Binary Collision Model Research Articles

3D simulation optimization and design of multicusp ion source

In this paper, a permanent magnet of multicusp ion source is calculated in theory, using the binary collision model to deal with coulomb collision between electrons. Collision between electrons and hydrogen species is treated with the null-collision model. Therefore, the three-dimensional PIC-MCC simulation algorithm is developed. Two optimization design models of multicusp ion source, ET-60U, are simulated by the software. Also, the spatial distribution characteristics and the relevant issues of the volume negative hydrogen ion production rate of the two kinds of ion sources are explored. Finally, The basic idea about the design of the negative hydrogen ion source is proposed. indicating that appropriately regulating the magnetic field distribution of the multicusp ion source can produce uniform ion beam, and that appropriately adjusting the size of the extraction magnetic field and the ion source structure can obtain both the ion beam spatial uniformity and the high production rate.

Particle Collisions in a Lumped Particle Model

AbstractThis paper presents an extension of the lumped particle model in [1] to include the effects of particle collisions. The lumped particle model is a flexible framework for the modeling of particle laden flows, that takes into account fundamental features, including advection, diffusion and dispersion of the particles. In this paper, we transform a binary collision model and concepts from kinetic theory into a collision procedure for the lumped particle framework. We apply this new collision procedure to investigate numerically the role of particle collisions in the hindered settling effect. The hindered settling effect is characterized by an increase in the effective drag coefficient CD that influences each particle in the flow. This coefficient is given by , where ϕ is the volume fraction of particles, is the drag coefficient for a single particle, and n ≃ 4.67 for creeping flow. We obtain an approximation for CD/CD by calculating the effective work done by collisions, and comparing that to the work done by the drag force. In our numerical experiments, we observe a minimal value of n = 3.0. Moreover, by allowing high energy dissipation, an approximation for the classical value for creeping flow, n = 4.7, is reproduced. We also obtain high values for n, up to n = 6.5, which is consistent with recent physical experiments on the sedimentation of sand grains.

The interaction of hyperthermal nitrogen with N-covered Ag(111)

A mixed beam of hyperthermal N atoms and N(2) molecules was scattered from the N-covered Ag(111) surface held at 300 K. The angular distribution of scattered N atoms is very broad. In contrast, N(2) molecules exhibit a sharp angular distribution. Taking into account the relative mass ratio, N loses more energy at the surface than N(2). In terms of energy loss, the atoms approximately follow the binary collision model while the molecules do not. Instead, the energy curves of scattered N(2) are more comparable to the parallel momentum conservation model for near specular outgoing angles (40°-65°). For both atoms and molecules the angle-resolved intensity and final energy curves are very similar to those from the bare surface. However, the N-covered surface yields non-negligible N(2) intensity for a broad range of outgoing angles, including along the surface normal. This was not the case from the clean surface, where the measured intensity distribution was confined to the narrower angular range indicated above. Backscattering and direct abstraction reactions are evaluated as possible origins of this additional N(2) signal. Of these, an abstraction mechanism appears to be the most consistent with the measured data.

A simplified model for calculating R AA and R CP of cold nuclear matter effects

An incoherent binary nucleon-nucleon collision model of AA collisions is presented for simulating particle production in cold nuclear matter. With a simple phenomenological parameter, the mean nucleon energy loss fraction, this model yields pseudorapidity density distributions that are comparable to those of experiment, as well as those of HIJING. Particle production data for a given binary collision is extracted from the PYTHIA event generator. The nuclear geometry is described by the Glauber model. The preliminary RAA and RCP results are also presented and discussed, with a proposal that RAA be redefined.

Vibrational relaxation of azide ions in liquid-to-supercritical water

The dynamics of vibrational energy relaxation (VER) of the aqueous azide anion was studied over a wide temperature (300 K ≤ T ≤ 663 K) and density (0.6 g cm(-3) ≤ ρ ≤ 1.0 g cm(-3)) range thereby covering the liquid and the supercritical phase of the water solvent. Femtosecond mid-infrared spectroscopy on the ν(3) band associated with the asymmetric stretching vibration of the azide anion was used to monitor the relaxation dynamics in a time-resolved fashion. The variation of the vibrational relaxation rate constant with temperature and density was found to be rather small. Surprisingly, the simple isolated binary collision model is able to fully reproduce the experimentally observed temperature and density dependence of the relaxation rate provided a local density correction around the vibrationally excited solute based on classical molecular dynamics simulations is used. The simulations further suggest that head-on collisions of the solvent with the terminal nitrogen atoms rather than side-on collisions with the central nitrogen atom of the azide govern the vibrational energy relaxation of this system. Finally, the importance of hydrogen bonding for the VER dynamics in this system is briefly discussed.

