Table of contents

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

Sibylle Guenter Chair of the Programme Committee

Pawel GasiorJerzy Wolowski Guest Editors

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

The H-mode is a confinement mode of toroidal plasmas, which may make the goals of fusion possible—the development of a clean energy source at competitive electricity costs. The most challenging aspect of the H-mode physics is the sudden disappearance of the edge turbulence whereas its driving forces—the gradients—increase. As the physics behind the H-mode is subtle many features are not yet clarified. There is, however, substantial experimental and theoretical evidence that turbulent flows, which normally limit the confinement, are diminished by sheared poloidal flow residing at the plasma edge. There are many conceivable mechanisms giving rise to sheared flow. The most intriguing of these is that fluctuations themselves induce the flow, which acts back to its generating origin and annihilates the turbulence. This review concentrates mostly on the transition physics, describes one line of understanding the H-mode in more detail, recalls some of the older observations and summarizes the achievements in the H-mode for both tokamaks and stellarators.

This paper summarizes recent experimental characterization of radio frequency (RF)-induced scrape-off layer (SOL) modifications in ASDEX-Upgrade (AUG), JET and Tore Supra (TS). Geometrical aspects are emphasized: complex SOL patterns are observed by several indicators visualized in one or two dimensions transverse to the magnetic field lines. Results are ascribed to inhomogeneous RF-induced SOL biasing around powered ion cyclotron range of frequencies antennas and associated E × B₀ density convection (D'Ippolito et al 1993 Phys. Fluids B 5 3603). Within a simple RF sheath model (Perkins 1989 Nucl. Fusion29 583), the shape of convective cells on TS can be interpreted in terms of RF-sheath generation by parallel RF currents. Some lessons are drawn for future machines.

Results are presented from probe measurements in the low field side scrape-off layer (SOL) region of TCV during plasma current scan experiments. It is shown that with decreasing plasma current the radial particle density profile becomes broader and the fluctuation levels and turbulence driven radial particle flux increase. In the far SOL the fluctuations exhibit a high degree of statistical similarity and the particle density and flux at the wall radius scale inversely with the plasma current. Together with previous TCV density scan experiments, this indicates that plasma fluctuations and radial transport increase with plasma collisionality. Such a collisionality dependence is consistent with a recent theory for radial blob motion, which suggests that filamentary structures become electrically disconnected from the target sheaths at large collisionality and thus experience less sheath dissipation. This increases the radial convective transport and is possibly linked to the discharge density limit.

ASDEX Upgrade has recently finished its transition towards an all-W divertor tokamak, by the exchange of the last remaining graphite tiles to W-coated ones. The plasma start-up was performed without prior boronization. It was found that the large He content in the plasma, resulting from DC glow discharges for conditioning, leads to a confinement reduction. After the change to D glow for inter-shot conditioning, the He content quickly dropped and, in parallel, the usual H-Mode confinement with H factors close to one was achieved. After the initial conditioning phase, oxygen concentrations similar to that in previous campaigns with boronizations could be achieved. Despite the removal of all macroscopic carbon sources, no strong change in C influxes and C content could be observed so far. The W concentrations are similar to the ones measured previously in discharges with old boronization and only partial coverage of the surfaces with W. Concomitantly it is found that although the W erosion flux in the divertor is larger than the W sources in the main chamber in most of the scenarios, it plays only a minor role for the W content in the main plasma. For large antenna distances and strong gas puffing, ICRH power coupling could be optimized to reduce the W influxes. This allowed a similar increase of stored energy as yielded with comparable beam power. However, a strong increase of radiated power and a loss of H-Mode was observed for conditions with high temperature edge plasma close to the antennas. The use of ECRH allowed keeping the central peaking of the W concentration low and even phases of improved H-modes have already been achieved.

The propagation of a superintense laser pulse in an underdense, inhomogeneous plasma has been studied numerically by two-dimensional particle-in-cell simulations on a time scale extending up to several picoseconds. The effects of the ion dynamics following the charge-displacement self-channeling of the laser pulse have been addressed. Radial ion acceleration leads to the 'breaking' of the plasma channel walls, causing an inversion of the radial space-charge field and the filamentation of the laser pulse. At later times a number of long-lived, quasi-periodic field structures are observed and their dynamics is characterized with high resolution. Inside the plasma channel, a pattern of electric and magnetic fields resembling both soliton- and vortex-like structures is observed.

The development of high intensity lasers has opened up new opportunities for nuclear physics studies in extreme conditions which cannot be reached with conventional particle accelerators. A laser is a unique tool to produce plasma and very high fluxes of photon and particle beams in very short duration pulses. Both aspects are of great interest for fundamental nuclear physics studies. In plasma the electron–ions collisions may modify atomic and nuclear level properties. This is of prime importance for the population of isomeric states and the issue of energy storage in nuclei. Nuclear properties in the presence of very high electromagnetic fields, nuclear reaction rates or properties in hot and dense plasmas are new domains of investigation. Our group has launched an experimental program to evaluate the possibilities for such nuclear physics studies at high intensity laser facilities. This program and its first results are presented.

Designs for fast ignition demonstration facilities such as HiPER rely on predictions of the rapid heating of the DT fuel by relativistic electrons generated by ultra-intense laser beams. While there is much agreement on the physics processes underlying the transport and energy deposition of these enormously high current beams there remains a degree of uncertainty which can only be addressed by careful experiments with lasers very much smaller than would be needed for a facility such as HiPER. In many ways the smaller scale experiments are harder to model than the real ignition requirement and some of the physics and computational issues are discussed.

The peculiarity of a dusty plasma is related to the unique capacity of dust particles to self-organize themselves into various structures. Dust structures in a plasma are perfect examples of complex systems because of many various constituents, with intensive interactions between them, as well as various space and time scales involved. The emergence of structures involves numerous processes of generation and loss of plasma electrons and ions, in particular on the surfaces of the dust grains. The main interest is related to the processes of formation, arrangement, symmetry and transitions appearing in open dissipative systems of interacting dust particles. Furthermore, the grain structures are often non-extensive containing a limited number of particles interacting via non-collective long-range forces. The non-extensive structures in complex plasma systems, such as dust particle molecules and clusters, attract particular attention since they can be easily obtained in experiments and allow theoretical treatment at the most fundamental level. Here, attention is paid mainly to the recently observed and/or theoretically fundamental questions.

The ionosphere is the only large-scale plasma laboratory without walls that we have direct access to. Here we can study, both in situ and from the ground, basic small- and large-scale processes and fundamental physical principles that control planet Earth's interaction with its space environment. From results obtained in systematic, repeatable experiments, where we can vary the stimulus and observe its response in a controlled, laboratory-like manner, we can draw conclusions on similar physical processes occurring naturally in the Earth's plasma environment as well as in parts of the plasma universe that are not easily accessible to direct probing.

