Table of contents

Measurements of the suprathermal tail of the energy distribution function of deuterium ions, in plasmas containing MeV energy ICRH driven minority He³ ions and majority deuterium ions, revealed that the suprathermal tail ion density exceeded by nearly an order of magnitude that expected due to nuclear elastic scattering (NES) of He³ projectile ions on deuterium target ions. The experiments were performed on the Joint European Torus (JET), measurements of the line-of-sight integrated energy distribution functions of He³ and suprathermal deuterium ions were made using a high energy neutral particle analyzer. The NES or 'knock-on' deuterium ion energy distribution function was simulated using the FPP-3D Fokker–Plank code (Zaitsev et al2002 Nucl. Fusion42 1340) which solves the 3D trajectory averaged kinetic equations in JET tokamak geometry while taking into account NES of He³ ions on the deuterium ions. The required input energy distribution function of ICRH driven He³ ions was simulated using the SELFO code (Hedin et al2002 Nucl. Fusion42 527). The comparison between measurement and simulation in the He³ ICRH experiments is contrasted with an analogous previous comparison between measurements and simulation of JET plasmas in which 3.5 MeV DT fusion alpha-particles were the projectile ions, where measurement and simulation roughly agreed. Possible explanations for the observed excess knock-on deuterium tail in the experiments with He³ minority ICRH are discussed. The importance of D + He³ fusion products as additional drivers of suprathermal fuel ions is underlined.

Anisotropy in the magnetic fluctuation spectrum (stochastic anisotropy) and magnetic shear induce variations of global averaged quantities such as the running and the asymptotic diffusion tensors that can be investigated using a semi-analytical method. The study considers ranges for the anisotropy parameter, magnetic Kubo number and shear parameter leading to contrasting dynamical behaviors. In particular, the trapping of the stochastic magnetic field lines is analyzed. An asymptotic 'poloidal' velocity larger for stronger anisotropy is obtained for the wandering of the magnetic field lines for different values of the parameters.

In the present paper we report on a novel mechanical probe, which is able to measure the plasma pressure directly. The probe consists of two pendulums whose heads are exposed to the tokamak edge plasma, while the deflection is measured very sensitively outside the plasma by means of semi-conductor strain gauges. The plasma pressure was successfully measured in the ISTTOK edge plasma, its value being in good agreement with that derived from the electrical probe data (p_p = 1–10 Pa). Furthermore, we discuss the possibility of determining the ion temperature T_i = p_p/n − T_e by combining the pressure measurement with those of n and T_e from the electrical probes. Although the derived ion temperatures—besides that in the region close to the limiter—were reasonable, its uncertainty is still very large.

A novel diagnostic, the tunnel probe, is used to investigate the edge plasma of the CASTOR tokamak. Comparison with conventional small, cylindrical Langmuir probes (typical of those usually employed for turbulence measurements in magnetized plasmas) demonstrates the superiority of the tunnel probe. The collectors of the tunnel probe are concave, eliminating in theory all uncertainty of the effective collecting area, and thereby rendering the measurement of parallel ion current density, electron temperature, and floating potential more reliable. Two tunnel probes, mounted back-to-back in a Mach probe arrangement, are used to investigate directional asymmetries of the plasma parameters. The tunnel probes are used as standard Langmuir probes by applying voltage sweeps simultaneously to all their internal conductors. The measured electron temperature is higher on the electron side than on the ion side, and the floating potential is lower. The observed asymmetries, measured at low density and collisionality in CASTOR, could be consistent with a hot tail of non-thermal electrons flowing in the counter-current direction. The ratio of ion saturation currents to the internal conductors of the tunnel probe provides a second independent measurement of electron temperature whose directional asymmetry is less pronounced, in agreement with recent theoretical predictions that tunnel probes should be less sensitive to non-thermal electrons than Langmuir probes in certain conditions.

Thermal electron cyclotron emission (ECE) is measured on a medium size Aditya tokamak by a multi-channel Ka-band radiometer and another multi-channel E-band radiometer. The optically thick second harmonic Ka-band radiometer measured signal is affected by the right-hand cutoff effect beyond ∼25 ms. Due to this cutoff, the electron temperature cannot be measured beyond this time. The plasma density is evaluated for the cutoff frequency channel. It is not possible to also determine the electron temperature from the third harmonic optically thin E-band measurements. Yet these measurements are useful to study sawtooth oscillation phenomena. The sawtooth period and amplitude dependence on measurable plasma parameters are determined and new scaling laws are established for Aditya plasma sawtooth. The propagation delays of inverse sawtooth at different radial channels are used to determine thermal diffusivity. The measured diffusivity ( ) is found and compared with , which is determined from power balance of background Aditya plasma. The ratio is 2–3 for the Aditya plasma discharge. This ratio is comparable with a previous study of heat diffusion on medium size tokamaks.

