Spatial Distribution Of Charged Particles Research Articles

Investigation of sheath structure in surface flashover induced by high-power microwave

Flashover is a major limiting factor for the transmission and miniaturization of high-power microwave (HPM) devices. We conducted a study to investigate the developmental process of surface flashover on HPM dielectric windows through particle-in-cell-Monte Carlo collision simulations. A one-dimensional spatial distribution and three-dimensional velocity distribution model is established, encompassing the entire process of surface flashover, which includes electrode field emission, single-surface multipactor, outgassing, and gas breakdown. The nonuniform mesh generation method is employed to enhance the simulation accuracy. The growth rates of electron and ion densities increase as gas pressure rises. Additionally, the discharge transitions gradually from multipactor to gas ionization dominance. Notably, a space-charge-limited (SCL)-like sheath occasionally forms during an rf cycle near the surface under intermediate background pressure (∼0.05 Torr). The SCL-like sheath cannot exist stably. Instead, it periodically disappears and appears as the rf electric field changes. The underlying physics are explained by the variations of the rf electric field, which lead to the variations in the surface charge density, thereby affecting the normal electric field. The normal electric field interacts with the spatial distribution of charged particles, ultimately leading to the formation of the SCL-like sheath. This work may facilitate a comprehensive understanding of the developmental processes of surface flashover.

First principles simulation of early stage plasma initiation process in ITER-scale tokamak

A first principles 6D kinetic model is developed to study the earliest times of unassisted plasma breakdown in an International Thermonuclear Experimental Reactor (ITER)-scale tokamak. This is then used for a comparative study of the predicted ionisation rate and the electron parallel velocity between the standard model for tokamak breakdown, assuming a zero-D (OD) Townsend avalanche, and the new kinetic model. The detailed model allows us to study the influence of the magnetic field configurations on the formation of plasma while explicitly resolving the electron trajectories. We introduce a ‘back-traced’ connection length L bt as a useful predictive tool for the spatial distribution of charged particles during the breakdown process. It is also found that the ionisation rate and the mean electron parallel velocity from the kinetic model generally exceed the 0D model predictions, demonstrating a growth in the total electron population from 103 to the order of 108 in approximately 1 ms. This implies that the 0D model can still serve as a conservative prediction for the first plasma campaign on ITER.

Spatial distribution modulation of laser-accelerated charged particles with micro-tube structures

We present experimental studies on the spatial distribution of charged particles using a linearly polarized femtosecond laser interacting with a micro-structure target composed of micro-tube structure and planar foil. For protons, a six-lobed structure was observed in the low-energy region, while a smaller angular divergence was measured in the high-energy region. Electron distribution exhibits a circular distribution at low energies and double-lobed structure at high energies. These results are well reproduced by 3D particle-in-cell simulations, showing that the profile of electrons driven by a laser pulse is manipulated by the micro-tube structure, which maps into the spatial distribution of protons via a strong charge separation field. These results demonstrate the effect of micro-structures on laser-driven particle sources and provide a possible approach for spatial manipulation of the particle beams.

To the Statistical Description of the Structure Formation in Coulomb-like Systems

A new solution to the problem of the calculation of the partition function for a Coulomb-like system is proposed. The quantum-field-theory approach is used to give a statistical description of a system of interacting particles with due regard to an arbitrary spatially inhomogeneous configuration. The formation of structures in a Coulomb-like system is analyzed and applied to thedusty plasma treatment. A necessary condition for the crystal formation in a three-dimensional system of dust particles is obtained. In the one-dimensional case, an exact solution for the spatial distribution of charged particles is presented.

Spatial distribution of the dropless ESI charged particles at IMS entrance

An experimental study and comparison of spatial distributions of charged particles for conventional electrospray (ESI) and for dropless electrospray with a dynamic flow splitter of analyzed solution at atmospheric pressure and room temperature was carried out. Comparison of distributions shows that the characteristic regions of ion formation differ significantly. The obtained dropless electrospay spatial distributions are matched with inlet parameters of optimized transfer system of an ion mobility spectrometer (IMS) based on electrostatic focusing of the charged particles.

