Influence Of Space Charge Effect Research Articles

Enhanced dielectric and tunable performance in BCZT91/BCZT87 bilayer ceramics

The BCZT91/BCZT87 bilayer ceramics are prepared via solid-state reaction method to investigate the dielectric and tunable performance. The results indicate that the permittivity of bilayer ceramics is larger than that of monolayer ceramics due to the influence of space charge effect existing at interface. Meanwhile, a model evolving from the series equivalent circuit model and Landau-Devonshire theory is used to study the tunability of bilayer ceramics. The results indicate that the tunability of bilayer ceramics is obviously improved from ∼29% to ∼39% at ∼ -400 kV/m due to the influence of space charge effect when the thickness ratio of BCZT91 layer is 0.67. The similar result is also obtained when the thickness ratio is 0.50. The enhanced tunability accompanying with low loss tangent makes the figure of merit of bilayer ceramics precede monolayer ceramics. The results indicate that it is an effective method to improve the tunable performance of ceramics by introducing bilayer structure.

High time-resolution detector based on THz pulse accelerating and scanning electron beam

Terahertz pulses accelerating and scanning electron beam can break through the limitation of accelerating electric field between cathodes and grids in traditional streak tubes, thus reducing the time dispersion and enhancing the temporal resolution of time-scanning detectors. Based on this new technology, in this paper an ultra-small structured time-resolved detector with no focusing pole is designed. The terahertz pulse coupling/enhancing device suitable for acceleration zone and scanning zone is designed and optimized. The enhanced coefficient of the terahertz pulse electric field in the device reaches 9.39. In the paper, the relationship between time dispersion in acceleration zone and the moment of electrons emission is analyzed theoretically. We also analyze the influence of space charge effect on time dispersion. The electronic trajectory tracking is used to calculate and analyze the time dispersion of this detector, and finally the time resolution is better than 50fs.

Polarisation of a small-scale cometary plasma environment

Context.The plasma near the nucleus of a comet is subjected to an electric field to which a few different sources contribute: the convective electric field of the solar wind, the ambipolar electric field due to higher electron than ion speeds, and a polarisation field arising from the vastly different ion and electron trajectories.Aims.Our aim is to show how the ambipolar and polarisation electric fields arise and develop under the influence of space charge effects, and in doing so we paint a qualitative picture of the electric fields in the inner coma of a comet.Methods.We use an electrostatic particle-in-cell model to simulate a scaled-down comet, representing comet 67P/Churyumov-Gerasimenko with parameters corresponding to a 3.0 AU heliocentric distance.Results.We find that an ambipolar electric field develops early in the simulation and that this is soon followed by the emergence of a polarisation electric field, manifesting itself as an anti-sunward component prevalent in the region surrounding the centre of the comet. As plasma is removed from the inner coma in the direction of the convectional electric field of the solar wind, a density maximum develops on the opposite side of the centre of the comet.Conclusions.The ambipolar and polarisation electric fields both have a significant influence on the motion of cometary ions. This demonstrates the importance of space charge effects in comet plasma physics.

Fluorescence detection as a new diagnostics tool for electrostatic ion beam traps

In the development towards the Multi Ion Reflection Apparatus for Collinear Laser Spectroscopy (MIRACLS), an optical detection region for the observation of fluorescent light is added to an electrostatic ion beam trap (EIBT). In addition to its use for highly sensitive collinear laser spectroscopy, this fluorescence detection is introduced as a diagnostics tool for the study of the ion dynamics inside an EIBT. First measurements of collision-induced fluorescence in an EIBT demonstrate the technique’s diagnostics power by tracking the evolution of an ion bunch’s temporal width over its storage time inside the ion trap. Thereby, the time-focus point of the ion bunch can be determined and the influence of space-charge effects in the EIBT can be investigated. Good qualitative agreement is obtained between the measured trend of temporal widths and the simulations of the ions’ trajectories in the trap. Particularly, the observation of self-bunching on the ion-bunch structure for many simultaneously stored ions is reproduced.