Tungsten is foreseen for a full W-divertor of JET where tungsten will totally replace carbon as the material for the target plate. Also ITER operation is planned to be carried out with tungsten as one of the first wall materials, e.g. in the upper regions of the lower divertor. For the characterization of the accompanying plasma surface interaction a thorough spectroscopic diagnostic of the W influx into the plasma is of utmost importance. In order to upgrade the experimental and theoretical spectroscopic data beyond the present use of the W I transition (5d⁵6s⁷ S₃–5d⁵6p⁷P₄) at 4008 Å, an extension to lines of other (preferably longer) wavelengths has experimentally been carried out and accompanied by calculations. The survey resulted in an assessment of four additional lines in the longer (4294.61, 4886.90, 4982.59 and 5053.28 Å) and two in the shorter wavelength range (2551.35 and 2681.42 Å). The lines emitted from tungsten particles which were released by the plasma from tungsten plates and limiters in the TEXTOR edge plasma were observed with different (also high resolution) spectrometers and the Zeeman pattern was studied in order to identify possible influences of nearby interfering plasma spectral lines. The effect of the ground state level population as well as cascading from higher levels is included in the calculation of the relative line intensities and of the respective S/XB-values, the conversion factor for photon into particle fluxes. Measured and calculated S/XB-values for the 4008 Å line agrees well whereas some of the other lines are probably strongly affected by not yet identified factors.

The radial structure of toroidal Alfvén eigenmodes (TAEs) is of great importance for comparison with theoretical predictions. A dual-channel fast frequency hopping millimeter-wave reflectometer installed on the ASDEX Upgrade tokamak is capable of measuring density fluctuations from the plasma edge to core, allowing the radial eigenfunction of n = 4 TAE and edge MHD modes to be obtained using phase perturbation and coherence data analysis techniques. The two techniques reveal similar results, and in particular the radial structure of the n = 4 TAE is found to be in good agreement with numerical predictions from linear gyrokinetic simulations. The first results of the radial localization of Alfvén cascades are also presented.

Nanostructure surfaces are especially promising as highly absorbing targets for high-peak-power sub-picosecond laser–matter interaction. Efficient hot electron, fast ion and thermonuclear neutron production with moderate laser intensity have already been reported. Despite these experimental successes, theoretical investigations on the use of porous targets for the efficient generation of K_α and thermal x-ray emission remain scarce. In this report we use simple physical arguments combined with three-dimensional kinetic simulations to establish the timescales for the destruction of porous targets heated by a PW-class laser pulse.

We present an algorithm for solving the linear dispersion relation in an inhomogeneous, magnetised, relativistic plasma. The method is a generalisation of a previously reported algorithm that was limited to the homogeneous case. The extension involves projecting the spatial dependence of the perturbations onto a set of basis functions that satisfy the boundary conditions (spectral Galerkin method). To test this algorithm in the homogeneous case, we derive an analytical expression for the growth rate of the Weibel instability for a relativistic Maxwellian distribution and compare it with the numerical results. In the inhomogeneous case, we present solutions of the dispersion relation for the relativistic tearing mode, making no assumption about the thickness of the current sheet, and check the numerical method against the analytical expression.

Effects of radio frequency heating on particle confinement have been observed in various tokamaks, where it was found that impurities can be effectively pumped out of the plasma core when sufficient central ion cyclotron (ICH) and/or electron cyclotron heating (ECH) power is applied. It has been proposed that radio frequency heating prevents impurity accumulation by modifying the gradients of temperature and current and hence the turbulence regime responsible for particle anomalous flow. In this paper we present a study of the behavior of molybdenum injected in full lower-hybrid current drive plasmas in the Frascati Tokamak Upgrade with strong ECH. Three similar discharges with increasing level of ECH power are discussed in terms of plasma and power deposition profiles. Strong accumulation of the impurity is observed during off axis heating, while for central ECH deposition the concentration of molybdenum in the core of the discharges decreases at the highest level of ECH power (P_ECH = 1.2 MW). Microturbulence stability analysis has been carried out for the three plasmas and the relative importance of the off diagonal terms in the transport matrix for the pinch velocity of molybdenum has been studied with reference to FTU results on electron transport and in the framework of recent theoretical results.

