Transverse Drift Velocity Research Articles

Simulation and Experimental Study on Jetting Projectile Charge Penetrating Multi-Layer Spaced Targets with Large Spacing

To study the ability of shaped charges to penetrate typical ship targets, two shaped charges with the same diameter of 200 mm but different configurations are designed to generate two forms of jetting projectile charge (JPC). Based on the protective structure of typical ship targets, static penetration tests are performed using the two types of a shaped charge with copper liner and 10-layer spaced targets with a total span of 16 m which is made in 921A steel. Numerical simulations under the same working conditions are also carried out. It is found that the simulation results of the penetration depth and the number of layers of target perforated by the JPC are much greater than the experimental results. In fact, the JPC breaks up when moving to a certain distance, and the JPC segments after breakup have a transverse drift velocity, causing the segment to deviate from the original penetrating channel. The influence of drift velocity after JPC fracture cannot be considered in numerical simulation, resulting in significant differences between numerical simulation and experimental results. Thus, this paper proposed a segment-based numerical simulation method and analyzed the penetration process of JPC fragments after JPC fracture. Combined with experimental results, the radial motion after JPC fracture and the final distribution of penetration holes can be well revealed. It is found that the penetration depth and the number of layers of target perforated by the JPC depend on the tip velocity of each segment and the jet length.

High power terahertz radiation generation by optical rectification of a shaped pulse laser in axially magnetized plasma

An analytical expression has been derived for terahertz (THz) emission by optical rectification of a laser pulse having a Gaussian as well as hyperbolic-secant shape in axially magnetised ripple density plasma. The interaction between short laser pulses of sub picoseconds duration and plasma leads to the radiation of a wave having frequency in THz regime. The non-uniform intensity profile, say supper-Gaussian, of laser beam exerts a quasi-static ponderomotive force to the electron. The electron acquired a nonlinear transverse drift velocity component. Hence, a strong transient current density having a frequency component in the THz regime produces due to coupling of this velocity component with ripple density plasma and derives a strong THz wave. The generated THz field amplitude is directly proportional to the amplitude of the density ripple and field amplitude of the laser beam. In this generation mechanism, the ripple wave number plays a critical role. The THz field amplitude is maximized when cyclotron frequency approaches to the THz frequency and higher value of profile index. For typical laser plasma parameter, the emitted normalised amplitude of THz field is on the order of 10−2.

High‐frequency radar ground clutter spatial correlation analysis: Transverse ionospheric drift velocity

AbstractA method of evaluating transverse ionospheric winds from oblique high‐frequency radar ground scatter is presented. Measurements of the two‐point, two‐time mutual coherence function (MCF) of ground clutter targets made by the Kodiak Super Dual Auroral Radar Network (SuperDARN) HF‐phased array radar illustrate that the spatial distribution of the backscattered electric field moves coherently across the radar aperture over time. Diffraction theory is applied to illustrate that the observations are consistent with an ionospheric drift transverse to the look direction of the radar. A general theoretical expression for the MCF is derived whose amplitude contours in the space‐time plane may be simply related to the azimuth angular spectrum and Doppler spectrum of the incident signal and a transverse ionospheric drift between the radar and the illuminated area. A method of estimating ionospheric drift from the observed MCF is developed and applied to observations made by the Kodiak SuperDARN radar.

Measurement of the drift velocity and transverse diffusion of electrons in liquid xenon with the EXO-200 detector

The EXO-200 Collaboration is searching for neutrinoless double beta decay using a liquid xenon (LXe) time projection chamber. This measurement relies on modeling the transport of charge deposits produced by interactions in the LXe to allow discrimination between signal and background events. Here we present measurements of the transverse diffusion constant and drift velocity of electrons at drift fields between 20~V/cm and 615~V/cm using EXO-200 data. At the operating field of 380~V/cm EXO-200 measures a drift velocity of 1.705$_{-0.010}^{+0.014}$~mm/$\mu$s and a transverse diffusion coefficient of 55$\pm$4~cm$^2$/s.

Control of Hall angle of Skyrmion driven by electric current**Project supported by the National Natural Science Foundation of China (Grant No. 51331006) and the Fund from the Chinese Academy of Sciences (Grant No. KJZD-EW-M05).

Skyrmions are very promising for applications in spintronics and magnetic memory. It is desired to manipulate and operate a single skyrmion. Here we report on the thermal effect on the motion of current-driven magnetic Skyrmions in magnetic metal. The results show that the magnon current induced by the thermal gradient acts on Skyrmions via magnonic spin-transfer torque, an effect of the transverse and longitudinal Skyrmions drift velocities, thus leading to the effective manipulation of the Hall angle through the ratio of thermal gradient to electric current density, which can be used as a Skyrmion valve.

