scholarly journals Magnetic field generation in a jet-sheath plasma via the kinetic Kelvin-Helmholtz instability

2013 ◽  
Vol 31 (9) ◽  
pp. 1535-1541 ◽  
Author(s):  
K.-I. Nishikawa ◽  
P. Hardee ◽  
B. Zhang ◽  
I. Duţan ◽  
M. Medvedev ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Magnetic Fields ◽  
Electric Field ◽  
Flow Direction ◽  
Transverse Magnetic ◽  
Velocity Shear ◽  
Helmholtz Instability ◽  
Magnetic Field Generation ◽  
Relativistic Jet

Abstract. We have investigated the generation of magnetic fields associated with velocity shear between an unmagnetized relativistic jet and an unmagnetized sheath plasma. We have examined the strong magnetic fields generated by kinetic shear (Kelvin–Helmholtz) instabilities. Compared to the previous studies using counter-streaming performed by Alves et al. (2012), the structure of the kinetic Kelvin–Helmholtz instability (KKHI) of our jet-sheath configuration is slightly different, even for the global evolution of the strong transverse magnetic field. In our simulations the major components of growing modes are the electric field Ez, perpendicular to the flow boundary, and the magnetic field By, transverse to the flow direction. After the By component is excited, an induced electric field Ex, parallel to the flow direction, becomes significant. However, other field components remain small. We find that the structure and growth rate of KKHI with mass ratios mi/me = 1836 and mi/me = 20 are similar. In our simulations saturation in the nonlinear stage is not as clear as in counter-streaming cases. The growth rate for a mildly-relativistic jet case (γj = 1.5) is larger than for a relativistic jet case (γj = 15).

PARTICLE ACCELERATION AND MAGNETIC FIELD GENERATION IN SHEAR-FLOWS

2014 ◽  
Vol 28 ◽  
pp. 1460195
Author(s):  
K.-I. NISHIKAWA ◽  
P. HARDEE ◽  
Y. MIZUNO ◽  
I. DUŢAN ◽  
B. ZHANG ◽  
...  
Keyword(s):  
Particle Acceleration ◽  
Magnetic Fields ◽  
Lorentz Factor ◽  
Velocity Shear ◽  
Magnetic Field Generation ◽  
Electron Positron ◽  
Relativistic Jet ◽  
Unmagnetized Plasma ◽  
Alternating Magnetic Fields ◽  
Transverse Deflection

We have investigated the generation of magnetic fields associated with velocity shear between an unmagnetized relativistic (core) jet and an unmagnetized sheath plasma by the kinetic Kelvin-Helmholtz instability for different mass ratios (m i /m e = 1, 20, and 1836) and different jet Lorentz factors. We found that electron-positron cases have alternating magnetic fields instead of the DC magnetic fields found in electron-ion cases. We have also investigated particle acceleration and shock structure associated with an unmagnetized relativistic jet propagating into an unmagnetized plasma for electron-positron and electron-ion plasmas. Strong magnetic fields generated in the trailing shock lead to transverse deflection and acceleration of the electrons. We have self-consistently calculated the radiation from the electrons accelerated in the turbulent magnetic fields for different jet Lorentz factors. We find that the synthetic spectra depend on the bulk Lorentz factor of the jet, the jet temperature, and the strength of the magnetic fields generated in the shock.

Kelvin–Helmholtz instability under horizontal rotation and magnetic fields

1998 ◽  
Vol 59 (2) ◽  
pp. 193-209
Author(s):  
L. A. DÁVALOS-OROZCO
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Fluid Layer ◽  
Maximum Growth ◽  
Maximum Growth Rate ◽  
Density Stratification ◽  
Velocity Shear ◽  
Sufficient Condition ◽  
Horizontal Shear ◽  
Helmholtz Instability

