Using a system analysis code, plasma parameter ranges required for a Tokamak reactor to generate net electric power (P_e^net) were investigated. The investigation revealed that in order for a Tokamak to produce a net electric power of 0 MW under foreseeable engineering conditions, it is required to achieve simultaneously the following ranges of parameters, i.e., normalized beta value 1.2 ≤ β_N ≤ 2.7, confinement improvement factor for H-mode scaling 0.8 ≤ HH, and the ratio of Greenwald density limit 0.4 ≤ fn_GW ≤ 1.1, for a major radius R ≤ 8.5 m. It also revealed that a reactor to produce a net electric power of 1,000 MW requires the simultaneous achievement of β_N ≥ 3.0, HH ≥ 0.9 and fn_GW ≥ 0.9.

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Electron heat transport in low-collisionality LHD plasma is investigated in order to study the neoclassical transport optimization effect on thermal plasma transport with an optimization level typical of so-called “advanced stellarators”. In the central region, a higher electron temperature is obtained in the optimized configuration, and transport analysis suggests the considerable effect of neoclassical transport on the electron heat transport assuming the ion-root level of radial electric field. The obtained experimental results support a future reactor design in which the neoclassical and/or anomalous transports are reduced by magnetic field optimization in a non-axisymmetric configuration.

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A ray tracing code, TRECE, of electron cyclotron resonance heating (ECRH) has been developed for the helical-axis heliotron, Heliotron J. The accurate power absorption profile can be obtained for the three dimensional structure of flux surfaces and magnetic field in Heliotron J. The calculation shows that the launching condition of the 70 GHz ECRH system assures a well localized power deposition.

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This paper reviews a novel and simple technique for measuring electron density using a plasma absorption probe (PAP). The PAP enables the measurement of local absolute electron density even when the probe surface is soiled with processing plasmas. The technique relies on the absorption of surface waves (SWs) resonantly excited around the probe head at critical frequencies which depend on the electron density. The PAP consists of a small antenna connected to a coaxial cable and is enclosed in a tube of dielectric constant ε_d inserted in a plasma of electron plasma frequency ω_p. A network analyzer feeds a rf signal to the antenna and displays the frequency dependence of the power absorption. A series of resonant absorptions is observed at frequencies slightly above the SW resonance frequency, ω_SW = ω_p/(1+ε_d)½, which allows us to determine the electron density. Typical examples of measured PAP data and future challenges are presented.

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Recent observations of electric field structures in the high altitude polar ionosphere made by FAST satellite are introduced, placing emphasis on the electric potential drops along the magnetic field lines. Though these potential drops have not been demonstrated by direct measurements of parallel electric field, they have been consistently inferred from measurements of perpendicular electric fields and velocity distribution of plasma particles. There are two types of field structure, the upward and the downward electric field. The characteristic difference between these two structures are discussed, referring to FAST high time resolution observations.

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The history, benefits, suitability, and limitations of the laboratory simulation of space plasma processes are reviewed. Aspects of waves, instabilities, nonlinearities, particle transport, reconnection, and hydrodynamics are addressed in terms of interrelated experiments performed in space and the laboratory. Over time, the degree to which the interrelated experiments can be compared has increased, thanks to improved diagnostic techniques in space and closer attention to matching dimensionless space parameters in the laboratory.

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Laboratory investigations on the formation of space-related electric fields have been performed using collisionless magnetized-plasma flows. In a set of experments, potential differences are externally applied along magnetic-field lines, different plasmas come into contact with each other under the currentless condition, a high-speed plasma flow is injected into a region of converging manetic-field lines, large-amplitude electron plasma waves are generated in a uniform magnetic field, and local electron-cyclotron resonances occur in various kinds of nonuniform magnetic fields. It is found that the elcetric field is formed in the region of density gradient, a U-shaped double layer (DL) is accompaned by ion-cyclotron oscillations, a DL is formed in the currentless system, and that an electron local-plug results in the formation of a potential dip and hump with a scale length of the order of Debye length. Electron- and ion-acceleration electric fields with a scale lengths of a magnetic-field gradient are also found to be formed by passing ions and electrons through nonuniform magnetic fields, respectively.

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Numerical simulation is a powerful tool for investigating the formation of electric potential structure in plasmas. By means of a self-consistent open boundary two-and-a-half-dimensional particle simulation model, it is demonstrated that a V-shaped dc potential structure is created by a current-driven electrostatic ion-cyclotron instability. A potential difference along the magnetic field is generated by anomalous resistivity. This difference becomes larger for a longer system along the magnetic field; thus, the potential difference may become several kV for a thousand km anomalous resistivity region.

