Table of contents

The full text of this introduction is available in the PDF.

Boris Sharkov Programme Committee Chairman ITEP-Moscow, Russia

Gregorio Vlad Scientific Secretary ENEA, Frascati, Italy

The full text of this introduction is available in the PDF.

In the past, JET results have been prominent in defining ITER. Only absolute performances matter in a reactor, and these have to be already optimised, JET can still increase the fusion power and energy produced. The main difficulty toward a reactor is the low performance of the divertor. An hybrid fusion-fission reactor could be an intermediate solution as the fusion power demand is reduced by a factor 10. In this respect, ITER is sufficient to be the core of such an hybrid reactor.

Some of the crucial physics aspects of burning plasmas magnetically confined in toroidal systems are presented from the viewpoint of nonlinear dynamics. Most of the discussions specifically refer to tokamaks, but they can be readily extended to other toroidal confinement devices. Particular emphasis is devoted to fluctuation induced transport processes of mega electron volts energetic ions and charged fusion products as well as to energy and particle transports of the thermal plasma. Long time scale behaviours due to the interplay of fast ion induced collective effects and plasma turbulence are addressed in the framework of burning plasmas as complex self-organized systems. The crucial roles of mutual positive feedbacks between theory, numerical simulation and experiment are shown to be the necessary premise for reliable extrapolations from present day laboratory to burning plasmas. Examples of the broader applications of fundamental problems to other fields of plasma physics and beyond are also given.

The development of the ultraintense laser continues to open up new fields of physics. The laser accelerator development is now entering a new matured stage at which it becomes possible to manipulate in a controllable way the parameters of accelerated charged particle beams. In the electron acceleration the particle injection by breaking wake waves left by the laser pulse in underdense plasmas results in the quasi-monoenergetic beam production. When the ions are accelerated during the laser–matter interaction the tailored multi-layer foil targets provide conditions for the high quality proton beam generation.

Advanced tokamak (AT) research seeks to develop steady-state operating scenarios for ITER and other future devices from a demonstrated scientific basis. Normalized target parameters for steady-state operation on ITER are 100% non-inductive current operation with a bootstrap current fraction f_BS ⩾ 60%, q₉₅ ∼ 4–5 and . Progress in realizing such plasmas is considered in terms of the development of plasma control capabilities and scientific understanding, leading to improved AT performance. NSTX has demonstrated active resistive wall mode stabilization with low, ITER-relevant, rotation rates below the critical value required for passive stabilization. On DIII-D, experimental observations and GYRO simulations indicate that ion internal transport barrier (ITB) formation at rational-q surfaces is due to equilibrium zonal flows generating high local E × B shear levels. In addition, stability modelling for DIII-D indicates a path to operation at β_N ⩾ 4 with q_min ⩾ 2, using broad, hollow current profiles to increase the ideal wall stability limit. Both NSTX and DIII-D have optimized plasma performance and expanded AT operational limits. NSTX now has long-pulse, high performance discharges meeting the normalized targets for an spherical torus-based component test facility. DIII-D has developed sustained discharges combining high beta and ITBs, with performance approaching levels required for AT reactor concepts, e.g. β_N = 4, H₈₉ = 2.5, with f_BS > 60%. Most importantly, DIII-D has developed ITER steady-state demonstration discharges, simultaneously meeting the targets for steady-state Q ⩾ 5 operation on ITER set out above, substantially increasing confidence in ITER meeting its steady-state performance objective.

The dynamic ergodic divertor (DED) on the TEXTOR tokamak allows for the reproducible destabilization of the m/n = 2/1 tearing mode which is phase locked to the external static or rotating perturbation field. In combination with its flexible heating systems (co- and counter-neutral beam injection, ion cyclotron resonance heating, electron cyclotron resonance heating (ECRH) with steerable launcher) dedicated experiments to study the mode onset, properties of large islands and mode stabilization can be performed. The dependence of the mode excitation threshold (field penetration) on the plasma rotation shows a resonance character, with minimum threshold when the external perturbation frequency matches the MHD frequency of the 2/1 mode. Mode stabilization by ECRH heating shows that for the TEXTOR plasma heating is more effective than the current drive in O-point. Extrapolation to ITER yields a significant contribution to the mode suppression originating from the temperature increase within the island. Alfvén-like modes, which have been previously identified in the vicinity of large islands on FTU (Buratti et al2005 Nuclear Fusion45 1446), are found to be created already before island formation above a certain threshold of the externally applied perturbation field.