Thermodynamical interpretation of the geometrical variables associated with null surfaces

The emergent gravity paradigm interprets gravitational field equations as describing the thermodynamic limit of the underlying statistical mechanics of microscopic degrees of freedom of the spacetime. The connection is established by attributing a heat density Ts to the null surfaces where T is the appropriate Davies-Unruh temperature and s is the entropy density. The field equations can be obtained from a thermodynamic variational principle which extremizes the total heat density of all null surfaces. The explicit form of s determines the nature of the theory. We explore the consequences of this paradigm for an arbitrary null surface and highlight the thermodynamic significance of various geometrical quantities. In particular, we show that: (a) A conserved current, associated with the time development vector in a natural fashion, has direct thermodynamic interpretation in all Lanczos-Lovelock models of gravity. (b) One can generalize the notion of gravitational momentum, introduced in arXiv 1506.03814 to all Lanczos-Lovelock models of gravity such that the conservation of the total momentum leads to the relevant field equations. (c) The thermodynamic variational principle which leads to the field equations of gravity can also be expressed in terms of the gravitational momentum in all Lanczos-Lovelock models. (d) Three different projections of gravitational momentum related to an arbitrary null surface in the spacetime lead to three different equations, all of which have thermodynamic interpretation. The first one reduces to a Navier-Stokes equation for the transverse drift velocity. The second can be written as a thermodynamic identity TdS = dE + P dV. The third describes the time evolution of the null surface in terms of suitably defined surface and bulk degrees of freedom. The implications are discussed.

Transverse drift velocity of a pulsed-plasma in a curved magnetic field

Recent experimental evidence suggests the importance of fast radial plasma transport in the scrape-off-layer (SOL) of tokamaks. The outward transport appears to be convective rather than diffusive, extends into the far SOL, and can produce significant recycling from the main-chamber walls, partially bypassing the divertor. A plausible theoretical mechanism to explain this phenomenon is the radial transport of blobs of locally dense plasma created by turbulent processes. In our experiment, a blob of plasma is produced using a plasma-gun and injected transverse to a non-uniform curved magnetic field inside a curved vacuum chamber. The plasma-blob from the washer stacked plasma gun interacts with the curved magnetic field, which has been created by a pair of coils. The coil is being energized by a capacitor bank. In this paper we report the radial velocity of the plasma-blob in presence of magnetic field. The radial velocity of plasma-blob decreases in the presence of magnetic field in comparison with the velocity without magnetic field.

Generating Spin Currents in Semiconductors with the Spin Hall Effect

We investigate electrically induced spin currents generated by the spin Hall effect in GaAs structures that distinguish edge effects from spin transport. Using Kerr rotation microscopy to image the spin polarization, we demonstrate that the observed spin accumulation is due to a transverse bulk electron spin current, which can drive spin polarization nearly 40 microns into a region in which there is minimal electric field. Using a model that incorporates the effects of spin drift, we determine the transverse spin drift velocity from the magnetic field dependence of the spin polarization.

The behavior of N/sub 2/ + SF/sub 6/ gas mixtures subjected to orthogonal electric and magnetic fields

The limiting equivalent electric fields in N/sub 2/+SF/sub 6/ binary gas mixtures due to Townsend discharges are evaluated directly from a Monte-Carlo simulation when the mixture is subjected to orthogonal electric and magnetic fields. Along with the limiting equivalent electric fields, transverse and perpendicular drift velocities, electron mean energies and collision frequencies are also determined within the scope of the Monte-Carlo simulation. The equivalent reduced electric field (EREF) concept for the corresponding limiting electric fields is also investigated for the calculated mean energy levels and collision frequencies. The EREF values are found to be in good agreement with the previously published limiting electric field data.

Radial velocity and doppler spectral width of echoes from field‐aligned irregularities localized in the sporadic E region

The effects of along and transverse radar beam drifts of sporadic E (Es) field‐aligned irregularities localized in the expected echoing region on mean Doppler velocity and spectral width are theoretically investigated in this article. We show that the mean Doppler velocity of the irregularities is not only governed by the along and transverse beam drift velocities, but also affected by the mean position and zonal extent of the organized plasma structure in the expected echoing region that can be determined by using IGRF2000. Detailed analysis indicates that the Doppler velocity nearly linearly proportional to the mean angular distance of the irregularities from the radar beam axis decreases with the increase of the horizontal dimension of the plasma structure. Theoretical results also predict that the Doppler spectral width of the Es field‐aligned irregularities is not only the function of the transverse beam drift velocity, but also related to the zonal extent of the plasma structure. Quantitative estimation shows that the beam broadening spectral width induced by the geomagnetically zonal drift of the irregularities at the velocity of 150 m/s can be more than 9 m/s if the zonal dimension of the plasma structure located at height 105 km is 5 km. Therefore it suggests that the beam broadening effect caused by the drift of the field‐aligned irregularities across the radar beam in the geomagnetically zonal direction may play a role in broadening the Doppler spectral width.

