As an alternative to research nuclear reactors, a compact accelerator-driven neutron generator that uses a lithium beam driver could be a promising candidate since it produces almost no undesired radiation. However, providing an intense lithium-ion beam has been difficult, and it has been thought that the practical application of such a device would be impossible. The most critical problem of insufficient ion fluxes has been solved by applying a direct plasma injection scheme. In this scheme, a pulsed high-density plasma from a metallic lithium foil generated by laser ablation is efficiently injected and accelerated by a radio-frequency quadrupole linear accelerator (RFQ linac). We have obtained a peak beam current of 35 mA accelerated to 1.43 MeV, which is two orders of magnitude higher than a conventional injector and accelerator system can deliver.

In this study, we investigated the role of redox potential in the ability of nano-synthesis by plasma–liquid interactions. From redox potential, a parameter featured the standard Gibbs free energy, and the equilibrium constant of a reduction reaction can be determined. Our calculation showed that the reactions of ${\mathrm{AuCl}}_4^{-}/{\mathrm{Au}}^0$ with a redox potential of 1.0 V and ${\mathrm{Cu}}^{2+}/{\mathrm{Cu}}^0$ of 0.34 V have equilibrium constants of approximately ${10}^{50}$ and ${10}^{11}$ , respectively. The results are significant to explain the failure in the copper nanoparticle synthesis in the process of nucleation through the Lamer theory. To compare these results to experimental data, the nanoparticles synthesized in a mixed solution of ${\mathrm{AuCl}}_4^{-}$ and ${\mathrm{Cu}}^{2+}$ by AC glow discharge were characterized. The experimental results showed that there were only gold nanoparticles synthesized even though the concentration of gold ions is 200 times smaller. Other results of silver and platinum nanoparticles were also agreeable to the theory. Our findings provide a prediction to explain the ability in the nano-synthesis by plasma in contact with liquid for any noble metals.

Plasma contacting with liquid (PCL) provides many charged particles and reactive species into the liquid. The difficulty in controlling or selecting each specific species has significantly limited its applications in industry. Here, we present a study on using voltage polarity to regulate the type of charged particles absorbing from the plasma into the liquid. A detailed understanding of the processes at the plasma–liquid interface and electrolysis due to switching in voltage polarity was determined via a visual pH observation, measuring the concentration of H ₂ O ₂ and solvated electrons. The results indicated that changes in voltage polarity strongly affect the plasma properties, chemical properties and electrolysis process in liquid, and also in the types of reducing species for gold nanoparticle (GNP) synthesis. The results also showed that using a suitable frequency could improve the efficiency of absorption of H ₂ O ₂ from plasma into the bulk liquid as well as the yield in the production of GNPs. The results provide a way to select desired species from the plasma to be transferred into the liquid for a distinct purpose and to accompany other properties in the system of PCL.

We investigated the propulsive performance of laser ablation propulsion using a high-power and highly repetitive pulsed laser. We demonstrated 100 shots of burst laser irradiation with an aluminum target using repetition frequencies of 0.017 Hz and 1 kHz. The impulse and plasma exhaust velocities were measured using a pressure sensor and an orifice probe. The momentum-coupling coefficient and the specific impulse were estimated from the aforementioned measurements for every shot. The results showed that the momentum-coupling coefficient increased with highly repetitive laser irradiation. The specific impulse increased with increasing shot number for the case of high-repetition frequency. Therefore, high-repetition operation improves the propulsive performance, especially the specific impulse.

We are proposing a compact neutron generator based on a Li beam driver. The proposed neutron generator comprises a laser ion source, a radio-frequency quadrupole linear accelerator (RFQ linac), a drift tube linac, and a target containing protons. In the generator, the lithium ion is used as a projectile instead of protons to utilize the kinematic focusing technique. The technique enables us to enhance the neutron flux without increasing the beam energy, which is important to develop a clean compact neutron generator. Moreover, the combination of a laser ion source and a RFQ linac with the direct plasma injection scheme will provide several tens of mA of a fully ionized lithium beam, which is much higher than that of conventional heavy ion sources comparable with proton drivers. Neutrons are generated by the nuclear reaction of the lithium ions and protons in the beam target. In this paper, we reported the current status of the development. For RFQ, we designed the RFQ rods to accelerate 40 mA of ⁷Li³⁺. We fabricated and installed the rods into a cavity, and, as a first test, accelerated 10 mA of C⁶⁺ successfully.