Theoretical analysis and simulation of W-band sheet beam extended interaction klystron amplifier

The sheet beam extended interaction klystron is an important kind of millimeter-wave and sub-millimeter-wave vacuum electron device, which has extensive applications such as in high resolution radar, imaging system, satellite communication and precision guided missiles. Compared with conventional pencil beam klystron, the sheet beam extended interaction klystron, in which a thin rectangular sheet beam is used, can generate higher power by obtaining higher current and reducing space-charge-effect of electron beam. Kinematical theory and space charge wave theory are extensively used to analyze the bunching process of electrons. Kinematical theory is precise when electron beam is especially small because the influence of space charge effect is ignored, while space charge wave theory is accurate when the modulation of electron beam is small since it is based on the premise of small amplitude. Electron flow oscillatory theory is a compromise between kinematical theory and space charge wave theory, which adapts to the bigger modulation of electron beam than space charge wave theory, while it is inaccurate in the case of big bunching parameter. Based on electron flow oscillatory theory under the small signal condition, the influence of electron beam on standing wave electric field of 2π mode in a three-gap cavity is analyzed, and the expressions of beam loading conductance and beam loading susceptance in a three-gap cavity are obtained. The influences of plasma frequency, transit angle of single gap and transit angle of drift on the interaction of beam and wave in a three-gap cavity are discussed. The results show that space-charge-effect of beam is unbeneficial to the interaction between beam and wave, otherwise beam loading conductance and beam loading susceptance fluctuate with the increasing of transit angle of single gap and transit angle of drift. A W-band sheet beam extended interaction klystron is designed by theoretical analysis and 3D PIC software. The output power of 5773 W at 94.47 GHz is obtained with an efficiency of 8.46%, a gain of 37.6 dB and a 3 dB bandwith of about 140 MHz, when beam voltage is 19.5 kV, current is 3.5 A and focus magnetic field is 0.85 T. This research is important for the engineering of the W-band sheet beam extended interaction klystron amplifier.

Theoretical analysis and design of G-band extended interaction klystron amplifier

Extended interaction klystron is a very important millimeter-wave and sub-millimeter-wave vacuum electron device with many actual and potential applications, such as space-borne cloud profiling radar, communication, imaging system, precision guided missiles, etc. Kinematical theory and space charge wave theory are extensively used to analyze the bunching process of electrons. Kinematical theory is precise when electron beam is especially small because the influence of space charge effect is ignored, while space charge wave theory is accurate when the modulation of electron beam is small since it is based on the premise of small amplitude. Based on kinematical theory, law of induce current, principle of charge conservation in a one-dimensioanl mode and small signal condition, the influence of electron beam on standing wave electric field in multiple-gap cavity is analyzed, and the expression of beam-loading conductance and beam-loading susceptance in multiple-gap cavity are derived. The influence of the direct current transmit angle of single gap, the number of multiple gaps and the direct current transmit angle of between center of adjacent gaps on beam-loading conductance and beam-loading susceptance are analyzed. The results show that the beam-loading conductance and beam-loading susceptance of multiple-gap cavity can change to a bigger extent when the number of cavity gaps is bigger, which means that the maximum beam-wave conversion efficiency and the range of loaded frequency increase with the number of cavity gaps increasing. The results also show that the direct current transmit angle between centers of adjacent gaps is the most important parameter for the beam-wave interaction effect. Based on the above analysis, a G-band extended interaction klystron amplifier consisting of three five-gap cavities is designed by an three-dimensional PIC code. An output power of 225.5 W at 217.94 GHz with an efficiency of 6.26%, whose gain and 3 dB bandwidth are 30.5 dB and 470 MHz respectively, is obtained by simulation. This study is of great significance for the physical design and process in engineering the G-band extended interaction klystron amplifier.

空间电荷效应对时间展宽分幅变像管时空性能的影响

空间电荷效应对时间展宽分幅变像管时空性能的影响

Influence of space charge effect in femtosecond electron bunch on coherent transition radiation spectrum

This paper numerically and experimentally demonstrates the influence of the space charge forces in short electron bunches on the spectrum of coherent transition radiation. To estimate and optimize dimensions of a short electron bunches produced by the KEK LUCX RF gun, ASTRA software was employed. Obtained results indicate that the modification of the femtosecond UV laser pulse transverse profile allows to decrease the space charge forces. The simulation results were confirmed experimentally with the good agreement.

