Directional motion of dust particles at different gear structures in a plasma

Directional motion of dust particles in a dusty plasma ratcnet is observed experimentally.The dusty plasma ratcnet consists of two concentric gears with asymmetric sawtooth.It is found that the sawtooth number affects the directional motion of dust particles along the saw channel.With the inerease of the sawtooth number,the particle velocity increases firstly and then decreases,and there is an optimum number of the sawtooth which could induce fast rotation of dust particles.The velocities of dust particles change as they are flowing along the saw channel.We also explore the force acting on the dust particle experimentally.     

Three-junction SQUID rocking ratchet

We investigate three-junction SQUIDs which show voltage rectification if biased with an ac current drive with zero mean value. The Josephson phase across the SQUID experiences an effective ratchet potential, and the device acts as an efficient rocking ratchet, as demonstrated experimentally for adiabatic and nonadiabatic drive frequencies. For high-frequency drives the rectified voltage is quantized due to synchronization of the phase dynamics with the external drive. The experimental data are in excellent agreement with numerical simulations including thermal fluctuations.     

Behaviour of two‐dimensional liquid dusty plasmas under perpendicular magnetic fields

The collective behaviour of two‐dimensional (2D) liquid dusty plasmas under perpendicular magnetic fields is studied using Langevin dynamic simulations. Based on the positions and velocities of the simulated dust particles, the dynamic parameters of intermediate scattering functions and probability distribution functions are calculated. It is found that, under different 2D liquid dusty plasma conditions, the motion of individual dust particles tends to be more super‐diffusive under stronger perpendicular magnetic fields, well consistent with the previous finding using a different diagnostic technique.     

空间尘埃等离子体对量子卫星通信性能的影响

为了研究尘埃等离子体中带电尘埃的粒子半径、粒子浓度和带电荷数对量子通信性能的影响,首先根据Mie散射理论得到单个带电尘埃粒子的光散射截面;然后通过粒子浓度求出总的消光截面,得出链路衰减的数学模型,提出了带电粒子特性与量子纠缠度的关系;针对退极化信道,当单个尘埃粒子所吸附带电粒子的个数为50时,给出了尘埃粒子半径、粒子浓度与信道容量和量子误码率的定量关系.仿真结果表明,当量子信号的传输距离为10km时,尘埃粒子浓度从1×10~(10) m~(-3)增加到10×10~(10) m~(-3),信道容量从0.6726降低到0.1075;尘埃粒子半径从0.1μm增加到10μm时,量子误码率由1.334×10~(-3)增加到5.309×10~(-3).由此可见,尘埃等离子体中带电尘埃粒子的半径和浓度对量子卫星通信性能有显著的影响.因此,为确保量子通信的可靠性,应根据所探测到的等离子体环境的状况,调整卫星通信系统的各项指标参数.     

Asymmetric step-like characteristics in a tilted rocking ratchet potential

The overdamped Langevin dynamics has been employed to study the directional transport of particles driven in a tilted rocking ratchet potential. The system subjected to a constant direct force undergoes an asymmetrical dynamic transition from a static state to a sliding state at two different critical forces that are consistent with the predicted values. When an additional alternating force is applied to the system, the time-averaged velocity shows several steps of equal height as the direct force increases. These steps are similar to the Shapiro steps in an rf-driven Josephson junction, and appear whenever the system's natural frequency given by the direct force matches an integer multiple of the applied frequency. When the alternating force exceeds a certain critical value which can be also estimated for a slow rocking, a directional motion known as the rectification effect occurs even at zero direct force.     

Screening and attraction of dust particles in plasmas

The potential around a dust particle in a plasma is found using the collisional hydrodynamic equations of dusty plasmas, taking into account ion-dust and ion-neutral collisions and considering the plasma source proportional to the dust density. The linear screening is strongly influenced by the collisions and can substantially differ from Debye screening. Attraction of negatively charged dust particles can occur due to overscreening by the ion fluxes in the presence of friction forces.     