Unified classical and quantum radiation mechanism for ultrarelativistic electrons in curved and inhomogeneous magnetic fields

We analyse the general radiation emission mechanism from a charged particle moving in a curved inhomogeneous magnetic field. The consideration of the gradient makes the vacuum magnetic field compatible with the Maxwell equations, and adds a non-trivial term to the transverse drift velocity, and, consequently, to the general radiation spectrum. To obtain the radiation spectrum in the classical domain a general expression for the spectral distribution and characteristic frequency of an electron in arbitrary motion is derived, by using Schwinger's method. The radiation patterns of the ultrarelativistic electron are represented in terms of the acceleration of the particle. The same results can be obtained by considering that the motion of the electron can be formally described as an evolution caused by magnetic and electric forces. By defining an effective electromagnetic field, which combines the magnetic field with the fictitious electric field associated to the curvature and drift motion, one can obtain all the physical characteristics of the radiation by replacing the constant magnetic field with the effective field. The power, angular distribution and spectral distribution of all three components (synchrotron, curvature and gradient) of the radiation are considered, in both the classical and the quantum domain, within the framework of this unified formalism. In the quantum domain the proposed approach allows the study of the effects of the inhomogeneities and curvature of the magnetic field on the radiative transition rates of electrons between low-lying Landau levels and the ground state.

Limiting equivalent electric field response in Ar+SF/sub 6/ subjected to orthogonal electric and magnetic fields

The limiting equivalent electric fields in Ar+SF/sub 6/ binary gas mixtures due to Townsend discharges are evaluated directly from a Monte-Carlo simulation when the mixture is subjected to orthogonal electric and magnetic fields. Along with the limiting equivalent electric fields, transverse and perpendicular drift velocities, electron mean energies and collision frequencies are also determined within the scope of the Monte-Carlo simulation. The equivalent reduced electric field (EREF) concept for the corresponding limiting electric fields is also investigated for the calculated mean energy levels and collision frequencies. The EREF values are found to be in good agreement with the previously published limiting electric field data.

Monte Carlo simulation of electron transport coefficients in magnetically confined CO2 gas laser discharges

A Monte Carte simulation of electrons emitted from the cathode of a CO2 gas laser discharge is presented. The influence of a perpendicular magnetic field on the electron transport coefficients has been studied. Data on transverse and perpendicular velocities and electron energy distributions are evaluated at various magnetic field types and strengths. Ionization coefficients and excitation coefficients of 27 useful energy levels of CO2, N2 and He are obtained at the same time. The result shows that the application of a magnetic field perpendicular to the electric field decreases the transverse drift velocity, the mean energy and thus the ionization coefficient. As a result, the magnetic field leads to a very high perpendicular velocity, which may be responsible for the stability of our discharge experiments (where a perpendicular magnetic field near the cathode is used to stabilize the direct current discharge of a CO2 gas laser and to gain a higher input power loading). It is also found that the magnetic field distributions, as well as the field strength, had great effects on the electron transport coefficients and the discharge properties.

Critical Ionization Velocity (CIV) experiment XANI onboard the INTERCOSMOS 24 — “ACTIVE” satellite

Satellite INTERCOSMOS-24 “ACTIVE” was launched on September 30 1989, with an initial apogee 2500 km, perigee 530 km and an orbital inclination of 82.2°. Under “ACTIVE” project, a wide number of plasma diagnostics instruments were especially designed to study the ionospheric response to high power VLF transmitter emissions, by means of satellite-subsatellite system during this mission. As a separate part of this project, a Critical Ionization Velocity (CIV) experiment called XANI (Xenon ANomalous Ionization) had been carried out to study neutral gas/plasma interaction processes in the ionosphere using neutral Xe gas injection. Seven Xe gas release experiments had been realized at daytime high latitude ionosphere. In this paper an Ion Drift Meter (IDM) and Retarding Potential Analyzer (RPA) data concerning transverse ion drift velocity vector measurements and total ion density variations during gas release experiment are shown. Two examples of the RPA data, taken after the beginning of Xe injection, show some prompt ionization at the ionization front about 30% in comparison with the background ion concentration. Horizontal ion drift of few hundred meters per second, transversal to the satellite velocity vector, had been observed at the ionization front.

Simulation of electron swarms in SF6 in uniform E*B fields

Reports electron swarm parameters in SF6 in uniform E*B fields employing a Monte Carlo simulation technique. The parameters studied are transverse and perpendicular drift velocities, magnetic deflection angle, collision frequency, mean energy and effective ionization coefficients for 30<or=E/p<or=200 V cm-1 Torr-1 and 0<or=B/p<or=6*10 T Torr-1. At a given E/p, application of a magnetic field causes decreases in the transverse drift velocity, the mean energy and the effective ionization coefficient. The validity of the effective reduced electric field concept is also investigated for the evaluated collision frequency, mean energy and effective ionization coefficient.

