Table of contents

Extragalactic jets are prominent astrophysical objects that are characterized by extended synchrotron emission. In situ acceleration in extragalactic jets cause the non-thermal radio up to x-ray radiation. Hadrons can, in principle, be accelerated up to the highest energies measured for ultrahigh energy cosmic rays. In particular, the Centaurus A jet seems to be a plausible source of the highest cosmic ray photons. Magnetic reconnection can locally convert magnetic energy to particle acceleration in field-aligned electric fields. These fields are associated with electric currents by a finite collisionless resistance.

Achieving long-duration, high-performance discharges in magnetic fusion devices is one of the most important challenges en route to a fusion reactor. At this stage, we need to bring together many physical concepts and technological achievements that hitherto have been considered as separate issues. In the course of a long duration pulse, one encounters a sequence of progressively increasing characteristic timescales, ranging from milliseconds for MHD events, seconds for energy and particle transport times, tens of seconds for current diffusion times and up to hundreds of seconds for wall processes, such as saturation and erosion, to reach equilibrium. Although many present-day experiments have pulse lengths long enough to allow studies of the MHD and transport issues in conditions that are effectively quasi steady state, most have pulse lengths that are marginal for studying current diffusion phenomena and, generally, all are too short to study wall saturation and erosion. Very few present-day experiments bring together the necessary hardware (magnets, power supplies, heating and current drive systems, cooling loops, etc) to properly address issues on timescales greater than 10 s.

This paper reviews the status of present-day long pulse experiments in tokamaks and stellarators in terms of the technology and physics. We start by defining the requirements of long pulse experiments and discussing the technology that is needed. Then, we consider the relevant physics including the important interactions between physics and technology. Finally, we consider the issues that must be addressed to go beyond long pulses in order to reach full steady-state operation.

The Mega Ampère Spherical Tokamak (MAST) is now accessing regimes with high normalized confinement relative to international scalings, H_H(IPB98(y, 2))>∼1 at high normalized density, _e>60% of the Greenwald density. Data from MAST H-modes suggest that the aspect ratio dependency of international confinement and L–H threshold scalings may need to be modified to improve predictions for ITER. Access to H-mode on MAST is strongly affected by both the divertor magnetic geometry and fuelling location, with the formation of an edge transport barrier being facilitated by operation near the symmetric, connected double-null configuration and with poloidally localized inboard gas puffing. The ELMs on MAST appear to be Type III in nature, even in the highest performance plasmas and with the maximum available auxiliary heating power. ELM energy losses are less than 4% of stored energy in all regimes so far explored. These Type III ELMs are associated with a reduction in the pedestal density but no significant change in the pedestal temperature or temperature profile, indicating that energy is convected from the pedestal region into the scrape-off layer. Analysis of the energy observed to arrive at the divertor targets indicates that ELM losses are predominantly on the low field side. ELM effluxes are observed up to 20 cm from the plasma edge at the outboard mid-plane and are associated with the radial motion of a feature at an average velocity of 1.2 km s⁻¹.

In order to provide greater confidence in the advanced steady-state operation in ITER, recent high-performance campaign in JT-60U has emphasized maximizing the capabilities of internal and edge transport barriers by the elaborate profile control using NB, electron cyclotron heating and other non-inductive current drive (CD) schemes as well as the strong shaping. Accordingly, it is highlighted by the reliable reproduction of the D–T equivalent fusion amplification gain (Q_DT^eq) of over 1.2 transiently and sustainment of Q_DT^eq at 0.8 for 0.55 s in reversed shear plasmas. On the other hand, increased triangularity up to 0.6 has also provided the improved confinement at higher density and sustainment of high normalized β (β_N) above 2.7 for over 7 s in high-β poloidal H-mode. In addition, increased negative ion based neutral beam heating and CD power up to 5.7 MW contributed much to achieve the β_N of 2.4 and confinement enhancement factor of 1.2 over the ITER98(y, 2) scaling simultaneously under full non-inductive CD at 1.8 MA. Furthermore, impact of electron heating on transport barriers was investigated, and it was found that strong barriers survive T_e⩾T_i. With regard to the exploratory control of transport barriers using the perturbative schemes, the effect of asymmetric pressure fluctuations and Maxwell stress has been investigated. The suggested approaches could be applied in steady-state burning plasmas with transport barriers, where the external heating fraction is reduced and electron heating is predominant.