Impurity accumulation has been observed in many tokamak plasma experiments and predicted by collisional transport theory. However in most experimental cases observed transport departs from the collisional predictions ('anomalous transport'), admittedly due to turbulent effects. Diffusion is used as a criterion to assess the relative contributions of collisions and turbulence to observed impurity transport in the published literature. In the ITER relevant confinement modes (H-mode and internal transport barrier scenarios) turbulence always contributes but with large variations. The predicted parametric dependences of impurity transport are reviewed when available. Information on turbulent diffusion is scarce. Predicted collisional and turbulent convection velocities can be directed either inwards or outwards. The collisional predictions match satisfactorily a number of observations. Theoretical predictions of the turbulent convection velocity including recent quasilinear gyrokinetic results are in qualitative agreement with a dedicated experiment. This is only a first step toward a complete validation of the turbulent impurity convection theoretical models and predictive modelling of impurity transport in tokamaks.

The adoption of a non-uniform dopant profile has substantially increased the tolerance to high mode deformations of our baseline indirect-drive design. In addition, a low deuterium–tritium (DT) gas density, obtained by 'dynamic quenching' at 2.3 K below triple point, could partly compensate for the decrease in robustness due to DT ageing. Finally, the net margin regarding all laser and target technological defects is about 2. As soon as a sufficient amount of laser beams and diagnostics is available, we will shoot pre-ignition experiments to tune the point design. We are studying new targets which need less energy for these campaigns.

We have estimated different direct-drive schemes using indirect-drive beams. The optimal LMJ polar direct-drive configuration is a 2-cone one and leads to marginally igniting targets. A new 2-cone direct-drive scheme, associated with focal spot zooming, allows us to reach ignition with enough margin.

Laser wakefield accelerators offer the possibility of compact electron acceleration. However one of the key outstanding issues with the results reported to date is the electron beam stability. Experiments on two laser systems reveal that the contrast ratio between the ASE pedestal and main pulse is an important factor in determining the quality of the electron beam. With a high contrast ratio (10⁸) the electron beam profile is a well collimated single beam having a low pointing instability (<10 mrad rms). With a lower contrast (10⁶) the beam profile contains multiple beamlets which exhibit a large pointing instability (≃50 mrad rms). A high contrast ratio not only improves the beam pointing stability (≃6 mrad) but also stabilizes the electron beam energy reproducibility (5%).

Dust charge and density fluctuations can substantially change basic plasma properties—dispersion of low frequency modes, plasma fluctuations—and introduce new effects—attraction of negatively charged dust particles, dust and ion stochastic heating—which cannot be found if dust fluctuations are neglected. The kinetic theory of fluctuations is used to describe these effects, in particular the changes in the spectral densities of the plasma fluctuations in un-magnetized plasmas in the presence of dust.

Low-k materials are among the promising interlayer dielectric in terms of reducing the circuit transmission time. H₂/N₂ plasma is currently considered to be appropriate for organic low-k material etching, with both N and H radicals playing important roles on the feature profile of the etching. We have numerically estimated the influence of active species on the feature profile evolution of an organic low-k by changing the H₂/N₂ mixture ratio by using a hybrid numerical model (extended-VicAddress), through the predictive image of the two frequency capacitively coupled plasma in H₂/N₂. We also discuss typical external plasma conditions producing a taper and bowing profiles. The predicted etch rate and feature profile reasonably reproduce the previous experimental results.

The interaction of powder particles, which are confined in the sheath of an asymmetric capacitively coupled rf-plasma, with an external ion beam has been investigated. In contrast to other experiments where particle displacement and oscillations are excited by electric fields or laser radiation, respectively, we excite the particles by additional energetic ions. By this suitable diagnostics, optimization and adjustment of ion beam sources for thrusters or applications in surface treatment can also be provided. By observing the position and movement of the particles in dependence on the discharge parameters we obtained information on the electric field (2.5 × 10³ V m⁻¹) in front of the electrode as well as on the ion drag (1–5 × 10⁻¹⁴N).

Solar flares are generally agreed to be impulsive releases of magnetic energy. Reconnection in dilute plasma is the suggested trigger for the coronal phenomenon. It releases up to 10²⁶ J, accelerates up to 10³⁸ electrons and ions and must involve a volume that greatly exceeds the current sheet dimension. The Ramaty High-Energy Solar Spectroscopic Imager satellite can image a source in the corona that appears to contain the acceleration region and can separate it from other x-ray emissions. The new observations constrain the acceleration process by a quantitative relation between spectral index and flux. We present recent observational results and compare them with theoretical modelling by a stochastic process assuming transit-time damping of fast-mode waves, escape and replenishment. The observations can only be fitted if additional assumptions on trapping by an electric potential and possibly other processes such as isotropization and magnetic trapping are made.

