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Elena Dzifcakova - One of the best experts on this subject based on the ideXlab platform.
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plasma diagnostics from active region and quiet sun spectra observed by hinode eis quantifying the departures from a Maxwellian Distribution
arXiv: Solar and Stellar Astrophysics, 2020Co-Authors: Juraj Lörinčík, Elena Dzifcakova, Jaroslav Dudík, Giulio Del Zanna, Helen E. MasonAbstract:We perform plasma diagnostics, including that of the non-Maxwellian $\kappa$-Distributions, in several structures observed in the solar corona by the Extreme-Ultraviolet Imaging Spectrometer (EIS) onboard the Hinode spacecraft. To prevent uncertainties due to the in-flight calibration of EIS, we selected spectral atlases observed shortly after the launch of the mission. One spectral atlas contains an observation of an active region, while the other is an off-limb quiet Sun region. To minimize the uncertainties of the diagnostics, we rely only on strong lines and we average the signal over a spatial area within selected structures. Multiple plasma parameters are diagnosed, such as the electron density, differential emission measure, and the non-Maxwellian parameter $\kappa$. To do that, we use a simple, well-converging iterative scheme based on refining the initial density estimates via the DEM and $\kappa$. We find that while the quiet Sun spectra are consistent with a Maxwellian Distribution, the coronal loops and moss observed within active region are strongly non-Maxwellian with $\kappa$ $\lessapprox$ 3. These results were checked by calculating synthetic ratios using DEMs obtained as a function of $\kappa$. Ratios predicted using the DEMs assuming $\kappa$-Distributions converged to the ratios observed in the quiet Sun and coronal loops. To our knowledge, this work presents a strong evidence of a presence of different electron Distributions between two physically distinct parts of the solar corona.
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Plasma Diagnostics From Active Region and Quiet Sun Spectra Observed by Hinode/EIS: Quantifying the Departures from a Maxwellian Distribution.
arXiv: Solar and Stellar Astrophysics, 2020Co-Authors: Juraj Lörinčík, Elena Dzifcakova, Jaroslav Dudík, Giulio Del Zanna, Helen E. MasonAbstract:We perform plasma diagnostics, including that of the non-Maxwellian $\kappa$-Distributions, in several structures observed in the solar corona by the Extreme-Ultraviolet Imaging Spectrometer (EIS) onboard the Hinode spacecraft. To prevent uncertainties due to the in-flight calibration of EIS, we selected spectral atlases observed shortly after the launch of the mission. One spectral atlas contains an observation of an active region, while the other is an off-limb quiet Sun region. To minimize the uncertainties of the diagnostics, we rely only on strong lines and we average the signal over a spatial area within selected structures. Multiple plasma parameters are diagnosed, such as the electron density, differential emission measure, and the non-Maxwellian parameter $\kappa$. To do that, we use a simple, well-converging iterative scheme based on refining the initial density estimates via the DEM and $\kappa$. We find that while the quiet Sun spectra are consistent with a Maxwellian Distribution, the coronal loops and moss observed within active region are strongly non-Maxwellian with $\kappa$ $\lessapprox$ 3. These results were checked by calculating synthetic ratios using DEMs obtained as a function of $\kappa$. Ratios predicted using the DEMs assuming $\kappa$-Distributions converged to the ratios observed in the quiet Sun and coronal loops. To our knowledge, this work presents a strong evidence of a presence of different electron Distributions between two physically distinct parts of the solar corona.
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The Updated fe Ionization Equilibrium for the Electron K-Distributions
Solar Physics, 2002Co-Authors: Elena DzifcakovaAbstract:In the past few years new calculations of the ionization and recombination rates have been published. The new Fe ionization equilibrium for these new rates is available for a Maxwellian Distribution. Therefore the updated Fe ionization equilibrium for the non-thermal κ-Distribution with an enhanced number of particles in the high-energy tail is presented. Results for the various deviations from a Maxwellian Distribution are given in tabular form and these are compared with previous ones. A method for the determination of an energy Distribution different from the Maxwellian one is suggested.
