plasma properties throughout the chamber, the device is optimized for better ion confinement and ion flow behavior. A well-established comparison of plasma properties, such as ion density and potential in this new arrangement, has been carried out with the single-gridded IECF system. The triple grid arrangement switches to a lower working pressure region, and hence high energetic ion beams are procured. Because of the different discharge mechanisms, variations in plasma potential profile and ion confinement processes are observed when compared to the single-gridded IECF device.

Investigation of geometric effects on fast neutron radiography using IECF

One of the most useful non-destructive techniques for imaging low Z materials hidden behind high Z materials is fast neutron radiography (FNR). Inertial Electrostatic Confinement Fusion (IECF) as a small neutron source is an excellent apparatus for neutron radiography because of its ability to generate high-flux fast neutrons. In this study, the effects of geometric parameters on images obtained by a FNR system were investigated using MCNPX2.7 Monte-Carlo code. Geometric unsharpness can be reduced by optimizing the source-object and object-detector distance. The results showed that the contribution of scattered neutrons is approximately 0.1 % of that of transmitted ones for object-detector distances greater than five times the size of the side of the object perpendicular to the beam axis. The optimal detector-object distance was 50 cm. By increasing the source- object distance, better contrast and a higher fitting between the image and the object in terms of the position was observed. The optimal source-object distance was considered 150 cm.

Helicon Injected Inertial Plasma Electrostatic Rocket

The Helicon Injected Inertial Plasma Electrostatic Rocket (HIIPER) is a space propulsion system developed at the University of Illinois Urbana-Champaign. The HIIPER couples a helicon tube with an inertial electrostatic confinement (IEC) fusion system. Its operating principle involves a helicon ionization stage followed by an electrostatic grid (IEC cathode grid) extraction stage. The helicon setup used in the HIIPER is modified to include a helicon bias grid at the upstream end of the tube. This grid is applied with a positive direct-current voltage to increase the plasma potential and the most probable ion energy of the plasma injected into the IEC fusion chamber. The IEC cathode grid in the HIIPER uses an innovative asymmetric design, graphically depicted through a computational model, that ejects a stream of electrons that accelerate the exhaust ions and simultaneously neutralize the exhaust jet. The model is also used to plot ion trajectories inside the HIIPER to identify any wall collision losses. A separate numerical study was undertaken to show augmentation of plasma kinetic energy on adding a magnetic nozzle as the final propulsion stage of the HIIPER. Experimental results were used to establish a relation between the input parameters and the ion density of the resulting plasma. Langmuir probe measurements were performed at two locations to validate corresponding computational results, indicating ion losses due to ion-wall collisions inside the helicon-IEC coupling. The results in this study add to the proof of concept of the HIIPER and allow for designing an upgrade of the propulsion system. Increasing thrust while maintaining plasma densities between 1017 and 1018 throughout the system is the current aim of HIIPER research. This study summarizes the various performance parameters of the propulsion system, along with a discussion of ongoing research and future scope.

The Plasma Characterization of Argon and Helium Gases in Inertial Electrostatic Confinement Fusion Plasma Device

The Plasma Characterization of Argon and Helium Gases in Inertial Electrostatic Confinement Fusion Plasma Device

Neutron imaging with an inertial electrostatic confinement fusion neutron source.

A compact inertial electrostatic confinement (IEC) fusion neutron source was developed. Imaging tests using the cylindrical IEC neutron source were conducted with the indirect imaging plate (IP) method using dysprosium foil and an imaging plate. An array of B4C powder contained in a stainless-steel blade and Cd pins was successfully imaged. To calculate thermal neutron flux of the device, we tested multiple types of IP and IP scanners with the indirect IP method to create a calibration curve, and it was confirmed that dental IP scanners, which are more widely used than industrial ones, can be applied to the indirect IP method.

Neutron and x-ray emission from a cylindrical inertial electrostatic confinement fusion device and their applications

Table-top neutron/x-ray sources are of great interest for uses in neutron activation analyses, in neutron/x-ray radiography, and also in medical applications. Inertial electrostatic confinement fusion (IECF) is a multiple neutron source that can emit neutrons, protons, x rays, etc., as basic products when operated in both continuous and pulsed modes. In this work, D-D neutrons are produced in the steady-state mode using a cylindrical IECF device. The neutron production rate has been optimized by using cathodes having different dimensions and geometrical transparencies. The maximum neutron production rate is found to be approaching 107n/s, using a cathode having eight grid wires and a diameter of 3 cm. The neutrons are successfully used for neutron activation analysis of materials containing explosive elements. X-ray spectrum having a wide range of photon energies (30–70 keV) has been detected from this device while operated in the continuous mode. X-ray radiography of high density objects has also been performed and reported for the first time using the cylindrical IECF source with negative polarity of the central grid in this paper.