We present the temporal evolution of magnetic field topology (FT) and its 'bifurcation', i.e. 'magnetic reconnection' taking place in the magnetotail with a southward interplanetary magnetic field. According to the FT theory, the magnetic FT is uniquely determined by the signs of real part of Jacobian matrix eigenvalues of the critical points (CPs) i.e. magnetic null points, if their Jacobian matrix of the CPs is not degenerated. This is because FT can change only at CP locations. The signs of the real part of eigenvalues characterize the magnetic field patterns around CPs. At the CP locations, the magnetic field becomes zero. The CPs can be classified into different types of 'saddles points'. In the saddles points, the eigenvectors span characteristic both one- and two-dimensional manifolds, according to their signs. These manifolds and CPs form FT 'skeletons' and determine essentially the global FT. These FT 'skeletons' that include the CPs, characteristic curves and surfaces which are spanned by the eigenvectors of their CPs provide a clear view of the three-dimensional FT. The change in the skeleton, i.e. the change in the FT, is the so-called 'bifurcation' and allows us to show the occurrence of the magnetic reconnections.

Particle acceleration in collisionless shocks is believed to be responsible for the production of cosmic-rays over a wide range of energies, from a few GeV to > 10²⁰ eV, as well as for the non-thermal emission of radiation from a wide variety of high energy astrophysical sources. A theory of collisionless shocks based on first principles does not, however, exist. Observations of γ-ray burst (GRB) 'afterglows' provide a unique opportunity for diagnosing the physics of relativistic collisionless shocks. Most GRBs are believed to be associated with explosions of massive stars. Their 'afterglows', delayed low energy emission following the prompt burst of γ-rays, are well accounted for by a model in which afterglow radiation is due to synchrotron emission of electrons accelerated in relativistic collisionless shock waves driven by the explosion into the surrounding plasma. Within the framework of this model, some striking characteristics of collisionless relativistic shocks are implied. These include the generation of downstream magnetic fields with energy density exceeding that of the upstream field by ∼8 orders of magnitude, the survival of this strong field at distances ∼10¹⁰ skin-depths downstream of the shock and the acceleration of particles to a power-law energy spectrum, d log n/d logε ≈ −2, possibly extending to 10²⁰ eV. I review in this talk the phenomenological considerations, based on which these characteristics are inferred, and the challenges posed to our current models of particle acceleration and magnetic field generation in collisionless shocks. Some recent theoretical results derived based on the assumption of a self-similar shock structure are briefly discussed.

Recent advances in hydrodynamics theory and experiments at the Laboratory for Laser Energetics are described. Particular emphasis is laid on improvements in the implosion stability achieved by shaping the ablator adiabat and on the newly developed designs for fast ignition fuel assembly. The results of two-dimensional simulations and a recent set of implosion experiments on OMEGA are presented to verify the role of adiabat shaping on the hydrodynamic stability of direct-drive implosions. Adiabat shaping laser pulses are also used to implode massive capsules on a low adiabat and low implosion velocity in order to assemble high density plasmas for fast ignition. The areal densities measured in implosion experiments of such targets on OMEGA are among the highest ever recorded in a laser-driven compression experiment. Slow low-adiabat implosions of massive wetted-foam DT capsules are used in the simulations to generate the fuel assemblies for different driver energies. Such dense cores are then ignited by a fast electron beam and the resulting thermonuclear yield is used to compute the target gain. It is shown that a 200 kJ UV laser can assemble fuel yielding about 18 MJ of energy when ignited by 15 kJ of 1–2 MeV electrons.

The present paper reviews the status of the knowledge on materials for fusion power plants, pointing out that they constitute one of the main key issues on the path to future reactors. Specific issues concerning plasma-facing materials, functional materials and structural materials are successively reviewed. The main candidate materials are presented, with emphasis on the remaining open issues in the field of selection and qualification of materials for fusion power reactors.

The impact of large scale flows on turbulent transport in magnetized plasmas is explored by means of various kinetic models. Zonal flows are found to lead to a non-linear upshift of turbulent transport in a 3D kinetic model for interchange turbulence. Such a transition is absent from fluid simulations, performed with the same numerical tool, which also predict a much larger transport. The discrepancy cannot be explained by zonal flows only, despite they being overdamped in fluids. Indeed, some difference remains, although reduced, when they are artificially suppressed. Zonal flows are also reported to trigger transport barriers in a 4D drift-kinetic model for slab ion temperature gradient (ITG) turbulence. The density gradient acts as a source drive for zonal flows, while their curvature back stabilizes the turbulence. Finally, 5D simulations of toroidal ITG modes with the global and full-f GYSELA code require the equilibrium density function to depend on the motion invariants only. If not, the generated strong mean flows can completely quench turbulent transport.

