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D-D Fusion Reaction. A common technique for explosives detection utilizing thermal neutron activation analysis uses neutrons produced from the radioactive decay of 252 Cf. However, this method of explosives detection poses a significant health hazard and there is no way to stop the radioactive decay of 252 Cf and radiation protection is always a concern. 3 Furthermore, if an explosive device were detonated during inspection using a 252 Cf source, a significant health hazard would arise from the fragmentation of the 252 Cf source.
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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...
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... D-D fusion reaction can potentially be used for explosives detection using the University of Wisconsin (UW) IEC Device. 1 Figure 1 shows the D-D fusion reaction. The 2.45 MeV neutrons generated from this reaction can activate, for detection purposes, the low Z materials found in explosives. ...
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... operation, the inner and outer grids form a potential well within the center of the IEC device. Deuterium ions can recirculate through this potential well leading to the D-D fusion reaction shown in Figure 1. ...
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... second grid consisted of a 20 cm, WRe, latitude/longitude design. A comparison of the neutron production rates from these two inner grids as a function of current is shown in Figure 10. ...
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... "rollover" in the neutron production rate is due to the experiments being performed at a constant metered voltage (the true cathode voltage decreases with increasing current). Figure 11 shows the dependence of neutron production rate on true voltage at various currents. Although this voltage scan is for one run of a 10 cm diameter, WRe, latitude/longitude grid, it is representative of all of the runs that were performed with 10 cm grids regardless of geometry or material composition. ...
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... Linear accelerators, magnetic confinement fusion reactors, laser-based fusion reactors are some of the well-known neutron sources. Unlike these sources, the inertial electrostatic confinement (IEC) fusion device draws the attention of the research communities due to its compact and simple configuration, operational variability (pulsed and continuous), and its numerous applications [3,4]. ...
A detailed design and testing of a pulsed power system (PPS) which has been developed in order to drive a table-top inertial electrostatic confinement (IEC) fusion device are presented over here. A 0.04 µF, 100 kV capacitor has been used to store the energy for generating the pulse. Along with the capacitor, other critical components such as high-voltage spark gap switch, high-voltage power supply, high power resistors, and diodes, triggering unit have been combined to develop the PPS. The discharge current and voltage pulse have been recorded by using high voltage and current probes, respectively. A current peak of ∼ 17.5 A at an input potential of − 70 kV and a power dissipation peak of ∼ 1200 kW have been observed when the spherical IEC fusion device is used as the load in the PPS.
... It is notable, however, that the Wisconsin device runs at substantially higher powers, 1-6 kW and, therefore, operates in a different regime to that described above. Nevertheless, there is increasing interest around the choice of the cathode material as a means of enhancing the fusion rate in IEC devices, 6,8,11,12 and thus, it is important to examine the ways in which the surface fusion effect may be utilized. In particular, graphite has shown extreme promise as a cathode material due to its capacity to trap and retain deuterium gas, even at elevated temperatures. ...
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.
... Inertial electrostatic confinement (IEC) fusion scheme is one of the most favorable techniques for the production of continuous and pulsed neutrons compared to other schemes like plasma focus, Z-pinch, accelerator-based etc. Researchers have analyzed various schemes for IEC devices that could deliver a stable source and could significantly increase the density of oscillating ions in the core region of the cathode resulting in high neutron production rate (NPR) [7,8]. An IEC device is configured both for spherical (isotropic) and cylindrical (anisotropic) geometries, running by an electrical discharge on D-D/D-T/D- 3 He as fuel gases. ...
The adaption of new generation portable neutron sources has been increasingly marked in a wide range of research fields compared to the large-scale neutron generators. In this context, we have successfully demonstrated some essential parameters required for the emission of 2.45 MeV DD fusion neutrons from a steady state portable linear neutron source based on inertial electrostatic confinement scheme. The parameters that control the production of neutrons are the working pressure of the fuel gas, applied voltage, measured current and cathode geometries. The neutrons emitted from the source are confirmed using neutron monitor, bubble dosimeters, nuclear track detectors, and He-3 proportional counter. Presently, the device produces neutrons up to the order of ∼ 10⁶ n/sec at discharge voltage ranging from -60 kV to -80 kV, and discharge current of 20 mA to 30 mA.
... The detector array was placed 0.3 m away from the back wall of the container. The neutron source was defined with an initial energy of 2.5-MeV corresponding to deuterium-deuterium (DD) (Vainionpaa et al., 2015;Wehmeyer et al., 2005) fusion neutron generators. Photon sources were defined with an initial energy of 6-MeV (Cashmore, 2008;Najem et al., 2015). ...
