scholarly journals Ionization and Attachment Coefficients in C4F7N Gas Measured by the Steady-State Townsend Method

2019 ◽  
Vol 9 (18) ◽  
pp. 3686 ◽  
Author(s):  
Zhaoyu Qin ◽  
Yunxiang Long ◽  
Zhenyu Shen ◽  
Cheng Chen ◽  
Liping Guo ◽  
...  
Keyword(s):  
Steady State ◽  
Electric Field ◽  
Electric Fields ◽  
Room Temperature ◽  
Ionization Coefficient ◽  
Ionization Coefficients ◽  
Insulation Performance ◽  
Attachment Coefficient ◽  
Good Agreement ◽  
Effective Ionization

The normalized Townsend first ionization coefficient α/N and normalized attachment coefficient η/N in pure C4F7N were measured by using the steady-state Townsend (SST) method for a range of reduced electric fields E/N from 750 to 1150 Td at room temperature (20 °C). Meanwhile, the effective ionization coefficients are obtained. All SST experimental results show good agreement with pulsed Townsend (PT) experiment results. Comparisons of the critical electric fields of C4F7N with SF6 and other alternative gases such as c-C4F8 and CF3I indicate that C4F7N has a better insulation performance with a much higher normalized critical electric field at 959.19 Td.

scholarly journals Effective ionization coefficients for low current dc discharges in alcohol vapours at low pressure

2021 ◽  
Vol 75 (6) ◽  
Author(s):  
Jelena Marjanović ◽  
Dragana Marić ◽  
Gordana Malović ◽  
Zoran Lj. Petrović
Keyword(s):  
Electric Field ◽  
Low Pressure ◽  
Operating Conditions ◽  
Gas Density ◽  
Emission Profile ◽  
Standard Operating ◽  
Ionization Coefficients ◽  
Townsend Discharge ◽  
Good Agreement ◽  
Effective Ionization

Abstract This paper presents results for effective ionisation coefficients ($$\alpha _{\mathrm {eff}}/N$$ α eff / N , N—gas density) obtained from the breakdown voltage and emission profile measurements in low-pressure dc discharges in vapours of alcohols: methanol, ethanol, isopropanol, and n-butanol. Our results for $$\alpha _{\mathrm {eff}}/N$$ α eff / N are determined from the axial emission profiles in low-current Townsend discharge and lay in the interval of reduced electric field E/N (E—electric field, N—gas density), from 1 kTd to 8.8 kTd. We also give a comparison of our experimental results with those from the available literature. Our data cover the high E/N range of the standard operating conditions and in the region where other data are available we have a good agreement. Graphic abstract

A study of ionization coefficients and electrical breakdown in hydrogen

1956 ◽  
Vol 235 (1202) ◽  
pp. 334-348 ◽  
Keyword(s):  
Electric Fields ◽  
Electrical Breakdown ◽  
Theoretical Calculations ◽  
Maxwellian Distribution ◽  
Ionization Mechanism ◽  
Experimental Measurements ◽  
Ionization Coefficient ◽  
Ionization Coefficients ◽  
Good Agreement ◽  
Gas Pressures

Experimental measurements of the Townsend ionization coefficient α for hydrogen have been made from a study of pre-breakdown currents in uniform electric fields over a range of the parameter E/p from 15 to 40 V/cm mmHg. The results indicate that earlier measurements may be in error below E / p = 25 V/cm mmHg, and show good agreement with the theoretical calculations of Emeléus, Lunt & Meek (1936) which are based on a Maxwellian distribution of electron energies. Furthermore, measurements made at different gas pressures for the same value of the parameter E/p show that α/p is a function of E/p . The growth of pre-breakdown currents has been measured to within a small percentage of the sparking distance and is found to be well represented by the Townsend equation i = i 0 e αd /1- γ (e αd -1), showing the existence of a secondary ionization mechanism denoted by γ . The results are discussed in the light of existing theories of electrical breakdown, and it is concluded that the Townsend mechanism is sufficient to explain the initiation of breakdown in hydrogen up to a pd value of at least 2800 cm mmHg.

scholarly journals Electron Swarm Parameters and Dielectric Properties of the Superconducting Binary Mixtures of He-H2