Mechanisms underlying the retention of fuel species in tokamaks with carbon plasma-facing components are presented, together with estimates for the corresponding retention of tritium in ITER. The consequential requirement for new and improved schemes to reduce the tritium inventory is highlighted and the results of ongoing studies into a range of techniques are presented, together with estimates of the tritium removal rate in ITER in each case. Finally, an approach involving the integration of many tritium removal techniques into the ITER operational schedule is proposed as a means to extend the period of operations before major intervention is required.

Bursts of the x-ray and electron cyclotron emission are observed in tokamaks during sawteeth and disruption instability. Analysis of the tangential view x-ray emissivity in the T-10 tokamak has indicated that the bursts are connected with the nonthermal electrons (E_RA ∼ 15–150 keV) localized around the magnetic islands. Dynamics of the x-ray bursts are compared with the phenomenologically similar bursts of electron cyclotron emission observed in experiments in TCV (Klimanov I et al 2005 Rev. Sci. Instrum.76 093504) and DIII-D (Heidbrink W W et al1999 Nucl. Fusion39 1369). Analysis of the magnetic field evolution during a sawtooth crash has indicated that the nonthermal electrons can be connected with reconnection of the helical magnetic fluxes around the q = 1 surface. Localization of the bursts around X-points of the magnetic islands and growth of the bursts amplitude in plasma with increased reconnection rate indicated that nonthermal electrons can be connected with direct acceleration in strong electric fields induced during a sawtooth crash. The possible effect of the magnetic reconnection on the generation of the powerful runaway beams during major disruptions is discussed.

Fast electron transport in matter is a key issue for assessing the feasibility of fast ignition; however several important points are not clear yet. Therefore we realized an experiment with ultra-intense lasers (⩽ 6 10¹⁹ W cm⁻²) studying transport in metallic (Al) and insulating (CH) foil targets. The dynamics of fast electron propagation versus target thickness was investigated by optical self-emission from targets rear side. In Al targets we distinguished two-components in the fast electron population: moderately relativistic electrons and a highly collimated micro-bunched relativistic tail. A large ohmic heating at the rear of the thinner targets was observed due to the background return current. In CH, optical emission is mainly due to the Cherenkov effect and is much larger than in Al. We also observed that in insulators the fast-electron beam undergoes strong filamentation and the number of filaments increases with thickness. This behaviour was attributed to an ionization front instability.

An analysis of the current state of the plasma focus (PF) research is presented. Some new opportunities for the use of PF in studies on high-energy-density physics are discussed. The main attention is paid to the results obtained on one of the world's largest PF-type facilities PF-3 at the Kurchatov Institute. Experimental results of the studies of foam liners and the tungsten wire arrays dynamics in the PF discharge are presented. A new approach to load formation using a cloud of free fine-disperse particles of condensed matter (dust) is proposed. Being a source of additional mass, the dust particles essentially affect the development of MHD and RT instabilities. It is manifested, in particular, in an increase in MHD stability. The main tendencies in PF research, including application problems, are discussed.

Contemporary capacitive discharges are often driven by a combination of at least two frequencies to achieve independent control of the ion flux and the ion energy impacting the electrodes. This multiple frequency excitation leads to new electron heating mechanisms that are discussed in this paper. Firstly, we show that electron heating in the sheath is greatly enhanced by the combination of two frequencies, i.e. the heating produced is much larger than the sum of the two single contributions. Secondly, we show that when the higher frequency is such that the corresponding wavelength becomes comparable to the electrode size, electromagnetic effects become important and a significant amount of heating is provided by the inductive field. The discharge experiences a capacitive-to-inductive transition when the high frequency voltage amplitude is raised.

Shocks at solar wind stream interaction regions, coronal mass ejections and magnetospheric obstacles have long been known for their intimate link with particle acceleration. Much enhanced capabilities to determine mass and charge composition at interplanetary shocks with ACE and SOHO have enabled us to identify sources and acceleration processes for the energetic particles. Both solar wind and interstellar pickup ions are substantial sources for particle acceleration in corotating interaction regions and at coronal mass ejections driven shocks and that flare particles are re-accelerated. Suprathermal distributions, such as pickup ions and pre-existing flare populations are accelerated much more efficiently than particles out of the solar wind. Recent results of the termination shock crossing by Voyager I and the scientific goals of the upcoming IBEX mission will be discussed.