Numerical analysis of applied magnetic field dependence in Malmberg-Penning Trap for compact simulator of energy driver in heavy ion fusion

To simulate a pulse compression process of space charge dominated beams in heavy ion fusion, we have demonstrated a multi-particle numerical simulation as an equivalent beam using the Malmberg-Penning trap device. The results show that both transverse and longitudinal velocities as a function of external magnetic field strength are increasing during the longitudinal compression. The influence of space-charge effect, which is related to the external magnetic field, was observed as the increase of high velocity particles at the weak external magnetic field.

Study on space charge effect in an electrostatic ion analyzer applied to measure laser produced ions

The abundance of different ions produced by laser ion sources is usually analyzed by an electrostatic ion analyzer (EIA). Ion current intensities in the range of several mA/cm(2) at the position of the EIA have been achieved from the laser ion source developed by the Institute of Modern Physics; this indicates that a noticeable influence of space charge effect during the ion transmission will occur. Hence, while the parameters of the EIA or the beams are changed, such as ion species, current intensity, the ions' transmission efficiency through the EIA is different, which will result in an uncertainty in the estimation of the ions' yields. Special attention is focused on this issue in this paper. Ion's transmissions through the EIA under different circumstances are studied with simulations and experiments, the results of which are consistent with each other.

Acceptor related photoluminescence and field emission of ZnO:P nanostructures

ZnO:P nanobelts were self-assembly synthesized by thermal evaporation of Zn power and P2O5 mixture. The temperature dependence photoluminescence of ZnO:P nanostructures was studied from 81 to 291 K. As the temperature increased from 81 to 111 K, the PL intensity of DAP emission was obviously enhanced. The abnormal PL intensities were ascribed to the acceptor vibration with local phonon and lattice phonon assistant. The PL of zinc vacancy and its replica were well resolved due to the strenuous vibration of Zn vacancy. The replica of zinc vacancy emission increased while the visible emission gradually decreased with the temperature increase. It suggested that there were intensive deep acceptor vibration. The field emission properties of the ZnO:P nanostructures have been investigated according to the acceptor-related PL spectra. The influence of space charge effect on the field emission behaviors was also discussed.

Study of Displacement Value of the Electron-Beam in the Electron Gun in Electron-Beam Furnace

The concept of maximal and minimal displacement value of the electron-beam was proposed considering the influence of space charge effect based on the displacement value of the electron-beam in the process of magnetic deflection scanning in the ideal condition. The deduction of mathematical model of the maximal and minimal displacement value was accomplished. The position of the beam spot can be more accurately controlled by the model, thus it is made sure that un-molten metal is bombarded by the beam spot accurately, which can increase the melt quality.

Influence of space charge effect on Nottingham effect in thermal field emission

High current electron beam emitting from a thermal field emission cathode has an intense space charge effect. In order to investigate the mechanism for the influence of space charge effect on Nottingham effect in thermal field emission, the results of Nottingham effect with and without space charge effect at different work functions and various applied electric fields are obtained numerically on the basis of the theoretical analyses of space charge effect and Nottingham effect. The results demonstrate that the space charge effect has a significant influence on the steady electric field at the cathode surface, and thus the effect of space charge on Nottingham effect is not ignorable. When the work function is in a range of 3.0–4.52 eV and the applied electric field is in a scope of 3×109–9×109 V/m, the average energy delivered per electron in thermal field emission is in a span of 0–2.5 eV larger than that in the case without space charge effect, and the higher the cathode temperature or applied electric field, the larger the difference between them is. The average energy delivered by per electron emitting from cathode is observed to nonlinearly decrease with the increasing of applied electric field when the space charge effect is included. When the cathode temperature is high, the cooling effect in Nottingham effect can be intensified as the gap distance of diode increases.

Time-resolved photocurrent response of metal-semiconductor-metal photodetectors to double-pulse excitation

The photocurrent response of a GaAs metal-semiconductor-metal (MSM) photodetector was measured after excitation with two femtosecond pulses having a variable delay Δt of 0 ps≤Δt≤100 ps. At low excitation densities the influence of the first pulse on the pulse shape of the second is negligible for Δt≥20 ps. This corresponds to a resolvable pulse train of 50 GHz repetition rate for the detectors used in our experiments. The influence of space charge effects at higher excitation density and/or lower bias could be shown.

