Longitudinal Variability of the Vertical Drift Velocity Inferred from Ground-Based Magnetometers and C/NOFS Observations in Africa

This study aims at discussing longitudinal effects on the variability of the vertical E × B drift velocity at low latitudes, specifically over African sector. To this effect, observations from ground-based magnetometers and the Ion Velocity Meter experiment onboard C/NOFS satellite are analyzed in conjunction with equatorial electric field and neutral wind model estimates under geomagnetically quiet conditions in the years 2012-2013. Notwithstanding the limitation in data over Africa, the combination of ground-based and in-situ observations confirmed the existence of longitudinal differences in the E × B between the Atlantic, Western and Eastern African sectors. This was well reproduced by the equatorial electric field model (EEFM) which showed that during noon, the peak of the equatorial electric field (EEF) was the lowest in the Atlantic sector, with an increasing trend towards the Eastern longitude. The Horizontal Wind Model 14 (HWM14) showed that the eastward zonal (poleward meridional) wind velocity was the lowest (highest) in the Eastern sector. Furthermore, the zonal (meridional) wind increased (decreased) from the Eastern to the Atlantic sector. These results highlight the contribution of the neutral wind velocity in driving the longitudinal difference in the vertical drift velocity over Africa.

The effective ionization coefficients and electron drift velocities in gas mixtures of CF_3I with N_2 and CO_2 obtained from Boltzmann equation analysis

The electron swarm parameters including the density-normalized effective ionization coefficients（α-η）/N and the electron drift velocities V e are calculated for a gas mixture of CF3I with N2 and CO2 by solving the Boltzmann equation in the condition of a steady-state Townsend（SST） experiment.The overall density-reduced electric field strength is from 100 Td to 1000 Td（1 Td = 10-17V·cm2）,while the CF3I content k in the gas mixture can be varied over the range from 0% to 100%.From the variation of（αη）/N with the CF3I mixture ratio k,the limiting field strength（E/N） lim for each CF3I concentration is derived.It is found that for the mixtures with 70% CF3I,the values of（E/N） lim are essentially the same as that for pure SF 6.Additionally,the global warming potential（GWP） and the liquefaction temperature of the gas mixtures are also taken into account to evaluate the possibility of application in the gas insulation of power equipment.

Wellbore drift flow relation suitable for full flow pattern domain and full dip range

Aiming at the simulation of multi-phase flow in the wellbore during the processes of gas kick and well killing of complex-structure wells(e.g.,directional wells,extended reach wells,etc.),a database including 3561 groups of experimental data from 32 different data sources is established.Considering the effects of fluid viscosity,pipe size,interfacial tension,fluid density,pipe inclination and other factors on multi-phase flow parameters,a new gas-liquid two-phase drift flow relation suitable for the full flow pattern and full dip range is established.The distribution coefficient and gas drift velocity models with a pipe inclination range of-90°–90°are established by means of theoretical analysis and data-driven.Compared with three existing models,the proposed models have the highest prediction accuracy and most stable performance.Using a well killing case with the backpressure method in the field,the applicability of the proposed model under the flow conditions with a pipe inclination range of-90°–80°is verified.The errors of the calculated shut in casing pressure,initial back casing pressure and casing pressure when adjusting the displacement are 2.58%,3.43%,5.35%,respectively.The calculated results of the model are in good agreement with the field backpressure data.

Effect of E × B electron drift and plasma discharge in dc magnetron sputtering plasma

Study of electron drift velocity caused by E ×B motion is done with the help of a Mach probe in a dc cylindrical magnetron sputtering system at different plasma discharge parameters like discharge voltage, gas pressure and applied magnetic field strength. The interplay of the electron drift with the different discharge parameters has been investi- gated. Strong radial variation of the electron drift velocity is observed and is found to be maximum near the cathode and it decreases slowly with the increase of radial distance from the cathode. The sheath electric field, E measured experimentally from potential profile curve using an emissive probe is contributed to the observed radial variation of the electron drift velocity. The measured values of the drift velocities are also compared with the values from the con- ventionM theory using the experimental values of electric and magnetic fields. This study of the drift velocity variation is helpful in providing a useful insight for determining the discharge conditions and parameters for sputter deposition of thin film.