Laser–plasma interaction (LPI) physics is one the major issues for the realization of inertial fusion. Parametric instabilities may be driven by the incident laser beams during their propagation in the underdense plasma surrounding the fusion capsule. These instabilities may result in various effects detrimental to a good energy transfer from the laser beams to the target: the backscattering of the incident beams, the generation of energetic electrons which might preheat the fusion fuel, and the spoiling of the laser beam alignment. The control of the linear growth of these instabilities, together with the understanding of their nonlinear saturation mechanisms are therefore of fundamental importance for laser fusion. During the past few years, a series of new concepts have emerged, deeply modifying our approach to LPI physics. In particular, LPI experiments are now carried out with laser beams which are optically smoothed by means of random phase plates. Such beams are characterized inside the plasma by randomly distributed intensity maxima. Filamentation instabilities may locally increase the laser intensity maxima and deplete the electron density, leading to an intricate coupling between various nonlinear processes. One of the most striking features of this intricate coupling is the resulting ability of the plasma to induce additional temporal and spatial incoherence to the laser beams during their propagation. The increased incoherence may in turn reduce the level of backscattering instabilities.

Recent experiments at ASDEX Upgrade have achieved advanced scenarios with high β_N (>3) and confinement enhancement over ITER98(y, 2) scaling, H^H98y2 = 1.1–1.5, in steady state. These discharges have been obtained in a modified divertor configuration for ASDEX Upgrade, allowing operation at higher triangularity, and with a changed neutral beam injection (NBI) system, for a more tangential, off-axis beam deposition. The figure of merit, β_NH^ITER89-P, reaches up to 7.5 for several seconds in plasmas approaching stationary conditions. These advanced tokamak discharges have low magnetic shear in the centre, with q on-axis near 1, and edge safety factor, q₉₅ in the range 3.3–4.5. This q-profile is sustained by the bootstrap current, NBI-driven current and fishbone activity in the core. The off-axis heating leads to a strong peaking of the density profile and impurity accumulation in the core. This can be avoided by adding some central heating from ion cyclotron resonance heating or electron cyclotron resonance heating, since the temperature profiles are stiff in this advanced scenario (no internal transport barrier). Using a combination of NBI and gas fuelling line, average densities up to 80–90% of the Greenwald density are achieved, maintaining good confinement. The best integrated results in terms of confinement, stability and ability to operate at high density are obtained in highly shaped configurations, near double null, with δ = 0.43. At the highest densities, a strong reduction of the edge localized mode activity similar to type II activity is observed, providing a steady power load on the divertor, in the range of 6 MW m⁻², despite the high input power used (>10 MW).

The physics of tokamak plasmas, in which electrons are heated by electron cyclotron heating (ECH) and whose current is driven by electron cyclotron current drive (ECCD), is investigated in this paper together with applications on tokamak à configuration variable (TCV) using modifications of the pressure and current profiles to improve the operational regimes. In order to explain the experimentally determined current drive efficiency and hard x-ray and electron cyclotron emission measurements, it is shown that quasi-linear effects and radial transport of the suprathermal electrons are necessary. Plasmas with fully non-inductively driven currents were obtained with 0.9 MW of off-axis ECCD and 0.45 MW of on-axis counter ECCD. The combination of the driven current and the bootstrap current, accounting for 50% of the total current and peaking off-axis, yields a reversed safety factor profile and a wide and stable electron internal transport barrier. This barrier leads to an enhancement in the energy confinement by a factor of 4.5. ECH is also used to broaden the current profile of high elongation, low normalized-current plasmas whose vertical position would otherwise be uncontrollable on TCV, but whose MHD stability properties should allow high β values. An elongation of 2.47 at a normalized-current of 1.05 MA mT⁻¹ is obtained with off-axis ECH absorbed at an optimized normalized radius between 0.55 and 0.7. Finally, third harmonic ECH is tested in various scenarios, all using vertical beam launching. In particular, high density Ohmic target and preheating with second harmonic ECH are presented. The fraction of third harmonic power absorbed reaches 65% and 85%, respectively.

