Table of contents

A brief summary is given of the early studies of Landau damping, followed by a discussion of the issues of singularities in the distribution function, reversibility and nonlinear constraints. A difference is emphasized between the evolution of a single-scale localized Langmuir perturbation and a long quasimonochromatic wavetrain. Applicability conditions of the quasilinear approximation are discussed. Examples of the use of the concept of Landau damping in hydrodynamics, astrophysics and other systems are presented.

A review of experimental results obtained in JET D-T plasmas is presented. In discussing the underlying physics, results previously obtained on tokamak fusion test reactor (TFTR) are also taken into account. In JET, the maximum fusion power output of 16.1 MW has been obtained in an edge localized mode (ELM)-free hot-ion H-mode featuring an edge confinement barrier in a single-null divertor plasma with a where is the total input power to torus. A steady-state H-mode discharge, with plasma shape and safety factor q similar to that of ITER, produced 4 MW for 5 s (22 MJ). The steady-state results extrapolate well to ignition with ITER parameters using the normalized plasma pressure achieved on JET. Also, the advanced tokamak regime using optimized magnetic shear configuration featuring an internal transport barrier produced 8.2 MW of fusion power. With regards to reactor physics issues, a clear identification of electron heating by fusion born -particles has been made both in JET and TFTR. The JET experiments show that the H-mode threshold power has approximately an inverse isotopic mass dependence and that it does not depend on the method of auxiliary heating. The global energy confinement time in the TFTR D-T supershot regime scales as but in the JET H-modes, it is found to be practically independent of isotopic mass where A is the atomic mass of the hydrogenic species. In JET, the plasma core and the edge appear to have different underlying confinement physics, the former follows the gyro-Bohm transport model whereas the edge pedestal energy scales as . The maximum edge pressure in H-modes is analysed in relation to the ion poloidal Larmor radius at the edge. The fast ions driven by neutral beam injections (NBI) or ion cyclotron resonance heating (ICRH) could play an important role in setting the width of the edge pedestal. The thermal ELMy H-mode confinement both in D or T gas fuelled plasmas decreases significantly when the plasma density exceeds 0.75 of the Greenwald limit and the maximum density achieved is . The ICRH scenarios for a reactor have been evaluated. For example, minority in 50:50 D:T and tritium-dominated plasmas showed strong bulk ion heating leading to ion temperatures up to 13 keV with ICRH alone. Deuterium-minority ion cyclotron heating in tritium plasmas at a power level of 6 MW produced steady-state record values of for more than 2.5 s. Finally, the on-site closed-cycle tritium reprocessing plant and remote handling tools at JET have been used routinely and provided an integrated demonstration of safe and reliable operations of a tokamak device in reactor-relevant conditions.

The dusty plasma is a system that consists of many strongly-charged fine dust particles suspended in a plasma background. The slow dynamics and strong coupling due to the large mass and charges lead to the formation of highly-ordered dust crystal structures suspended in the plasma background, which can be directly observed. The dusty plasma forms a link to the area of condensed matter physics for the study of many interesting microscopic phenomena from order to disorder. In this paper, we introduce the special properties of this system from the viewpoint of conventional plasma physics, then we briefly review past works on the structure and dynamical behaviour from the highly-ordered state, through the melting and liquid states with associated vortex-type excitation and anomalous diffusion, to the state with self-organized macroscopic dust waves after losing microscopic order. The first observation of strongly-coupled dust Coulomb clusters with small numbers of particles from a few to a few hundred, which resemble classical atoms, is also demonstrated.

Quasi-static, magnetic-field-aligned (parallel) potentials have been considered the primary source of charged particle acceleration in the aurora where precipitating electrons create a visible display. This finding has been controversial since, at one time, it was widely believed that parallel potentials could not be supported by a collisionless plasma. We present observations from the fast auroral snapshot (FAST) satellite which strongly support this acceleration mechanism and, moreover, show evidence of a second plasma regime region which supports quasi-static parallel potentials. The uncovering of parallel potentials in two plasma regimes suggests that they may be fundamental in astrophysical plasmas, supplementing the classical mechanisms of Fermi and betatron acceleration. We summarize the observations that demonstrate this acceleration mechanism. We also summarize evidence of Debye-scale plasma structures which are associated with these parallel potentials. These small-scale structures appear to be three-dimensional electron phase space holes, a new type of plasma structure.

Recent work on laser produced plasmas is presented focusing on the theoretical studies of four topics which have been carried out at the Institute of Laser Engineering (ILE), Osaka University, after a brief explanation of the six physics issues to be studied for plasma physics related to the laser fusion. The importance of integrated code development is emphasized and it is shown that the growth of the Rayleigh-Taylor instability at the ablation front is reduced partly due to non-local electron transport. Non-uniformity of implosion dynamics is studied by comparing a two-dimensional simulation with a spectroscopic post-processing package. It is concluded that all the available experimental data are consistently explained. The fast-ignition with ultra-high power laser is studied. The ignition criteria are clarified with a two-dimensional burning wave simulation. The possibility to study astrophysics by designing model experiments with intense lasers is introduced. The computational design of models of the ejecta-ring collision of SN1987A is shown by comparing with the event in the space.

The design of an experimental thermonuclear reactor requires both cutting-edge technology and physics predictions precise enough to carry forward the design. The past few years of worldwide physics studies have seen great progress in understanding, innovation and integration. We will discuss this progress and the remaining issues in several key physics areas.

(1) Transport and plasma confinement. A worldwide database has led to an `empirical scaling law' for tokamaks which predicts adequate confinement for the ITER fusion mission, albeit with considerable but acceptable uncertainty. The ongoing revolution in computer capabilities has given rise to new gyrofluid and gyrokinetic simulations of microphysics which may be expected in the near future to attain predictive accuracy. Important databases on H-mode characteristics and helium retention have also been assembled.

(2) Divertors, heat removal and fuelling. A novel concept for heat removal - the radiative, baffled, partially detached divertor - has been designed for ITER. Extensive two-dimensional (2D) calculations have been performed and agree qualitatively with recent experiments. Preliminary studies of the interaction of this configuration with core confinement are encouraging and the success of inside pellet launch provides an attractive alternative fuelling method.

(3) Macrostability. The ITER mission can be accomplished well within ideal magnetohydrodynamic (MHD) stability limits, except for internal kink modes. Comparisons with JET, as well as a theoretical model including kinetic effects, predict such sawteeth will be benign in ITER. Alternative scenarios involving delayed current penetration or off-axis current drive may be employed if required. The recent discovery of neoclassical beta limits well below ideal MHD limits poses a threat to performance. Extrapolation to reactor scale is as yet unclear. In theory such modes are controllable by current drive profile control or feedback and experiments should be forthcoming soon. Recent results on JET and TFTR have confirmed qualitative understanding of alpha particle driven toroidal Alfvén eigenmodes (TAEs). Present predictions for TAE effects in ITER are favourable, but require further work. The large stored energies in ITER have focused attention on disruption physics. Databases for thermal and current quenches, vertical displacement events (VDEs) and halo currents have enabled thermomechanical design. Some questions remain open as to the production, confinement and localization of runaway electrons in potentially unstable plasmas and mitigation strategies have been proposed. Other crucial ITER needs such as diagnostics, control and heating appear to have acceptable solutions.

