Experimental results such as nonlinear Landau damping, induced electron scattering and the stochastic acceleration of electrons are explained well by our intensity dependent theory which treats the interaction between beam electrons in the presence of ions. We also explain the mechanism for observing nonlinear waves by the time-of-flight of solitons.

An inductive coupled plasma (ICP) source of a new type for dry etching has been developed. It is driven by a planar inductive coil, which is placed at the top of the channel formed by two coaxial dielectric cylinders. At low pressure, the radial component of the radiofrequency (RF) magnetic field causes a ponderomotive force acting on the electrons directed towards the bottom of the channel. Charge separation gives rise to an ambipolar electric field, which retards electrons and accelerates ions. The source represents an electrodeless electromagnetic accelerator (EMA) and can create an axially directed flux of ions. EMA has been modeled as an axisymmetric ICP discharge in argon gas based on experimental data of the plasma density and electron temperature profile. The magnetic field and RF current densities obtained have been used for calculation of the Lorentz force acting on the electrons and ambipolar plasma potential. Simulations of electron trajectories show that electrons are trapped in the EMA channel and make a number of oscillations before leaving the channel. The ponderomotive potential produces acceleration of the ions in the channel up to 13–16 eV.

A magneto plasma sail (MPS) is a new propulsion system which has the possibility of realizing low-cost and short-time travel in planetary exploration and space trips in the near future. We investigate by using a three-dimensional hybrid code whether MPS could receive momentum force from the Solar wind and whether thrust power could be obtained. The hybrid code has some problems in calculating instability under the low-density plasma and has restrictions on grid size. We pay attention to these problems and we estimate the thrust power by calculating the momentum change and confirm that MPS could obtain thrust power from the Solar wind.

This paper presents the numerical modeling of nonlinear magnetohydro- dynamic (MHD) instabilities containing the effects of finite Larmor radius (FLR) in spherical tokamak geometry. Our results contain the comparison of small, intermediate, and large effects of the FLR. For small values, the linear and nonlinear behavior is not greatly modified, but with intermediate and large FLR, stabilizing effects on the higher wave number components are observed in the linear phase but in the nonlinear phase the overall properties are dominated by MHD effects. Similar filamentary structures are reproduced as found in some of the experimental observations as a result of the development of ballooning modes. The formation and the properties of filamentary type structures during edge-localized modes are also discussed.

The motions of relativistic particles in a magnetosonic shock wave propa- gating obliquely to an external magnetic field are studied. In the zeroth-order theory, particles continue to move nearly parallel to the external magnetic field in the shock transition region, when the shock speed is close to $c \cos \theta$, where $c$ is the speed of light and $\theta$ is the propagation angle. Perturbations to this zeroth-order motion are also analyzed for positrons and ions. The perturbation frequency of positrons is $\omega \sim \Omega_{\rm p0} \gamma^{-1}$ and that of ions is $\omega \sim \Omega_{\rm i0} \gamma^{-1/2}$, where $\Omega_{\rm p0}$ and $\Omega_{\rm i0}$ are the non-relativistic gyrofrequencies of positrons and of ions, respectively, and $\gamma$ is the Lorentz factor. These theoretical predictions are confirmed with numerical simulations.

A neutral beam injection (NBI) into a field-reversed configuration (FRC) is simulated by the electron-fluid and ion-particle method. The neutral beam particle is injected tangentially to the field-null circle, and the simulation is done on a two-dimensional cross section of the FRC. An initial equilibrium state is obtained from the Grad–Shafranov equation including the beam current term. It is found that the start of radial ion flow is delayed by the NBI.

Low-frequency perpendicular electromagnetic fluctuations and energy transport in multi-ion-species plasmas are studied theoretically and numerically. In thermal equilibrium, the amplitudes of heavy-ion cutoff modes, whose frequencies are slightly higher than the heavy-ion cyclotron frequencies, can be comparable to that of the magnetosonic mode. The heavy-ion cutoff modes can cause damping of the magnetic fluctuations. Long time evolution of a macroscopic magnetic disturbance is also investigated with particle simulations. It is demonstrated that the disturbance is damped more quickly than the prediction of the linear theory. Owing to the damping, ion kinetic energy is increased.

The equilibria and stability of the least-dissipated relaxed state are derived from a generalized theory of self-organization for open or closed general nonlinear and dissipative dynamical systems. An application of the general theory is presented for the two-fluid model of plasmas. The concept of selective decay, together with helicity invariance, is analytically shown to have no connection with relaxed states derived from helicity invariance.

The Cherenkov instability used in slow-wave devices has been well studied in the literature. However, in previous analyses, the beam motion is restricted to the longitudinal direction assuming an infinitely strong magnetic field. For the finite strength magnetic field, the transverse beam perturbation cannot be ignored and leads to the slow cyclotron instability. Recently, a new version of self-consistent field theory considering three-dimensional perturbation has been developed based on a solid beam, in which the effect of the transverse perturbation appears as a surface charge at a fixed boundary. In the case of a thin annular beam, the boundary is modulated and is essentially different from the solid beam case. We propose a self-consistent field theory considering the moving modified boundary surface. The slow cyclotron instability due to the modulation of an infinitesimally thin annular electron beam is presented.

This paper presents the hydrodynamic efficiency of ablation plasma produced by a pulsed ion beam, as obtained on the basis of the ion beam–target interaction concept. We used a one-dimensional hydrodynamic model to explain the ablation acceleration behavior. Hydrodynamic variables are evaluated in terms of ablation velocity, conversion efficiency and ablation efficiency. We obtained 18% value for the energy conversion efficiency, while an ablation efficiency of about 70% is achieved at an ion-beam energy density of 60J cm$^{-2}$ (beam power density of $\approx$1 GW cm$^{-2}$). A thrust producing capability is also investigated.