Taking into account the advantages of both neutron- and photon-based systems, we propose combined neutron-photon computed tomography (CT) under a sparse-view setting and demonstrate its performance for 3D object visualization and material discrimination. We use a high-performance regularization method for CT reconstruction by combining regularization based on total variation (TV) and curvelet transform in cone beam geometry. It is coupled with proposed 2D material signatures which is pairs of photon to neutron transmission ratios and neutron transmission values per object space voxels. Classification of materials is performed by association of a voxel signature with library signatures; and per object - by majority of voxels in the object. Representation of object-material pairs, for the model in our experiment, a complex scene with group of high-Z and low-Z materials, attains the reconstruction accuracy of 92.1% and the overall high-Z discrimination accuracy of object representation is 85%, and by about 7.5% higher discrimination accuracy than that with 1D signatures which are ratios of photon to neutron transmissions. With a relative noise level of 10%, the method yields the reconstruction accuracies of 87.2%. The analyses are performed in cone beam configuration, with Monte Carlo modeling of neutron-photon transport for the model of object geometry and material contents.
... The detector array was positioned behind the container 370 mm away from its back wall. In the model, neutron sources were defined with energies of 2.5 MeV and 14 MeV that corresponds to deuterium-deuterium (DD) (Vainionpaa et al., 2015;Wehmeyer et al., 2005) and deuterium-tritium (DT) (Chichester et al., 2007;Hayes et al., 2014) fusion generators of neutrons, respectively. Photon sources were defined with end energies of 0.3 MeV, 1 MeV, 3 MeV, and 6 MeV (Cashmore, 2008;Clayton et al., 2015;Najem et al., 2014). ...
The application of combined neutron-photon tomography for 3D imaging is examined using MCNP5 simulations for objects of simple shapes and different materials. Two-dimensional transmission projections were simulated for fan-beam scans using 2.5 MeV deuterium-deuterium and 14 MeV deuterium-tritium neutron sources, and high-energy x-ray sources, such as 1 MeV, 6 MeV and 9 MeV. Photons enable assessment of electron density and related mass density, neutrons aid in estimating the product of density and material-specific microscopic cross section- the ratio between the two provides the composition, while CT allows shape evaluation. Using a developed imaging technique, objects and their material compositions have been visualized.
... Reported results in previous works suggest that using the D-T gas mixture and increasing the ion current via ion source would give a neutron rate of 7.3 × 10 12 n/sec at 1.2 mTorr, 75 kV, and 1.5 A ion current [6, 8, 9]. Researchers in Wisconsin University, in order to increase and optimize the neutron production rate in the UW IECF device, studied effect of cathode's size (diameter), geometry, and material composition on NPR [10]. Dietrich in MIT University investigated multigrid IEC device theoretically and experimentally for improving particle confinement [11]. ...
Artificial neural network (ANN) is applied to predict the number of produced neutrons from IR-IECF device in wide discharge current and voltage ranges. Experimentally, discharge current from 20 to 100 mA had been tuned by deuterium gas pressure and cathode voltage had been changed from −20 to −82 kV (maximum voltage of the used supply). The maximum neutron production rate (NPR) of 1.46 × 107 n/s had occurred when the voltage was −82 kV and the discharge current was 48 mA. The back-propagation algorithm is used for training of the proposed multilayer perceptron (MLP) neural network structure. The obtained results show that the proposed ANN model has achieved good agreement with the experimental data. Results show that NPR of 1.855 × 108 n/s can be achieved in voltage and current of 125 kV and 45 mA, respectively. This prediction shows 52% increment in maximum voltage of power supply. Also, the optimum discharge current can increase 1270% NPR.
... The calculation assumes that the incident radiation is in the form of 3.02 MeV protons with fluxes that vary from 1x10 10 protons cm -2 s -1 to 1x10 14 protons cm -2 s -1 . The temperature of the semiconductor material was assumed to be held at room temperature (300 K) which may not be realistic for the higher proton fluxes presented here 10,11,12,13,14,15,16,17,18,19 . The efficiency of proton collection by the radiation cell is assumed to be 100% for the purposes of this calculation. ...
