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A method to compute the dielectric tensor for an arbitrary distribution function is proposed. It allows one to study wave propagation and damping of electromagnetic waves at arbitrary cyclotron harmonics. As an example cyclotron heating of a beam of energetic particles is discussed.

In this paper we summarize the present status of experimental tokamak confinement studies. Under quiescent conditions, ion heat and impurity transport can be close to the neoclassical level. Generally, however, radial transport is enhanced by instabilities. There is evidence that anomalous ion heat and momentum transport may be caused by turbulence driven by the ion temperature gradient. The same level of understanding is not reached in electron heat and particle transport. Electron heat transport is characterized by a highly nonlinear relation between heat flux and temperature gradient. Particle transport is strongly governed by off-diagonal contributions. Where possible, the tokamak results are compared with those from stellarators, in particular with those from W7-AS. Such a comparison is meaningful because stellarators and tokamaks share many transport aspects. In both cases transport is generally anomalous, degrades with heating power and increases toward the edge. Bifurcations such as the tokamak H-mode transition are also observed in the W7-AS stellarator. Transport in stellarators, although anomalous, seems to be less confused by additional complexities such as large off-diagonal contributions, profile resilience, disparities between steady-state and perturbatively determined transport coefficients and an isotopic mass dependence in energy and particle transport. Differences in magnetic field and minor radius scaling seem to be introduced by operational restrictions: rotational transform iota is constant in stellarator field or size scans whereas q_a generally varies with current, field, or size in tokamaks.

A beam of injected fast atomic hydrogen presents a superb probe for hot fusion plasmas. The neutral particles experience excitation and ionization by collisions with electrons and ions as they penetrate into a plasma. The emitted characteristic line radiation is Doppler shifted and the spectral lines are split due to motional Stark fields. Measurements of wavelength, intensity and polarization of the Balmer- alpha emission reveal information about the neutral beam, such as beam attenuation, beam-geometry, beam-divergence and species mix. Local pitch angles and toroidal fields can be derived from the simultaneous measurement of the polarization pattern and the wavelength separation of the Stark multiplet. The implementation and application of beam emission spectroscopy as a quantitative diagnostic tool on the Joint European Torus (JET) experiment is reviewed.

We present a numerical and analytical study of the modifications induced in the collective scattering spectra by the ohmic current governing the equilibrium magnetic configuration in toroidal plasmas. The spectral density function is calculated assuming equilibrium distributions for the (bulk and impurity) ion species and a Spitzer-like distribution to describe the response of the electrons to the applied DC electric field. As expected, the spectral asymmetries can be non-negligibly enhanced in the region of the ion-acoustic frequency. They reach their maxima for tangential scattering geometries, where the magnetic effects on the spectra are negligible. This justifies the assumption of the non-magnetized spectra. The role of the spectral asymmetries in affecting the ion temperature measurements is investigated, and the possibility of inferring the local ohmic current density from the analysis of the low-frequency part of the spectra is verified. The additional effects due to the presence of impurities affecting the spectral shapes are also discussed under realistic conditions. Reference is made to the widely complementary FTU and JET tokamak plasmas, taken as examples of high- and medium-current density regimes, respectively. As a general result, mainly due to the absence of a true ion acoustic resonance in tokamak plasmas (related to a low electron to ion temperature ratio), the peculiarities of the high-current density regimes (high density, low impurity content, etc.) must be met for the current-induced asymmetry in the spectra to become measurable. The ion temperature measurements can be made unaffected by the asymmetries using a simple symmetrization procedure which applies in all cases. In conclusion, a theoretically motivated potential exists for a more detailed experimental investigation of the feasibility of current-density measurements in ohmic plasmas, based on collective scattering.

We report on a numerical analysis of luminescence signals observed during pellet injection into magnetically confined plasmas. Data from the ASDEX tokamak and the Wendelstein W7-AS advanced stellarator are considered in the form of a comparative study. We investigate how far the safety factor q and other plasma parameters influence the luminescence signals. Thus, we try to clarify the validity of the so-called neutral gas shielding model and an extension of it that takes into account the influence of resonant surfaces on the ablation process. Resonant values play only a minor role in the appearance of minima in the luminescence signals.

The JET neutron emission profile monitor was used to study ohmically heated deuterium discharges. The radial profile of the neutron emissivity is deduced from the line-integral data. The profiles of ion temperature, T_i, and ion thermal diffusivity, chi _i, are derived under steady-state conditions. The inferred chi _i, for 0.3 < p = r/a < 0.5, is in the range 0.5-2.5m²s^-1. The ion thermal diffusivity is higher than, and its scaling with plasma current opposite to, that predicted by neoclassical theory.

Reconnection is a universal plasma-physics process which has as one of its main characteristics the energization of plasma through the conversion of magnetic field energy. Interest in reconnection is multidisciplinary, and reconnection-associated phenomena are observed in astrophysical, solar system and laboratory plasmas. However, even though energy conversion is studied as a matter of practical interest and much fundamental research has been devoted to reconnection, this process has not been exploited very effectively in technological applications. To highlight the potential of reconnection for practical applications, we describe this process from a general point of view and present a theoretical model which is applicable to both non-relativistic and relativistic plasmas. Relativistic plasmas can be created under laboratory conditions, and the model predicts that such plasmas could be energized to very high energies. Experiments on reconnection may therefore lead to practical applications, such as hot plasma injectors in fusion reactors. Furthermore, we suggest that fusion reactors such as the tokamak can be modified so that plasma heating through reconnection is intrinsic to the device.

The main theme of the 11th European Tokamak Programme Workshop was the physics of steady-state operation of fusion plasmas. In addition, the latest results of JET and the status of ITER were presented and discussed. Summaries of the sessions on steady-state operation of fusion plasma and the presentation of JET results are given