Table of contents

Recent experiments show the impact of resonant magnetic perturbations (RMPs) on the density (Schmitz et al2008 Plasma Phys. Control. Fusion50 124029, Evans et al2008 Nucl. Fusion48 024002, Kirk et al2008 Nucl. Fusion50 024002, Liang et al 2007 Phys. Rev. Lett.98 265004), leading to a so-called density pump-out. Previous comparisons between DIII-D and TEXTOR have focused on the similarities of the deformation of the separatrix and the creation of striations at the intersection of the main chamber wall (Schmitz et al2008 Plasma Phys. Control. Fusion50 124029; Schmitz et al 2009 Phys. Rev. Lett.103 165005). In this paper, we compare the difference in magnitude of the experimentally observed density pump-out in L-mode with H-mode in two diverted tokamaks: MAST and DIII-D. In order to address the differences in magnetic field from the coils, plasma shape and q₉₅ between the two devices, we compute a weighted magnetic diffusion coefficient with a vacuum field line tracing code. This allows us to compare the changes in density pump-out with the weighted magnetic diffusion coefficient, using a simple particle diffusion model. We find that the density pump-out is vastly different in the two confinement regimes, suggesting different particle transport mechanisms. Since one main difference in transport characteristics between L- and H-mode is turbulence, we compare turbulent particle characteristics. We find that in L-mode (MAST) the fluctuations and E × B shear increase at the plasma edge, whereas in H-mode (DIII-D) the fluctuations decrease at the plasma edge. Deeper inside the core, the E × B shear remains similar in L-mode (MAST), whereas a large decrease that quickly saturates with RMP strength is observed in H-mode (DIII-D). These results suggest that the RMP-induced particle transport at the plasma edge in L-mode (MAST) is the result from increases in turbulent particle transport, whereas the results in H-mode (DIII-D) suggest a decrease in turbulent particle transport.

Flat density profiles in tokamak plasmas are characterized by a sudden density rise at the plasma periphery, which may prevent LH waves from penetrating deeper into the center. The reasons may be the deviation of the ray trajectories toward the plasma edge or the lack of validity of the linear optics approximation (WKB). In this paper we solve the wave equations in full wave limit to analyze if outward reflections take place. The results indicate that unless the density rises as a very sharp jump, the reflection is negligible and the linear WKB wave equations are a valid tool to describe the wave ray tracing. These trajectories are deviated across the density rise but their deviation depends on the central density value and scarcely on the rise steepness.

Sheared toroidal rotation is found to increase the ideal external kink stability limit, thought to be the ultimate performance limit in fusion tokamaks. However, at rotation speeds approaching a significant fraction of the Alfvén speed, the toroidal rotation shear drives a Kelvin–Helmholtz-like global plasma instability. Optimizing the rotation profile to maximize the pressure before encountering external kink modes, but simultaneously avoiding flow-driven instabilities, can lead to a window of stability that might be attractive for operating future high-performance fusion devices such as a spherical tokamak component test facility.

In this paper the 0D description of magnetized toroidal hydrogen–helium RF discharges is presented. The model has been developed to obtain insight into the ICRF plasma parameters, particle fluxes to the walls and the main collisional processes, which is especially relevant for the comprehension of RF wall conditioning discharges. The 0D plasma description is based on the energy and particle balance equations for nine principal species: H, H⁺, H₂, , , He, He⁺, He²⁺ and e⁻. It takes into account (1) elementary atomic and molecular collision processes, such as excitation/radiation, ionization, dissociation, recombination and charge exchange, and elastic collisions, (2) particle losses due to the finite dimensions of the plasma volume and confinement properties of the magnetic configuration, and particle recycling, (3) active pumping and gas injection, (4) RF heating of electrons (and protons) and (5) a qualitative description of plasma impurities. The model reproduces experimental plasma density dependences on discharge pressure and coupled RF power, both for hydrogen RF discharges (n_e ≈ (1–5) × 10¹⁰ cm⁻³) and for helium discharges (n_e ≈ (1–5) × 10¹¹ cm⁻³). The modeled wall fluxes of hydrogen discharges are in the range of what is estimated experimentally: ∼10¹⁹–10²⁰ m⁻² s⁻¹ for H atoms, and ∼10¹⁷–10¹⁸ m⁻² s⁻¹ for H⁺ ions. It is found that experimentally evidenced impurity concentrations have an important impact on the plasma parameters, and that wall desorbed particles contribute largely to the total wall flux.

Single helical axis (SHAx) states are the improved confinement RFP helical states, which have been observed at high plasma currents (beyond 1 MA) in the RFX-mod device. A reconstruction of these equilibrium configurations has been implemented in a code named SHEq, where SHAx states are modelled as pure single helicity (SH) states. We consider the helical flux in this work, which happens to be a good flux function for SH equilibrium, and its contours give the shape of the flux surfaces in the helical equilibrium. New curvilinear and non-orthogonal 'helical' coordinate systems are defined in SHEq, with the fundamental request that angles are defined with respect to the helical axis. We look for helical coordinates beginning from the canonical form of the magnetic field B and the Hamiltonian mechanics theory enables us to obtain straight-field-line helical coordinates computing action–angle coordinates.

These coordinate systems are used to determine the helical safety factor q, using the simple formula valid in action–angle coordinates. Very good agreement with the computation of the safety factor using the ORBIT code has been found.