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.

Scattering of hyperthermal argon atoms from clean and D-covered Ru(0001) surfaces

Hyperthermal Ar atoms were scattered from a Ru(0001) surface held at temperatures of 180, 400 and 600 K, and from a Ru(0001)-(1×1)D surface held at 114 and 180 K. The resultant angular intensity and energy distributions are complex. The in-plane angular distributions have narrow (FWHM ≤ 10°) near-specular peaks and additional off-specular features. The energy distributions show an oscillatory behavior as a function of outgoing angle. In comparison, scattered Ar atoms from a Ag(111) surface exhibit a broad angular intensity distribution and an energy distribution that qualitatively tracks the binary collision model. The features observed for Ru, which are most evident when scattering from the clean surface at 180 K and from the Ru(0001)-(1×1)D surface, are consistent with rainbow scattering. The measured TOF profiles cannot be adequately described with a single shifted Maxwell-Boltzmann distribution. They can be fitted by two components that exhibit complex variations as a function of outgoing angle. This suggests at least two significantly different site and∕or trajectory dependent energy loss processes at the surface. The results are interpreted in terms of the stiffness of the surface and highlight the anomalous nature of the apparently simple hcp(0001) ruthenium surface.

Meniscus-Shear Particle Detachment in Foam-Based Cleaning of Silicon Wafers with an Immersion/Withdrawal Cell

New experimental data collected at Lam Research Corporation and theoretical analyses are presented for aqueous-foam cleaning of silicon wafers contaminated with strongly adhered 90 nm Si 3 N 4 particles (Freer et al. 2010). We analyze the distribution of contaminant removal along the wafer surface and the influence of foam quality in a vertical rectangular slot upon wafer immersion/withdrawal. At zero foam quality, particle removal along the wafer surface is uniform. Increased foam quality leads to improved overall removal. Removal, however, is no longer uniform with larger detachment rates toward the bottom of the wafer. To explain the observed nonuniform particle removal, we adopt a binary-collision model that demands a linear dependence of removal rate on the surface shear rate. Perturbation analysis provides the distribution of the wall shear rate along the wafer surface in an unfoamed solution. Calculations show that the wall shear rate on the wafer surface is strongly peaked in the meniscus just above the liquid-filled slot. Thus, with no foam present, removal in the meniscus zone dominates the overall removal process. Because the time of exposure to this high shear is the same for all parts of the surface, we obtain uniform cleaning. With foam bubbles present, the wall shear rate in the slot is enhanced, leading to significant removal in the bulk of the slot. Because the residence time of a wafer in the bulk cleaning solution varies for different parts of the wafer, contaminant removal in the bulk of the slot depends on the vertical position. Combined particle removal in the meniscus zone and in the slot leads to the observed nonuniform distribution of contaminant particles remaining on the wafer surface. Increasing foam quality increases the slot wall shear rate and, hence, the removal rate inside the immersion/ withdrawal cell.

PIC simulation of kinetic effects of plasma and consequences for physical sputtering

Impurities in a fusion plasma device such as carbon, beryllium and tungsten are one of major concerns about performance of the plasma and also engineering design. In simulation codes of impurity transport and redeposition, the physical sputtering yield due to the background plasma is calculated by an empirical model and a Monte Carlo code based on the binary collision model for a plasma without the magnetic field. In this work, kinetic effects of ions in a magnetized plasma on the physical sputtering yield were investigated by using a particle-in-cell simulation code and a sputtering model. An increasing effect of the magnetic field on the yield was found when the field was nearly parallel to the surface. The effect becomes strong when the field is strong and the plasma density is low.