All this rich physics requires experimental validation by a reactor-scale plasma and care has been taken to provide sufficient flexibility for ITER to cover a wide range of scenarios.

In many cases, the analytical understanding of the complex nonlinear behaviour of plasmas is simplified by the fact that the plasma dynamics is low-dimensional. Then, quite universal descriptions, which can predict quite sophisticated phenomena, are available. This aspect, and the corresponding appearance of spatially coherent structures, are first discussed for the single-mode dynamics in a weakly unstable (or marginal) regime. The procedure is then generalized to a few modes. The following examples are used to point out the benefits from a low-dimensional description: ionization wave instability, Pierce instability, interchange instability and electron drift instability. Special emphasis is put on the following aspects. Low-dimensional dynamics is quite rich and allows one to apply modern control mechanisms. Coherent structures are present in the dynamics and may contribute to the understanding of transport scalings. The overview is concluded by pointing out some similarities to high-dimensional situations. In the latter, structures (singularities) also have a signature in the dynamical behaviour. They allow us to understand more deeply certain scaling behaviour.

The reversed field pinch (RFP) is an effective tool in the study of the macroscopic consequences of magnetic fluctuations, such as the dynamo effect and anomalous transport. Several explanations exist for the dynamo (the self-generation of plasma current) - the magnetohydrodynamic dynamo, the kinetic dynamo and the diamagnetic dynamo. There is some experimental evidence for each, particularly from measurements of ion velocity and electron pressure fluctuations. Magnetic fluctuations are known to produce energy and particle flux in the RFP core. Current profile control is able to decrease fluctuation-induced transport by a factor of five. Improved confinement regimes are also obtained at deep reversal and, possibly, with flow shear.

Spherical torus magnetic confinement systems, covering spheromaks and spherical tokamaks (STs), are reviewed. As well as being potentially very important for fusion, spherical tori research is enhancing our understanding of magnetic confinement systems with wider applications than fusion research. The studies contribute to the conventional tokamak, for example, ITER via a range of scalings, as well as to our understanding of `quiescent' plasmas and those subject to `turbulent magnetohydrodynamic (MHD) relaxation'. The theoretical and experimental properties are described, showing how these vary with configuration and contrasting them with the conventional aspect ratio tokamak. Topics covered include equilibrium, refuelling, helicity injection, influence of trapped particle fraction, plasma heating, confinement, stability (including pressure limits and energetic particle instabilities) and disruption resilience.

The main features of advanced stellarators are the optimized coil system which can be extrapolated to reactor size, improved properties of plasma equilibrium with reduced Shafranov shift and a stability limit which is sufficient to meet the requirements of a commercial fusion reactor. The key element to achieve these goals is the proper shape of the magnetic surfaces and minimization of the geodesic curvature of magnetic field lines. As a consequence, Pfirsch-Schlüter currents and radial particle transport are reduced. Neoclassical transport becomes small enough so that ignition is not endangered. The theoretical basis of the advanced stellarator is a systematic procedure to compute plasma equilibria with reduced Pfirsch-Schlüter currents. The close relation between neoclassical transport and viscous damping indicates that a reduction of geodesic curvature not only reduces radial transport but also leads to a reduction of viscous damping, and thus, facilitates the rotational spin-up of the plasma. For this reason achievement of shear flow and reduced anomalous transport may be expected in advanced stellarators.

The paper discusses the various aspects of advanced stellarators and describes their basic properties.

As a result of advances in fast pulsed-power technology and cylindrical load fabrication, the Z pulsed-power accelerator at Sandia National Laboratories drives currents approaching 20 MA with a rise time of approximately 100 ns through cylindrically-symmetric loads (typically a cylindrical array consisting of a few hundred wires) to produce plasma densities in excess of , x-ray output energies approaching 2 MJ, radiation pulses as short as 4 ns and peak x-ray powers as high as . More than 15% of the stored electrical energy in the Z pulsed-power accelerator is converted into x-rays. The plasma pressures at peak compression are several TPa with electron temperatures that can exceed 3 keV at containment magnetic fields exceeding 1000 T. Depending on the atomic number and composition of the imploding plasma, these z-pinches can be tailored to produce intense sources of thermal x-rays, keV x-rays or neutrons. Although applications of these x-ray sources have included research in radiation material interaction, equations of state, opacity, astrophysics and x-ray lasers, the principal focus of the present research is to use them for indirect-drive inertial confinement fusion (ICF).

Control of the plasma-wall interaction is a difficult challenge to cope with in controlled fusion research. A straightforward idea consists of destroying the magnetic configuration at the plasma edge by field line stochastization: this can easily be achieved by applying helical magnetic perturbations. Interestingly enough, most of the physics properties stem directly from the description of the chaotic nature of the field lines. This is readily expected whenever parallel transport largely exceeds transverse anomalous transport, a standard property for most boundary plasmas. While quasilinear theory gives access to the poloidally and radially averaged values of heat and particle energy transport, it can then be shown that the understanding of energy transport through the stochastic boundary and especially power deposition onto the target plates requires a non-averaged calculation. Indeed, ergodization is limited by the bounded length of the field lines themselves before they hit a plasma facing component within the tokamak chamber. The so-called ergodic layer is consequently surrounded by a generalized scrape-off layer: the laminar zone. Towards the plasma core, the vanishing ergodization is shown to give rise to an internal transport barrier.

Outstanding experimental results such as impurity screening and increased radiation at reduced core contamination indicate that transport monitored by a controlled stochasticity provides a powerful means to tackle major issues of fusion physics. Significant advances in ergodic divertor physics give us confidence that this open divertor concept is an alternative to the closed axisymmetric divertor which relies heavily on mechanical baffling of neutrals. Experimental evidence is given by a worldwide family of devices such as Tore Supra, TEXT, TEXTOR and CSTN-II.

The synchronous firing of dense and strongly ionized plasmas with the time structure of bunched and energetic multicharged ion beams allows us to probe, for the first time, the long searched for enhanced plasma stopping and enhanced projectile charge at the target exit.

Correlated ion stopping of charged debris resulting from the fragmentation of energetic cluster ions focusing on Au foam converters is considered for indirectly driving a thermonuclear capsule. The one-dimensional (1D) simulation of converter time evolution demonstrates a very high conversion efficiency of projectile energy into hard x-ray photons building up a very hot ( eV) thermal bath. Intense and energetic cluster ion beams thus demonstrate considerable potential as a novel driver for inertial confinement fusion.

We discuss the importance of plasma physics in various areas of cosmology and astrophysics: (1) the primordial plasma spectrum, (2) the cosmic microwave background, (3) the large-scale structure of the universe, (4) reionization and the metalicity of the primordial universe, (5) the first objects, (6) the primordial magnetic field, (7) clusters of galaxies, (8) galaxy formation, (9) star formation, (10) nuclear reactions, (11) accretion onto black holes, (12) cosmic rays, (13) relativistic jets and (14) gamma ray bursters.