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A diagram of the real phase velocity vs. the imaginary wave number clearly demonstrates the existence region of one-dimentional electrostatic localized structures: sheaths, solitons, electron holes, and ion holes. Especially in collisionless space plasma, electron holes survive for a relatively long time because of alackofelectron reflection.

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The present paper provides a basic introduction to the mechanism of so-called“kinetic” Alfvén wave propagation and associated parallel electric field generation. It is clarified that kinetic effects are not essential for the“kinetic” Alfvén waves, either in propagation or in parallel electric flied generation. The derivation of the “kinetic”Alfvén wave here is based simply on: polarization currents carried by ions; equations of electron parallel motion; and Maxwell equations. One major application of “kinetic”Alfvén waves to the magnetospheric physics is the problem of auroral particle acceleration; recent observational, experimental, and theoretical developments on this topic are briefly reported.

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The radial transport due to the Coulomb collision (collisional stochasticity) in torus plasmas is treated as a diffusion process, when the locality of the radial orbits or the scale separation is satistied (R≡Δr/L«1) where Δr and L are a collisionless radial orbit width in the ballistic phase and an equilibrium radial scale length or a size of the system, respectively. A deterministic stochasticity due to perturbed electromagnetic fields may lead to chaotic, no-local particle orbits, so that the scale separation will break down:(R<1). In such a situation, it is not so clear whether the transport process is treated as a diffusion process. In order to clarify this issue, the transport under the deterministic stochasticity is revisited.

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A Fokker-Planck equation in a presence of fluctuations is studied by using the functional integral representation that is analogous to the Feynman's path integral. With the help of the mathematical techniques used in the quantum field theory, a closed set of equations for an ensemble-averaged distribution function and a response function is derived. As an application, the effect of fluctuations on the radial profile of rf-induced current density is also studied.

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Magnetic null points act as scattering centers where particles describe chaotic orbits and the mixing effect increases the kinetic entropy. In an open system where convection of particles into/from the chaos region exists, the saturation of the entropy can be avoided, and continuous dissipation is achieved. The chaos-induced collisionless resistivity of ions enables fast magnetic reconnection. By matching the microscopic (kineticprocess) and the macroscopic parameters of reconnection, we obtain a self-consistent model of the diffusion region.

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To develop a statistical theory, one has to define a probability density on the phase space of ensemble. The measure of the space, then, must be invariant against the map (flow) representing the dynamics. This property is warranted by the Liouville theorem in the canonical Hamitonian dynamics. For some infinite dimension dynamics, we can construct an ”invariant measure” by an appropriate eigenfunction expansion of fields, which provides a basis to construct statistical mechanical theory of the fields.

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There are several different computer systems in LHD (Large Helical Device) experiment, and therefore the coalition of these computers is a key to perform the experiment. Real-time monitoring system is also important because the long discharge is needed in the LHD experiment. In order to achieve these two requirements, the technique of IP multicast is adopted.The authors have developed three new systems, the first one is the real-time monitoring system, the next one is the delivery system of the shot number and the last one is the real-time notification system of the plasma data registration. The first system can deliver the real-time monitoring data to the LHD experimental LAN through the firewall of the LHD control LAN in NIFS. The other two systems are used to realize high coalition of the different computers in the LHD plasma experiment. We can conclude that IP multicast is very useful both in the LHD experiment and a future large plasma experiment from various experiences.

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Fluctuation in detached recombining plasmas has been investigated experimentally in the linear divertor plasma simulator, NAGDIS-II. As increasing neutral gas pressure, floating potential fluctuation of the target plate installed at the end of the NADIS-II device becomes larger and bursty negative spikes are observed in the signal associated with a transition from attached to detached plasmas. The fluctuation property has been analyzed by using Fast Fourier Transform (FFT), probability distribution function (PDF) and wavelet transform. The PDF of the floating potential fluctuation in the attached plasma condition obeys the Gaussian distribution function, on the other hand, the PDF in detached plasma shows a strong deviation from the Gaussian distribution function, which can be characterizedbyflatnessandskewness.Comparisonofthefluctuation properties between the floating potential and the optical emission from the detached plasma has been done based on the wavelet transform to show that a strong correlation between them, which could indicate bursty transport of energetic electrons from upstream to downstream region along the magnetic field.

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