2021 ◽  
Vol 36 (1) ◽  
pp. 420-432
Author(s):  
Mohammad M. Othman ◽  
Sherzad A. Taha ◽  
Saeed O. Ibrahim
Keyword(s):  
Distribution Function ◽  
Boltzmann Equation ◽  
Field Strength ◽  
Electric Field ◽  
Dielectric Strength ◽  
Ionization Coefficient ◽  
Experimental Values ◽  
Attachment Coefficient ◽  
Term Approximation ◽  
Effective Ionization

In this study, the electron energy distribution function EEDF, the electron swarm parameters, the effective ionization coefficients, and the critical field strength (dielectric strength) in binary He-H2 gas mixture which used as cryogenic for high-temperature superconducting power application, are evaluated by using two-term approximation of the Boltzmann equation over the range of E/N ( the electric field to gas density) from 1 to 100 Td ( 1 Td=10-17 Vcm2) at temperature 77 K and pressure 2MPa, taking into account elastic and inelastic cross-section. Using the calculated EEDF, the electron swarm parameters (electron drift velocity, mean electron energy, diffusion coefficient, electron mobility, ionization and attachment coefficient) are calculated. At low reduced electric field E/N, the EEDF close Maxwellian distribution, at high E/N, due to vibrational excitation of H2 the calculated distribution function is non-Maxwellian. Besides, in the He-H2 mixture, it is found that increasing small amount of H2 enhances to shift the tail of EEDF to the lower energy region, the reduced ionization coefficient α/N. reduced effective ionization coefficient (α-η)/N) decreases, while, reduced attachment coefficient η/N, reduced critical electric field strength (E/N)crt. and critical electric field Ecrt. Increases, because of hydrogen’s large ionization cross-sections. The dielectric strength of 5% H2 in mixture is in good agreement with experimental values, it is found that dielectric strength depend on pressure and temperature. The electron swarm parameters in pure gaseous helium (He) and hydrogen (H2), in satisfying agreement with previous available theoretical and experimental values. The validity of the calculated values has been confirmed by two-term approximation of the Boltzmann equation analysis.

Numerical study of electric field effects on the deformation of two-dimensional liquid drops in simple shear flow at arbitrary Reynolds number

2009 ◽  
Vol 626 ◽  
pp. 367-393 ◽  
Author(s):  
STEFAN MÄHLMANN ◽  
DEMETRIOS T. PAPAGEORGIOU
Keyword(s):  
Steady State ◽  
Shear Flow ◽  
Electric Field ◽  
Electric Fields ◽  
Simple Shear ◽  
Simple Shear Flow ◽  
Physical Parameters ◽  
Shear Stresses ◽  
Two Dimensional ◽  
Liquid Drops

The effect of an electric field on a periodic array of two-dimensional liquid drops suspended in simple shear flow is studied numerically. The shear is produced by moving the parallel walls of the channel containing the fluids at equal speeds but in opposite directions and an electric field is generated by imposing a constant voltage difference across the channel walls. The level set method is adapted to electrohydrodynamics problems that include a background flow in order to compute the effects of permittivity and conductivity differences between the two phases on the dynamics and drop configurations. The electric field introduces additional interfacial stresses at the drop interface and we perform extensive computations to assess the combined effects of electric fields, surface tension and inertia. Our computations for perfect dielectric systems indicate that the electric field increases the drop deformation to generate elongated drops at steady state, and at the same time alters the drop orientation by increasing alignment with the vertical, which is the direction of the underlying electric field. These phenomena are observed for a range of values of Reynolds and capillary numbers. Computations using the leaky dielectric model also indicate that for certain combinations of electric properties the drop can undergo enhanced alignment with the vertical or the horizontal, as compared to perfect dielectric systems. For cases of enhanced elongation and alignment with the vertical, the flow positions the droplets closer to the channel walls where they cause larger wall shear stresses. We also establish that a sufficiently strong electric field can be used to destabilize the flow in the sense that steady-state droplets that can exist in its absence for a set of physical parameters, become increasingly and indefinitely elongated until additional mechanisms can lead to rupture. It is suggested that electric fields can be used to enhance such phenomena.

scholarly journals Mapping of steady-state electric fields and convective drifts in geomagnetic fields – Part 1: Elementary models

