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Electron acceleration and small‐scale coherent structure formation by an Alfvén wave propagating in coronal interplume region  

Khalil Daiffallah   Submitted: 2017-07-28 16:54

We use the 2.5-D electromagnetic particle-in-cell simulation code to investigate the acceleration of electrons in solar coronal holes through the interaction of Alfvén waves with an interplume region. The interplume is modeled by cavity density gradients that are perpendicular to the background magnetic field. The aim is to help explain the observation of suprathermal electrons under a relatively quiet Sun. Simulations show that Alfvén waves interacting with the interplume region give rise to a strong local electric field that accelerates electrons in the direction parallel to the background magnetic field. Suprathermal electron beams and small-scale coherent structures are observed within interplume of strong density gradients. These features result from the nonlinear evolution of the electron beam plasma instability.

Authors: K.Daiffallah, F.Mottez
Projects: None

Publication Status: Published
Last Modified: 2017-07-31 11:04
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f-mode interaction with models of sunspot: near-field scattering and multifrequency effects  

Khalil Daiffallah   Submitted: 2016-06-07 05:55

We use numerical simulations to investigate the interaction of an f-mode wave packet with small and large models of a sunspot in a stratified atmosphere. While a loose cluster model has been largely studied before, we focus in this study on the scattering from an ensemble of tightly compact tubes. We showed that the small compact cluster produces a slight distorted scattered wave field in the transverse direction, which can be attributed to the simultaneous oscillations of the pairs of tubes within the cluster aligned in a perpendicular direction to the incoming wave. However, no signature of a multiple-scattering regime has been observed from this model, while it has been clearly observable for the large compact cluster model. Furthermore, we pointed out the importance of the geometrical shape of the monolithic model on the interaction of f-mode waves with a sunspot in a high-frequency range (ν = 5 mHz). These results are a contribution to the observational effort to distinguish seismically between different configurations of magnetic flux tubes within sunspots and plage.

Authors: K.Daiffallah
Projects: None

Publication Status: Published in MNRAS (2016), Volume 460, Issue 1, p.1077-1085
Last Modified: 2016-06-07 17:22
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Simulation of f-Mode Propagation Through a Cluster of Small Identical Magnetic Flux Tubes  

Khalil Daiffallah   Submitted: 2013-07-18 04:14

Motivated by the question of how to distinguish seismically between monolithic and cluster models of sunspots, we have simulated the propagation of an f-mode wave packet through two identical small magnetic flux tubes (R=200 km), embedded in a stratified atmosphere. We want to study the effect of separation d and incidence angle chi on the scattered wave. We have demonstrated that the horizontal compact pair of tubes (d/R=2, chi=0) oscillate as a single tube when the incident wave is propagating, which gives a scattered wave amplitude of about twice that from a single tube. The scattered amplitude decreases with increasing d when d is about lambda/2pi where lambda is the wavelength of the incident wave packet. In this case the individual tubes start to oscillate separately in the manner of near-field scattering. When d is about twice of lambda/2pi, scattering from individual tubes reaches the far-field regime, giving rise to coherent scattering with an amplitude similar to the case of the compact pair of tubes. For perpendicular incidence (chi=pi/2), the tubes oscillate simultaneously with the incident wave packet. Moreover, simulations show that a compact cluster oscillates almost as a single individual small tube and acts more like a scattering object, while a loose cluster shows multiple-scattering in the near-field and the absorption is largest when d within the cluster is about lambda/2pi. This is the first step to understand the seismic response of a bundle of magnetic flux tubes in the context of sunspot and plage helioseismology.

Authors: K. Daiffallah
Projects: None

Publication Status: Accepted for publication in Solar Physics
Last Modified: 2013-07-18 18:47
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3D Numerical Simulations of f-Mode Propagation Through Magnetic Flux Tubes  

Khalil Daiffallah   Submitted: 2010-09-02 04:39

Three-dimensional numerical simulations have been used to study the scattering of a surface-gravity wave packet by vertical magnetic flux tubes, with radii from 200 km to 3 Mm, embedded in stratified polytropic atmosphere. The scattered wave was found to consist primarily of m=0 (axisymmetric) and m=1 modes. It was found that the ratio of the amplitude of these two modes is strongly dependant on the radius of the flux tube: The kink mode is the dominant mode excited in tubes with a small radius while the sausage mode is dominant for large tubes. Simulations of this type provide a simple, efficient and robust way to start understanding the seismic signature of flux tubes, which have recently began to be observed.

Authors: K. Daiffallah, T. Abdelatif, A. Bendib, R. Cameron, L. Gizon
Projects: None

Publication Status: Submitted to Solar Physics (Topical issue in Helio- and Asteroseismology to appear in 2010)
Last Modified: 2010-09-02 12:38
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3D Numerical Simulations of f-Mode Propagation Through Magnetic Flux Tubes  

Khalil Daiffallah   Submitted: 2010-09-02 04:39

Three-dimensional numerical simulations have been used to study the scattering of a surface-gravity wave packet by vertical magnetic flux tubes, with radii from 200 km to 3 Mm, embedded in stratified polytropic atmosphere. The scattered wave was found to consist primarily of m=0 (axisymmetric) and m=1 modes. It was found that the ratio of the amplitude of these two modes is strongly dependant on the radius of the flux tube: The kink mode is the dominant mode excited in tubes with a small radius while the sausage mode is dominant for large tubes. Simulations of this type provide a simple, efficient and robust way to start understanding the seismic signature of flux tubes, which have recently began to be observed.

Authors: K. Daiffallah, T. Abdelatif, A. Bendib, R. Cameron, L. Gizon
Projects:

Publication Status: Published in Solar Physics (2011), 268, 309-320.
Last Modified: 2013-07-17 10:54
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Abstracts by Author
Electron acceleration and small‐scale coherent structure formation by an Alfv?n wave propagating in coronal interplume region
f-mode interaction with models of sunspot: near-field scattering and multifrequency effects
Simulation of f-Mode Propagation Through a Cluster of Small Identical Magnetic Flux Tubes
3D Numerical Simulations of f-Mode Propagation Through Magnetic Flux Tubes
3D Numerical Simulations of f-Mode Propagation Through Magnetic Flux Tubes

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