Test particle simulations of resonant interactions between energetic electrons and discrete, multi-frequency artificial whistler waves in the plasmasphere

Modulated high frequency （HF） heating of the ionosphere provides a feasible means of artificially generating ex- tremely low frequency （ELF）/very low frequency （VLF） whistler waves, which can leak into the inner magnetosphere and contribute to resonant interactions with high energy electrons. Combining the ray tracing method and test particle simulations, we evaluate the effects of energetic electron resonant scattering driven by the discrete, multi-frequency arti- ficially generated ELF/VLF waves. The simulation results indicate a stochastic behavior of electrons and a linear profile of pitch angle and kinetic energy variations averaged over all test electrons. These features are similar to those associated with single-frequency waves. The computed local diffusion coefficients show that, although the momentum diffusion of relativistic electrons due to artificial ELF/VLF whistlers with a nominal amplitude of ~ 1 pT is minor, the pitch angle scattering can be notably efficient at low pitch angles near the loss cone, which supports the feasibility of artificial triggering of multi-frequency ELF/VLF whistler waves for the removal of high energy electrons from the magnetosphere. We also investigate the dependences of diffusion coefficients on the frequency interval （△f） of the discrete, multi-frequency waves. We find that there is a threshold value of Af for which the net diffusion coefficient of multi-frequency whistlers is inversely proportional to △f （proportional to the frequency components Nw） when △f is below the threshold value but it remains unchanged with increasing Af when △f is larger than the threshold value. This is explained as being due to the fact that the resonant scattering effect of broadband waves is the sum of the effects of each frequency in the ＇effective frequency band＇. Our results suggest that the modulation frequency of HF heating of the ionosphere can be appropriately selected with reasonable frequency intervals so that better performance of controlled precipitation of high energy electrons in the plasmasphere by artificial ELF/VLF whistler waves can be achieved.

Study on electron stochastic motions in the magnetosonic wave field: Test particle simulations

Using the test particle simulation method, we investigate the stochastic motion of electrons with energy of 300 keV in a monochromatic magnetosonic(MS) wave field. This study is motivated by the violation of the quasi-linear theory assumption, when strong MS waves(amplitude up to ~1 nT) are present in the Earth's magnetosphere. First, electron motion can become stochastic when the wave amplitude exceeds a certain threshold. If an electron initially resonates with the MS wave via bounce resonance, as the bounce resonance order increases, the amplitude threshold of electron stochastic motion increases until it reaches the peak at about the 11 th order in our study, then the amplitude threshold slowly declines. Further, we find that the coexistence of bounce and Landau resonances between electrons and MS waves will significantly reduce the amplitude threshold. In some cases, the electron motion can become stochastic in the field of an MS wave with amplitudes below 1 nT. Regardless, if neither the bounce nor Landau resonance condition is satisfied initially, then the amplitude threshold of stochastic motion shows an increasing trend for lower frequencies and a decreasing trend for higher frequencies, even though the amplitude threshold is always very large(> 5 nT). Our study suggests that electron stochastic motion should also be considered when modeling electron dynamics regulated by intense MS waves in the Earth's magnetosphere.

Development of the PARASOL Code and Full Particle Simulation of Tokamak Plasma with an Open-Field SOL-Divertor Region Using PARASOL

The PARASOL code and the simulation by using PARASOL are introduced briefly. The PARASOL code with particle-in-cell （PIC） method and binary collision model was developed in JAERI and JAEA. Simulations using PARASOL code were carried out in order to investigate the power and particle control with diveror system in fusion reactors. The one-dimensional （1D） version of PARASOL was adopted to investigate the Bohm criterion, the supersonic flow, the SOL heat conduction, and so on. The heat propagation due to edge localized mode （ELM） was studied with the 1D-dynamic PARASOL. The two-dimensional version of PARASOL for the whole tokamak plasma including scrape-off-layer （SOL）-divertor region was useful for simulating the SOL flow pattern, the electric field formation etc. Based on PARASOL simulation results, improved physics modeling for the fluid simulation was built up.