A class of exact axisymmetric tokamak equilibria with sheared flows parallel to the magnetic field is constructed, generalizing previous work on the subject (Kuiroukidis 2010 Plasma Phys. Control. Fusion52 015002). The additional free parameters associated with new terms in the solution make it possible to construct up–down asymmetric configurations with a divertor X-point and desirable values of confinement figures of merit as the safety factor on the magnetic axis and plasma betas; in particular, we construct a number of ITER-pertinent equilibria. Their stability with respect to linear MHD perturbations is also examined by applying a sufficient condition.

This study examines single-particle electron motions in both a plane electromagnetic wave and a Gaussian focus in vacuum. Exact, explicit analytic expressions for relativistic electron trajectories in a plane wave are obtained, using the proper time as a parameter, in the general case of arbitrary initial positions and velocities. It is shown that previous analyses can be completed using the proper-time parameter. The conditions under which localized oscillatory motions ('figure-of-eight' orbits) occur are derived from the new solutions. The general solutions are also connected with the figure-of-eight orbits by a Lorentz transformation. The analytic solutions for arbitrary initial conditions and an arbitrary initial field phase can be used to determine the ranges of electron ejection angle and emerging electron energy in a vacuum laser accelerator, in which electrons are ejected externally, and provide a basis for explaining the spectrum of nonlinear Thomson scattering radiation. Numerical solutions are used for electron motions in the focus of a Gaussian laser beam, and the mean motion allows one to test a new expression for the relativistic ponderomotive force. It is suggested that plane wave solutions can provide a basis for approximating the orbital motion of particles in Gaussian beams.

The plasma motion near the ion front in an expanding collisionless plasma is studied. The boundary of quasineutrality, the range of application of the analytical quasineutral solution and the features of the space charge region are considered. Analytical solutions in combination with computer simulations give the quantity distributions in space and time in the analytical forms. The ion temperature effect and the electron cloud evolution are discussed.

We consider the radial transport of test particles due to the E × B drift motion in the guiding-center approximation. Using an explicit expression to modify the electrostatic potential, we show that it is possible to construct a transport barrier which suppresses radial transport. We propose an algorithm for the implementation of this local modification computed from an electrostatic potential known on a spatio-temporal grid. The number of particles which escape the inner region defined by the barrier measures the efficiency of the control. We show that the control is robust by showing a significant reduction in radial transport, when applied with a reduced number of probes aligned on a circle.

The presence of impurities is considered in gyrokinetic calculations of ion temperature gradient (ITG) instabilities and turbulence in the reversed field pinch device RFX-mod. This device usually exhibits hollow carbon/oxygen profiles, peaked in the outer core region. We describe the role of the impurities in ITG mode destabilization, and analyze whether ITG turbulence is compatible with their experimental gradients.

The Edge Monte Carlo 3D (EMC3)-Eirene code package is applied to simulate the deuterium plasma and neutral particle as well as the tungsten impurity transport in ASDEX Upgrade. Good agreement is found for the deuterium bulk plasma for an L-mode discharge both in the upstream and downstream profiles. The tungsten concentration in the core is computed for a point source placed at different positions around the outer strike point. Comparing the mean impurity residence time for divertor and main chamber sources yields the divertor retention factor R, which shows a very strong dependence on the location of the source relative to the strike point and also on the discharge parameters. While the tungsten transport is strongly suppressed directly at the strike point, it becomes much more efficient in the region 20–100 mm away from it in the far scrape-off layer.

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This paper surveys the basic ideas and results on fundamental models of drift wave turbulence, the formation of zonal flows, shear suppression of turbulence and transport, coupled drift wave and zonal flow dynamics and application to transport bifurcations and transitions. Application to vortex dynamics and zonal flow phenomena in EMHD systems are discussed, as well. These are relevant to aspects of ICF and laser plasma physics. Throughout, an effort is made to focus on fundamental physics ideas.

Progress in the worldwide development of high-power gyrotrons for magnetic confinement fusion plasma applications is described. After technology breakthroughs in research on gyrotron components in the 1990s, significant progress has been achieved in the last decade, in particular, in the field of long-pulse and continuous wave (CW) gyrotrons for a wide range of frequencies. At present, the development of 1 MW-class CW gyrotrons has been very successful; these are applicable for self-ignition experiments on fusion plasmas and their confinement in the tokamak ITER, for long-pulse confinement experiments in the stellarator Wendelstein 7-X (W7-X) and for EC H&CD in the future tokamak JT-60SA. For this progress in the field of high-power long-pulse gyrotrons, innovations such as the realization of high-efficiency stable oscillation in very high order cavity modes, the use of single-stage depressed collectors for energy recovery, highly efficient internal quasi-optical mode converters and synthetic diamond windows have essentially contributed. The total tube efficiencies are around 50% and the purity of the fundamental Gaussian output mode is 97% and higher. In addition, activities for advanced gyrotrons, e.g. a 2 MW gyrotron using a coaxial cavity, multi-frequency 1 MW gyrotrons and power modulation technology, have made progress.

Numerical modelling of the effects of ion cyclotron resonance heating (ICRH) on the stability of the internal kink mode suggests that ICRH should be considered as an essential sawtooth control tool in ITER. Sawtooth control using ICRH is achieved by directly affecting the energy of the internal kink mode rather than through modification of the magnetic shear by driving localized currents. Consequently, ICRH can be seen as complementary to the planned electron cyclotron current drive actuator, and indeed will improve the efficacy of current drive schemes. Simulations of the ICRH distribution using independent RF codes give confidence in numerical predictions that the stabilizing influence of the fusion-born alphas can be negated by appropriately tailored minority ³He ICRH heating in ITER. Finally, the effectiveness of all sawtooth actuators is shown to increase as the q = 1 surface moves towards the manetic axis, whilst the passive stabilization arising from the alpha and NBI particles decreases.

