Table of contents

The TCV tokamak offers outstanding variability of the plasma shape. Using x-ray tomography, the shape of the inner flux surfaces of a poloidal cross section of the plasma can be reconstructed, including fast variations due to MHD activity. Both the hardware and the software of the 200 channel system developed for TCV are described.

A new `dynamical' calibration takes actual plasma parameters into account to determine the spectrum-dependent detector efficiency, resulting in an enhanced quality of reconstructions.

Tomographic inversions are obtained using a variety of methods such as maximum entropy, linear regularization and a newly developed method based on the Fisher information. The merits of the different algorithms, which have been implemented as MATLAB functions, are compared.

Inversion results are analysed with the help of singular-value decomposition, allowing, for example, identification of MHD modes without using any a priori information on the poloidal mode structure.

Recent results on the dependence of sawtooth activity on the plasma triangularity are presented to demonstrate the performance of the soft x-ray tomography system.

A simple isothermal model for the scrape-off layer (SOL) which includes toroidal geometry and radial electric field effects, but ignores viscosity and plasma - neutral interactions, is presented. For finite toroidicity and for the case of zero radial electric field , the model predicts pressure asymmetry in favour of the outer target and a non-zero radial current due to pressure-gradient terms. For the case of non-zero , is changed somewhat. The dependence of the current on the radial electric field, however, is too weak and non-monotonic against to explain experimental results on ion mobility obtained in biasing experiments on the tokamak de Varennes (TdeV). This may indicate that anomalous processes, not considered here, are dominant in TdeV. The direction of the pressure-gradient-driven current is inwards for the `normal' toroidal field (ion drift towards the single null divertor), and outwards for the `reversed' field. The current can cause significant changes in radial flux in the SOL between the two field directions in the case when the SOL width approaches the ion poloidal Larmor radius. Its effect on the SOL is proposed as a mechanism responsible for the dependence on the direction of the toroidal field of the threshold power needed to cause the L - H transition. The dependence of the current on the toroidicity , found in the calculations, suggests that the beneficial effects of the `normal' field direction on the confinement should be more pronounced at larger .

Tokamak experiments have revealed that the L - H power threshold depends on the ion drift direction. This experimental result could be explained by resistive interchange micro-instabilities in the SOL. It is shown that the sheath resistance near the target plates depends on the direction of the longitudinal SOL current. In conjunction with the curvature of the toroidal magnetic field and the ion drift direction, these effects lead to an asymmetry in the turbulence near the plasma edge; hence a different L - H power threshold is required to reduce this turbulence.

Ordinary wave reflectometry in a plasma containing a localized density perturbation is studied with a one-dimensional (1D) model. The phase response is studied as a function of the wavenumber and position of the perturbation. It is shown that it strongly depends upon the perturbation shape and size. For a small perturbation wavenumber, the response is due to the oscillation of the cut-off layer. For larger wavenumbers, two regimes of resonant Bragg scattering are found: for a broad perturbation, the phase response is an image of the perturbation itself; for a narrow perturbation, it is an image of the Fourier transform. These features are enhanced for a broadband perturbation (modulated square wave) and scattering can occur over the whole region up to the cut-off. Furthermore, in that case there is a specific behaviour at the cut-off due to the sharp boundary effects of this perturbation. Because of this peculiarity, the phase response obtained for a damped square perturbation reproduces the results of an earlier experiment (Rhodes et al, Rev. Sci. Instrum. 1992).

Experimental results related to deuteron-beam production and its correlation with the neutron yield and hard x-ray production in a low-energy plasma focus device (30 kV, 5 kJ) are presented. After performing corrections in the ion energy spectrum (within an ion energy range from 50 keV to 1.5 MeV) for elastic and inelastic interactions of the ions with the background gas, it is found that the ion density at low ion energy is very high and plays an important role in the neutron production of this plasma focus device.

The particle confinement time of ohmic double-null discharges in Tokamak de Varennes (TdeV) is determined by two different techniques, the conventional method and a new technique based on the temporal decay of the total core population following the injection of a gas puff. Both methods show a confinement time increasing with density up to a maximum of 13 ms at and decreasing at larger densities, with very little dependence on plasma current. Particle transport is analysed using fast gas puffing and Abel inversion of the seven-chord submillimetre (SMM) interferometer together with the source profiles determined by measurements. The incremental transport coefficients are obtained by testing the standard form of the particle flux function against the data during the transitory period towards equilibrium. Both perturbed diffusion and convection coefficients are found to vary approximately as the inverse of the density and almost proportionally to the plasma current. The equilibrium transport coefficients are then deduced from the experimental equilibrium density profiles and the measured incremental coefficients using a transport model developed from the data. The model is finally used to predict confinement times to be compared with experiment. The effect of divertor plate biasing on transport is also discussed.

