No abstract available

[en] The influence of magnetic turbulence on runaway transport has been studied. The evolution of runaway distribution function has been calculated using Electra a 2D code in momentum space and 1D in radius coordinate. The code considers the effect of averaging the turbulence by runaway orbits. Then Hard X-Ray emission spectrum is estimated and compared with experimental results of TJ-1 tokamak, obtaining a remarkable agreement. (Author) 15 refs

[en] The objective of the Symposium on Fusion Technology (SOFT) is to exchange information on design, construction and operation of fusion experiments and the technology which is bieng developed for present and next step machines and for power plant devices. It includes oral and poster presentations, as well as an industrial and Rand D exhibition. The symposium will be held at the Pacio de Congresos de Madrid. Paseo de la Castellana 99, in the centre of Madrid, from 11th to 15 th september 2000. It is hosted by the CIEMAT and organized by the Asociacion EURATOM-CIEMAT represented by the Laboratorio Nacional de Fusion por Confinamiento Magnetico. This 21st Symposium includes invited and contributed papers on all the aspects of the following. a. Plasma Facing Components. B. Plasma Heating and Current Drive. C Plasma Engineering and Control. D. Experimental Systems. E. Diagnositcs Engineering, Data Acquisistion and Remote Participation. F. Magnets and Power Supplies. G. Fuel Technologies. H. Remote Handling. I. Blamket and Shield Technologies. J. System Engineering and Next Step Devices. K. Safety and Environment, Power Plant and Socio-Economic Studies. L. Inertial Confinement Engineering and Technologies. (Author)

[en] In this paper hard X-ray spectra are obtained and compared in hydrogen and deuterium discharges in the TJ-I tokamak and magnetic turbulence characteristics are deduced from these. Significant differences are found in the spectra and, hence, in the magnetic turbulence characteristics of the two types of plasma. In deuterium discharges these changes are interpreted to be due to a reduction of magnetic turbulence amplitude and an enlargement of radial correlation length of the turbulence. The runaway diffusion coefficients for both types of plasma are obtained. (Author)

[en] Runaway electrons are a good probe of magnetic turbulence. They suffer very rare collisions and are little sensitive to electrostatic turbulence, therefore their transport is mainly governed by magnetic structure. The modification of this one by magnetic turbulence will influence the runaway electron confinement and the rate of runaway production. Experimental results on runaway confinement time are conflicting: In some tokamaks, runaway confinement time, τ_r, is about thermal electron confinement time and in other ones is many times longer. These discrepancies can be explained in terms of magnetic turbulent transport if the dependence on energy of the diffusion coefficient is considered. In the TJ-I tokamak, runaway confinement time has been deduced from HXR spectra measured by an NaI(Tl) detector, using a simple dynamic model; the intensity spectra are fitted by a single slope between the lowest detected energy and energies with sufficient statistics. Results are obtained under very different plasma conditions, and τ_r at the maximum of plasma current ranges from 0.2 to 2.5 ms. (author) 5 refs., 2 figs

No abstract available

[en] The generation and behaviour of superthermal electrons are studied as a function of magnetic configuration in the TJ-IU torsatron. Characterization of fast electrons is carried out with soft x-ray (SXR) and hard x-ray (HXR) diagnostic systems, covering the range from 0.4 keV to several MeV. The mean energies reached by the superthermal electron populations are found to be consistent with the occurrence of electron cyclotron (EC) off-axis absorption for the different radial magnetic field ripples at the axis. The interpretation of the experimental observations has been based on the influence of trapping factors at the magnetic axis and electron density profiles in the superthermal electron mean energy and density. (author)

[en] The isotope effect, i.e. the improved confinement of deuterium fuelling compared with hydrogen fuelling, shows up in nearly all tokamaks with various type of wall conditioning and in various confinement regimes. Many empirical scalings for energy confinement include a dependence of the energy replacement time τ_E ∝ A_i^α where α ∼ 1/2, and A_i is the atomic mass of the plasma ion species. However, no convincing theoretical justification has so far been found for such a dependence; classical transport would lead us to expect α 1/2, as would some theories for anomalous transport (e.g. those based on drift wave turbulence). This empirical scaling effect has been reviewed along with other relevant theories in a recent paper. The main conclusion drawn therein was that this effect was an unsolved fundamental problem in tokamak transport theory. In this paper, we put forward the hypothesis that the isotope effect is a consequence of magnetic transport in the plasma which we can support by observed reductions in the magnetic turbulence level in deuterium operated plasmas. The proposition is supported by data which we claim give some information about the level of stochastic magnetic turbulence within the plasma. These data show a reduction for the deuterium in the difference between the apparent temperature of a central ion (C V) and that of the main ion, hydrogen or deuterium. This can account for the isotope enhancement factors. In addition, preliminary results from sawtooth propagation in both hard and soft X-ray monitors supports the former proposition. To outline this, firstly the isotope documentation in the TJ-I tokamak is reported and then a plausible interpretation within a magnetic transport model is discussed. (author) 6 refs., 4 figs

[en] The runaway diffusion coefficient, D_r, for the TJ-I tokamak has been deduced using two different methods: in the first, D_r is obtained using a steady state approach for values of the runaway confinement time τ_r deduced from hard X ray (HXR) bremsstrahlung spectra; in the second, D_r is deduced from sawtooth oscillations of HXR flux, and from the soft X ray intensity, recorded simultaneously. Data have been taken in a scan with the toroidal magnetic field B_T. Averaged values obtained for D_r=5-10 m²·s^-1, decreasing with B_T, are in both cases consistent. Assuming that magnetic turbulence is responsible for their transport, from D_r and averaged value of b-tilde/B_T, the magnetic fluctuations level, can be deduced. The thermal conductivity coefficient χ_e, obtained using other diagnostics in TJ-I, is compared with D_r. The results are in good agreement with those obtained in TJ-I using probes, spectroscopic methods, power balance analysis and a coupled analysis for temperature and density pulses. (author). 31 refs, 6 figs

[en] The TJ-II stellarator presently in operation at the National Laboratory of Fusion is subject to radiological surveillance in compliance with the Spanish Nuclear Regulation. During its pulsed operation hard X-rays are emitted by the runaway electrons, and soft X-rays are generated by Bremsstrahlung of thermalized electrons. Inside the experimental hall, the plasma heating systems and some active diagnostics are additional sources of radiation. Outside the experimental hall, some auxiliary systems, such as high-voltage power supplies, must be checked for radiological influence. In order to verify the adequate radiological classification of the different working areas, 15 dosemeters are distributed in radiologically controlled areas close to the machine, as well as in areas of public use in the TJ-II building. The integrated dose equivalent is analyzed to help establish the range of radiological influence of the stellarator. The results of the period 2015-20 are presented and analyzed. (authors)