Quantum ratchet effect for vortices

We have measured a quantum ratchet effect for vortices moving in a quasi-one-dimensional Josephson junction array. In this solid-state device the shape of the vortex potential energy, and consequently the band structure, can be accurately designed. This band structure determines the presence or absence of the quantum ratchet effect. In particular, asymmetric structures possessing only one band below the barrier do not exhibit current rectification at low temperatures and bias currents. The quantum nature of transport is also revealed in a universal/nonuniversal power-law dependence of the measured voltage-current characteristics for samples without/with rectification.     

Adiabatic dust-acoustic double layers in two temperature electron dusty plasma

Large amplitude adiabatic double layers are investigated in the case of positively charged dusty plasma. The dust grains provide the inertia and the background plasma is formed of two electron populations, hot and cold, in thermal equilibrium. Using fluid equations and the pressure balance equation, the Sagdeev pseudo-potential is driven in the stationary frame. The dependence of the double layers amplitude and Mach number on various parameters such as the hot to cold electron densities, the temperature ratio and the dust drift velocity have been numerically examined. The critical parameters, for which a nature change occurs, are found.     

Drift ratchet

We consider a silicon wafer, pierced by millions of identical pores with periodically varying diameters but without spatial inversion symmetry (ratchet profile). When a liquid is periodically pumped back and forth through the pores, our theory predicts a net transport of suspended micrometer-sized particles (drift ratchet). The direction of this particle current depends very sensitively on the size of the particles. For typical parameter values of the experiment, two different types of particles at an initially homogeneous 1:1 mixture are spatially separated with a purity beyond 1:1000 on a time scale of a few hours in comparably large quantities. This result is due to the highly parallel architecture of the device. The experimental realization of the setup, presently under construction, thus appears to be a promising new particle separation device, possibly superior to existing methods for particles sizes on the micrometer scale.     

Nonlinear development of the dust acoustic instability in acollisional dusty plasma

We study the nonlinear behavior of the low-frequency dust acoustic instability in a collisional dusty plasma by means of particle simulations. The instability arises due to the streaming of plasma ions and neutrals relative to charged dust grains. According to linear theory, the presence of collisions between the plasma ions and a neutral gas background reduces the growth rate of the instability. Nonlinearly, however, the presence of drifting neutrals maintains the initial relative drift between plasma and dust ions until the unstable waves grow to large amplitude and collisions due to wave-particle interactions exceed the neutral collisions. As a result, stronger nonlinear effects, as manifested by enhanced fluctuations, larger amounts of plasma and dust heating, and a temporary reduction of the relative drift velocity, can occur in the presence of collisions     

Streaming instability of dust-acoustic mode with helical wavefronts

Making use of the kinetic approach for plasma species, the electrostatic twisted dust-acoustic (DA) waves are studied in a collisionless unmagnetized multi-component dusty plasma consisting of electrons, singly ionized positive ions and charged massive dust grains. The Vlasov-Poisson equations are coupled together to obtain a generalized response function by using the Laguerre-Gaussian (LG) perturbed electrostatic potential and distribution function in the paraxial limit. The dispersive properties and growth rate instability of twisted DA waves are examined with distinct OAM states in a multi-component dusty plasma. Various significant modifications associated with the real wave frequency and growth rate are shown with respect to twist parameter and dust concentration. It is examined that dust concentration enhances the growth rate of twisted DA waves, whereas an increase in twist parameter reduces the growth rate instability. The excitation of twisted DA mode is also found to enhance with streaming speed of inertialess electrons. Our results may be useful for particle transport and trapping phenomena due to wave excitation in laboratory dusty plasmas.     

Electrostatic sheath at the boundary of a collisional dusty plasma

Considering the Boltzmann response of the ions and electrons in plasma dynamics and inertial dynamics of the dust charged grains in a highly collisional dusty plasma, the nature of the electrostatic potential near a boundary is investigated. Based on the fluid approximation, the formation as well as the characteristic behaviours of the sheath is studied. It is expected that the presence of dust charged grains will lead to a very different behaviour of the sheath as compared to that of electron-ion plasma. Moreover, the collisions of the dust charged grains with the neutrals are expected to exhibit novel features.     