The helicity injected tokamak (HIT) experiment uses coaxial helicity injection to drive current in a low aspect-ratio tokamak. In order to accurately calculate the equilibria of such objects, a model which includes the essential physics of the injector and edge region must be included. Such a model is also crucial in determining the performance of future helicity injector designs. We present a model for the helicity injector that treats the open field lines as being in a force-free equilibrium determined by the field line length, the applied injector voltage, and an effective resistivity , which can have both resistive and dynamic components. This model agrees well with data for plasmas with little or no closed flux, using a uniform as the fitting parameter.

Particle transport is modified in lower hybrid current drive discharges of JT-60U. The density profile becomes broad during the lower hybrid wave injection and the profile change depends on the injected wave spectrum. Particle transport coefficients (diffusion coefficient and profile peaking factor) were evaluated using gas-puff modulation experiments. The diffusion coefficient in the current drive discharges is about three times larger than that in the ohmic discharges. The profile peaking factor decreases in the current drive discharges and the evaluated values are consistent with the measured density profiles.

A local linear stability theory of the interchange mode, the drift-resistive interchange mode and the drift-dissipative mode, in the presence of ionization and radiative drives, is examined. It is found that diffusive effects (which are responsible for providing a steady state in equilibrium) give a damping which overwhelms the ionization drive for the drift mode except for very long wavelengths. However, flute-type perturbations are found to be unstable owing to additional effects arising through the temperature dependence of the ionization cross section. Finally, the radial eigenvalue problem for simple drift-ionization instability is examined numerically and it is found that the mode is unstable for long wavelength perturbations only when the rate of diffusion damping of the perturbation is substantially smaller than the rate of diffusive damping of the equilibrium gradients.

This paper discusses the structure of drift waves in a rotating toroidal plasma. The rotation destroys an underlying symmetry that is the basis for the conventional ballooning representations of perturbations in a torus and alternative descriptions are needed. One such description exploits the residual symmetry that persists despite rotation. It shows that sheared rotation annuls the toroidal coupling between perturbations associated with different magnetic surfaces, so that cylinder criteria rather than toroidal `ballooning' criteria again become relevant. As expected, sheared rotation reduces the radial mode width, and presumably, therefore, the anomalous transport. It can also alter the scaling of anomalous transport with magnetic field from Bohm to gyro-Bohm.

Another description of perturbations leads, as is well known, not to eigenmodes but to perturbations with a Floquet-like time dependence on a magnetic surface. We show that this Floquet solution actually conceals an arbitrary time dependence of the perturbation! At the usual leading order in a high mode number expansion, the Floquet form and the eigenmode form are equivalent and are equally valid descriptions. However, in a more accurate theory only the eigenmode form persists. The Floquet form, and its short-term growth rate, should be regarded as transients associated with particular starting conditions and with the use of an idealized (linear) velocity profile.

The kinetic theory of low-frequency Alfvén modes in tokamaks is presented. The inclusion of both diamagnetic effects and finite core-plasma ion compressibility generalizes previous theoretical analyses (Tsai S T and Chen L 1993 Phys. Fluids B 5 3284) of kinetic ballooning modes and clarifies their strong connection to beta-induced Alfvén eigenmodes. The derivation of an analytic mode dispersion relation allows us to study the linear stability of both types of modes as a function of the parameters characterizing the local plasma equilibrium and to demonstrate that the most unstable regime corresponds to a strong coupling between the two branches due to the finite thermal ion temperature gradient. In addition, we also show that, under certain circumstances, non-collective modes may be present in the plasma, formed as a superposition of local oscillations which are quasi-exponentially growing in time.

An error in the printing process led to pages 1797 and 1798 being reproduced in the wrong order. We apologise to the authors for this mistake.

Transport and optical properties of nonideal plasma presents in seven chapters an accessible survey of theoretical and experimental research in the field of nonideal plasmas. The contents of the book are wide-ranging, covering not only transport and optical properties, but also including a systematic treatment of the thermodynamics and analysis of plasma oscillations in nonideal plasmas.

The field of nonideal or simply dense plasmas has developed rapidly over the past decades, and it is now characterized by a better understanding of the fundamental processes, although essential properties are still not measured as systematically as under ideal conditions. In this respect, this book is a useful tool and reference for specialists in the field since it presents an accurate picture of current concepts and developments. For those just starting basic research in the field of nonideal plasmas, it provides the necessary theoretical background and explains the experimental techniques to produce and diagnose such media.

