On the interpretation and applicability of<i>κ</i>-distributions

Lazar, M.; Fichtner, H.; Yoon, Peter H.

doi:10.1051/0004-6361/201527593

Cited by 109 publications

(111 citation statements)

References 19 publications

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“…first and second kinds, and forms where either the "temperature" or "thermal velocity" is kappa dependent e.g. Lazar et al (2016), Livadiotis (2015Livadiotis ( , 2014, Livadiotis & McComas (2009), Hellberg et al (2009), Leubner (2004. The physical interpretation of the value of κ obtained from the line fitting, in terms of the ion velocity distribution, therefore depends on the form of the ion kappa distribution used.…”

Section: Non-thermal Ion Motionmentioning

confidence: 99%

First evidence of non-Gaussian solar flare EUV spectral line profiles and accelerated non-thermal ion motion

Jeffrey

Fletcher

Labrosse

2016

A&A

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Context. The properties of solar flare plasma can be determined from the observation of optically thin lines. The emitting ion distribution determines the shape of the spectral line profile, with an isothermal Maxwellian ion distribution producing a Gaussian profile. Non-Gaussian line profiles may indicate more complex ion distributions. Aims. We investigate the possibility of determining flare-accelerated non-thermal ion and/or plasma velocity distributions. Methods. We study EUV spectral lines produced during a flare SOL2013-05-15T01:45 using the Hinode EUV Imaging Spectrometer (EIS). The flare is located close to the eastern solar limb with an extended loop structure, allowing the different flare features: ribbons, hard X-ray (HXR) footpoints and the loop-top source to be clearly observed in UV, EUV and X-rays. EUV line spectroscopy is performed in seven different regions covering the flare. We study the line profiles of the isolated and unblended Fe XVI lines (λ262.9760 Å ) mainly formed at temperatures of ∼2 to 4 MK. Suitable Fe XVI line profiles at one time close to the peak soft X-ray emission and free of directed mass motions are examined using: 1. a higher moments analysis, 2. Gaussian fitting, and 3. by fitting a kappa distribution line profile convolved with a Gaussian to account for the EIS instrumental profile. Results. Fe XVI line profiles in the flaring loop-top, HXR footpoint and ribbon regions can be confidently fitted with a kappa line profile with an extra variable κ, giving low, non-thermal κ values between 2 and 3.3. An independent higher moments analysis also finds that many of the spectral line kurtosis values are higher than the Gaussian value of 3, even with the presence of a broad Gaussian instrumental profile. Conclusions. A flare-accelerated non-thermal ion population could account for both the observed non-Gaussian line profiles, and for the Fe XVI "excess" broadening found from Gaussian fitting, if the emitting ions are interacting with a thermalised ∼4 MK electron population, and the instrumental profile is well-approximated by a Gaussian profile.

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Section: Non-thermal Ion Motionmentioning

confidence: 99%

First evidence of non-Gaussian solar flare EUV spectral line profiles and accelerated non-thermal ion motion

Jeffrey

Fletcher

Labrosse

2016

A&A

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“…We have invetigated the effects of suprathermal populations on the plasma waves and instabilities using two alternative approaches, which assume the effective temperature to be either constant (Lazar et al 2011;Mace et al 2011;Lazar 2012), or increasing with the increase of suprathermal populations, i.e., with decreasing the power-index κ (Luebner and Schupfer 2000; Lazar et al 2015Lazar et al , 2016. Being more convenient computationally the approach with a κ-independent temperature has been widely invoked in similar theoretical predictions of plasma instabilities.…”

Section: Governing Dispersion Relationmentioning

confidence: 99%

“…Being more convenient computationally the approach with a κ-independent temperature has been widely invoked in similar theoretical predictions of plasma instabilities. However, have recently shown and Lazar et al (2016) have extended the comparative analysis to add supplementary arguments that a Kappa model with the effective temperature increasing with growing suprathermal population, i.e., with decreasing value of the power index κ, reproduces much better the Maxwellian core in the limit κ → ∞, and thus enables a more realistic characterization of the suprathermal populations and their destabilizing effects. For a collisionless and homogenous electron-proton plasma described by the distributions (1)-(6), the dispersion relations for the electromagnetic modes propagating parallel to the stationary magnetic field read…”

Section: Governing Dispersion Relationmentioning

confidence: 99%

Effects of suprathermal electrons on the proton temperature anisotropy in space plasmas: Electromagnetic ion-cyclotron instability