Backward wave oscillators (BWOs) have been studied as a candidate high-power microwave source. To increase the operation frequency, an oversized slow-wave structure (SWS) is used. The operation at reduced voltage is preferable for practical applications. This work is aimed at numerically examining the operation mode of a weakly relativistic oversized BWO. We examine not only the axisymmetric transverse magnetic mode but also the non-axisymmetric hybrid modes of the oversized SWS. Both of them are candidates for the operation modes. These modes are surface waves whose fields are concentrated near the SWS wall. They overlap in frequency and are not separated by stop-bands. For an efficient beam interaction, the injected electron beam needs to be controlled more accurately than in the non-oversized SWS case.

Using a relativistic electromagnetic particle code, we investigate positron acceleration in a shock wave propagating obliquely to an external magnetic field ${\bf B} _0 $ in an electron–positron–ion plasma. After an encounter with a shock wave, some positrons are reflected and then accelerated along the magnetic field. They stay in the shock transition region and have velocities nearly parallel to ${\bf B} _0 $. Owing to the deformation of the wave profile, the acceleration can become stagnant. However, if the shock speed $v_{\rm sh}$ is close to $c \cos \theta $, where $c$ is the speed of light and $\theta $ is the angle between the wave normal and ${\bf B} _0 $, the acceleration can start again. In this second stage acceleration, three types of motion are found. The first type is the same as that in the first stage. In the second type, particles gain energy from the electric field perpendicular to the magnetic field in association with large-radius gyromotion. The third type of motion resembles the curtate cycloid in the wave frame. We give theoretical estimates for the energy increase in these processes.

The interaction of high-intensity laser pulses with overdense plasmas is studied by three-dimensional particle-in-cell (PIC) simulations. Self-generated magnetic fields are observed in the plasma target owing to Weibel-type instability. The growth rates of the self-generated magnetic field in our simulation are in good agreement with the results of our theoretical calculations.

Structure formation and plasma instabilities in collisionless driven reconnection are investigated by three-dimensional electromagnetic (EM) particle simulation in an open system. In the early period, the lower-hybrid drift instability is excited in the periphery of the current layer. In the intermediate period, magnetic islands are created in the downstream due to magnetic reconnection, and they become unstable against a kink instability. In the late period, after the magnetic islands go out through the boundary, a wide, thin current sheet is generated and a low-frequency EM mode is excited in the central region. This mode has a frequency comparable to the ion gyration frequency, and thus it is considered to be the drift kink instability.

We study a combined effect of wave trapping due to oppositely propagating narrow band whistler mode waves and discuss its dependence on the background plasma density. In the case where forward and backward traveling whistler mode waves coexist, rapid scattering of resonant electrons occurs owing to the overlapping of diffusion curves of both waves. Simulation results show that the low-density plasma condition, where the electron plasma frequency is close to the electron gyrofrequency, is favorable for the significant resonant scattering of high energetic electrons. The results of the present study suggest that the combined effect plays an important role in energizing relativistic electrons in the equatorial region of the Earth's inner magnetosphere during the recovery phase of geomagnetic storms.

Large-amplitude waves associated with a relativistic ion beam in a magnetized plasma are investigated by means of relativistic electromagnetic particle simulations. In the simulations, it is shown that electromagnetic fields are induced by an ion bunch which has Gaussian density distribution and that their profiles are similar to those of magnetosonic solitons. Further, when an ion beam propagates obliquely to the external magnetic field, it is found that an induced electric field has a parallel component along the magnetic field. Then, as the next step, giving another positron bunch, it is observed that some particles in a positron bunch are accelerated by the parallel electric field.

A new simulation model is developed, in which the interaction between the macroscopic and microscopic plasma processes is able to be taken into account self-consistently. Magnetohydrodynamic (MHD) simulation and particle-in-cell (PIC) simulation are directly connected and performed simultaneously. This MHD–PIC connection model is first applied to the study of the quiet auroral arc formation process. It is an example of our challenge to create the holistic simulation framework, that is, the heterogeneous schemes that can be unified by the state-of-the-art numerical technique. In this paper, we will explain the algorithm of our new model and show the results which have been calculated on the Earth Simulator.

The increasing resolution in space and time with which multi-directional velocity distribution functions can be measured in laboratory and space plasmas makes it feasible to initialize particle-in-cell (PIC) simulations from experimental observations. We showcase this emerging capability for ion velocity space shells where the ion macro-particles are initialized in the PIC simulations according to the velocity distribution measured by the Cluster satellites.

The basic idea of a cross-hierarchy model for magnetic reconnection in an open system is proposed, where a microscopic system is surrounded by a macroscopic system and the interaction between the two systems is expressed by the plasma inflow and outflow through the system boundary. Collisionless driven reconnection in two-dimensional and three-dimensional open systems is demonstrated using an open particle simulation model developed as a microscopic part of a cross-hierarchy model. It is found that the openness of the system and scale-coupling effects play crucial roles in collisionless driven reconnection.

The three-field reduced magnetohydrodynamic (MHD) model is extended to describe the resistive drift wave turbulence in a linear device. Using this model, the linear eigenmode analysis has been performed to identify the unstable modes, which give an estimation of a necessary condition for the turbulence excitation in the Larger Mirror Device designed by Kyushu University. The parameter scan predicts the experimental condition for the excitation of the resistive drift wave turbulence. It is found that ion–neutral collision strongly stabilizes the resistive drift wave. A nonlinear simulation has also been performed to examine the saturation amplitude of the resistive drift wave turbulence.