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

Abstract

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 Â 10 7 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.

Effects of Metal Hydride Coatings at the Electrodes on Neutron Production Rate in a Discharge-Type Fusion Neutron Source

“…The dependence of NPR on voltage and current is consistent with previous studies [10], [11] regarding both cathodes. However, as the voltage was increased, the NPR became smaller than this tendency.…”

“…In the prior study, the increasing ratio of the NPR as a function of cathode voltage between pure Ti and stainless steel cathodes ranged from 1.36 to 1.64 in an applied voltage range from 20 to 70kV [11]. On the other hand, the increasing ratio in this study between two cathodes ranged from 1.30 to 1.48, which is the same level as the prior study.…”

“…The prior studies experimentally measured the contribution of the fusion reaction on the electrode surface. Though no material dependence of cathode was observed in the experiments using the grid cathode with a very low surface area [9], the improvement in NPR was observed in the experiment using the electrodes made of a material that retains hydrogen isotopes [10][11][12]. In addition, the simulations which calculated atomic and molecular processes with the Monte Carlo collision scheme also indicated the contribution of the fusion reaction that occurred on the electrode [13].…”

“…On the other hand, the increasing ratio in this study between two cathodes ranged from 1.30 to 1.48, which is the same level as the prior study. As the experimental system was the same as the initial study [11] except for the cathode, it is suggested that the metal hydride coating on the electrodes coating with the metal hydride might have comparable performance to the electrodes made of the pure metal forming the hydride.…”

“…This result might be due to the increase in the temperature of the cathodes as the electric input power increases. For example, in the case of the prior study [11] using the spherical cathode, the temperature of the stainless steel cathode was 860 ± 3 ℃ at 2.4 kW (30 kV, 80 mA). In addition, another prior study indicates that as the cathode temperature rises, the desorption of hydrogen gas from the cathode progresses, and the NPR gain decreases [16].…”