2016 ◽  
Vol 34 (1) ◽  
pp. 55-65 ◽  
Author(s):  
A. D. M. Walker ◽  
G. J. Sofko
Keyword(s):  
Magnetic Field ◽  
Steady State ◽  
Electric Field ◽  
Electric Fields ◽  
Magnetic Field Line ◽  
Geomagnetic Field ◽  
Geomagnetic Field Models ◽  
Spatial Derivatives ◽  
Field Lines ◽  
The Magnetic Field

Abstract. When studying magnetospheric convection, it is often necessary to map the steady-state electric field, measured at some point on a magnetic field line, to a magnetically conjugate point in the other hemisphere, or the equatorial plane, or at the position of a satellite. Such mapping is relatively easy in a dipole field although the appropriate formulae are not easily accessible. They are derived and reviewed here with some examples. It is not possible to derive such formulae in more realistic geomagnetic field models. A new method is described in this paper for accurate mapping of electric fields along field lines, which can be used for any field model in which the magnetic field and its spatial derivatives can be computed. From the spatial derivatives of the magnetic field three first order differential equations are derived for the components of the normalized element of separation of two closely spaced field lines. These can be integrated along with the magnetic field tracing equations and Faraday's law used to obtain the electric field as a function of distance measured along the magnetic field line. The method is tested in a simple model consisting of a dipole field plus a magnetotail model. The method is shown to be accurate, convenient, and suitable for use with more realistic geomagnetic field models.

Analytical approach for transient photoconductivity in undoped a-Si:H

1995 ◽  
Vol 377 ◽  
Author(s):  
M. Goerlitzer ◽  
P. Pipoz ◽  
H. Beck ◽  
N. Wyrsch ◽  
A. V. Shah
Keyword(s):  
Steady State ◽  
Theoretical Model ◽  
Analytical Approach ◽  
Room Temperature ◽  
Free Electrons ◽  
Recombination Time ◽  
Sample Quality ◽  
Transient Photoconductivity ◽  
Light Intensities ◽  
Good Agreement

ABSTRACTTransient photoconductive response of undoped a-Si:H has been studied; the changes were analysed between two slightly different steady-state illumination conditions, at room temperature. A theoretical model is developed to describe transient photoconductivity; it yields good agreement with the measured curves for a whole range of light intensities. Numerical evaluations allows one to extract the recombination time of electrons. Comparison with steady-state photoconductivity yields a band mobility of free electrons between 0.1 and 6 cm2V−1s−1, depending upon sample quality.

The Electric Field Measuring by Phase Selective Photoreflectance

1996 ◽  
Vol 421 ◽  
Author(s):  
J. S. Hwang ◽  
W. Y. Chou ◽  
S. L. Tyan ◽  
Y. C. Wang ◽  
H. Shen
Keyword(s):  
Electric Field ◽  
Theoretical Calculation ◽  
Buffer Layer ◽  
Electric Fields ◽  
Phase Angle ◽  
Substrate Interface ◽  
Field Measuring ◽  
Lock In ◽  
Good Agreement ◽  
Reference Phase

AbstractThe built-in electric fields in a MBE grown δ-doped GaAs homojunction have been investigated by the techniques of photoreflectance and phase suppression. Two Franz-Keldysh oscillation features originating from two different fields in the structure superimpose with each other in the photoreflectance spectrum. By properly selecting the reference phase of the lock-in amplifier, one of the features can be suppressed, thus enabling us to determine the electric fields from two different regions. We have demonstrated that only two PR spectra, in-phase and outphase components, are needed to find the phase angle which suppresses one of the features. The electric field in the top layer is 3.5 ± 0.2 × 105 V/cm, which is in good agreement with theoretical calculation. The electric field in the buffer layer is 1.2 ± 0.1 × 104 V/cm, which suggests the existence of interface states at the buffer/substrate interface.

scholarly journals Synthesis and characterization of lead-free ternary component BST–BCT–BZT ceramic capacitors