Intragranular Xe bubble population evolution in UO2: A first passage Monte Carlo simulation approach

Abstract We introduce a first passage based Monte Carlo [1] code to investigate the population evolution of Xe fission gas bubbles in UO 2 fuels. Growth laws are obtained for homogeneous and heterogeneous re-solution models for a wide range of gas and bubble diffusivities. Under certain irradiation conditions, bubble populations find dynamic steady states. Homogeneous re-solution is included using a Monte Carlo binary collision model, while heterogeneous re-solution is modeled as the ad hoc destruction of bubbles.

Lattice location of dopant atoms: An N-body model calculation

The channelling and scattering yields of 1 MeV α-particles in the 〈100〉, 〈110〉 and 〈111〉 directions of silicon implanted with bismuth and ytterbium have been simulated using N-body model. The close encounter yield from dopant atoms in silicon is determined from the flux density, using the Bontemps and Fontenille method. All previous works reported in literature so far have been done with computer programmes using a statistical analytical expression or by a binary collision model or a continuum model. These results at the best gave only the transverse displacement of the lattice site from the concerned channelling direction. Here we applied the superior N-body model to study the yield from bismuth in silicon. The finding that bismuth atom occupies a position close to the silicon substitutional site is new. The transverse displacement of the suggested lattice site from the channelling direction is consistent with the experimental results. The above model is also applied to determine the location of ytterbium in silicon. The present values show good agreement with the experimental results.

Effect of rolling friction on binary collisions of spheres

Foerster et al. [Phys. Fluids 6, 1108 (1994)] proposed a binary collision model for spheres and a way to measure the constant impact parameters in the model. These three parameters were necessary to describe the translational momentum exchange during a collision. An extensive data set for a variety of materials was made possible using these measurements. In recent years many studies have shown that rolling friction between particles has strong effects on the bulk behavior of granular materials. In the present paper, an expansion of the previous collision model is studied to include rolling friction. It is shown that rolling friction does not affect the postcollision linear relative velocities for the conditions used in the impact experiments. Furthermore, it is suggested that the same impact experiment could potentially be used to measure the coefficient of rolling friction.

Electron Parallel Heat Transport in the Scrape-off Layer Using a Particle-in-Cell Code

Electron heat transport parallel to the magnetic field in the scrape-off layer plasma is investigated with the use of the particle-in-cell code PARASOL. Coulomb collisions are simulated correctly by a binary collision model. The heat flux is lost by radiation cooling, in addition to convection/conduction to the divertor plates. It is confirmed for the collisional case that the conductive heat flux is given by the Spitzer-Harm expression. For the long mean free path case, the conductive heat flux is limited to a factor αe of the free streaming value. It is found that αe is small (∼0.1 of the sheath-limited value) for the low radiation condition, but becomes large (∼1.0) for the high radiation condition.

Centrality and system size dependence of (multi-strange) hyperons at40Aand158A GeV: A comparison between a binary collision model and a Boltzmann+hydrodynamic hybrid model

We present results on the centrality and system size dependence of (multi-strange)hyperons in Pb+Pb collisions at 40$A$ and 158$A$ GeV from the Ultra-relativistic Quantum Molecular Dynamics (UrQMD-v2.3) model and a coupled Boltzmann+hydrodynamics calculation. The second approach is realized in a hybrid fashion based on UrQMD with an intermediate hydrodynamical evolution for the hot and dense stage of the collision. This implementation allows a comparison of microscopic transport calculations with hydrodynamic simulations to explore the transition from a system that is not fully equilibrated such as C+C or Si+Si collisions, to a supposedly fully equilibrated system, such as that created in Pb+Pb reactions. The results of our calculation are compared to measurements of the (anti-)hyperon yields at midrapidity ($\mid$y$\mid$ $\leq$ 0.5) and total multiplicities performed by the NA49 and NA57 Collaborations at 40$A$ and 158$A$ GeV. Furthermore, we compared our predictions to the centrality dependence of $\Lambda$, $\bar{\Lambda}$ and $\Xi^{-}$ rapidity spectra and total multiplicities at 40$A$ and 158$A$ GeV, where possible.