Of particular interest is electromagnetic turbulence excited in the ionosphere by beams of particles (photons, electrons) and its manifestation in terms of secondary radiation (electrostatic and electromagnetic waves), structure formation (solitons, cavitons, alfveons, hybrons, striations) and the associated exchange of energy, linear momentum and angular momentum.

The primarily astrophysics-oriented, distributed radio telescope Low Frequency Array (LOFAR) currently under construction in the Netherlands, Germany and France, will operate in a frequency range (10–240 MHz), close to fundamental ionospheric plasma resonance/cut-off frequencies, with a sensitivity that is orders of magnitude higher than any radio (or radar) facility used so far. The LOFAR Outrigger in Scandinavia (LOIS) radio and radar facility, with one station in Växjö in southern Sweden and three more planned in the same area (Ronneby, Kalmar, Lund) plus one near Poznan in Poland, supplements LOFAR with optimized Earth and space observing extensions. For this purpose LOIS will operate in the same frequency range as LOFAR (but extended on the low-frequency side) and will augment the observation capability to enable direct radio imaging of plasma vorticity.

To study the structural and dynamical properties of finite 3D dust clouds (Yukawa balls) new diagnostic tools have been developed. This contribution describes the progress towards 3D diagnostics for measuring the particle positions. It is shown that these diagnostics are capable of investigating the structural and dynamical properties of Yukawa balls and gaining insight into their basic construction principles.

Strong shocks and blast wave collisions are commonly observed features in astrophysical objects such as nebulae and supernova remnants. Numerical simulations often underpin our understanding of these complex systems, however modelling of such extreme phenomena remains challenging, particularly so for the case of radiative or colliding shocks. This highlights the need for well-characterized laboratory experiments both to guide physical insight and to provide robust data for code benchmarking. Creating a sufficiently high-energy-density gas medium for conducting scaled laboratory astrophysics experiments has historically been problematic, but the unique ability of atomic cluster gases to efficiently couple to intense pulses of laser light now enables table top scale (1 J input energy) studies to be conducted at gas densities of >10¹⁹ particles cm⁻³ with an initial energy density >5 × 10⁹ J g⁻¹. By laser heating atomic cluster gas media we can launch strong (up to Mach 55) shocks in a range of geometries, with and without radiative precursors. These systems have been probed with a range of optical and interferometric diagnostics in order to retrieve electron density profiles and blast wave trajectories. Colliding cylindrical shock systems have also been studied, however the strongly asymmetric density profiles and radial and longitudinal mass flow that result demand a more complex diagnostic technique based on tomographic phase reconstruction. We have used the 3D magnetoresistive hydrocode GORGON to model these systems and to highlight interesting features such as the formation of a Mach stem for further study.

Wave–particle interactions are central in plasma physics. They can be studied in a traveling wave tube (TWT) to avoid intrinsic plasma noise. This led to detailed experimental analysis of the self-consistent interaction between unstable waves and an either cold or warm beam. More recently a test cold electron beam has been used to observe its non-self-consistent interaction with externally excited wave(s). The velocity distribution function of the electron beam is recorded with a trochoidal energy analyzer at the output of the TWT. An arbitrary waveform generator is used to launch a prescribed spectrum of waves along the slow wave structure (a 4 m long helix) of the TWT. The nonlinear synchronization of particles by a single wave responsible for Landau damping is observed. The resonant velocity domain associated with a single wave is also observed, as well as the transition to large scale chaos when the resonant domains of two waves and their secondary resonances overlap. This transition exhibits a 'devil's staircase' behavior when increasing the excitation amplitude in agreement with numerical simulation. A new strategy for control of chaos by building barriers of transport which prevent electrons from escaping from a given velocity region as well as its robustness are successfully tested. The underlying concepts extend far beyond the field of electron devices and plasma physics.

After a long history of theoretical predictions, turbulence induced poloidal flows—'zonal flows' (ZF)—are nowadays ubiquitously detected in tokamaks and stellarators. The difference in character of ZFs in a torus in comparison with those in a cylinder is discussed. The reduction in symmetry leads to a fundamentally three-dimensional flow pattern, a second oscillating flow type and several additional interaction mechanisms between flows and turbulence equal in importance to the perpendicular Reynolds stress of the two-dimensional flows in a cylinder.

An intense laser pulse interacting with a near discontinuous plasma vacuum interface causes the plasma surface to perform relativistic oscillations. The reflected laser radiation then contains very high order harmonics of fundamental frequency and—according to current theory—must be bunched in radiation bursts of a few attoseconds duration. Recent experimental results have demonstrated x-ray harmonic radiation extending to 3.3 Å (3.8 keV, order n > 3200) with the harmonic conversion efficiency scaling as η(n) n^−2.5 over the entire observed spectrum ranging from 17 nm to 3.3 Å. This scaling holds up to a maximum order, n_RO 8^1/2γ³, where γ is the peak value of the Lorentz factor, above which the harmonic efficiency decreases more rapidly. The coherent nature of the generated harmonics is demonstrated by the highly directional beamed emission, which for photon energy h ν > 1 keV is found to be into a cone angle ∼4°, significantly less than that of the incident laser cone (20°).

A toroidal, nonlinear, electrostatic fluid-kinetic hybrid electron model is formulated for global gyrokinetic particle simulations of driftwave turbulence in fusion plasmas. Numerical properties are improved by an expansion of the electron response using a smallness parameter of the ratio of driftwave frequency to electron transit frequency. Linear simulations accurately recover the real frequency and growth rate of toroidal ion temperature gradient (ITG) instability. Trapped electrons increase the ITG growth rate by mostly not responding to the ITG modes. Nonlinear simulations of ITG turbulence find that the electron thermal and particle transport are much smaller than the ion thermal transport and that small scale zonal flows are generated through nonlinear interactions of the trapped electrons with the turbulence.

Critical physical issues can be specifically tackled with the global full-f gyrokinetic code GYSELA. Three main results are presented. First, the self-consistent treatment of equilibrium and fluctuations highlights the competition between two compensation mechanisms for the curvature driven vertical charge separation, namely, parallel flow and polarization. The impact of the latter on the turbulent transport is discussed. In the non-linear regime, the benchmark with the Particle-In-Cell code ORB5 looks satisfactory. Second, the transport scaling with ρ_* is found to depend both on ρ_* itself and on the distance to the linear threshold. Finally, a statistical steady-state turbulent regime is achieved in a reduced version of GYSELA by prescribing a constant heat source.

The response of plasma parameters and broad wavenumber turbulence (1–39 cm⁻¹, kρ_s = 0.1–10, relevant to ion temperature gradient, trapped electron mode and electron temperature gradient mode turbulence, here ρ_s = ion gyroradius) to auxiliary electron cyclotron heating (ECH) is reported on. One fluid thermal fluxes and diffusivities increase appreciably with ECH. Significant changes to the density fluctuations over the full range of measured wavenumbers are observed, with an increase for lower wavenumbers and a more spatially complicated response at high k. Spatially resolved high k measurements (k = 39 cm⁻¹, kρ_s = 4–10) show a varying response to ECH, with decreasing at r/a = 0.35 and increasing at r/a = 0.6 and 1. These variations were found to have a positive correlation with ∇T_e evaluated at nearby locations, consistent with a ∇T_e drive. Comparison of the changes in high k fluctuation levels with linear gyrokinetic growth rates show qualitative agreement at the innermost location, r/a = 0.35 and disagreement at r/a = 0.6.