Electron transport coefficients in mercury vapour in E*B fields

The influence of a magnetic field on electron transport coefficients in mercury vapour has been studied using a Monte-Carlo simulation technique. The ranges of parameters studied are 10<or=E/N<or=1000 Td and O<or=B/N<or=20*10-19T cm3 (where E is the electric field, B the magnetic field and N the gas number density). Data on ionization coefficients, transverse and perpendicular drift velocities and mean energy are evaluated at various magnetic field strengths. The results are examined in the light of the effective reduced electric field (EREF) concept. It is found that the EREF is a good approximation for the mean energy, collision frequency and ionization coefficient if the appropriate collision frequency which is dependent on E/N and B/N (instead of a constant collision frequency) is used in EREF calculations. As a result, the application of a magnetic field perpendicular to the electric field decreases the transverse drift velocity, mean energy and ionization coefficient. The influence of the magnetic field on the energy distribution function is also studied.

A Theory for the Sparkover Time of a Low Pressure Magnetic Switch

In this paper the theory developed by the author for the formative time lags of gases on the right-hand side of Paschen's minimum in crossed electric and magnetic fields has been extended to cover the left-hand side of the Paschen minimum. A coaxial cylindrical geometry has been considered and the theory takes into account the radial change of the electric field and of Townsend's first ionization coefficient. The temporal and spatial growth of current in oxygen has been calculated in electric fields only, as a first step and good agreement is shown to exist between the theory and experiment. The theory is then extended to a magnetic switch which operates on the left-hand side of the Paschen minimum by considering the influence of a magnetic field on the transverse drift velocity of electrons and on Townsend's first ionization co efficient. An increase in the applied magnetic field has been shown to reduce the sparkover time at a constant applied voltage, and reach a minimum value. On further increas, e in the applied magnetic field, the sparkover time begins to rise and a cut-off magnetic field strength at which breakdown is not possible at all is shown to exist at these low pressure ranges. An increased ap plied voltage causes breakdown at the cut-off magnetic field strength and at this operating point a higher cut-off magnetic field strength exists.

Anomalously enhanced plasma diffusion transverse to a magnetic field in n-Ge

From the broadening of a narrow plasma sheet drifting along E x × B, we measured the transverse diffusion coefficient D ⊥ in n-Ge. Contrary to the classical theory, D ⊥ increases with the electric field E x , increases with the magnetic field B up to μ + B ≈ 1, and decreases proportional to 1 B in higher magnetic fields. The transverse drift velocity v ⊥ measured simultaneously shows a classical behavior over the whole field ranges of E x = 3–110 V cm and B = 0.1–2.3 T, which were used in our experiment. The results correspond to those gained previously in n-InSb[13,14]. However, whereas in InSb plasma instabilities were observed together with the anomalous diffusion, no instabilities could be found in Ge. Various ways to arrive at an explanation of the anomalous effect are discussed and possible applications are indicated.

Electron energy distributions and transport coefficients in N2inE × Bfields

Using the concept of energy-dependent effective field intensity, electron transport coefficients in nitrogen have been determined in E × B fields (E = electric field intensity, B = magnetic flux density) by the numerical solution of the Boltzmann transport equation for the energy distribution of electrons. It has been observed that as the value of B/p (p = gas pressure) is increased from zero, the perpendicular drift velocity increased linearly at first, reaches a maximum value, and then decreases with increasing B/p. In general, the electron mean energy is found to be a function of Eavet/p ( Eavet = averaged effective electric field intensity) only, but the other transport coefficients, such as transverse drift velocity, perpendicular drift velocity, and the Townsend ionization coefficient, are functions of both E/p and B/p.

Interaction between two hybrid modes in n-GaAs

Small-signal temporal instability has been studied in n-GaAs in the range of the electric field for which the electron concentration in the central and the satellite valleys are comparable to each other. The samplo is subjected to a crossed d.e. electric field E 0 and magetic field B 0 and the wave is assumed to be propagating perpendicular to the plane of E 0 and B 0. The light electron hybrid mode (E 1x, E 1z) interacts with the heavy electron hybrid mode and thus produces hybrid-hybrid interaction. The diffusion-incorporated dispersion relation has been derived, taking into account the appropriate scattering mechanisms at 300°K. It is analysed to look for instability for real k and complex ω (= ωr + iωt). One of the modes becomes unstable and propagates with a phase velocity equal to the transverse drift velocity of the light electrons. Instability is possible in the range of the magnetic field 2.5  B 0  6.0 Tesla. The instability is observed only for small values of k. At large k the modes are dampe...