Shaaban

Lazar

Poedts³

et al. 2016

Astrophys Space Sci

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In collision-poor plasmas from space, e.g., the solar wind and planetary magnetospheres, the kinetic anisotropy of the plasma particles is expected to be regulated by the kinetic instabilities. Driven by an excess of ion (proton) temperature perpendicular to the magnetic field (T ⊥ > T ), the electromagnetic ion-cyclotron (EMIC) instability is fast enough to constrain the proton anisotropy, but the observations do not conform to the instability thresholds predicted by the standard theory for bi-Maxwellian models of the plasma particles. This paper presents an extended investigation of the EMIC instability in the presence of suprathermal electrons which are ubiquitous in these environments. The analysis is based on the kinetic (Vlasov-Maxwell) theory assuming that both species, protons and electrons, may be anisotropic, and the EMIC unstable solutions are derived numerically providing an accurate description for conditions typically encountered in space plasmas. The effects of suprathermal populations are triggered by the electron anisotropy and the temperature contrast between electrons and protons. For certain conditions the anisotropy thresholds exceed the limits of the proton anisotropy measured in the solar wind considerably restraining the unstable regimes of the EMIC modes.

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“…The effects of a varying κ (including the Maxwellian limit κ → ∞) are also easier to parametrize if temperature is taken constant. However, for studies intended to outline the effects of suprathermal populations, Lazar et al (2015aLazar et al ( , 2016a have shown that only the approach assuming a κ-dependent temperature may provide a fairly rigorous comparison of the global Kappa describing the observed distribution, with the cooler Maxwellian κ → ∞ limit reproducing the core of the distribution. Moreover, only in this case the instabilities driven by the kinetic anisotropies of plasma particles are systematically stimulated by the suprathermals (i.e., lowering the values of κ), confirming the expectation that these populations should contribute with an additional free energy (Lazar et al 2015a(Lazar et al , 2016b.…”

Section: Introductionmentioning

confidence: 99%

“…However, a global Kappa does not always provide a good fit to the observed distributions, as we will arXiv:1703.01459v1 [physics.plasm-ph] 4 Mar 2017 see here below, e.g., the analysis in section 2 (also Figs. 1 and 2), which suggests that a global Kappa is just a simplified (or idealized) approach that artificially constrains the core and suprathermal populations to be described by the same parameters, e.g., density, temperature, anisotropy (not fully justified yet, although some studies in this direction have been done by Leubner (2004); Lazar et al (2015aLazar et al ( , 2016a). It may be, therefore, that fitting measurements of the observed distributions with global Kappa models can not provide relevant evidences to support any of the two alternatives of a temperature either dependent or independent of the power-index κ.…”

Section: Introductionmentioning

confidence: 99%

Dual Maxwellian-Kappa modeling of the solar wind electrons: new clues on the temperature of Kappa populations

Lazar

Pierrard

Shaaban

et al. 2017

A&A

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Context. Recent studies on Kappa distribution functions invoked in space plasma applications have emphasized two alternative approaches which may assume the temperature parameter either dependent or independent of the power-index κ. Each of them can obtain justification in different scenarios involving Kappa-distributed plasmas, but direct evidences supporting any of these two alternatives with measurements from laboratory or natural plasmas are not available yet. Aims. This paper aims to provide more facts on this intriguing issue from direct fitting measurements of suprathermal electron populations present in the solar wind, as well as from their destabilizing effects predicted by these two alternating approaches. Methods. Two fitting models are contrasted, namely, the global Kappa and the dual Maxwellian-Kappa models, which are currently invoked in theory and observations. The destabilizing effects of suprathermal electrons are characterized on the basis of a kinetic approach which accounts for the microscopic details of the velocity distribution. Results. In order to be relevant, the model is chosen to accurately reproduce the observed distributions and this is achieved by a dual Maxwellian-Kappa distribution function. A statistical survey indicates a κ-dependent temperature of the suprathermal (halo) electrons for any heliocentric distance. Only for this approach the instabilities driven by the temperature anisotropy are found to be systematically stimulated by the abundance of suprathermal populations, i.e., lowering the values of κ-index.

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On the interpretation and applicability ofκ-distributions

Cited by 109 publications

References 19 publications

First evidence of non-Gaussian solar flare EUV spectral line profiles and accelerated non-thermal ion motion

First evidence of non-Gaussian solar flare EUV spectral line profiles and accelerated non-thermal ion motion

Effects of suprathermal electrons on the proton temperature anisotropy in space plasmas: Electromagnetic ion-cyclotron instability

Dual Maxwellian-Kappa modeling of the solar wind electrons: new clues on the temperature of Kappa populations

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