Spatial distribution of the dropless ESI charged particles at IMS entrance

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".

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

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.

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.

Amorphous silicon pixel radiation detectors and associated thin film transistor electronics readout

Amorphous silicon based radiation detectors

Model of the evolution of the plasmasphere during a geomagnetic storm

Compared to pure SF6 gas, the SF6/CF4 gas mixture exhibits certain advantages in reducing greenhouse effects, lowering the liquefaction temperature, and decreasing the sensitivity to non-uniform electric fields, demonstrating significant application potential in high-voltage electrical equipment. This study employs a two-dimensional plasma fluid model to investigate the partial discharge phenomena induced by free metallic particles in SF6/CF4 gas mixtures, analyzing the spatiotemporal evolution characteristics of key parameters, such as the charged particle density and axial electric field, under different mixing ratios. The simulation results show that there are two kinds of positive stream discharge phenomena, "continuous and decaying", when the gas mixture ratio is 90%CF4-10%SF6 and 40%CF4-60%SF6. The proportion of CF4 in the gas mixture will affect the spatial distribution of charged particles and the production and disappearance of electrons. When the proportion of CF4 is 90%, the content of positive ions in the discharge channel is the highest, and the electric field formed by the positive space charge of CF4+ in the stream head promotes the continuous propagation of the stream. As the concentration of CF4 decreases, the main ionization reaction at the stream head shifts from CF4 to SF6, and a negative space charge region dominated by SF6- particles is also formed near the stream head, changing the electric field distribution near the flow head. The adhesion reaction rate is greater than the ionization reaction rate, resulting in the disappearance of electrons greater than the production, and the stream phenomenon tends to decay. These simulation results are helpful to understand the dynamic process of positive stream discharge induced by free metal particles in SF6/CF4 gas mixtures, and they provide a theoretical basis for better solutions to equipment damage caused by partial discharge.

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.

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.

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.

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.

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 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.

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