One of the more ambitious uses of intense microwaves in tokamaks or in other magnetic confinement deuterium-tritium (DT) fusion devices would be to divert power from energetic -particles to waves. This so-called `-channelling' would be a large step towards achieving economical fusion power. The intense waves, amplified by the substantial free energy in the -particles, damp on fuel ions, resulting in a hot ion mode, doubling the fusion power of the reactor at the same confined pressure. If the waves damp preferentially on electrons or ions travelling in one direction, current can be driven. This tutorial explains the key concepts and recent advances that lead us to believe in the plausibility of such an effect, at the same time showing how experiments to date give us a measure of confidence in both the simulations themselves, the underlying physical assumptions and ultimately the reasonableness of the application of these ideas to -channelling in a tokamak reactor.

The primary purpose of this paper is to extract a grand view of self-organization through an extensive computer simulation of plasmas. The assertion is made that self-organization is governed by three key processes, i.e. the existence of an open complex system, the existence of information (energy) sources and the existence of entropy generation and expulsion processes. We find that self-organization takes place in an intermittent fashion when energy is supplied continuously from outside. In contrast, when the system state is suddenly changed into a non-equilibrium state externally, the system evolves stepwise and reaches a minimum energy state. We also find that the entropy production rate is maximized whenever a new ordered structure is created and that if the entropy generated during the self-organizing process is expelled from the system, then the self-organized structure becomes more prominent and clear.

This paper is devoted to the presentation of various theories describing wave-particle interaction in the case of one-dimensional (1D) turbulence. The results obtained from recent experiments and simulations are compared with the theoretical predictions.

The paper is devoted to a tutorial review of the relaxation process in reversed field pinch (RFP) plasmas. Both magnetic and thermal aspects of the relaxation process are discussed and the main models proposed to explain it in the framework of nonlinear magnetohydrodynamics are reviewed. Particular attention is paid to the bifurcation between single helicity and multiple helicity states which is present in the phase space of a quasirelaxed RFP. Experimental evidence of transitions between bifurcated states, observed in many experiments and leading to enhanced confinement regimes, are discussed and a possible explanation for them is proposed. The role of Prandtl number in controlling transitions is discussed.

The Lyapunov exponent has been investigated both numerically and analytically for various plasma states. With the use of a three-dimensional particle code that calculates Coulomb forces among individual particles, instantaneous expansion rates of nearby trajectories in a phase space are studied. It is found that the Lyapunov exponent has different dependences on the Coulomb coupling constant corresponding to dilute, liquid and solid plasmas. An analytical model is also developed and it gives a relation between the Lyapunov exponent and the dielectric response function. The model indicates that the Lyapunov exponent is of the order of the plasma frequency in a dilute plasma, which agrees with simulation results. In a dilute plasma, large fluctuation of the instantaneous expansion rate is shown to be caused by a close encounter which breaks the symmetry of force and leads to trajectory instability.

Physics studies are carried out on the plasma of the large helical device (LHD), the experiment which began at the National Institute for Fusion Science (NIFS). LHD is a flexible device and can operate in various configurations. Characteristics of the plasma are investigated and confinement improvement is discussed.

The access to overdense plasmas for both the electron Bernstein (EB) wave heating and the EB wave diagnostic via the O-X-B mode conversion window was successfully demonstrated at W7-AS. In the EB wave heating experiments clear evidence for both mode conversion steps were detected and resonant absorption with a narrow profile was demonstrated. Also, the inverse process, the EB wave radiation of an overdense plasma was measured with an oblique viewing angle. The spectrum consists of a local cyclotron emission part and a non-local broadband high-frequency part. Edge temperature perturbations excited by carbon injection were used to demonstrate the relation between frequency and position of emission.

Since for EB waves no density limit exists, the operation window of the electron cyclotron heating and diagnostic could be extended to densities above the cut off density.

The discovery of dark halos, spectroscopic evidence that elliptical galaxies are dominated by collisionless dynamics and the opening of new observational windows (especially in the near-infrared) able to provide direct information on the underlying mass distribution in spiral galaxies, have significantly changed our perception of the internal structure of galaxies. The modelling tools and the theories developed to explain many interesting observations (from the study of global spiral and bar modes of galaxy disks to the construction of self-consistent anisotropic collisionless models to explain the universality of the luminosity profile of elliptical galaxies) present many analogies with parallel work in the physics of electromagnetic plasmas. Beyond specific mechanisms, the main source of similarities between the two fields is probably to be found in the common semi-empirical approach, where the major struggle is to set up the most appropriate equations to describe inherently complex systems, governed by collective behaviour in the presence of long-range forces. At the frontier of current research in extragalactic astrophysics, the Hubble space telescope and new large telescopes from the ground are giving us a view of the early dynamical stages of galaxies and on the small scale for relatively nearby galaxies, unprecedented accurate data on their structure and kinematics. After focusing on some recent results relative to the collective dynamics of stellar systems, we will identify a few basic questions that remain unresolved, where the study of galaxies as gravitational plasmas may help significantly towards further progress.

The linear and nonlinear evolution of two configurations of interest for the solar corona are presented. The first case examined refers to a cylindrically symmetric twisted magnetic flux tube which is intended to model a solar coronal loop which has evolved quasi-statically through sequences of equilibria with increasing twist due to the application of localized photospheric vortex flows. It is well known that when the twist exceeds a critical value that depends on its radial profile and on the loop length, the loop becomes kink-unstable. The nonlinear evolution of the instability is followed using a three-dimensional magnetohydrodynamic (MHD) code in cylindrical geometry in a magnetic field configuration where the net axial current is zero and radially confined, so that the magnetic field is an axial potential one in the external regions. It is shown that, during the nonlinear phase of the instability, loops develop current sheets and consequently their evolution becomes resistive with the occurrence of magnetic reconnection. The details of the reconnection phenomenon and the resistive dissipation mechanism are examined, along with the impact of the results in the understanding of coronal activity.

The second case refers to a neutral sheet embedded in a plane fluid wake, which is a simplified representation of a streamer beyond the underlying coronal helmet. This wake- neutral sheet configuration is characterized by two parameters which vary with distance from the Sun: the ratio of the cross-stream velocity scale to the neutral sheet width and the ratio of the typical Alfvén velocity to the typical flow speed far from the neutral sheet. Depending on the values of these parameters, the linear theory predicts that three kinds of instability can develop when this system is perturbed: a tearing instability and two ideal fluid instabilities with different cross-stream symmetries (varicose and sinuous). In the innermost, magnetically-dominated region beyond the helmet cusp, we find that the streamer is resistively and ideally unstable, evolving from tearing-type reconnection in the linear regime to a nonlinear varicose fluid instability. Travelling magnetic islands are formed and the centre of the wake is accelerated and broadened slightly. Past the Alfvén point, where the kinetic energy exceeds the magnetic energy, the tearing mode is suppressed but an ideal sinuous fluid mode can develop, producing additional acceleration up to typical slow wind speeds and substantial broadening of the wake. Farther from the Sun, the system becomes highly turbulent due to the development of ideal secondary instabilities, thus halting the acceleration and producing strong filamentation throughout the core of the wake.

