Wang Deyu

First Principles Study on NaxLi1−xFePO4 As Cathode Material for Rechargeable Lithium Batteries

The electronic structure and ionic dynamic properties of pure and Na doped (Li site) LiFePO4 have been investigated by first-principles calculations. The band gap of the Na doped material is much narrow than that of the undoped one, indicating of better electronic conductive properties. First-principles based molecular dynamic simulations have been performed to examine the migration energy barriers for the Li ion diffusion. The results shown that the energy barriers for Li diffusion decreased a little along the one-dimensional diffusion pathway, indicating that the ionic conductive property is also improved, as compared with the high valance doping (such as Cr) cases.

Envelope Soliton in Solar Radio Emission

Several envelope soliton fine structures have been observed in solar radio metric-wave emission. We present a model of longitudinal modulational instability to explain these fine structures. It is found that this instability can only occur in the condition of sound velocity being larger than Alfven velocity in corona. Therefore, the envelope soliton fine structures should display in the coronal region with high temperature and low magnetic field, which corresponds to the solar radio emission in the legion of meter and decameter wavelength.

Electron Acceleration by a Finite-Amplitude Solitary Kinetic Alfvén Wave

The electron acceleration by a finite-amplitude solitary kinetic Alfven wave (SKAW) in the low-β magnetized plasma is presented. It is found that the electron can be efficiently accelerated in both the parallel and the transverse directions of ambient magnetic field by a finite-amplitude SKAW up to several tenfold Alven velocity within the time 0.08 μs. These results are greatly different from the case of the electron accelerated by a small-amplitude SKAW.

Effect of Electron Drift Velocity on Whistler Instability in Collisionless Magnetic Reconnection

The whistler instability is studied under the condition that the electron and ion velocities can be described in a bi-Maxwellian distribution with a field-aligned electron outflow drift velocity. It is found that the electron outflow drift velocity might obviously make the threshold condition of whistler instability decrease when this velocity is parallel to the magnetic field, whereas the electron outflow drift velocity might increase the threshold condition when this velocity is anti-parallel to the magnetic field in collisionless magnetic reconnection.

Ions preheated in He-3-rich solar particle events

A wave-particle resonance absorption model in the two-ion plasma is suggested in explanation to the coronal ions preheating in He-3-rich solar particle events. It is found that He-3 and Fe ions are preferably preheated by the ion-ion hybrid waves at their fundamental and second harmonic ion cyclotron frequencies, respectively.

A study of the mechanism of acceleration of 3He and heavy ions by Alfven turbulence in impulsive flares

Prompted by the observational result that in He-3-rich events the energetic He-3 and heavy ions exhibit similar power-law distributions, we study by means of numerical solution of Fokker-Planck equation, the characteristics of the evolution of the distribution of ions after they are accelerated by Alfven turbulence. The results of computation show that the plasma density in the source region of acceleration and the energy density of Alfven turbulence play the chief role in the energy spectrum of the particles. For a plasma density n = (0.1 - 1) 10(10) cm(-3) a magnetic field B = 50 - 100 G and a turbulence energy density 0.4-2 ergs cm(-3) the turbulent Alfven waves can accelerate He-3 and heavy ions to the order of magnitude of 10 MeV/nucleon then in about 1 second. The index of the energy spectrum is 2.0-3-5. The result of the theoretical calculation basically agrees with the observation.

Modulation Instability of Low Frequency Whistler Waves

A self-focusing modulation instability of whistler wave has been investigated in the frequency region of ωci < ω ωce. It is found that the ion term contribution should be taken into account. The results show that the necessary condition of instability depends on the pitch angle of perturbation wave.

Electron acceleration by small-amplitude solitary kinetic Alfven wave in a low-beta plasma

In the case of a low beta plasma ? me/mi, the electron acceleration by small amplitude solitary kinetic Alfv?n wave is studied. It is found that the electron can be only accelerated along the ambient magnetic field. The maximum velocity of accelerated electron approaches to twice Alfv?n velocity. In the perpendicular direction, the dc electric field acceleration term and surfing acceleration term almost cancel each other out.

Particle Acceleration at Reconnecting X points in Solar Flares by Electrostatic Waves

In the impulsive phase of solar flares, the electrostatic waves can be excited during magnetic reconnection. The proton and electron at reconnecting X points can be accelerated by perpendicular propagating electrostatic waves.

Heavy ion acceleration in impulsive solar flares

The abundance enhancements of heavy ions Ne, Mg, Si and Fe in impulsive solar energetic particle (SEP) events are explained by a plasma acceleration mechanism. In consideration of the fact that the coronal plasma is mainly composed of hydrogen and helium ions, we think that the ion-ion hybrid wave and quasi-perpendicular wave can be excited by the energetic electron beam in impulsive solar Bares. These waves may resonantly be absorbed by heavy ions when the frequencies of these waves are close to the second-harmonic gyrofrequencies of these heavy ions. This requires the coronal plasma temperature to be located in the range of T similar to (5 - 9) x 10(6) K in impulsive solar fares and makes the average,onic charge state of these heavy ions in impulsive SEP events higher than the average ionic charge state of these heavy ions in gradual SEP events. These pre-heated and enhanced heavy ions can successively and stochastically be accelerated by Alfven turbulence and then form a power-law distribution in impulsive SEP events.