Energetic Laser-Ion Acceleration by Strong Charge-Separation Field

The laser-ion acceleration from the ultra-short and ultra-intense laser-matter interactions attracts more and more interest nowadays. When a laser pulse interacts with a target, relativistic electrons are generated in a period of few femtoseconds and driven away by the ponderomotive force, then a huge charge-separation field forms. In general cases, the ion acceleration is determined by this charge-separation field and the scale length of the plasma density. A general time-dependent solution is obtained to describe laser-plasma isothermal expansions into a vacuum, which is the fundamental theory of the laser-ion acceleration. It is adequate for non-quasi-neutral plasmas and different types of the scale length of the density gradient. The previous solutions are some special cases of our general solution. It is found that there exist both a compression layer of the ion velocity distribution and a potential well for sorue initial conditions. However, many unaccounted idiographic solutions, which may be used to reveal new mechanisms of ion acceleration, may be deduced from our general solutions.

Effect of Residual Charge Carrier on the Performance of a Graphene Field Effect Transistor

The temperature-dependent effect of residual charge carrier （no）, at the Dirac point, on mobility is studied. We fabricate and characterize a graphene field effect transistor （GFET） using 7nm TiO2 as the top-gate dielectric. The temperature-dependent gate voltage-drain current and room temperature gate capacitance are measured to extract the carrier mobility and to estimate the quantum capacitance of the GFET. The device shows the mobility value of gOO cm^2 /V.s at room temperature and it decreases to 45 cm^2 /V.s for 20 K due to the increase of n0. These results indicate that the phonon scattering is not the dominant process for the unevenness dielectric layer while the coulomb scattering by charged impurities degrades the device characteristically at low temperature.

Resistance and Reactance of Monopole Fields Induced by a Test Charge Drifting Off-Axis in a Cold and Collisional Cylindrical Plasma

We study the interaction of a uniform, cold and collisional plasma with a test charged particle moving off-axis at a constant speed down a cylindrical tube with a resistive thick metallic wall. Upon matching the electromagnetic field components at all interfaces, the induced monopole electromagnetic fields in the plasma are obtained in the frequency domain. An expression for the plasma electric resistance and reactance is derived and analyzed numerically for some representative parameters. Near the plasma resonant frequency, the plasma resistance evolves with frequency like a parallel RLC resonator with peak resistance at the plasma frequency pe, while the plasma reactance can be capacitive or inductive in nature depending on the frequency under consideration.

CALCULATION AND EXPERIMENTAL INVESTIGATION OF ELECTRIC FIELDS INDUCED BY ELECTRODES IN ELECTROSTATIC CHARGED POWDER SPRAYING TECHNIQUE

Electric fields induced by ring and pin electrodes in electrostatic charged powder sprayingtechnique are analysed. The fundamental formulae to deseribe these fields have been built up. Theseformulae could be used to design electrostatic charged podwer spraying system. The chargingeffectiveness of ring and pin electrode is experimentally investigated and compared each other. Theperformance of ring electrode is better than that of pin electrode.

Research on the field emission mechanism of nano-structured carbon film

The field emission （FE） characteristics of nano-structured carbon films （NSCFs） are investigated. The saturation behaviour of the field emission current density found at high electric field E cannot be reasonably explained by the traditional Fowler-Nordheim （F-N） theory. A three-region E model and the curve-fitting method are utilized for discussing the FE characteristics of NSCFs. In the low, high, and middle E regions, the FE mechanism is reasonably explained by a modified F-N model, a corrected space-charge-limited-current （SCLC） model and the joint model of F N and SCLC mechanism, respectively. Moreover, the measured FE data accord well with the results from our corrected theoretical model.

Curbing Charging Currents in Pulsed Field Emission by Prolonging Pulse Edges

In field emission under a non-dc voltage, a displacement current is inevitable due to charging the cathode–anode condenser. Under an often-used square voltage pulse, in which the voltage rises from zero to a certain value abruptly, the charging current in the circuit is very large at the rising and falling edges. This large charging current makes measurement of the actual emissive current from the cathode difficult, constitutes a threat to the components in the circuit and causes attenuation of the emissive current within the pulse. To alleviate these drawbacks, trapezoid voltage pulses, whose rising edges are extended dramatically in comparison with square voltage pulses, are employed to extract the field emission. Under a trapezoid voltage pulse, the charging current is clearly lowered as expected. Furthermore, the heat generated by the charging current under the trapezoid voltage pulse is much smaller than that under the square voltage pulse. Hence the emissive current does not show any attenuation within the pulse. Finally, the average emissive currents are found to decrease with the repetition frequency of the pulses.

RESEARCH ON AMAGNETIC FIELD IN ELECTROLYTIC LAPPING

Taking electrolytic lapping stainless steel for example, the principle of electrolytic lapping with a magnetic field is described, the movement of charged particles in the magnetic field is analyzed in tems of theory. Using a computer, the motion loci of the charged particles in the magnetic field are simulated. The theory and the experiment show that the magnetic field can accelerate the diffusion and mobility of the charged particles, accelerate the electrochemical reaction and reduce the surface roughness of the work more quickly, which improves the lapping efficiency.

