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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.

We found that strong proton acceleration leading to the complete magnetic reconnection where both poloideal and axial magnetic fields reconnect.

We apply the obtained simulationresults to the proton acceleration during solar flares.

We found that the electron Bernstein waves in the high density plasma are converted to the X-mode in the low density plasma through the linear mode conversion process due to the density inhomogeneity.

The counter-streaming instability in magnetized and positron (pair) plasmas is investigated by using two dimensional, electromagnetic, relativistic Particle-In-Cell (PIC) code. It is shown that the electrostatic waves are strongly generated by the counter-streaming instability in a strongly magnetized pair plasmas ( ωce/ωpe=2). It is also show that the high-frequency electromagnetic waves are generated in the saturated phase of the electrostatic waves. The plasma maser process that the electrostatic waves can be converted to the high frewquency electromagnetic waves could be a possible mechanism for the electromagnetic wave emission in the pulsar magnetosphere.

We investigate the plasma dynamics during coalescence of two parallel current loops by using a resistive MHD code. We investigate the orbit of many protons in the electromagnetic fields obitained from the MHD simunations. We investigate two cases of the coalescence precess: as the original loop current for both cases of co-helicity and counter-helicity.

We investigate a new model of single-loop flare based on the fact that a magnetic flux tube with axial current can be explosively sistupted during collision of two moving solitary magnetic kinks (MoSMaK), particulary paying attention to an acceleration mechanism of high energy protons. At this time, we investigate a model which flow cross-section is not same as the collision cross-section. By using three-dimensional electromagnetic fields obtained from a resistive three-dimensional MHD equations during the single-loop flare, we investigate the orbit of many protons to obtain their energy spectra. We found that the protons can be accelerated to γ-ray emitting energies. The protons are accelerated mainly in one direction along the loop by electric field produced near the three-dimensional localized current associated with the magnetic reconnection process in the disrupted loop.

We investigate sissipation process of magnetic field energy in collisionless electron-positron (pair) plasmas by using two-dimensional, fully relativistic, electromagnetic particle-in-cell code. We consider the force-free magnetic configuration with no current-driven Bunneman instability. A half of initial magnetic field energy dissipates by the tearing instability. The dissipated energy can be converted into plasma kinetic energy as well as plasma heating. The trowth rate of tearing instability is two times larger than the heory of elefcron-ion tearing instabilty.

The electromagnetic counterstreaming instability in unmagnetized pair (electron-positron) plasmas which is influenced by the external magnetic field paralled to the streaming direction is investigated numerically. The simulation show that the counterstreaming instability changes its character from magnetic to electrostatic nature. The electrostatic waves growing due to the electrostatic counterstreaming instability play an important role for producing fast electrons and positrons with energy of MeV. The process of high-energy particle production in relativistic shocks in magnetized pair plasmas may be applied to gamma-ray burst events.

We investigate the generation mechanism of magnetic fields by shear-flow instability in pair plasmas, by using a 2-dimensional particle-in-cell code. We also investigate the effeciency of the conversion of the flow energy to the magnetic field energy by changing the external magnetic field intensity. We found that the energy conversion is very efficient with about 20% for the moderate intensity of the external magnetic field.

We investigate the dynamics of the relativistic flow in pair plasmas with force-free magnetic configuration, using a three-dimensional fully relativistic electromagnetic particle-in-cell (PIC) code. We observed that three-dimensional Alfven waves with magnetic helical structures can be excited through complicated three-dimensional tearing instability triggered from the stresming instability. During these dynamical processed the pair plasma can be heated through the magnetic field dissipation and also the high-energy particles are generated.

We investigate the magnetohydrodynamic (MHD) instability of the magnetic loop in association with the solar flare. We use 'safety factor' q to describe the local twist of the magnetic loop where low q value means the strong twist, then it becomes more unstable for the MHD instability.We present the q profile on the equilibrium for two types which may correspond to small and large flare. One type corresponding to small flare is the slim cylindrical untwisted magnetic loop in initial stage. When the tube is twisted, low q region is localized around the axis of the center of the loop. We conclude that the localized low q region must be ring shaped. The energy release by MHD instability can be localized with the ring shaped region. The other type is barrel shaped untwisted magnetic loop which may correspond to the large flare. After the twist, low q region is wide along the axis. The MHD instability is caused on the whole magnetic loop, therefore the energy release is global.

We present a model for high-energy solar flare explosions driven by 3-dimensional X-type current loop coalescence. The 3-dimensional X-type loop coalescence, where two crossed fluxtubes interact in one point, is a fundamentally new process as compared to the 1-D and 2-D cases studied earlier. It is shown that, following the strong plasma collapse due to pinch effect, a point-like plasma explosion can be driven and also fast magnetosonic shock waves can be excited;We found that the conditions in the area producing the remarkable flare bursts of 21 May 1984 were indeed such that the many flare spikes could have been due to 3-D explosive X-type current loop coalescence. We also show, by studing the conding the conditions of shock formation in a Gamma ray flare, that the time delay of γ-rays from the impulsive phase could be the time needed for the shock formation in the flaring region.We draw some general conclusions on the question why certain flares do emit γ-rays in the Mev energy range, and why other, apparently important and large flares, do not. We accentuate the fact that a well-developed high-energy flare has three phases of particle acceleration.

We studied the acceleration conditions in the small but fairly energetic flare of May 21, 1984 at 13:26 UT. The most pronounced aspect of this flare was a series of 13 microwave / x-ray spikes, each lasting for about 0.1s. A previous study has shown that each of these was due to a series of successive sudden formations of small plasma knots of high energy particles. Each of these knots lost its energy in about 50 ms. In the present study we show that these knots can originate by the process of x-type (3-D) flux tube coalescence. The predicted rise time (30 to 50 ms) and energy are in good agreement with the observationally derived parameters.

The coronal explosion, discovered by De Jager and Boelee (1984), and interpreted by them as manifestations of plasma streaming out of the flare kernels, can also be interpreted as signatures of current loop coalesscence in the flaring region.