共查询到20条相似文献,搜索用时 31 毫秒
1.
V. Weinzettl V. Piffl J. Matejicek E. Dufkova J. Zajac R. Dejarnac V. Perina 《Czechoslovak Journal of Physics》2005,55(12):1607-1614
The effect of the use of different electrode materials for edge-plasma biasing on plasma density and floating-potential profile
modifications has been recently investigated on the CASTOR tokamak. Dependences of biasing current, edge plasma density and
floating potential on biasing voltage have been measured. Induced relaxation events and fast (10–50) kHz oscillations are
shown and surface changes of the biasing electrodes are discussed in the paper.
Presented at the Workshop “Electric Fields, Structures and Relaxation in Edge Plasmas”, Tarragona, Spain, July 3–4, 2005. 相似文献
2.
V. A. Alimov F. I. Vybornov E. N. Myasnikov A. V. Rakhlin 《Radiophysics and Quantum Electronics》2008,51(11):874-879
We show the results of the first experimental studies of the multifractal structure of the developed artificial ionospheric
turbulence. As a result of the special multifractal analysis of the recorded amplitudes of signals from the orbital satellites,
which were obtained during the experiments on radio tomography of the irregularities excited in the ionosphere by the powerful
mid-latitude heating facility “Sura,” it is found that the characteristic multifractal structure of these records is caused
by the nonuniform spatial distribution of the small-scale fluctuations of the electron number density in the artificial irregularities
of the ionospheric plasma. Comparative analysis is performed for the multifractal spectra of fluctuations of both the amplitudes
and energies of signals received from the orbital satellites upon radio transmission probing of the region of artificial ionospheric
turbulence by these signals at three observation points located near the “Sura” heating facility and spaced apart to a distance
of about 100–150 km.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 11, pp. 970–976, November 2008. 相似文献
3.
Using multifractal analysis we study extended, self-similar and non-self-similar type of wave functions in the Fibonacci model.
Extended states arising due to commutation of transfer matrices for certain blocks of atoms in quasiperiodic systems are shown
to have the same signature as the Bloch states in terms of the singularity spectrum withf(α)=α=1. Numerically, however, the extended states show a typical multifractal behaviour for finite chain lengths. Finite
size scaling corrections yield results consistent with that obtained analytically. The self-similar states at the band edges
show a multifractal behaviour and they are energy dependent in the case of blocks of atoms arranged in a Fibonacci sequence.
For non-self-similar states we obtain a non-monotonic behaviour off(α) as a function of the chain length. We also show that in cases where extended states exist, the cross-over from extended
to non-self-similar states in gradual. 相似文献
4.
We present the results of studies of the multifractal structure of slow (of duration τ ≈ 10 s) fluctuations of the received-signal
amplitudes in special experiments on radio-raying of the midlatitude ionosphere by signals from orbital satellites in 2004–2006.
It is shown, in particular, that the method of multifractal analysis of amplitude records of the received signals yields information
on the spectrum of large-scale ionospheric inhomogeneities, which is inaccessible for the classical method of radio scintillations.
From the results of measurements with the use of multifractal processing of experimental data, we found that large-scale (tens
of kilometers) quasiregular electron-density inhomogeneities of traveling ionospheric disturbances (TIDs) have a power-law
spectrum. It is exactly the power-law form of the spatial spectrum of large-scale inhomogeneities of TIDs that can be the
reason for the observed multifractal structure of the intermittency of slow fluctuations of the received-signal amplitudes.
However, under conditions of a developed small-scale turbulence of TIDs, the observed multifractal structure of the received
signals is, as a rule, stipulated by the spatial inhomogeneity of the variance of the integral electron-density fluctuations
of small-scale inhomogeneities on scales comparable with the sizes of large-scale inhomogeneities of TIDs.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 3, pp. 191–198, March 2008. 相似文献
5.