The inertial electrostatic confinement (IEC) device confines energetic ions in a spherically symmetric, negative potential well between two nearly transparent metallic grids. Diagnostics were developed and implemented to understand IEC device operation. A plasma diagnostic to measure concentrations of molecular deuterium ions in the edge plasma region of the UW-Inertial Electrostatic Confinement (IEC) fusion device was developed and implemented. This diagnostic measured the phase velocity of multi-species ion acoustic waves in the source plasma of the UW-IEC device. It was concluded that the source plasma, when run with deuterium fuel, is dominated (>50% by ion density) by D3 + ions. A fusion product Doppler shift diagnostic for the measurement of energetic deuterium velocity spectra within the intergrid region of an inertial electrostatic confinement fusion device was developed and implemented. The diagnostic measured the Doppler shift imparted to high energy fusion protons from the deuterium reactants within the device. This work measured, for the first time, the high energy deuterium spectra within an IEC device. This diagnostic documented the deuterium spectra variations over a wide range of device parameters. A dominant fraction of the energetic deuterons had energies between 10-20 keV for cathode potentials between 50-100 kV. A technique to resolve the location of the fusion reactions along a chord through the center of an inertial electrostatic confinement fusion device was developed and implemented. Two opposed silicon charged particle detectors determine the fusion reaction location by recording the difference in arrival time between the high energy proton and triton resulting from a D-D fusion reaction. Preliminary results indicate that, at 50 kV, 30 mA, and 2 mTorr of neutral gas, 50% of the fusion reactions occur within the 10 cm radius cathode of the UW-IEC device. A magnetic deflection energy analyzer and Faraday trap diagnostic were used to measure divergent negative ion flow in the UW-IEC experiment. Energy spectra obtained using a magnetic deflection energy analyzer diagnostic indicate the presence of D2-, and D- ions are produced through charge transfer processes, and thermal electron attachment. These negative ions can account for up to 30% of the fusion rate.
A glow discharge (GD) fusion neutron source that utilizes nuclear fusion reactions of deuterium has been upgraded. The fusion reactions in this device mainly occur by collisions between the charged or neutral particles and the hydrogen isotopes trapped at the surface of electrodes. In addition, it is known that the metal hydride coating on the electrode enhances the neutron production rate (NPR). Therefore, the elemental distribution, including deuterium, in the depth direction on the electrode is an essential factor in neutron production. However, the distribution on the electrode has not been experimentally investigated. This study aims to analyze the distribution experimentally and indicate the effect of the metal hydride coatings. To achieve this purpose, we prepared the titanium (Ti)-coated cathode and the uncoated cathode, of which the base material was stainless steel. After that, the neutron production test was performed in the range of from 5-to 40-mA currents and from 20-to 60-kV applied voltage. This test indicated that the NPR was improved by coating the cathode with Ti than the uncoated cathode. In addition, depth profiling on the cathodes by glow discharge optical emission spectroscopy (GD-OES) was performed. While the analysis indicated that the concentration of deuterium on both cathodes was increased after the test, there was no significant difference in the concentration of deuterium between both cathodes. Furthermore, the concentration of Ti on the Ti-coated cathode was vastly decreased. The cause of these changes needs to be investigated.
Inertial electrostatic confinement offers a relatively simple and cost-effective means of generating fusion plasmas for research and industrial applications. Here, we present the experimental setup and discharge characteristics of the inertial electrostatic confinement device at the Dept. of Physics, Technical Univ. of Denmark. Special features of this setup include a cylindrical anode and the novel use of 3D printed soccerball-like cathode grids of different sizes. Measurements with these grids show 25% higher fusion neutron rates than with manually manufactured grids with larger wire spacings. Additionally, we observe significantly higher neutron rates with smaller grids, with spherical rather than cylindrical cathodes, and when using the vacuum chamber, rather than a second spherical grid, as the anode. Ion–orbit simulations predict a core density in the ion distribution in good agreement with optical measurements, confirming that asymmetries in the cathode grid potential prevent a fully convergent ion flow. The simulations also demonstrate that the asymmetry of the electric field induced by the voltage stalk lowers the characteristic ion recirculation by a factor of four, and we discuss measures to circumvent this. Comparing measurements and simulations conducted with a spherical and cylindrical grid reveals tentative evidence that fusion reactivity is highly core-localized, pointing to ion–neutral fusion as the dominant reaction. We also quantify the thermionic and impact-induced secondary electron emission in the device, showing that only the latter can potentially suppress the ion current during normal operation.
Grid geometry plays an important role in the performance of a gridded spherical IEC device because the ion recirculation, and hence the reaction rate, is strongly affected by the orientation and size of openings in the cathode in grid design. In Chap. 3 we learned that cathodes with reasonably large openings face each other so that an ion could easily recirculate via ion microchannels (corresponding to a high effective transparency) and perform much better than either a solid cathode or a cathode with holes that do not point directly at each other (i.e., causing a low effective transparency). Aside from these major features, various researchers have investigated the effect of a variety of grid opening geometries [1]. However, these experiments have been generally inconclusive, because they operated in the grid performance “saturation” regime, wherein the maximum symmetry is already achieved and any further increase in symmetry through addition of more wires does not cause significant improvement in the observed reaction rate.