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The Ionization Equilibrium in the Solar Corona for the Electron Power Distribution
Solar Physics, 1998Co-Authors: Elena DzifcakovaAbstract:The influence of an electron non-Maxwellian Distribution (power Distribution) on the ionization equilibrium of Fe in the solar corona is demonstrated. The results can be used for specific applications in the solar corona, especially in the description of the ionization state of plasma during the impulsive phase of solar flares, where deviations from the Maxwellian Distribution may be significant.
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the fe ionization equilibrium in the solar corona with a non Maxwellian Distribution function
1991Co-Authors: Elena DzifcakovaAbstract:It is shown that for ionization equilibria in the solar transition layer and corona, non-Maxwellian Distribution functions are important.
M. N. S. Qureshi - One of the best experts on this subject based on the ideXlab platform.
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Whistler waves with electron temperature anisotropy and non-Maxwellian Distribution functions
AIP Advances, 2018Co-Authors: M. Usman Malik, M. N. S. Qureshi, W. Masood, Arshad M. MirzaAbstract:The previous works on whistler waves with electron temperature anisotropy narrated the dependence on plasma parameters, however, they did not explore the reasons behind the observed differences. A comparative analysis of the whistler waves with different electron Distributions has not been made to date. This paper attempts to address both these issues in detail by making a detailed comparison of the dispersion relations and growth rates of whistler waves with electron temperature anisotropy for Maxwellian, Cairns, kappa and generalized (r, q) Distributions by varying the key plasma parameters for the problem under consideration. It has been found that the growth rate of whistler instability is maximum for flat-topped Distribution whereas it is minimum for the Maxwellian Distribution. This work not only summarizes and complements the previous work done on the whistler waves with electron temperature anisotropy but also provides a general framework to understand the linear propagation of whistler waves with electron temperature anisotropy that is applicable in all regions of space plasmas where the satellite missions have indicated their presence.The previous works on whistler waves with electron temperature anisotropy narrated the dependence on plasma parameters, however, they did not explore the reasons behind the observed differences. A comparative analysis of the whistler waves with different electron Distributions has not been made to date. This paper attempts to address both these issues in detail by making a detailed comparison of the dispersion relations and growth rates of whistler waves with electron temperature anisotropy for Maxwellian, Cairns, kappa and generalized (r, q) Distributions by varying the key plasma parameters for the problem under consideration. It has been found that the growth rate of whistler instability is maximum for flat-topped Distribution whereas it is minimum for the Maxwellian Distribution. This work not only summarizes and complements the previous work done on the whistler waves with electron temperature anisotropy but also provides a general framework to understand the linear propagation of whistler waves with...
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Whistler waves in magnetosheath with observed flat top Distributions
2015 IEEE International Conference on Plasma Sciences (ICOPS), 2015Co-Authors: M. N. S. QureshiAbstract:Whistler waves having frequencies nearly centered around 100 Hz are frequently observed in the magnetosheath. Cluster observed such low frequency Whistler waves named as Lion roars and electron velocity Distribution function within the magnetosheath during its several crossings. The observed electron velocity Distribution functions clearly show non-Maxwellian feature such as flat tops at low energies. These observed lion roars were studied and interpreted using bi-Maxwellian Distribution function by employing the kinetic theory but could not justify the observations both quantitatively as well as qualitatively. The obvious reason was to employ idealized Maxwellian Distribution function instead of using non-Maxwellian Distribution function. We derived the dispersion relation of Whistler waves by using generalized (r, q) Distribution function which is the generalized form of kappa and Maxwellian Distribution functions. It is supposed to be the best Distribution when the real Distributions contain flat tops. We employed kinetic theory to obtain the modified expressions for real frequency and established the necessary and sufficient condition to achieve growth/damping rates based on the generalized (r, q) Distribution function. We then compare our numerical values of real and damping/growth rates with the Cluster observations, a good quantitative and qualitative agreement between the observed and theoretically obtained values have been found.
