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In the context of present and future long pulse tokamak experiments yielding a growing size of measured data per pulse, automating data consistency analysis and comparisons of measurements with models is a critical matter. To address these issues, the present work describes an expert system that carries out in an integrated and fully automated way (i) a reconstruction of plasma profiles from the measurements, using Bayesian analysis (ii) a prediction of the reconstructed quantities, according to some models and (iii) a comparison of the first two steps. The first application shown is devoted to the development of an automated comparison method between the experimental plasma profiles reconstructed using Bayesian methods and time dependent solutions of the transport equations. The method was applied to model validation of a simple heat transport model with three radial shape options. It has been tested on a database of 21 Tore Supra and 14 JET shots. The second application aims at quantifying uncertainties due to the electron temperature profile in current diffusion simulations. A systematic reconstruction of the Ne, Te, Ti profiles was first carried out for all time slices of the pulse. The Bayesian 95% highest probability intervals on the Te profile reconstruction were then used for (i) data consistency check of the flux consumption and (ii) defining a confidence interval for the current profile simulation. The method has been applied to one Tore Supra pulse and one JET pulse. [ABSTRACT FROM AUTHOR]

Particle transport has been studied in the Tore Supra tokamak by using modulated ion cyclotron resonance heating to generate perturbations of density and temperature. For the first time, a reversal of the particle convective velocity and a strong increase in the turbulent particle flux have been clearly observed. When the mixed critical gradient ζc=R/LT+4(R/Ln)=22 is exceeded, the particle flux increases sharply and the convective velocity reverses from inward to outward. These observations are in agreement with quasilinear, gyrokinetic calculations. The critical gradient corresponds to a transition from an instability driven by the ion temperature gradient to the onset of another instability caused by trapped electrons. [ABSTRACT FROM AUTHOR]

In parallel to the direct contribution to the procurement phase of ITER and Broader Approach, CEA has initiated research & development programmes, accompanied by experiments together with a significant modelling effort, aimed at ensuring robust operation, plasma performance, as well as mitigating the risks of the procurement phase. This overview reports the latest progress in both fusion science and technology including many areas, namely the mitigation of superconducting magnet quenches, disruption-generated runaway electrons, edge-localized modes (ELMs), the development of imaging surveillance, and heating and current drive systems for steady-state operation. The WEST (W Environment for Steady-state Tokamaks) project, turning Tore Supra into an actively cooled W-divertor platform open to the ITER partners and industries, is presented. [ABSTRACT FROM AUTHOR]

Fully non-inductive operation with lower hybrid current drive (LHCD) in the Tore Supra tokamak is achieved using either a fully active multijunction (FAM) launcher or a more recent ITER-relevant passive active multijunction (PAM) launcher, or both launchers simultaneously. While both antennas show comparable experimental efficiencies, the analysis of stability properties in long discharges suggest different current profiles. We present comparative modelling of LHCD with the two different launchers to characterize the effect of the respective antenna spectra on the driven current profile. The interpretative modelling of LHCD is carried out using a chain of codes calculating, respectively, the global discharge evolution (tokamak simulator METIS), the spectrum at the antenna mouth (LH coupling code ALOHA), the LH wave propagation (ray-tracing code C3PO), and the distribution function (3D Fokker-Planck code LUKE). Essential aspects of the fast electron dynamics in time, space and energy are obtained from hard x-ray measurements of fast electron bremsstrahlung emission using a dedicated tomographic system. LHCD simulations are validated by systematic comparisons between these experimental measurements and the reconstructed signal calculated by the code R5X2 from the LUKE electron distribution. An excellent agreement is obtained in the presence of strong Landau damping (found under low density and high-power conditions in Tore Supra) for which the ray-tracing model is valid for modelling the LH wave propagation. Two aspects of the antenna spectra are found to have a significant effect on LHCD. First, the driven current is found to be proportional to the directivity, which depends upon the respective weight of the main positive and main negative lobes and is particularly sensitive to the density in front of the antenna. Second, the position of the main negative lobe in the spectrum is different for the two launchers. As this lobe drives a counter-current, the resulting driven current profile is also different for the FAM and PAM launchers. [ABSTRACT FROM AUTHOR]