A simplified formulation of wire-plate corona discharge in air: Application to the ion wind simulation

The spatial distribution of charged particles (electrons, negative ions and positive ions) and electric field have been evaluated using a semi-analytical approach of the positive and negative corona discharge for a wire-to-plate electrode system. Thus, approximate formulas useful for the characterization and control of corona discharge devices are provided, which helps to significantly reduce computational costs. Based on the obtained results, the electro-hydrodynamic (EHD) force generated by the corona discharge has been determined, and it has been used in the Navier-Stokes equations to compute the spatial distribution of the gas velocity. As a result, the influence of the corona plasma region in the flow pattern, particularly in the vicinity of the corona electrode, has been brought to light, which helps to understand the different flow velocities observed in positive and negative coronas. Moreover, the influence of voltage, wire radius, and inter-electrode separation on the electric wind velocity has been investigated.

Liquid scintillator composition optimization for use in ultra-high energy cosmic ray detector systems

The Horizon-T (HT) detector system and the currently under R&D HT-KZ detector system are designed for the detection of Extensive Air Showers (EAS) with energies above ∼10 16 eV (∼10 17 eV for HT-KZ). The main challenges in both detector systems are the fast time resolutions needed for studying the temporary structure of EAS, and the extremely wide dynamic range needed to study the spatial distribution of charged particles in EAS disks. In order to detect the low-density of charged particles far from the EAS axis, a large-area detector is needed. Liquid scintillator with low cost would be a possible solution for such a detector, including the recently developed safe and low-cost water-based liquid scintillators. Liquid organic scintillators give a fast and high light yield (LY) for charged particle detection. It is similar to plastic scintillator in properties but is cost effective for large volumes. With liquid scintillator, one can create detection volumes that are symmetric and yet retain high LY detection. Different wavelength shifters affect the scintillation light by changing the output spectrum into the best detection region. Results of the latest studies of the components optimization in the liquid scintillator formulae are presented.

Localized enhancements of energetic particles at oblique collisionless shocks

We investigate the spatial distribution of charged particles accelerated by non-relativistic oblique fast collisionless shocks using three-dimensional test-particle simulations. We find that the density of low-energy particles exhibit a localised enhancement at the shock, resembling the "spike" measured at interplanetary shocks. In contrast to previous results based on numerical solutions to the focused transport equation, we find a shock spike for any magnetic obliquity, from quasi-perpendicular to parallel. We compare the pitch-angle distribution with respect to the local magnetic field and the momentum distribution far downstream and very near the shock within the spike; our findings are compatible with predictions from the scatter-free shock drift acceleration (SDA) limit in these regions. The enhancement of low-energy particles measured by Voyager 1 at solar termination shock is comparable with our profiles. Our simulations allow for predictions of supra-thermal protons at interplanetary shocks within ten solar radii to be tested by Solar Probe Mission. They also have implications for the interpretation of ions accelerated at supernova remnant shocks.

Spatial Distributions of Charged Particles and Plasma Potential before and during Beam Extraction in a Negative Hydrogen Ion Source for NBI

Spatial Distributions of Charged Particles and Plasma Potential before and during Beam Extraction in a Negative Hydrogen Ion Source for NBI

The effect of a direct current field on the microparticle charge in the plasma afterglow

Residual charges of individual microparticles forming dense clouds were measured in a RF discharge afterglow. Experiments were performed under microgravity conditions on board the International Space Station, which ensured particle levitation inside the gas volume after the plasma switch-off. The distribution of residual charges as well as the spatial distribution of charged particles across the cloud were analyzed by applying a low-frequency voltage to the electrodes and measuring amplitudes of the resulting particle oscillations. Upon “free decharging” conditions, the charge distribution had a sharp peak at zero and was rather symmetric (with charges concentrated between −10e and +10e), yet positively and negatively charged particles were homogeneously distributed over the cloud. However, when decharging evolved in the presence of an external DC field (applied shortly before the plasma switch-off) practically all residual charges were positive. In this case, the overall charge distribution had a sharp peak at about +15e and was highly asymmetric, while the spatial distribution exhibited a significant charge gradient along the direction of the applied DC field.

