Particle-in-Cell Investigation on Temporal Evolution of High-Voltage Sheath of Mixed Deuterium-Titanium Plasmas

Using a self-programmed 1-D particle-in-cell (PIC) code coupled with Boltzmann electron (BE) model, the temporal evolution process of high-voltage sheath of mixed deuterium-titanium plasmas was numerically investigated by hybrid simulation. The simulation results demonstrate as follows. Time-delay (the interval between initial time and entering-time of steady phase) decreases with the increase of D+ proportion or ion (D+ or Ti2+) kinetic energy. Time-delay is hardly influenced by target voltage or plasma density. Moving velocity of plasma meniscus (sheath interface) increases with plasma density or ion (D+ or Ti2+) kinetic energy and decreases with the increase of target voltage or D+ proportion. When target current equal to plasma emitted current from plasma inlet, the system enters steady phase and the plasma meniscus no longer moves. In steady phase, plasma emitted current finally balances with space limited current. Steady sheath width increases with target voltage or D+ proportion, and decreases with the increase of plasma density or ion kinetic energy. Steady electric intensity on target increases with target voltage, plasma density, mixing proportion of Ti2+, or ion (D+ or Ti2+) kinetic energy. In steady phase, the value of D+ density is always lower than Ti2+ in high-voltage sheath. The above numerical results could give some helpful references for experiments of plasma immersion ion implantation (PIII) or ion extraction.