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Terrestrial lion roars and non‐Maxwellian Distribution
Journal of Geophysical Research: Space Physics, 2014Co-Authors: M. N. S. Qureshi, H. A. Shah, Warda Nasir, W. Masood, Peter H. Yoon, Steven J. SchwartzAbstract:Lion roars are low-frequency (∼100 Hz) whistler waves frequently observed in the Earth's magnetosheath. By analyzing both wave and electron data from the Cluster spacecraft, and comparing with linear Vlasov kinetic theory, Masood et al. (2006) investigated the underlying cause of the lion roar generation. However, the analysis based upon the bi-Maxwellian Distribution function did not adequately explain the observations qualitatively as well as quantitatively. This outstanding problem is revisited in the present paper, and a resolution is put forth in which, the flat-top non-Maxwellian Distribution function with a velocity power law energetic tail, known as the (r,q) Distribution, or the generalized kappa Distribution is employed. Upon carrying out the linear stability analysis of the (r,q) Distribution against the whistler wave perturbation, and upon comparison with the Cluster data, good qualitative and quantitative agreements are found between theory and data.
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terrestrial lion roars and non Maxwellian Distribution
Journal of Geophysical Research, 2014Co-Authors: M. N. S. Qureshi, H. A. Shah, Warda Nasir, W. Masood, Peter H. Yoon, Steven J. SchwartzAbstract:Lion roars are low-frequency (∼100 Hz) whistler waves frequently observed in the Earth's magnetosheath. By analyzing both wave and electron data from the Cluster spacecraft, and comparing with linear Vlasov kinetic theory, Masood et al. (2006) investigated the underlying cause of the lion roar generation. However, the analysis based upon the bi-Maxwellian Distribution function did not adequately explain the observations qualitatively as well as quantitatively. This outstanding problem is revisited in the present paper, and a resolution is put forth in which, the flat-top non-Maxwellian Distribution function with a velocity power law energetic tail, known as the (r,q) Distribution, or the generalized kappa Distribution is employed. Upon carrying out the linear stability analysis of the (r,q) Distribution against the whistler wave perturbation, and upon comparison with the Cluster data, good qualitative and quantitative agreements are found between theory and data.
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Landau Damping in Space Plasmas with Two Electron Temperature Non-Maxwellian Distribution Functions
Journal of Physics: Conference Series, 2014Co-Authors: M. N. S. Qureshi, Sumbul Sehar, H. A. ShahAbstract:Space plasmas generally posses Distribution functions that exhibit high or super thermal energy tails in velocity space which can have different temperatures, a dense cold population and a hot population. Moreover, in laboratory plasmas when a laser or electron beam is passed through a dense plasma, hot low density electron populations can be generated. Presence of such low density electron Distributions can act to increase the magnitude of the wave damping rate. In this paper we employ non-Maxwellian Distribution function such as the generalized (r, q) Distribution function with two electron temperatures to study the Landau damping of electrostatic waves. The results show that the Landau damping increases significantly when the percentage of high energy particles increases and with the increase of the high energy tail and less pronounced shoulders in the profile of the Distribution function.
Ghulam Murtaza - One of the best experts on this subject based on the ideXlab platform.
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Weibel instability with semirelativistic Maxwellian Distribution function
Physics of Plasmas, 2007Co-Authors: S. Zaheer, Ghulam MurtazaAbstract:A macroscopic description of the linear Weibel instability, based on semirelativistic Distribution in an unmagnetized plasma is presented. In particular, analytical expressions are derived for the real and imaginary parts of the dielectric constant for the Maxwellian and semirelativistic Maxwellian Distribution functions under the conditions of ξ=ωk‖θ‖≫1 and ≪1. The real frequency and the growth rate of the instability for the semirelativistic case now depends upon the factor χ generated from the relativistic term in the Distribution function. The presence of χ which is always greater than unity favors the Weibel instability to occur even for the small anisotropy of temperature. As we increase the value of χ large enough that it dominates over other terms, the damping changes into growth. In the limiting case, i.e., χ=1, the results approach the Maxwellian situation.
