scholarly journals Sheath collapse at critical shallow angle due to kinetic effects

2021 ◽  
Author(s):  
Robert James Ewart ◽  
Felix I Parra ◽  
Alessandro Geraldini
Keyword(s):  
Magnetic Field ◽  
Small Angle ◽  
Potential Drop ◽  
Fluid Models ◽  
Square Root ◽  
Mass Ratio ◽  
Wall Potential ◽  
Kinetic Effects ◽  
The Magnetic Field ◽  
Bulk Plasma

Abstract The Debye sheath is known to vanish completely in magnetised plasmas for a sufficiently small electron gyroradius and small angle between the magnetic field and the wall. This angle depends on the current onto the wall. When the Debye sheath vanishes, there is still a potential drop between the wall and the plasma across the magnetic presheath. The magnetic field angle corresponding to the predicted sheath collapse is shown to be much smaller than previous estimates, scaling with the electron-ion mass ratio and not with the square root of the mass ratio. This is shown to be a consequence of the kinetic electron and finite ion orbit width effects, which are not captured by fluid models. The wall potential with respect to the bulk plasma at which the Debye sheath vanishes is calculated. Above this wall potential, it is possible that the Debye sheath will invert.

scholarly journals Feasibility of Probing the Filler Restructuring in Magnetoactive Elastomers by Ultra-Small-Angle Neutron Scattering

2021 ◽  
Vol 11 (10) ◽  
pp. 4470
Author(s):  
Inna A. Belyaeva ◽  
Jürgen Klepp ◽  
Hartmut Lemmel ◽  
Mikhail Shamonin
Keyword(s):  
Magnetic Field ◽  
Neutron Scattering ◽  
Small Angle ◽  
Small Angle Neutron Scattering ◽  
Iron Particles ◽  
Filler Particles ◽  
The Magnetic Field ◽  
Magnetoactive Elastomer

Ultra-small-angle neutron scattering (USANS) experiments are reported on isotropic magnetoactive elastomer (MAE) samples with different concentrations of micrometer-sized iron particles in the presence of an in-plane magnetic field up to 350 mT. The effect of the magnetic field on the scattering curves is observed in the scattering vector range between 2.5 × 10−5 and 1.85 × 10−4 Å−1. It is found that the neutron scattering depends on the magnetization history (hysteresis). The relation of the observed changes to the magnetic-field-induced restructuring of the filler particles is discussed. The perspectives of employing USANS for investigations of the internal microstructure and its changes in magnetic field are considered.

Kinetic Alfvén solitons in a low-beta plasma

1997 ◽  
Vol 57 (2) ◽  
pp. 235-245 ◽  
Author(s):  
B. C. KALITA ◽  
R. P. BHATTA
Keyword(s):  
Magnetic Field ◽  
Mach Number ◽  
Solitary Waves ◽  
Magnetic Pressure ◽  
Hot Electrons ◽  
Mass Ratio ◽  
Ion Motion ◽  
Electron Inertia ◽  
Theoretical Investigations ◽  
The Magnetic Field

Kinetic Alfvén solitons with hot electrons and finite electron inertia in a low-beta (β=8πn0T/B2G, the ratio of the kinetic to the magnetic pressure) plasma is studied analytically, with the ion motion being considered dominant through the polarization drift. Both compressive and rarefactive kinetic Alfvén solitons are found to exist within a definite range of kz (the direction of propagation of the kinetic Alfvén solitary waves with respect to the direction of the magnetic field) for each pair of assigned values of β and M (Mach number). Unlike in previous theoretical investigations, β appears as an explicit parameter for the kinetic Alfvén solitons in this case. In addition, consideration of the electron pressure gradient is found to suppress the speed of both the Alfvén solitons considerably for A (=2QM2/βk2z, with Q the electron-to-ion mass ratio) less than unity.

scholarly journals Non-stationarity of the quasi-perpendicular bow shock: comparison between Cluster observations and simulations

2011 ◽  
Vol 29 (2) ◽  
pp. 263-274 ◽  
Author(s):  
H. Comişel ◽  
M. Scholer ◽  
J. Soucek ◽  
S. Matsukiyo
Keyword(s):  
Magnetic Field ◽  
Bow Shock ◽  
Field Profile ◽  
Mass Ratio ◽  
Poynting Flux ◽  
Magnetic Field Profile ◽  
Low Mass ◽  
Low Mass Ratio ◽  
The Waves ◽  
The Magnetic Field

