Theoretical Study and PIC Verification on High-Voltage Child-Sheath of Mixed Deuterium–Titanium Plasmas

In this article, we build a universal kinetic model of a high-voltage Child-sheath formed by any mixed multicomponent plasmas with arbitrary mixing proportions and arbitrary sheath-entering velocities. Based on the model, the characteristics of high-voltage Child-sheath of mixed deuterium-titanium plasmas are numerically studied. The theoretical and numerical results demonstrate as follows. The width of the Child-sheath will increase and the electric field intensity on target will decrease by decreasing the sheath-entering velocity of D+ or Ti2+, increasing the mixing proportion of D+, or decreasing the density of mixed plasmas. Through the above ways, extracted ions could achieve convergent transportations and the risk of breakdown on target could be also reduced. As the increase of applied voltage, the range of the stable ion-extraction operating region will be first enlarged and then reduced. By increasing the mixing proportion of D+ or decreasing the sheath-entering velocity of D+ or Ti2+, the range of stable ion-extraction operating region could be notably increased. The proposed kinetic model is verified by using a self-programed 1-D and three velocity components-particle in cell (1-D3V-PIC) code, the PIC simulation results agree with the theoretical solutions of the kinetic model very well. The presented universal kinetic model could give a fast estimation of stable operation region for ion extraction, and the above theoretical results could also give some beneficial references for experiments.