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Weibel instability with non-Maxwellian Distribution functions
Physics of Plasmas, 2007Co-Authors: S. Zaheer, Ghulam MurtazaAbstract:The Weibel instability in an unmagnetized plasma is investigated for non-Maxwellian Distribution functions. In particular, analytical expressions are derived for the real and imaginary parts of the dielectric constant for the Maxwellian, kappa (κ), and (r,q) Distribution functions under the conditions of ξ=ω∕k‖θ‖⪢1 and ⪡1. The real frequency and the growth rate of the instability now depend upon the values of the spectral indices of the Distribution functions. In general, the growth rate is suppressed for small values of κ and q (keeping r fixed) and for negative values of r (keeping q fixed) instability transforms into damping. In the limiting cases (i) κ→∞ and (ii) r=0, q→∞, the results approach to the Maxwellian situation.
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dust charge fluctuations with non Maxwellian Distribution functions
Physica Scripta, 2006Co-Authors: N Rubab, Ghulam MurtazaAbstract:Dust grains immersed in a plasma can exhibit charge fluctuations in response to the oscillatory plasma currents flowing onto them. The fluctuation electrodynamics of dusty plasmas are determined by taking into account the dynamics of charging processes associated with plasma currents. Expressions for the charging currents are derived using kappa and generalized (r, q) Distribution functions. The dispersion relation of dust-acoustic waves is modified while taking into account these Distribution functions. Further, it is found that in the limit (i) r = 0, q → ∞ and (ii) κ → ∞, the expressions of the current modified with (r, q) and kappa Distributions reduce to the Maxwellian current.
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Some electrostatic modes based on non-Maxwellian Distribution functions
Physics of Plasmas, 2004Co-Authors: S. Zaheer, Ghulam Murtaza, H. A. ShahAbstract:A comparative study of fundamental modes such as Langmuir waves, dust ion acoustic waves, and dust-acoustic waves using non-Maxwellian Distribution functions is presented. The real frequency and the growth rate of the modes are calculated by using kappa and generalized (r,q) Distribution functions and results are compared with those of Maxwellian Distribution. It is noted that in the limit (i) r=0, q→∞ for generalized (r,q) Distributions and (ii) κ→∞ for kappa Distributions, the non-Maxwellian functions reduce to Maxwellian.
H. A. Shah - One of the best experts on this subject based on the ideXlab platform.
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Terrestrial lion roars and non‐Maxwellian Distribution
Journal of Geophysical Research: Space Physics, 2014Co-Authors: M. N. S. Qureshi, H. A. Shah, Warda Nasir, W. Masood, Peter H. Yoon, Steven J. SchwartzAbstract:Lion roars are low-frequency (∼100 Hz) whistler waves frequently observed in the Earth's magnetosheath. By analyzing both wave and electron data from the Cluster spacecraft, and comparing with linear Vlasov kinetic theory, Masood et al. (2006) investigated the underlying cause of the lion roar generation. However, the analysis based upon the bi-Maxwellian Distribution function did not adequately explain the observations qualitatively as well as quantitatively. This outstanding problem is revisited in the present paper, and a resolution is put forth in which, the flat-top non-Maxwellian Distribution function with a velocity power law energetic tail, known as the (r,q) Distribution, or the generalized kappa Distribution is employed. Upon carrying out the linear stability analysis of the (r,q) Distribution against the whistler wave perturbation, and upon comparison with the Cluster data, good qualitative and quantitative agreements are found between theory and data.
