Dynamical Response Studies Of A Two-dimensional Dusty Plasma On A Periodic Substrate Driven By An External Force

Laboratory dusty plasma generally refers to an ionized gas containing micronsized dust particles.Due to the high electric charges of these dust particles,the potential energy between them is typically higher than their averaged kinetic energy,i.e.,these dust particles become strongly coupled,so that the collection of a large number of dust particles exhibits the typical properties of solids and liquids.In the plasma discharge chamber,these dust particles are suspended and confined by the electric field in the plasma sheath,so that they can self-organize into a monolayer suspension,which is just the so-called two-dimensional(2D)dusty plasma.More importantly,in experiments,the motion of each dust particle inside this 2D suspension can be directly recorded by high-speed cameras and then accurate ely tracked during data analysis.From the first experimental observation of laboratory dusty plasma in the plasma etching of the semiconductor chip manufacturing about thirty years ago,dust plasma has been developed to an important experiment model system,through which many microphysics mechanisms of various fundamental physics processes in solids and liquids are investigated at the individual particle kinetic level.The current investigations of dusty plasmas are mainly about the collective behaviors of dust particles themselves.However,the complicated electromagnetic plasma environment can substantially modify their collective dynamical behaviors.The strong coupling between dust particles is able to interact with the external field,so that the competition and matching may occur to generate a series of new effects.In this thesis,Langevin dynamical simulations are performed to mimic the dynamical behaviors of 2D dusty plasma modulated by 1D periodic substrate.The properties of phase transition between different phases of this 2D dusty plasma system driven by various DC driving forces are systematically studied.Furthermore,the structure and dynamic behaviors of this 2D dusty plasma under pure AC driving forces with various values of the amplitude and the frequency are also investigated.While a DC driving force applied to 2D dusty plasma on a 1D periodic substrate increases from zero gradually,from the static structure of the fraction of sixfold coordinated particles and the dynamical collective drift velocity along the direction of the DC driving force,three completely different non-equilibrium dynamical states are discovered,which are the pinning state,the disordered plastic flow state,and the moving ordered state.Meanwhile,from the particle trajectories,especially in the moving coordinate of the whole system,the discovered three dynamical states are further confirmed.Then,based on the continuous or discontinuous properties of these two diagnostics of the static structure and the collective drift velocity,it is demonstrated that the depth of the 1D periodic substrate is able to significantly modulate the transition properties between these dynamical phases.In addition,when the driving force increases monotonically from zero to its maximum,and then decreases monotonically to zero,it is found that the collective drift velocity of particles exhibits a typical hysteresis loop for the discontinuous phase transition.However,for the continuous phase transition,this hysteresis loop disappears completely.Thus,the observed continuous or discontinuous phase transitions are confirmed from different diagnostics.Finally,the results of the kinetic temperature corresponding to the particle motion in the two directions during the depinning process are plotted,where the continuous or discontinuous properties of the phase transition are also exhibited.When the substrate is deep enough,the particle motion exhibits a strong anisotropy,and the variation trend is not so synchronous as that for shallower substrates.For 2D dusty plasma modulated by a 1D periodic substrate,in addition to the above results driven by an external constant DC driving force,a preliminary investigation of the effect driven by an external pure AC driving force is also performed in this thesis.By analyzing the simulation data with different conditions,it is found that the arrangement and the collective motion of particles both substantially respond to the low-frequency pure AC driving forces.The simulation results show that the frequency and amplitude of the pure AC driving force have significant modulation effects on the depinning threshold of the studied system.The influence of the pure AC driving force frequency on the depinning threshold is monotonical.The lower the frequency,the smaller the depinning threshold.The influence of the pure AC driving force amplitude on the depinning threshold of the studied system exhibits a bell curve,where the peak value of the depinning threshold is related to the parameters of the 1D periodic substrate.It is found that the frequency of the pure AC driving force has a significant influence on the structure of different non-equilibrium dynamic phases of the studied system during the depinning process.The lower the frequency,the more stable the structure of the three non-equilibrium dynamic phases.In addition,the simulation data also indicate that,during the whole process of the depinning dynamics,the properties of the nonequilibrium depinning phase transitions in the studied system are not affected by the applied pure AC driving forces.