Studies in open systems in the world are reviewed from viewpoints of the potential confinement and magnetohydrodynamic (MHD) stability. The tandem mirror GAMMA 10 has shown the potential confinement of a high-ion-temperature plasma from an analysis of the time evolution of end-loss ion current and end-loss ion energy distributions. The central cell density was increased by 50% by the potential confinement. In the HIEI tandem mirror H-mode-like phenomena were observed with an increase in density and diamagnetic signal in a limiter biasing experiment. Potential formation phenomena in plasmas are studied by -like Upgrade under different magnetic field configurations and plasma conditions. The fully axisymmetric tandem mirror AMBAL-M is under construction and its end mirror system has been assembled. Heating experiments of a plasma gun produced plasma by neutral beam injection and ICRF heating are in progress. The gas dynamic trap (GDT) experiment has successfully produced an MHD-stable high-temperature, high-density plasma. In GOL-3-II, a high-density plasma with several 100 eV temperature is created by powerful relativistic electron beam injection. Construction of HANBIT has been completed and experiments on plasma production and ICRF heating have begun.

The reversed field pinch (RFP) is a highly-sheared nearly force-free magnetic field configuration, which is almost entirely self-generated, via a dynamo process. A still open question is the level of turbulence entailed by the dynamo and how it could be mitigated in order to improve plasma confinement. The paper addresses the issue, first discussing the properties of the magnetic profiles of RFX in relation to other RFPs, then analysing some transient enhanced confinement modes which suggest that the improved confinement is due to a reduced dynamo action.

The role of magnetic shear in affecting electron transport is discussed on the basis of the Frascati tokamak upgrade (FTU) data with central electron cyclotron resonance heating (ECRH) on the current ramp phase and with pellet injection. The results point out that strongly negative magnetic shear is not a necessary condition in order to have good electron transport and that magnetohydrodynamic (MHD) activity plays a crucial role in affecting the electron transport in the region with low/negative magnetic shear. The theoretical arguments for the dependence of transport on magnetic shear are reviewed and compared with the experimental evidence.

Experiments on edge localized magnetohydrodynamic (ELMy) H-modes and reversed shear modes in JT-60U are presented. In ELMy H-mode discharges in conjunction with a W-shaped pumped divertor, efficient helium exhaust is demonstrated by inner divertor pumping when particle recycling is high in the inner divertor. Despite suppression of the backflow of neutrals, degradation of global energy confinement with the W-shaped divertor is similar to that with an open divertor. In recent reversed shear experiments, the nominal DT fusion power gain reached 1.25. By modulated helium gas puffing to a reversed shear plasma with an internal transport barrier, an inward particle pinch was confirmed in the internal transport barrier (ITB) region. In central ion cyclotron resonance frequency (ICRF) heating of a strongly reversed shear plasma, a hollow heating profile was found while the heating profile in normal (positive) shear peaked at the centre. The measured shine through of a 350 keV hydrogen beam agrees well with theoretical prediction.

This paper summarizes results from a two-dimensional (2D) physics analysis of the transition to and stable operation of the partially detached divertor (PDD) regime induced by deuterium injection in DIII-D. The analysis [1] shows that PDD operation is characterized by a radiation zone near the X-point at -15 eV which reduces the energy flux into the divertor and thereby also reduces the target plate heat flux, an ionization zone below the X-point which provides a deuterium ion source to fuel parallel flow down the outer divertor leg, an ion-neutral interaction zone in the outer leg which removes momentum and energy from the flow and finally a volume recombination zone above the target plate which reduces the particle flux to the low levels measured on the plates and thereby also contributes to reduction in target plate heat flux.

A simple model for the operation of the Hall current plasma accelerator, a crossed field discharge device that accelerates a flow of quasi-neutral plasma, is used to calculate the performance of an actual device at various configurations and operating conditions. The solutions demonstrate that the performance, characterized by the ionized fraction of the flow, the mass-averaged exit flow velocity and the total efficiency, improves as the flow rate or the accelerator length are increased at a given discharge voltage, trends that were also observed experimentally. Nevertheless, the calculated values for the longer lengths, especially the total efficiencies, are significantly higher than the measured ones, indicating the importance of an accurate solution of the electron energy equation and the need to include in the model plasma-wall interactions.

The plasma chemistry of an expanding thermal plasma in argon/hydrogen mixtures in interaction with silane is discussed. Based on Langmuir probe measurements and (appearance potential) mass spectrometry, it is argued that under optimal conditions in terms of the a-Si:H deposited the fluxes reaching the growing film mainly consist of and atomic hydrogen. The surface chemistry, hydrogen incorporation, growth rate and dependence on substrate temperature are discussed and the results obtained are compared with growth models as proposed by Matsuda, Gallagher and Perrin. It is argued that although atomic hydrogen plays no role in the modification of the bulk properties, atomic hydrogen is probably responsible for the creation of dangling bond sites by hydrogen abstraction. Possible consequences for the substrate temperature dependence of the growth rate are discussed.

An overview is presented of recent experiments with radiating mantles on limiter and divertor machines, realizing simultaneously high confinement and high density at high-radiation levels. A variety of operational regimes has been observed and the characteristics of each are documented. High-performance plasmas (i.e. edge localized mode (ELM)-free H-mode confinement quality and normalized beta values simultaneously) with radiating mantles have been demonstrated under quasistationary conditions during the maximum flattop time of the machine (equal to tens of confinement times) on DIII-D and TEXTOR-94. Maximum values for up to 4 and for the advanced tokamak confinement-stability product up to 13, have been obtained in very high confinement mode (VH-mode) like discharges with radiating mantles in DIII-D. There is a striking similarity between improved ohmic confinement discharges (with or without Ne seeding) and radiating mantle discharges, indicating a possible common origin for the confinement improvement observed. Possible scenarios for the application of radiating mantles on larger machines such as JET and JT-60U are indicated.

A key element in future toroidal magnetic fusion machines like ITER is the design of a divertor, which allows for safe particle and power exhaust in parallel with high bulk plasma performance. Correspondingly, the definition and design of an optimized divertor is a major task within the ongoing international ITER research and development effort. In order to provide a profound physics basis for such a divertor optimization, different divertor geometries are being tested on major tokamaks.

This paper describes the effects of these divertor modifications on plasma performance in ASDEX Upgrade and in JET. In conclusion, increasing closure improves divertor performance without limiting the core plasma performance in ELMy H-modes.

