Table of contents

A hydrodynamic description is used to investigate the generation of ion-sound waves by intense neutrino beams in a dense plasma. The excited ion-sound waves can mediate the transfer of energy and momentum from the neutrinos to the plasma environment of Type II supernova. Since the growth rate of the neutrino-driven ion-sound waves is proportional to G_F^2/3, where G_F (≡10⁻⁴⁹ erg cm⁻³) is the Fermi coupling constant, it is likely that they can contribute to enhance the stalled supernova shock front.

Anomalous perpendicular viscosity is incorporated into transport threshold models of neoclassical tearing modes (NTMs). It is shown that this viscosity, influencing the bootstrap drive, is stabilizing if NTMs rotate in the ion diamagnetic drift direction and destabilizing in the contrary case.

In the new high-density H-mode of the W7-AS stellerator with island divertor several thermal instabilities were found. Marfes (multifaceted asymmetric radiation from the edge) were observed inboard crossing midplane. This phenomenon has much in common with the Marfe of a divertor tokamak. For some edge configurations of W7-AS, the Marfe is unstable. Simultaneously the plasma is poloidal symmetrically detached. Such a stationary poloidal symmetric detachment is already known from limiter tokamaks while the coexistent Marfe fluctuations are observed for the first time.

In this paper we study the effects of the presence of an internal transport barrier (ITB) on the current drive efficiency and power deposition profiles in the case of electron cyclotron waves interacting with an extended tail generated by lower hybrid (LH) waves. We study the subject by numerically solving the Fokker–Planck equation, with temperature and density profiles corrected along the time evolution at each collision time, based on the actual time-evolving electron distribution function. The results obtained show that the LH and electron cyclotron (EC) power absorption profiles and the current driven by the combined action of both types of waves are weakly dependent on the depth of the ITB, slightly more dependent on the level of magnetic turbulence and much more dependent on the level of EC wave power.

For the measurement of the divertor retention at ASDEX Upgrade, a sublimation probe has been built with which it is possible to puff metallic impurities into the divertor plasma. This probe offers the opportunity to cross calibrate the influx of the metal with the influx of carbon or oxygen. For the measurement of the divertor retention R, a special deposition probe was used in the main chamber. The value found for R is in good agreement with earlier estimations from long-term deposition probes and computer modelling. The different measurements suggest a propagation of tungsten within the scrape-off layer from the divertor into the main chamber and from there across the separatrix into the confined plasma.

Effect of divertor pumping on the scrape-off layer (SOL) plasma and impurities has been studied in many divertor tokamaks. Recent experimental studies of particle exhaust and SOL flow in JT-60U are reviewed. Pumping flux at the inner and outer pumping slots of the W-shaped divertor was investigated under the attached and detached divertor conditions. The SOL flow pattern was determined, for the first time, at three locations, i.e. at the low-field-side SOL (the outer midplane and divertor X-point) and at the high-field-side SOL (above the inner baffle), using three reciprocating Mach probes. The measured profiles were compared with modelling results from two-dimensional plasma simulations, UEDGE-code, with the ion drift effects included.

Intrinsic impurity behaviour in neutral beam heated LHD long pulse discharges with a discharge duration of 10 s was investigated. Spectroscopic and bolometric measurements showed a remarkable temporal increase of core radiation due to metallic impurities. Central impurity accumulation was found in a narrow plasma density region (_e = 1–3×10¹⁹ m⁻³) for both density ramp-up discharges and constant density discharges. In the density ramp-up discharges, high-Z impurities were accumulated in the low-density region and diffused out from the core plasma in the high-density region. The impurity behaviour was compared with neoclassical predictions.

The characteristics of the impurity transport in the RFX reversed field pinch experiment during enhanced confinement regimes, such as those obtained performing pulsed poloidal current drive and oscillating poloidal current drive, have been investigated. It is found that during the enhanced confinement period, the ratio between the Ly α line of C VI and the resonance line of C V increases systematically well beyond the expected enhancement due to the temperature improvement.