Intense beams of protons and heavy ions have been observed in ultra-intense laser–solid interaction experiments. Thereby, a considerable fraction of the laser energy is transferred to collimated beams of energetic ions (e.g. up to 50 MeV protons; 100 MeV fluorine), which makes these beams highly interesting for various applications. Experimental results indicate a very short-pulse duration and an excellent beam quality, leading to beam intensities in the TW range. To characterize the beam quality and its dependence on laser parameters and target conditions we performed experiments using the 100 TW laser system at Laboratoire pour l'Utilisation des Lasers Intenses at the Ecole Polytechnique, France, with focused intensities exceeding 10¹⁹ W cm⁻². We found a strong dependence on the target rear surface conditions allowing to tailor the ion beam by an appropriate target design. We also succeeded in the generation of heavy ion beams by suppressing the proton amount at the target surface.

We will present recent experimental results demonstrating a transverse beam emittance far superior to the accelerator based ion beams. Finally, we will discuss the prospect of laser accelerated ion beams as new diagnostics in laser–solid interaction experiments. Special fields of interest are proton radiography, electric field imaging, and relativistic electron transport inside the target.

We have studied fast heating of highly compressed plasmas using multi 100 TW laser light. Efficient propagation of the ultra-intense laser light and heating of the imploded plasmas were realized with a cone-attached shell target. Energy deposition rate of the ultra-intense laser pulse into high-density plasmas was evaluated from neutron measurements. Generation and propagation property of energetic electrons in the ultra-intense laser interactions were also investigated with solid density targets. About 40% of the laser energy converted to mega electron volts energetic electrons in the interactions with solid targets at intensities of 10¹⁹ W cm⁻². These electrons propagated in the high-density plasmas with a divergence of 20–30° or jet-like collimation. Taking account of these experimental results, heating laser spot size is optimized for laser fusion ignition with a simple estimation.

This paper addresses the key requirements for fusion materials, as these have emerged from studies of commercial fusion power plants. The objective of the international fusion programme is the creation of power stations that will have very attractive safety and environmental features and viable economics. Fusion power plant studies have shown that these objectives may be achieved without requiring extreme advances in materials. But it is required that existing candidate materials perform at least as well as envisaged in the environment of fusion neutrons, heat fluxes and particle fluxes. The development of advanced materials would bring further benefits. The work required entails the investigation of many intellectually exciting physics issues of great scientific interest, and of wider application than fusion. In addition to giving an overview, selected aspects of the science, of particular physics interest, are illustrated.

The measurements of the current density and the radial electric field profiles in tokamaks have considerably gained importance since advanced operational scenarios have come into play. A detailed knowledge of these profiles is desirable for operational scenarios involving reversed magnetic shear and/or the active control of internal and edge transport barriers. Unfortunately, the current density as well as the radial electric field are among the plasma parameters that are most difficult to diagnose. Routine methods to measure the current density profile are based on the Faraday effect (i.e. polarimetry) and the motional Stark effect (MSE). The most advanced diagnostics for the measurement of the radial electric field in the plasma core are the heavy ion beam probe and again the MSE. This paper will briefly explain the need for detailed measurements of the current density and radial electric field profile. Subsequently, the various diagnostics to measure these parameters will be reviewed. The emphasis will be especially put on recent trends, rather than on an exhaustive overview.