Carbon ion velocity profiles are measured in TCV with a charge exchange diagnostic using a negligibly perturbing diagnostic neutral beam. These 'intrinsic' rotation profiles are measured up to the plasma edge in the toroidal and poloidal directions for both limited and diverted plasma configurations in Ohmic plasmas and in the presence of strong second harmonic electron cyclotron heating (ECH). Absolute toroidal velocities are shown to scale with peak ion temperature and inversely with plasma current. The plasma edge rotation is always small in limited configurations but evolves smoothly with the core density for diverted configurations. A strong intrinsic rotation builds up in the plasma core in the counter-current direction for limited configurations but is observed in the co-current direction for diverted plasmas. Unexpectedly, above a given density threshold, the rotation profile reverses to the co-current direction for limited configurations (and surprisingly, in the counter-current direction for diverted configurations). This threshold density is found to depend on plasma current, the presence of ECH and the magnetic topology. Poloidal velocity measurements are used to deduce the radial electric field change across the transition. A strong dependence of the rotation profile on plasma triangularity is reported and possible physics models for these observations are discussed. The origin of the momentum drive, its reversal and its magnitude are not yet clearly understood even for these relatively 'simple' experimental configurations.

We describe recent measurements in which a novel imaging technique was used to investigate the transport of high energy electrons produced by the interaction of a femtosecond laser pulse with a three-layer target at an intensity of 5 × 10¹⁹ W cm⁻². The imaging system was configured to work in a single-photon detection regime to identify the energy of the x-ray photons and to discriminate among Kα photons generated in each target layer. Electrons emerging from the rear side after propagation through all the target layers were also detected using a custom developed detector. The results on fast electron propagation are combined with the information obtained from electron diagnostics and are modelled using analytical and numerical codes to obtain a detailed description of electron propagation dynamics.

An experimental investigation of low- and medium-mass ion acceleration from resistively heated thin foil targets, irradiated by picosecond laser pulses at intensities up to 5 × 10²⁰ W cm⁻², is reported. It is found that the spectral distributions of ions, up to multi-MeV/nucleon energies, accelerated from the rear surface of the target are broadly consistent with previously reported measurements made at intensities up to 5 × 10¹⁹ W cm⁻². Properties of the backward-directed beams of ions accelerated from the target front surface are also measured, and it is found that, compared with the rear surface, higher ion numbers and charges, and similar ion energies are produced. Additionally, the scaling of the maximum ion energy as a function of ion charge and laser intensity are measured and compared with the predictions of a numerical model.

Theoretical studies of microdischarges are less advanced than their experimental counterparts. The knowledge of fundamental mechanisms that account for dc microplasma generation and that control the remarkable stability of the discharge at high gas pressure is still incomplete. Here we present results from modelling of 3-electrode microdischarge configuration consisting of a microhollow cathode discharge (MHCD) (used as plasma cathode) and a microcathode sustained discharge (MCSD) (maintained in the volume between the plasma cathode and a third positive electrode). It is shown that the MCSD is similar to a positive plasma column and that it can be modelled separately from the MHCD, thereby eliminating the complexity inherent in modelling the cathode regions. This approach allows us to concentrate more on the plasma chemistry and to use the model as an efficient diagnostic tool.

Hydrocarbon flame speed and flame structure modifications have been studied using a low dc applied electric field opposing the gas flow directions. Our electrode configuration leads to a relatively high conduction current with a low applied voltage drop in the flame that permits to collect ∼10¹¹ cm⁻³ chemi-ion density at the pre-heat flame zone, which seems to simulate DBDs and other plasma assisted combustion enhancement conditions. The dissociative recombination of major positive chemi-ions H₃O⁺ and HCO⁺ produces 10¹¹ cm⁻³ H, O and OH radicals modifying both combustion kinetics and fluidics. Also, flame electrical conductivity measurement was found to correlate very well with the CH, OH and C₂ chemiluminescence intensity fluctuations.

Coherent drift modes and drift wave turbulence are studied in a collisionality dominated high-density helicon plasma. The drift wave instability is identified by comparison of the drift mode density fluctuation characteristics with a linear dispersion relation, which reproduces the experimentally observed bent eigenmode structures due to the radial gradients of the collisionality profile. Attention is especially paid to the parallel currents associated with the drift mode density fluctuations, which are in agreement with the basic drift wave instability mechanism. A coupling of the drift mode to the externally excited Alfvén waves is found, which results in the frequency changes of the drift mode. The parallel currents associated with radially propagating density fluctuation structures in drift wave turbulence are similar to the drift mode case, which strongly suggests that polarization of the structures is a result of the parallel electron dynamics.

In an effort to better understand plasma transport, we measure fluctuations associated with drift instabilities resolved in the ion phase-space. Primary attention is given to fluctuations near the electron drift frequency where there are two general components to the observed fluctuations. From two (spatial) point measurements of the ion distribution function with a variable separation along the magnetic field, a number of statistical measures of the fluctuations are calculated including cross-correlation and cross-bicoherence. Both fluid (ω/k ≫ v_ti) and kinetic (ω/k ∼ v_ti) components are observed in the fluctuations. The nonlinear interactions are found to depend strongly on the ion particle velocity.

A common feature of magnetized plasmas is the presence of fluctuations, which can lead to fully developed turbulence. Often large events—called bursts—emerge from the remaining low-level turbulence, giving an intermittent character to fluctuations; namely the statistical properties of fluctuations are found to depend on the temporal scale over which the investigation is conducted.

In magnetized plasmas, the bursts are generally believed to be due to the presence of magnetic-field-aligned structures. Moreover, it has been experimentally shown that the intermittent events detected in the signals are associated with a relevant contribution to the loss of particles from the plasma.

All these observations are common to plasmas spanning a wide range of temperature and density and magnetically confined both in linear and toroidal devices. In particular, in high-temperature plasmas for thermonuclear fusion, research aims at devising suitable ways to control transport by acting on the plasma structures, for instance by biasing the plasma edge using electrodes.

This paper gives a characterization of the structures found in magnetized plasmas and of their contribution to the particle transport; moreover, the effect of the velocity shear on structures is addressed. Emphasis will be laid on to the most advanced diagnostics allowing the reconstruction of turbulent structures by optical and electrostatic techniques.