Experimental data have been reproduced by means of a one-dimensional, time dependent, collisional–radiative impurity transport code, which simulates several C and O lines, continuum emission and radiated power. In standard RFX plasmas the typical diffusion coefficient is ∼20 m² s⁻¹ at the plasma centre decreasing to ∼1 m² s⁻¹ at the edge. Best simulations of the spectroscopic data during the enhancement confinement phases are obtained by expanding the low diffusion region at the edge from r/a = 0.9 to r/a = 0.8±0.05 and shrinking the neutral density profile at the edge.

The addition of a divertor into the W7-AS stellarator has allowed access to a high density regime where the radiation profiles reach a steady state. In earlier limiter discharges, the plasma suffered a radiative collapse at high densities. In contrast to limiter experiments, where the impurity confinement time measured by Al laser blow-off increased with increasing line integrated density, in divertor discharges, above a density threshold, the impurity confinement time decreased with increasing line integrated density. The observation that the divertor plasma radiates mainly at the plasma edge rather than the plasma centre is a further indication that changes to the impurity transport coefficients at these high densities are the basis for the achievement of steady state discharges in the divertor configuration of W7-AS.

The maximum line integrated density reached with a divertor is compared to that reached with a limiter. The previously derived scaling law for the density limit with a limiter shows that the achieved densities do not exceed those predicted when the higher deposited power is taken into account. In a divertor the radiated power is located at the plasma edge and increasing the density, cooling the plasma edge and radiating sufficient power to cause plasma detachment determines the density limit.

Electrostatic turbulence, associated convective transport and poloidal plasma rotation at the edge of a tokamak plasma are strongly modified in a layer of stochastic magnetic field lines. Experimental observations during ergodic divertor operation show a decrease of density fluctuations but there is no evidence of a change of the turbulent cross field diffusivity. In this paper, the underlying mechanisms are studied using three-dimensional numerical simulations of flux driven resistive ballooning turbulence. Three key elements are found to determine the characteristics of transport due to fluctuations in the stochastic layer: first, long-lived stationary eddies appear due to modified equilibrium pressure and potential. Second, large scale pressure fluctuations decrease but small scale velocity fluctuations tend to increase. Third, the poloidal plasma rotation is suppressed and zonal flows are reduced by an anomalous friction due to stochasticity. In total, the level of convective flux associated with fluctuations is not quenched by the magnetic field perturbation. The impact of stochastic field lines on electrostatic turbulence is of interest for many experimental situations such as the stochastic boundary of stellarators and transport in the vicinity of the separatrix of standard tokamak divertors.

Perturbative transport experiments have been performed in JET low or reverse magnetic shear plasmas either in conditions of fully developed internal transport barrier (ITB) or during a phase where an ITB was not observed. Transient peripheral cooling was induced either by laser ablation or by shallow pellet injection, and the ensuing travelling cold pulse was used to probe the plasma transport in the electron and, for the first time, also in the ion channel. Cold pulses travelling through ITBs are observed to erode the ITB outer part, but, if the inner ITB portion survives, it strongly damps the propagating wave. The result is discussed in the context of proposed possible pictures for ITB formation. In the absence of an ITB, the cold pulse shows a fast propagation in the outer plasma half, which is consistent with a region of stiff transport, while in the inner half it slows down but shows the peculiar feature of amplitude growing while propagating. The data are powerful tests for the validation of theoretical transport models.

