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Simulation of collision of two current loops in the upper chromosphere using two fluids model  

Jun-ichi Sakai   Submitted: 2005-12-25 22:32

This is a first paper of simulation results of plasma dynamics with protons and neutral hydrogens, taking into account of transport processes of proton-neutral hydrogen collision, heat conduction, recombination and ionization that are important in solar transition region as well as chromosphere. We investigate the collision process of two current loops with counter-helicity in the upper chromosphere where the density of protons and neutral hydrogens are comparable. We found that two fluids dynamics of protons and neutral hydrogens is different from a single fluid MHD approximation. We found that about 79% of magnetic field energy can dissipate to heat protons and there occur bi-directional jets of protons coupled well with hydrogen. The obtained results may be applicable to the footpoints heating of coronal loops and the explosive events that are strongly localized high velocity jets in the transition region.

Authors: J.I. SAKAI, K. TSUCHIMOTO, and I. V. SOKOLOV
Projects:

Publication Status: ApJ(in press)
Last Modified: 2006-01-17 10:32
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Electron heating by large amplitude shear Alfvén waves in the upper chromosphere with force-free magnetic configuration  

Jun-ichi Sakai   Submitted: 2005-12-20 21:44

We investigate how large amplitude shear Alfvén waves (AWs) can heat the upper chromosphere with magnetic force-free configuration, by using a 2D3V fully relativistic electromagnetic particle-in-cell (PIC) simulation. We found that the shear AWs with linear polarization and about one period can excite quasi-electrostatic waves driven by the Modified Two-Stream Instability (MTSI), resulting in electron heating within short time tsimeq50{omegaci}-1. The obtained results could be applied to the electron heating in the upper chromosphere where small-scale magnetic flux tubes are interacting with each other, causing shear magnetic field structures between them.

Authors: J.I. Sakai and S. Saito
Projects:

Publication Status: A & A (in press)
Last Modified: 2006-01-23 02:06
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Particle simulation of plasma heating by large amplitude shear Alfvén wave through its transverse modulation in collisionless plasmas  

Jun-ichi Sakai   Submitted: 2005-10-19 13:32

We investigate the nonlinear dynamics of large amplitude shear Alfvén wave (AW) with circular polarization in collisionless plasmas by using 2D3V fully relativistic electromagnetic particle-in-cell (PIC) simulation code. We found that when the amplitude, A=delta B/B_0 of the shear AW is larger than A_c=frac{vth,i}{c} frac{{omega}pe}{kc}frac{{omega}pe}{{omega}ce}, the shear AW spontaneously becomes unstable for the Modified Two-Stream Instability (MTSI), resulting in the excitation of small-scale quasi-electrostatic waves with electric fields parallel to uniform magnetic field. We found that the electrons are heated mostly in the direction parallel to the magnetic field due to the quasi-electrostatic lower hybrid waves by the MTSI. Subsequently the shear AW becomes unstable with strong transverse modulation, resulting in the excitation of ion acoustic waves that can heat ions. About 70% of the AW energy can be converted to plasma heating of both electrons and ions. The plasma heating time is within about 250 {omegaci}-1 that is shorter than the collision time between protons and neutral hydrogens in upper chromosphere. The obtained results could be very important for plasma heating of coronal loops in upper chromosphere.

Authors: J.I. Sakai, W.Yamamura, S.Saito, H.Washimi, D. Tsiklauri and G. Vekstein
Projects:

Publication Status: New Journal of Physics(accepted)
Last Modified: 2005-11-01 08:01
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Simulation on solar Type II radio bursts associated with corona mass ejections  

Jun-ichi Sakai   Submitted: 2005-06-20 11:41

The wave emission process of solar Type II radio bursts associated with Coronal Mass Ejections (CME) is investigated by using two dimensional, electromagnetic, relativistic Particle-In-Cell (PIC) code. Two simulation results are shown: the first case is that the CME propagates perpendicular to the local magnetic field, and the second case is that the CME propagates obliquely to the local magnetic field where two cases of the propagation angle of 80 and 40 degrees are shown. It is shown that fast magnetosonic shock wave is formed with both protons and electrons accelerated by the surfatron acceleration mechanism. It is also shown from the first case that near the shock front the electron Bernstein waves are generated and they can be converted to the extra-ordinary electromagnetic waves (Type II radio bursts) through the direct linear mode conversion. It is found from the second case that near the shock front the electrostatic Langmuir waves (Z-mode) are generated and they can be also converted to the extra-ordinary electromagnetic waves through the direct linear mode conversion.

Authors: J.I. Sakai, T. Mori and S. Saito
Projects: None

Publication Status: A & A (in press)
Last Modified: 2005-06-20 11:41
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Simulation on solar Type III radio bursts from magnetic reconnection region  

Jun-ichi Sakai   Submitted: 2005-02-22 03:56

We investigate the wave emission process of solar Type III radio bursts from magnetic reconnection region in a solar flare by using two dimensional, electromagnetic, relativistic Particle-In-Cell (PIC) code. We initially impose two plasma populations, background dense plasma and hot electrons that can be generated by magnetic reconnection process in a solar flare. We investigated two cases: model (1) where the hot electron beams propagate obliquely to the magnetic field, while in model (2) the hot electron beams propagate along the magnetic field. We found that hot electron plasmas lead to the generation of Langmuir waves and the generated Langmuir waves can be converted to the electromagnetic waves (solar Type III radio bursts) through the linear direct mode conversion process. The second harmonic emission is generated with time delay and the amplitude larger than that of fundamental emission.

Authors: J.I. SAKAI, T. KITAMOTO and S. SAITO
Projects: None

Publication Status: ApJLetters(in press)
Last Modified: 2005-02-22 03:56
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PROTON ACCELERATION AND ITS ENERGY SPECTRA DURING THE COALESCENCE OF TWO CROSS CURRENT LOOPS  

Jun-ichi Sakai   Submitted: 2005-02-22 03:50

We investigate the plasma dynamics during coalescence of two cross current loops by using a resistive three-dimensional MHD simulation code, particularly paying attention to find the most effective electromagnetic fields for the production of high-energy protons. Next we investigate the orbit of many protons in the electromagnetic fields obtained from the MHD simulations. We found that the proton acceleration is more efficient compared with the case of two parallel loops coalescence. It is shown that the maximum proton energy is about 25 MeV and exceeds the energy (2.223 MeV) of the observed prompt nuclear de-excitation lines of gamma-ray and the proton energy spectrum is a power-law type with an index of about 2 - 2.3. The simulation results imply that proton-associated gamma-ray sources are located near the footpoints with magnetic north polarity. We found that strong proton acceleration leading to the observed prompt line gamma-ray emissions can be realized only when there occurs the complete magnetic reconnection where both poloidal and axial magnetic fields reconnect.

Authors: J.I. SAKAI AND K. SHIMADA
Projects: None

Publication Status: A&A(in press)
Last Modified: 2005-02-22 03:50
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Abstracts by Author
Simulation of collision of two current loops in the upper chromosphere using two fluids model
Electron heating by large amplitude shear Alfven waves in the upper chromosphere with force-free magnetic configuration
Particle simulation of plasma heating by large amplitude shear Alfven wave through its transverse modulation in collisionless plasmas
Simulation on solar Type II radio bursts associated with corona mass ejections
Simulation on solar Type III radio bursts from magnetic reconnection region
PROTON ACCELERATION AND ITS ENERGY SPECTRA DURING THE COALESCENCE OF TWO CROSS CURRENT LOOPS

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