An improved understanding of strongly driven laser-plasma coupling is important for optimal use of the National Ignition Facility (NIF) for both inertial fusion and for a variety of advanced applications. Such applications range from high-energy x-ray sources and high-temperature hohlraums to fast ignition and laser radiography. We discuss a novel model for the scaling of strongly driven stimulated Brillouin and Raman scattering. This model postulates an intensity-dependent correlation length associated with spatial incoherence due to filamentation and stimulated forward scattering. We first describe the model and then relate it to a variety of experiments. Particular attention is paid to high-temperature hohlraum experiments, which exhibit low to modest stimulated Brillouin scattering even though this instability is strongly driven. We also briefly discuss the strongly nonlinear interaction physics for efficient generation of high-energy electrons either by irradiating a large plasma with near quarter-critical density or by irradiating overdense targets with ultra-intense laser light.

We experimentally studied laser-hole boring with 100 ps/1 TW laser light and ultra-intense laser-plasma interactions using a 0.5 ps/100 TW laser system. Investigation into laser-hole boring was made by measurements of backscattered light spectra, x-ray image and electron density profiles in under- and overdense regions. For the first time x-ray laser light was used to directly observe the channel in the overdense plasma. We further examined short pulse laser interactions as well as the generation of high-energy particles with 100 TW laser light. Neutrons by D-D fusion reaction in the interaction plasma were measured to diagnose ion acceleration. High-energy electrons (MeV) were measured by a x-ray method.

Cosmic ray and gamma-ray astrophysics provides an arena where concepts drawn from many branches of plasma physics can assist in answering questions of fundamental - indeed cosmological - significance. In recent years, striking advances have been made in the quality and resolution of the data available in this field. The present generation of cosmic ray detection arrays and space-based x-ray and gamma-ray observatories, coupled to measurements in other wavebands, are yielding information which invites detailed quantitative interpretation in terms of plasma processes. In parallel with these developments, a systematic picture of the behaviour of energetic particle populations in magnetically confined plasmas has emerged from the deuterium-tritium experimental campaigns on JET and TFTR, and the acceleration of electrons to highly relativistic energies has been demonstrated in laser-plasma interaction experiments. This review is written primarily to assist the deployment in energetic particle astrophysics of methodologies used for studying high-temperature fusion plasmas: three topics are examined. What are the major plasma-oriented questions in energetic particle astrophysics? What solutions have been proposed? How can plasma physics assist in deepening, strengthening and extending current understanding?

We discuss the observation and theory of nonlinear wave interactions in astrophysical and space plasmas. Observational evidence of nonlinear mode-mode coupling in solar type III radio bursts, auroral whistler-mode radiation and active experiments in space is reviewed. The transition from order to chaos in nonlinear plasma wave interactions is analysed. For Hamiltonian four-wave interactions, the nonlinear dynamical process may undergo a chaotic transition via the quasi-periodicity route. For dissipative three-wave interactions, the nonlinear system may evolve from order to chaos via two different routes: period doubling and intermittency. It is shown that chaos in dissipative nonlinear three-wave coupling can be controlled by applying a small sinusoidal wave to the system.

Highly charged and massive dust grains have much smaller characteristic frequencies than electrons and ions and lead to interesting modifications of existing modes and to exciting new possibilities for modes and instabilities at the lower frequency end of the spectrum. Space observations of planets and comets have shown wave-like behaviour which can only be explained by the presence of charged dust grains. Two typical solar system applications are spokes and braids in the rings of Saturn and the influence of charged dust on the pickup process of ions of cometary origin by the solar wind. As dust is ubiquitous in the universe, the Jeans instability in astrophysics is modified by incorporating plasma and charged dust and treating electromagnetic and self-gravitational aspects together. Besides the usual mechanism based upon thermal agitation, other ways of countering gravitational contraction are via excitation of electrostatic dust-acoustic modes or via Alfvén-Jeans instabilities for perpendicular magnetosonic waves. The unstable wavelengths tend to be much larger, due to the dominance of plasma and magnetic pressures in inhibiting gravitational collapse.

The radiation pressure of a chopped laser beam is used to excite low-frequency (f = 0.4-5 Hz) waves in plasma crystals. The first system studied is a linear chain of spherical plastic particles of m diameter. The second system is a single-layer crystal with hexagonal structure made of the same kind of particles. The measured dispersion and damping of longitudinal compressional waves is compared with a model for dust lattice waves in a system of particles interacting by Yukawa-type potentials. From the best fit the shielding factor is determined. The finding that the measured shielding length is comparable with the interparticle distance is supported by Monte Carlo simulations.

Recent advances in the study of collective effects and particle motions in plasma-dust crystals are presented. Plasma collective processes influence arrangements and vibrations of dust particles in these Coulomb structures. The important effect is the wake potential formation leading to the vertical alignment of dust grains in the experiments. Oscillations of dust particles in the lattices are strongly affected by collective processes in the ambient plasma, in particular, by the wake. Modes associated with vertical vibrations of dust grains, which can provide a useful tool for diagnostics in the sheath region, are identified, and their dispersion characteristics are discussed.

Solitary waves of the fast beam mode in a positive ion-beam and a quasi-neutral three-component plasma system are investigated theoretically and experimentally. The plasma is assumed to be composed of electrons, positive ions and negative ions. When the concentration r of the negative ions is larger than a critical value, a small rarefactive (negative) soliton propagates instead of a compressive (positive) one. When the beam is injected into the plasma, the ion-acoustic wave gradually converts to the fast beam mode. The rarefactive soliton exists when the beam velocity is less than or equal to a threshold value and a compressive soliton exists when the beam velocity is greater than the threshold value. The threshold beam velocity is measured as a function of r and is compared with the theoretical prediction.

Generation of anomalous resistivity and dynamical development of collisionless reconnection in the vicinity of a magnetically neutral sheet are investigated by means of a three-dimensional particle simulation. For no external driving source, two different types of plasma instabilities are excited in the current layer in the same way as the two-dimensional case. The lower hybrid drift instability is observed to grow in the periphery of the current layer, but it cannot penetrate into a high-beta region near the neutral sheet. Instead, a low-frequency electromagnetic (EM) instability is excited at the neutral sheet after saturation of the lower hybrid drift wave. Thus, the interaction between this EM wave and charged particles can cause an anomalous resistivity in the neutral sheet. When an external driving flow exists, collisionless reconnection is triggered by the particle kinetic effect and the anisotropic ion distribution is formed through the anomalous ion heating inside the current layer.

Theoretical results on Alfvén wave (AW) heating, current drive and plasma flow, which may be relevant for improved confinement scenarios, are presented. It is shown that a small population of light impurities, such as carbon, in a hydrogen plasma can strongly modify the dispersion of global Alfvén waves and the Alfvén continuum. The current drive and plasma flow induced by AWs are studied for magnetized weakly collisional plasmas. We find that plasma flow and ion banana orbit squeezing by the radial electric field shear induced by AWs may be a convenient trigger for the formation of transport barriers in tokamaks. These effects are explored via a series of numerical calculations for the heating conditions foreseen for the tokamak chauffage Alfvén wave heating experiment in Brazil (TCABR).