Magnetic Field Improvement in End Region of Rectangular Planar DC Magnetron Based on Particle Simulation

For a rectangular planar direct current （DC） magnetron, anomalous target erosion may occur in the curve-out region and inner side of the curved region. One key factor is that the magnetic field in the end region is weaker than that in the straight region, and another important factor may be that there is a circumferential component of the magnetic field in the curved region. Through a calculation of three-dimensional magnetic field for the rectangular magnetron, a magnet structure shimmed by permanent magnet bars and ferromagnetic bars is proposed to solve the above problems. Through a three-dimensional non-self-consistent particle simulation and the Yamamura/Tawara formula, the target erosion profile could be predicted. The simulation results show that for an improved uniformity in magnetic field, the entire target utilization could be much enhanced.

Estimate of Lifetime of Ion Thruster Optics Based on Particle Simulation

A three-dimensional particle simulation of ion thruster optics with charge-exchange collision was developed in this study. The simulation code was based on tracking ions using the particle-in-cell method, and the Monte Carlo technique was used to model the charge-exchange collision. Simulations were performed for a 20 cm ion thruster optics. The results were compared with the corresponding experimental data from a test of the ion thruster optics for a duration of 800 hours. The Depth-From-Focus （DFF） method was used to measure the erosion depth of the downstream surface of the accelerator grid. The predicted erosion depth of the accelerator grid was consistent reasonably with the corresponding experimental data. The simulation results showed that the accelerator grid would be burned through after 1333 hours.

Particle Simulation of an Improved Axially Extracted Vircator

An axially extracted virtual cathode oscillator (vircator) with a feedback annulus is proposed and configured through particle-in-cell (PIC) simulation in Ref. [1]. In this paper, the effects of the feedback mechanism are studied through PIC method. The simulated results indicate that the improved new vircator can increase the output power twice large than that of the axially-extracted conventional vircator under the same condition. On the other hand, it can narrow the bandwidth and purify the modes.

Sample size adaptive strategy for time-dependent Monte Carlo particle transport simulation

When multiphysics coupling calculations contain time-dependent Monte Carlo particle transport simulations, these simulations often account for the largest part of the calculation time, which is insufferable in certain important cases. This study proposes an adaptive strategy for automatically adjusting the sample size to fulfil more reasonable simulations. This is realized based on an extension of the Shannon entropy concept and is essentially different from the popular methods in timeindependent Monte Carlo particle transport simulations, such as controlling the sample size according to the relative error of a target tally or by experience. The results of the two models show that this strategy can yield almost similar results while significantly reducing the calculation time. Considering the efficiency, the sample size should not be increased blindly if the efficiency cannot be enhanced further. The strategy proposed herein satisfies this requirement.

Refinement of Adaptive Dynamical Simulation of Quantum Mechanical Double Slit Interference Phenomenon

We applied adaptive dynamics to double slit interference phenomenon using particle model and obtained partial successful results in our previous report. The patterns qualitatively corresponded well with experiments. Several properties such as concave single slit pattern and large influence of slight displacement of the emission position were different from the experimental results. In this study we tried other slit conditions and obtained consistent patterns with experiments. We do not claim that the adaptive dynamics is the principle of quantum mechanics, but the present results support the probability of adaptive dynamics as the candidate of the basis of quantum mechanics. We discuss the advantages of the adaptive dynamical view for foundations of quantum mechanics.

DISCRETE PARTICLE SIMULATION OF SIZE SEGREGATION OF PARTICLE MIXTURES IN A GAS FLUIDIZED BED

This paper presents a study of the mixing/segregation behaviour of particle mixtures in a gas fluidized bed by use of the discrete particle simulation. Spherical particles with diameters 2 mm （jetsam） and 1 mm （flotsam） and density 2 500 kg.m^-3 are used as solid mixtures with different volume fractions. The particles are initially packed uniformly in a rectangular bed and then fluidized by gas uniformly injected at the bottom of the bed. The gas injection velocities vary to cover fixed, partially and fully fluidized bed conditions. Segregation/mixing behaviour is discussed in terms of flow patterns, solid concentration profile and mixing kinetics. The results show that segregation, as a transient fluidization process, is strongly affected by gas injection velocities for a given particle mixture. With the increase of the volume fraction of flotsam, size segregation appears at lower velocities.

Full Torus Electromagnetic Gyrokinetic Particle Simulations with Kinetic Electrons

The full torus electromagnetic gyrokinetic particle simulations using the hybrid model with kinetic electrons in the presence of magnetic shear is presented.The fluid-kinetic electron hybrid model employed in this paper improves numerical properties by removing the tearing mode,meanwhile,preserves both linear and nonlinear wave-particle resonances of electrons with Alfven wave and ion acoustic wave.