The heating of the solar coronal plasma has remained one of the most important problems in solar physics. An explanation of the electron and ion heating rests on the identification of the energy source and appropriate physical mechanisms via which the energy can be channelled to the plasma particles. In this paper, we discuss two important nonlinear aspects of the electron and ion heating caused by finite amplitude obliquely propagating dispersive Alfvén (DA) waves and magnetic field-aligned circularly polarized electromagnetic ion–cyclotron Alfvén (EMICA) waves that may exist in the solar terrestrial environment. Specifically, DA waves may contribute to the solar coronal electron heating via Joule heating involving electron–wave interactions, and resonant ion EMICA wave interactions may contribute to differential ion heating in the solar corona.

We present analytical and numerical studies of the dynamics of relativistic electron and ion holes in a collisionless plasma. Electromagnetic radiation can be trapped in relativistic electron phase-space holes mainly due to the relativistic mass increase of the electrons that are accelerated by the potential of the phase-space hole and by the quivering component of the electromagnetic field. Relativistic ion holes may exist in plasmas where the electrons are thermalized to extremely ultra-relativistic energies. They may be responsible for the acceleration of particles to GeV energies in active galactic nuclei and supernova remnant shocks. The analytic solutions are employed as initial conditions for numerical simulations in which the dynamics and stability of the phase-space holes are investigated. The results have relevance for intense laser–plasma experiments and for astrophysical plasmas.

The recent fast heating of a compressed core to 0.8–1 keV temperature as well as the previous high-density compression of 600 times liquid density have provided proof-of-principle of the fast ignition (FI) concept. These results have significantly contributed to official approval of the first phase of the FI realization experiment (FIREX) project. The goal of FIREX-I is to demonstrate fast heating of a fusion fuel up to the ignition temperature of 5–10 keV. Although the fuel of FIREX-I is too small to be actually ignited, sufficient heating will provide the scientific viability of ignition and burn by increasing the laser energy, thereby increasing the fuel size. The FIREX programme is being carried out in collaboration with the Institute of Laser Engineering, Osaka University and the National Institute for Fusion Science, including the development of cryogenic targets, holistic simulation systems and diagnostic equipment.

Plasmas are magnetically confined if the orbits of the charged particles around the magnetic field lines are small compared to the system size. Nevertheless, particles and energy are lost via transport resulting from the fluid-like drifts of these orbits across the magnetic field. Computation of this type of low frequency electromagnetic turbulence is introduced with emphasis on nonlinear character and energetics. The physical situation is low frequency dynamics with perpendicular forces in quasistatic balance and fast gyrofrequency leading to treating the orbit gyrocentres rather than the particles themselves. The broadband turbulence necessarily involves the ion gyroradius scale in any tokamak application. Hence the use of 'gyrofluid' and 'gyrokinetic' computational models. Computations must also treat the interplay between electromagnetic wave dynamics along the magnetic field and fluid-like turbulence across it, with a method independently checked against both of these sub-processes. Tokamak core and edge turbulence differ according to the ratios of the parallel (electron) and perpendicular (E-cross-B) transit frequencies. The turbulence is also in energetic contact with flows and currents associated with the equilibrium, so computations must be well behaved over very long run times and at least the perturbed equilibrium carried self-consistently. These considerations are illustrated by treating the case of ion temperature gradient instabilities giving rise to turbulence which is then suppressed by self generated E-cross-B flows. The methods of diagnosis of the physical processes are detailed. The situation of edge turbulence and interaction with the equilibrium is briefly addressed.

In collisionless space plasmas most phenomena are governed by wave particle interaction and by the interaction with the large scale fields. Low frequency magnetic turbulence in the solar wind is relatively well characterized and understood. The situation is more complicated for magnetic turbulence in and around the Earth's magnetosphere, where the turbulence feature can vary widely with the location. Recent spacecraft observations of magnetic turbulence in the magnetosheath, in the polar cusp regions and in the magnetotail are considered. Turbulence features like the fluctuation level, the spectral power law index, the turbulence drivers and the turbulence anisotropy and intermittency are addressed. The influence of such a turbulence on the plasma transport and dynamics is briefly described, also using the results of numerical simulations.