Central to the book is the discussion of the thermodynamic properties (ionization equilibrium, equation of state). The reason is that any analysis of optical and transport phenomena in nonideal plasmas depends sensitively on the thermodynamic state variables. The high-density corrections relevant to plasmas under extreme conditions are very difficult to calculate, and this book is an attempt to deal with the subject as a whole in a detailed manner. Transport and optical properties of nonideal plasmas features a number of topics not covered in other books on this subject, including generation and diagnostics of dense plasmas, and the application of nonideal plasmas in modern technology.

Written by leading experts from the Institute for High Temperatures of the Russion Academy of Science, this book is partly based on pioneering research in nonideal plasmas done in Russia over an extended period of time. This is a well written book for anyone working on topics related to nonideal plasmas.

This new book edited by R Janev covers in 16 chapters almost all important atomic and molecular collision processes of relevance for the modelling and diagnostics of fusion edge plasmas. These processes include excitation, ionization of atoms and molecules by electrons, as well as electron - ion recombination processes and low-energy charge exchange collisions of impurity ions with neutral atoms. In addition, a chapter about the spectroscopic characteristics of plasma edge constituents is included. Each chapter deals with a specific type of collision process and comprises contributions from specialists in the respective fields. The book contains contributions from 27 authors.

The primary purpose of the book is to provide the fusion plasma researcher with a source of critically assessed information on atomic and molecular collision processes. Many chapters give a basic introduction to the most commonly applied experimental and theoretical methods of how presented collision data are gained. Physical mechanisms of collision processes are described briefly on a rather fundamental level. Very helpful for a reader who is looking for more detailed information on a specific collision process are the comprehensive lists of references at the end of each chapter. Atomic data, such as cross sections, are represented by figures, tables and often (most helpful for quick and convenient application) by fitting parameters to analytic formulae. This book has to be regarded as an excellent review of the present day status of available data for low-energy collision processes between electrons, ions, atoms and molecules. Although this book is intended mainly for fusion plasma researchers, it might also be of interest for students and scientists working in atomic collision physics who are looking for an overview of this field.

This book covers the most important issues of plasma - wall interactions in nuclear fusion devices. Several authors, all actively working in that particular field, have written articles on surface phenomena (erosion mechanisms, particle recyling, wall coatings and ablation) and bulk material properties (thermal stability, radiation damage). The latest developments and findings are provided. Nevertheless, the basic principles are also given for each issue in a concise style, such that this book may serve as an excellent introduction for everyone entering the field of plasma - wall interactions. For other scientists in fusion, in particular the non-specialists, this book provides a useful survey of the present status of plasma - wall interaction issues and the most important processes involved, a broad knowledge of which is of growing importance in solving the problems of energy and particle exhaust in fusion devices.

The book Diagnostics for experimental thermonuclear reactors gathers together the papers presented at the Workshop on Diagnostics for ITER organized by the International School of Plasma Physics in Varenna, Italy, in August 1995. The authors had clearly done an enormous amount of work in preparation for the Workshop, and this book will serve as an excellent tutorial for anyone involved in diagnostic design for any future fusion device, let alone one with the complex design issues of ITER.

This book has three very important strengths. The first is in the focus in meeting requirements for the measurements of plasma parameters set down by the ITER organization. These measurements appear formidable, but the standards of physics studies and code development on the current devices require such localization and accuracy. In the descriptions of the diagnostic equipment, there is little detail about the physics of the measurement of the specific techniques presented, but a great deal about the practical implementation of such techniques. For example, there is considerable discussion about microwave reflectometry for measurement of electron density profiles, a rapidly evolving technique but one which requires special consideration in the flattish profiles and high electron temperatures anticipated for ITER. Another case is spectroscopy where measurements in the core of such parameters as the density of the helium ash, left in the core of the plasma after the alpha-particles have given up their energy to the surrounding plasma, for which a seed beam is essential. There is extensive treatment of neutron spectroscopic techniques to benefit from the production of copious neutrons for new and better plasma measurement.

The second strength is in its summation of the state of the art of diagnostics on the currently operating devices. It is seldom possible to find summarized so conveniently the experience of some of the most able diagnostic physicists in the world. While some of the measurements are explicitly described, elsewhere the quality of measurement is implicit and the publications making use of those measurements are referenced. There is significant information about the capability of magnetic diagnostics for providing plasma control capability. The section on diagnostics of the divertor plasmas brings together well the measurements needed for this very important region. It is a very rapidly growing area of measurement, and very important in the near term for qualifying computer code predictions of the behaviour of divertor plasmas. Spectroscopy and total radiation in the divertor are very well treated and it is clear that vacuum ultraviolet measurement will be an important tool.