A unique parabolic relation is observed to link skewness and kurtosis of density fluctuation signals, measured over the whole cross-section of the simple toroidal device TORPEX for a broad range of experimental conditions. This relationship is also valid for density fluctuation signals measured in the scrape-off layer of the TCV tokamak. All the probability density functions (PDFs) of the measured signals, including those characterized by a negative skewness, are universally described by a special case of the beta distribution. In TORPEX, fluctuations in the drift-interchange frequency range are necessary and sufficient to assure that PDFs can be described by this specific beta distribution. For a more detailed plasma scenario, it is shown that electron temperature and plasma potential fluctuations have different statistical properties compared with the density.

The present status of understanding of toroidal and poloidal momentum transport in tokamaks is presented in this paper. Similar energy confinement and momentum confinement times, i.e. τ_E/τ_ϕ ≈ 1 have been reported on several tokamaks. It is more important though, to study the local transport both in the core and edge plasma separately as, for example, in the core plasma, a large scatter in the ratio of the local effective momentum diffusivity to the ion heat diffusivity χ_ϕeff/χ_i,eff among different tokamaks can be found. For example, the value of effective Prandtl number is typically around χ_ϕeff/χ_i,eff ≈ 0.2 on JET while still τ_E/τ_ϕ ≈ 1 holds. Perturbative NBI modulation experiments on JET have shown, however, that a Prandtl number χ_ϕ/χ_i of around 1 is valid if there is an additional, significant inward momentum pinch which is required to explain the amplitude and phase behaviour of the momentum perturbation. The experimental results, i.e. the high Prandtl number and pinch, are in good qualitative and to some extent also in quantitative agreement with linear gyro-kinetic simulations. In contrast to the toroidal momentum transport which is clearly anomalous, the poloidal velocity is usually believed to be neo-classical. However, experimental measurements on JET show that the carbon poloidal velocity can be an order of magnitude above the predicted value by the neo-classical theory within the ITB. These large measured poloidal velocities, employed for example in transport simulations, significantly affect the calculated radial electric field and therefore the E × B flow shear and hence modify and can significantly improve the simulation predictions. Several fluid turbulence codes have been used to identify the mechanism driving the poloidal velocity to such high values. CUTIE and TRB turbulence codes and also the Weiland model predict the existence of an anomalous poloidal velocity, peaking in the vicinity of the ITB and driven dominantly by the flow due to the Reynold's stress. It is worth noting that these codes and models treat the equilibrium in a simplified way and this affects the geodesic curvature effects and geodesic acoustic modes. The neo-classical equilibrium is calculated more accurately in the GEM code and the simulations suggest that the spin-up of poloidal velocity is a consequence of the plasma profiles steepening when the ITB grows, following in particular the growth of the toroidal velocity within the ITB.

The universality of the observed characteristics of sheared flows points to a general ingredient to explain the damping/driving mechanisms responsible for the development of these flows in the plasma boundary region of fusion devices. Experiments in the TJ-II stellarator showing that the generation of spontaneous sheared flows at the plasma edge requires a minimum plasma density or density gradient, open a unique possibility to characterize the dynamics of sheared flow development in fusion plasmas.

The effective viscosity at the plasma edge can be deduced by means of the decay rate of the perpendicular flow measurement once the driving force has been removed. Changes in the plasma rotation and turbulence have been studied when an electric field is externally applied at the plasma edge. The relaxation of flows and radial electric fields has been compared in the edge plasma region of TJ-II stellarator and CASTOR tokamak showing a striking similarity. The findings can help to test neoclassical and anomalous damping mechanisms in fusion plasmas.

Finally, the emergence of the plasma edge sheared flow as a function of plasma density can be explained using a simple second-order phase transition model that reproduces many of the features of the TJ-II experimental data while capturing the qualitative features of the transition near the critical point.

Momentum confinement was investigated on DIII-D as a function of applied neutral beam torque at constant normalized beta β_N, by varying the mix of co (parallel to the plasma current) and counter neutral beams. Under balanced neutral beam injection (i.e. zero total torque to the plasma), the plasma maintains a significant rotation in the co-direction. This 'intrinsic' rotation can be modeled as being due to an offset in the applied torque (i.e. an 'anomalous torque'). This anomalous torque appears to have a magnitude comparable to one co neutral beam source. The presence of such an anomalous torque source must be taken into account to obtain meaningful quantities describing momentum transport, such as the global momentum confinement time and local diffusivities.

Studies of the mechanical angular momentum in ELMing H-mode plasmas with elevated q_min show that the momentum confinement time improves as the torque is reduced. In hybrid plasmas, the opposite effect is observed, namely that momentum confinement improves at high torque/rotation. GLF23 modeling suggests that the role of E × B shearing is quite different between the two plasmas, which may help to explain the different dependence of the momentum confinement on torque.

Magnetic reconnection and collisionless dissipation are common phenomena of astrophysical and fusion plasmas. While reconnection is responsible for disruptions of a fusion confinement, it causes flare explosions at the Sun and stars, in galaxies, planetary magnetospheres, and it causes aurorae and structure formation in the Universe as well as penetration through magnetic boundaries. Due to the weak coupling in astrophysical and fusion plasmas, dissipation is due to collective phenomena such as plasma waves and micro-turbulence rather than direct particle–particle collisions. Since astrophysical plasmas usually are not directly observable, laboratory investigations may help to verify theoretical plasma astrophysical predictions but for the transfer of knowledge one has to take into account some specifics of astroplasmas, their density, temperature, currents and magnetic field strengths, geometry and even topology. As an example we discuss magnetic reconnection in the solar corona which requires collisionless dissipation. Both are highly nonlinear processes that occur at totally different scales. Hence, we refer to numerical simulations. Finally, we list the most urgent open questions in plasma astrophysics which should be addressed in the near future.

The predictions of the generalised Rutherford equation for the stabilisation of neoclassical tearing modes (NTMs) are reviewed. They suggest that the stabilisation efficiency can be maximised by maximising the current density within the island, favouring narrow deposition over maximum total current. Also, for ITER, where it is expected that the minimum island size before stabilisation will be small with respect to the deposition width, a loss of efficiency for continuous injection is predicted, but can be recovered by phased injection with respect to the island's O-point. The paper compares in detail these predictions with dedicated experiments on ASDEX Upgrade and finds good qualitative agreement with the generalised Rutherford equation. For quantitative agreement, the experimental database is not yet firm enough. The conclusion for ITER is that J_ECCD should be optimised and that modulation capability of the gyrotrons should be foreseen to ensure optimum stabilisation efficiency in the small island regime.