This article was scheduled to appear in issue 7 of Plasma Phys. Control. Fusion. To access this Special issue please follow this link: http://stacks.iop.org/0741-3335/44/i=7

Following our calculations of electron impact dissociation rates of molecular H₂, D₂ and T₂ (Trevisan and Tennyson 2002 Plasma Phys. Control. Fusion44 1263–76), calculations for the mixed isotopomers HD, HT and DT have been made. Total cross sections and energy differential cross sections at threshold energies as a function of vibrational states (v) for HD: v = 0–5, for HT: v = 0–5 and for DT: v = 0–7 are calculated for the electron impact dissociation through excitation to the b ³Σ_u⁺ excited electronic state, which is the dominant dissociation process at such energies. The rates of dissociation as a function of electron temperature for each state are parametrized. Coinciding with our previous results, near-threshold rates are shown to be so critically dependent on the vibrational level that dissociation from very high-lying vibrational levels must be included in calculations of the rate at local thermal equilibrium (LTE) even at low temperature. Rates for the higher vibrational levels are obtained by extrapolation following the procedure discussed in our previous publication, and are then used to calculate the LTE rate. The LTE rate is an order of magnitude greater than the v = 0 rate. A scaling law for the electron impact dissociation cross sections of vibrationally excited H₂ and its isotopomers has been derived.

Measurements of electron cyclotron emission (ECE) from the high field side of the TCV tokamak have been made on plasmas heated by second and third harmonic X-mode electron cyclotron heating (ECH) and electron cyclotron current drive (ECCD). Suprathermal ECE, up to a factor of six in excess of thermal emission, is detected in the presence of second harmonic X-mode (X2) ECCD and of third harmonic X-mode (X3) ECH. The measured ECE spectra are modelled using a bi-Maxwellian describing the bulk and the suprathermal electron populations. Suprathermal temperatures between 10 and 50 keV and densities in the range 1×10¹⁷−6×10¹⁸ m⁻³ are obtained, and correspond to 3–15 bulk temperatures and 1–20% bulk densities. Good agreement between ECE suprathermal temperatures and energetic photon temperatures, measured by a hard x-ray camera, is found. For optically thin X3 low field side injection in the presence of X2 CO-ECCD, the suprathermal population partly explains the discrepancy between global and first pass absorption measurements.

Spectra of the O II ion were obtained with temporal and spatial (along the poloidal radius) resolution by injecting of oxygen-containing molecules through a block of the upper poloidal limiter of TEXTOR-94 into the boundary plasma. Three different wavelength regions (4660±100, 4340±100, 3730±100 Å) were observed during reproducible TEXTOR-94 discharges with n_e = 1×10¹⁸ m⁻³, T_e = 90 eV at the last closed flux surface (LCFS). For calibration purposes the oxygen emission was simultaneously registered in all discharges with a 2D camera using the light from an O II line at 4416 Å. Radial intensity distributions of lines corresponding to the transitions 2p²[³P]3s–2p²[³P]3p (components of the multiplets ⁴P–⁴S, ⁴P–⁴P, ⁴P–⁴D, ²P–²D) and 2p²[¹D]3s–2p²[¹D]3p (doublet ²D–²D) were measured. It is shown that the relative intensities of the lines inside the multiplets are in good agreement with theoretical data calculated in SL-coupling. An appropriate collisional-radiative model (the level list and the corresponding atomic database) has been developed and calculations have been carried out using the GKU kinetic code developed at the P.N. Lebedev Institute. Cross-sections of atomic processes have been calculated using the ATOM code by the K-matrix method. A comparison of theoretical and experimental data is presented. It is shown that the relative multiplet intensities have a weak dependence on electron density and temperature. The populations of the ground configuration states of O II were investigated. Absolute values for the `ionization per photon' were measured and a comparison with modelled values is given.

The internal inductance l_i and the magnetic axis radial position R_MAG are important elements in the development of a reliable real-time control system.

Specific algorithms have been developed to obtain these quantities and, with the aim of comparing the relative performances, l_i and R_MAG have also been determined with suitable neural networks. Both procedures rely on the Shafranov integrals, which have been computed on the plasma last closed flux surface using an updated version of the fast boundary code XLOC.

The two approaches have been verified on several classes of equilibrium and both in the limiter and x-point phases of the discharges. Their results have been measured against the estimates of the off-line JET equilibrium code EFIT and it has been found that they provide quite good evaluations of the required quantities, since the differences between their estimates and the EFIT ones are of the order of a few per cent. They also provide similar performances in terms of accuracy and computational speed and are quite robust in the case of poor quality signals.