An inertial electrostatic confinement fusion system based on graphite

Inertial electrostatic confinement (IEC) devices use concentric electrodes to accelerate ions to sufficient energies to produce nuclear fusion. In a previous publication, we have indicated that, when operating at low power, fusion events largely occur when high energy ions impact neutral molecules that are adsorbed on the cathode surface. The selection of the cathode material therefore plays an important role in determining the absolute fusion output of an IEC machine. A study is presented in which a pair of matching IEC cathodes were constructed from 316 stainless steel and graphite and the fusion characteristics of the grids examined as a function of system pressure and discharge power. Graphite is shown to be an excellent cathode material, producing fusion rates 2.2–4 times that of stainless steel. Due to the excellent deuterium trapping properties of graphite, it is likely this enhancement factor will continue to grow as operating power is further increased.

Characterization of an ultra-compact neutron source based on an IEC fusion device and its prospective applications in radiography

Our group is developing an ultra-compact neutron source based on inertial electrostatic confinement (IEC) fusion device for various applications at Kyoto University. This IEC device is configured from a titanium anode and a molybdenum cathode with diameters of 17 and 6 cm, respectively. A high-intensity neutron source operated in a stable pulse shape is mandatory to increase the system’s reliability. Applying a higher voltage is a straightforward way to increase the neutron yield from the system. However, a contradiction between the increase of the applied voltage and the reduction of the system size limits such a proposal. A three-stage feedthrough system is employed in the developed compact IEC to address this contradiction. A feedback control system was developed and applied to the input and output parameters, such as the applied voltage and the neutron yield, to increase its stability in long-term operation. Characterization of the developed system was performed by scanning the neutron yield as a function of applied voltage and cathode current. To date, a maximum neutron yield of 9.2 × 107n·s–1 at 6.4 kW (80 kV and 80 mA) has been obtained. A study of the feasibility of using the IEC system for neutron radiography was performed. Preliminary analysis of the resulting images showed there was good contrast between the sample and the background. The results suggest that optimization of the experimental parameters is needed to perform higher accuracy neutron radiography.

Study of inertial electrostatic confinement fusion using a finite-volume scheme for the one-dimensional Vlasov equation.

While the majority of fusion energy research is focused on magnetic confinement, there have been several alternative confinement methods aimed at the development of smaller and less expensive reactors. A number of these alternative reactors are based on a spherically convergent beam of recirculating ions and include designs such as inertial electrostatic confinement (IEC), multigrid IEC, and the periodically oscillating plasma sphere concept. Here, a fully time-dependent GPU-based Vlasov solver was developed in order to study these spherically convergent devices. This code solves the Vlasov equation for a spherically symmetric system using a finite-volume method with a modified flux to account for electrode transparency. The solver accounts for secondary electron emission, interactions between the charged particles, and collisional effects such as ionization and charge exchange. This code was used to investigate a system similar to the ion-injected device described by Hirsch (see [R. L. Hirsch, J. Appl. Phys. 38, 4522 (1967)10.1063/1.1709162]), who had reported a neutron production rate for deuterium-deuterium reactions in the range of 10^{6}to10^{7} neutrons per second, which was attributed to the formation of a virtual electrode structure near the center of the chamber. Attempts to reproduce this experiment [B. J. Egle, Ph.D. thesis, 2010] yielded similar fusion rates, though the majority of the reactions were found not to occur near the center of the chamber. The results of this Vlasov solver, considering only beam-beam and beam-background fusion reactions, show that beam-background reactions would be dominant in such an ion-injected device. This result is consistent with work by Baxter and Stuart, who proposed a simplified steady-state Boltzmann model. However, the result of both models are inconsistent with the experimental results, which indicate a higher neutron production rate, and an inverse pressure scaling trend. It is shown that the higher experimental rates may be explained by beam-target fusion between the ion beam and deuterium embedded on the inner surface of the cathode.