The third strength is in its comprehensiveness, covering the whole range of diagnostics from the most sophisticated newly developed techniques down to Langmuir probes and pressure gauges (though the reader will find that these last two become fairly sophisticated in an ITER-like environment). There is good coverage of the measurement of the confined alpha particles using collective scattering, not yet fully demonstrated on an operating tokamak, and also discussion of the use of laser-induced fluorescence in divertor measurements, particularly of the neutral species, which could be very important with a highly radiating divertor plasma.

As in any such collection of papers the referencing and figures are not always of the highest quality, but nevertheless, the overall presentation is surprisingly good. The book will be extremely valuable for graduate students and for anyone looking for a perspective on the best possible ways to measure the plasmas in high temperature magnetic fusion devices, including stellarators as shown in two of the closing papers on the diagnostics for the W7-X and LHD stellarators, both now under construction.

This book is a collection of lecture notes for seven courses presented at the Astrophysics School VII, organized by the European Astrophysics Doctoral Network and held at San Miniato, Italy, in October 1994. The topics of each of the seven courses are independent of each other. This has the advantage that most readers with a general interest in astrophysics are likely to find some courses of particular interest, but has the disadvantage that there is no obvious theme or overview of the subject matter covered. As with any collection of lecture notes, there is considerable diversity in style, length and depth of coverage of the specific topic. The notes are arranged into four sections on basic theory: magnetic reconnection by D Biskamp (30 pages), winds by J Heyvaerts (70 pages), particle acceleration by J Kuijpers (62 pages) and turbulence by A Pouquet (50 pages) and three sections on observational and instrumental methods: radio by A O Benz (28 pages), x-ray spectroscopy by R Pallavicini (44 pages) and x-ray instrumentation by H W Schnopper (41 pages). The level of each of the courses is appropriate for a graduate student with a background in physics. All four basic theory courses presuppose that the reader has some knowledge of MHD theory.

The usefulness of a book such as this is strongly dependent on whether or not it contains material in a form or style that is not readily available elsewhere. Based on this criterion, this reviewer considers the book a useful addition to his library. Worth particular mention are the notes on rotating MHD winds in which Heyvaerts provides a systematic, self-contained and thorough introduction to a field that has not been reviewed extensively. The notes on turbulence by Pouquet contain material that is not readily available to most astrophysicists, and although these notes are not as readable as those by Heyvaerts, this is offset by extensive references to the literature. This reviewer is familiar with most of the subject matter in the notes by Biskamp, Kuijpers, Benz and Pallavicini, and found each of them well presented, with a balance between review of background ideas and introduction to current research. The notes by Schnopper are a summary of past, present and planned x-ray spacecraft, together with description of the observational techniques used.

In brief, this book is likely to be a useful addition to any astrophysicist's library. This reviewer will value it particularly for the notes by Heyvaerts on MHD winds.

17 - 18 February 1997 Plasma '97: 21st Australian Institute of Nuclear Science and Engineering Plasma Science and Technology Conference Sydney, Australia Contact: Margaret Lanigan, Conference Manager, PMB 1, MENAI NSW 2234, Australia. Fax +61-(0)2-439-6561, E-mail ainse@ansto.gov.au.

6 - 11 April 1997 10th Joint Workshop on Electron Cyclotron Emission and Electron Cyclotron Resonance Heating Ameland, The Netherlands Contact: J Hamers-Smit, FOM - Instituut voor Plasmafysica 'Rijnhuizen', Postbus 1207, 3430 BE Nieuwegein. Tel +31-30-6096999, Fax +31-30-6031204, E-mail ec10@rijnh.nl. Application and abstract deadline: 17 January 1997.

8 - 12 September 1997 12th International Conference on Gas Discharges and their Applications Greifswald, Germany Contact: Dr G Babucke, Inst. f. Niedertemperatur-Plasmaphysik, Robert-Blum-Str. 8 - 10, 17489 Greifswald, Germany. Tel +49-3834-554411, Fax +49-3834-554301, E-mail gd97@public.inp.uni-greifswald.de.

8 - 19 September 1997 3rd Carolus Magnus Summer School on Plasma Physics Spa, Belgium Contact: Dr G van Oost, c/o Institut für Plasmaphysik, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany. Tel +49-2461-61-5626, Fax +49-2461-61-3331, E-mail vanoost@fusion.rma.ac.be. Application deadline: 15 May 1997, abstract deadline: 15 July 1997.