Intense particle beams have emerged as an additional, very efficient and highly flexible tool to study high energy density (HED) physics in the laboratory. Theoretical work has shown that particle beams can be employed using two very different dynamic schemes to generate large samples of HED matter in the laboratory. First, by isochoric and uniform heating of the targets and second, by shock compression of matter. GSI Helmholzzentrum für Schwerionenforschung is a very well-known laboratory due to its unique accelerator capabilities. Construction of the Facility for Antiprotons and Ion Research (FAIR) at Darmstadt will increase the beam parameters substantially. This will allow the scientists to perform new experiments in the field of HED physics in unaccessed regions of the parameter space. Over the past decade, extensive theoretical work that is based on sophisticated two- and three-dimensional numerical simulations as well as analytic modeling has been carried out to design new HED physics experiments for the FAIR facility. Four different experiments have been proposed so far and an overview of this work is presented in this paper.

Bifurcated magnetohydrodynamic (MHD) tokamak equilibrium states with axisymmetric or helical core structure are computed. When a peaked pressure profile is chosen, the helical core structures appear like the snakes that are observed in the JET tokamak. They also have the allure of saturated ideal internal kinks. The existence of a magnetic island is not a requisite condition. Novel equilibrium states that can model the snake are obtained for a JET configuration when the q-profile has weak reversed magnetic shear with minimum q values in the range 0.94 to 1.03. At the lower end of this q_min range, the equilibrium snake structure lies radially well inside the domain for which q_min ⩽ 1. Free boundary equilibria computed for the TCV tokamak develop helical cores when β_N exceeds 0.3 and have a significant axis excursion for β_N ⩾ 0.4. At fixed ⟨β⟩ = 1.6%, the distortion of the magnetic axis is large in the range 0.95 ⩽ q_min ⩽ 1.01. The plasma–vacuum interface is not significantly altered by the internal helical deformations.

In this paper we describe in detail the application of laser induced fluorescence (LIF) to the OH density measurement in a dielectric barrier discharge (DBD) at atmospheric pressure in Ar–H₂O, He–H₂O mixtures, and with small N₂ additions. Measurements are reported in which OH density is measured in a pulsed DBD, together with its decay in the post-discharge. The variation of macroscopic discharge parameters, such as the applied voltage, the water vapour content, the gas mixture composition and the discharge duration, has a large effect on the OH loss rate and a smaller one on OH density. These effects are described and briefly discussed as a valuable help for the understanding of the complex microscopic kinetics of water containing discharges.

State-to-state non-equilibrium plasma kinetics is widely used to characterize cold molecular and reentry plasmas. The approach requires a high level of dynamical information, and demands a large effort in the creation of complete databases of state-resolved cross sections and rate coefficients. Recent results, emphasizing the dependence of elementary process probability on both the vibrational and rotational energy content of the H₂ molecule, are presented for those channels governing the microscopic collisional dynamics in non-equilibrium plasmas, i.e. electron-impact induced resonant processes, vibrational deactivation and dissociation in atom–diatom collisions and atomic recombination at the surface. Results for H₂ plasmas, i.e. negative ion sources for neutral beam injection in fusion reactors, RF parallel-plate reactors for microelectronics, atmospheric discharges and the shock wave formed in the hypersonic entry of vehicles in planetary atmosphere for aerothermodynamics, are discussed.

In direct drive inertial confinement fusion (ICF) the uniformity of the irradiation of the capsule still represents a crucial issue. The quality of the capsule irradiation in the context of the shock-ignition (SI) scheme has been assessed numerically. Schemes characterized by different directions of irradiation associated with a single laser beam or a bundle of laser beams have been considered. Beam imperfections as power imbalance and pointing errors have been taken into account and show that the focal spot that minimizes the root-mean-square deviation depends on these beam imperfections. We discuss the advantages provided by laser facilities accounting for a large number (up to a few thousand) of beamlets. Preliminarily results concerning the use of the Laser-Megajoule facility associated with a SI scheme will be discussed.

We have demonstrated the promising radiation pressure acceleration (RPA) mechanism of laser-driven ion acceleration at currently achievable laser and target parameters through a large number of two-dimensional particle-in-cell simulations and experiments. High-density monoenergetic ion beams with unprecedented qualities such as narrow-peaked spectrum, lower-divergence and faster energy-scaling are obtained, compared with the conventional target normal sheath acceleration. The key condition for stable RPA from thin foils by intense circularly polarized lasers has been identified, under which the stable RPA regime can be extended from ultrahigh intensities >10²² W cm⁻² to a currently accessible range 10²⁰–10²¹ W cm⁻². The dependences of the RPA mechanism on laser polarization, intensity and on the target composition and areal density have been studied.

Methods and tools for design and modelling of tokamak operation scenarios are discussed with particular application to ITER advanced scenarios. Simulations of hybrid and steady-state scenarios performed with the integrated tokamak modelling suite of codes CRONOS are presented. The advantages of a possible steady-state scenario based on cyclic operations, alternating phases of positive and negative loop voltage, with no magnetic flux consumption on average, are discussed. For regimes in which current alignment is an issue, a general method for scenario design is presented, based on the characteristics of the poloidal current density profile.