SPLITTING OF THE SPECTRAL DOMAIN ELECTRICAL DYADIC GREEN’S FUNCTION IN CHIRAL MEDIA

A new method of formulating dyadic (Green's) functions in lossless,reciprocal and unbounded chiral medium was presented.Based on Helmholtz theorem and the non-divergence and irrotational splitting of dyadic Dirac delta-function was this method, the electrical vector dyadic (Green's) function equation was first decomposed into the non-divergence electrical vector dyadic (Green's) function equation and irrotational electrical vector dyadic (Green's) function equation,and then (Fourier's) transformation was used to derive the expressions of the non-divergence and irrotational component of the spectral domain electrical dyadic (Green's) function in chiral media.It can avoid having to use the wavefield decomposition method and dyadic (Green's) function eigenfunction expansion technique that this method is used to derive the dyadic (Green's) functions in chiral media.

Light-induced acoustic effect in LiNbO3：Fe：Ce crystals

The phenomena of acoustic emission in LiNbO3：Fe：Ce crystals have been observed in the process of light-induced quasi-breakdown. It is found that the ultra-high frequency acoustic signal introduced into the crystal is modulated by the low frequency acoustic waves. Its frequency increases with the increase of the intensity of incident light and its jump period of breakdown is the same as that of the photovoltaic current Ic, the change of light-induced refractive index △n and the diffracted light intensity L. This phenomenon has been analysed in this paper, which is caused by the inverse piezoelectric strain effect of the jump of space charge field during the quasi-breakdown.

Impact of the Vertical Velocity Field on Charging Processes and Charge Separation in a Simulated Thunderstorm

A three-dimensional（3D） charging-discharging cloud resolution model was used to investigate the impact of the vertical velocity field on the charging processes and the formation of charge structure in a strong thunderstorm. The distribution and evolution of ice particle content and charges on ice particles were analyzed in different vertical velocity fields. The results show that the ice particles in the vertical velocity range from 1 to 5 m s-1obtained the most charge through charging processes during the lifetime of the thunderstorm. The magnitude of the charges could reach 1014 n C. Before the beginning of lightning activity,the charges produced in updraft region 2（updraft speed 13 m s-1） and updraft region 1（updraft speed between 5 and 13 m s-1） were relatively significant. The magnitudes of charge reached 1013 n C, which clearly impacted upon the early lightning activity. The vertical velocity conditions in the quasi-steady region（updraft speed between -1 and 1 m s-1） were the most conducive for charge separation on ice particles on different scales. Accordingly, a net charge structure always appeared in the quasi-steady and adjacent regions. Based on the results, a conceptual model of ice particle charging, charge separation, and charge structure formation in the flow field was constructed. The model helps to explain observations of the＂lightning hole＂ phenomenon.

Jet dispersion and deposition of charged particles in confined chambers

Dispersion and surface deposition of charged particles by gas-solids jets in confined chambers are constantly encountered in many industrial applications such as in electrostatic precipitation and dry powder coating processes. Understanding and control of flow patterns and trajectories of charged particles are important to the optimal design and operation of such devices. In this study, modeling of flow fields and particle trajectories of dilute gas-solid two-phase flows with charged particles in confined chambers is performed. The dilute gas-solid two-phase flows are simulated by use of a hybrid Eulerian-Lagrangian approach with the one-way coupling between the gaseous phase and particle phase. The space charge distribution is included as a source term in equations of motion or Lagrangian equation of charged particles, which in turn depends on the particle trajectories that determine the space charge distribution. Our modeling predictions suggested that the electrostatic charge plays a significant role in particle radial dispersion. Effect of voltage has limited influence on particle trajectories however it can have a big impact on the residence time. Cone angle has a significant effect on the structure of flow field. For cone with a larger cone angle （typically over 15°）, there will be a flow separation along the side wall near the flow entrance region. By comparing with the conical chamber, the cylindrical chamber has a big vortex and three smaller vortexes in the lower part of the chamber, which would complicate the particle dispersion with or without the coupling of charging.

Survival of charged ρ condensation at high temperature and density

The charged vector ρ mesons in the presence of external magnetic fields at finite temperature T and chemical potential μ have been investigated in the framework of the Nambu-Jona-Lasinio model.We compute the masses of charged ρ mesons numerically as a function of the magnetic field for different values of temperature and chemical potential.The self-energy of the ρ meson contains the quark-loop contribution,i.e.the leading order contribution in 1/NC expansion.The charged ρ meson mass decreases with the magnetic field and drops to zero at a critical magnetic field eBc,which indicates that the charged vector meson condensation,i.e.the electromagnetic superconductor can be induced above the critical magnetic field.Surprisingly,it is found that the charged ρ condensation can even survive at high temperature and density.At zero temperature,the critical magnetic field just increases slightly with the chemical potential,which indicates that charged ρ condensation might occur inside compact stars.At zero density,in the temperature range 0.2 — 0.5 GeV,the critical magnetic field for charged ρ condensation is in the range of 0.2 — 0.6 GeV^2,which indicates that a high temperature electromagnetic superconductor might be created at LHC.

Two-dimensional analytical model of double-gate tunnel FETs with interface trapped charges including effects of channel mobile charge carriers

A two-dimensional analytical model of double-gate（DG） tunneling field-effect transistors（TFETs） with interface trapped charges is proposed in this paper. The influence of the channel mobile charges on the potential profile is also taken into account in order to improve the accuracy of the models. On the basis of potential profile,the electric field is derived and the expression for the drain current is obtained by integrating the BTBT generation rate. The model can be used to study the impact of interface trapped charges on the surface potential, the shortest tunneling length, the drain current and the threshold voltage for varying interface trapped charge densities, length of damaged region as well as the structural parameters of the DG TFET and can also be utilized to design the charge trapped memory devices based on TFET. The biggest advantage of this model is that it is more accurate,and in its expression there are no fitting parameters with small calculating amount. Very good agreements for both the potential, drain current and threshold voltage are observed between the model calculations and the simulated results.