Shocks play a key role in plasma thermalization and particle acceleration in the near Earth space plasma, in astrophysical plasma and in laser plasma interactions. An accurate understanding of the physics of plasma shocks is thus of immense importance. We give an overview over some recent developments in particle-in-cell simulations of plasma shocks and foreshock dynamics. We focus on ion reflection by shocks and on the two-stream instabilities these beams can drive, and these are placed in the context of experimental observations, e.g. by the Cluster mission. We discuss how we may expand the insight gained from the observation of proton beam driven instabilities at near Earth plasma shocks to better understand their astrophysical counterparts, such as ion beam instabilities triggered by internal and external shocks in the relativistic jets of gamma ray bursts, shocks in the accretion discs of micro-quasars and supernova remnant shocks. It is discussed how and why the peak energy that can be reached by particles that are accelerated by two-stream instabilities increases from keV energies to GeV energies and beyond, as we increase the streaming speed to relativistic values, and why the particle energy spectrum sometimes resembles power law distributions.

Much of plasma behaviour is governed by multiple distinct nonlinear processes, operating on a wide range of lengthscales and timescales, that are coupled together in innumerable feedback loops. Capturing and quantifying this nonlinear behaviour is crucial at all levels of description, ranging from individual events to global phenomenology. In recent years, a range of techniques derived from complex systems science has been applied successfully to nonlinear plasma datasets. The present paper reviews several of these techniques in the context of applications spanning fusion, space, solar and astrophysical plasmas. Topics include non-Gaussian probability density functions, notably extreme event distributions in fusion and astrophysics and power law distributions in the solar context; differencing and rescaling of fluctuation data, which has yielded information on the number of dominant plasma turbulent processes, and the spatiotemporal ranges over which they operate, in plasmas ranging from microquasar accretion discs to L-mode and dithering H-mode fusion plasmas in the MAST tokamak; quantitative measures of mutual information content and pattern repetition between causally linked but spatiotemporally separated nonlinear events in solar wind and magnetospheric plasmas; global statistics of full-disc solar irradiance; and ELMing, considered as a sequence of pulsed events, in H-mode fusion plasmas in the JET tokamak. These developments in nonlinear plasma data characterization provide fresh additional insights into the underlying plasma physics. They also provide new opportunities for comparing models with data, and with each other, and open avenues for the development of a more rigorous predictive capability in this field.

An overview of the interactions between waves and particles in plasmas is given. Interest is focused on cases where special particle populations, like energetic particle tails, interact with waves. The two basic, but inter-related, mechanisms through which waves and particles can exchange energy, resonance and stochastization are briefly illustrated. The basic non-collisional interaction mechanisms and their description through quasilinear theory are reviewed. The present state of modelling and comparison with experiments in fusion plasmas is addressed. With respect to astrophysical plasmas, three topics are examined: (i) the generation of cosmic rays, (ii) the heating and fast particle generation in the solar corona and (iii) the whistler wave generation in the magnetosphere.

During the last ten years, the ability of high power lasers to generate high energy density shocks has made them a reliable tool to study extreme states of matter. These states of matter are relevant in many important physics areas such as astrophysics, planetology and ICF physics. Here, we present some representative studies performed by using a driven laser shock: melting of iron at pressures relevant for geophysics, developments of new techniques to measure the density of highly compressed matter and a study of a radiative shock.

Electron cyclotron resonance heating (ECRH) is a mature technology that has progressed constantly over a period of forty years, particularly as a tool in magnetic confinement fusion. As with other heating methods, this technique has seen a steady increase in the sophistication of its applications, from bulk heating through profile tailoring and finally to distribution function engineering. By comparison with other techniques, ECRH presents the significant advantages of good coupling, localized power deposition, easy launching and precise directionality. This paper reviews some recent applications related to third harmonic ECRH and highlights the role of the relaxation dynamics of suprathermal electrons, both in real space and in velocity space, in regulating the overall effect of ECRH on fusion plasmas. A technique for direct visualization of these relaxation phenomena, using modulated ECRH, is described and demonstrated.

The RFX reversed field pinch experiment has been modified (RFX-mod) to address specific issues of active control of MHD instabilities. A thin shell (τ_Bv∼50 ms) has replaced the old thick one (τ_Bv∼500 ms) and 192 (4 poloidal × 48 toroidal) independently powered saddle coils surround the thin shell forming a cage completely covering the torus. This paper reports the results obtained during the first year of operation. The system has been used with various control scenarios including experiments on local radial field cancellation over the entire torus surface to mimic an ideal wall ('virtual shell') and on single and multiple mode feedback control. Successful virtual shell operation has been achieved leading to: a 3-fold increase in pulse length and well controlled 300 ms pulses(∼6 shell times) up to ∼1 MA plasma current; one order of magnitude reduction of the dominant radial field perturbations at the plasma edge and correspondingly 100% increase in global energy confinement time. Robust feedback stabilization of resistive wall modes has been demonstrated in conditions where rotation does not play a role and multiple unstable modes are present.