Electric propulsion (EP) is nowadays a mature technology used on board space vehicles. In comparison with chemical thrusters, electric thrusters can advantageously accelerate propellant at a high exhaust speed. The corresponding propellant mass saving makes essential the utilization of electric thrusters for low thrust and long duration missions. Different types of EP devices have been developed for covering a large variety of maneuvers and mission requirements. To date, EP appears as a solid candidate for future manned missions. Research and development programs about EP standard technologies and new concepts are still ongoing in Europe, Russia, United States and Japan to fulfil future needs.

The transverse filamentation of beams of fast electrons transported in solid targets irradiated by ultraintense (5 × 10²⁰ W cm⁻²), picosecond laser pulses is investigated experimentally. Filamentation is diagnosed by measuring the uniformity of a beam of multi-MeV protons accelerated by the sheath field formed by the arrival of the fast electrons at the rear of the target, and is investigated for metallic and insulator targets ranging in thickness from 50 to 1200 µm. By developing an analytical model, the effects of lateral expansion of electron beam filaments in the sheath during the proton acceleration process is shown to account for measured increases in proton beam nonuniformity with target thickness for the insulating targets.

Core momentum and particle transport in ASDEX Upgrade (AUG) have been examined in a wide variety of plasma discharges and via several different methods. Experiments were performed in which ECRH power was added to NBI heated H-modes causing the electron and impurity ion density profiles to peak and the core toroidal rotation to flatten. Turbulence calculations of these plasmas show a change in the dominant regime from ITG to TEM due to the ECRH induced changes in the electron and ion temperature profiles. The impurity and electron density behavior can be fully explained by the changes in the turbulent particle transport. Momentum transport analyses demonstrate that in the TEM regime there is a core localized, counter-current directed, residual stress momentum flux of the same order of magnitude as the applied NBI torque. The initial results from momentum modulation experiments performed on AUG confirm that the Prandtl number in AUG NBI heated H-modes is close to 1 and that there exists a significant inward momentum pinch. Lastly, an intrinsic toroidal rotation database has been developed at AUG which can be used to test theoretically predicted dependences of residual stress momentum fluxes. Initial results show a linear correlation between the gradient of the toroidal rotation and both the electron density gradient scale length and the frequency of the dominant turbulent mode.

The ASDEX Upgrade tokamak is currently being enhanced with a set of in-vessel saddle coils for non-axisymmetric perturbations aiming at mitigation or suppression of edge localized modes (ELMs). Results obtained during the first experimental campaign are reported. With n = 2 magnetic perturbations, it is observed that type-I ELMs can be replaced by benign small ELM activity with strongly reduced energy loss from the confined plasma and power load to the divertor. During these phases with ELM mitigation, no density reduction (density 'pump-out') is observed. ELM mitigation has, so far, been observed in plasmas with different shape and different heating mixes and, therefore, different momentum input. The ELM mitigation regime can be accessed with resonant and non-resonant perturbation field configurations. The main threshold requirement appears to be a critical minimum plasma edge density which depends on plasma current. So far it is not possible to distinguish whether this is an edge collisionality threshold or a critical fraction of the Greenwald density limit.

The modern view of plasma turbulence has been established due to the discovery of zonal flows and other structures which drift-waves generate, and contributes to exploring new manners of understanding turbulence-driven transport and structural formation in magnetized plasmas and astronomic objects. This paper presents the recent development of laboratory experiments, in particular, for drift-wave turbulence which have advanced understanding and have made the paradigm shift. The topics include the discovery of mesoscale structures, such as zonal flows and streamers, the recent development of analyzing techniques to quantify the couplings between different scale structures and methods to elucidate energy transfer direction, and turbulence transport and barrier formation. Finally, future experiments are suggested for establishing the first-principle laws of turbulence transport and structural formation.

In the simple magnetized torus TORPEX, field-aligned blobs originate from ideal interchange waves and propagate radially outward due to ∇B and curvature induced drifts. Time-resolved two-dimensional measurements of the field-aligned current density J_∥ associated with blobs are obtained from conditionally sampled data from a single-sided Langmuir probe and a specially designed current probe. The profile of J_∥ exhibits an asymmetric dipolar structure, which originates from the polarization of the blob and is consistent with sheath boundary conditions. The asymmetry results from the non-linear dependence of J_∥ at the sheath edge upon the floating potential. Using internal measurements, we directly confirm the existence of two regimes, in which parallel currents to the sheath do or do not significantly damp charge separation and thus blob radial velocity. To investigate the effect of the observed asymmetry of J_∥ on the blob motion, we carried out numerical simulations of seeded blobs, using a two-field fluid model, which evolves electron density and vorticity. Simulations are performed spanning a wide range of blob sizes covering both regimes. We use either the complete or a linearized form for the sheath dissipation term in the vorticity equation. The structure of the parallel current density and plasma potential is found to be different in the two cases. Asymmetric profiles are observed in simulations with the complete form, while symmetric profiles are obtained when a linearized form is used. Negligible effects are, however, observed in terms of blob radial velocity. The relevance of the present results for fusion devices is also discussed.