Wake potential in a self-gravitating dusty plasma

Using a test particle approach, the dynamical wake potential has been examined in a homogeneous self-gravitating dusty plasma. The periodic oscillatory potential might lead to an alternative approach to the Jeans instability for the formation of dust agglomeration leading to gravitational collapse of the self-gravitating systems.     

Entropy in quantum ratchet for a delta-kicked model

We investigate the evolution of Shannon entropy in quantum ratchet effect for a delta-kicked model, where a particle with initial momentum zero is periodically kicked by an asymmetric potential. It is shown that the evolution of Shannon entropy of the particle can remarkably reflect whether quantum resonance emerges and gives rise to ratchet current or not. Furthermore, for different kinds of quantum resonances, low-order or high-order quantum resonances, the evolutions of the entropy are quite different.     

Linear propagation of dust acoustic modes in the presence of an electron beam

The physical and optical properties of plasmas are depended on dynamics of species in the discharge volume. Then, the presence of an electron beam, as a separate component, in a dusty plasma can modify the plasma structures through altering the discharge parameters. In this report, the linear propagation of acoustic modes in a collisionless dusty plasma contains electrons, ions and charged dust grains is investigated in the presence of an electron beam. Our analysis indicates that the electron beam can modify the dispersion relations of dust acoustic modes which resulted different data transportation in dusty plasmas. The obtained results are also examined for negative and positive charged dust grains with different number densities. The charge of dust grains represents an important role in the dynamics of the low frequency waves. Additionally, our findings reveal that the propagation of acoustic waves in dusty plasmas can be controlled by adjusting the electron number density of the beam and the cathode potential. Lastly, we obtian the destabilizing effects, originated from dust charge fluctuation, by reconsidering the dispersion relations of both dust acoustic modes.     

Formation of dust-acoustic shock waves in a strongly coupled cryogenic dusty plasma

The nonlinear propagation of ultra-low-frequency dust-acoustic (DA) waves in a strongly coupled cryogenic dusty plasma has been investigated, by using the Boltzmann distributed electrons and ions, as well as modified hydrodynamic equations for strongly coupled charged dust grains. The reductive perturbation technique is used to derive the Burger equation. It is shown that strong correlations among negatively charged dust particles acts like a dissipation, which is responsible for the formation of the DA shock waves. The latter are associated with the negative potential, i.e. with the compression of negatively charged cryogenic dust particle density. It is also found that the effective dust-temperature, which arises from electrostatic interactions among negatively charged dust particles, significantly affects the height of the DA shock structures. New laboratory experiments at cryogenic temperature should be conducted to verify our theoretical prediction.     

Impacts of neutral shadowing force on dust particle dynamics in cryogenic plasma

Recently, it was shown that the neutral shadowing force can have a strong impact on the structural properties of the charged dust particles in cryogenic dusty plasmas. Therefore, in this work, we have investigated the impact of the neutral shadowing force on the dynamical properties by means of molecular dynamics simulations. By computing the velocity auto‐correlation function of particles and their spectrum, we found that the neutral shadowing force has a strong impact on the dust particle dynamics if the mean free path of neutrals exceeds the mean inter‐dust particle distance.     

New physical concept of the formation of dust crystals

A clear physical model is proposed for phase transitions in a dusty plasma. According to this model, the formation of plasma dust crystals is associated with the nonlinear effect of the collective attraction of dust particles. The nonlinear collective attraction between negatively charged dust particles corresponds to large charges of dust particles used in the available experiments. This concept provides a new physical model of crystallization that is attributable to the capture of dust particles in an attractive potential well rather than to the strong interaction between them. Calculation using this model yields the depth of the attractive potential well and the critical coupling constant in good agreement with the available experimental data.     

Size of dust voids as a function of the power input in dusty plasma

A dust void is a dust-free region in dusty plasma. Theory demonstrates that the void results from the balance of the electrostatic and plasma (such as the ion drag) forces acting on a dust particle. In dusty plasma experiments, physical properties of the void show clear dependence on the power input into the plasma (in particular, its size increases with the increase of the applied power). Here, the theory and numerical results are presented for such a dependence. The text was submitted by the authors in English.