DEM simulation of particle flow on a single deck banana screen

A mathematical study of particle flow on a banana screen deck using the discrete element method (DEM) was presented in this paper. The motion characteristics and penetrating mechanisms of particles on the screen deck were studied. Effects of geometric parameters of screen deck on banana screening process were also investigated. The results show that when the values of inclination of discharge and increment of screen deck inclination are 10° and 5° respectively, the banana screening process get a good screening performance in the simulation. The relationship between screen deck length and screening efficiency was further confirmed. The conclusion that the screening efficiency will not significantly increase when the deck length L≥430 mm (L/B ≥ 3.5) was obtained, which can provide theoretical basis for the optimization of banana screen.

Simulation of random mixed packing of different density particles

This paper presents the effects of density difference on the three-dimensional （3D） distribution of random mixed packing. The random mixed packing dynamics of particles of two different densities are simulated. The initial state is homogeneous, but the final packing state is inhomogeneous. The segregation phenomenon （inhomogeneous distribution） is also observed. In the final state, the top layers are composed of mostly light particles. The several layers beneath the top contain more heavy particles than light particles. At the bottom, they also contain more heavy particles than light particles. Furthermore, at both the top and the bottom, particle clustering is observed. The current study also analyses the cause of this inhomogeneity in detail. The main cause of this phenomenon is the velocity difference after collision of these two types of particles induced by the density difference. The present study reveals that even if particles were perfectly mixed, the packing process would lead to the final inhomogeneous mixture. It suggests that special treatment may be required to get the true homogeneous packing.

Potential application of particle based simulations in reservoir security management

In order to model the movement progress in case of risks such as dam collapse and coastal inundation, particle-based simulation methods, including the discrete-element method and smoothed particle hydrodynamics, which have specific advantages in modeling complex three-dimensional environmental fluid and particulate flows, are adopted as an effective way to illustrate environmental applications possibly happening in the real world. The theory of these methods and their relative advantages compared with traditional methods are discussed. Examples of 3-D flows on realistic topography including the flooding of a river valley as a result of a dam collapse and coastal inundation by a tsunami are introduced. Issues related to validation and quality data availability are also discussed. The results show that the simulations provide a valuable insight in a given situation for the security management of reservoir dams. Validation can only be performed where both the initial and final states can be very well characterized.

Physical Simulation of Nonmetallic Particle Movement in Al Melt under Electromagnetic Field

Physical simulation is used to study the movement of nonmetallic particles in Al melt in electro- magnetic field. It is found that the terminal velocity of particles in different Reynolds number range has different functions. By confirming drag force coefficient of nonmetallic particles with Reynolds number in the range of 0.2-10 and 10-25 respectively, two functions of terminal ve- locity for spherical nonmetallic particles have been got accordingly, which provide a theoretical basis for separating nonmetallic inclusions from Al melt in electromagnetic field.

Location and Capacity Determination Method of Electric Vehicle Charging Station Based on Simulated Annealing Immune Particle Swarm Optimization

As the number of electric vehicles(EVs)continues to grow and the demand for charging infrastructure is also increasing,how to improve the charging infrastructure has become a bottleneck restricting the development of EVs.In other words,reasonably planning the location and capacity of charging stations is important for development of the EV industry and the safe and stable operation of the power system.Considering the construction and maintenance of the charging station,the distribution network loss of the charging station,and the economic loss on the user side of the EV,this paper takes the node and capacity of charging station planning as control variables and the minimum cost of system comprehensive planning as objective function,and thus proposes a location and capacity planning model for the EV charging station.Based on the problems of low efficiency and insufficient global optimization ability of the current algorithm,the simulated annealing immune particle swarm optimization algorithm(SA-IPSO)is adopted in this paper.The simulated annealing algorithm is used in the global update of the particle swarm optimization(PSO),and the immune mechanism is introduced to participate in the iterative update of the particles,so as to improve the speed and efficiency of PSO.Voronoi diagram is used to divide service area of the charging station,and a joint solution process of Voronoi diagram and SA-IPSO is proposed.By example analysis,the results show that the optimal solution corresponding to the optimisation method proposed in this paper has a low overall cost,while the average charging waiting time is only 1.8 min and the charging pile utilisation rate is 75.5%.The simulation comparison verifies that the improved algorithm improves the operational efficiency by 18.1%and basically does not fall into local convergence.