Deuterium fueling profiles across the separatrix have been calculated with the edge fluid codes UEDGE, SOLPS and EDGE2D/EIRENE for lower single null, ohmic and low-confinement plasmas in DIII-D, ASDEX Upgrade and JET. The fueling profiles generally peak near the divertor x-point, and broader profiles are predicted for the open divertor geometry and horizontal targets in DIII-D than for the more closed geometries and vertical targets in AUG and JET. Significant fueling from the low-field side midplane may also occur when assuming strong radial ion transport in the far scrape-off layer. The dependence of the fueling profiles on upstream density is investigated for all three devices, and between the different codes for a single device. The validity of the predictions is assessed for the DIII-D configuration by comparing the measured ion current to the main chamber walls at the low-field side and divertor targets, and deuterium emission profiles across the divertor legs, and the high-field and low-field side midplane regions to those calculated by UEDGE and SOLPS.

Detailed measurements of the 2D mode structure of Alfvén instabilities in the current ramp-up phase of neutral beam heated discharges were performed on ASDEX Upgrade, using the electron cyclotron emission imaging (ECEI) diagnostic. This paper focuses on the observation of reversed shear Alfvén eigenmodes (RSAEs) and bursting modes that, with the use of the information from ECEI, have been identified as beta-induced Alfvén eigenmodes (BAEs). Both RSAEs with first and second radial harmonic mode structures were observed. Calculations with the linear gyro-kinetic code LIGKA revealed that the ratio of the damping rates and the frequency difference between the first and second harmonic modes strongly depended on the shape of the q-profile. The bursting character of the BAE type modes, which were radially localized to rational q surfaces, was observed to sensitively depend on the plasma parameters, ranging from strongly bursting to almost steady state.

In the past years, one of the focal points of the JET experimental programme was on ion-cyclotron resonance heating (ICRH) studies in view of the design and exploitation of the ICRH system being developed for ITER. In this brief review, some of the main achievements obtained in JET in this field during the last 5 years will be summarized. The results reported here include important aspects of a more engineering nature, such as (i) the appropriate design of the RF feeding circuits for optimal load resilient operation and (ii) the test of a compact high-power density antenna array, as well as RF physics oriented studies aiming at refining the numerical models used for predicting the performance of the ICRH system in ITER. The latter include (i) experiments designed for improving the modelling of the antenna coupling resistance under various plasma conditions and (ii) the assessment of the heating performance of ICRH scenarios to be used in the non-active operation phase of ITER.

Auroral Kilometric Radiation (AKR), observed by satellites in the Earth's magnetosphere, is naturally generated in regions of partial plasma depletion (auroral density cavity) in the polar magnetosphere at approximately 3200 km altitude. As an electron descends through these regions of partial plasma depletion along magnetic field lines towards the Earth's ionosphere, the field lines increases and, through conservation of the magnetic moment, the electron gives up axial velocity in favour of perpendicular velocity. This results in a horseshoe-shaped distribution function in parallel/perpendicular-velocity space which is unstable to X-mode radiation, near the cyclotron frequency. Power levels as high as GW levels have been recorded with frequencies around 300 kHz. The background plasma frequency within the auroral density cavity is approximately 9 kHz corresponding to a plasma density 1 cm⁻³. A laboratory experiment scaled from auroral frequency to microwave frequency has previously been reported. Here, the addition of a Penning trap to simulate the background plasma of the density cavity is reported, with measurements n_e ∼ 2 × 10¹⁴–2.17 × 10¹⁵ m⁻³, f_pe ∼ 128–418 MHz and f_ce ∼ 5.21 GHz giving a ratio of ω_ce/ω_pe comparable to the magnetospheric AKR source region.

The generation of coherent radiation in the extreme ultraviolet regime by the interaction of a relativistically intense laser pulse with an over-dense plasma makes a new class of experiments accessible. The availability of isolated attosecond pulses orders of magnitude higher in intensity than those produced in gaseous media would allow for the first time XUV-pump/XUV-probe type experiments with real time resolution on the attosecond timescale. The utilization of these pulses, however, demands complete control over generation and transport parameters. We present a dedicated beamline for generation, transport, application and full characterization of spatial as well as temporal properties of attosecond pulses off solid density targets.

TJ-II is a medium-sized Heliac-type stellarator operating at low magnetic shear. Low-order rational values of the rotational transform (magnetic resonances, for brevity) can be introduced anywhere in its plasmas causing modifications in the electric potential and, consequently, radial structures in the radial electric fields that can be used to alter transport and stability in an externally controllable way. The ability of the Heliac to perform dynamic configuration scans has been used to illustrate these aspects and find practical realizations, such as exerting control on the L–H transition.

High-cadence space-based observations, available for over a decade now, have revealed globally propagating wave-like disturbances in the solar corona. These coronal waves have now been imaged in a wide range of spectral channels, yielding a wealth of information. Still, no consensus on their physical nature has been reached yet. While many findings are consistent with fast-mode MHD waves and/or shocks, other characteristics have given rise to alternative models which involve magnetic reconfiguration in the framework of an erupting coronal mass ejection. In this paper, the observational signatures of coronal waves will be reviewed, and the different physical interpretations of coronal waves and how they are motivated by observations will be discussed. Finally, the potential of using coronal waves as a diagnostic tool for the corona will be shown.