2-D Measurement of Charged Particles Diffusing From a Double DC Corona Discharge Ionizer

Spatial distributions of charged particles diffusing from a double dc corona discharge ionizer operated in air and nitrogen atmospheres are 2-D measured. It is experimentally demonstrated that static electricity on a silicon wafer downstream side of the ionizer is eliminated only in the area where the local net charge flux becomes zero. The 2-D profiles of the local net ion current clearly show that the spatial profile of the local net ion current can be controlled by a balance between the positive and negative discharge voltages. Hence, it is demonstrated that the balance can yield the control of the charge elimination area.

Pressure and Free Flight Time Effects on Glow Discharge Characteristics

this work, a model for a DC glow discharge at low pressure, used in many applications has been developed. This model allows the determination of plasma characteristics distributions in 2D geometry. The proposed theoretical model is applied to collisional argon plasma at low pressure in a reactor consisting of two plane parallel electrodes where the cathode is heated to a voltage of -250 V. The proposed code is based on solving the continuity equation coupled with Poisson's equation and electrons mean energy's equation. The particles trajectories simulation requires the knowledge of all collisional processes through their cross sections. The probability of during a free flight time can not be known without performing integrations of non-analytical cross sections. The proposed solution to this problem consists in the application of the null collision concept. The simulation results are shown in terms of spatial distribution of charged particles, potential, electric field, electrons energy and velocity. The study of the pressure (0.1-1Torr) and the free flight time (5.11x10 -9 to 1.46 x10 - 7 s) effect, on the

A semi-analytical stationary model of a point-to-plane corona discharge

A semi-analytical model of a dc corona discharge is formulated to determine the spatial distribution of charged particles (electrons, negative ions and positive ions) and the electric field in pure oxygen using a point-to-plane electrode system. A key point in the modeling is the integration of Gauss' law and the continuity equation of charged species along the electric field lines, and the use of Warburg's law and the corona current–voltage characteristics as input data in the boundary conditions. The electric field distribution predicted by the model is compared with the numerical solution obtained using a finite-element technique. The semi-analytical solutions are obtained at a negligible computational cost, and provide useful information to characterize and control the corona discharge in different technological applications.

Statistical description of Coulomb-like systems

The solution of the problem of the partition function calculation for a Coulomb-like system is proposed. The quantum-field-theory approach is used to give a statistical description of a system of interacting particles with due regard to arbitrary spatially inhomogeneous configurations. Formation of structures in a Coulomb-like system is analyzed and applied to the case of of dusty crystals and two-dimensional colloidal crystals. In the one-dimensional case, an exact solution for the spatial distribution of charged particles is obtained. In the two- dimensional case, the exact partition function for homogeneous distribution of particles is presented. We have analytically derived the necessary condition for the crystal formation in a system of interacting particles in the three-dimensional case.

Dependence of the particle density spectrum in giant air showers on the spatial distribution of charged particles

The shape of the particle quantity spectrum of giant air cosmic-ray showers is studied. The Nishimura-Kamata-Greisen function describing the spatial distribution in the electron-photon cascade theory and the function calculated in [1] taking into account the nuclear-cascade process are considered.

Measurement of Three-Dimensional Velocity Distributions of the Products of Cl2, NO, and HCl Photodissociation or Photoionization