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terrestrial lion roars and non Maxwellian Distribution
Journal of Geophysical Research, 2014Co-Authors: M. N. S. Qureshi, H. A. Shah, Warda Nasir, W. Masood, Peter H. Yoon, Steven J. SchwartzAbstract:Lion roars are low-frequency (∼100 Hz) whistler waves frequently observed in the Earth's magnetosheath. By analyzing both wave and electron data from the Cluster spacecraft, and comparing with linear Vlasov kinetic theory, Masood et al. (2006) investigated the underlying cause of the lion roar generation. However, the analysis based upon the bi-Maxwellian Distribution function did not adequately explain the observations qualitatively as well as quantitatively. This outstanding problem is revisited in the present paper, and a resolution is put forth in which, the flat-top non-Maxwellian Distribution function with a velocity power law energetic tail, known as the (r,q) Distribution, or the generalized kappa Distribution is employed. Upon carrying out the linear stability analysis of the (r,q) Distribution against the whistler wave perturbation, and upon comparison with the Cluster data, good qualitative and quantitative agreements are found between theory and data.
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Landau Damping in Space Plasmas with Two Electron Temperature Non-Maxwellian Distribution Functions
Journal of Physics: Conference Series, 2014Co-Authors: M. N. S. Qureshi, Sumbul Sehar, H. A. ShahAbstract:Space plasmas generally posses Distribution functions that exhibit high or super thermal energy tails in velocity space which can have different temperatures, a dense cold population and a hot population. Moreover, in laboratory plasmas when a laser or electron beam is passed through a dense plasma, hot low density electron populations can be generated. Presence of such low density electron Distributions can act to increase the magnitude of the wave damping rate. In this paper we employ non-Maxwellian Distribution function such as the generalized (r, q) Distribution function with two electron temperatures to study the Landau damping of electrostatic waves. The results show that the Landau damping increases significantly when the percentage of high energy particles increases and with the increase of the high energy tail and less pronounced shoulders in the profile of the Distribution function.
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Nonlinear Landau damping of high frequency waves in non-Maxwellian plasmas
Chinese Physics B, 2013Co-Authors: M. N. S. Qureshi, Sumbul Sehar, Shi Jingyuan, H. A. ShahAbstract:Space plasmas often possess non-Maxwellian Distribution functions which have a significant effect on the plasma waves. When a laser or electron beam passes through a dense plasma, hot low density electron populations can be generated to alter the wave damping/growth rate. In this paper, we present theoretical analysis of the nonlinear Landau damping for Langmuir waves in a plasma where two electron populations are found. The results show a marked difference between the Maxwellian and non-Maxwellian instantaneous damping rates when we employ a non-Maxwellian Distribution function called the generalized (r, q) Distribution function, which is the generalized form of the kappa and Maxwellian Distribution functions. In the limiting case of r = 0 and q → ∞, it reduces to the classical Maxwellian Distribution function, and when r = 0 and q → κ + 1, it reduces to the kappa Distribution function.
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Effect on Landau damping rates for a non-Maxwellian Distribution function consisting of two electron populations
Chinese Physics B, 2013Co-Authors: M. N. S. Qureshi, H. A. Shah, Sumbul Sehar, J. B. CaoAbstract:In many physical situations where a laser or electron beam passes through a dense plasma, hot low-density electron populations can be generated, resulting in a particle Distribution function consisting of a dense cold population and a small hot population. Presence of such low-density electron Distributions can alter the wave damping rate. A kinetic model is employed to study the Landau damping of Langmuir waves when a small hot electron population is present in the dense cold electron population with non-Maxwellian Distribution functions. Departure of plasma from Maxwellian Distributions significantly alters the damping rates as compared to the Maxwellian plasma. Strong damping is found for highly non-Maxwellian Distributions as well as plasmas with a higher density and hot electron population. Existence of weak damping is also established when the Distribution contains broadened flat tops at the low energies or tends to be Maxwellian. These results may be applied in both experimental and space physics regimes.
Chin-wook Chung - One of the best experts on this subject based on the ideXlab platform.
