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1
Content available A new method of determining the parameters of thermonuclear plasma on the basis of multichannel polarimetric measurements
Chrzanowski J., Kravtsov Y.A.
Nukleonika
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2013
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Vol. 58, No. 2
281--285
EN
A gradient method has been proposed as an effective procedure to reconstruct real parameters of tokamak plasma by means of multichannel polarimetric measurements. High efficiency of the suggested procedure is illustrated by numerical calculations performed for a given plasma model taking into account the poloidal component of magnetic field. Polarization state of electromagnetic wave traditionally is characterized by azimuthal – ψ and ellipticity – χ angles. Evolution of these parameters along the ray is described by the equations of angular variables technique (AVT) introduced in previous works of the present authors. Numerical simulations have approved that the gradient procedure provides acceptable accuracy of inversion already after several iterations.
2
Content available Unconventional procedure for inversion of polarimetric data: numerical calculation for a simple model of toroidal plasma
Chrzanowski J., Kravtsov , Y. A., Mazon D.
Nukleonika
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2012
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Vol. 57, No. 1
37-41
EN
A gradient method is proposed for inversion of polarimetric data for tokamak plasma. It is assumed that the electron density and the normalized magnetic profile along the ray are known from experiments (scattering and magnetic measurements) in the spirit of the EFIT approach. Under these assumptions the maximum value of the electron density and maximum value of the magnetic field may be estimated by the gradient method. It is shown that with this method it is possible to achieve accuracy of about 0.1% already after 3-4 iterations.
3
Content available Oscillations of the work function for thin metal layers
Chrzanowski J., Kravtsov Y. A.
Zeszyty Naukowe / Akademia Morska w Szczecinie
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2011
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nr 26 (98)
15-20
EN
The nonlocal potential and the nearest neighbor approximation (NNA) is used to obtain a simple analytical equation for the work function. In contrast to earlier approaches to the problem, the present treatment does not involve any extra coefficients. The work function is exactly defined function of the electron density n and screening parameter ks. What is more, the presented treatment allows to calculate changes of work function when the physical dimensions of metallic sample reduces to nanoscale.
PL
Nielokalny potencjał oraz przybliżenie "najbliższego sąsiada" (NNA) zostało wykorzystane do uzyskania prostego analitycznego wyrażenia na pracę wyjścia. W odróżnieniu od wcześniejszych metod prezentowany model nie zawiera żadnych dodatkowych parametrów. Praca wyjścia jest dokładnie zdefiniowaną funkcją gęstości elektronów n oraz parametru ekranowania ks. Co więcej, zaprezentowany model pozwala obliczyć zmiany pracy wyjścia, gdy rozmiary metalowej próbki redukują się do nanoskali.
4
Content available Numerical modeling of polarization effects in a plasma at the W7-X stellarator
Bieg B., Hirsch M., Kravtsov Y. A.
Zeszyty Naukowe / Akademia Morska w Szczecinie
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2011
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nr 26 (98)
5-9
EN
The interferometer-polarimeter in the stellarator W7-X will operate in the far infrared band in the double passage regime: the electromagnetic beam will be reflected back from a corner cube retroreflector and thus pass through the magnetized plasma twice. Evolution of the polarization state of the beam along the polarimeter sightline in the standard magnetic field configuration of W7-X is analyzed on the basis of differential equations, for traditional polarization parameters – azimuthal angle [psi] and ellipticity angle [chi]. The influence of the Faraday and the Cotton-Mouton phenomena on polarization parameters [psi] and [chi] are analyzed. Calculations are performed for different plasma densities. Finally the potential sources of inaccuracy are considered, such as the shift in the probing beam position.
