Table of contents

It is proposed that a dust-acoustic instability driven by streaming ions could be a possible mechanism for the excitation of dust waves in an inductive gas-discharge plasma experiment reported by Zobnin et al (Zobnin A V, Usachev A D, Petrov O F and Fortov V E 2002 J. Exp. Theoret. Phys.95 429). We assume that the ions drift relative to the charged dust due to the presence of a background electric field. Comparisons with features of the experimental results are discussed.

Understanding the cause of magnetospheric substorms is a challenging problem in space physics but is also very rewarding since it relates to many energetic phenomena in the Earth's magnetosphere and to other impulsive energetic events in space plasmas. Substorm models can be classified into four different categories, namely: (1) internally triggered or externally driven processes in the near-Earth magnetosphere region, (2) magnetic reconnection in the mid-tail region, (3) coupling between the ionosphere and magnetosphere, and (4) simplified or abstract description of the magnetospheric system. The first category includes a rich variety of macro- and micro-instabilities (ballooning, cross-field current, lower hybrid drift, entropy anti-diffusion, and parallel current driven instabilities). This category is the most promising one since it can naturally account for several observational constraints on the substorm onset process. In particular, the model invoking a combination of the kinetic ballooning and the cross-field current instabilities is described, together with results from particle simulation on this mechanism. Crucial elements of substorm models in the other three categories are synthesized into this model as well.

This article was scheduled to appear in issue 5 of Plasma Phys. Control. Fusion. To access this Special issue please follow this link: http://www.iop.org/EJ/toc/0741-3335/45/5

The main features of radiation received from pulsars imply that they are neutron stars which contain an extremely intense magnetic field and emit coherently in the radio domain. Most recent studies attribute the origin of the coherence to plasma instabilities arising in pulsar magnetospheres; they mainly concern the linear, or the nonlinear, character of the involved unstable waves.

We briefly introduce radio pulsars and specify physical conditions in pulsar emission regions: geometrical properties, magnetic field, pair creation processes and repartition of relativistic charged particles. We point to the main ingredients of the linear theory, extensively explored since the 1970s: (i) a dispersion relation specific to the pulsar case; (ii) the characteristics of the waves able to propagate in relativistic pulsar plasmas; (iii) the different ways in which a two-humped distribution of particles may arise in a pulsar magnetosphere and favour the development of a two-stream instability.

We sum up recent improvements of the linear theory: (i) the determination of a `coupling function' responsible for high values of the wave field components and electromagnetic energy available; (ii) the obtention of new dispersion relations for actually anisotropic pulsar plasmas with relativistic motions and temperatures; (iii) the interaction between a plasma and a beam, both with relativistic motions and temperatures; (iv) the interpretation of observed `coral' and `conal' features, associated with the presence of boundaries and curved magnetic field lines in the emission region; (v) the detailed topology of the magnetic field in the different parts of the emission region and its relation to models recently proposed to interpret drifting subpulses observed from PSR 0943+10, showing 20 sub-beams of emission.

We relate the nonlinear evolution of the two-stream instability and development of strong turbulence in relativistic pulsar plasmas to the emergence of relativistic solitons, able to form elementary structures for pulsar radiation. We explain how nonlinear interactions between unstable waves and particles provide a canvas to explain `microstructures' (i.e. fluctuations on the microsecond timescale) observed in individual radio pulses and estimates for the level of electromagnetic energy reliable to pulsar radio emission.

This emphasizes the importance of collective plasma effects in pulsar emission regions able to provide the degree of coherence required, to explain characteristic features of observed individual pulses and account for the high level of pulsar radio emission.

This article was scheduled to appear in issue 5 of Plasma Phys. Control. Fusion. To access this Special issue please follow this link: http://www.iop.org/EJ/toc/0741-3335/45/5

Results from a Q-machine experiment are used to illustrate the dispersion-relation regimes associated with ion-acoustic and ion-cyclotron waves modified by the presence of shear in the magnetic-field-aligned (parallel) ion flow. Identifying the regimes requires knowledge of the sign of the ratio of wavevector components and the sign of parallel-velocity shear. Ion-temperature anisotropy is shown to influence significantly the propagation direction of oblique ion-acoustic waves. The necessity of documenting the instability mechanism with measurements of the electron and ion distribution functions, the electron and ion parallel-velocity shear, the flow-frame Doppler shifts, both small and large values of propagation angle, and the growth rate is illustrated. The existence of these shear-modified, low-frequency waves at values of parallel electron-drift velocity substantially smaller than the excitation thresholds predicted by homogeneous-plasma theory demonstrates the suitability of parallel-velocity shear for playing a role in the mechanism responsible for broadband extremely-low-frequency waves observed in the auroral ionosphere where there exists spatial variations and filamentation in the parallel plasma flow.

