Modelling of nitrogen multi-energy ion implantation into WC-Co indexable knives for wood-based materials machining

Modelling of nitrogen multi-energy ion implantation into WC-Co indexable knives for wood-based materials machining. The paper presents the results of the modelling of multi-energy ion implantation processes of nitrogen to WC-Co indexable knives for wood-based materials machining. The modelling was performed for implantation of N++N2+ ions, for implanters without and with mass separation. Additionally, modelling for average charge state and for the extended implantation case was executed. The best results, i.e. flat and long plateau region and the most favourable plateau/multi ratio were obtained for N+ ions.

Dependence of silicon ablation regimes on fluence during ultrafast laser irradiation

Models and experiments were developed to study femtosecond laser ablation of silicon using 800 nm, 40 fs pulses with fluences ranging from 0.5 to 35 J/cm2. At low fluences, ablation was found to occur due to bubble formation and splashing within the melt layer. At higher fluences, it was found that the ablation depth exceeded the melt layer depth due to shockwave ablation. The variation in ion flux and ion velocity was also studied both experimentally and theoretically. It was found that the variation in ion flux is mainly dependent on the variation in the average charge state, with only a small variation in the total number of ions above $\sim \!\!1.5\; \,{\rm J/c}{{\rm m}^2}$. Comparisons between the theoretical and experimental ion flux showed that higher charge state ions received greater portion of the laser energy compared with lower charge state ions.

Signature of gyro-phase drift

Gyro-phase drift is a guiding center drift that is directly dependent on the charging rate limit of dust grains. The effect of introducing a gyro-phase-dependence on the grain charge leads to two orthogonal components of guiding-center drift. One component, referred to here as grad-q drift, results from the time-varying, gyro-phase angle dependent, in-situ-equilibrium grain charge, assuming that the grain charging is instantaneous. For this component, the grain is assumed to be always in its in-situ-equilibrium charge state and this state gyro-synchronously varies with respect to the grain's average charge state. The other component, referred to here as the gyro-phase drift, arises from any non-instantaneous-charging-induced modification of the diamagnetic drift and points in the direction of -∇RLd (where RLd is the grain gyro-radius), i.e. the direction associated with increasing magnitude of in-situ-equilibrium charge state. For this component, the grain gyro-synchronously undercharges and overcharges with respect to its gyro-synchronously varying, in-situ-equilibrium charge state. These characteristics are illustrated with a single-particle code for predicting grain trajectory that demonstrates how gyro-phase drift magnitude and direction could be exploited, using an extended version of the presented model, as sensitive indicators of the charging time of dust grains because of the cumulative effect of the ever-changing charge state of a grain making repeated excursions in inhomogeneous plasma over many gyro-periods.

Charge state of Zn projectile ions in partially ionized plasma: Simulations

This study deals with the simulation of the experimental study of Roth et al. (2000) on the interaction of energetic Zn projectiles in partially ionized laser produced carbon targets, and with similar type experiments. Particular attention is paid to the specific contributions of the K and L shell target electrons to electron recombination in the energetic Zn ionic projectile. The classical Bohr–Lindhard model was used for describing recombination, while quantum mechanical models were also introduced for scaling the L to K cross-section ratios. It was found that even for a hydrogen-like carbon target, the effect of the missing five bound electrons brings about an increase of only 0.6 charge units in the equilibrium charge state as compared to the cold target value of 23. A collisional radiative calculation was employed for analyzing the type of plasma produced in the experimental study. It was found that for the plasma conditions characteristic of this experiment, some fully ionized target plasma atoms should be present. However in order to explain the experimentally observed large increase in the projectile charge state a very dominant component of the fully ionized plasma must comprise the target plasma. A procedure for calculating the dynamic evolvement of the projectile charge state within partially ionized plasma is also presented and applied to the type of plasma encountered in the experiment of Roth et al. (2000). The low temperature and density tail on the back of the target brings about a decrease in the exiting charge state, while the value of the average charge state within the target is dependent on the absolute value of the cross-sections.