Not long ago, it seemed unrealistic for molecular dynamics of photodissociation processes that the escape velocity and direction of photoproducts could be directly measured given an exact knowledge of the quantum states of these photoproducts and of the initial molecule. However, a breakthrough was made in 1987 with the advent of an imaging technique that made it possible to determine the three-dimensional spatial distribution of charged particles [1]. In this technique, resonance-enhanced multiphonon ionization (REMPI) is used for ionizing photofragments and the nascent fragment ions are accelerated by an electric field and detected as scintillations on a phosphorescent screen. Recently (1997), an improved version of this method— velocity map imaging [2, 3]—was suggested. In this method, due to the application of electrostatic lenses, all ions with the same initial velocity vector are mapped onto the same point on the detector irrespective of their initial positions. In this paper, we describe a new version of the imaging technique, an alternative to velocity map imaging, in which a homogeneous electric field is used and a phosphorescent screen is exchanged for a delay-line detector (DLD) with high time resolution. This new method makes it possible to measure all three components of the velocity of a photodissociation or photoionization product. A setup consists of a time-of-flight mass spectrometer, a chamber for creating a molecular beam, and a laser system (Fig. 1). The mass spectrometer consists of a chamber with a homogeneous electric field, in which a molecular beam (the Y axis) and a laser beam (the X axis) intersect. Positive photoions created by laser radiation are accelerated by the electric field (along the Z axis) and are detected by means of the DLD. The ion detecting system is a multichannel plate 8 cm in diameter, each channel of which is a photoelectron multiplier; the DLD is located behind this plate. In principle, such detectors have been known for half a century, but they have heretofore been used only in nuclear physics [4, 5]. The detector used in this work

Model of the evolution of the plasmasphere during a geomagnetic storm

The morphology of the plasmasphere during a geomagnetic storm is simulated by considering the two dimensional E × B drift motion of plasmaspheric charged particles in the equatorial plane. Assuming a time-independent dipolar magnetic field and a corotation electric field plus, a spatially uniform dawn–dusk convection electric field varying with K p index, the spatial distributions of charged particles at different time during a geomagnetic storm are obtained. Our results show that if K p increases with time, some particles inside the original plasmapause will convect into the magnetopause, forming a long tail that stretches from the plasmasphere to the magnetopause in the afternoon region. The particle convection weakens as K p decreases, and as K p returns to its normal value, the plasmasphere develops a thin tail that wraps around the Earth.

Scaling laws for the spatial distributions of the plasma parameters in the positive column of a dc oxygen discharge

Comprehensive self-consistent simulations of the positive column plasma of a dc oxygen discharge are performed with the help of commercial CFDRC software (http://www.cfdrc.com/~cfdplasma), which enables one to carry out computations in an arbitrary 3D geometry using fluid equations for heavy components and a kinetic equation for electrons. The main scaling laws for the spatial distributions of charged particles are determined. These scaling laws are found to be quite different in the parameter ranges that are dominated by different physical processes. At low pressures, both the electrons and negative ions in the inner discharge region obey a Boltzmann distribution; as a result, a flat profile of the electron density and a parabolic profile of the ion density are established there. In the ion balance, transport processes prevail, so that ion heating in an electric field dramatically affects the spatial distribution of the charged particles. At elevated pressures, the volume pro- cesses prevail in the balance of negative ions and the profiles of the charged particle densities in the inner region turn out to be similar to each other. © 2003 MAIK "Nauka/Interperiodica".

Spatial distribution of charged particles in a magnetic neutral loop discharge etcher: experimental results and numerical simulations

This paper reports a result of rather sophisticated measurement in a magnetic neutral loop discharge (NLD) etcher system. The spatial profiles of electron temperature T e and density n e were measured for an extended region including the downstream of the source using laser Thomson scattering technique. Also, based on these profiles and ion current density measured by a double probe, experimental and numerical investigation for the entire structure of electron behavior was performed. The results showed that the high-density plasma produced around the magnetic neutral loop (NL) is transferred from the NL region to the downstream region along magnetic force lines.

Negative ions in processing plasmas and their effect on the plasma structure

Three fundamental issues: (1) how many negative ions exist in processing plasmas, (2) how negative ions affect the spatial distribution of charged particles, and (3) how negative ions affect the structure of the sheath, are discussed on the basis of knowledge attained in the past decade. Photodetachment techniques for measuring negative ion density are reviewed and results of measurements for low density as well as high-density plasmas containing halogenated gases and oxygen are discussed from a view point of how the negative ion/electron density ratio varies as a function of electron/feedstock gas density ratio. The effect of negative ions on the spatial distributions of charged particles is illustrated by solving plasma balance equations based on an ambipolar diffusion model for various electron attachment rate coefficients and electron densities; some comparisons of the results with other model studies are made. The structure of the sheath in electronegative plasmas recently clarified by a number of workers is illustrated and discussed by giving typical fluid model solutions in the spherical symmetry.