scholarly journals Theoretical constraints on the cross-tail width of bursty bulk flows

2013 ◽  
Vol 31 (12) ◽  
pp. 2179-2192 ◽  
Author(s):  
C. X. Chen
Keyword(s):  
Magnetic Field ◽  
Cross Section ◽  
Plasma Sheet ◽  
Unstable Mode ◽  
Force Balance ◽  
Larmor Radius ◽  
The Cross ◽  
Fast Flow ◽  
Flow Burst ◽  
Bursty Bulk Flows

Abstract. The characteristic cross-tail width of bursty bulk flows (BBFs) in earth's plasma sheet was investigated at two stages of its life, one at its onset, the other when it is fully developed. Equilibrium domains with gradient of magnetic field are constructed. Interchange instability analysis of such domains yields the most unstable mode with the half wave length comparable with the observed cross-tail width of a flow burst and the inverse of growth rate comparable with its duration. The thickness of the plasma sheet for the most unstable mode is also comparable to the width of BBFs in the north–south direction. We found that viscosity, the dimension of the unstable domain, the thickness of the plasma sheet and gradient of the magnetic field together determine the most unstable mode. The ion Larmor radius plays an important role in viscosity as half effective mean free path. For a fully developed flow, however, velocity-caused pressure difference between the leading and trailing sides of a flow burst also plays a role. The equatorial cross section of flow is reshaped and its cross-tail width is changed as well. Representing the surrounding medium with empirical magnetic field and plasma models, the force balance of the fast flow is analyzed. The cross-section area of flow burst is estimated to be one to several square earth radii, and the cross-tail width of fast flow is estimated to be 1 to 3 earth radii, which is consistent with observations of BBFs.

Magnetic-field dependence of the cross section formJmixing in2P1/2Cs and Rb atoms

1994 ◽  
Vol 49 (6) ◽  
pp. 4540-4548 ◽  
Author(s):  
W. Kedzierski ◽  
Ju Gao ◽  
W. E. Baylis ◽  
L. Krause
Keyword(s):  
Magnetic Field ◽  
Cross Section ◽  
Field Dependence ◽  
Magnetic Field Dependence ◽  
The Cross

scholarly journals Rotating magnetic field effect on convection and its stability in a horizontal cylinder subjected to a longitudinal temperature gradient

2010 ◽  
Vol 664 ◽  
pp. 108-137 ◽  
Author(s):  
D. V. LYUBIMOV ◽  
A. V. BURNYSHEVA ◽  
H. BENHADID ◽  
T. P. LYUBIMOVA ◽  
D. HENRY
Keyword(s):  
Magnetic Field ◽  
Temperature Gradient ◽  
Prandtl Number ◽  
Cross Section ◽  
Rotating Magnetic Field ◽  
Shear Mode ◽  
Convective Flows ◽  
Longitudinal Temperature Gradient ◽  
Longitudinal Temperature ◽  
The Cross

A rotating magnetic field (RMF) is used in crystal growth applications during the solidification process in order to improve the crystal quality. Its influence on the convective flows in molten metals and on their stability is studied here in the case of a horizontal infinite cylindrical channel subjected to a longitudinal temperature gradient. The steady convective flows, which correspond to the usual longitudinal counterflow structure, with four vortices in the cross-section for non-zero Prandtl number, Pr, are modified by the RMF (parametrized by the magnetic Taylor number Tam). For zero Prandtl number, the flow in the cross-section corresponds to circular streamlines and the longitudinal flow structure is moved in the direction of the magnetic field rotation, with a decrease in its intensity and an asymptotic variation as 1/Tam. For non-zero Prandtl numbers, depending on the respective values of Tam on one side and Prandtl and Grashof numbers on the other side, different structures ranging from the circular streamlines with transport by rotation of the longitudinal velocity and the temperature field, to the more usual counterflow structure almost insensitive to the RMF with four cross-section vortices, can be obtained. The decrease in the flow intensity with increasing Tam is also delayed for non-zero Pr, but the same asymptotic limit is eventually reached. The stability analysis of these convective flows for Tam = 0 shows a steep increase of the thresholds around Pr = Prt,0 ≈ 3 × 10−4, corresponding to the transition between the usual counterflow shear mode and a new sidewall shear mode. This transition is still present with an RMF, but it occurs for smaller Pr values as Tam is increased. Strong stabilizing effects of the rotating magnetic field are found for Pr < Prt,0, particularly for Pr = 0 where an exponential increase of the threshold with Tam is found. For Pr > Prt,0 (i.e. in the domain where the sidewall instability is dominant), in contrast, the stabilization by the RMF is weak.

scholarly journals Radial distribution of electrons rotation moment in hall effect and plasma-ion thrusters