We present the results of studying the multifractal structure of intermittency in a developed ionospheric turbulence during
special experiments on radio-raying of the midlatitude ionosphere by signals from orbital satellites in 2005–2006. It is shown,
in particular, that the determination of multidimensional structural functions of the energy fluctuations of received signals
permits one to obtain the necessary information on multifractal spectra of the studied process of radio-wave scattering in
the ionosphere. Experimental data on multifractal spectra of slow fluctuations in the received-signal energy under conditions
of a developed small-scale turbulence are compared with the existing concept of the radio-wave scattering within the framework
of the statistical theory of radio-wave propagation in the ionosphere. It is inferred that under conditions of a developed
ionospheric turbulence, the multifractal structure of the intermittency of slow fluctuations in the received-signal energy
is a consequence of the intermittency of small-scale fluctuations in the electron number density of the ionospheric plasma
on relatively large spatial scales of about several ten kilometers.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 6, pp. 485–493, June 2008. 相似文献
6.
S. M. Mukhamedin 《Russian Physics Journal》2011,54(1):28-31
Fraktal theory allows specifics of turbulence inhomogeneities of different types to be considered in the spectral theory of
self-affine multifractals. Experiments demonstrate that the turbulence possesses the multifractal properties. Nowadays the
multifractal analysis is widely used in various branches of modern physics. The structural elements of the homogeneous and
isotropic turbulence – vortices – represent a self-similar multifractal with the same similarity coefficient for all spatial
variables. 相似文献
7.
We present the results of the studies of fractal properties of the small-scale inhomogeneities of traveling ionospheric disturbances
in special experiments on radio-raying of the midlatitude ionosphere by signals from orbital satellites in 2004–2006. Along
with the conventional correlation processing of the received signals, we performed their multifractal analysis, as well as
fractal processing of signals by the correlation-integral method. Important information on fractal properties of the small-scale
turbulence for the least studied part of the upper-ionosphere inhomogeneity spectrum in the interval of characteristic scales
l ≈ 1–10 km is obtained. In particular, it is noted that the fractal structure of these inhomogeneities can be originated
from the nonlinear “destruction” of several large-scale sinusoidal structures in a quasistable traveling disturbance. It is
also noted that the multifractal spectra of amplitude fluctuations of the received signals obtained in the experiments in
different years, in different time of the day, and in different seasons of the observations are quite similar. This is evidence
that intermittency is a universal property of the plasma turbulence, at least for the midlatitude upper ionosphere.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 1, pp. 22–30, January 2008. 相似文献
8.
T. Loarer E. Gravier J. Gunn J. L. Lachambre K. H. Finken M. Lehnen G. Mank S. Jachmich H. Van Goubergen G. Van Oost 《Czechoslovak Journal of Physics》2000,50(12):1441-1450
The superconducting tokamak Tore Supra will be equipped with an actively cooled toroidal pump limiter (TPL), in the framework
of the CIEL (Composants Internes Et Limiteurs) project, dedicated to plasma facing component design for steady state operation.
The TPL is equipped with throats, located only on the high field side, for particle collection allowing the control of plasma
density which is essential for long plasma discharges. The present design work of the CIEL includes a biasing system in order
to enhance the particle pumping. A fluid model, based on the classical fluid equation, is used to estimate the effects of
the electric field on the particle flows in the Scrape-Off Layer (SOL). The modifications of the density, the particle flow
(toroidal and poloidal) and the position of the stagnation point are discussed as a function of the bias voltage. The model
clearly illustrates the different resulting effects on particle pumping for a divertor and a limiter configuration which are
designed respectively for poloidal or parallel particle collection.
The model is used to interpret the ALT-biasing experiments recently carried out on TEXTOR-94. The pumping capability is shown
to be improved by about (15–20)% for positive biasing while the experimental measurements of parallel Mach number are reproduced
as a function of the applied voltage. The e-folding length of the edge density in the SOL is also shown to increase from 1.5
to about 2.0 cm for a biased voltage of −400 to 400 V, respectively, in accordance with the model. Finally, the model is used
to extrapolate the TEXTOR-94 results to CIEL suggesting that pumping speed enhancement of 25 to 30% may be obtained.
