[en] Stationary plasmas in various gases were generated at pressures of some 10 Pa in weak magnetic fields by microwave heating. Quantitative spectroscopy of atomic lines and molecular bands was applied for diagnostic of plasmas in hydrogen, nitrogen, methane and argon-helium mixtures. Simple model calculations were based on the well-known balance equations of glow discharges including chemical reactions especially for methane. Some tests were also performed in nitrogen glow discharges. Excitation, ionisation and dissociation rate coefficients for diagnostic or modelling purposes were taken from nuclear fusion research of calculated from experimental cross sections assuming a Maxwellian energy distribution. The electron temperatures of the discharges, predicted from electron confinement times and ionisation rate coefficients (≅ 1-4 eV), were well confirmed by the experiment. Due to additional energy losses into vibrational excitation and dissociation, there is a substantial difference in plasma size between atomic and molecular plasmas at given input power. The electron density in molecular plasmas was of the order of the cut-off density, i.e. ≅ 10¹¹ cm^-3, almost independent of the pressure. The kinetic temperature of the heavy particles was determined form N₂ band rotational intensity distribution (≅ 500 K), while the rotational temperature of CH bands and the hydrogen gas temperature are higher - a proof of energy gain during CH₄ dissociation. Hydrogen and CH densities were measured in methane plasmas by adding a small amount of argon and comparing H_α and CH molecular bands to Ar line intensities. H and CH particle densities were also derived from model calculations using electron dissociation rate coefficients and respective confinement times for the dissociation products. Some neutral-neutral reactions were also included. (orig./KP)

[en] A novel auto-correlation function (ACF) method has been investigated for determining the oscillation frequency and the decay ratio in BWR stability analyses. The report describes not only the method but also documents comprehensively the used and developed FORTRAN codes. The neutron signals are band-pass filtered to separate the oscillation peak in the power spectral density (PSD) from background. Two linear second-order oscillation models are considered. The ACF of each model, corrected for signal filtering and with the inclusion of a background term under the peak in the PSD, is then least-squares fitted to the ACF estimated on the previously filtered neutron signals, in order to determine the oscillation frequency and the decay ratio. The procedures of filtering and ACF estimation use fast Fourier transform techniques with signal segmentation. Gliding 'short-time' ACF estimates along a signal record allow the evaluation of uncertainties. Some numerical results are given which have been obtained from neutron signal data offered by the recent Forsmark I and Forsmark II NEA benchmark project. They are compared with those from other benchmark participants using different other analysis methods. (author)

[en] The Wiener-Hermite functional (WHF) method is applied to the stochastic oscillator model under stable system conditions. The application concerns a non-linear trivariate-input/single-output problem. Gaussian random noise sources are assumed. A set of coupled integral equations is established in the frequency domain for any required approximation accuracy (WHF-N approximation), from which noise signature functions of the response can be derived. The oscillator model is explicitly treated in a second-order approximation (WHF-2 approximation) with white noise sources and the resulting steady-state value and the power spectral density of the response are compared with exact results derived by the Fokker-Planck method. The approximative results exhibit the same structure as recently found in the application of the WHF method to point reactor kinetics driven by random reactivity fluctuations. (author)

[en] Impurities, including helium produced in the respective reaction, are still an important subject in controlled nuclear Fusion research. Spectroscopy of the plasma edge, mainly in the visible spectral range, provides information on hydrogen and impurity influxes, on impurity production mechanisms and on particle confinement. Spectroscopic models for the interpretation of such measurements are discussed with particular emphasis on collisional radiative calculations for helium. A first application of plasma edge spectroscopy is the investigation of atom and ion particle flux densities at the boundary of tokamaks or stellarators. Results are shown for oxygen, carbon and chromium in JET. Then, the attention is focused on molecular particle fluxes, like H₂, D₂ and CH₄. The interpretation of the shape and intensity of molecular band emission is explained, and results are presented with respect to chemical carbon production. Finally, the mechanisms of impurity screening at the plasma edge are investigated and respective measurements are shown. (orig.)

[en] Impurity densities in the plasma interior and bulk impurity transport are usually studied by means of vuv and X-ray spectroscopy. Resonance lines are the main object of investigation, but continuum radiation is also used, especially for fully ionised species. Spectrometers and spectra, mainly form JET, are discussed with respect to diagnostic potential and calibration problems. Spatial scan facilities or multi-chord diagnostics are essential for transport investigations, and several possibilities are shown. The interpretation of spectral line radiation usually requires the availability of impurity transport codes, which calculate the ionisation balance in the presence of transport, the line emissivities and the total impurity radiation. Some atomic physics prerequisites of such codes are discussed. Then, theoretical and experimental approaches to the transport problem are investigated using ASDEX and JET results for anomalous transport. The occasional observation of neoclassical accumulation, e.g. after pellet injection, is presented and respective modelling is described. Some H-mode transport phenomena are mentioned. (orig.)

[en] The present report contains two lectures held at the 4th workshop on magnetic confinement fusion: Diagnostics for tokamaks and stellarators, Santander (Spain), 22-24 June 1992. See hints under relevant topics. (WL)

[en] A power noise model of point reactor kinetics with instantaneous negative reactivity feedback is considered. It is driven by stationary coloured Gaussian random reactivity noise. The model contains one group of delayed neutrons. They show partially destabilizing effects at intermediate power states. The neutron steady-state value and the neutron RMS value are obtained as functions of the reactivity excitation strength for different power states via computer simulation. The reactivity noise data are generated by a method based on the Rice formula, and the Langevin equations of the model are directly treated by the Runge-Kutta method. Results are compared with data obtainable from the Wieer-Hermite functional method in a first-order approximation

[en] An off-line method of detrending non-stationary noise data is given. It uses a least-squares spline approximation of the noise data with equally spaced breakpoints. Subtraction of the spline approximation from the noise signal at each data point gives a residual noise signal. The method acts as a high-pass filter with very sharp frequency cut-off. The cut-off frequency is determined by the breakpoint distance. The steepness of the cut-off is controlled by the spline order

[en] 'STRAHL' is an interactive, stand-alone impurity transport code which is used on JET for the interpretation of spectroscopic measurements. It calculates the impurity ionisation balance on the basis of given plasma parameters and empirical transport models, using atomic physics data sets especially compiled for that purpose. The paper explains the basic ideas and formulas behind STRAHL in order to allow potential users to design their own special version. (U.K.)

[en] A novel auto-correlation function (ACF) method has been investigated for determining the oscillation frequency and the decay ratio in BWR stability analyses. The neutron signals are band-pass filtered to separate the oscillation peak in the power spectral density (PSD) from background. Two linear second-order oscillation models are considered. These models, corrected for signal filtering and including a background term under the peak in the PSD, are then least-squares fitted to the ACF of the previously filtered neutron signal, in order to determine the oscillation frequency and the decay ratio. Our method uses fast Fourier transform techniques with signal segmentation for filtering and ACF estimation. Gliding 'short-term' ACF estimates on a record allow the evaluation of uncertainties. Numerical results are given which have been obtained from neutron data of the recent Forsmark I and Forsmark II NEA benchmark project. Our results are compared with those obtained by other participants in the benchmark project. The present PSI report is an extended version of the publication K. Behringer, D. Hennig 'A novel auto-correlation function method for the determination of the decay ratio in BWR stability studies' (Behringer, Hennig, 2002)