The polarization reversal from a left-hand (LHPW) to a right-hand polarized wave (RHPW) and the resultant electron cyclotron damping of the LHPW are experimentally observed for the first time. Our experimental results indicate that the polarization reversal arises simultaneously with the conversion of the propagation angle of the wave, in which finite-plasma boundary conditions are considered to be inherent.

View full abstract

The complex refractive index (n + ik) of ultra-short-pulse laser heated gold metal was measured with a new ellipsometric pump-probe technique. Two ratios of four different probe-beam polarizations were used to determine s- and p-reflectivity and their phase difference. In the early stage of heating, only the imaginary part of the dielectric constant ε(Im[ε] = 2nk) increased while real part of e (Re[ε] = n²-k²) was almost constant. This agrees with the Drude model. We observe a pause in the rise of Im[ε] at the boiling temperature. Beyond this point, Re[ε] started to change and the observed parameters disagree with the Drude theory. It was found that the parameters of the expanding plasma follow a unique trajectory in n, k space, even though time variation of Re[ε] and Im[ε] are different for various pump intensities. This means the gold remains in a unique state such as the neutral groundstate in this intensity range.

View full abstract

The evaluation of induced activity in a fusion system was made. The activity at the first wall and blanket structures are critical from the viewpoint of environmental safety and materials for low activation should be developed. The present status of development of candidate materials such as ferritic steels, vanadium alloys and SiC composites are viewed. Furthermore, isotope controlled materials and annihilation of radioactive nuclides are discussed.

View full abstract

The importance of the methodology of computer simulation has been recognized in plasma physics since the early era of computer evolution. In particular, the goal of simulation in this research field has been characterized by attempts to treat phenomena in a self-consistent manner as much as possible. Owing to the astonishing progress in recent supercomputer technology, we are now standing on a doorway to open a new stage in the simulation research in this direction, that is, an execution of multi-layer model simulation to understand complex phenomena in plasmas.

View full abstract

A hierarchical model for plasma transport is proposed which includes nonlinear interaction between different scale lengths. Two examples are shown for the application of this model. One is non-local transport based on transport-MHD model. Plasma rotation is produced by E×B nonlinearity, which converts heating source to momentum. Synergetic effect between plasma rotation and local (gyro-Bohm) transport produces non-local transport in this model. The other example involves multi-scale turbulence by ion temperature gradient-driven drift wave, and short wavelength ion temperature gradient driven drift wave. It is shown that non-adiabatic electron response produces the particle pinch effect. Future trends of simulation research regarding plasma turbulence are also discussed.

View full abstract

High performance magnetically confined fusion plasma is realized by having a ”structure”. A typical example in fusion plasma is the so-called ”Internal Transport Barrier (ITB)”, where a prominent thermal inhibition is revealed in a local thin layer inside the tokamak plasma column. Those phenomena are dominated by fluctuation dynamics having different time and spatial scales and are categorized as the characteristics of ”Multiple-Hierarchical Complex Plasma”. Here, we review turbulence and zonal flow systems and the resultant multiple-hierarchical interactions, which may be important to explain structure formation in magnetic fusion plasmas. Specifically, we emphasize the importance of large-scale advanced numerical computations in cooperation with experiments for achieving fusion program.

View full abstract

Reviewed is the development of the integrated simulation code related to laser fusion plasma research. In particular, the simulation system for describing ultra-intense laser interaction with high density plasmas is discussed. In ultra-intense laser plasma interaction, the relativistic electron current reaches a few hundred mega amperes and generates strong magnetic fields which control the electron transport. Therefore, the simulation system should include particle-in-cell simulation for laser plasma interactions, Fokker-Planck simulation and hybrid simulation for transport and dense plasma heating, and radiation hydrodynamic simulation for laser implosion and fusion burning. This paper reports the present status of the research regarding those simulations and how the above 4 simulation codes are interconnected as parts of the study of multi-space-time scale laser fusion plasma phenomena.

View full abstract

Although magnetic reconnection is believed to be a key process in solar flares, the flares' triggering mechanism remains a long-standing problem. In order to resolve this issue, the physical linkage between the magnetohydrodynamic (MHD) process in the macroscopic scale and the plasma kinetics in the microscopic scale has to be understood. Multiple-scale simulation, which can precisely describe the nonlinear process of the MHD equations as well as the complexity in the solar corona, will play a crucial role in this field of study.

View full abstract

We intend to reveal the physics of the evolution of the Universe from the pre-formation stage of the first stars to the structure and phenomena of the present solar system through the use of large-scale supercomputing. This project is named ”Computational Observatory” and sixteen research groups from throughout Japanare attempting simulations of four subjects in the different phases of the evolution of the Universe after the dark ages. This project involves finding numerical methods to very hierarchical problems regarding space and time. At the same time, a variety of complex physics should be modeled in the codes that are to be developed. A so-called integrated code for each subject should be developed. The integrated codes, of course, should be checked and improved through comparisons with observational and experimental data. Throughout this project, we would like to analyze not only observational data but also to predict, for example, what new findings we could obtain if we increase the resolution of observation instruments in the future. This project consists a great challenge in computer science in regard to developing a highly integrated system with very hierarchical phenomena..

View full abstract

This article is a lecture on vacuum technique. The discussion matter is outgassing characteristics of water vapor and hydrogen in a vacuum chamber. The role of surface treatment of vacuum chamber is also mentioned from the view of reduction of outgassing rate.

View full abstract