DIII-D experiments show that the resistive wall mode (RWM) can remain stable in high β scenarios despite a low net torque from nearly balanced neutral beam injection heating. The minimization of magnetic field asymmetries is essential for operation at the resulting low plasma rotation of less than 20 krad s⁻¹ (measured with charge exchange recombination spectroscopy using C VI emission) corresponding to less than 1% of the Alfvén velocity or less than 10% of the ion thermal velocity. In the presence of n = 1 field asymmetries the rotation required for stability is significantly higher and depends on the torque input and momentum confinement, which suggests that a loss of torque-balance can lead to an effective rotation threshold above the linear RWM stability threshold. Without an externally applied field the measured rotation can be too low to neglect the diamagnetic rotation. A comparison of the instability onset in plasmas rotating with and against the direction of the plasma current indicates the importance of the toroidal flow driven by the radial electric field in the stabilization process. Observed rotation thresholds are compared with predictions for the semi-kinetic damping model, which generally underestimates the rotation required for stability. A more detailed modeling of kinetic damping including diamagnetic and precession drift frequencies can lead to stability without plasma rotation. However, even with corrected error fields and fast plasma rotation, plasma generated perturbations, such as edge localized modes, can nonlinearly destabilize the RWM. In these cases feedback control can increase the damping of the magnetic perturbation and is effective in extending the duration of high β discharges.

RFX-mod is a reversed field pinch (RFP) experiment equipped with a system that actively controls the magnetic boundary. In this paper we describe the results of a new control algorithm, the clean mode control (CMC), in which the aliasing of the sideband harmonics generated by the discrete saddle coils is corrected in real time. CMC operation leads to a smoother (i.e. more axisymmetric) boundary. Tearing modes rotate (up to 100 Hz) and partially unlock. Plasma–wall interaction diminishes due to a decrease of the non-axisymmetric shift of the plasma column. With the ameliorated boundary control, plasma current has been successfully increased to 1.5 MA, the highest for an RFP. In such regimes, the magnetic dynamics is dominated by the innermost resonant mode, the internal magnetic field gets close to a pure helix and confinement improves.

In this paper we report on observations and interpretations of a new class of global MHD eigenmode solutions arising in gaps in the low frequency Alfvén–acoustic continuum below the geodesic acoustic mode frequency. These modes have been just reported (Gorelenkov et al 2007 Phys. Lett.370 70–7) where preliminary comparisons indicate qualitative agreement between theory and experiment. Here we show a more quantitative comparison emphasizing recent NSTX experiments on the observations of the global eigenmodes, referred to as beta-induced Alfvén–acoustic eigenmodes (BAAEs), which exist near the extrema of the Alfvén–acoustic continuum. In accordance to the linear dispersion relations, the frequency of these modes may shift as the safety factor, q, profile relaxes. We show that BAAEs can be responsible for observations in JET plasmas at relatively low beta <2% as well as in NSTX plasmas at relatively high beta >20%. In NSTX plasma observed magnetic activity has the same properties as predicted by theory for the mode structure and the frequency. Found numerically in NOVA simulations BAAEs are used to explain the observed properties of relatively low frequency experimental signals seen in NSTX and JET tokamaks.

Long period sawteeth have been observed to result in low-β triggering of neo-classical tearing modes, which can significantly degrade plasma confinement. Consequently, a detailed physical understanding of sawtooth behaviour is critical, especially for ITER where fusion-born α particles are likely to lead to very long sawtooth periods. Many techniques have been developed to control, and in particular to destabilize the sawteeth. The application of counter-current neutral beam injection (NBI) in JET has resulted in shorter sawtooth periods than in Ohmic plasmas. This result has been explained because, firstly, the counter-passing fast ions give a destabilizing contribution to the n = 1 internal kink mode—which is accepted to be related to sawtooth oscillations—and secondly, the flow shear strongly influences the stabilizing trapped particles. A similar experimental result has been observed in counter-NBI heated plasmas in MAST. However, the strong toroidal flows in spherical tokamaks mean that the sawtooth behaviour is determined by the gyroscopic flow stabilization of the kink mode rather than kinetic effects. In NBI heated plasmas in smaller conventional aspect-ratio tokamaks, such as TEXTOR, the flow and kinetic effects compete to give different sawtooth behaviour. Other techniques applied to destabilize sawteeth are the application of electron cyclotron current drive (ECCD) or ion cyclotron resonance heating (ICRH). In JET, it has been observed that localized ICRH is able to destabilize sawteeth which were otherwise stabilized by a co-existing population of energetic trapped ions in the core. This is explained through the dual rôle of the ICRH in reducing the critical magnetic shear required to trigger a sawtooth crash, and the increase in the local magnetic shear which results from driving current near the q = 1 rational surface. Sawtooth control in ITER could be provided by a combination of ECCD and co-passing off-axis negative-NBI fast ions.

A few years ago, several experiments showed that laser-plasma accelerators can produce high-quality electron beams, with quasi-monoenergetic energy distributions at the 100 MeV level. These experiments were performed by focusing a single ultra-short and ultraintense laser pulse into an underdense plasma. Here, we report on recent experimental results of electron acceleration using two counter-propagating ultra-short and ultraintense laser pulses. We demonstrate that the use of a second laser pulse provides enhanced control over the injection and subsequent acceleration of electrons into plasma wakefields. The collision of the two laser pulses provides a pre-acceleration stage which provokes the injection of electrons into the wakefield. The experimental results show that the electron beams obtained in this manner are collimated (5 mrad divergence), monoenergetic (with relative energy spread <10%), tuneable (between 50 and 250 MeV) and, most importantly, stable.

During the last few years laser-driven plasma accelerators have been shown to generate quasi-monoenergetic electron beams with energies up to several hundred MeV. Extending the output energy of laser-driven plasma accelerators to the GeV range requires operation at plasma densities an order of magnitude lower, i.e. 10¹⁸ cm⁻³, and increasing the distance over which acceleration is maintained from a few millimetres to a few tens of millimetres. One approach for achieving this is to guide the driving laser pulse in the plasma channel formed in a gas-filled capillary discharge waveguide. We present transverse interferometric measurements of the evolution of the plasma channel formed and compare these measurements with models of the capillary discharge. We describe in detail experiments performed at Lawrence Berkeley National Laboratory and at Rutherford Appleton Laboratory in which plasma accelerators were driven within this type of waveguide to generate quasi-monoenergetic electron beams with energies up to 1 GeV.

Properties of thin films such as the crystallinity of silicon deposited from SiH₄–H₂ discharges are governed by the plasma composition. Therefore, it is crucial to measure the plasma composition in order to understand and optimize the deposition rate, deposition efficiency and material quality of thin film deposition, such as for microcrystalline silicon, which is a key material for silicon thin film photovoltaic solar cells. This task can be performed by using Fourier transform infrared absorption spectroscopy or optical emission spectroscopy. This work compares these two techniques and shows their range of applicability and their limitations.

An RF microplasma jet working at atmospheric pressure has been developed for thin film deposition application. It consists of a capillary coaxially inserted in the ceramic tube. The capillary is excited by an RF frequency of 13.56 MHz at rms voltages of around 200–250 V. The plasma is generated in a plasma forming gas (helium or argon) in the annular space between the capillary and the ceramic tube. By adjusting the flows, the flow pattern prevents the deposition inside the source and mixing of the reactive species with the ambient air in the discharge and deposition region, so that no traces of air are found even when the microplasma is operated in an air atmosphere. All these properties make our microplasma design of great interest for applications such as thin film growth or surface treatment. The discharge operates probably in a γ-mode as indicated by high electron densities of around 8 × 10²⁰ m⁻³ measured using optical emission spectroscopy. The gas temperature stays below 400 K and is close to room temperature in the deposition region in the case of argon plasma. Deposition of hydrogenated amorphous carbon films and silicon oxide films has been tested using Ar/C₂H₂ and Ar/hexamethyldisiloxane/O₂ mixtures, respectively. In the latter case, good control of the film properties by adjusting the source parameters has been achieved with the possibility of depositing carbon free SiO_x films even without the addition of oxygen. Preliminary results regarding permeation barrier properties of deposited films are also given.

