Time scales and efficiency of resonant absorption in periodically driven resistive plasmas

The time scales and efficiency of plasma heating by resonant absorption of Alfvén waves are studied in the framework of linearized compressible and resistive magnetohydrodynamics. The configuration considered consists of a straight cylindrical axisymmetric plasma column surrounded by a vacuum region and a perfectly conducting shell. The plasma is excited periodically by an external source, located in the vacuum region. The temporal evolution of this driven system is simulated numerically. It is shown that the so-called ‘ideal quasi-modes’ (or ‘collective modes’) play a fundamental role in resonant absorption, and affect both the temporal evolution of the driven system and the efficiency of this heating mechanism considerably. The variation of the energetics in periodically driven resistive systems is analysed in detail for three different choices of the driving frequency, viz an arbitrary continuum frequency, the frequency of an ideal ‘quasi-mode’, and a discrete Alfvén wave frequency. The consequences for Alfvén wave heating of both laboratory plasmas and solar coronal loops are discussed.

Download Full-text

Alfvén-wave heating in resistive MHD

Journal of Plasma Physics ◽

10.1017/s0022377800014173 ◽

1989 ◽

Vol 42 (1) ◽

pp. 27-58 ◽

Cited By ~ 38

Author(s):

Stefaan Poedts ◽

Wolfgang Kerner ◽

Marcel Goossens

Keyword(s):

Stationary State ◽

Plasma Heating ◽

Resonant Absorption ◽

Energy Dissipation Rate ◽

Alfven Waves ◽

Alfven Wave ◽

Numerical Code ◽

Alfvén Waves ◽

Element Discretization ◽

Equilibrium Profiles

Resonant absorption of Alfvén waves in tokamak plasmas is studied numerically using the linearized equations of resistive magnetohydrodynamics. A numerical code based on a finite-element discretization is used for determining the stationary state of a cylindrical plasma column that is excited by an external periodic driver. The energy dissipation rate in the stationary state is calculated and the dependence of the plasma heating on electrical resistivity, the equilibrium profiles, and the wavenumbers and frequency of the external driver is investigated. Resonant absorption is extremely efficient when the plasma is excited with a frequency near that of a so-called ‘collective mode’. The heating of a plasma by driving it at the frequencies of discrete Alfvén waves is also investigated.

Download Full-text

Systematic study of magnetar outbursts

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317007323 ◽

2017 ◽

Vol 13 (S337) ◽

pp. 326-327

Author(s):

Francesco Coti Zelati

Keyword(s):

Time Scales ◽

Systematic Study ◽

Decay Time ◽

Temporal Evolution ◽

Triggering Mechanism ◽

X Ray ◽

Characteristic Decay Time

AbstractWe present the results of a systematic study of all magnetar outbursts observed to date through a reanalysis of data acquired in about 1100 X-ray observations. We track the temporal evolution of the luminosity for all these events, model empirically their decays, and estimate the characteristic decay time-scales and the energy involved. We study the link between different parameters, and reveal several correlations between different quantities. We discuss our results in the framework of the models proposed to explain the triggering mechanism and evolution of magnetar outbursts.

Download Full-text

Ion-scale break of the plasma fluctuation spectra in different large-scale solar wind streams

10.5194/egusphere-egu21-13569 ◽

2021 ◽

Author(s):

Maria Riazantseva ◽

Liudmila Rakhmanova ◽

Yuri Yermolaev ◽

Irina Lodkina ◽

Georgy Zastenker ◽

...

Keyword(s):

Solar Wind ◽

Large Scale ◽

Plasma Heating ◽

Coronal Holes ◽

Magnetic Clouds ◽

Alfven Wave ◽

Slow Solar Wind ◽

P Value ◽

High Temporal Resolution ◽

Turbulent Cascade

<p>Appearance of measurements of the interplanetary medium parameters with high temporal resolution gave rise to a variety of investigations of turbulent cascade at ion kinetic scales at which processes of plasma heating was believed to operate. Our recent studies based on high frequency plasma measurements at Spektr-R spacecraft have shown that the turbulent cascade was not stable and dynamically changed depending on the plasma conditions in different large-scale solar wind structures. These changes was most significant at the kinetic scales of the turbulent cascade. Slow undisturbed solar wind was characterized by the consistency of the spectra to the predictions of the kinetic Alfven wave turbulence model. On the other hand, the discrepancy between the model predictions and registered spectra were found in stream interaction regions characterized by crucial steepening of spectra at the kinetic scales with slopes having values up to -(4-5). This discrepancy was clearly shown for plasma compression region Sheath in front of the magnetic clouds and CIR in front of high speed streams associated with coronal holes. Present study is focused on the break preceding the kinetic scales. Currently the characteristic plasma parameters associated with the formation of the break is still debated. Number of studies demonstrated that the break was consistent with distinct characteristic frequencies for different values &#8203;&#8203;of the plasma proton parameter beta &#946;p. Present study consider the ratio between the break frequency determined for ion flux fluctuation spectra according to Spektr-R data and several characteristic plasma frequencies used traditionally in such cases. The value of this ratio is statistically compared for different large-scale solar wind streams. We analyze both the classical spectrum view with two slopes and one break and the spectrum with flattening between magnetohydrodynamic and kinetic scales.&#160; Our results show that for the Sheath and CIR regions characterized typically by &#946;p &#8804;1 the break corresponds statistically to the frequency determined by the proton gyroradius. At the same time such correspondence are not observed either for the undisturbed slow solar wind with similar &#946;p value or for disturbed flows associated with interplanetary manifestations of coronal mass ejections, where &#946;p << 1. The results also shows that in slow undisturbed solar wind the break is closer to the frequency determined by the inertial proton length. Thus, apparently the transition between streams of different speeds may result in the change of dissipation regimes and plays role in plasma heating at these areas. This work was supported by the RFBR grant No. 19-02-00177a</p>