Experiments are conducted on the JET tokamak to demonstrate the diagnostic potential of Magneto-Hydro-Dynamics (MHD) spectroscopy, for the plasma bulk and its suprathermal components, using Alfvén eigenmodes (AEs) excited by external antennas and by energetic particles. The measurements of AE frequencies and mode numbers give information on the bulk plasma. Improved equilibrium reconstruction, in particular in terms of radial profiles of density and safety factor, is possible from the comparison between the antenna driven spectrum and that calculated theoretically. Details of the time evolution of the non-monotonic safety factor profile in advanced scenarios are reconstructed from the frequency behaviour of ICRH-driven energetic particle modes. The plasma effective mass is inferred from the resonant frequency of externally driven AEs in discharges with similar equilibrium profiles. The stability thresholds and the nonlinear development of the instabilities give clues on energy and spatial distribution of the fast particle population. The presence of unstable AEs provides lower limits in the energy of ICRH generated fast ion tails. Fast ion pressure gradients and their evolution are inferred from the stability of AEs at different plasma radial positions. Finally, the details of the AE spectrum in the nonlinear stage are used to obtain information about the fast particle velocity space diffusion.

Significant progress has been made in recent years in achieving levels of energy confinement in existing tokamaks which scale to that required for ITER. In particular, high confinement is achieved routinely in the plasma edge and in the plasma core, leading to steep density and temperature gradients. These gradients can drive non-inductive currents which could reduce significantly the requirements for externally applied current drive in a steady state tokamak. However, high confinement can also lead to deleterious effects related to pressure and current driven magnetohydrodynamic instabilities and to impurity accumulation. Experimental effort is now turning to the real time control of plasma and current profiles to facilitate the achievement of high confinement and to prevent the deleterious effects which could otherwise inhibit the development of a fully coherent operating scenario for a reactor.

Stellarators have the intrinsic property of steady state operation. However, on present-day stellarators the pulse length is usually not only limited due to technical reasons, but also by physical problems. Lack of density control and a subsequent radiation collapse terminate the discharges quite often at high densities. To improve the control of the plasma–wall interaction, the island divertor concept was developed for optimized stellarators. To test this divertor concept on W7-AS, all limiters were removed and replaced by ten divertor modules. In subsequent divertor experiments a promising new plasma operational regime has been discovered which is termed `high density H-mode' (HDH-mode). During the transition into that regime a clear reduction of ELM-like events and turbulent fluctuations is observed. The HDH-mode combines good energy confinement with very low impurity confinement resulting in low core radiation, but high edge-localized radiation. Consequently, stationary discharges at densities of typically 2×10²⁰ m⁻³ can be performed within the accessible pulse length of about 1 s. At densities above 3×10²⁰ m⁻³ a controlled transition from attached to partially detached plasmas is observed. The still edge-localized radiation reaches 90% of the heating power so that the power load onto the divertor target plates is further reduced. At a lower toroidal field of 0.9 T average β-values could be raised from earlier 2% to more than 3% in magnetic field configurations with rather smooth flux surfaces at the plasma boundary. The recently obtained results render excellent prospects for W7-X, the larger superconducting successor experiment of W7-AS.

We report on the development of a multi-millijoule, ultra high-brightness Ne-like soft x-ray laser (XRL) at the wavelength of 21.2 nm, recently undertaken at the PALS Centre. The device has been implemented as a routine radiation source delivering about 4 mJ of energy in pulses with a duration of ∼100 ps, in a narrowly collimated beam exhibiting high spatial quality and possessing high spatial coherence. The peak power of about 40 MW, generated by this device, is the largest value attained by an XRL to date. The same holds true for the peak spectral brightness, amounting to 10²⁷ photons s⁻¹ mm⁻² mrad⁻² 0.1%BW⁻¹. The active medium consists of a 3 cm long plasma column, sequentially generated from a slab target by an energy of ∼500 J delivered by the iodine 1.315 μm driving laser. The population inversion is produced by focusing tightly down to the line ∼500 J of energy into a much wider preplasma column, which makes it possible to create a lasing medium with a reduced lateral density gradient and thereby to minimize the lateral refraction of the x-ray beam. The multi-millijoule output is generated in double-pass amplification regime, achieved by a carefully designed half cavity using a flat multilayer Mo : Si mirror positioned a few millimetres near the plasma end. We describe the measured characteristics of the output beam generated by double-pass amplification, and illustrate its spatial beam coherence obtained using a Fresnel wavefront splitting interferometer. Given the available energy, peak power and brightness in a single pulse, the demonstrated XRL constitutes a tool for novel applications in both solid state and plasma physics. Examples of such applications are the generation of high-energy density, low-temperature plasmas relevant to laboratory astrophysics, x-ray interferometry of plasmas and solids with spatial resolution ranging from a micron to a few nanometres according to the specific experimental arrangement, or study of soft x-ray photoionization.