The currently accepted value for the upper bound for the photon mass, m_ph, is 22 orders of magnitude less than the electron mass. As the mass m_ph is so incredibly small, it has essentially no effect on atomic and nuclear physics; and it is very difficult to improve this estimate by laboratory experiments. However, even a very small mass may have a significant effect on astrophysical phenomena occurring on a scale exceeding the photon Compton length (where for the currently accepted mass). A set of magnetohydrodynamic equations (assuming a finite photon mass) are used to analyze properties of the solar wind at Pluto's orbit. This yields an improved (reduced) by a factor of 70 estimate of the photon mass. Possible opportunities and challenges for the further reduction of the upper limit for m_ph based on the properties of larger-scale astrophysical objects are discussed.

Magnetic field line reconnection in collisionless fluid plasma regimes is discussed with the aim of understanding the role of conserved topological quantities in the nonlinear development of the reconnection instability, the role of the guide field in the transition from the Alfvènic regime to the whistler regime and the onset of secondary instabilities.

Large-scale magnetic fields of celestial bodies are thought to be generated by the joint action of differential rotation and what is generally known as the alpha-effect—associated with a violation of mirror-symmetry in rotating convection or turbulence. The Coriolis force acting on rotating vortices in a stratified media results in an excess of right-hand vortices in one hemisphere and left-hand vortices in the other. This asymmetry gives a component of the mean electromotive force parallel to the mean magnetic field (the electromotive force and the electric current are perpendicular to the magnetic field in mirror-symmetric media). This is the famous alpha-effect which plays a key role in magnetic field self-excitation (the so-called mean-field dynamo) and leads to the solar cycle and other phenomena in astrophysical plasma.

A new finding in this field is that the nonlinear saturation of the dynamo instability is determined by transport properties of the magnetic helicity, which is an inviscid integral of motion and describes the mirror asymmetry of the magnetic field generated. We discuss first observational results concerning helicity transport in the solar cycle in the context of solar dynamo models.

Functional arrays of microplasmas were designed for the purpose of controlling electromagnetic waves in the range 10–100 GHz. A two-dimensional square-lattice array of microplasma columns was proved to have photonic-crystal-like properties showing the presence of photonic band gaps and flat bands. A one-dimensional linear array of cold cathode fluorescent lamps (CCFLs) embedded in between the truncated strip lines showed the resonant transmission characteristics due to the surface-wave modes corresponding to the flat-band frequencies. Another one-dimensional configuration of CCFLs vertically aligned along both sides of a coplanar strip line showed peculiar behavior at the lower and higher edges of the band gap. These unique wave-propagation properties are attributed to the periodic structures of which pitches are comparable to or smaller than the wavelengths of electromagnetic waves. Therefore, these artificial arrays are potential metamaterials, which can be used for plasma devices controlling electromagnetic waves.

The kinetic and extended magnetohydrodynamic (MHD) simulation methods are discussed in the context of their ability to simulate macroscopic plasma evolution on an MHD evolution time scale with microturbulence in toroidal magnetized plasmas. To properly model the evolution of neoclassical equilibrium, it is important to use full-f gyrokinetic calculation with sufficient accuracy for perpendicular viscosity. Similarly in MHD problems, a good accuracy in constructing the closures, in particular for the viscosity stress elements, is required. Although evidence of spontaneous reduction of transport with the consequent rapid steepening of the pressure gradient is found in simulations with full-f 5D gyrokinetic and 3D Braginskii fluid equations, no simulation of the transport barrier formation in agreement with experimental observations has yet been presented. For a comprehensive description of edge plasma dynamics, including L–H transition, pedestal formation, and ELM oscillation problems, full-f 5D gyrokinetic simulation is a necessity, at least in hybrid with 3D MHD. With present-day computers, the global transport time scale can be reached with full-f gyrokinetic simulations in small tokamaks (ρ^* ≤ 50–100), while fluid simulation has to be used for MHD evolution time scale in medium-sized tokamaks.

The two simplest axisymmetric systems (multi-mirror and gas dynamic) for plasma heating and confinement are described. Significant progress in understanding the key physical phenomena in heating and confinement of plasma made it possible to suppress longitudinal electron thermal conductivity (by three orders of magnitude, in the case of the multi-mirror system), to stabilize MHD instabilities in axisymmetric geometry. As a result of such suppression, in the case of the multi-mirror trap, a dense plasma (n_e ∼ 10²¹ m⁻³) was heated up to T_e ≈ T_i ≈ 2 keV or even higher. Until now no limitations preventing further growth of plasma parameters have been observed. The main goal of the gas dynamic trap studies is a demonstration of the feasibility of a 14 MeV neutron source (NS) with a neutron flux density of 2 MW m⁻², and a testing zone area of 1 m² for structural tests of fusion materials. In this paper, the most important results on the MHD stability of plasma in axisymmetric geometry, as well as the formation of fast sloshing ions population and the D–D neutrons generation are presented. Currently, the upgrade of the GDT device has been completed. We also report on the construction of new neutral beam injectors with total power of up to 10 MW and heating pulse duration of 5 ms (corresponding to a steady state regime). According to calculations, the feasibility of a 'moderate' NS with a neutron flux of 0.5 MW m⁻² can be demonstrated with the new neutral beam injection system in the near future. Preliminary experiments with the first two new NB injectors are currently being carried out at the Budker Institute of Nuclear Physics.

A high density regime with an internal diffusion barrier (IDB) has been extended to the helical divertor (HD) configuration in the Large Helical Device (LHD). Avoidance of the local enhancement of neutral pressure is necessary to enable IDB formation, which is consistent with earlier works by using the Local Island Divertor (LID) with efficient active pumping. The central pressure reached 1.3 times atmospheric pressure, where n_e(0) = 6 × 10²⁰ m⁻³ and T_e(0) = 660 eV. The plasmas with an IDB are located in the plateau collisionality regime. The significant impurity effect has not been observed throughout the discharges in spite of the existence of a negative radial electric field. A central pressure limiting event is observed in the plasmas with an IDB using the HD. During this event which is referred to as the core density collapse (CDC), particles are flushed out from the core on the time scale of a few hundreds of microseconds. The suppression of the Shafranov shift by vertical elongation (κ) is effective to mitigate CDC. At κ = 1.2, the central β value is increased up to 6.6% at 1 T.