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Relatively high plasma density in low pressure inductive discharges
Physics of Plasmas, 2015Co-Authors: Hyun-ju Kang, Yu-sin Kim, Chin-wook ChungAbstract:Electron energy probability functions (EEPFs) were measured in a low pressure argon inductive discharge. As radio frequency (RF) power increases, discharge mode is changed from E-mode (capacitively coupled) to H-mode (inductively coupled) and the EEPFs evolve from a bi-Maxwellian Distribution to a Maxwellian Distribution. It is found that the plasma densities at low RF powers (
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Power dependence of electron density at various pressures in inductively coupled plasmas
Physics of Plasmas, 2014Co-Authors: June Young Kim, Dong-hwan Kim, Ju-ho Kim, Sang Bum Jeon, Sung Won Cho, Chin-wook ChungAbstract:Experimental observation of the electron density variation in inductively coupled plasmas with the electron energy probability function (EEPFs) was performed at various gas pressures at two RF powers (25 W and 200 W). The measured EEPFs at high power discharges (200 W) showed a Maxwellian Distribution, while evolution of the EEPFs from a bi-Maxwellian Distribution to a Druyvesteyn-like Distribution was observed at low RF powers (25 W) with increasing pressure. A discrepancy of the electron density variation between the two RF powers was observed. This difference is explained by the modified collisional loss and the Bohm velocity from the EEPF of the bi-Maxwellian Distribution and the Druyvesteyn–like Distribution.
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effect of adding small amount of inductive fields to o2 ar o2 capacitively coupled plasmas
Journal of Applied Physics, 2012Co-Authors: Chin-wook ChungAbstract:Electron energy Distribution functions (EEDFs) of low pressure O2 plasma were measured by adding small amount of coil power in a capacitive discharge. When the plasma was generated by bias power only, the measured EEDF showed a bi-Maxwellian Distribution. However, when a very small coil power (a few Watts) was added, the EEDF evolved abruptly into a Maxwellian Distribution, while the electron density was decreased. In an Ar/O2 mixture discharge, this EEDF evolution to the Maxwellian was also observed at a relatively higher coil power. This abrupt change in EEDFs with a very small coil power appears to be attributed to a combined effect of collisionless heating by capacitive and induced electric fields.
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Floating harmonics method for measuring electron temperature in non-Maxwellian plasmas
Journal of Applied Physics, 2010Co-Authors: Jin Young Bang, Aram Kim, Chin-wook ChungAbstract:Electron temperatures obtained from the slope of the electron energy probability function (EEPF) at the floating potential were compared with those measured by the floating harmonics method in various electron Distributions. Basically, these two types of the electron temperatures should be same in a Maxwellian electron Distribution. As expected, discrepancies were observed between them in cases of non-Maxwellian Distribution. In this study, the second and third harmonics of probe current were used to obtain the electron temperature in non-Maxwellian Distribution. The experimental results were shown that the electron temperature obtained using this method was in good agreement with the electron temperature from the slope of the EEPF at floating potential, regardless of the electron Distribution.
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Experimental investigation of the Boltzmann relation for a bi-Maxwellian Distribution in inductively coupled plasmas
Physics of Plasmas, 2009Co-Authors: Jin Young Bang, Chin-wook ChungAbstract:In plasma, the Boltzmann relation is often used to connect the electron density to the plasma potential because it is not easy to calculate electric potentials on the basis of the Poisson equation due to the quasineutrality. From the Boltzmann relation, the electric potential can be simply obtained from the electron density or vice versa. However, the Boltzmann relation assumes that electrons are in thermal equilibrium and have a Maxwellian Distribution, so it cannot be applied to non-Maxwellian Distributions. In this paper, the Boltzmann relation for bi-Maxwellian Distributions was newly derived from fluid equations and the comparison with the experimental results was given by measuring electron energy probability functions in an inductively coupled plasma. It was found that the spatial Distribution of the electron density in bulk plasma is governed by the effective electron temperature, while that of the cold and hot electrons are governed by each electron temperature.