Fast electrons generated in front of lower hybrid (LH) grills can cause damage to tokamak divertor and first wall components. It is therefore of interest to identify possible edge electron acceleration mechanisms and suggest measures to limit these. One possible acceleration process described here depends on mode overlap in the antenna electric field spectrum and on the presence of high- modes, resonant with the ambient ( eV) edge electrons. These electrons then diffuse throughout the globally stochastic region of -space whose upper bound is given by the last overlapping mode. It is shown that the described acceleration is seriously aggravated by the presence of higher order waveguide modes generated at sharp waveguide-plasma transitions and that rounding-off the waveguide septa can considerably reduce the fields and electron acceleration associated with these higher order modes. Additional antenna field non-uniformities arising from a grill modular structure and random fields generated at the plasma edge through parametric decay and scattering of the LH slow wave from plasma density fluctuations can further enhance the edge electron energy.

It has long been common to use ideal magnetohydrodynamic (MHD) steady states as a zeroth approximation for confined plasmas, even when the behaviour of `resistive' instabilities was under discussion. Implicitly, the zeroth order resistive terms discarded are formally larger than the first order ones kept. Most of our normal mode vocabulary derives from these (ideal, zero-flow) MHD steady states and their perturbed behaviour. If the plasma is regarded as resistive, with both Ohm's law and Faraday's law being taken seriously along with the equation of motion and boundary conditions are included, then the situation becomes much more complex. It is far from clear which, if any, of the ideal zero-flow steady states are close to a realizable resistive one. We have been reconsidering this problem in the spirit of hydrodynamic shear flows, and have reached somewhat different conclusions than have been reached in previous decades. In a toroid, vortical flows seem to be a universal feature of the resistive steady states that are found. These flows involve both toroidal vorticity and (higher order) toroidal velocity and have characteristic patterns that are more or less unique for a given set of boundary conditions. Arbitrary `source' terms for the supply of mass and the maintenance of pressure gradients are unnecessary. No expansions in the inverse aspect ratio are involved. The numerical value of the kinematic viscosity and the correct form of the viscous stress tensor are important and reliable experimental information on these seems to be in short supply. A reconsideration of the fundamentals of confinement theory seems to be in order.

A systematic laboratory study of controlled density and temperature filaments having transverse scale length comparable to the electron skin-depth has been performed in the large plasma device (LAPD) at UCLA. It is found that large amplitude shear Alfvén waves develop spontaneously and are localized within the filaments. As the plasma conditions change (e.g., lowering the plasma beta parameter or increasing the heating power) the highly coherent eigenmodes develop into broad band Alfvénic turbulence. A kinetic description that includes the effect of coulomb collisions has been developed to understand the linear properties of the modes. Excellent agreement with the measured eigenfunctions is found for the density filaments in the higher beta regime in which the modes remain strongly coherent. The similarity between the broad band fluctuation spectra generated in a variety of plasma configurations suggest the possibility of a universal process involving filamentary structures and spontaneously generated Alfvénic turbulence.

The propagation and interaction characteristics of nonlinear coherent structures for the electron magnetohydrodynamic (EMHD) model are studied numerically. A point vortex model (PVM) for EMHD is developed which provides a good qualitative understanding of the underlying processes observed numerically. A methodology to extend the PVM for quantitative understanding of the interaction amongst extended structures is also outlined.

The first experimental campaign of the TJ-II stellarator has been conducted using electron cyclotron resonance heating (, ) with a pulse length of . The flexibility of the device has been used to study five different configurations varying plasma volume and rotational transform. In this paper, the main results of this campaign are presented and, in particular, the influence of plasma-wall interaction phenomena on TJ-II confinement is briefly discussed.

At W7-AS, confinement properties are analysed and compared mainly with neoclassical predictions for quite different conditions. Low-density electron cyclotron resonance heating (ECRH) discharges allow access to the very-long-mean-free-path regime for electrons ( up to 6 keV) whereas pure neutral beam injections (NBI) and combined NBI/ECRH discharges at high density ( at ) lead to high performance ( up to 50 ms). Depending on the achieved temperatures, the experimental transport analysis in the plasma core is consistent with the neoclassical predictions. The experimentally observed `electron root' feature with strong is driven by the convective flux of ripple-trapped suprathermal electrons generated by the ECRH absorption. `Optimum' confinement is obtained in discharges with narrow density, but broad temperature profiles with steep gradients in the region of low densities and strong close to the plasma edge. The large radial electric fields, both positive and negative, strongly reduce neoclassical transport. The achieved temperatures, however, are limited by the strong temperature dependence of the neoclassical transport.

Radial electric field is a key physical quantity in determining the structure of toroidal helical plasmas, owing to the nonlinear dependence of transport on the radial electric field. It has been observed that the potential profiles show various interesting patterns in space and time in the compact helical system (CHS) plasmas. In particular, the phenomenon of electric pulsation, clearly demonstrates the nature of bifurcation of radial electric field in toroidal helical plasmas.

Global and local edge parameters at the H-mode transition are investigated at edge densities below and near the H-mode density limit. Conditions for onset of edge magnetohydrodynamic (MHD) instability (ELMs) and sustaining the H-mode define an operational window for H-mode with a maximum edge density, which can only be reached with optimum adjustment of both heating and fuelling fluxes. Careful experiments are carried out to vary the edge density in a wide range and allow comparison with H-mode theories in various collisionality regimes.

Magnetic and electrostatic fluctuations are measured in the CASTOR tokamak with a reasonable spatial and temporal resolution to better understand the nature of turbulent processes in tokamaks. We have found that the broadband magnetic fluctuations in the plasma core are nearly independent of the safety factor q(a). However, their level is dramatically reduced (by a factor of three) when the aspect ratio increases from 5.4 to 6.6. The character of electrostatic structures in the edge plasma was found to be quite similar to that observed in large tokamak experiments. Furthermore, the fluctuations of the longitudinal current have been identified in the scrape-off layer. These fluctuations might represent a link between the magnetic and electrostatic components of plasma turbulence in this region.

Extensive studies of a steady-state tokamak reactor have been carried out on the superconducting tokamak TRIAM-1M. A discharge of lasting more than 2 h has been demonstrated using a 2.45 GHz lower hybrid current drive (LHCD). A high-density plasma of has been sustained for 1 min using a 8.2 GHz LHCD under the high average wall loading of on the limiter. Recently, a single-null divertor configuration with high elongation was also successfully maintained for 1 min by the 2.45 GHz LHCD. A transition of the ion temperature from 0.6 keV to about 2.5 keV is observed in 2.45 GHz LHCD plasmas; this operational regime is called the `high ion temperature (HIT)' mode. The `HIT' mode is characterized by the existence of a steep gradient near . It is found that the `HIT' mode appears in a narrow window of the electron density and horizontal plasma position. The `HIT' mode can be successfully maintained for over 1 min with accurate control of the density and position.

