[en] The investigation of various aspects of tokamak physics is performed with a combination of experiments carried out in different machines, to improve the statistical basis of the results and to cover a sufficient wide region of the operational space. Therefore, in the last decades, various multimachine databases have been built to address general and specific physical questions, particularly related to the extrapolation of present results to the next generation of devices. In this paper, a methodology of analysis is presented, to assess whether a multimachine data set is sufficiently coherent to really substantiate the conclusions, which are expected to be derived from it. A series of statistical and information theoretical tools have been refined to address the consistency of the data provided by the different devices. The developed techniques allow determination of whether it is reasonable to expect that the physics is the same in the various devices and/or that the entries do not present unacceptable bias. To exemplify the potential of the proposed approach, a systematic analysis of the ITPA database of the confinement time has been performed, using both dimensional and dimensionless quantities. The results obtained strongly suggest that better care should be taken in ensuring the coherence of data obtained from different experiments on different devices. (special topic)

[en] A novel method for measuring the particle confinement time by using spectroscopic data has been developed. The electron influx into plasma is estimated from the intensity of the H_α line. The first results obtained by this method in the L-2M stellarator are discussed.

[en] Scaling laws for plasma confinement are derived from similarity considerations based on the plasma diffusion equations. (author)

[en] A marked increase in the confinement time of injected impurities was measured during detachment of the plasmas in the TEXTOR tokamak. Non-recycling, metallic elements were introduced via laser blow-off, and scaling studies were performed. As the electron density increased, a threshold was reached beyond which the decay time of the brightness of the injected impurity transition was seen to increase from 75 ms to greater than 500 ms. The detachment of the plasma appeared coincident with the onset of this long confinement regime. (author). Letter-to-the-editor. 15 refs, 4 figs

[en] The first experimental results are presented investigating confinement time dependence on the big radius in the T-13 device. In experiments the main plasma parameters are ranged as follows: the big radius of the plasma filament - 41 cm <= R <= 81 cm, the small radius - 5 cm <= a < 8,5 cm, discharge current - 5,8 kA <= J <= 16 kA, the stability margin coefficient - 2 <= q <= 8, the electron temperature overage over section - 40 eV <= < Te > <= 90 eV, plasma density overage over section - 0,3x10¹³ cm^-3 <= < h> <= 0,8x10¹³ cm^-3. The maximum toroidal field with the radius R=40 cm consituted Bsub(T)=9,2 kGs. The results obtained show that confinement time dependence of electron component on the big radius of plasma filament is absent for the above plasma parameters of the T-13 device within the limit of experiment accuracy

[en] Cooling a hermetically sealed aluminum vessel to 80 K lowers the probability for the loss of ultracold neutrons to a level near the theoretical level. The additional loss in aluminum vessels is shown to be caused by a heating of the ultracold neutrons, for which the probability depends strongly on the temperature. A ''clean'' vessel in which ultracold neutrons can be stored for a time equal to their lifetime with respect to ß decay can be produced by freezing heavy ice on the surface of an aluminum vessel

[en] Oxygen gas was injected during the current plateau of a quasi-stationary T.F.R. deuterium plasma. As a consequence of the injection, the molybdenum density inside the plasma decreased, apparently because of a decreased molybdenum flux entering the plasma. The decrease in the density has a time constant which is a measurement of the impurity particle confinement time tausub(p). In this way, the confinement time was measured, values obtained were tausub(p)=50msec at the plasma center, and tausub(p)=20msec at the periphery. The discharges studied has been simulated by using different forms of the anomalous impurity diffusion. It is concluded that, under the conditions imposed by the experiments, the anomalous diffusion used must be proportional to the impurity density gradients

[en] In recent years, the limitations of scalings in power-law form that are obtained from traditional log regression have become increasingly evident in many fields of research. Given the wide gap in operational space between present-day and next-generation devices, robustness of the obtained models in guaranteeing reasonable extrapolability is a major issue. In this paper, a new technique, called symbolic regression, is reviewed, refined, and applied to the ITPA database for extracting scaling laws of the energy-confinement time at different radiated fraction levels. The main advantage of this new methodology is its ability to determine the most appropriate mathematical form of the scaling laws to model the available databases without the restriction of their having to be power laws. In a completely new development, this technique is combined with the concept of geodesic distance on Gaussian manifolds so as to take into account the error bars in the measurements and provide more reliable models. Robust scaling laws, including radiated fractions as regressor, have been found; they are not in power-law form, and are significantly better than the traditional scalings. These scaling laws, including radiated fractions, extrapolate quite differently to ITER, and therefore they require serious consideration. On the other hand, given the limitations of the existing databases, dedicated experimental investigations will have to be carried out to fully understand the impact of radiated fractions on the confinement in metallic machines and in the next generation of devices. (paper)

[en] Progress of statistical modelling of thermal transport of fusion plasmas based on (2–4 a) a transport analysis database is described. Statistically induced ion and electron thermal diffusivities are checked with an actual discharge which had not been included in the database. Usefulness of this statistical approach is explained in terms of (1) extracting important parameters through the application of information criterion, and (2) making possible for discussing exponents of regression expression and then implying the thermal transport property. The statistical approach reported in this paper could provide a new insight for thermal transport modelling for fusion plasmas, complementing conventional global scalings on the energy confinement time. (paper)

[en] The aim of this paper is to calculate, in a new manner, a general expression for the anomalous particle flux Γ_A due to electromagnetic turbulence, including the parallel components of the magnetic field fluctuations. The calculus of the flux Γ_A uses the anomalous distribution function f_A defined as the difference between the total distribution function and the neoclassical one. Besides the well known low-beta result, we also obtain the transport flux induced by parallel (to the equilibrium magnetic fields) fluctuations. Comparing the different components of the anomalous radial particle flux we specify the conditions when the effect of parallel fluctuations can be important. (author)