Evaluation of 3D printed buckyball-shaped cathodes of titanium and stainless-steel for IEC fusion system

An inertial electrostatic confinement (IEC) fusion device accelerates ions, such as deuterium (D) or tritium (T), to produce nuclear fusion and generate neutrons. The IEC's straightforward configuration consists of a concentric spherical transparent cathode at a negative bias surrounded by a grounded spherical anode. The effects of cathode properties on the neutron production rate (NPR) remain, to date, inadequately studied. This study aims to determine the impact of the cathode material on the NPR by investigating fusion reactions on the cathode surface. Two buckyball-shaped cathodes made of stainless steel (SS) and titanium (Ti), both of 5 cm diameter, fabricated by selective laser melting and 3D printing, are used for this investigation. A SS spherical chamber of 25 cm inner diameter is used as an anode in this experiment. A performance evaluation of surface fusion reaction in the IEC using SS and Ti grids is conducted by examining the NPR as a function of the applied voltage and grid currents at different gas pressures. So far, IEC with Ti and SS cathodes achieves NPRs of 2.32 and 1.41 × 107 n/s, respectively, at 5.6 kW (70 kV, 80 mA). The normalized NPRs (NPR/I-cathode) from IEC using SS and Ti cathodes are compared. The results demonstrate that fusion reaction occurs on the cathode surface, and fusion increases with the applied voltage. The measured NPR/I-cathode using the Ti cathode is higher than that of the SS cathode by factors of 1.36–1.64 across the 20–70 kV range. Moreover, fusion on the Ti cathode surface enhances the total NPR significantly compared to the SS cathode under the same conditions. The Ti's considerable ability to accumulate D ions and molecules compared with that of SS explains the difference of measured NPR results.

Analysis of postoperation radiation hazards in inertial electrostatic confinement fusion neutron source facility at center of plasma physics under institute for plasma research

Center of Plasma Physics-Institute for Plasma Research, Nazirakhat, Assam, has the neutron source based on Inertial Electrostatic Confinement of Fusion. In order to scale up the source, it is planned to build a neutron source facility. The facility needs the construction approval from AERB India for occupational radiation safety during the operation and after the operation. It will also assess the short-term and long-term radiological hazards due to the neutron source. In order to evaluate the post irradiation radiation hazards due the neutron source, the radioactivation analysis of laboratory is carried out and reported here. The radioactivity in the laboratory building and source components after short-term and long-term operation has been assessed. The tritium activity in the soil is also evaluated. The calculation is also done for the contact dose rate estimations after operation to assess the maintenance applicability inside the laboratory. The inhalation dose inside the laboratory after the operation has been also calculated to avoid any hazards after operation maintenance activities. The article provides the complete details of post operation hazards analysis for the Inertial Electrostatic Confinement Fusion neutron source facility.

Kinetic characteristics of ions in an inertial electrostatic confinement device.

The kinetic analyses are quite important when it comes to understanding the particle behavior in any device as they start to deviate from a continuum nature. In the present study, kinetic simulations are performed using the particle-in-cell method to analyze the behavior of ions inside a cylindrical inertial electrostatic confinement fusion (IECF) device which is being developed as a tabletop neutron source. Here, the lighter ions, like deuterium, are accelerated by applying an electrostatic field between the chamber wall (anode) and the cathode (cylindrical gridded wire), placed at the center of the device. The plasma potential profiles obtained from the simulated results indicate the formation of multiple potential well structures inside the cathode grid depending upon the applied cathode potential (from -1 to -5 kV). The ion density at the core region of the device is found to be of the order of 10^{16}m^{-3}, which closely resembles the experimental observations. Spatial variation of ion energy distribution function has been measured in order to observe the characteristics of ions at different cathode voltages. Finally, the simulated results are compared and found to be in good agreement with the experimental profiles. The present analysis can serve as a reference guide to optimize the technological parameters of the discharge process in IECF devices.

Anode shape dependency of discharge characteristics and neutron yield of a linear type inertial electrostatic confinement fusion neutron source

AbstractA linear inertial electrostatic confinement fusion neutron source equipped with a cooling system for high power operation was developed and its discharge characteristics and neutron production performance were tested under a wide range of discharge conditions. Four different types of discharge anodes were prepared and the dependencies of the device performance on the anode shape were precisely investigated. A maximum neutron production rate of 3.4×106 n/s was achieved when the device was operated with single‐cylinder‐type anodes under a discharge voltage of 94 kV, a current of 20 mA, and a deuterium gas pressure of 0.5 Pa. By comparing the discharge characteristics and neutron generation rates under different anode shapes, we found that the larger inner diameter of the anode leads to longer effective gap length and lower operating pressure, which may result in relatively high fusion reaction rate observed with the single‐cylinder‐type anodes.

Anode Shape Dependency of Discharge Characteristics and Neutron Yield of a Linear Type Inertial Electrostatic Confinement Fusion Neutron Source

Abstract A linear inertial electrostatic confinement fusion neutron source equipped with a cooling system for high power operation was developed and its discharge characteristics and neutron produc...