This article was scheduled to appear in issue 5 of Plasma Phys. Control. Fusion. To access this Special issue please follow this link: http://www.iop.org/EJ/toc/0741-3335/45/5

The radial electric field E_r is of crucial importance for the global confinement properties of a stellarator plasma. In particular, in the long-mean-free-path regime, which is characterized by strongly enhanced neoclassical transport, the ambipolar E_r can help to reduce the unfavourably large neoclassical transport coefficients. In the stellarator Wendelstein 7-AS (W7-AS), E_r is increased by the almost perpendicular injection of highly energetic neutral particles. The induced fast-ion orbit losses, drive the ambipolar E_r more negative. Changes of the radial electric field up to −20 000 V m⁻¹ are attained in the gradient region of W7-AS. The observed increase of the global energy confinement time is in the range of 10% in the best examples. In parallel to the experiments, numerical Monte-Carlo simulations of the ion orbit losses and the formation of the nonambipolar E_r are performed.

A statistical theory of plasma turbulence which is composed of multiple-scale fluctuations is examined. Influences of statistical noise and variance of rapidly changing variable in an adiabatic approximation are investigated. It is confirmed that the contributions of noise and variance remain higher order corrections. Transition rate of the turbulence with multiple scale lengths is obtained under the refined adiabatic approximation.

Transport and confinement within the resistive-g paradigm are investigated by means of two-dimensional numerical simulations. The system is driven by a constant incoming heat flux at the inner radial boundary. Different confinement and transport states are identified, involving self-sustained sheared poloidal flows. At the onset of turbulent convection the probability distribution functions of pressure and radial velocity fluctuations measured in the centre of the plasma layer have a nearly Gaussian form. Further increasing the heat flux drive these distributions become increasingly non-Gaussian, developing exponential tails. This large-scale intermittency is ascribed to the presence of bursting in the domain averaged convective transport and the fluctuation energy integrals. The quasi-periodic bursts are separated by shear-dominated quiescent periods in which the mean flow energy decreases and the confined heat increases on diffusive timescales. The time-averaged thermal energy confined within the plasma layer shows a power law dependence and significant increase with the injected power over the range of turbulent convection investigated.

A large variety of JET discharges with internal transport barriers (ITBs) has been analysed in order to determine the main features which characterize turbulence stabilization at the barrier. It is found that the location of barriers is well correlated with regions where the E×B flow shearing rate exceeds the linear growth rate of the ion temperature gradient mode instability (γ_ηi). A key point is the dependence of γ_ηi on the magnetic shear: in the discharges of this database the reduction of γ_ηi associated to very low or null magnetic shear favours the formation of an ITB. After the ITB formation a positive feedback occurs in which the E×B flow shear mechanism has the leading role and the position of the barrier may be no longer linked to the low shear region.

This paper briefly reviews the surface-wave-induced-magnetic reconnection (SWIMR) model based on the Alfven resonance theory near the neutral point. Extending this model to magnetosonic waves it is seen that it not only has features of formation of current sheets and plasmoids as in the incompressible case but in addition energy considerations show the triggering of solar flares by the catastrophic loss of equilibrium. The similarity of SWIMR model to the emerging flux and plasmoid induced magnetic reconnection model for solar flares is discussed.