The author's previous work on the Rayleigh–Taylor instability is extended to the Kelvin–Helmholtz instability, and the maximum growth rate of a perturbation and an estimate of its upper bound is obtained for an infinite fluid layer under horizontal rotation where the density, horizontal velocity (shear) and magnetic field are continuously stratified in the direction of gravity. Conclusions are drawn about the possibility of stability for some directions of propagation of the perturbation, even in the case of unstably stratified density. It is also shown that the new terms that appear owing to the interaction of the horizontal shear flow, horizontal rotation and stratified magnetic field increase the range of values that contribute to the estimate of the maximum growth rate compared with previous work. Furthermore, a generalization of the sufficient condition for stability under horizontal rotation alone obtained by Johnson is calculated in the presence of density stratification. A new method is also given to obtain a sufficient condition for stability when a magnetic field is present in addition to rotation and density stratification.

Radio Measurements of Coronal Magnetic Fields

1994 ◽  
Vol 144 ◽  
pp. 21-28 ◽  
Author(s):  
G. B. Gelfreikh
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Active Regions ◽  
High Sensitivity ◽  
Coronal Magnetic Field ◽  
Transverse Magnetic ◽  
Radio Sources ◽  
Radio Waves ◽  
Solar Active Regions

AbstractA review of methods of measuring magnetic fields in the solar corona using spectral-polarization observations at microwaves with high spatial resolution is presented. The methods are based on the theory of thermal bremsstrahlung, thermal cyclotron emission, propagation of radio waves in quasi-transverse magnetic field and Faraday rotation of the plane of polarization. The most explicit program of measurements of magnetic fields in the atmosphere of solar active regions has been carried out using radio observations performed on the large reflector radio telescope of the Russian Academy of Sciences — RATAN-600. This proved possible due to good wavelength coverage, multichannel spectrographs observations and high sensitivity to polarization of the instrument. Besides direct measurements of the strength of the magnetic fields in some cases the peculiar parameters of radio sources, such as very steep spectra and high brightness temperatures provide some information on a very complicated local structure of the coronal magnetic field. Of special interest are the results found from combined RATAN-600 and large antennas of aperture synthesis (VLA and WSRT), the latter giving more detailed information on twodimensional structure of radio sources. The bulk of the data obtained allows us to investigate themagnetospheresof the solar active regions as the space in the solar corona where the structures and physical processes are controlled both by the photospheric/underphotospheric currents and surrounding “quiet” corona.

scholarly journals An 84-μG Magnetic Field in a Galaxy at Z=0.692?

2008 ◽  
Vol 4 (S254) ◽  
pp. 95-96
Author(s):  
Arthur M. Wolfe ◽  
Regina A. Jorgenson ◽  
Timothy Robishaw ◽  
Carl Heiles ◽  
Jason X. Prochaska
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Faraday Rotation ◽  
Large Scale ◽  
Dynamo Model ◽  
Magnetic Field Generation ◽  
Interstellar Gas ◽  
Splitting Technique ◽  
Average Value ◽  
The Magnetic Field

AbstractThe magnetic field pervading our Galaxy is a crucial constituent of the interstellar medium: it mediates the dynamics of interstellar clouds, the energy density of cosmic rays, and the formation of stars (Beck 2005). The field associated with ionized interstellar gas has been determined through observations of pulsars in our Galaxy. Radio-frequency measurements of pulse dispersion and the rotation of the plane of linear polarization, i.e., Faraday rotation, yield an average value B ≈ 3 μG (Han et al. 2006). The possible detection of Faraday rotation of linearly polarized photons emitted by high-redshift quasars (Kronberg et al. 2008) suggests similar magnetic fields are present in foreground galaxies with redshifts z > 1. As Faraday rotation alone, however, determines neither the magnitude nor the redshift of the magnetic field, the strength of galactic magnetic fields at redshifts z > 0 remains uncertain.Here we report a measurement of a magnetic field of B ≈ 84 μG in a galaxy at z =0.692, using the same Zeeman-splitting technique that revealed an average value of B = 6 μG in the neutral interstellar gas of our Galaxy (Heiles et al. 2004). This is unexpected, as the leading theory of magnetic field generation, the mean-field dynamo model, predicts large-scale magnetic fields to be weaker in the past, rather than stronger (Parker 1970).The full text of this paper was published in Nature (Wolfe et al. 2008).