Abstract. We have performed full particle electromagnetic simulations of a quasi-perpendicular shock. The shock parameters have been chosen to be appropriate for the quasi-perpendicular Earth's bow shock observed by Cluster on 24 January 2001 (Lobzin et al., 2007). We have performed two simulations with different ion to electron mass ratio: run 1 with mi/me=1840 and run 2 with mi/me=100. In run 1 the growth rate of the modified two-stream instability (MTSI) is large enough to get excited during the reflection and upstream gyration of part of the incident solar wind ions. The waves due to the MTSI are on the whistler mode branch and have downstream directed phase velocities in the shock frame. The Poynting flux (and wave group velocity) far upstream in the foot is also directed in the downstream direction. However, in the density and magnetic field compression region of the overshoot the waves are refracted and the Poynting flux in the shock frame is directed upstream. The MTSI is suppressed in the low mass ratio run 2. The low mass ratio run shows more clearly the non-stationarity of the shock with a larger time scale of the order of an inverse ion gyrofrequency (Ωci): the magnetic field profile flattens and steepens with a period of ~1.5Ωci−1. This non-stationarity is different from reformation seen in previous simulations of perpendicular or quasi-perpendicular shocks. Beginning with a sharp shock ramp the large electric field in the normal direction leads to high reflection rate of solar wind protons. As they propagate upstream, the ion bulk velocity decreases and the magnetic field increases in the foot, which results in a flattening of the magnetic field profile and in a decrease of the normal electric field. Subsequently the reflection rate decreases and the whole shock profile steepens again. Superimposed on this 'breathing' behavior are in the realistic mass ratio case the waves due to the MTSI. The simulations lead us to a re-interpretation of the 24 January 2001 bow shock observations reported by Lobzin et al. (2007). It is suggested that the high frequency waves observed in the magnetic field data are due to the MTSI and are not related to a nonlinear phase standing whistler. Different profiles at the different spacecraft are due to the non-stationary behavior on the larger time scale.

Filamentation and collapse of Langmuir waves in a weak magnetic field

1982 ◽  
Vol 28 (1) ◽  
pp. 19-36 ◽  
Author(s):  
P. Rolland ◽  
S. G. Tagare
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Small Angle ◽  
Nonlinear Interaction ◽  
High Frequency ◽  
Weak Magnetic Field ◽  
Low Frequency ◽  
Langmuir Waves ◽  
The Magnetic Field

The filamentation and collapse of Langmuir waves in a weak magnetic field are analysed in two particular cases of low-frequency acoustic perturbations: (i) adiabatic perturbations which correspond to subsonic collapse, and (ii) nonadiabatic perturbations which correspond to supersonic collapse. Here the existence of Langmuir filaments and Langmuir collapse in a weak magnetic field are due to nonlinear interaction of high-frequency Langmuir waves (which make small angle with the external magnetic field) with low-frequency acoustic perturbations along the magnetic field.

Propagation of whistlers at a small angle to the magnetic field in hot anisotropic plasma

1981 ◽  
Vol 24 (8) ◽  
pp. 628-634
Author(s):  
S. S. Sazhin ◽  
O. A. Kobeleva ◽  
E. M. Sazhina ◽  
S. P. Varshavskii
Keyword(s):  
Magnetic Field ◽  
Small Angle ◽  
Anisotropic Plasma ◽  
The Magnetic Field

Propagation along the magnetic field of a pulse current originated disturbance in a cold two-fluid plasma

1967 ◽  
Vol 1 (4) ◽  
pp. 435-449
Author(s):  
G.J. Lewak
Keyword(s):  
Magnetic Field ◽  
Pulse Current ◽  
Airy Function ◽  
Extraordinary Wave ◽  
Mass Ratio ◽  
The Mean ◽  
Elliptically Polarized ◽  
The Magnetic Field ◽  
Two Fluid ◽  
Linear Plasma

The propagation, along the magnetic field, of a point disturbance in a cold two fluid linear plasma is solved asymptotically in various space-time régimes. The main disturbance is a pulse front travelling at approximately the Alfvén speed divided by the electron to ion mass ratio. Its proffle envelope is an Airy function. It oscillates at the mean of the gyro-frequencies and is effiptically polarized. The disturbances remaining behind this front are of two kinds: an oscillation at the sum of the gyro-frequencies which is circularly polarized and represents the ‘extraordinary’ wave, and an oscillation at the ion gyro-frequency which is elliptically polarized with changing eccentricity and orientation of axis.

