Paper PS-WeA9
A Mixed Mode Parameter/Physical Driven Particle-in-cell (PIC) Code for Capturing Transient Response and Evolution Behavior of Laboratory Plasma

Wednesday, November 1, 2017, 5:00 pm, Room 23

A baseline 1d3v full particle-in-cell (PIC) code has been modified extensively and is described. Modifications include the addition of a local densityadjustment (LDA) to the Monte-Carlo-Collision (MCC) algorithm to facilitate the study of plasma transients due to external pulsed stimulus and evolution behavior of plasma in general. The LDA-MCC adjusts for conditions involving transient volume density distributions and population inversions, collisions outside the sputter injected material wavefront, zero population cells, extreme volume density gradients, and collisional vs. colliding species role reversals. Additional modifications were made to accommodate collisional interactions between the working gas neutrals (WG), ions (WG⁺), and electrons (e^-) with cathode target material neutrals (T_n) and ions (T⁺). The MCC was further altered to distinguish WG fast neutrals (WG_fn) and excited atoms (WG^*) to support de-excitation and Penning collisions important in high power impulse magnetron sputtering (HiPIMS). A comparative summary of particle-particle interactions supported vs. the baseline code are shown in Table 1 supplemental. Further changes were made to support parameter, physical, and mixed mode driven simulation regarding secondary emission coefficients (SEEC), target emission coefficients (TAEC), and their underlying implementation at the cathode. A physical driven model to support electron emission δ_e and a parameter driven target ion sticking coefficient has also been incorporated at the anode. Further revisions were made to accommodate SEECs and TAECs greater than 100% requiring changes to the charge adjustment algorithm. Finally, the particle mover and injection push algorithms were modified to support a decaying magnetic field B_z parallel to and sourced from the cathode.

When new material is introduced via sputter injection or HiPIMS is utilized, new material wavefronts and locally high volume densities can arise, Fig. 1 supplemental, causing incorrect collision statistics if treated as a uniformly distributed density throughout the plasma. Furthermore, large numbers of zero population cells can exist for individual species for periods of time during plasma evolution. These characteristics can produce collision results where source material is non-existent, Figs. 2-3 supplemental, and infer more collisions than existing source material. These discrepancies can be insignificant after the plasma has equilibrated but are unacceptable when studying transient behavior or the details of plasma evolution. The LDA-MCC makes adjustment for these scenarios.