The results of two different series of experiments on generation lasing action in the soft x-ray region are presented. In the first series lasing in hydrogen-like Li III ions at 13.5 nm (2-1 transition to ground state) in a 5 mm long LiF microcapillary at 2 Hz repetition rate is demonstrated. The initial plasma was created in a 0.3 mm diameter microcapillary by a low power Nd:YAG laser (0.1 J in 5 ns), whereas the plasma pumping was proceeded with a 50 mJ, 250 fs UV laser. In the second series lasing is demonstrated in hydrogen-like B V ions at 26.2 nm (3-2 transition) using a very small Nd:YAG pumping laser (0.45 J in 8 ns) at a repetition rate of 1 Hz. The preplasma in a microcapillary was created from wall ablation with a 0.2 J (20 ns) KrF laser, and the whole soft x-ray lasing system takes up less space than is available on a m optical table. In the last part of the paper the development of soft-x-ray lasers (SXLs) for application in lithography and soft x-ray microscopy is discussed.

Key phenomena controlling the transport barrier in H-mode plasmas on the Alcator C-Mod tokamak are discussed. Type I edge localized modes (ELMs) are not observed. Instead the particle transport barrier is continuously degraded giving rise to `enhanced ' operation which avoids the deleterious impurity accumulation observed in `ELM-free' H-modes. The dependence of operational regime on plasma parameters suggests that the instability responsible for barrier degradation is enhanced by higher pressure and longer field-line connection. Detailed analysis of the magnetic structure of fluctuations associated with the different H-mode regimes shows that these field-aligned fluctuations propagate with large perpendicular velocities believed to represent the large velocity shear responsible for barrier formation. In the enhanced regime the fluctuations are generally more incoherent, but have not otherwise yet shown a specific distinctive character.

The isotope dependence of the H-mode power threshold and the energy confinement time have been examined in dedicated experiments on the Joint European Torus (JET) in hydrogen, deuterium and tritium plasmas. The results show that: (1) The H-mode power threshold is inversely proportional to the effective isotopic mass, M, of the plasma. (2) The edge electron pedestal temperature at the L to H-mode transition scales as . (3) The global thermal energy confinement time, , does not depend strongly on M, i.e. in the ohmic, L-mode, edge localized modes (ELMy) and ELM-free H-mode confinement regimes with , if the engineering parameters such as current, magnetic field, density, power and geometry are kept fixed. (4) In the ELMy H-mode regime the transport in the core and the edge of the plasma scale differently with M, i.e. the core transport increases weakly with M whereas the edge transport decreases strongly with M.

Recent progress in plasma polarization spectroscopy (PPS) research is reviewed. Besides discharge plasmas and solar plasmas, the first class of plasma which has become the subject of PPS research is laser-produced plasmas. Polarization is observed for emission lines and recombination continuum, indicating a spatially (directionally) anisotropic velocity distribution of electrons, especially in very-low-energy regions. Tokamak plasmas are the second class; impurity ion lines are found polarized. A kinetic model, the population-alignment collisional-radiative model, was constructed and the experimental line intensity and polarization are interpreted in terms of the electron velocity distribution function. Recently, atomic physics relevant for PPS has made substantial progress. Several facets, experimental and theoretical, are mentioned.

Previous calculations of turbulent magnetohydrodynamic (MHD) eddy viscosity and anomalous resistivity are reviewed. Emphasis is laid on a new approach to fully developed turbulence proposed by Canuto and Dubovikov, containing both systematic and heuristic elements for the ultraviolet (UV) and infrared (IR) parts of the nonlinear interactions in hydrodynamics. Their method is extended so that the magnetic and velocity fluctuations are treated on an equal footing. The effective magnetic Prandtl number is obtained as a function of the residual energy spectral density.

Recent results and future challenges in the systematic analytical description of plasma turbulence are described. First, the importance of statistical realizability is stressed and the development and successes of the realizable Markovian closure are briefly reviewed. Next, submarginal turbulence (linearly stable but nonlinearly self-sustained fluctuations) is considered and the relevance of nonlinear instability in neutral-fluid shear flows to submarginal turbulence in magnetized plasmas is discussed. For the Hasegawa-Wakatani equations, a self-consistency loop that leads to steady-state vortex regeneration in the presence of dissipation is demonstrated and a partial unification of recent work of Drake (for plasmas) and of Waleffe (for neutral fluids) is given. Brief remarks are made on the difficulties facing a quantitatively accurate statistical description of submarginal turbulence. Finally, possible connections between intermittency, submarginal turbulence and self-organized criticality (SOC) are considered and outstanding questions are identified.

As a result of turbulence and finite Larmor radius effects, random radial currents are present in a tokamak plasma and these drive sheared axisymmetric poloidal flows. We model these currents with a noise source with given statistical properties and calculate the linear kinetic response to this source. Without collisions, there is no long term damping of these flows; when collisions are included, poloidal flows are damped. The mean square potential associated with these flows is given in terms of the linear response function we calculate and a model correlation function for the current source. Without collisions, the mean square flow increases linearly with time, but with collisions, it reaches a steady state. In the long correlation time limit, the collisionless residual flows are important in determining the mean square flow.

It is becoming clear that anomalous transport in an L-mode tokamak plasma is dominated by radially extended non-local modes in toroidal geometry. This indicates that various improved modes such as the internal transport barrier (ITG) formed in a recent reversed magnetic shear experiment can be achieved by suppressing such a global structure of the toroidal mode. We investigate the role of plasma shear rotation and negative/weak and also reversed magnetic shear on these non-local modes by employing our toroidal simulation code together with a non-local theory. From simulations, in addition to the overall reduction of the wave excitation in the entire negative magnetic shear region, we find that the weak or zero magnetic shear which appears near the minimum q (safety factor) surface breaks up toroidal coupling. This leads to a discontinuity (or gap) in wave excitation around the -surface, leading to the emergence of the transport barrier. The plasma shear rotation which is observed in the experiment enhances the discontinuity so that the performance of the discontinuity is increased. We also investigate the structure of the self-generated radial electric field induced by such ITG modes and the related plasma shear rotation (referred to as the zonal flow) which influence the fluctuation level in the steady state.

Plasma transport at the magnetic axis in toroidal confinement systems is systematically investigated by means of a variational principle for the rate of irreversible entropy production. All the transport coefficients are derived in the banana regime, among them, the bootstrap current and the ion heat conductivity in tokamaks. In the reactor scale, the bootstrap current density may reach 10% of the total plasma current density at the magnetic axis in contrast to the traditional neoclassical results, for which the bootstrap current vanishes at the magnetic axis. The ion heat conductivity has weaker dependence on the magnetic field. We call it Bohm-like diffusion. High temperature is favourable in confinement. The scaling of the transport can be understood in terms of a random walk process in the step of the so-called potato width.

The problem of magnetic reconnection in three-dimensional (3D) magnetic configurations has been studied experimentally. The research has concentrated on the possibilities of formation of current sheets, which represent crucial objects for a realization of magnetic reconnection phenomena. Different types of 3D magnetic configurations were examined, including configurations with singular lines of the X-type, non-uniform fields containing isolated magnetic null-points and without null-points. It was revealed that formation of quasi-one-dimensional current sheets is the universal process for plasma dynamics in 3D magnetic fields both with null-points and without. At the same time the peculiarities of current sheets, plasma dynamics and magnetic reconnection processes depend essentially on characteristics of 3D magnetic configurations. The result of principal significance obtained was that magnetic reconnection phenomena can take place in a wide range of 3D magnetic configurations as a consequence of their ability to form current sheets.