2021 ◽  
pp. 28-34
Author(s):  
Zongshuai Guo
Keyword(s):  
Magnetic Field ◽  
Hall Effect ◽  
Cross Section ◽  
Radial Distribution ◽  
Electric Propulsion ◽  
Mirror Reflection ◽  
Radial Magnetic Field ◽  
Ion Thrusters ◽  
Wall Conductivity ◽  
The Cross

The subject matter of the article is the radial distribution of electrons movement parameters inside electric propulsion thrusters with closed electrons drift. The radial magnetic field in Hall effect thrusters is the limits the axial flow of electrons because of interaction with azimuth electron current. In turn, this azimuth current exists as a result of rivalry between the attempt of the magnetic field to transform electrons current completely closed one and the loss of electrons rotation moment in collisions. Similar processes take place in the ionization chamber of plasma-ion thrusters with the radial magnetic field. The attempts to estimate electrons parameters through only collisions with ions and atoms inside volume have given the value of axial electrons current much lower than really being. This phenomenon is called anomalous electrons conductivity, which was tried to be explained as a consequence of various effects including "near-the-wall-conductivity", which was explained as a result of non-mirror reflection of electrons from the Langmuir layer near the walls of the thruster channel. The disadvantage of this name is the fact that the reflection of the electron occurs before reaching the surface from the potential barrier at the plasma boundary with any environment: the wall, but also with the environment vacuum. The potential distribution in the Langmuir layer is non-stationary and inhomogeneous due to the presence of so-called plasma oscillations. The definition of "conductivity" is just as unfortunate in this name, because the collisions are always not a factor of conductivity, but on the contrary – of resistance. The goal is to solve the task of electrons rotation moment distribution in the thruster channel. The methods used are the formulation of the kinetic equation for electrons distribution function over the velocities, radius, and projections of the coordinates of the instantaneous center of cyclotron rotation; solution of this equation and finding with its use the distribution of the gas-dynamic parameters of electrons along the cross-section of the channel. Conclusions. A mathematical model of electrons rotation moment dynamics is proposed, which allows using plasma-dynamics equations to analyze its distribution along the cross-section of thruster channel and to estimate the effect of "near-the-wall-conductivity" using appropriate boundary conditions.

scholarly journals Three-dimensional earthward fast flow in the near-Earth plasma sheet in a sheared field: comparisons between simulations and observations

2009 ◽  
Vol 27 (6) ◽  
pp. 2297-2302 ◽  
Author(s):  
K. Kondoh ◽  
M. Ugai
Keyword(s):  
Magnetic Field ◽  
Plasma Sheet ◽  
Three Dimensional ◽  
The Real ◽  
Mhd Simulations ◽  
Simulation Domain ◽  
Three Dimensional Configuration ◽  
Fast Flow ◽  
Reconnection Model ◽  
Fast Reconnection

Abstract. Three-dimensional configuration of earthward fast flow in the near-Earth plasma sheet is studied using three-dimensional magnetohydrodynamics (MHD) simulations on the basis of the spontaneous fast reconnection model. In this study, the sheared magnetic field in the plasma sheet is newly considered in order to investigate the effects of it to the earthward fast flow, and the results are discussed in comparison with no-shear simulations. The virtual probes located at different positions in our simulation domain in shear/no-shear cases could explain different behavior of fast flows in the real observations.

scholarly journals Collision of a Positron with the Capture of an Electron from Lithium and the Effect of a Magnetic Field on the Particles Balance

Chemosensors ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 45
Author(s):  
Elena V. Orlenko ◽  
Alexandr V. Evstafev ◽  
Fedor E. Orlenko
Keyword(s):  
Magnetic Field ◽  
Strong Magnetic Field ◽  
Cross Section ◽  
Dynamic Equilibrium ◽  
Mass Effect ◽  
Alpha Particles ◽  
Exchange Effects ◽  
The Cross ◽  
Living Tissues ◽  
Comparison Of The Results

The processes of scattering slow positrons with the possible formation of positronium play an important role in the diagnosis of both composite materials, including semiconductor materials, and for the analysis of images obtained by positron tomography of living tissues. In this paper, we consider the processes of scattering positrons with the capture of an electron and the formation of positronium. When calculating the cross-section for the capture reaction, exchange effects caused by the rearrangement of electrons between colliding particles are taken into account. Comparison of the results of calculating the cross-section with a similar problem of electron capture by a proton showed that the mass effect is important in such a collision process. The loss of an electron by a lithium atom is more effective when it collides with a positron than with a proton or alpha particles. The dynamic equilibrium of the formation of positronium in the presence of a strong magnetic field is considered. It is shown that a strong magnetic field during tomography investigation shifts the dynamic equilibrium to the positronium concentration followed by positron annihilation with radiation of three gamma-quants.