A measure of ionospheric irregularities:zonal velocity and its implications for L-band scintillation at low-latitudes

We estimate the zonal drift velocity of small-scale ionospheric irregularities at low latitude by leveraging the spaced-receivers technique applied to two GNSS receivers for scintillation monitoring installed along the magnetic parallel passing in Presidente Prudente(Brazil,magnetic latitude 12.8°S).The investigated ionospheric sector is ideal to study small-scale irregularities,being located close to the expected position of the southern crest of the equatorial ionospheric anomaly.The measurement campaign took place between September 2013 and February 2014,i.e.equinox and summer solstice seasons under solar maximum,during which the probability of formation of small-scale irregularities is expected to maximize.We found that the hourly average of the velocity increases up to 135 m/s right after the local sunset at ionospheric altitudes and then smoothly decreases in the next hours.Such measurements are in agreement with independent estimations of the velocity made by the Incoherent Scatter Radar located at the Jicamarca Radio Observatory(magnetic latitude 0.1°N),by the Boa Vista Ionosonde(magnetic latitude 12.0°N),and by applying a recently-developed empirical regional short-term forecasting model.Additionally,we investigated the relationship with the percentage occurrence of amplitude scintillation;we report that it is exponentially dependent on the zonal velocity of the irregularities that cause it.

Shear Flow Dispersion Under Wave and Current

The longitudinal dispersion of solute in open channel flow with short period progressive waves is investigated. The waves induce second order drift velocity in the direction of propagation and enhance the mixing process in concurrent direction. The 1-D wave-period-averaged dispersion equation is derived and an expression for the wave-current induced longitudinal dispersion coefficient （WCLDC） is propased based on Fiscber＇ s expression （1979） for dispersion in unidirectional flow. The result shows that the effect of waves on dispersion is mainly due to the cross-sectional variation of the drift velocity. Furthermore, to obtain a more practical expression of the WCLDC, the longitudinal dispersion coefficient due to Seo and Cheong （1998） is modified to incluee the effect of drift velocity. Laboratory experiments have been conducted to verify the propased expression. The experimental results, together with dimensional analysis, show that tbe wave effect can be reflected by the ratio between the wave amplitude and wave period. A comparative study between the cases with and without waves demonstrates that the magnitude of the longitudinal dispersion coefficient is increased nnder the presence of waves.

Interactions of nonlinear gravity waves and uniform current in Lagrangian system

The particle trajectory on a weakly nonlinear progressive surface wave obliquely interacting with a uniform current is studied by using an Euler-Lagrange transformation.The third-order asymptotic solution is a periodic bounded function of Lagrangian labels and time,which imply that the entire solution is uniformly-valid.The explicit parametric solution highlights the trajectory of a water particle and mass transport associated with a particle displacement can now be obtained directly in Lagrangian form.The angular frequency and Lagrangian mean level of the particle motion in Lagrangian form differ from those of the Eulerian.The variations in the water particle orbits resulting from the oblique interaction with a steady uniform current of different magnitudes are also investigated.

Electron Transport Coefficients and Effective Ionization Coefficients in SF_6-O_2 and SF_6-Air Mixtures Using Boltzmann Analysis

The electron drift velocity, electron energy distribution function （EEDF）, densitynormalized effective ionization coefficient and density-normalized longitudinal diffusion velocity are calculated in SF6-O2 and SFs-Air mixtures. The experimental results from a pulsed Townsend discharge are plotted for comparison with the numerical results. The reduced field strength varies from 40 Td to 500 Td （1 Townsend=10-17 V.cm2） and the SF6 concentration ranges from 10% to 100%. A Boltzmann equation associated with the two-term spherical harmonic expansion approximation is utilized to gain the swarm parameters in steady-state Townsend. Results show that the accuracy of the Boltzlnann solution with a two-term expansion in calculating the electron drift velocity, electron energy distribution function, and density-normalized effective ionization coefficient is acceptable. The effective ionization coefficient presents a distinct relationship with the SF6 content in the mixtures. Moreover, the E/Ncr values in SF6-Air mixtures are higher than those in SF6-O2 mixtures and the calculated value E/Ncr in SF6-O2 and SF6-Air mixtures is lower than the measured value in SFB-N2. Parametric studies conducted on these parameters using the Boltzmann analysis offer substantial insight into the plasma physics, as well as a basis to explore the ozone generation process.