Simulation to Predict Target Erosion of Planar DC Magnetron

Plasma properties in a planar DC magnetron system are simulated by a non-self- consistent particle method in two dimensions. Through tracing the trajectories of the energetic electrons in the specified electric field and the magnetic field, and treating the collision process by Monte Carlo method, the spatial profile of ionization events can be obtained conveniently. Assuming that the ions speed up from the ionization points and bombard the target with the energy at these points, and according to the Yamamura/Tawara method, the target erosion can be predicted. The magnetic field is calculated by the finite element method, and the electric field is estimated according to the self-consistent simulation and measured results. The influence of the time step size on the target erosion profile is analysed first to find a proper step size. Then the influence of electric field estimated on the erosion profile is discussed. The erosion profile may become narrower if the sheath thickness is increased. Finally, considering the dynamic erosion process, the erosion profile may get wider over time for the magnetron with shunt bar.

Numerical Simulation of Ion Extraction Through Ion Thruster Optics

Based on the particle-in-cell （PIC） method, a two-dimensional numerical scheme was developed to investigate the ion beam extraction phenomena through the ion thruster optics. According to the calculated results, the plasma sheath upstream of the screen grid, the electric field in the calculation domain, and the ion and electron spatial distributions are obtained for different accelerator grid voltages. The results indicate that the accelerator grid voltage affects the plasma sheath upstream of the screen grid significantly. It is found that a moderate accelerator grid voltage results in an ion optical performance better than either a higher or lower voltage, from a point of ion extraction from the discharge chamber and erosion mitigation of the accelerator grid due to the direct ion impingement.

Three Dimensional Simulation of Ion Thruster Plume-Spacecraft Interaction Based on a Graphic Processor Unit

Based on the three-dimensional particle-in-cell （PIC） method and Compute Unified Device Architecture （CUDA）, a parallel particle simulation code combined with a graphic processor unit （GPU） has been developed for the simulation of charge-exchange （CEX） xenon ions in the plume of an ion thruster. Using the proposed technique, the potential and CEX plasma distribution are calculated for the ion thruster plume surrounding the DS1 spacecraft at different thrust levels. The simulation results are in good agreement with measured CEX ion parameters reported in literature, and the CPU＇s results are equal to a CPU＇s. Compared with a single CPU Intel Core 2 E6300, 16-processor GPU NVIDIA GeForce 9400 GT indicates a speedup factor of 3.6 when the total macro particle number is 1.1 × 10^6. The simulation results also reveal how the back flow CEX plasma affects the spacecraft floating potential, which indicates that the plume of the ion thruster is indeed able to alleviate the extreme negative floating potentials of spacecraft in geosynchronous orbit.

Three-dimensional particle-in-cell method of simulating high power terahertz gyrotrons with planar structure

Based on analyzing the large-signal theory of the planar gyrotron, it is suggested that a simplified structure of the device is used for simulating this kind of device, with the working characteristics of the device kept unchanged, i.e., the same as those of the device with the original structure. Thus, the computational burden can be significantly reduced. Using the proposed method, we simulate a planar gyrotron with its simplified parameters by using the UNIPIC-3D code. Numerical results show that the working frequency, output power, and electron efficiency are respectively about 0.813 THz, 14 kW, and 21%.

考虑混合工艺的自动化码头多设备资源协同调度优化模型和算法设计

Considering the uncertainty of the speed of horizontal transportation equipment,a cooperative scheduling model of multiple equipment resources in the automated container terminal was constructed to minimize the completion time,thus improving the loading and unloading efficiencies of automated container terminals.The proposed model integrated the two loading and unloading processes of“double-trolley quay crane+AGV+ARMG”and“single-trolley quay crane+container truck+ARMG”and then designed the simulated annealing particle swarm algorithm to solve the model.By comparing the results of the particle swarm algorithm and genetic algorithm,the algorithm designed in this paper could effectively improve the global and local space search capability of finding the optimal solution.Furthermore,the results showed that the proposed method of collaborative scheduling of multiple equipment resources in automated terminals considering hybrid processes effectively improved the loading and unloading efficiencies of automated container terminals.The findings of this study provide a reference for the improvement of loading and unloading processes as well as coordinated scheduling in automated terminals.