Beam instability excited by space charge effect is investigated by particle simulations during final beam bunching in heavy ion inertial fusion. The beam current is continuously increased along the beam transport line with longitudinal bunch compression. A transverse particle-in-cell simulation is carried out with a simple model of beam current increase. The multiparticle simulation shows emittance growth accompanied by the restructuring of charge distribution in the interior of the beam. An analytical stability criterion for the high-current beam transport predicts the growth of density fluctuation by the space charge effect. Although results indicate that an abrupt emittance growth is induced by the space charge oscillation at critical tune depression in the final buncher, the increase of emittance can be estimated as high as 23% at the worst case during the bunching process.

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.

A large diameter plasma window was developed for accelerator applications. In this study, a pressure separation using the plasma window was demonstrated, and the maximum diameter of the plasma window reached up to 20 mm. The prediction formula based on the viscous flow for confinement pressure cannot be applied in the case of large diameters due to low input power density to the plasma.

The reaction of congo red, a well-known toxic azo dye, occurred after irradiation by a pulsed intense relativistic electron beam (PIREB). An aquation of congo red was irradiated by PIREB (2 MeV, 0.36 kA, 140 ns). After PIREB irradiation, the solution was measured by electrospray ionization-mass spectrometry and liquid chromatography/mass spectrometry. It was found that congo red underwent a reaction (77% conversion after five shots of PIREB irradiation) and the hydroxylated compounds of the dye were observed as reaction products.