Table of contents

Purely growing sawtooth precursors have been identified in high current, high-density discharges of the Frascati Tokamak Upgrade. On the basis of the observed helical structure and growth rate, these precursors are identified as the early non-linear stage of the m = 1 instability in the semicollisional regime. The precursor stage is followed by a fast collapse during which the growth rate of plasma displacement increases by an order of magnitude. During the precursor, a transition from semicollisional to collisionless reconnection regimes occurs, as the non-linear resistive width falls below the collisionless skin depth; such a cross-over is proposed as the trigger mechanism for the fast collapse phase. This simple scheme, in which the crossing of a linear stability boundary triggers the precursor, while a non-linear effect triggers the fast collapse, emerges in plasmas where the diamagnetic rotation frequency is smaller than the precursor growth rate. Diamagnetic effects complicate the picture as they reduce precursor growth rate, but the basic mechanisms are likely to be the same in all cases.

The dynamics of spherical torus (ST) plasmas, when the external toroidal magnetic field is decreased to zero and then increased in the opposite direction, has been investigated using three-dimensional magnetohydrodynamic (MHD) numerical simulations. It has been found that the flipped ST configuration is self-organized after the ST configuration collapses because of the growth of the n = 1 mode in the open flux region and a following magnetic reconnection event. During the transition between these configurations, not only the paramagnetic toroidal field but also the poloidal field reverses polarity spontaneously.

In the theoretical description of the neoclassical tearing mode the bootstrap current is assumed to completely vanish inside the magnetic island if finite perpendicular transport can be neglected. In this paper, the effects due to both the finite-orbit width of the trapped ions and their toroidal precession (not included in the standard analytic theory) on the island current are investigated. The evolution of the ion distribution function in toroidal geometry in the presence of a perturbed magnetic equilibrium is computed numerically employing the δf method, collisions being implemented by means of a Monte Carlo procedure. It is shown that a significant fraction of the (ion) bootstrap current survives inside the island when the ion banana width w_b approaches the island width W, and no loss is observed for w_b/W⩾1. This effect is reduced when the collision time becomes longer than the toroidal drift time. The value of the current is found to be inconsistent with the local gradients in the island region. The finite-banana-width effect leads to a linear scaling of the value of the poloidal β at the mode onset with the normalized ion poloidal gyroradius ρ*_p, in agreement with the experimental results of ASDEX Upgrade.

Measurements of Si I- and Si II-emission lines were performed in the front of a test limiter under two different conditions: (i) silicon is sputtered from a silicon layer deposited on a graphite test limiter, (ii) silane is puffed into the plasma through a gas inlet in the limiter head, setting Si-atoms free from the dissociation of SiD₄ molecules. It was shown that the relative intensities of the emission lines within the multiplets are in good agreement with theoretical data calculated in the SL-coupling scheme. The values for `ionization per photon' were calculated for the electron temperature range below 100 eV using the GKU kinetic code and compared with measured ones. The measured and theoretical values for the Si II-emission lines are in reasonable agreement within a deviation of 30%. It was found that experimentally measured values for Si I lines match the calculated ones only when a LTE-population of 3p² SL terms (³P, ¹D and ¹S) is assumed.

Heat wave experiments are performed on TJ-II stellarator plasmas to estimate both heat diffusivity and power deposition profiles. High frequency electron cyclotron resonance heating (ECRH) modulation experiments are used to obtain the power deposition profile, which is observed to be wider and duller than that estimated by ray tracing techniques. The causes of this difference are discussed in the paper. Fourier analysis techniques are used to estimate the heat diffusivity in low frequency ECRH modulation experiments. This includes the power deposition profile as a new ingredient. ECRH switch-on/off experiments are exploited to obtain power deposition and heat diffusivities profiles. These quantities are compared with those obtained by modulation experiments and transport analysis, showing good agreement.

The distribution of antenna-driven fields of electromagnetic waves in the local Alfvén resonance (AR) region is studied under resonant conditions, when the axial period of the fundamental harmonics of magnetohydrodynamic oscillations in the axial direction is twice as large as the pitch length, and the poloidal number of the fundamental harmonics is twice as small as the polarity of the helical coils. It is shown that taking into account the helical inhomogeneity of the steady magnetic field can remove infinite discontinuity of the wave fields, which is present in the case of a straight confining magnetic field, rather than electron inertia or finite ion Larmor radius. Radio frequency power absorption within the local AR is compared with the case when AR structure is governed by electron inertia or finite ion Larmor radius. Another approach is proposed to explain the helicity induced gap in the Alfvén continuum.