This work proposes a method to measure the I–V characteristic of a plane probe for each one of the ion species present in a low-pressure plasma, by using as the ammeter a mass spectrometer whose probe entrance can be biased at an arbitrary electric potential. From the I–V characteristic, the corresponding ion energy probability distribution function of each ion species in the plasma is obtained. Moreover, the corresponding ion temperature and the plasma potential are obtained. These results are in good agreement with those obtained from classical Langmuir probes and mass spectrometry methods.

We discuss the progress in the development of extreme light sources that will open new horizons for studying a wide range of fundamental science and astrophysics problems. The regimes of dominant radiation reaction, which completely change the electromagnetic wave–matter interaction, will be revealed, resulting in a new extremely powerful source of ultrashort high-brightness gamma-ray pulses. The possibility of abundant electron–positron pair creation via multi-photon processes and the possibility of reaching the critical field of quantum electrodynamics, which would lead to vacuum polarization and breakdown, are attracting considerable attention.

A laser generated proton beam was used to measure the megagauss strength self-generated magnetic fields from a nanosecond laser interaction with an aluminum target. At intensities of 10¹⁵ W cm⁻², the significant hot electron production and strong heat fluxes result in non-local transport becoming important to describe the magnetic field dynamics. Two-dimensional implicit Vlasov–Fokker–Planck modeling shows that fast advection of the magnetic field from the focal region occurs via the Nernst effect at significantly higher velocities than the sound speed, v_N/c_s ≈ 10.

In this paper, we present global nonlinear gyrokinetic simulations including finite β_e effects and collisions in tokamak geometry. Global electromagnetic simulations using conventional δf particle in cell methods are very demanding, with respect to numerical resources, in order to correctly describe the evolution of the non-adiabatic part of the electron distribution function. This difficulty has been overcome using an appropriate adjustable control variate method in the conventional δf scheme. Linearized inter-species and like-species collision operators have also been introduced in the model. The inclusion of the collisional dynamics makes it possible to carry out simulations of microturbulence starting from a global neoclassical equilibrium and to study the effect of collisions on the transport induced by electrostatic microinstabilities.

The role played by electron density fluctuations near the plasma edge on rf current drive in tokamaks is assessed quantitatively. For this purpose, a general framework for incorporating density fluctuations in existing modelling tools has been developed. It is valid when rf power absorption takes place far from the fluctuating region of the plasma. The ray-tracing formalism is modified in order to take into account time-dependent perturbations of the density, while the Fokker–Planck solver remains unchanged. The evolution of the electron distribution function in time and space under the competing effects of collisions and quasilinear diffusion by rf waves is determined consistently with the time scale of fluctuations described as a statistical process.

Using the ray-tracing code C3PO and the 3D linearized relativistic bounce-averaged Fokker–Planck solver LUKE, the effect of electron density fluctuations on the current driven by the lower hybrid (LH) and the electron cyclotron (EC) waves is estimated quantitatively. A thin fluctuating layer characterized by electron drift wave turbulence at the plasma edge is considered. The effect of fluctuations on the LH wave propagation is equivalent to a random scattering process with a broadening of the poloidal mode spectrum proportional to the level of the perturbation. However, in the multipass regime, the LH current density profile remains sensitive to the ray chaotic behaviour, which is not averaged by fluctuations. The effect of large amplitude fluctuations on the EC driven current is found to be similar to an anomalous radial transport of the fast electrons. The resulting lower current drive efficiency and broader current profile are in better agreement with experimental observations. Finally, applied to the ITER ELMy H-mode regime, the model predicts a significant broadening of the EC driven current density profile with the fluctuation level, which can make the stabilization of neoclassical tearing mode potentially more challenging.

Based on the successful result of fast heating of a shell target with a cone for heating beam injection at Osaka University in 2002 using the PW laser (Kodama et al 2002 Nature418 933), the FIREX-1 project was started in 2004. Its goal is to demonstrate fuel heating up to 5 keV using an upgraded heating laser beam. For this purpose, the LFEX laser, which can deliver an energy up to10 kJ in a 0.5–20 ps pulse at its full spec, has been constructed in addition to the Gekko-XII laser system at the Institute of Laser Engineering, Osaka University. It has been activated and became operational since 2009. Following the previous experiment with the PW laser, upgraded integrated experiments of fast ignition have been started using the LFEX laser with an energy up to 1 kJ in 2009 and 2 kJ in 2010 in a 1–5 ps 1.053 µm pulse. Experimental results including implosion of the shell target by Gekko-XII, heating of the imploded fuel core by LFEX laser injection, and increase of the neutron yield due to fast heating compared with no heating have been achieved. Results in the 2009 experiment indicated that the heating efficiency was 3–5%, much lower than the 20–30% expected from the previous 2002 data. It was attributed to the very hot electrons generated in a long scale length plasma in the cone preformed with a prepulse in the LFEX beam. The prepulse level was significantly reduced in the 2010 experiment to improve the heating efficiency. Also we have improved the plasma diagnostics significantly which enabled us to observe the plasma even in the hard x-ray harsh environment. In the 2010 experiment, we have observed neutron enhancement up to 3.5 × 10⁷ with total heating energy of 300 J on the target, which is higher than the yield obtained in the 2009 experiment and the previous data in 2002. We found the estimated heating efficiency to be at a level of 10–20%. 5 keV heating is expected at the full output of the LFEX laser by controlling the heating efficiency.

Solar flares represent the release of stored magnetic energy through magnetic reconnection. Large numbers of high-energy ions and electrons are produced in flares. We present models showing how energy may be released by reconnection during the nonlinear phase of kink instability in twisted coronal loops. The strong electric fields associated with this reconnection can accelerate charged particles. We also show how particles may be accelerated at 3D magnetic null points.