In local island (m/n = 1/1) divertor discharges in the large helical device a stable super dense core plasma develops when a series of pellets are injected. A core region with a density as high as 4.6 × 10²⁰ m⁻³ and a temperature of 0.85 keV is maintained by an internal diffusion barrier with a very high density gradient. In a study of island dynamics, we find that an externally imposed large island (m/n = 1/1) as large as 15% of the minor radius is healed when beta at the island exceeds a critical value.

We present in this paper a discussion of the properties of plasmas generated in microhollow cathode geometries and in microcathode sustained discharge geometries. The results presented here are derived from models. This work is part of a joint modelling/experimental programme whose objective is the evaluation of the potential of the high-pressure, non-thermal plasmas created in microdischarges (e.g. discharges in small, 100s of micrometre sized geometries) for the production of large quantities of radical species, and in particular oxygen singlet delta (metastable) molecules, O₂(¹Δ).

A simple model is developed for the self-consistent charging of a dust layer in an electrode plasma sheath, as well as for the force balance in this layer. The anisotropy of the plasma pressure near the plasma boundary makes it possible to introduce the notion of surface tension. The equilibrium charge, the height at which the dust layer levitates above the electrode, and the plasma surface tension are calculated numerically as functions of the dust density. In all the cases under analysis, the presence of dust is shown to increase the plasma surface tension, which indicates that the plasma sheath may become structurally unstable.

A thorough analysis of the electromagnetic instabilities encountered in the beam plasma interaction physics shows that the most unstable modes are not the ones usually studied. We characterize these most unstable modes and determine the patterns they create. A fluid model able to reproduce the kinetic results in the small temperature regime is presented, as well as exact kinetic calculations in the high temperature limit.

This paper describes and further develops the understanding of toroidal momentum transport. Nonlinear gyro-kinetic simulations of the ion temperature gradient mode with adiabatic electrons show a strong coupling between the momentum and ion heat transport, with the ratio of the transport coefficients close to 1. Linear theory using a global description predicts an off-diagonal contribution to the momentum flux even in the absence of a radial electric field. The influence of the toroidal velocity gradient on the ion temperature profile is found to be small in the H-mode. These predictions are in qualitative agreement with experimental observations.

Over the last years, owing to hardware progress and the development of new methods, reflectometry has become a common diagnostic on plasma fusion devices. This paper presents some results obtained with reflectometry on transport, turbulence and magnetohydrodynamic (MHD). The emphasis is put on some new results from Tore-Supra. Combining the density profile and fluctuation measurement, it was shown on Tore-Supra that the particle pinch inside the q = 1 surface is close to the neoclassical value in ohmic plasma, while the observed small diffusion is in agreement with a very low level of density fluctuations inside the q = 1 surface. In β scaling experiments, no change in the fluctuation levels was found on Tore-Supra, in agreement with the observation of weak confinement degradation with increasing β. Zonal flows have been detected by Doppler reflectometry in ASDEX-U and with correlation reflectometry in T-10. On Tore-Supra, a fast decrease in the density fluctuation level at high poloidal wavenumbers was measured with Doppler reflectometry, suggesting a minor role of electron temperature gradient driven modes. Various forms of Alfvén eigenmodes (toroidal Alfvén eigenmodes, Alfvén cascades and possibly beta Alfvén eigenmodes) have been detected with reflectometry in TFTR, JET and Tore-Supra. The density fluctuations induced by the mode were found to be higher on the high-field side.

The boundary of the tokamak core plasma, or scrape-off layer, is normally characterized in terms of average parameters such as density, temperature and e-folding lengths suggesting diffusive losses. However, as is shown in this paper, localized filamentary structures play an important role in determining the radial efflux in both L mode and during edge localized modes (ELMs) on MAST. Understanding the size, poloidal and toroidal localization and the outward radial extent of these filaments is crucial in order to calculate their effect on power loading both on the first wall and the divertor target plates in future devices. The spatial and temporal evolution of filaments observed on MAST in L-mode and ELMs have been compared and contrasted in order to confront the predictions of various models that have been proposed to predict filament propagation and in particular ELM energy losses.