Various aspects of gravitational wave propagation in plasmas and vacuum are discussed. First, we analyse single particle trajectories, study the resonant interaction of gravitational waves with photons, and show that photons can be strongly energized by gravitational waves. Second, this exchange of energy between the photons and the gravitational waves is treated statistically, using a kinetic equation for photons. Gravitational wave instabilities induced by intense photon beams are considered. The effects are very much dependent on the gravitational wave dispersion in the plasma medium, and in particular, on its turbulent state.

The interaction of high intensity laser pulses (up to I∼10²⁰ W cm⁻²) with plasmas can generate very high order harmonics of the laser frequency (up to the 75th order have been observed). Measurements of the properties of these harmonics can provide important insights into the plasma conditions which exist during such interactions. For example, observations of the spectrum of the harmonic emission can provide information of the dynamics of the critical surface as well as information on relativistic non-linear optical effects in the plasma. However, most importantly, observations of the polarization properties of the harmonics can provide a method to measure the ultra-strong magnetic fields (greater than 350 MG) which can be generated during these interactions. It is likely that such techniques can be scaled to provide a significant amount of information from experiments at even higher intensities.

In this paper, the basic theory of runaway electron production is reviewed and recent progress is discussed. The mechanisms of primary and secondary generation of runaway electrons are described and their dynamics during a tokamak disruption is analysed, both in a simple analytical model and through numerical Monte Carlo simulation. A simple criterion for when these mechanisms generate a significant runaway current is derived, and the first self-consistent simulations of the electron kinetics in a tokamak disruption are presented. Radial cross-field diffusion is shown to inhibit runaway avalanches, as indicated in recent experiments on JET and JT-60U. Finally, the physics of relativistic post-disruption runaway electrons is discussed, in particular their slowing down due to emission of synchrotron radiation, and their ability to produce electron–positron pairs in collisions with bulk plasma ions and electrons.

Liquid and crystalline phases can be formed in so-called complex plasmas—plasmas enriched with solid particles in the nano- to micrometre range. The particles absorb electrons and ions and charge negatively up to a few volts. Due to their high mass compared to that of electrons and ions the particles dominate the processes in the plasma and can be observed on the most fundamental—the kinetic level. Through the strong Coulomb interaction between the particles it is possible that the particle clouds form fluid and crystalline structures. The latter is called `plasma crystal'. In this review we present an overview on the physics of this new area in plasma physics on the basis of theory and dedicated experiments performed in the laboratory and under microgravity conditions on the International Space Station.

Experiments on strong Langmuir turbulence (LT) driven by electron beam are reported. The technique of cold high-current relativistic electron beam (REB) permits to set up experimental conditions that are practically important but difficult for theoretical treatment of LT. These conditions include strong kinetic effects of plasma non-Maxwellian electrons, ion-acoustic oscillations which are weakly damped due to plasma non-isothermality and dispersion of Langmuir waves that are considerably modified by external magnetic field. A relatively dense plasma permits the use of the Thomson scattering method for observation of spectra of plasma fluctuations, electron distribution function, and local dynamics of plasma density. LT is studied in two operating modes that are characterized by moderate and increased current of REB. The experimental results with moderate REB current do not support the widely accepted picture when most of the Langmuir oscillations are trapped in density cavities. The energy flow through turbulence to plasma electrons is explained without major contribution of fully developed collapse, whereas, with increased REB current dynamic density cavities of spatial scale much less than the size of turbulent region are directly observed.