Partner in Trilateral Euregio Cluster
Partner in Trilateral Euregio Cluster
Presented at the Workshop on Role of Electric Fields in Plasma Confinement and Exhaust, Budapest, 18–19 June 2000. 相似文献
9.
We achieve the multifractal analysis of a class of complex valued statistically self-similar continuous functions. For we
use multifractal formalisms associated with pointwise oscillation exponents of all orders. Our study exhibits new phenomena
in multifractal analysis of continuous functions. In particular, we find examples of statistically self-similar such functions
obeying the multifractal formalism and for which the support of the singularity spectrum is the whole interval [0, ∞]. 相似文献
10.
We consider the problem of diagnostics of the local structure of small-scale ionospheric turbulence using the multifractal
analysis of received signals from the Earth’s orbital satellites after the radio sounding of the inhomogeneous ionosphere
by these signals. In particular, it is shown that analysis of the multifractal structure of the received-signal amplitude
records by the method of multidimensional structural functions allows one to determine the indices of the multipower local
spectra of the small-scale ionospheric turbulence, which are inherent in it due to the nonuniform spatial distribution of
small-scale fluctuations of the electron number density. It is noted that information on the multipower spectrum of small-scale
ionospheric turbulence is not available for the conventional radio scintillation method based on the classical spectral analysis
of received signals during the remote radio sounding of the ionosphere. At the same time, the method of multidimensional structural
functions is efficient under conditions of actual nonstationarity of the process of scattering of the HF radio waves by the
randomly inhomogeneous ionospheric plasma. The method of multidimensional structural functions is used for the multifractal
processing of received signals of orbital satellites during special experiments on radio sounding of the midlatitude ionosphere
under natural conditions and its modification by high-power HF radio waves. First data on the indices of the multipower local
spectra of small-scale ionospheric turbulence are obtained.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 52, No. 1, pp. 14–22, January 2009. 相似文献
11.
C. Silva B. Goncalves M. A. Pedrosa C. Hidalgo K. McCarthy E. Calderon J. Herranz I. Pastor O. Orozco 《Czechoslovak Journal of Physics》2005,55(12):1589-1596
Edge polarization experiments were carried out on TJ-II using an electrode. It has been found that the plasma response is
different at densities below and above the threshold value to trigger the spontaneously development of E × B sheared flows. At low densities, the edge plasma potential is fully controlled by external biasing, while at higher densities
it is determined not only by external biasing but also by the electric fields spontaneous developed. Although an improvement
in particle confinement is observed for both polarities, a larger increase is observed for negative electrode bias.
Presented at the Workshop “Electric Fields, Structures and Relaxation in Edge Plasmas”, Tarragona, Spain, July 3–4, 2005. 相似文献
12.
V. A. Alimov F. I.Vybornov E. N. Myasnikov A. V. Rakhlin V. L. Frolov 《Radiophysics and Quantum Electronics》2009,52(9):609-617
We present the results of the experiment on studying the multifractal structure (with inhomogeneity sizes from tens to hundreds
of meters across the Earth’s magnetic field) of the artificial ionospheric turbulence when the midlatitude ionosphere is affected
by high-power HF radio waves. The experimental studies were performed on the basis of the “Sura” heating facility with the
help of radio sounding of the disturbed region of the ionospheric plasma by signals from the Earth’s orbital satellites. The
influence of the magnetic zenith effect on measured multifractal characteristics of the small-scale artificial turbulence
of the midlatitude ionosphere was examined. In the case of vertical radio sounding of the disturbed ionosphere region, the
measured multipower and generalized multifractal spectra of turbulence coincide well with similar multifractal characteristics
of the ionospheric turbulence under natural conditions. This result is explained by the fact that the scattering of signals
by weak quasi-isotropic small-scale inhomogeneities of the electron number density in a thick layer with a typical size of
several hundred kilometers above the region of reflection of high-power HF radio waves gives the major contribution to the
observed amplitude fluctuations of received signals. In the case of oblique sounding of the disturbance region at small angles
between the line of sight to the satellite and the direction of the Earth’s magnetic field, the nonuniform structure of the
small-scale turbulence with a relatively narrow multipower spectrum and small variations in the generalized multifractal spectrum
of the electron number density was detected. Such a fairly well ordered structure of the turbulence is explained by the influence
of the magnetic zenith effect on the generation of anisotropic small-scale artificial turbulence in a thin layer having a
typical size of several ten kilometers and located below the pump-wave reflection height in the upper ionosphere. 相似文献
13.