Intermittent Bursts in the Boundary Plasma of HT-7

Intermittent characteristics of turbulence induced by coherent structures （blobs） was clearly observed in the ion saturation current signal, density fluctuation, particle flux and heat flux in HT-7. It is obvious that ion saturation current signal has deviated from Gaussian distribution and the skewness （S） and flatness （K） of signal increase radially outwards in the scrape-off layer （SOL）. Using conditional analysis （CA）, asymmetric character of the intermittent bursts are demonstrated. Owing to the radial propagation of the coherent structures, the particle density profile in SOL is non-exponential and flat outwards from the last close flux surface （LCFS）. It is found around LCFS that the large burst fluctuations （above 2.5 rms） are responsible for about 50% of the total particle transport. Burst events move radially outwards with Ee ~ B velocity, and the blob size can be calculated as 5r ~ V^rc. Our experiment shows that the blob size, life time and drift velocity experienced a pronounced decorrelation in the shear layer. The electrostatic Reynolds stress components become very strong and show a radially steep gradient in the proximity of the shear layer. These experimental findings may imply that the coherent structures are titled by the developed shear flow in the E × B shear layer.

Modelling of Electrical Conductivity of a Silver Plasma at Low Temperature

During the working of electrical fuses, inside the fuse element the silver ribbon first begins to melt, to vaporize and then a fuse arc appears between the two separated parts of the element. Second, the electrodes are struck and the burn-back phenomenon takes place. Usually, the silver ribbon is enclosed inside a cavity filled with silica sand. During the vaporization of the fuse element, one can consider that the volume is fixed so that the pressure increase appears to reach pressures higher than atmospheric pressure. Thus, in this paper two pressures, 1 atm and 10 atm, are considered. The electrical field inside the plasma can reach high values since the distance between the cathode surface and the anode surface varies with time. That is to say from zero cm to one cm order. So we consider various electrical fields： 102 V/m, 103 V/m, 5×103 V/m, 104 V/m at atmospheric pressure and 105 V/m at a pressure of 10 atm. This study is made in heavy species temperature range from 2,400 K to 10,000 K. To study the plasma created inside the electric fuse, we first need to determine some characteristics in order to justify some hypotheses. That is to say： are the classical approximations of the thermal plasmas physics justified？ In other words： plasma frequency, the ideality of the plasma, the Debye-Hückel approximation and the drift velocity versus thermal velocity. These characteristics and assumptions are discussed and commented on in this paper. Then, an evaluation of non-thermal equilibrium versus considered electrical fields is given. Finally, considering the high mobility of electrons, we evaluate the electrical conductivities.

Lorentz Force from a Current-Carrying Wire on a Charge in Motion under the Assumption of Neutrality in the Symmetrical Frame of Reference

It is commonly assumed that a wire conducting an electric current is neutral in the laboratory frame of reference (the rest frame of the lattice of positive ions). Some authors consider that the wire is neutral only in a symmetrical frame of reference, in which the velocities of electrons and protons have equal norm and opposite direction. In this paper, we discuss the Lorentz transformation between different frames of reference in the context of the special theory of relativity for a current-carrying conducting wire and a probe charge in motion with respect to the wire. A simple derivation of the Lorentz force in the laboratory frame of reference for the assumed neutrality in a symmetrical frame of reference is presented. We show that the Lorentz force calculated assuming neutrality in the symmetrical frame of reference and the one assuming neutrality in the laboratory frame of reference differ by a term corresponding to a change in the test charge speed of one half the drift velocity of the electrons.

