Effects of Heavy Ions on Kinetic Alfvén Waves

Kinetic Alfvén Wave (KAW) is one of the low-frequency electromagnetic fluctuations that are identified extensively in space plasmas by in situ observations of satellites and has been an interesting topic for discussion widely in the fields of laboratory, space, and astrophysical plasmas because of its potential importance in plasma particle energization. Some satellite observations show that the number density ratio of the oxygen ions to the ambient plasma is 30%～50%, sometimes, even as high as 80%. In this paper, effects of heavy ion species on KAWs are studied in a low-beta plasma. The results show that heavy ions not only considerably reduce the propagation speed of KAWs, but also remarkably influence the parallel component of perturbed electric field of KAWs (to the ambient magnetic field). The ratio of parallel to perpendicular components of perturbed field decreases (or increases) with the heavy ion abundance for KAWs dominated by the electron inertial length (or by ion acoustic gyroradius). In particular, the resonant condition of KAWs with thermal electrons is modified by the heavy ion species.     

Effects of Charge in Heavy Ions on Solitary Kinetic Alfvén Waves in Double-Ion Plasmas

After the charge of heavy ions is considered, a Sagdeev equation is obtained for the solitary kinetic lfvén waves (SKAWs) in a low-β (m_e/m_p « β « or m_p/m_e » α » 1), three-component (electrons, protons, and highly charged heavy ions) plasma. Numerical results show that the charge number q of heavy ions can cause the width of the solitary structure to decrease, but increase for the maximum of electron density n_em≤ 1.2 and the initial abundance of heavy ions C_b0 ≤ 0.1. The parallel phase speed of the waves increases with larger q.     

Effects of Ion Temperature and Inertia on Kinetic Alfvén Waves

Kinetic Alfvén wave (KAW) has been an interesting topic for discussion extensively in the fields of labora-tory, space, and astrophysical plasmas. A general dispersion equation is derived from the exact two-fluid model in thisambient magnetic field. For the short wavelength cases of kλi >> 1, where λi = vA/ωci and ωci are the ion inertial lengthand gyrofrequency, respectively, our dispersion relations are appropriate for discussing effects of the ion temperatureand inertia on KAWs. The present results show that both the ion temperature and inertia can affect considerably thebehaviors of KAWs in propagation, resonance, and polarization. In particular, our results may be a great help to un-derstanding some salient features of the low-frequency (in comparison with the ion gyrofrequency ωci) electromagneticfluctuations frequently observed by the FREJA and FAST satellites in the auroral zone of the Earth's ionosphere andmagnetosphere.     

Electron Acceleration by a Finite-Amplitude Solitary Kinetic Alfvén Wave

The electron acceleration by a finite-amplitude solitary kinetic Alfvén 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 Alvén velocity within the time 0.08μs. These results are greatly different from the case of the electron accelerated by a small-amplitude SKAW.     

Effect of Kinetic Alfvén Waves on Electron Transport in an Ion-Scale Flux Rope

At the Earth's magnetopause, the electron transport due to kinetic Alfvén waves(KAWs) is investigated in an ion-scale flux rope by the Magnetospheric Multiscale mission. Clear electron dropout around 90° pitch angle is observed throughout the flux rope, where intense KAWs are identified. The KAWs can effectively trap electrons by the wave parallel electric field and the magnetic mirror force, allowing electrons to undergo Landau resonance and be transported into more field-aligned directions. The pitch angle range for the trapped electrons is estimated from the wave analysis, which is in good agreement with direct pitch angle measurements of the electron distributions. The newly formed beam-like electron distribution is unstable and excites whistler waves,as revealed in the observations. We suggest that KAWs could be responsible for the plasma depletion inside a flux rope by this transport process, and thus be responsible for the formation of a typical flux rope.     

Numerical Simulation of MHD Jet Flows

Liquid metal free surface flows （films, jets and droplets） are considered as diverter/ limiter system and first wall in fusion reactor, but the knowledge Of liquid metal free surface under a non-uniform magnetic field is very limited. In this article, the stability of a jet flow under a gradient magnetic field is investigated, and its MHD effects are the top concern. Based on numerical simulation and experimental results, a simplified model is developed to analyze the MHD effects of the jet flow and to explain the reason why it can keep stable under a strong non-uniform magnetic field.     