Results of the investigation on the formation of double layers in double plasma device are presented. By appropriate modifications
in the biasing conditions, we have been able to obtain both weak (eΔφ<10KT
e
) and strong double layers (eΔφ>10kT
e
) in the device. Unlike previous experiments, we have not been limited to potential jumps equal to ionisation potential of
the neutral gas. A detailed investigation has been carried out to find out why earlier experiments in similar devices were
limited to only weak double layers.
We have also investigated the phenomenon of the so-called psuedo-double layers and have shown that they are potential jumps
over the thickness of the order of Debye length and precede plasma expanding with velocity many times the ion-acoustic velocity.
They do not represent metastable states of the plasma as suggested by earlier investigators. 相似文献
14.
Given a multifractal spectrum, we consider the problem of whether it is possible to recover the potential that originates
the spectrum. The affirmative solution of this problem would correspond to a “multifractal” classification of dynamical systems,
i.e., a classification solely based on the information given by multifractal spectra. For the entropy spectrum on topological
Markov chains we show that it is possible to have both multifractal rigidity and multifractal “nonrigidity”, by appropriately
varying the Markov chain and the potential defining the spectrum. The “nonrigidity” even occurs in some generic sense. This
strongly contrasts to the usual opinion among some experts that it should be possible to recover the potential up to some
equivalence relation, at least in some generic sense.
Supported by the Center for Mathematical Analysis, Geometry, and Dynamical Systems, through FCT by Program POCTI/FEDER and
the grant SFRH/BD/10154/2002. 相似文献
15.
M. Spolaore E. Martines J. Brotankova J. Stockel J. Adamek E. Dufkova I. Duran M. Hron V. Weinzettl P. Peleman G. Van Oost P. Devynck H. Figueiredo G. Kirnev 《Czechoslovak Journal of Physics》2005,55(12):1597-1606
In this paper we present the first experimental results obtained in the CASTOR tokamak by using a segmented biasing electrode,
which is composed of five segments radially separated by 3 mm. The basic idea of choosing such configuration was to allow
a spatial distribution of the biasing voltage in the radial direction. In the described experiments, one or more selected
segments can be biased up to +300V, while the remaining segments can be either grounded or floating. Two rake probes measure
the edge radial profiles of the floating potential and the ion saturation current at the top and low field side of the torus.
A Gundestrup probe, located at the top of the torus, measures the parallel and perpendicular Mach numbers together with the
local electron temperature and density. A clear and reproducible transition to a regime with improved particle confinement
is routinely observed, if the electrode is inserted deep enough into the plasma (r/a ≈ 0.5) and if one or two segments are biased up to +250V (the remaining segments are floating). The steepening of the radial
profiles of the plasma density and potential demonstrate the formation of a transport barrier just inside the last closed
flux surface. Fast relaxations of the edge profiles, with a frequency of about 10 kHz or higher, are observed when the value
of the average radial electric field within the barrier reaches values of about 20 kV/m and the density gradient increases
up to a factor 3 with respect to the ohmic phase. A detailed analysis of the spatial-temporal behavior of these relaxations
is presented.
Presented at the Workshop “Electric Fields, Structures and Relaxation in Edge Plasmas”, Tarragona, Spain, July 3–4, 2005. 相似文献
16.