Electron Bernstein waves (EBW) can propagate between electron cyclotron harmonics in hot, dense plasmas with no high-density cutoff (unlike electron cyclotron waves). ARIES-ST is a spherical tokamak (ST) reactor study. A promising method of heating and driving current in such an ST reactor would be with electron Bernstein waves. These could be mode converted from microwave vacuum modes (X-mode and O-mode) launched from the edge. In this paper, fully relativistic ray-tracing calculations (both damping and propagation) of EBWs in ARIES-ST are presented, using the relativistic dispersion solver R2D2 and the ray-tracing code GENRAY. The ray paths, damping locations, and polarizations are compared with the more commonly used non-relativistic EBW ray-tracing. A range of frequencies are shown for EBWs with small n_∥ that could be produced by the X-B mode conversion process, and EBWs with large n_∥ ≈ 0.6, produced by the O-X-B mode conversion process. With the density and temperature profile chosen for this paper, the greatest depth into the core that could be reached with mode-converted EBWs is a radial location of approximately ρ = 0.4. Although the radial location of the damping in most cases was not significantly different between the relativistic and non-relativistic cases, there are differences in the poloidal locations, as well as in the polarizations of the wave along the ray path, especially in the damping region.

A new version of the Weiland model has been used in predictive JETTO simulations of toroidal rotation. The model includes a self-consistent calculation of the toroidal momentum diffusivity (χ_ϕ) which contains both diagonal and non-diagonal (pinch) contributions to the momentum flux. Predictive transport simulations of JET H-mode, L-mode and hybrid discharges are presented.

It is shown that experimental temperatures and toroidal velocity were well reproduced by the simulations. The model predicts the ion heat diffusivity (χ_i) to be larger than the momentum diffusivity and it gives Prandtl numbers (Pr = χ_ϕ/χ_i) between 0.1 and 1. The Prandtl numbers are often, depending on the plasma conditions, predicted to be significantly smaller than unity. This is in accordance with experimental findings.

The internal structural measurements of electric field and density using twin heavy ion beam probes have been performed to elucidate the nonlinear evolution of the magneto-hydro-dynamic (MHD) bursty phenomenon driven by the interaction with high-energy particles in a toroidal plasma. The results have given the finest observation of the internal structure of plasma quantities, such as electric field, density and magnetic field distortion, which nonlinearly develop during the MHD phenomenon. In particular, the finding of a new kind of oscillating zonal flow driven by interaction between energetic particles and MHD modes should be emphasized for burning state plasmas.

This book provides a timely review of our present understanding of plasma phenomena in magnetized terrestrial and solar space plasmas. The author's emphasis is on the fluid and particle modeling and interpretation of observed active processes in space plasmas, i.e. `the physical background of large plasma eruptions in space'. It is somewhat alarming for a plasma physicist to read that an emphasis on processes in spatially inhomogeneous plasmas means that the work `... excludes a considerable fraction of the available methods in space plasma physics, such as the theory of waves, instabilities and wave particle interactions on a homogeneous background', particularly in light of the fact that much of our knowledge of these plasmas is derived from observations of such waves. However, it is clear on reading the book that such a restriction is not a disadvantage, but allows the author to concentrate on the main theme of the book, namely the use of fluid and particle pictures to model the equilibrium and active states of space plasmas. There are many other books which cover the wave aspects of space plasmas, and would complement this book.

The book's coverage is based on the extensive and profound research of the author and his colleagues in the area of fluid and particle modeling of space plasma structures. After an introduction to the physical setting of active plasmas, and a necessarily concise, but effective, discussion of the fluid and particle models to be used, the steady states of the magnetized plasmas of interest are treated, including the magnetosphere, solar plasmas and current sheets. Next the dynamics of unstable states is covered, including MHD and tearing instabilities, and nonlinear aspects, with a detailed discussion of magnetic reconnection. Finally, the models are applied to magnetospheric and solar observations.

The book is attractively written and produced, and this reviewer managed to find a minimum number of errors. A particularly attractive feature is the author's effort to explain in physical terms the concepts and ideas behind the processes discussed, rather than rely on bare equations. Indeed, this reviewer gained some new insights from the author's careful discussion of various points. This feature helps to make the book ideal background reading for researchers entering this field, after an entry-level introduction like, for example, the book of Kivelson and Russell.