Both methods are consequently suitable for reliable real-time control systems in JET.

This book treats in detail, as indicated in the title, the transport phenomena in multicomponent plasmas. Here, the term `transport' applies to the study of mass and energy transfer in plasmas due to the interactions between pairs of particles only. Radiation is legitimately omitted; anyway, radiative transfer is another field of study.

As the author himself mentions in the introduction, `the term multicomponent plasma implies a partially or fully ionized mixture of arbitrary number of species of neutral and charged particles satisfying the condition of quasi-neutrality'. In fact, this book treats a large variety of plasmas applying to different systems ranging from

low-pressure systems which may be far from local thermodynamic equilibrium (LTE) conditions, to thermal plasmas in LTE or near-LTE states with special attention to two-temperature systems;

partially ionized plasmas with low ionization degree for which electron-neutral interactions are predominant, to systems with higher ionization degrees in which charged particle interactions are no more negligible.

In addition, for all the above stated situations, the author treats both plasmas which are subjected to an external electromagnetic field and those which are not (homogeneous and inhomogeneous cases). Furthermore, in the last chapters a special discussion concerning molecular plasmas is presented.

Taking into account the evolution of plasma modelling in the last few years, the subject is of current interest and the reader will find in the book a large amount of information necessary for a good understanding of transport phenomena in plasmas: for a plasma simulation specialist, this book may be regarded as reference text, which includes all necessary mathematical relations for his work. However, it should not be considered a simple formulary; the reader will also find here an excellent description of the theoretical basis necessary for the derivation of all given expressions. To this point of view this book, at least the first few chapters, may be used as a very good complement to other textbooks for plasma physics Masters students (or even PhD beginners) and engineers who are looking for some specialization in this domain.

It should be noticed here, and this is highly appreciated, that in all cases the author starts by treating the full problem and then continues with a case-study of different, commonly accepted situations. For example, in the first chapter the reader, starting from the Boltzmann equation, will find an excellent `fundamental' discussion on the effective cross sections: beginning with the general case with an arbitrary interaction potential, the author then develops the case of the simplest approximation (hard spheres potential) followed by the `power-law' potential which is more realistic for elastic scattering between neutral particles. He then continues with charged-neutral interactions with special mention of charge transfer reactions. The cases of the Coulomb potential and shielded Coulomb potential are discussed for the description of interactions between charged particles. Last, but not the least, other types of interactions described by the Lennard-Jones and Born-Mayer potentials are also stated and discussed. This very methodical way of description is used in all chapters of this book-this is highly appreciated!

This book fills a gap in the literature of this subject-to my knowledge, during the last years very few new studies have been published in the crucial domain of multicomponent plasmas. In most cases, all the studies are based on the Chapman-Enskog expansion method while the present document mainly uses the moment expansion better known as `Grand's' method. However, the author systematically gives a critical comparison between the two methods; this is very useful for the reader who has to decide which one of these formalisms is convenient for him.

Besides all the positive points stated in the above paragraphs, there are, ineluctably, some negative points: the text in this book is really very dense, only three to four figures are included for the full book. This may have an offputting effect on the reader. Fortunately, the organization in chapters and paragraphs is very clear and easy to follow. Thus, after reading the first chapter which includes all necessary symbol conventions and notations the reader may go directly to the chapter which interests him. In my opinion, reading this book from the first to the last page is rather improbable! Another point that I would like to mention is that some `expressions' are rather unusual when compared to other literature in the subject; this is probably due to the translation from the Russian. However, this is a minor problem, since~once the reader is familiar with these expressions~everything~becomes smooth again. Finally, a table summarizing the notations and symbols used in this book could be of great help for the user, but, unfortunately this is missing for this edition.

In conclusion, this extended re-edition of a Russian document (first published in 1982) is an excellent reference book; I could compare the book to a `Swiss army knife' for plasma physicists. This book is, for all the above reasons, a necessary complement to a plasma physicist's library.

G Zissis