scholarly journals Collisional transport across the magnetic field in drift-fluid models

2016 ◽  
Vol 23 (3) ◽  
pp. 032306 ◽  
Author(s):  
J. Madsen ◽  
V. Naulin ◽  
A. H. Nielsen ◽  
J. Juul Rasmussen
Keyword(s):  
Magnetic Field ◽  
Fluid Models ◽  
The Magnetic Field

scholarly journals Ion dynamics in magnetosonic shocks front

2018 ◽  
Vol 4 (4) ◽  
pp. 23-31 ◽  
Author(s):  
Геннадий Кичигин ◽  
Gennadiy Kichigin
Keyword(s):  
Magnetic Field ◽  
Shock Front ◽  
Small Angle ◽  
Critical Angle ◽  
Field Vector ◽  
Potential Difference ◽  
Magnetic Field Vector ◽  
Ion Dynamics ◽  
Pickup Ions ◽  
The Magnetic Field

I address the ion dynamics at the front of magnetosonic shocks moving at different angles θ to the magnetic field vector. I employ a shock discontinuity model in which the ramp potential difference is taken into account. The analysis conditionally separates all the ions incoming to the front of oblique magnetosonic shocks into the following categories: 1) transient, 2) reflected, 3) gyrating in front of the ramp, 4) pickup in the ramp. Both gyrating and pickup ions are shown to be present temporarily at the magnetosonic shock front at any angles θ. In the end, both the former and the latter appear to be transient in a strictly transversal magnetosonic shock; and either transient or reflected, in an oblique magnetosonic shock. I have found the critical angle θ* that separates ions into transient and reflected in an oblique magnetosonic shock. The critical angle θ* depends both on the velocity of the particles, incident on ramp, and on dimensions of the ramp potential difference. The most important results are that I have identified the physical cause of the production of the reflected ions having a significant energy and have revealed the mechanism for their acceleration in the ramp (surfing). In the near-Earth shock ion foreshock, these very ener-getic ions (from tens to hundreds of keV) escaping from the magnetosonic shock front at a small angle to the front plane manifest themselves in observations in the form of so-called field-aligned beams (FABs) and form the ion foreshock boundary.

Application of small-angle neutron scattering to the study of forces between magnetically chained monodisperse ferrofluid emulsion droplets

2013 ◽  
Vol 47 (1) ◽  
pp. 41-52 ◽  
Author(s):  
N. Jain ◽  
C. K. Liu ◽  
B. S. Hawkett ◽  
G. G. Warr ◽  
W. A. Hamilton
Keyword(s):  
Magnetic Field ◽  
Neutron Scattering ◽  
Droplet Size ◽  
Small Angle ◽  
Small Angle Neutron Scattering ◽  
Colloidal Particles ◽  
Optical Measurements ◽  
Magnetic Field Direction ◽  
Emulsion Droplets ◽  
The Magnetic Field

The optical magnetic chaining technique (MCT) developed by Leal-Calderon, Stora, Mondain-Monval, Poulin & Bibette [Phys. Rev. Lett.(1994),72, 2959–2962] allows precise measurements of force profiles between droplets in monodisperse ferrofluid emulsions. However, the method lacks anin situdetermination of droplet size and, therefore, requires a combination of separately acquired measurements of droplet chain periodicityversusan applied magnetic field from optical Bragg scattering and droplet diameter inferred from dynamic light scattering (DLS) to recover surface force–distance profiles between the colloidal particles. Compound refractive lens (CRL) focused small-angle neutron scattering (SANS) MCT should result in more consistent measurements of droplet size (form factor measurements in the absence of field) and droplet chaining period (from structure factor peaks when the magnetic field is applied), and, with access to shorter length scales, extend force measurements to closer approaches than possible by optical measurements. This article reports on CRL-SANS measurements of monodisperse ferrofluid emulsion droplets aligned in straight chains by an applied field perpendicular to the incident beam direction. Analysis of the scattering from the closely spaced droplets required algorithms that carefully treated resolution and its effect on mean scattering vector magnitudes in order to determine droplet size and chain periods to sufficient accuracy. At lower applied fields, scattering patterns indicate structural correlations transverse to the magnetic field direction owing to the formation of intermediate structures in early chain growth.

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