scholarly journals Effect of a magnetic field on the growth rate of the Rayleigh–Taylor instability of a laser-accelerated thin ablative surface

2004 ◽  
Vol 22 (1) ◽  
pp. 29-33 ◽  
Author(s):  
N. RUDRAIAH ◽  
B.S. KRISHNAMURTHY ◽  
A.S. JALAJA ◽  
TARA DESAI
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Transverse Magnetic Field ◽  
Plasma Layer ◽  
Fusion Energy ◽  
Transverse Magnetic ◽  
Taylor Instability ◽  
Electrically Conducting ◽  
Rayleigh Taylor Instability ◽  
Thin Plasma

The Rayleigh–Taylor instability (RTI) of a laser-accelerated ablative surface of a thin plasma layer in an inertial fusion energy (IFE) target with incompressible electrically conducting plasma in the presence of a transverse magnetic field is investigated using linear stability analysis. A simple theory based on Stokes-lubrication approximation is proposed. It is shown that the effect of a transverse magnetic field is to reduce the growth rate of RTI considerably over the value it would have in the absence of a magnetic field. This is useful in the extraction of IFE efficiently.

Modified Morris-Lecar neuron model: Effects of very low frequency electric fields and of magnetic fields on the local and network dynamics of an excitable media

2021 ◽  
Author(s):  
Karthikeyan Rajagopal ◽  
Irene Moroz ◽  
Balamurali Ramakrishnan ◽  
Anitha Karthikeyan ◽  
Prakash Duraisamy
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Electric Field ◽  
Neuron Model ◽  
Low Noise ◽  
Spiral Waves ◽  
Excitable Media ◽  
Field Frequency ◽  
Electric And Magnetic Fields ◽  
Electric Field Frequency

Abstract A Morris-Lecar neuron model is considered with Electric and Magnetic field effects where the electric field is a time varying sinusoid and magnetic field is simulated using an exponential flux memristor. We have shown that the exposure to electric and magnetic fields have significant effects on the neurons and have exhibited complex oscillations. The neurons exhibit a frequency-locked state for the periodic electric field and different ratios of frequency locked states with respect to the electric field frequency is also presented. To show the impact of the electric and magnetic fields on network of neurons, we have constructed different types of network and have shown the network wave propagation phenomenon. Interestingly the nodes exposed to both electric and magnetic fields exhibit more stable spiral waves compared to the nodes exhibited only to the magnetic fields. Also, when the number of layers are increased the range of electric field frequency for which the layers exhibit spiral waves also increase. Finally the noise effects on the field affected neuron network are discussed and multilayer networks supress spiral waves for a very low noise variance compared against the single layer network.

scholarly journals New Calibration Parameter for Observations of Transverse Solar Magnetic Fields in the Fe I 5324.19 Å Line

1993 ◽  
Vol 141 ◽  
pp. 196-198
Author(s):  
Weihong Song ◽  
Guoxiang Ai
Keyword(s):  
Magnetic Field ◽  
Numerical Analysis ◽  
Magnetic Fields ◽  
Computational Model ◽  
Transverse Magnetic Field ◽  
Transverse Magnetic ◽  
Square Root ◽  
Solar Magnetic Fields ◽  
Doppler Broadening ◽  
Theoretical And Numerical Analysis

AbstractAdopting the computational model of papers I and II (Song et al. 1990, 1992) we have found that for a better fit of the center of the Fe I 5324.19 Å line, the effect of turbulent Doppler broadening has to be taken into account. Through theoretical and numerical analysis we conclude that the square root of the modulus of Stokes Q and U is an appropiate observational parameter to represent the transverse magnetic field, since it is approximately linearly proportional to the strength of the transverse magnetic field for suitable positions of the filter passband.

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