We have performed a systematic study of beam propagation (400 ps, I = 10¹⁰–10¹⁴ W cm⁻²) in underdense plasmas (n_e = 10¹⁹–10²⁰ cm⁻³) at a level of reduced complexity compared with the smoothed beams currently used in inertial confinement fusion studies, using one or two well-controlled filaments. These experiments have been performed on the LULI 100 TW laser facility. The use of well-controlled, diffraction-limited single filaments is possibly due to the use of adaptative optics. We have used either a single filament or two filaments having variable distance, delay, intensity ratio and polarization. The single filament configuration allows to study basic beam propagation and reveals occurrence of filamentation at low intensity levels. The use of two filaments demonstrates the occurrence of beam coupling and merging, and the importance of cross-talk effects supported by the plasma.

The most common man-made discharge is a lamp. Even though lamps are often considered a mature technology, the discharge physics is often poorly understood. Two recent initiatives discussed here show that plasma research can help to make significant improvements. First we discuss color separation in metal halide lamps, which is a problem that prevents these highly efficient lamps from being used in more applications. Secondly a novel lamp concept is presented that may replace the current mercury based fluorescent lamps.

Previous results are reviewed and new results are presented on the Rayleigh–Taylor instability in inertial confined fusion, flames and supernovae including gravitational and thermonuclear explosion mechanisms. The instability couples micro-scale plasma effects to large-scale hydrodynamic phenomena. In inertial fusion the instability reduces target compression. In supernovae the instability produces large-scale convection, which determines the fate of the star. The instability is often accompanied by mass flux through the unstable interface, which may have either a stabilizing or a destabilizing influence. Destabilization happens due to the Darrieus–Landau instability of a deflagration front. Still, it is unclear whether the instabilities lead to well-organized large-scale structures (bubbles) or to relatively isotropic turbulence (mixing layer).

The role of drift turbulence in momentum creation is studied for conditions prevalent in some space and laboratory plasmas. A new approach is presented to analyze non-linear kinetic simulations and to extract the role of wave–particle interaction in momentum creation. The approach is applied to the lower-hybrid drift instability where it is shown that the anomalous resistivity generated does not penetrate into the plasma even when electromagnetic fluctuations are considered.

A key issue for steady-state tokamak operation is to determine the edge conditions that are compatible both with good core confinement and with the power handling and plasma exhaust capabilities of the plasma facing components (PFCs) and divertor systems. A quantitative response to this open question will provide a robust scientific basis for reliable extrapolation of present regimes to an ITER compatible steady-state scenario. In this context, the JET programme addressing steady-state operation is focused on the development of non-inductive, high confinement plasmas with the constraints imposed by the PFCs. A new beryllium main chamber wall and tungsten divertor together with an upgrade of the heating/fuelling capability are currently in preparation at JET. Operation at higher power with this ITER-like wall will impose new constraints on non-inductive scenarios. Recent experiments have focused on the preparation for this new phase of JET operation. In this paper, progress in the development of advanced tokamak (AT) scenarios at JET is reviewed keeping this long-term objective in mind. The approach has consisted of addressing various critical issues separately during the 2006–2007 campaigns with a view to full scenario integration when the JET upgrades are complete. Regimes with internal transport barriers (ITBs) have been developed at q₉₅ ∼ 5 and high triangularity, δ (relevant to the ITER steady-state demonstration) by applying more than 30 MW of additional heating power reaching β_N ∼ 2 at B_o ∼ 3.1 T. Operating at higher δ has allowed the edge pedestal and core densities to be increased pushing the ion temperature closer to that of the electrons. Although not yet fully integrated into a performance enhancing ITB scenario, Neon seeding has been successfully explored to increase the radiated power fraction (up to 60%), providing significant reduction of target tile power fluxes (and hence temperatures) and mitigation of edge localized mode (ELM) activity. At reduced toroidal magnetic field strength, high β_N regimes have been achieved and q-profile optimization investigated for use in steady-state scenarios. Values of β_N above the 'no-wall magnetohydrodynamic limit' (β_N ∼ 3.0) have been sustained for a resistive current diffusion time in high-δ configurations (at 1.2 MA/1.8 T). In this scenario, ELM activity has been mitigated by applying magnetic perturbations using error field correction coils to provide ergodization of the magnetic field at the plasma edge. In a highly shaped, quasi-double null X-point configuration, ITBs have been generated on the ion heat transport channel and combined with 'grassy' ELMs with ∼30 MW of applied heating power (at 1.2 MA/2.7 T, q₉₅ ∼ 7). Advanced algorithms and system identification procedures have been developed with a view to developing simultaneously temperature and q-profile control in real-time. These techniques have so far been applied to the control of the q-profile evolution in JET AT scenarios.

The dynamics of fast ion populations in the TEXTOR tokamak are measured by collective Thomson scattering of millimetre wave radiation generated by a gyrotron operated at 110 GHz and 100–150 kW. Temporal evolution of the energetic ion velocity distribution at switch on of neutral beam injection (NBI) and the slowdown after switch off of NBI are measured. The turn on phase of the NBI has, furthermore, been measured in plasmas with a range of electron densities and temperatures. All of these measurements are shown to be in good agreement with simple Fokker–Planck modelling. Bulk ion rotation velocity is also measured.

For heating and current drive the neutral beam injection system for ITER requires a deuterium beam with an energy of 1 MeV for up to 1 h. In order to inject the required 17 MW the ion source has to deliver 40 A of negative ion current. For an accelerated current density of 200 A m⁻² at the specified source pressure of 0.3 Pa the extraction area is 0.2 m² resulting in a large area source of 1.5 × 0.6 m². Two types of sources have been under discussion, the filamented arc source and the inductively driven RF source, the latter now having been chosen for the ITER reference design. The development of negative ion RF sources, which fulfil these specifications is being carried out at the Max–Planck-Institut für Plasmaphysik at three test facilities in parallel. The required current densities at the ITER relevant pressure have been achieved and even exceeded in a test facility equipped with a small ion source (extraction area of 0.007 m²) at limited pulse length (<4 s). The extraction area can be extended up to 0.03 m² and the pulse length up to 3600 s at a second test facility which is dedicated to long pulse operation experiments where pulses up to 800 s have already been achieved. The ion source at the third test facility has roughly the full width and half the height of the ITER source but is not equipped with an extraction system. The aim is to demonstrate the size scaling and plasma homogeneity of RF ion sources. First results from different diagnostic techniques (optical emission spectroscopy and Langmuir probe) are very promising.