Alpha particle loss due to the toroidal field ripple is significantly enhanced in reversed shear plasmas, especially in a high-q regime. To ensure a tolerable heat load on the wall due to the loss of alpha particle in reversed shear discharges with various q profiles, ferritic steel (FS) inserts are considered as a countermeasure for reducing the ripple amplitude at a low cost. With this being the situation, an assessment of ripple loss for various conditions in ITER is an important study that should to be conducted in the International Tokamak Physics Activities. This paper describes an assessment result, indicating that FS inserts lead to a dramatic reduction of ripple loss. When the arrangement of the FS inserts is optimized, the resulting alpha particle loss is anticipated to be reduced by an order of magnitude or more, and the power loss fraction is as low as 1% even for a reversed shear plasma with a relatively high q_min of 3.

Toroidal asymmetries in the measured ripple losses during ion cyclotron range of frequencies (ICRF) heating have been observed on the Tore Supra tokamak. Such asymmetries have been detected in plasmas heated by low levels of ICRF power. In contrast, the ripple losses appear to be almost symmetrical (more precisely periodically symmetric) during high power ICRF heating. A theoretical analysis of the losses indicates that asymmetries can arise because a larger fraction of the ICRF power is absorbed in the ripple well region during low power ICRF heating.

The Langevin equations for quasi-linear wave–particle interaction are obtained taking advantage of the unequivocal equivalence between the Fokker–Planck equation and the former ones. The Langevin equations are solved numerically and, hence, the evolution of a single particle embedded in an electromagnetic field in momentum space is obtained. The equations are relativistic and valid for any wave. It is also shown that the stochastic part of the equations is negligible in comparison with the deterministic term, except for the momentum close to the resonance condition for the main parallel refractive index.

A rapid algorithm for tomographic inversion is presented that allows post-discharge reconstruction of the soft x-ray (SXR) emissivity evolution in the Tokamak à configuration variable (TCV). Simultaneously, it determines the centre of gravity of the emissivity that may serve as a reliable measurement of the plasma position, that is independent of magnetic measurements. Tests of the algorithm were performed using shaped phantom datasets and all past SXR measurements were processed to obtain plasma position statistics. Multiple linear regression is applied in matching the results with the magnetic axis data. Systematic functionalities including magnetic field dependence and drift of the magnetic axis are observed. The joint resolution limit of magnetic and SXR position measurements at TCV is derived from the residual discrepancies and equals 2.2 and 3.1 mm in the radial and vertical directions, respectively.

This book deals with the fundamental physics of numerous plasma processes that occur during laser plasma interactions. The subject matter is related to both basic plasma physics and applied physics. The author starts with the essentials of high power lasers whose duration ranges from nanoseconds to femtoseconds, and then builds up an introduction to plasma physics by describing ionization, well known transport coefficients (electrical and thermal conductivities, diffusion, viscosity, energy transport etc), Debye length, plasma oscillations and the properties of the laser induced plasma medium. The book contains plasma dynamical equations for describing the hydrodynamic and kinetic phenomena, and treating particle dynamics by computer simulation. The ponderomotive force is discussed for small amplitude electromagnetic fields in an unmagnetized plasma. However, for intense laser beams one should obtain new expressions for the relativistic ponderomotive force, which are totally absent from this book. Furthermore, in laser plasma interactions strong magnetic fields are produced which will drastically modify the relativistic ponderomotive force expressions. The physics of collisional absorption of electromagnetic waves and their propagation in a nonuniform unmagnetized plasma has been elegantly described. The phenomena of the resonance absorption of laser light is also discussed. Simple models for the parametric processes are developed, while there are no discussions of cavitons/envelope solitons. The latter are usually regarded as possible nonlinear states of the modulational/filamentational instabilities. Rather, the author presents a description of a K-dV equation for nonlinear ion-acoustic waves without the laser field. The description of a non-envelope ion-acoustic soliton has already appeared in many plasma physics textbooks.

The book contains a short chapter on the self-similar plasma expansion in vacuum, double layers, and charged particle acceleration. However, the author has not touched on the plasma based high energy charged particle accelerators, which involve short intense laser pulses and which are at the frontier of modern plasma physics. There is a nice chapter dealing with laser induced magnetic fields and waves in magnetized plasmas. The physics and mathematical details of the electron energy transport and heat waves, which are of significant interest in inertial confinement fusion, are described in depth. Comprehensive studies of shock waves and rarefaction waves are presented, and their relevance to high power pulsed laser drivers is discussed. Finally, the author has given a lucid description of hydrodynamic instabilities (i.e. the Rayleigh-Taylor, the Richtmyer-Meshkov, the Kelvin-Helmholtz), which are of great importance in laser-plasma interactions and in astrophysics. It would have been nice if the author would have also included a more physical description of the nonlinear evolution of those instabilities which play a significant role in the formation of fingers, bubbles and vortices in laboratories and in astrophysical settings.