A new plasma source, the so-called diffuse coplanar surface barrier discharge (DCSBD), is described. DCSBD allows a visually diffuse high-density 'cold' plasma to be sustained in atmospheric-pressure air at a high plasma power density exceeding 100 W cm⁻³ that permits high-speed surface processing of large-area webs and flat surfaces. This is demonstrated by the results on a successful in-line activation of thin polypropylene fabric at 450 m min⁻¹ and plasma exposures as short as 0.14 s. DCSBD basic features resulting in the observed high efficiency of plasma activation and the related plasmachemical mechanism are discussed briefly.

Plasma transport across magnetic field lines plays a key role not only in hot fusion plasmas but also in low-temperature plasma sources operating at low pressure, which often rely on external magnetic fields for their operation. Transport in these sources involves different physics than that in fusion plasmas: the ions are not (completely) magnetized, the plasma is sensitive to wall effects because the magnetic field lines intercept the chamber walls, and the neutral gas density is often much larger than the plasma density. This paper gives an overview of the main principles of magnetized low-temperature plasma transport as they are currently understood, including recent insights on the role of magnetic drift. Three important forms of magnetized low-temperature plasma transport are discussed: magnetized plasma diffusion, transport in E × B fields and magnetic drift. These phenomena are illustrated with recent numerical modeling results on a dipolar microwave source, an End-Hall ion source, and simplified version of the ITER negative ion source. For the latter source it is shown that obstructed magnetic drift can lead to plasma asymmetry and increased cross-field transport.

Detailed experimental studies of ion heat transport have been carried out in JET exploiting the upgrade of active charge exchange spectroscopy and the availability of multi-frequency ion cyclotron resonance heating with ³He minority. The determination of ion temperature gradient (ITG) threshold and ion stiffness offers unique opportunities for validation of the well-established theory of ITG driven modes. Ion stiffness is observed to decrease strongly in the presence of toroidal rotation when the magnetic shear is sufficiently low. This effect is dominant with respect to the well-known ω_E×B threshold up-shift and plays a major role in enhancing core confinement in hybrid regimes and ion internal transport barriers. The effects of T_e/T_i and s/q on ion threshold are found rather weak in the domain explored. Quasi-linear fluid/gyro-fluid and linear/non-linear gyro-kinetic simulations have been carried out. Whilst threshold predictions show good match with experimental observations, some significant discrepancies are found on the stiffness behaviour.

This paper presents an analysis of laser–plasma interaction risks of the shock ignition (SI) scheme and experimental results under conditions relevant to the corona of a compressed target. Experiments are performed on the LIL facility at the 10 kJ level, on the LULI 2000 facility with two beams at the kJ level and on the LULI 6-beam facility with 100 J in each beam. Different aspects of the interaction of the SI pulse are studied exploiting either the flexibility of the LULI 6-beam facility to produce a very high intensity pulse or the high energy of the LIL to produce long and hot plasmas. A continuity is found allowing us to draw some conclusions regarding the coupling quality and efficiency of the SI spike pulse. It is shown that the propagation of the SI beams in the underdense plasma present in the corona of inertial confinement fusion targets could strongly modify the initial spot size of the beam through filamentation. Detailed experimental studies of the growth and saturation of backscattering instabilities in these plasmas indicate that significant levels of stimulated scattering reflectivities (larger than 40%) may be reached at least for some time during the SI pulse.

Disruptions are very challenging to ITER operation as they may cause damage to plasma facing components due to direct plasma heating, forces on structural components due to halo and eddy currents and the production of runaway electrons. Electron cyclotron (EC) waves have been demonstrated as a tool for disruption avoidance by a large set of recent experiments performed in ASDEX Upgrade and FTU using various disruption types, plasma operating scenarios and power deposition locations. The technique is based on the stabilization of magnetohydrodynamic (MHD) modes (mainly m/n = 2/1) through the localized injection of EC power on the resonant surface. This paper presents new results obtained in ASDEX Upgrade regarding stable operation above the Greenwald density achieved after avoidance of density limit disruptions by means of ECRH and suitable density feedback control (L-mode ohmic plasmas, I_p = 0.6 MA, B_t = 2.5 T) and NTM-driven disruptions at high-β limit delayed/avoided by means of both co-current drive (co-ECCD) and pure heating (ECRH) with power ⩽1.7 MW (H-mode NBI-heated plasmas, P_NBI ∼ 7.5 MW, I_p = 1 MA, B_t = 2.1 T, q₉₅ ∼ 3.6). The localized perpendicular injection of ECRH/ECCD onto a resonant surface leads to the delay and/or complete avoidance of disruptions. The experiments indicate the existence of a power threshold for mode stabilization to occur. An analysis of the MHD mode evolution using the generalized Rutherford equation coupled to the frequency and phase evolution equations shows that control of the modes is due to EC heating close to the resonant surface. The ECRH contribution (Δ'_H term) is larger than the co-ECCD one in the initial and more important phase when the discharge is 'saved'. Future research and developments of the disruption avoidance technique are also discussed.