The statistics of energy levels for a disordered conductor are considered in the critical energy window near the mobility
edge. It is shown that, if the critical wave functions are multifractal, the one-dimensional gas of levels on the energy axis
is compressible, in the sense that the variance of the level number in an interval is 〈 (δN)2〉∼χ〈N〉 for 〈N〉≫1. The compressibility, χ=η/2d, is given exactly in terms of the multifractal exponent η =d−D
2 at the mobility edge in a d-dimensional system.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 5, 355–360 (10 September 1996)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
17.
The analysis of the linearization effect in multifractal analysis, and hence of the estimation of moments for multifractal processes, is revisited borrowing concepts from the statistical physics of disordered systems, notably from the analysis of the so-called Random Energy Model. Considering a standard multifractal process (compound Poisson motion), chosen as a simple representative example, we show the following: (i) the existence of a critical order q∗ beyond which moments, though finite, cannot be estimated through empirical averages, irrespective of the sample size of the observation; (ii) multifractal exponents necessarily behave linearly in q, for q>q∗. Tailoring the analysis conducted for the Random Energy Model to that of Compound Poisson motion, we provide explicative and quantitative predictions for the values of q∗ and for the slope controlling the linear behavior of the multifractal exponents. These quantities are shown to be related only to the definition of the multifractal process and not to depend on the sample size of the observation. Monte Carlo simulations, conducted over a large number of large sample size realizations of compound Poisson motion, comfort and extend these analyses. 相似文献
18.
W. Jeżewski 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(1):133-138
Scaling properties of the Gibbs distribution of a finite-size one-dimensional Ising model are investigated as the thermodynamic
limit is approached. It is shown that, for each nonzero temperature, coarse-grained probabilities of the appearance of particular
energy levels display multiscaling with the scaling length ℓ = 1/M
n, where n denotes the number of spins and Mn is the total number of energy levels. Using the multifractal formalism, the probabilities are argued to reveal also multifractal
properties.
Received 10 July 2000 and Received in final form 6 November 2000 相似文献
19.
Using the method of radio sounding of the mid-latitude ionosphere by the satellite signals, we study the multifractal structure
of small-scale ionospheric turbulence during a solar eclipse. The measured multipower and generalized multifractal spectra
of small-scale ionospheric turbulence at the initial and closing stages of the eclipse turn out to be almost identical on
the space radio paths with different orientations. This is indicative of a sufficiently high stability of the nonuniform spatio-temporal
distribution of small-scale fluctuations of the ionospheric electron number density under conditions of geophysical disturbances
due to global physical processes in the ionospheric plasma during a solar eclipse.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 52, No. 4, pp. 302–306, April 2009. 相似文献
20.
P. Helander S. J. Fielding R. H. Cohen D. D. Ryutov 《Czechoslovak Journal of Physics》2000,50(12):1421-1430
It has been suggested that by electrically biasing the divertor tiles in a tokamak, one could create a toroidally-asymmetric
potential structure in the scrape-off layer (SOL) plasma. The resultingE×B convective motion should increase the plasma transport in the SOL and thereby reduce the heat load on the divertor plates.
This paper describes plans for such experiments on COMPASS-D and preliminary theoretical modelling. The COMPASS-D divertor
target consists of 24 graphite tiled toroidal segments. The inner and outer strike point tiles on all these segments will
be insulated from each other, and cabling will be installed to allow for biasing of individual tiles in any combination. Theoretical
analysis suggests that the electrostatic potential perturbations caused by the biasing will be confined to the divertor region
below the X-point, and that substantial SOL broadening can be achieved by applying modest voltages. Aside from active control
of SOL transport, it is hoped that the biasing will be useful to probe other divertor and SOL physics issues.
Presented at the Workshop on the Role of Electric Fields in Plasma Confinement and Exhaust, Budapest, 18–19 June, 2000.
This work was jointly funded by the UK Department of Trade and Industry and Euratom, and was supported by US DoE under contract
W-7405-ENG-48 at LLNL. 相似文献