PL
W interfero-polarymetrycznym systemie diagnostycznym stellaratora W7-X podczerwona wiązka pomiarowa ulega podwójnemu przejściu przez obszar namagnesowanej plazmy. Ewolucja stanu polaryzacji fali elektromagnetycznej, podczas jej propagacji w plazmie o standardowej konfiguracji pola magnetycznego, analizowana jest na podstawie równań różniczkowych, opisujących zmiany tradycyjnych parametrów polaryzacyjnych: kąta azymutu [psi] i kąta eliptyczności [chi]. Przeanalizowano wpływ zjawiska Faradaya i Cottona-Moutona na zmiany wartości parametrów [psi] i [chi] przy różnych gęstościach plazmy w stellaratorze. Zbadano również wpływ przesunięcia przestrzennego pozycji wiązki pomiarowej na obserwowane zmiany polaryzacji fali elektromagnetycznej.
5
Content available Modulation of weak Cotton-Mouton effect in conditions of strong Faraday rotation
Kravtsov Y. A., Chrzanowski J.
Zeszyty Naukowe / Akademia Morska w Szczecinie
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2011
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nr 26 (98)
47-51
EN
Evolution of polarization state is described by new mathematics, namely, by angular variables technique (AVT) which describes behavior of the angular parameters of polarization ellipse in magnetized plasma. From this point of view the polarization of electromagnetic waves in magnetized plasma is studied in conditions, when Cotton-Mouton effect is weak enough as compared with Faraday one. The method of consequent approximations is applied, which uses the ratio of Cotton-Mouton [omega], and Faraday [omega]3 parameters, as a small parameter of a problem and allows obtaining simple analytical expressions for ellipticity angles approximations.
PL
Przy pomocy nowego modelu matematycznego – techniki zmiennych kątowych (AVT), opisana jest ewolucja stanu polaryzacji z ukazaniem zachowania kątowych parametrów elipsy polaryzacji w namagnetyzowanej plazmie. Z tego punktu widzenia analizowany jest stan polaryzacji wiązki elektromagnetycznej w warunkach, gdy efekt Cottona-Moutona jest niewielki w porównaniu z efektem Faradaya. Zastosowana metoda kolejnych przybliżeń pozwala wykorzystać stosunek parametrów [omega] (Cotton-Mouton), oraz [omega]3 (Faraday), jako kolejny, mały parametr, pozwalający uzyskać proste analityczne wyrażenia dla kątów opisujących stan elipsy polaryzacji.
6
Content available Possible accuracy of the Cotton-Mouton polarimetry in a sheared toroidal plasma
Kravtsov , Y. A., Chrzanowski J.
Nukleonika
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2011
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Vol. 56, No. 2
175-177
EN
The Cotton-Mouton effect in the sheared plasma with helical magnetic lines is studied, using the equation for the complex amplitude ratio (CAR). A simple model for helical magnetic lines in plasma of toroidal configuration is suggested. Equation for CAR is solved perturbatively, treating the shear angle variations as a small perturbation, caused by the spiral form of the magnetic lines. It is shown that the uncertainty of the polarization measurements in the toroidal plasma with a spiral form of the magnetic lines does not exceed 1.0–2.0%, which determines the limiting accuracy of the Cotton-Mouton polarimetry. It is furthermore pointed out that the method of a priori subtraction of the “sheared” term may significantly improve the accuracy of the Cotton-Mouton polarimetry.
7
Content available Localized plasma polarimetry based on the phenomenon of normal mode conversion
Kravtsov , Y. A., Bieg B.
Nukleonika
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2011
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Vol. 56, No. 2
171-174
EN
A new geometry of microwave polarimetric measurements is presented, which realizes a localized plasma polarimetry based on the phenomenon of electromagnetic mode conversion. Such a conversion takes place in the tokamak plasma, in the vicinity of the point where the microwave beam is orthogonal to one of the helical magnetic lines. In distinction to the traditional plasma polarimetry, which deals with the line averaged plasma parameters, the new methodology allows for a measurement of the local values of plasma parameters near the point of orthogonality. This methodology was shown to be very efficient in studies of the solar radio emission and polarization properties of radio waves passing through the Earth ionosphere. In the following the theory of electromagnetic mode conversion is described and conditions of its applicability are analyzed. It is shown that localized polarimetric measurements of plasma parameters in the geometry of the international thermonuclear experimental reactor (ITER) device would require very high electron densities Ne, exceeding 1017 cm–3, i.e. thousand times higher than those envisaged in the ITER project.