Lattice Boltzmann Numerical Simulation of a Circular Cylinder

The lattice Boltzmann equation (LBE) model based on the Boltzmann equation is suitable for the numerical simulation of various flow fields.The fluid dynamics equation can be recovered from the LEB model.Howeverl,compared to the Navier-Stokes transport equation,the fluid dynamics equation derived from the LBE model is somewhat different in the viscosity transport term,which contains not only the Navier-Stokes transport equation but also nonsteady pressure and momentum flux terms.The two nonsteady terms can produce the same function as the random stirring force term introduced in the direct numerical or large-eddy vortex simulation of turbulence.Through computation of a circular cylinder,it is verified that the influence of the two nonsteady terms on flow field stability cannot be ignored,which is helpful for the study of turbulence.     

Numerical simulation of the multiple reversed shear Alfvén eigenmodes associated with the triangularity Alfvén gap

It was found that there are multiplicity of low shear toroidicity-induced Alfv′en eigenmodes in a zero beta limit if the inverse aspect ratio is larger than the magnetic shear at the mode location(Candy 1996 Phys. Lett. A 215 299). Because the reversed shear Alfv′en eigenmode(RSAE) and even the RSAE associated with the non-circular triangularity-induced Alfv′en eigenmode(NAE) gap(NAE–RSAE) usually reside near the shear-reversal point, the condition that the inverse aspect ratio is larger than the magnetic shear is naturally satisfied. For this reason, we numerically investigate the existence of multiplicity of core-localized NAE–RSAEs and mode characteristics in the present work. We firstly verify the existence of the multiplicity for zero beta plasma by using a D-shaped equilibrium. It is pointed out that, for a given toroidal mode number, the Alfv′en cascade spectrum accommodates down-sweeping and up-sweeping modes above and below the NAE range of frequencies. An analytical model for the existence of multiple RSAE modes is in good agreement with the simulation results. One notices that the triangularity has a greater effect on the odd-type modes than that on the even-type modes: the odd-type modes come into existence because of the plasma triangularity.     

Effect of Nonlinearity on Scattering Dynamics of Solitary Waves

We discuss the effect of nonlinearity on the scattering dynamics of solitary waves. The pure nth power model with the interaction potential V （Х） = Х^n/n is present, which is a paradigm model in the study of solitary waves. The dependence of the scattering property on nonlinearity is closely related to the topological structures of the solitary waves. Moreover, for one of the four collision types, the rates of energy loss increase with the strength of nonlinearity and would reach 1 at n ≥ 10, which means that the two solitary waves would become of fragments completely after the collision.     

Numerical Simulation of Shear-Horizontal-Wave-Induced Electromagnetic Field in Borehole Surrounded by Porous Formation

Seismoelectric fieM excited by purely torsional loading applied directly to the borehole wall is considered. A brief formulation and some computed waveforms show the advantage of using shear-horizontal （SH） transverseelectric （TE） seismoelectric waves logging to measure shear velocity in a fluid-saturated porous formation. By assuming that the acoustic field is not influenced by its induced electromagnetic field due to seismoeleetric effect, the coupling governing equations for electromagnetic field are reduced to Maxwell equations with a propagation current source. It is shown that this simplification is valid and the borehole seismoelectric conversion efficient is mainly dependent on the electrokinetic coupling coefficient. The receivers to detect the conversion electromagnetic field and to obtain shear velocity can be set in the borehole fluid in the SH-TE seismoelectric wave log.     

Direct Numerical Simulation of Supersonic Turbulent Boundary Layer Flow

Direct numerical simulations of a spatially evolving supersonic flat-plate turbulent boundary layer flow with free Mach number M∞ = 2.25 and Reynolds number Re = 365000/in are performed. The transition process from laminar to turbulent flow is obtained by solving the three-dimensional compressible Navier-Stokes equations, using high-order accurate difference schemes. The obtained statistical results agree well with the experimental and theoretical data. From the numerical results it can be seen that the transition process under the considered conditions is the process which skips the Tollmien-Schlichting instability and the second instability through the instability of high gradient shear layer and becomes of laminar flow breakdown. This means that the transition process is a bypass-type transition process. The spanwise asymmetry of the disturbance locally upstream imposed is important to induce the bypass-type transition. Furthermore, with increasing the time disturbance frequency the transition will delay. When the time disturbance frequency is large enough, the transition will disappear.     