This paper is an overview of the activity and state-of-the-art in the field of plasma aerospace applications. Both experimental results and theoretical ideas are analysed. Principal attention is focused on understanding the physical mechanisms of the plasma effect on hypersonic aerodynamics. In particular, it is shown that drag reduction can be achieved using a proper distribution of heat sources around a flying body. Estimates of the energetic efficiency of the thermal mechanism of aerodynamic drag reduction are presented. The non-thermal effect caused by the interaction of a plasma flow with a magnetic field is also analysed. Specifically, it is shown that appropriate spatial distribution of volumetric forces around a hypersonic body allows for complete elimination of shock wave generation. It should be noted that in an ideal case, shock waves could be eliminated without energy consumption.

This paper describes a series of experiments performed in TJ-II stellarator with the aim of studying the influence of magnetic configuration on stability and transport properties of TJ-II plasmas. Plasma potential profiles have been measured in several configurations up to the plasma core with the heavy ion beam probe diagnostic. Low-order rational surfaces have been positioned at different plasma radii observing the effect on transport features. Plasma edge turbulent transport has been studied in configurations that are marginally stable due to decreased magnetic well. Results show a dynamical coupling between gradients and turbulent transport. Experiments on the influence of magnetic shear on confinement are reported. Global confinement issues as well as enhanced confinement regimes found in TJ-II are discussed as well.

Trends and focii of interest in atomic modelling and data are identified in connection with recent observations and experiments in fusion and astrophysics. In the fusion domain, spectral observations are included of core, beam penetrated and divertor plasma. The helium beam experiments at JET and the studies with very heavy species at ASDEX and JET are noted. In the astrophysics domain, illustrations are given from the SOHO and CHANDRA spacecraft which span from the solar upper atmosphere, through soft x-rays from comets to supernovae remnants. It is shown that non-Maxwellian, dynamic and possibly optically thick regimes must be considered.

The generalized collisional-radiative model properly describes the collisional regime of most astrophysical and laboratory fusion plasmas and yields self-consistent derived data for spectral emission, power balance and ionization state studies. The tuning of this method to routine analysis of the spectral observations is described. A forward look is taken as to how such atomic modelling, and the atomic data which underpin it, ought to evolve to deal with the extended conditions and novel environments of the illustrations. It is noted that atomic physics influences most aspects of fusion and astrophysical plasma behaviour but the effectiveness of analysis depends on the quality of the bi-directional pathway from fundamental data production through atomic/plasma model development to the confrontation with experiment. The principal atomic data capability at JET, and other fusion and astrophysical laboratories, is supplied via the Atomic Data and Analysis Structure (ADAS) Project. The close ties between the various experiments and ADAS have helped in this path of communication.

Suppression of the resistive wall mode (RWM) has been successfully demonstrated in the DIII–D tokamak by using rotational stabilization in conjunction with a close-fitting vacuum vessel wall. The duration of the high-pressure discharge was extended to hundreds of times the wall skin time. Frequently, the plasma pressure reached the ideal-wall magnetohydrodynamic (MHD) kink limit. The confined pressure is up to twice as high as the no-wall ideal MHD kink limit. Near its marginal stability point, the RWM is found to resonate with residual non-axisymmetric fields (e.g. components of the error field). A magnetic feedback system has been used to identify and compensate for the residual non-axisymmetric fields. This is to the best of our knowledge, the first demonstration of the sustainment of a stable plasma with pressure at levels well above the no-wall pressure limit. This technique is expected to be applicable to other toroidal devices.