This article was scheduled to appear in issue 5 of Plasma Phys. Control. Fusion. To access this Special issue please follow this link: http://www.iop.org/EJ/toc/0741-3335/45/5

The comparison of technical economic indexes of different waste treatment methods and plasma pyrolysis is presented in the paper. It testifies that plasma technologies are economically expedient for these purposes. Physical prerequisites allowing realizing plasma technologies are presented. Reliable and economical (70–120 Euro per ton of treated product) plasma generation is the basic condition of the technology realization. In this connection, various types of powerful generators of dense plasma (plasmatrons) in the range from 100 kW to 3 MW and temperature of plasma jets from 2000 to 10 000 K, and also physical processes taking place in electric-discharge chambers are examined. Differences between AC and DC electric arc plasma generators are analysed. Temperature in arcs of plasma generators varies from 6000 to 20 000 K, electron concentration is n_e∼(10¹⁴–10¹⁹ cm⁻³). Specific ware of electrodes in various types of plasma generators intended for long-time operation modes is (10⁻⁷–10⁻⁴) g C⁻¹. Physicochemical processes in plasma reactors intended for waste treatment and pyrolysis are described.

Different types of technological processes on plasma treatment and pyrolysis of waste are analysed. Estimation of present situation of physical investigations and technological developments in this area and predictions for nearest future are included.

This article was scheduled to appear in issue 5 of Plasma Phys. Control. Fusion. To access this Special issue please follow this link: http://www.iop.org/EJ/toc/0741-3335/45/5

The HINT code is a three-dimensional MHD equilibrium calculation code which does not assume nested flux surfaces. This code has been applied to the study of helical system plasma and it has reproduced the phenomenon of magnetic islands in finite pressure equilibria. We modify the numerical scheme of HINT to make it more efficient. In particular, the calculation of the plasma pressure distribution is improved for the case of a low-shear stellarator like Heliotron J. Using the modified HINT code, we study the finite plasma pressure equilibria of Heliotron J plasmas. In the standard configuration of Heliotron J plasmas, the equilibrium with a peaked distribution of the plasma pressure has magnetic islands appearing at β∼0.8%. When β∼3%, the edge region of plasma is ergodized by the finite pressure effect and flux surfaces are broken. On the other hand, for a broad initial pressure distribution the island width is decreased, but the structure of magnetic field remains stochastic.

The major radius dependence of Alfvén mode stability is studied by creating plasmas with similar minor radius, shape, magnetic field (0.5 T), density (n_e≃3×10¹⁹ m⁻³), electron temperature (1.0 keV) and beam ion population (near-tangential 80 keV deuterium injection) on both NSTX and DIII-D. The major radius of NSTX is half the major radius of DIII-D. The super-Alfvénic beam ions that drive the modes have overlapping values of v_f/v_A in the two devices. Observed beam-driven instabilities include toroidicity-induced Alfvén eigenmodes (TAE). The stability threshold for the TAE is similar in the two devices. As expected theoretically, the most unstable toroidal mode number n is larger in DIII-D.

The effect of ion motion on rotating magnetic field (RMF) current drive in field reversed configurations is studied using a fully two-dimensional numerical code that solves the two fluid equations with massless electrons and constant uniform temperature. The ion momentum equation includes viscosity and collisions with neutrals, which remain fixed. The electrons are described with an Ohm's law that includes the Hall and pressure gradient terms. For full penetration of the RMF, ion spin-up due to collisions with electrons reduces the current drive efficiency and a large fraction of neutrals is needed to prevent the ions from acquiring high azimuthal velocities. For conditions that would result in incomplete penetration with the fixed ion model, ion rotation and variable density can facilitate the penetration of the RMF, thus increasing the efficiency. The rotation modifies the density profile and can trigger rotational instabilities.

Localized direct electron heating (EH) by mode-converted (MC) ion cyclotron range of frequencies (ICRF) waves in D(H) tokamak plasmas has been clearly observed for the first time in Alcator C-Mod. Both on- and off-axis (high field side) mode conversion EH (MCEH) have been observed. The MCEH profile was obtained from a break-in-slope analysis of electron temperature signals in the presence of radio frequency shut-off. The temperature was measured by a 32-channel high spatial resolution (⩽7 mm) 2nd harmonic heterodyne electron cyclotron emission system. The experimental profiles were compared with the predictions from a toroidal full-wave ICRF code TORIC. Using the hydrogen concentration measured by a high-resolution optical spectrometer, TORIC predictions were shown qualitatively in agreement with the experimental results for both on- and off-axis MC cases. From the simulations, the EH from MC ion cyclotron wave and ion Bernstein wave is examined.