Numerical Simulation of the Elastic Shrinkage Induced by Portevin-Le Chatelier Effect

A new one-dimensional phenomenological model based on the dynamic strain aging mechanism is developed. In order to account for the elastic shrinkage induced by the Portevin-Le Chatelier effect, elastic deformation is considered under the boundary conditions of the present model. The simulated results are found to be in good agreement with the experimental observations.     

Numerical Simulation of Leakage Effect for Quantum NOT Operation on Three-Josephson-Junction Flux Qubit

Superconducting flux qubits with three Josephson junctions are promising candidates for the building blocks of a quantum computer. We have applied the imaginary time evolution method to study the model of this qubit accurately by calculating its wavefunctions and eigenenergies. Because such qubits are manipulated with magnetic flux microwave pulses, they might be irradiated into non-computational states, which is called the leakage effect. By the evolution of the density matrix of the qubit under either hard-shaped π-pulse or Caussian-shaped π-pulse to carry out quantum NOT operation, it has been demonstrated that the leakage effect for a flux qubit is very small even for hard-shaped microwave pulses while Caussian-shaped pulses may suppress the leakage effect to a negligible level.     

Numerical Simulation of the Non-Fourier Heat Conduction in a Solid-State Laser Medium

A hyperbolic model of non-Fourier heat conduction with non-uniform heat source is used to simulate the transient heat transfer in a high-pulse-pumped solid-state laser medium. The temperature fields are numerically analysed using the finite difference method combined with the TDMA algorithm for different pump power densities, pulse durations, thermal relaxation time and cooling intensities, respectively. The calculated results are compared with those predicted by the parabolic heat conduction model based on the Fourier law. The results indicate that the non-Fourier heat conduction phenomenon in laser media should be considered when the pump power density exceeds 104 W/m^2 or under low pulse duration. In addition, the conditions of non-Fourier effects and their influencing factors are analysed.     

Numerical Simulation on Expansion Process of Ablation Plasma Induced by Intense Pulsed Ion Beam

We present a one-dimensional time-dependent numerical model for the expansion process of ablation plasma induced by intense pulsed ion beam （IPIB）. The evolutions of density, velocity, temperature, and pressure of the ablation plasma of the aluminium target are obtained. The numerical results are well in agreement with the relative experimental data. It is shown that the expansion process of ablation plasma induced by IPIB includes strongly nonlinear effects and that shock waves appear during the propagation of the ablation plasma.     

Observation of odd toroidal Alfvén eigenmodes

Experimental evidence is presented for the existence of the theoretically predicted odd toroidicity induced Alfvén eigenmode (TAE) from the simultaneous appearance of odd and even TAEs in a normal shear discharge of the joint European torus. The modes are observed in low central magnetic shear plasmas created by injecting lower hybrid current drive. A fast ion population was created by applying ion cyclotron heating at the high-field side to excite the TAEs. The odd TAEs were identified from their frequency, mode number, and timing relative to the even TAEs.     

Numerical Simulation of Ultrafast Laser Pulse Propagation in Tenuous Plasmas： Envelope Evolving and Modulation

We propose an effective and useful numerical simulation scheme for the investigation of the ultra-fast laser pulses in tenuous plasmas. The accuracy of the method is tested by numerical examples. We check some special examples to investigate the laser envelope evolving and modulation in plasmas. Asymmetric two-peak modulation structure is found and its underlying physics is analyzed. The advantages and shortages of the method are also discussed.     

Nonlinear Coupling of Reversed Shear Alfvén Eigenmode and Toroidal Alfvén Eigenmode during Current Ramp

Two novel nonlinear mode coupling processes for reversed shear Alfvén eigenmode(RSAE) nonlinear saturation are proposed and investigated. In the first process, the RSAE nonlinearly couples to a co-propagating toroidal Alfvén eigenmode(TAE) with the same toroidal and poloidal mode numbers, and generates a geodesic acoustic mode. In the second process, the RSAE couples to a counter-propagating TAE and generates an ion acoustic wave quasi-mode. The condition for the two processes to occur is favored during current ramp. Both the processes contribute to effectively saturate the Alfvénic instabilities, as well as nonlinearly transfer of energy from energetic fusion alpha particles to fuel ions in burning plasmas.