A Monte Carlo investigation of secondary electron emission from solid targets: Spherical symmetry versus momentum conservation within the classical binary collision model

A Monte Carlo scheme is described where the secondary electron generation has been incorporated. The initial position of a secondary electron due to Fermi sea excitation is assumed to be where the inelastic collision took place, while the polar and azimuth angles of secondary electrons can be calculated in two different ways. The first one assumes a random direction of the secondary electrons, corresponding to the idea that slow secondary electrons should be generated with spherical symmetry. Such an approach violates momentum conservation. The second way of calculating the polar and azimuth angles of the secondary electrons takes into account the momentum conservation rules within the classical binary collision model. The aim of this paper is to compare the results of these two different approaches for the determination of the energy distribution of the secondary electrons emitted by solid targets.

Molecular dynamics simulation of intragranular Xe bubble re-solution in UO 2

The homogeneous re-solution of Xe fission gas bubbles in UO 2 is investigated by combined Monte Carlo and molecular dynamics simulations. Using a binary collision model, based on the Ziegler–Littmark–Biersack potential [J.F. Ziegler, J.P. Biersack, U. Littmark, The Stopping and Range of Ions in Solids, Stopping and Ranges of Ions in Matter, vol. 1, Pergamon Press, New York, 1984], the recoil energy distribution of fission gas atoms is obtained. An extensive library of fission gas atom displacement cascades is then compiled using molecular dynamic simulations. It used for calculating recoil spectrum averaged quantities. The calculations yield a re-solution parameter for homogeneous re-solution and a displacement distribution of fission gas atoms around the fission gas bubbles. The results disagree considerably from past estimates. The importance of channeling and threshold energy for fission gas escape are discussed.

Indication of a Very Large Proton Diffusion in Ice Ih. III. Fluorescence Quenching of 1-Naphthol Derivatives

The effects of excess protons on the fluorescence quenching process of 1-naphthol-4-sulfonate (1N4S) and 1-naphthol-3-sulfonate (1N3S) in methanol-doped ice samples were studied by employing a time-resolved emission technique. We found that the fluorescence quenching of the deprotonated form RO(-)* of both photoacids by protonation is very efficient in ice, whereas in liquid water the proton fluorescence quenching is rather small. Using the Smoluchowski diffusion-assisted binary collision model under certain assumptions and approximations, we found that the calculated proton diffusion constant in ice in the temperature range of 240-260 K was 10 times greater than that of water at 295 K.

Indication of a Very Large Proton Diffusion in Ice Ih. 2. Fluorescence Quenching of Flavin Mononucleotide by Protons

A time-resolved emission technique was employed to study the effect of excess protons on the fluorescence quenching process of flavin mononucleotide (FMN) in methanol-doped ice samples. We found that an excess of protons in ice has a very large effect on the fluorescence quenching whereas in liquid water the proton fluorescence quenching is rather small. We analyzed the experimental data using the Smoluchowski diffusion-assisted binary collision model. Under certain assumptions and approximations, the calculated proton diffusion constant in ice in the range of 245−265 K is about 10 times that of water at 295 K.

Numerical methods for particle simulations at extreme densities and temperatures: Weighted particles, relativistic collisions and reduced currents

We present a fully relativistic energy-conserving binary collision model for particle simulations with large density scale plasmas. Our model deals with collisions between weighted particles of arbitrary species, conserving energy perfectly in each collision while momentum is conserved on the average. We also discuss a new method to model extremely high densities, applicable to a wide range of plasmas from the cold, non-relativistic to the ultra-relativistic regime in the high energy density physics.

The influence of surface forces on shear-induced tracer diffusion in mono and bidisperse suspensions

The shear-induced self-diffusivity of tracer particles of radius a (t) = lambda a in a suspension of particles having a radius, a, is calculated by Stokesian dynamics for different values of the size ratio, lambda , both in 2 and 3 dimensions in the binary-collision regime. The self-diffusion is found to decrease strongly when the size ratio becomes quite different from unity. On the other hand, for the same average distance of contact between two spheres, the presence of a soft force always increases greatly the diffusion compared to the effect of a hard shell which is used to model the roughness. This is particularly true for tracer particles smaller than the bath particles, where the shear-induced diffusion can be increased by many order of magnitudes in the presence of a soft force. For suspensions of monodisperse particles we show that, for low volume fraction, the diffusion coefficient is much smaller than the one predicted by the binary collision model, due to the existence of a layered structure. On the contrary at higher volume fraction, many-body collisions strongly enhance the diffusion and it appears that the value of the diffusion is quite sensitive to the presence of clusters of particles which are themselves determined by the range of interparticle forces.