Mohammad Davoudabadi

Dust particle dynamics in magnetized plasma sheath

In this paper, the structure of a plasma sheath in the presence of an oblique magnetic field is investigated, and dynamics of a dust particle embedded in the sheath is elaborated. To simulate the sheath, a weakly collisional two-fluid model is implemented. For various magnitudes and directions of the magnetic field and chamber pressures, different plasma parameters including the electron and ion densities, ion flow velocity, and electric potential are calculated. A complete set of forces acting on the dust particle originating from the electric field in the sheath, the static magnetic field, gravity, and ion and neutral drags is taken into account. Through the trapping potential energy, the particle stable and unstable equilibria are studied while the particle is stationary inside the sheath. Other features such as the possibility of the dust levitation and trapping in the sheath, and the effect of the Lorentz force on the charged dust particle motion are also examined. An interesting feature is captured for the variation of the particle charge as a function of the magnetic field magnitude.

Lateral motion of a dust particle in magnetized plasma sheath

In this paper, lateral mobilization of a dust particle through application of an oblique magnetic field in a plasma sheath with infinitely long lateral dimensions is studied. A weakly collisional two-fluid model is implemented to simulate the plasma. A single submicrometer-sized particle is released at the sheath edge with zero initial velocity and is tracked in Lagrangian frame, taking into account various forces. Various characteristics of the particle lateral motion such as time history of its horizontal position, velocity, and acceleration components are presented and discussed. Through investigation of power spectra of plasma and particle variables, the particle drift in the horizontal plane is explained. While varying parameters such as magnetic field intensity, particle density, and its radius, the particle horizontal velocity components are calculated. The variation of these velocity components is then explained by considering the ion velocity components at the particle location.

Effect of collisions on dust particle charging via particle-in-cell Monte-Carlo collision

In this paper, the effect of collisions on the charging and shielding of a single dust particle immersed in an infinite plasma is studied. A Monte-Carlo collision (MCC) algorithm is implemented in the particle-in-cell DEMOCRITUS code to account for the collisional phenomena which are typical of dusty plasmas in plasma processing, namely, electron-neutral elastic scattering, ion-neutral elastic scattering, and ion-neutral charge exchange. Both small and large dust particle radii, as compared to the characteristic Debye lengths, are considered. The trends of the steady-state dust particle potential at increasing collisionality are presented and discussed. The ions and electron energy distributions at various locations and at increasing collisionality in the case of large particle radius are shown and compared to their local Maxwellians. The ion-neutral charge-exchange collision is found to be by far the most important collisional phenomenon. For small particle radius, collisional effects are found to be imp...

On accuracy and performance of high-order finite volume methods in local mean energy model of non-thermal plasmas

In this paper, a high-order finite volume method is employed to solve the local energy approximation model equations for a radio-frequency plasma discharge in a one-dimensional geometry. The so called deferred correction technique, along with high-order Lagrange polynomials, is used to calculate the convection and diffusion fluxes. Temporal discretization is performed using backward difference schemes of first and second orders. Extensive numerical experiments are carried out to evaluate the order and level of accuracy as well as computational efficiency of the various methods implemented in the work. These tests exhibit global convergence rate of up to fourth order for the spatial error, and of up to second order for the temporal error.

Dust particle dynamics in low-pressure plasma reactor

In this paper, the structure of a rf plasma glow discharge in a parallel-plate geometry is revisited through a numerical solution of the well-known local field approximation model equations. The dynamics of a dust particle injected into the plasma is elaborated in a Lagrangian framework by solving the particle equations for its motion and charge. Different ion drag expressions are considered. For particles of three different sizes, magnitudes of various forces such as gravity, electricity, and ion drag acting on a stationary particle are compared to each other. Particle potential energy, together with its possible wells, is demonstrated for each case. Taking into account the neutral drag force, damping oscillations and final locations of the particles, depending on their initial injection position (top or bottom), are captured. The transient characteristic of the charging process of smaller particles with respect to their motion time scale is discussed. The effect of inclusion of ion thermal energy in the calculation of drag force on the motion of the particle is illustrated.

One-Dimensional Fluid Model of Methane Plasma for Diamond-Like Coating

Physical modeling with numerical simulation is very useful for researchers to understand and improve the plasma-enhanced chemical vapor deposition process for coating of diamond-like carbon (DLC) films. In this paper, we implement a fluid model including a chemical reaction mechanism for methane plasmas. Employing a finite-difference method, we solve for the low-pressure RF plasma phase in a parallel-plate reactor via the local field equilibrium approximation model, based on which the distribution of the electrons and ions along with the electric potential is obtained. The validation of our simulation is carried out by comparing the model predictions with the results from a previous particle-in-cell work. Our simulations show that the concentration of neutral species is much higher than that of charged species. CH3 is found to be the major contributing species for deposition as its concentration and boundary flux are higher than those of the other depositing species. The effects of the electrode gap, reactor pressure, and RF voltage amplitude on the species density distributions and depositing species boundary fluxes are studied. Although the deposition rate may be increased (when the number density and boundary flux of depositing species increase) by changing the operating conditions, the variation of C2H5 concentration and boundary flux requires more attention because it may affect the quality of DLC coating.

Effect of ion-neutral collisions on the charging of a dust particle

of ion-neutral charge-exchange collisional process on the charging and shielding of a single dust particle immersed in an infinite plasma under dierent operating conditions is studied. The fully kinetic evolution of the plasma is accounted for by use of a two-dimensional Particle-in-Cell method in a cylindrical symmetric geometry, where both ion and electron species are tracked. Collisions are considered as probabilistic events which depend on the specific collision frequency. The variation of the steady-state dust particle potential with increasing collisionality is presented and discussed. The ions energy distributions at various locations and at increasing collisionality are shown and compared to their local Maxwellian distributions.