A numerical model of current drive is developed in an infinitely long plasma cylinder, by means of two counter-rotating magnetic fields (RMFs) where the frequency of the (+) RMF is allowed to vary. The accessibility of steady state solutions where both RMFs penetrate into the plasma much farther than the classical skin depth, the electron fluid rotating synchronously with the (−) RMF and the ion fluid rotating synchronously with the (+) RMF, is examined. It is demonstrated that the steady state solutions are accessible from a broader class of initial conditions by allowing the frequency of the (+) RMF to decrease linearly. The rate of change in the frequency of the (+) RMF is required to be greater than the ion relaxation rate due to collisions with the electron fluid.

The behaviour of high-energy ions accelerated by an ion cyclotron range of frequency (ICRF) electric field in the large helical device (LHD) is discussed. A better confinement performance of high-energy ions in the inward-shifted magnetic axis configuration was experimentally verified by measuring their energy spectrum and comparing it with the effective temperature determined by an electron slowing down process. In the standard magnetic axis configuration a saturation of the measured tail temperature was observed as the effective temperature was increased. The ratio between these two quantities is a measure of the quality of transfer efficiency from high-energy ions to a bulk plasma; when this efficiency was compared with Monte Carlo simulations the results agreed fairly well.

The ratio of the stored energy of the high-energy ions to that of the bulk plasma was measured using an ICRF heating power modulation method; it was deduced from phase differences between total and bulk plasma stored energies and the modulated ICRF heating power. The measured high energy fraction agreed with that calculated using the injected ICRF heating power, the transfer efficiency determined in the experiment and the confinement scaling of the LHD plasma.

The 10th European Fusion Physics Workshop took place in December 2002 at Vaals in The Netherlands, hosted by the Trilateral Euregio Cluster (TEC: Associations EURATOM-ERM/KMS, FZJ and FOM), and sponsored by the European Commission and the Foundation SOFT. Within an overall theme of `Operational limits in toroidal devices, with particular reference to steady-state operation', four topics of importance to the future development of magnetically confined fusion were discussed in detail. In addition, a review of the JET scientific and technical programme under EFDA and an assessment of ITER's measurement requirements and diagnostic development programme were presented. The main issues discussed and the areas identified as requiring further study are summarized here.

To a beginner in plasma physics the subject of waves can be bewildering, with a seeming myriad of different wave modes and ways of approaching them though cold plasma equations, warm plasma equations or kinetic equations. Add to this the intricacies of Landau and cyclotron damping and the fact that real plasmas are rarely uniform and infinite in extent, even as a first approximation, and the need for a reliable guide through the maze becomes apparent.

This is a revised and extended version of a book which has already proved its value as an advanced text at postgraduate level. It contains a careful account of many of the properties of waves using the various possible levels of approach, and a good selection of graphs and surface plots which are a great help to the reader in visualising the behaviour of wave dispersion relations. As might be expected by anyone familiar with the author's research, there is an extensive discussion of waves in an inhomogeneous plasma and the phenomenon of mode conversion which plays a vital role in various plasma heating schemes using waves. Various aspects of the nonlinear theory of waves are discussed, including quasilinear theory, solitons, particle trapping and parametric instability.

The discussion throughout is characterised by a clear treatment of both the mathematical problems involved and the underlying physics, the second edition having provided an opportunity for refinement and clarification of the earlier presentation, as well as the addition of new material on recent advances in the subject. Any student who masters the material in this book and works through the problems it contains will have a very solid grounding in the theory of wave propagation. Research workers in the field will find it to be a comprehensive source of information on waves, including a number of topics which have only been found in research papers until now. I think that this is a very welcome addition to the literature which will be a valuable resource for teachers and researchers. Most people with a serious interest in plasma waves will probably think of the work by Stix (Stix T H 1992 Waves in Plasmas (New York: American Institute of Physics)) and its earlier edition as having been the standard work on plasma waves for many years and will wonder how this book compares. The answer is, I think, that the two works complement each other well. Where they overlap the discussion is generally somewhat different and can yield different insights, and each contains material absent from the other. Swanson's book is certainly worth a place beside Stix on the bookshelves of anyone who needs to know about plasma waves.

R A Cairns