The formation of turbulent structures in weakly developed drift-wave turbulence is investigated using experimental data obtained in a linear laboratory device. The findings are compared with fully non-linear numerical simulation results. The formation of structures occurs in a region, in which the divergence of the Reynolds stress, which is one term in the momentum balance, has a maximum. The generation of a time-averaged shear layer is not observed, but for transient events the shearing rate can become sufficiently strong to decorrelate the fluctuations. This happens when the energy flow into the shear flow is largely positive.

Plasma thrusters are challenging the monopoly of chemical thrusters in space propulsion. The specific energy that can be deposited into a plasma beam is orders of magnitude larger than the specific chemical energy of known fuels. Plasma thrusters constitute a vast family of devices ranging from already commercial thrusters to incipient laboratory prototypes. Figures of merit in plasma propulsion are discussed. Plasma processes and conditions differ widely from one thruster to another, with the pre-eminence of magnetized, weakly collisional plasmas. Energy is imparted to the plasma via either energetic electron injection, biased electrodes or electromagnetic irradiation. Plasma acceleration can be electrothermal, electrostatic or electromagnetic. Plasma–wall interaction affects energy deposition and erosion of thruster elements, and thus is central for thruster efficiency and lifetime. Magnetic confinement and magnetic nozzles are present in several devices. Oscillations and turbulent transport are intrinsic to the performances of some thrusters. Several thrusters are selected in order to discuss these relevant plasma phenomena.

A leading method of propelling plasma is through the electrical acceleration of ions through a cloud of rotating electrons, where the rotating electrons are held in place axially by a magnetic filter. However, in certain parameter regimes, devices based on this propulsion principle appear to work far better than they should, at least based on the accepted design principles. This unexpected fortunate performance is explained here by self-organizing features of supersonically rotating electron plasma. In fact, several ion acceleration mechanisms that narrow the plume can be identified. These useful acceleration mechanisms, which persist even as the electron temperature vanishes, are newly identified here and are common to rotating electron plasmas in a variety of settings.

A baseline type-I ELMy H-mode JET tokamak discharge in low triangularity has been analysed using the JINTRAC integrated code suite to obtain a self-consistent description of the plasma edge dynamics and core plasma confinement. The inter- and intra-ELM transport model of JINTRAC has been adapted as such to match the experimental pre- and post-ELM plasma pedestal profiles and at the same time to recover the observed ELM dynamics in terms of ELM frequency, ELM energy loss, target ELM wetted area and target heat flows. The presented and validated modelling results for the JET all-carbon device reference case are utilized to predict a type-I ELMy H-mode for the JET ITER-like wall (ILW) assuming a full-tungsten divertor and beryllium main-chamber wall using JINTRAC. By keeping all relevant transport parameters fixed for the inter- and intra-ELM phase as in the all-carbon reference case it is observed that a moderate amount of seeded neon impurity is necessary to compensate for a similar level of radiation when carbon is absent in the system. The results of the ILW model setup are finally taken to estimate the total amount of tungsten particles eroded per ELM from the target plates. A rough estimate of the core radiative fraction due to W accumulation is given, predicting that no substantial impact on typical a JET ILW type-I ELMy H-mode discharge core plasma performance is expected.

The use of beryllium, carbon and tungsten as plasma-facing materials (PFMs) in ITER calls for dedicated investigations on their behaviour under the expected particle and power loads and neutron irradiation. Their simultaneous use implies the formation of mixed materials during plasma operation, which can have significantly different properties compared with the initial materials concerning thermo-mechanical behaviour and T retention. This contribution presents the latest results on these issues mainly achieved under the umbrella of the European taskforce on plasma wall interaction. While laboratory results provide the basis for the understanding of the basic properties and the behaviour of PFMs, experiments in fusion devices are indispensable in order to test their integral performance, incorporating also the internal feedback on the plasma properties. For this reason ASDEX Upgrade has been converted to a full W device, while JET is beginning operation with its ITER-like wall consisting of Be main chamber plasma-facing components and a W divertor. In parallel, dedicated W experiments are performed in several devices in order to investigate specific uncertainties such as the characteristics of melt-layer movement in the presence of a strong magnetic field. Based on the results on ASDEX Upgrade, which reveal a narrower operational space as compared with the operation with graphite plasma-facing components but also provide tools for a successful operation with tungsten, the experiments at JET will provide a unique opportunity to address specific issues related to the parallel use of Be and W as PFMs with plasma parameters closest to those of ITER. Amongst these are the anticipated but still to be demonstrated reduction in hydrogen retention compared with a carbon device, the test of conditioning procedures, mixed materials effects, erosion and transport, the effect of edge localized modes (ELMs) and ELM mitigation methods as well as the behaviour of melt layers and their influence on plasma operation under steady state and transient heat loads.

This paper presents the goals and some of the results of experiments conducted within the Working Package 10 (Fusion Experimental Programme) of the HiPER Project. These experiments concern the study of the physics connected to 'advanced ignition schemes', i.e. the fast ignition and the shock ignition approaches to inertial fusion. Such schemes are aimed at achieving a higher gain, as compared with the classical approach which is used in NIF, as required for future reactors, and make fusion possible with smaller facilities.

In particular, a series of experiments related to fast ignition were performed at the RAL (UK) and LULI (France) Laboratories and studied the propagation of fast electrons (created by a short-pulse ultra-high-intensity beam) in compressed matter, created either by cylindrical implosions or by compression of planar targets by (planar) laser-driven shock waves. A more recent experiment was performed at PALS and investigated the laser–plasma coupling in the 10¹⁶ W cm⁻² intensity regime of interest for shock ignition.