Experiments to study inward heat transport phenomena have been performed in the Tore Supra tokamak with off-axis electron cyclotron resonance heating (ECRH). Both power balance and perturbation transport analysis have been done for low-frequency (1 Hz) ECRH modulation experiments. Heat diffusivity and heat pinch have been separately determined by fitting the experimental data of the amplitude and phase of the Fourier transform of the modulated temperature with a linear transport model including convection term. Comparison with the critical gradient model has shown that the heat pinch previously obtained could include a pseudo-pinch due to the non-linearity of the diffusivity and an additional non-diffusive heat pinch. The pinch effect is reduced for higher densities. [ABSTRACT FROM AUTHOR]

In this paper, a database of L-mode plasmas with Greenwald density fractions smaller than 0.8 is used to analyse the parametric dependences of the radiative power and the effective charge Zeff . It is found that the radiative power has a linear dependence on the total power and a linear fit is derived. In order to understand this parametric dependence, the changes in the radial extension of the radiation are studied with the help of bolometry measurements and it is found that the increase in Prad with Ptot can be explained by an increase in the neutral source of impurities (basically carbon erosion) during additional heating. A comparison of deuterium and helium plasmas shows that they radiate the same amount at the same total power. Significant positive deviations from the fit of the radiative power are observed for high ratios of Cu XIX/(ne). Zeff is also found to depend roughly linearly on the total power. The link found between Zeff and Prad is compatible with that of multimachine scaling (Matthews et al 1997 J. Nucl. Mater. 241-243 450). These results are obtained in a limiter machine, running in L-mode in the case where carbon is the dominant impurity. [ABSTRACT FROM AUTHOR]

The hot electron plasmas (T[sub e]>2T[sub i]) in Tore Supra (Equipe Tore Supra (presented by R. Aymar) in Plasma Physics and Controlled Nuclear Fusion Research [Proc. 12th Int. Conf., Nice, 1988 (IAEA, Vienna, 1989), Vol. 1, p. 9]) driven by fast wave electron heating (FWEH) are analyzed for thermal transport. Both neoclassical and anomalous transport processes are taken into account. The dominant power flow is through the electron channel of anomalous thermal diffusivity. The electron and ion temperature gradient driven instabilities are analyzed for a well documented discharge and shown to explain the diffusivities inferred from the steady state power balance analysis. The discharges are maintained in a quasi-steady state for periods up to 100 global energy replacement times. A large Tore Supra database is tested against two models for the turbulent electron thermal conductivity. Good correlation is obtained with an updated version of the collisionless skin depth formula. The electrostatic turbulence-based formula for electron temperature gradient (ETG) mode performs poorly in the core but well in the outer plasma. The electromagnetic turbulence theory based formula for ETG mode is benchmarked with the empirical Taroni-Bohm formula derived from Joint European Torus (JET) data. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Observations of lower hybrid (LH) radio frequency heating effects on toroidal plasma rotation in L-mode Tore Supra plasmas are reported. A database of more than 50 plasma discharges has been analysed. Core rotation is found to increment in co- or counter-current direction depending on the plasma current (Ip). At low plasma current, the induced rotation is up to +15 km s−1 in the co-current direction, the rotation profile being affected over the whole plasma minor radius. At higher plasma current, an opposite trend is observed, the core plasma rotation incrementing up to −15 km s−1 in the counter-current direction, the profile being affected up to r/a < 0.6 only. At the zero crossing point, which is defined when the plasma rotation profile is not affected by LH power injection, Ip ∼ 0.95 MA. In both low and high Ip cases, rotation increments are found to increase with the injected power. Several mechanisms in competition which can induce co- or counter-current rotation in Tore Supra LHCD plasmas are investigated and typical order of magnitude are discussed. How those effects evolve with plasma parameters and how they compete are important issues addressed in this paper. Rotation increment increase with Ip at fixed LH power is consistent with a dominant standard momentum confinement mechanism related to Ip increase. The co-current change in rotation is consistent with a fast electron ripple loss mechanism, while thermal ripple induced neoclassical friction and absorbed LH wave momentum from resonant electrons are expected to influence the rotation in the counter-current direction. Finally, the numerical simulations show that the radial turbulent momentum transport does impact the rotation behaviour inducing increment in co- or counter-current directions, depending on the plasma current amplitude. [ABSTRACT FROM AUTHOR]

Abstract: The scaling law for carbon erosion in Tore Supra previously established by Hogan et al. (ΦC (C/s)=5×1020 P cond (MW), where P cond is the conducted power) is revisited both from the experimental and the modelling point of view. New developments with the EIRENE code, that allow relating measured CII emission intensities to the total amount of carbon sputtered from the Toroidal Pumped Limiter, are presented. Recent measurements carried out at high input power show a good agreement with the database used to establish the scaling law. [Copyright &y& Elsevier]