Control of vacuum arc source cathode spots contraction motion by changing electromagnetic field

This paper investigates the magnetic field component impact on cathode spots motion trajectory and the mechanism of periodic contraction.Electromagnetic coils and permanent magnets were installed at the different sides of cathode surface,the photographs of cathode spots motion trajectory were captured by a camera.Increasing the number of magnets and decreasing the distance between magnets and cathode both lead to enhancing cathode spots motion velocity.Radii of cathode spots trajectory decrease gradually with the increasing of electromagnetic coil＇s current,from 40 mm at 0 A to 10 mm at 2.7 A.Parallel magnetic field component intensity influence the speed of cathode spots rotate motion,and perpendicular magnetic field component drives spots drift in the radial direction.Cathode spot＇s radial drift is controlled by changing the location of the ‘zero line＇ where perpendicular magnetic component shifts direction and the radius of cathode spots trajectory almost equal to ‘zero line＇.

A sensitivity analysis of millimeter wave characteristics of SiC IMPATT diodes

Ionization rate coefficients and saturation drift velocities for electrons and holes are the vital material parameters in determining the performance of an IMPATT diode.We have performed a sensitivity analysis of the millimeter wave characteristics of 4H-SiC and 6H-SiC IMPATT diodes with reference to the above mentioned material data and an operating frequency of 220 GHz.The effect of a small variation in the ionization rate and drift velocity on the device characteristics like break down voltage,efficiency,noise measure and power output has been presented here.

Hot electron transport in wurtzite-GaN:effects of temperature and doping concentration

The hot electron transport in wurtzite phase gallium nitride（Wz-GaN） has been studied in this paper. An analytical expression of electron drift velocity under the condition of impact ionization has been developed by considering all major scattering mechanisms such as deformation potential acoustic phonon scattering, piezoelectric acoustic phonon scattering, optical phonon scattering, electron-electron scattering and ionizing scattering. Numerical calculations show that electron drift velocity in Wz-GaN saturates at 1.44 ×10^5 m/s at room temperature for the electron concentration of 10^22 m^-3. The effects of temperature and doping concentration on the hot electron drift velocity in Wz-GaN have also been studied. Results show that the saturation electron drift velocity varies from 1.91 ×10^5-0.77 ×10^5 m/s for the change in temperature within the range of 10-1000 K, for the electron concentration of 10^22 m^-3; whereas the same varies from 1.44 ×10^5-0.91 ×10^5 m/s at 300 K for the variation in the electron concentration within the range of 10^22-10^25 m^-3. The numerically calculated results have been compared with the Monte Carlo simulated results and experimental data reported earlier, and those are found to be in good agreement.

Performance study of a novel sampling TPC prototype detector based on THGEM

Introduction Time projection chamber(TPC)with micropattern gaseous detectors(MPGDs)as readout has been one of the research hotspots in recent years.MPGD-based TPC has been applying to many experiments due to its high spatial and energy resolutions in 3D track measurement.Purpose A novel sampling TPC detector based on thick gaseous electron multiplier(THGEM)was developed to measure the low-energy electron tracks online from 0.1 to 50 MeV with a 100μm spatial resolution in a vacuum tank.The tracks will be extrapolated to determine the hit positions on a target about 200mm behind the TPC.Methods and materials A new type of self-developed THGEM detector was chosen as the TPC readout unit.The field cage has two 50×50mm2 windows welded by Gold-plated tungsten wires for low-energy electrons passing through.The front-end electronics was designed with a self-developed application specific integrated circuit chip,i.e.,CASA-GEM.Seven columns of readout pads were used to equidistantly sample the electron tracks in a length of 75mm.Each column has 72 pads of 0.56×0.56mm2 and two additional strips along each column for drift time measurement.Both Geant4 and Garfield++were chosen to simulate and optimize the detector,such as the penetration efficiency,electric field in field cage and operating gas pressure.Results The design and the preliminary performances of the TPC detector were verified by beam test andβsource test.A drift velocity of 3.415±0.103 cm/μs was measured at 125 V/cm in Ar+iC4H10(97:3)forπ−.The electron detection efficiency is about 88%forβsource.And the gain of the double THGEM reached more than 1.0×10^(4).