In current-free stellarators, the parallel current density is normally too weak to drive global external kink modes. However, at finite values of β, the bootstrap current (BC) can provide sufficient free energy to trigger this class of mode in some stellarator systems. The effect of the BC in the collisionless 1/ν regime has been investigated in several different types of stellarator reactor systems all with a volume V∼1000 m³. In quasiaxisymmetric and quasihelically symmetric stellarators, the BC is large at finite β and this can cause low order resonances to move into and emerge out of the plasma which in turn can destabilize global internal and external kink modes. In a six-field period system with poloidally closed contours of the magnetic field strength B, the BC is small and decreases the rotational transform only slightly. As a result, only intermediate to high n modes can become weakly destabilized. Furthermore, it is demonstrated in this system that the contours of the second adiabatic invariant _|| close poloidally for all trapped particles at finite β*∼6%. This condition leads to the loss of a very small fraction of the collisionless α-particle orbits. In Sphellamak configurations with peaked toroidal currents required to generate nearly isodynamic maximum-B confining field structures, the BC accounts only for a small fraction of the total current. The loss of α-particles born within the inner quarter of the plasma volume is negligible while about (1/3) of those born at half volume escape the device within a slowing down time.

The phase transition of an ion beam into its crystalline state has long been expected to dramatically influence beam dynamics beyond the limitations of standard accelerator physics. Yet, although considerable improvement in beam cooling techniques has been made, strong heating mechanisms inherent to existing high-energy storage rings have prohibited the formation of the crystalline state in these machines up to now. Only recently, laser cooling of low-energy beams in the table-top rf quadrupole storage ring PAaul Laser cooLing Acceleration System (PALLAS) has lead to the experimental realization of crystalline beams. In this article, the quest for crystalline beams as well as their unique properties as experienced in PALLAS will be reviewed.

One of the recurring problems in magnetic reconnection is the identification of the appropriate generalized Ohm's law. In weakly collisional plasmas with a strong magnetic guide field component, a fluid model may be adopted, where electron inertia and the electron pressure gradient play important roles. In the absence of collisions, electron inertia provides the mechanism for magnetic field-line breaking. Electron compressibility alters significantly the structure of the reconnection region and allows for faster reconnection rates, which are consistent with the fast relaxation times of sawtooth oscillations in tokamak plasmas. The Hall term may also become important when the guide field is weak. The very possibility of nonlinear, irreversible magnetic reconnection in the absence of dissipation is addressed. We show that in a collisionless plasma, magnetic islands can grow and reach a saturated state in a coarse-grained sense. Magnetic energy is transferred to kinetic energy in smaller and smaller spatial scale lengths through a phase mixing process. The same model is then applied to the interpretation of driven reconnection events in the vicinity of a magnetic X-line observed in the VTF experiment at MIT. The reconnection is driven by externally induced plasma flows in a background magnetic configuration that has a hyperbolic null in the reconnection plane and a magnetic guide field component perpendicular to that plane. In the limit where the guide field is strong, assuming the external drive to be sufficiently weak for a linear approximation to hold, a dynamic evolution of the system is obtained which does not reach a stationary state. The reconnection process develops in two phases: an initial phase, whose characteristic rate is a fraction of the Alfvén frequency, and a later one, whose rate is determined by the electron collision frequency.

The spatial and temporal scales of astrophysical phenomena are typically 10–20 orders of magnitude greater than those of laboratory experiments intended to simulate them. Accordingly, the issue of similarity between the astrophysical phenomenon and its laboratory counterpart becomes quite important. Note also that in astrophysics, one is often dealing with highly dynamical systems, where orders of magnitude variation of the parameters of interest occurs over the duration of an event. In this regard, the similarity problem is more challenging than, say, the familiar problem of establishing a scaling law for the energy confinement time in a steady-state fusion device. We concentrate on astrophysical phenomena which can be reasonably well described by magnetohydrodynamic equations (like, e.g. propagation of the supernova (SN) shock through the progenitor star, and interaction of SN ejecta with an ambient plasma) and formulate a broad class of similarities that can be applied to them. We discuss issues of scalability in situations where the transition to turbulent flows occurs and present the corresponding constraints. We illustrate the general principles by describing several laboratory experiments carried out in a scaled fashion. Discussion of the possibility of scalable experiments directed towards studies of photo-evaporated molecular clouds (thought to be `star nurseries') is presented. An emphasis on the potential role of random magnetic fields is made. A concept of an experiment to generate magnetized jets in Z-pinch devices is presented.