Vortical flow in the plasma sheet: Non-linear growth of flow burst surface wave?

2020 ◽  
Author(s):  
Ghai Siung Chong ◽  
Alexandre De Spiegeleer ◽  
Maria Hamrin ◽  
Timo Pitkanen ◽  
Sae Aizawa ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Plasma Sheet ◽  
High Speed ◽  
Velocity Shear ◽  
Vortical Flow ◽  
Boundary Crossing ◽  
Moving Plasma ◽  
Flow Evolution ◽  
Slow Moving ◽  
Flow Burst

&lt;p&gt;In contrast to the simple conventional plasma flow convection governed by the Dungey Cycle, past studies have revealed that the plasma flows in the magnetotail region are more complicated, hosting high-speed bursty and meandering vortical flows. We have utilized magnetic field and plasma data from the Cluster mission to investigate a high speed earthward propagating flow burst with a peak velocity of ~530 km/s in the magnetotail plasma sheet (X&lt;sub&gt;GSM&lt;/sub&gt; ~ -17R&lt;sub&gt;E&lt;/sub&gt;) on 20 September 2002. In the vicinity of this flow burst, a vortical flow, whose plasma vectors are first directed tailward then earthward, is also observed. The plasma data shows that the plasma population in the vortical flow is likely to originate from the associated flow burst. In addition, the boundaries of both structures are also found to be tangential discontinuities, clearly surrounded by the ambient slow moving plasma sheet. Inside the vortical flow, there exists a region where plasma originating from the flow burst and ambient plasma sheet are mixed. The local segment of inbound boundary crossing of the vortical flow is shown to have a thickness that is non-uniform. Coupled with the flow evolution in the vortical flow, these characteristics are consistent to a boundary crossing of a vortical flow. The magnetic field on the flow burst is quasi-perpendicular to the large velocity shear (~460 km/s) across the flow burst boundary. These results suggest that the formation of vortical flow can arise from the development and subsequent growth of flow burst boundary wave as a result of Kelvin-Helmholtz instability. In summary, this article presents a detailed observational study of a vortical flow and the formation of which would serve as the first direct observational consequence of an excited and growing flow burst boundary wave. Continuous scattering of the detached vortices may play an important role in the braking mechanism of earthward propagating flow bursts.&amp;#160;&lt;/p&gt;

scholarly journals The magnetic structure of an earthward-moving flux rope observed by Cluster in the near-tail

2007 ◽  
Vol 25 (7) ◽  
pp. 1471-1476 ◽  
Author(s):  
Y. C. Zhang ◽  
Z. X. Liu ◽  
C. Shen ◽  
A. Fazakerley ◽  
M. Dunlop ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Structure ◽  
Cross Section ◽  
Transverse Magnetic Field ◽  
Plasma Sheet ◽  
Principal Axis ◽  
Flux Rope ◽  
Transverse Magnetic ◽  
Magnetic Flux Rope ◽  
Ae Index

Abstract. We investigate the magnetic structure of a small earthward-moving flux rope observed by Cluster in the near-Earth plasma sheet through application of the Grad-Shafranov (GS) technique to reconstruct the transverse magnetic field distribution perpendicular to the flux rope axis at X=−14.75 RE. We find that the principal axis of the flux rope lies approximately along the dawn-dusk direction and that the diameter of the flux rope is about 1.5 RE. There is a strong duskward core magnetic field in the center of the flux rope. According to the AE index, there is no obvious substorm associated with the magnetic flux rope. Recent studies indicate that the formation of the flux rope in the plasma sheet can be understood in terms of simultaneous reconnection at multiple X-line points in the near-tail. The distribution of the transverse magnetic field on the cross section is the asymmetric circles, which requires that the reconnections at multiple X-line points occur. So our results also provide additional evidence for the occurrence of multiple-X line reconnection in the magnetotail.

scholarly journals Production Cross Sections of Axion in a Static Electromagnetic Field

2013 ◽  
Vol 23 (1) ◽  
pp. 21
Author(s):  
Dang Van Soa ◽  
Tran Dinh Tham
Keyword(s):  
Magnetic Field ◽  
Electromagnetic Field ◽  
Electric Field ◽  
Total Cross Section ◽  
Strong Magnetic Field ◽  
Cross Section ◽  
Cross Sections ◽  
Feynman Diagram ◽  
Production Cross ◽  
The Cross

Photon - axion conversions in staticelectromagnetic fields of the size \(a\times b \times c\) areconsidered in detail by the Feynman diagram methods. Thedifferential cross sections are presented and the numericalevaluations of the total cross section are given. Our result showsthat the conversion cross-sections in the electric field are quitesmall, while in the strong magnetic field, the cross-sections are much enhanced, which can be measurable in current experiments.

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