2014 ◽  
Vol 04 (02) ◽  
pp. 1450014 ◽  
Author(s):  
Venkata Sreenivas Puli ◽  
Dhiren K. Pradhan ◽  
Brian C. Riggs ◽  
Shiva Adireddy ◽  
Ram S. Katiyar ◽  
...  
Keyword(s):  
Phase Transition ◽  
Dielectric Constant ◽  
Energy Density ◽  
Electric Field ◽  
Hysteresis Loop ◽  
Electric Fields ◽  
Room Temperature ◽  
Thermal Hysteresis ◽  
Lead Free ◽  
Maximum Electric Field

Polycrystalline sample of lead-free 1/3( Ba 0.70 Sr 0.30 TiO 3) + 1/3( Ba 0.70 Ca 0.30 TiO 3) + 1/3( BaZr 0.20 Ti 0.80 O 3)( BST - BCT - BZT ) ceramic was synthesized by solid state reaction method. Phase purity and crystal structure of as-synthesized materials was confirmed by X-ray diffraction (XRD). Temperature-dependent dielectric permittivity studies demonstrated frequency-independent behavior, indicating that the studied sample has typical diffuse phase transition behavior with partial thermal hysteresis. A ferroelectric phase transition between cubic and tetragonal phase was noticed near room temperature (~ 330 K). Bulk P–E hysteresis loop showed a saturation polarization of 20.4 μC/cm2 and a coercive field of ~ 12.78 kV/cm at a maximum electric field of ~ 115 kV/cm. High dielectric constant (ε ~ 5773), low dielectric loss (tan δ ~ 0.03) were recorded at room temperature. Discharge energy density of 0.44 J/cm3 and charge energy density of 1.40 J/cm3 were calculated from nonlinear ferroelectric hysteresis loop at maximum electric field. Dielectric constant at variable temperatures and electric fields, ferroelectric to paraelectric phase transition and energy storage properties were thoroughly discussed.

ELECTRIC FIELD INFLUENCE ON TRAVELING WAVE PROPAGATION AND STATIONARY PATTERN FORMATION

1995 ◽  
Vol 05 (03) ◽  
pp. 797-807 ◽  
Author(s):  
J. MOSQUERA ◽  
M. GÓMEZ-GESTEIRA ◽  
V. PÉREZ-MUÑUZURI ◽  
A.P. MUÑUZURI ◽  
V. PÉREZ-VILLAR
Keyword(s):  
Wave Propagation ◽  
Pattern Formation ◽  
Electric Field ◽  
Electric Fields ◽  
Traveling Wave ◽  
Traveling Fronts ◽  
Spatial Terms ◽  
Oregonator Model ◽  
Field Influence ◽  
Good Agreement

The electric field influence on pattern formation and traveling wave propagation is investigated in the framework of the Oregonator model. When an electric field is applied to a system that can suffer spatial instabilities, Turing and Turing-like patterns (traveling fronts that become stationary patterns when reaching a zero-flux boundary) are observed. On the other hand, when an electric field is applied to a system that cannot become unstable by spatial terms and where wavefronts are propagating in the absence of electric fields, the velocity of these wavefronts is modified and can even be reversed. This is in good agreement with previous experimental results.

Monte Carlo Analysis of Effect of Alloy Scattering on Electron Transport in Wurtzite Zn1-xMgxO

2013 ◽  
Vol 873 ◽  
pp. 861-864
Author(s):  
Lin Lin Hu ◽  
Ping Wang ◽  
Tao Shang ◽  
Jiu Xu Song
Keyword(s):  
Monte Carlo ◽  
Steady State ◽  
Electric Field ◽  
Electric Fields ◽  
Drift Velocity ◽  
Monte Carlo Model ◽  
Monte Carlo Analysis ◽  
Alloy Scattering ◽  
Ensemble Monte Carlo ◽  
Velocity Decrease

Steady-state and transient electron characteristics of wurtzite Zn1xMgxO are studied in detail. An ensemble Monte Carlo model is established considering alloy scattering. From the steady-state characteristics, it is found that alloy scattering makes the drift velocity decrease at different electric fields. For 10% Mg, the transient peak drift velocity decreases from 2.48×107cm/s to 2.13×107cm/s at 2000 kV/cm. While for 20% Mg, a higher electric field is needed for the onset of the overshoot, which corresponds to the larger peak electric field in the steady-state velocity-field characteristics.

Sign in / Sign up

Export Citation Format

Share Document