The operational domain for active control of type-I edge localized modes (ELMs) with an n = 1 external magnetic perturbation field induced by the ex-vessel error field correction coils on JET has been developed towards more ITER-relevant regimes with high plasma triangularity, up to 0.45, high normalized beta, up to 3.0, plasma current up to 2.0 MA and q₉₅ varied between 3.0 and 4.8. The results of ELM mitigation in high triangularity plasmas show that the frequency of type-I ELMs increased by a factor of 4 during the application of the n = 1 fields, while the energy loss per ELM, ΔW/W, decreased from 6% to below the noise level of the diamagnetic measurement (<2%). No reduction of confinement quality (H98Y) during the ELM mitigation phase has been observed. The minimum n = 1 perturbation field amplitude above which the ELMs were mitigated increased with a lower q₉₅ but always remained below the n = 1 locked mode threshold. The first results of ELM mitigation with n = 2 magnetic perturbations on JET demonstrate that the frequency of ELMs increased from 10 to 35 Hz and a wide operational window of q₉₅ from 4.5 to 3.1 has been found.

The Z-pinch dynamic hohlraum (ZPDH) is a high-power x-ray source that has been used in a variety of high energy-density experiments including inertial confinement fusion (ICF) studies. The system consists of a tungsten wire-array Z pinch that implodes onto a low-density CH₂ foam converter launching a radiating shock that heats the hohlraum to radiation temperatures >200 eV. Through time-gated pinhole camera measurements, the mean shock speed is measured from 28 experiments to be 326 ± 4 µm ns⁻¹ with a shot-to-shot standard deviation of 7%. Broad-band x-ray measurements indicate that the shot-to-shot reproducibility in the power emission and pulse-shape of the source shock is <15% and ∼5%, respectively. Calculations have shown that an ICF capsule placed at the center of the foam in the ZPDH can absorb >40 kJ of x-ray energy, within a factor of 4 of the energy believed sufficient for ICF ignition. The capsule types imploded by the ZPDH have evolved over four years culminating in a design that produces record indirect-drive DD thermonuclear neutron yields of up to 3.5E11.

Recent progress in high-gain direct-drive inertial confinement fusion with the laser Mégajoule is reviewed. A new baseline direct-drive target design is presented which implodes with a two-cones irradiation pattern of indirect-drive beam configuration and zooming. Perturbation amplitudes and correlated growth rates of hydrodynamic instabilities in the compressed core of a directly driven inertial confinement fusion capsule are analyzed in planar and spherical geometries, with and without heat conduction, in the unsteady state regime of the deceleration. Shock propagation in heterogeneous media is addressed in the context of first shock. The neutron and photon emissions of high-gain direct-drive target are characterized. Numerical interpretations of directly driven homothetic cryogenic D₂ target implosion experiments on the Omega facility are presented.

Investigations of plasma jets produced by the action of a defocused laser beam on planar metallic targets and the interaction of supersonic plasma jets with dense gases (He and Ar) are presented. The experiment was carried out at the iodine laser facility (Prague Asterix Laser System (PALS)) using the third harmonic of laser radiation (0.438 µm) with a pulse duration of 250 ps (FWHM). In order to optimize the plasma jet parameters, the laser beam energy and the focal spot radius were changed in the ranges of 13–160 J and 35–600 µm, respectively. Besides, the focal point was located both before and inside the targets. The study was performed with the use of target materials of different mass densities (Cu, Ag and Ta). Finally, the optimized Cu plasma jets were used for shock wave generation in ambient gases of different pressures.

Information about the geometry of plasma expansion, plasma dynamics and electron density distributions was obtained by means of a 3-frame laser interferometric system. Additionally, a Photonic Science PE7051 x-ray pinhole camera and the crater replica method for the reconstruction of crater parameters were used.

Our experiment has shown that the plasma jet forming is a fundamental process which accompanies the expansion of the laser plasma produced by irradiating a massive planar target, made of a material of a relatively high atomic number, with a partly defocused laser beam. One can suppose that there are no laser energy limitations for the plasma jet creation. Illustrations of applications of such plasma jets for astrophysical and inertial confinement fusion investigations are also presented.

An unresolved question of magnetospheric physics concerns the creation of convergent and divergent electric field structures responsible for the acceleration of auroral particles to several kilo-electronvolt. Similarly, an unresolved problem of solar physics concerns the acceleration of particles producing the x-ray coronal emissions. Here we show that both these problems can be explained by electric field structures produced by nonlinear magnetosonic waves. The convergent electric field structures correspond to fast magnetosonic solitons, while divergent electric field structures are produced by slow solitons. Both types of solitons can build potentials of tens of kV in the magnetosphere and hundreds of kV in the solar corona. Such solitons can be created when linear magnetosonic and Alfvén waves propagate through regions of varying Alfvén speed, which occurs on auroral field lines at altitudes of 6000 km, and also above the chromosphere in the solar corona. The initial, linear MHD waves can be produced by bursty bulk flows in the Earth's magnetotail and by chromospheric/photospheric convective flows on the Sun.

The objective of advanced tokamak scenario research is to provide a candidate plasma scenario for continuous operation in a fusion power plant. The optimization of the self-generated non-inductive current by the bootstrap mechanism up to a level of 50% and above using high plasma pressure and improved confinement are the necessary conditions to achieve this goal. The two main candidate scenarios for continuous operation, the steady state scenario and long duration (up to 3000 s) high neutron fluency scenario (the hybrid scenario), both face physics challenges in terms of confinement, stability, power exhaust and plasma control. Resistive wall modes and Alfvénic fast ion driven instabilities are the main limitations for operating the steady state scenario at high pressure and low magnetic shear. In addition, this scenario demands a high degree of control over the plasma current and pressure profile and the steady state heat load on in-vessel plasma facing components. Understanding the confinement properties of hybrid scenario is still an outstanding issue as well as its modelling for ITER in particular with regard to the H-mode pedestal parameters. This scenario will also require active current profile control, although, less demanding than for the steady state scenario. To operate advanced tokamak scenario, broad current and pressure profile control appears as a necessary requirement on ITER actuators, in addition to the tools required for instability control such as error field coils or electron cyclotron current drive.

Fast ignition (FI) is an innovative approach to inertial confinement fusion, which has the potential for higher energy gain at lower overall driver energy and cost. If realized at full scale, it could open a route to inertial fusion energy. This paper is a brief review of basic FI concepts and the progress in FI research which has taken place in recent years. The requirements for the DT fuel and the ignitor (electron or proton beam) as well as for the laser drivers are discussed. Key issues related to electron FI and proton FI are considered. Prospects for FI-related experiments using next generation laser facilities just being constructed or designed are outlined.

The field of laser–matter interaction has branched out in two main directions. The first, motivated by laser inertial confinement fusion, warm-dense-matter, fast ignition and astrophysics in laboratory, and the second driven by ultra-high intensity, exotic physics, high-energy particle, photon beam generation and time-resolved attosecond (zeptosecond) science. The degree of maturity from both experimental and theoretical stand-points is such that a large European infrastructure for each branch is contemplated as part of the European Roadmap. The first one, HiPER-PETAL will be dedicated to fast ignition with the aim of obtaining a thermonuclear gain of 100, whereas the second, Extreme Light Infrastructure (ELI) could go beyond the relativistic regime to foray into the ultra-relativistic domain >10²⁴ W cm⁻². In this paper we highlight the intriguing perspectives that these two projects will offer.