Fine scale turbulence is considered nowadays as a possible candidate for the explanation of anomalous ion and electron energy transport in magnetized fusion plasmas. The unique correlative upper hybrid resonance backscattering (UHR BS) technique is applied at the FT-2 tokamak for investigation of density fluctuations excited in this turbulence. The measurements are carried out in Ohmic discharge at several values of plasma current and density and during current ramp up experiment. The moveable focusing antennas set have been used in experiments allowing probing out of equatorial plane. The radial wave number spectra of the small-scale component of tokamak turbulence are determined from the correlation data with high spatial resolution. Two small-scale modes possessing substantially different phase velocities are observed in plasma under conditions when the threshold for the electron temperature gradient mode excitation is overcome. The possibility of plasma poloidal velocity profile determination using the UHR BS signal is demonstrated.

Electron transport in fusion plasmas is intensively studied in coordinated experiments and great progress in physics understanding has been achieved during the past years. A threshold in normalized gradient explains most of the observations, both in steady-state and transient conditions. The results convincingly suggest that trapped electron modes (TEM) dominate electron transport at low and moderate collisionality, with electron heating. The stabilization of these modes at high collisionality predicted by theory is found in the experiments. Electron transport is then driven by the ion temperature gradient modes. At low collisionality, if TEM are stabilized by negative shear and Shafranov shift effects, electron internal transport barriers may develop.

This paper reports the impact of different confinement regimes on the 2D structure of edge turbulence. An image analysis method based on two-dimensional continuous wavelet transformation is used to localize structures (blobs) in the images and to extract their geometrical characteristics (position, scale, orientation angle and aspect ratio). We study the impact of edge shear-layers on these geometrical aspects of blobs. Results show a reduction in the angular dispersion of blobs as the shear layer is established in the boundary, as well as an increase in the elongation of these structures. Similar behaviour is found in NSTX image sequences when going from L to H mode plasmas. During improved confinement regimes the number of detected blobs decreases. Some indications are found suggesting that the turbulence reduction could be scale-selective in the biasing-induced improved confinement regime of TJ-II stellarator. Perpendicular flow reversal is visualized with the cameras and the time scales for flow reversal are found to be less than 50 µs. Radially propagating structures are found in the SOL with velocities in the range ∼1000 m/s and with a poloidally asymmetric spatial distribution.

The nonthermal and nonlinear coupling of strong laser light wave with plasma transfers a part of laser energy into hot electrons and fast ions. The efficiency of these effects depends on the characteristics of a laser pulse, target properties and irradiation geometry.

The reported studies were performed with the use of a high-power and high-energy iodine PALS laser system (energy up to 1 kJ in a 0.4 ns pulse at wavelength of 1315 nm and energy up to 250 J at wavelength of 438 nm). The properties of the laser-produced ion streams were determined with the use of ion diagnostics based on the time-of-flight method. The characteristics of x-rays were measured using various semiconductor detectors.

The main ion stream characteristics as well as the ion acceleration processes in plasmas of different Z numbers were studied in dependence on laser pulse parameters. The parameters of a fast ion group depend evidently on Z number of the ions. The influence of the electron density scale length on fast ion generation was investigated using a low intensity laser pre-pulses to generate preformed plasmas (pre-plasmas) with which the main laser pulse interacted. The obtained results suggest that ion acceleration processes were most effective at a specific electron density gradient scale length of pre-plasma determined by the pre-pulse parameters.

The understanding of detailed processes acting in magnetically confined plasmas is gradually increasing. This can be attributed to a number of reasons: more complete and powerful theoretical calculations and modelling, comparative experiments in different devices, better knowledge of plasma control algorithms and last but not least diagnostic advances (new techniques, higher spatial and temporal resolution, better plasma coverage). This paper will largely focus on new physics insights that can be more or less directly attributed to diagnostic advances. Various examples will be shown to illustrate this. The examples are organized around three main topics: sawtooth physics, imaging techniques and fast ion physics. It should be realized that in most cases it is not just the measurements on their own, but their detailed comparison with theoretical models that yields the better understanding.

The first experimental campaign for ignition, beginning in 2010 after NIF construction and commissioning are completed, will include experiments to measure and optimize key laser and target conditions necessary for ignition. These 'tuning campaigns' will precede the first ignition shots. Ignition requires acceptable target performance in several key areas: energetics, symmetry, shock timing and capsule hydrodynamics. Detailed planning and simulations for 'tuning campaigns' in each of these areas is currently underway, as part of the National Ignition Campaign (NIC) Program. Tuning and diagnostic methods are being developed and tested on present facilities, including the OMEGA laser at the Laboratory for Energetics (LLE), the Z facility at Sandia National Laboratories (SNL), and the Trident laser at Los Alamos National Laboratory (LANL). Target fabrication development is underway at General Atomics (GA), Lawrence Livermore National Laboratory (LLNL), and LANL.