Download Full-text

High-speed shear-driven dynamos. Part 1. Asymptotic analysis

Journal of Fluid Mechanics ◽

10.1017/jfm.2019.178 ◽

2019 ◽

Vol 868 ◽

pp. 176-211 ◽

Cited By ~ 4

Author(s):

Kengo Deguchi

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Solar Phys ◽

Wave Interaction ◽

Resonant Absorption ◽

Base Flow ◽

Transition To Turbulence ◽

Alfven Wave ◽

Hydrodynamic Theory ◽

Large Reynolds Number

Rational large Reynolds number matched asymptotic expansions of three-dimensional nonlinear magneto-hydrodynamic (MHD) states are the concern of this contribution. The nonlinear MHD states, assumed to be predominantly driven by a unidirectional shear, can be sustained without any linear instability of the base flow and hence are responsible for subcritical transition to turbulence. Two classes of nonlinear MHD states are found. The first class of nonlinear states emerged out of a nice combination of the purely hydrodynamic vortex/wave interaction theory by Hall & Smith (J. Fluid Mech., vol. 227, 1991, pp. 641–666) and the resonant absorption theories on Alfvén waves, developed in the solar physics community (e.g. Sakurai et al. Solar Phys., vol. 133, 1991, pp. 227–245; Goossens et al. Solar Phys., vol. 157, 1995, pp. 75–102). Similar to the hydrodynamic theory, the mechanism of the MHD states can be explained by the successive interaction of the roll, streak and wave fields, which are now defined both for the hydrodynamic and magnetic fields. The derivation of this ‘vortex/Alfvén wave interaction’ state is rather straightforward as the scalings for both of the hydrodynamic and magnetic fields are identical. It turns out that the leading-order magnetic field of the asymptotic states appears only when a small external magnetic field is present. However, it does not mean that purely shear-driven dynamos are not possible. In fact, the second class of ‘self-sustained shear-driven dynamo theory’ shows a magnetic generation that is slightly smaller in size in the absence of any external field. Despite its small size, the magnetic field causes the novel feedback mechanism in the velocity field through resonant absorption, wherein the magnetic wave becomes more strongly amplified than the hydrodynamic counterpart.

Download Full-text

Excitation of kinetic Alfvén turbulence by MHD waves and energization of space plasmas

Nonlinear Processes in Geophysics ◽

10.5194/npg-11-535-2004 ◽

2004 ◽

Vol 11 (5/6) ◽

pp. 535-543 ◽

Cited By ~ 23

Author(s):

Y. Voitenko ◽

M. Goossens

Keyword(s):

Magnetic Field ◽

Large Scale ◽

Energy Transport ◽

Plasma Heating ◽

Alfven Wave ◽

Mhd Waves ◽

Space Plasmas ◽

Small Scale ◽

The Magnetic Field ◽

Dissipation Range

Abstract. There is abundant observational evidence that the energization of plasma particles in space is correlated with an enhanced activity of large-scale MHD waves. Since these waves cannot interact with particles, we need to find ways for these MHD waves to transport energy in the dissipation range formed by small-scale or high-frequency waves, which are able to interact with particles. In this paper we consider the dissipation range formed by the kinetic Alfvén waves (KAWs) which are very short- wavelengths across the magnetic field irrespectively of their frequency. We study a nonlocal nonlinear mechanism for the excitation of KAWs by MHD waves via resonant decay AW(FW)→KAW1+KAW2, where the MHD wave can be either an Alfvén wave (AW), or a fast magneto-acoustic wave (FW). The resonant decay thus provides a non-local energy transport from large scales directly in the dissipation range. The decay is efficient at low amplitudes of the magnetic field in the MHD waves, B/B0~10-2. In turn, KAWs are very efficient in the energy exchange with plasma particles, providing plasma heating and acceleration in a variety of space plasmas. An anisotropic energy deposition in the field-aligned degree of freedom for the electrons, and in the cross-field degrees of freedom for the ions, is typical for KAWs. A few relevant examples are discussed concerning nonlinear excitation of KAWs by the MHD wave flux and consequent plasma energization in the solar corona and terrestrial magnetosphere.

Download Full-text

Plasma Heating by Alfvén Waves - Kinetic Properties of Magnetohydrodynamic Disturbances

Symposium - International Astronomical Union ◽

10.1017/s0074180900075860 ◽

1985 ◽

Vol 107 ◽

pp. 381-389

Author(s):

Akira Hasegawa

Keyword(s):

Electric Field ◽

Plasma Heating ◽

Alfven Wave ◽

Larmor Radius ◽

Alfvén Waves ◽

Kinetic Properties ◽

Parallel Electric Field ◽

Astrophysical Plasmas ◽

Finite Larmor Radius ◽

Wave Heating

Mechanisms of Alfvén wave heating in space-astrophysical plasmas are presented with particular emphasis on the parallel electric field generated in the magnetohydrodynamic perturbations due to the finite Larmor radius effects.

Download Full-text