A review of recent work on collective neutrino-plasma interactions is presented. The basic physical concepts of this new field as well as some possible astrophysical problems where the physics of collective neutrino-plasma interactions can have a radical impact, are discussed.

Current-vortex filament solutions to the two-fluid plasma equations that describe drift-Alfvén waves are presented. Such filament systems are Hamiltonian. Integrable three and four filament systems are discussed in some detail. A wide variety of orbit topologies exists in the plasma case. Special attention is paid to collapses where all filaments contract to a single point. The differences and extensions with respect to point vortex solutions in two-dimensional (2D) incompressible Euler systems is pointed out.

Spontaneous improvements of plasma confinement during auxiliary heating have been observed in many tokamaks when the q profile has been modified from its normal resistive equilibrium so that q>1 and the magnetic shear is reduced or reversed in a region near the magnetic axis. The effects on the overall plasma confinement result from the formation in the plasma interior of transport barriers, regions where the thermal and particle transport coefficients are substantially reduced. These internal barriers are sometimes tied to unique magnetic surfaces, such as the surface where the shear reverses. The reduction in transport appears to result from the suppression of turbulence by sheared plasma flow, which has now been measured in TFTR. Extensions of the theory for turbulence suppression show that this underlying paradigm may also explain other regimes of improved core confinement. The excitement generated by these discoveries must be tempered by the realization that transport and stability to pressure-driven MHD instabilities are intimately linked in these plasmas through the bootstrap current and the effect of the resulting current profile on the transport. Thus the development of control tools and strategies is essential if these improved regimes of confinement are to be exploited to improve the prospects for fusion energy production.

Formation of core regions in Tore Supra and JET tokamaks with reduced transport coefficients is reported. Characteristics of the enhanced confinement regions and the physics process involved in their formation and maintenance should be considered separately when the electron or ion components are predominantly heated.

In Tore Supra and JET, central electron temperature transitions are observed by injecting lower hybrid waves at modest power levels during the current ramp-up phase of the discharges. Transport analyses stress the importance of the low magnetic shear in the core to explain the anomalous electron transport reduction.

With high-power dominant ion heating schemes in JET (neutral beam injection and ion cyclotron resonance heating), internal transport barriers have been obtained in plasmas fuelled with a mixture of deuterium-tritium (D-T) ions leading to a successful production of fusion power (8.2 MW) in this regime. Similar additional power levels to those applied in pure deuterium (D-D) plasmas are required to establish internal transport barriers in D-T plasmas. In D-D and D-T plasmas, ion thermal diffusivities are reduced close to their neoclassical levels in the plasma core and electron thermal diffusivities decrease by one order of magnitude at midplasma radius. The combined role of magnetic shear and velocity shear can explain the formation and evolution of plasma core regions with low energy transport coefficients.

NIMROD is a code development project designed to study long-wavelength, low-frequency, nonlinear phenomena in toroidal plasmas with realistic geometry and dynamics. The numerical challenges of solving the fluid equations for a fusion plasma are discussed and our discretization scheme is presented. Simulations of a resistive tearing mode show that time steps much greater than the Alfvén time are possible without loss of accuracy. Validation tests of a resistive interchange mode in a shaped equilibrium, a ballooning mode and nonlinear activity in reversed-field pinches are described.

Pressure driven curvature instabilities at the boundary of a tokamak plasma are studied. First, three-dimensional turbulence simulations are presented including the case where magnetic field lines are stochastic. Three main features are observed: (i) the level of pressure fluctuations decreases in the ergodic layer. (ii) This is essentially due to a suppression of large-scale structures. (iii) The turbulent heat diffusivity does not decrease in the stochastic layer due to an increase of electric field fluctuations. These observations are in agreement with turbulence measurements on Tore Supra. Second, particle flux driven turbulence in the scrape-off layer (SOL) is studied using a two-dimensional code. The transverse transport is found to be ballistic and intermittent. Bursts propagate outwards with a radial velocity of the order of one tenth of the parallel velocity. Test particles undergo outward and inward trajectories. The order of magnitude of the e-folding SOL length is in agreement with experimental data.

This work presents results of two experiments accomplished at the Institute of Plasma Physics and Laser Microfusion (IPPLM) in Warsaw: (1) investigations of the influence of magnetic field on a laser-produced plasma in the presence or absence of the background plasma, (2) investigations of dynamics of laser-produced plasma in a strong magnetic field. The aim of experiment 1 (performed in collaboration with the Institute of Laser Physics (ILP) RAS, Novosibirsk, Russia) was laboratory simulation of depolarization and deflection of plasma streams drifting across magnetic field in geoplasma background. An Nd:glass laser (5 ns, 2 J) was used to produce the plasma inside Helmholtz coils . The diagnostics for studying the interaction processes were: ion collectors, Langmuir and magnetic probes and an image converter camera. We present a comparison of the effects investigated in that experiment with some phenomena occurring in the geoplasma. In experiment 2 the plasma was produced by means of a Nd:glass laser (1 ns, 10 J) focused on a solid target located in a single-turn coil . Plasma expansion was investigated with an automated interferometer along the magnetic field lines and perpendicular to these lines. From the interferograms, it has been revealed that the plasma stream has a clear asymmetry for caused by an unmagnetized ion Rayleigh-Taylor instability.

We present some results concerning the possibility of determining the structure of solar active regions using measurements of the vector magnetic field on the Sun surface as boundary conditions for the new numerical extrapolation codes. From these computations the main features of these configurations, as shear and twist (which are particular forms of magnetic helicity), are then used as ingredients to define model problems and solved for the magnetohydrodynamic (MHD) analysis of solar eruptive phenomena, in which ejection (or redistribution) of helicity occurs.

High-resolution numerical simulations on the one hand and solar wind data analysis on the other hand have allowed for much progress in our understanding of magnetohydrodynamic (MHD) turbulence. In particular the high resolution of solar wind measurements has allowed us to characterize the intermittency observed on small scales.

In this paper we will give a schematic view of the main properties of solar wind MHD turbulence and discuss some recent results obtained from the analysis of velocity and magnetic field data measured during the space experiments Helios and ISEE. In particular, we will show that applying Haar wavelets technique to about one year of data taken every minute during the ISEE space experiment, it is possible to calculate spectra and structure functions of the turbulence; moreover the definition of conditioned structure function allows:

(a) for the elimination of intermittency effects in spectra and thus for a clear identification of which kind of phenomenology of nonlinear cascade between Kolmogorov and Kraichnan is taking place in the solar wind turbulence;

(b) for the identification of the most intermittent structures which turn out to be either shock waves or one-dimensional current sheets, at variance with ordinary fluid intermittency, where the most intermittent structures are found to be two-dimensional vortices.