The book is well written and will serve as a valuable asset for graduate students and physicists working in the area of laser plasma interactions and high energy astrophysics. It should also be useful for teaching masters level courses on laser plasma interactions. The reviewer highly recommends the book to the interested reader.

P K Shukla

This book is a collection of papers, written by specialists in the field, on advanced topics of nuclear fusion diagnostics. The 78 contributions were originally presented at the International Conference on Advanced Diagnostics for Magnetic and Inertial Fusion held at Villa Monastero, Italy in September 2001. Both magnetically confined and inertial fusion programmes are quite extensively covered, with more emphasis given to the former scheme. In the case of magnetic confinement, since the present international programme is strongly focused on next-step devices, particular attention is devoted to techniques and technologies viable in an environment with strong neutron fluxes. Indeed, in the first section, the various methods are considered in the perspective of performing the measurements of the relevant parameters in conditions approaching a burning plasma, mainly in the Tokamak configuration. The most demanding requirements, like the implications of the use of tritium and radiation resistance, are reviewed and the most challenging open issues, which require further research and development, are also clearly mentioned.

The following three sections are devoted to some of the most recent developments in plasma diagnostics, which are grouped according to the following classification: `Neutron and particle diagnostics', `Optical and x-ray diagnostics' and `Interferometry, Polarimetry and Thomson Scattering'. In these chapters, several of the most recent results are given, covering measurements taken on the most advanced experiments around the world. Here the developments described deal more with the requirements imposed by the physical issues to be studied. They are therefore more focused on the approaches adopted to increase the spatial and time resolution of the diagnostics, on some methods to improve the characterisation of the turbulence and on fast particles. Good coverage is given to neutron diagnostics, which are assuming increasing relevance as the plasma parameters approach ignition. Spectroscopic systems and their recent developments are well represented, whereas edge diagnostics are somewhat thin on the ground. A dedicated section is devoted to the latest tests on radiation effects and technological issues. The problems of damage to optical components and the difficulties presented by the determination of the tritium inventory are described.

In the last part, the new diagnostic systems of the most recent experiments (under construction or recently operated) are reported. Various aspects of some diagnostics not included in the three previous sections are also covered, with particular emphasis on microwaves and infrared diagnostics.

The book is well suited for specialists and, more generally, for people involved in nuclear fusion, who need information about the most recent developments in the field of plasma diagnostics. The papers cover many aspects of the challenges and possible solutions for performing measurements in fusion machines approaching reactor conditions. On the other hand, the contributions are in general quite advanced and would be challenging for people without a significant background in plasma diagnostics and nuclear fusion. The quality of the paper is more than satisfactory both from the point of view of clarity and of graphics. Moreover, at the beginning of the book, several papers make a considerable effort to put diagnostic issues in the wider context of present day nuclear fusion research. For those topics, which are too involved to be completely described in a conference contribution, in general adequate references are provided for deeper investigation.

A Murari

Approximately one third of the papers included in this volume deal with diagnostics related to inertial confinement fusion plasmas (i.e., laser-produced plasmas and pulsed-power). These papers discuss recent developments in charged particle diagnostics, neutron diagnostics, optical and x-ray measurements along with laser and particle probing diagnostics. The resulting collection of papers is comprehensive and wide-ranging and all of the major laboratories in Europe, the US, and Japan are represented. There is important discussion on the development of diagnostics for the National Ignition Facility, LMJ, and future ultra-high intensity laser experiments as well as papers on wire array z-pinch experiments. It is especially useful to have the contributions from inertial confinement fusion experiments intermingled with those from magnetic confinement fusion. The separation between these two approaches to fusion is often unfortunately large, so one of the pleasing things about this book is that it is very easy for readers familiar with experimental research in one area to compare `state of the art' plasma diagnostics in the other area. Hopefully this will facilitate the development of new ideas in both areas. This book is a conference proceedings and as such, almost all of the papers included are quite brief and are highly technical. Consequently, the book is not particularly pedagogical and would be most useful to researchers already working in this area of physics. For these readers, however, Advanced Diagnostics for Magnetic and Inertial Confinement Fusion is an excellent overview of the present status of fusion plasma diagnostics.

K Krushelnick