10 research outputs found
Markov Properties of Electrical Discharge Current Fluctuations in Plasma
Using the Markovian method, we study the stochastic nature of electrical
discharge current fluctuations in the Helium plasma. Sinusoidal trends are
extracted from the data set by the Fourier-Detrended Fluctuation analysis and
consequently cleaned data is retrieved. We determine the Markov time scale of
the detrended data set by using likelihood analysis. We also estimate the
Kramers-Moyal's coefficients of the discharge current fluctuations and derive
the corresponding Fokker-Planck equation. In addition, the obtained Langevin
equation enables us to reconstruct discharge time series with similar
statistical properties compared with the observed in the experiment. We also
provide an exact decomposition of temporal correlation function by using
Kramers-Moyal's coefficients. We show that for the stationary time series, the
two point temporal correlation function has an exponential decaying behavior
with a characteristic correlation time scale. Our results confirm that, there
is no definite relation between correlation and Markov time scales. However
both of them behave as monotonic increasing function of discharge current
intensity. Finally to complete our analysis, the multifractal behavior of
reconstructed time series using its Keramers-Moyal's coefficients and original
data set are investigated. Extended self similarity analysis demonstrates that
fluctuations in our experimental setup deviates from Kolmogorov (K41) theory
for fully developed turbulence regime.Comment: 25 pages, 9 figures and 4 tables. V3: Added comments, references,
figures and major correction
Measurement of hydrogen transport in deuterium discharges using the dynamic response of the effective mass
Particle transport in ASDEX upgrade
Particle transport coefficients are estimated by modelling the time evolution of electron density as determined from the ASDEX-Upgrade DCN-interferometer in a variety of discharges. These include L-H transitions for ohmic, ICRF, and beam-heated H-modes, density ramps, and pellet injection. The density evolution can generally be modeled satisfactorily. The inward convection in ASDEX-Upgrade (AUG) is generally rather small, and a D #propor to# 0.5 m"2/s is required to fit the time evolution. As an equilibrium transport coefficient, this implies rather short particle confinement times; some alternatives are discussed. (orig.)SIGLEAvailable from TIB Hannover: RA 71(1/282) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman
Particle transport analysis of the density build-up after the L–H transition in ASDEX Upgrade
Predictive-iterative modelling has been performed to investigate the role of convective and diffusive particle transport in the edge during the density build-up after the L–H transition. For the time-dependent modelling, the 1.5D radial transport code ASTRA has been used. The convective velocity, diffusion coefficient and the particle source profiles have been parameterized. Their parameters were varied until the best match of the modelling to the density measurements was found. The extensive parameter scans show that the density build-up can be reproduced by assuming only a diffusive edge transport barrier (ETB) with reduced diffusion coefficient at the edge with respect to the core values. Moreover, the replacement of the diffusive ETB by a strong inwards directed convective velocity at the edge (edge pinch) did not succeed in describing the data. This indicates that a diffusive ETB is required to explain the density build-up. However, the addition of an edge pinch to the diffusive ETB barrier slightly enhances the agreement between modelling and experiment. The best agreement was found with an edge diffusion coefficient of 0.031 m2 s−1 and an edge convective velocity of −0.5 m s−1. Because of the large uncertainties in the source, it is not possible to pin down the exact value for the additional edge pinch. An upper limit for a possible edge convective velocity of −5 m s−1 was estimated. These findings could also be confirmed by analysing H-mode phases of a collisionality scan, in which the normalized collisionality varied from 3.5 to 5.5 at the pedestal top
Statistical tools for maximum possible earthquake magnitude estimation
Several procedures for the statistical estimation of the regioncharacteristic
maximum possible earthquake magnitude, mmax , are currently
available. This paper aims to introduce and compare the 12 existing
procedures. For each of the procedures given, there are notes on its
origin, assumptions made in its derivation, condition for validity, weak
and strong points, etc. The applicability of each particular procedure is
determined by the assumptions of the model and/or the available information
on seismicity of the area.http://www.springerlink.com/content/120084/nf201