Dielectric recovery of an axially blown SF6-Arc after current zero: part III-comparison of experiment and theory

A detailed comparison between experiment and theory is made on the basis of the results of Parts I and II. As a first step, a theoretical solution is derived which is based on experimental results for the turbulence onset and for the radial temperature profile at current zero. This solution is compared with the various measured data, e. g., the radius of the hot-gas channel as a function of time and the dielectric recovery characteristics. The influence of space-charge effects on the recovery are shown to depend on the time after current zero and the shape of the applied voltage. Recommendations for further research are made.

Photoconductivity of Crystalline Iodoform I.

Abstract Steady state photoconduction in iodoform has been studied between 210–400 nm. The photoconduction threshold is at 345 nm whereas the crystal absorption extends up to 480 nm. The photoconductivity action spectrum shows a steep rise of the photo carrier generation efficiency in the range 345–290 nm and a plateau at shorter wavelengths. Current-voltage characteristics measured under steady illumination show a square dependence of the photocurrent on applied voltage showing the influence of space charge effects. Electron photocurrents are three orders of magnitude lower than hole photocurrents. The lower limit of the photogeneration quantum yield is estimated as 6 × 10−3 charge carriers/photon with an applied field of 1 × 104 V/cm.

Theoretical analysis of space-charge effects in photochron streak cameras

The influence of space-charge effects on the nature and extent of intensity-dependent temporal broadening in picosecond and subpicosecond streak images has been investigated analytically. The results indicate that the limitations on the dynamic range of electron-optical streak cameras result primarily from space-charge effects which are most serious in regions of the streak tubes where the photoelectrons travel with low velocities for relatively long times. The predicted values of dynamic range have been found to be in reasonable agreement with experimental measurements for Photochron I and Photochron II streak cameras. Theoretical estimates of the dynamic range of the Photochron IV streak camera which is currently being developed have also been included.

Influence of space-charge effect on the ion distribution in evaporated SiO dielectrics

Equations are presented to calculate the ionic distribution in a thin film SiO capacitor at dc conditions. The space-charge effect on the potential distribution is taken into account. The theory can then be applied for high ion concentrations. Experimental results obtained with SiO and Al 2O 3SiOAl 2O 3 capacitors show that the space charge may not be neglected.

Photoconductivity of α-Methylnaphthalene Alone and with an Incorporated Solute

Exposure of α-methylnaphthalene to strongly absorbed uv light and externally applied voltage produced photocurrent in the range of 10−9 to 10−7 A/cm2; their magnitude depended on the polarity of the illuminated electrode. The illumination through the positive electrode gave a photocurrent 15 times greater than when the negative electrode was illuminated. The mobilities of the positive and negative carriers were determined to be 1.2×10−4 and 5×10−5 cm2/V·sec, respectively. The former value is of the same order of magnitude as the theoretical value calculated for a positively charged α-methylnaphthalene ion. The temperature dependence of the mobility of the positive carrier indicated that the carrier may be either an ion or a hole with a long hopping time. Current—voltage measurements show that saturation is not reached at the highest field strength employed, 40 000 V/cm, and most likely would not be reached below fields of 106 V/cm. On this basis a theoretical efficiency of 1% for charge production was estimated. A non-Ohmic behavior of the photocurrent was observed, which suggested the presence of either a potential well at the electrode or the influence of space charge effects. The incorporation of a solute, 9,10-diphenylanthracene, reduced the current to 25% of that for the solvent alone, indicating extensive energy transfer to the solute and not simply to differences in mobility. The mechanism of charge production was interpreted either as an exciton interacting with the electrode to produce holes or as ionization of the solvent near the electrode with differences in recombination rates of the charges with the electrode.

Numerical computation of the temporal development of currents in a gas discharge tube

The behavior of electrical currents in a gas discharge tube including space charge effects is investigated by numerical integration of the governing nonlinear partial differential equations. Both stationary solutions and the temporal development, under the influence of space charge effects, are considered. It is found that the truncation error can be greatly reduced by comparison with formal solutions for constant fields. The discussion is essentially restricted to the more mathematical questions. (auth)