The 29th EPS Conference on Plasma Physics and Controlled Fusion took place in Montreux, Switzerland, from June 17th to 21st 2002. It was organised by the Centre de Recherches en Physique des Plasmas (CRPP) of the Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland, on behalf of the Plasma Physics Division of the European Physical Society (EPS). The local organising committee was almost entirely composed of staff from CRPP:

Jo Lister, chairman

Yves R Martin, vice-chairman

Roland Behn, scientific secretary

Basil P Duval, ELISE manager and conference proceedings

Paula Halter, administrative secretary

Sarka Horackova, administrative secretary

The conference programme covered a wide range of topics in plasma physics in general and in controlled fusion research in particular: basic plasma physics, magnetic confinement experiments, inertial confinement, laser plasmas, short pulse phenomena, low-temperature plasmas, astrophysical and geophysical plasmas, plasma and magnetic confinement theory and modelling, plasma edge physics, plasma heating, plasma diagnostics, plasma applications, processing, radiation generation, and dusty plasmas. In addition three specialist sessions were held on the subjects of : `Laser Plasma Particle Acceleration', `Edge, SOL and Divertor Plasma Turbulence and Transport' and `Dusty and Complex Plasmas'. The scientific programme and paper selection were the responsibility of the International Programme Committee appointed by the Board of the EPS Plasma Physics Division. The committee was composed of:

C Varandas, chairman EURATOM-IST, Lisbon, Portugal

A Bécoulet EURATOM-CEA, Cadarache, France

A Boozer, contact person to APS Columbia University, New York, USA

D J Campbell EFDA-CSU, Garching, Germany

S C Cowley Imperial College, London, UK

J-C Gauthier Ecole Polytechnique Palaiseau, France

D Habs Ludwig-Maximilians-Universität, München, Germany

T C Hender UKAEA-Fusion, Abingdon, UK

J B Lister CRPP-EPFL, Lausanne, Switzerland

A G Litvak Institute of Applied Physics, Nizhny Novgorod, Russia

T Märk Universitt Innsbruck, Austria

P A Norreys Rutherford Appleton Laboratory, Chilton, UK

P Pavlo Institute of Plasma Physics, Prague, Czech Republic

J Sanchez EURATOM-CIEMAT, Madrid, Spain

G van Oost Ghent University, Ghent, Belgium

F Wagner MPI für Plasmaphysik, Greifswald, Germany

V Zanza EURATOM-ENEA, Frascati, Italy

This committee selected 30 invited talks, including review and tutorial lectures, and allocated 36 oral presentations. The majority of the contributed papers (450) were presented as posters in 4 sessions. The conference was attended by more than 620 participants from 37 countries, which made it a major forum for exchange of ideas and fruitful scientific discussion. A major event during the conference was the award of the Hannes Alfvén Prize to Professor Marshall Rosenbluth, University of California, San Diego, USA. The conference programme also included an evening session dedicated to a lecture by Professor I Fells, University of Newcastle, UK, on `Clean and Secure Energy for the 21st Century?'. A special exhibition presented the proposed ITER sites in France and Spain.

Following the tradition of this conference series, four-page summaries of all contributed papers are published as the Europhysics Conference Abstracts series, volume 26B. The publication is in the form of a CD-ROM sent free of charge to all participants and is also accessible via the website: http://elise.epfl.ch.

This special issue of Plasma Physics and Controlled Fusion contains papers of the invited talks at the 29th EPS Conference on Plasma Physics and Controlled Fusion. These papers have been assessed according to the standards of the journal and examined by referees selected from amongst the members of the International Programme Committee.

The guest editors would like to thank all authors for their efforts in providing a high quality paper in due time and Institute of Physics Publishing for the continuing support of this conference series. They express their gratitude to the members of the Programme Committee, who accepted the additional task of refereeing, with minimum delay, all the papers in this special issue.