8
Content available remote Propagation of electromagnetic waves in weakly anisotropic media: Theory and applications
Kravtsov Y. A., Bieg B.
Optica Applicata
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2010
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Vol. 40, nr 4
975--989
EN
Quasi-isotropic approximation (QIA) of geometrical optics is outlined, which describes properties of electromagnetic waves in weakly anisotropic media, including weakly anisotropic fibers, liquid crystals and weakly magnetized plasma. QIA equations stem directly from the Maxwell equations and have the form of coupled differential equations of the first order for transverse components of the electromagnetic field. Being applied to magnetized plasma, QIA describes combined action of Faraday and Cotton-Mouton phenomena and serves as a theoretical background of plasma polarimetry in FIR and microwave bands. The coupled equations of QIA can be reduced to a single equation for complex polarization angle (CPA), which characterizes all the parameters of polarization ellipse. At the same time, the equation for CPA allows obtaining equations for evolution of the traditional parameters of polarization ellipse. Besides, QIA makes it possible to derive in a consistent way Segre's equation for the Stokes vector evolution, which is widely used in microwave and FIR plasma polarimetry.
9
Content available remote Gaussian beam diffraction in inhomogeneous media of cylindrical symmetry
Berczyński P., Kravtsov Y. A., Żegliński G.
Optica Applicata
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2010
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Vol. 40, nr 3
705--718
EN
The method of paraxial complex geometrical optics (PCGO) is presented, which describes Gaussian beam (GB) diffraction in smoothly inhomogeneous media of cylindrical symmetry, including fibers. PCGO reduces the problem of Gaussian beam diffraction in inhomogeneous media to the system of the first order ordinary differential equations for the complex curvature of the wave front and for GB amplitude, which can be readily solved both analytically and numerically. As a result, PCGO radically simplifies the description of Gaussian beam diffraction in inhomogeneous media as compared to the numerical methods of wave optics. For the paraxial on-axis Gaussian beam propagation in inhomogeneous fibers, we compare PCGO solutions with numerical results for finite differences beam propagation method (FD-BPM). The PCGO method is shown to provide over 100-times higher rate of calculation than FD-BPM at comparable accuracy. This paper presents PCGO analytical solutions for width evolution of cylindrically symmetric GB in quadratic graded-index fiber, which is obtained in less complicated way comparing to the methods of wave optics. Besides, the influence of initial curvature of the wave front on GB evolution in graded-index fiber is discussed in this paper.
10
Content available Układ ultradźwiękowy do pomiaru zmiennych naprężeń w kadłubach statków
Bobrowski Z., Chmiel J., Dorobczyński L., Kravtsov Y. A.
Zeszyty Naukowe / Akademia Morska w Szczecinie
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2004
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nr 1 (73)
57-66
PL
Zaproponowano samodrgający układ akustyczny do ciągłego monitorowania deformacji w kadłubach statków. Układ korzysta z ultradźwięków o dość wysokiej (rzędu 1 MHz) częstotliwości, wzbudzających materiał kadłuba. Zmiany naprężeń objawiają się w małych, ale mierzalnych zakresach częstotliwości drgań. Zastosowany układ może być używany do monitorowania zmiennych naprężeń w kadłubach statków w warunkach silnego falowania, również podczas załadunku statku.
EN
A self-oscillating ultrasonic system is suggested for monitoring deformations in ship hulls. The system employs high frequency (about 1 MHz) ultrasounds exciting the hull material. Stress changes manifest themselves in small but detectable variations of frequency in the self-oscillating system. The suggested system can be applied for continuous stress changes monitoring in high seas as well as in nearly fully laden ship conditions.
11
Content available remote Range dependent radiation leakage from thin scattering columns due to multiple small angle scatter
Kravtsov Y. A., Apresyan L. A., Asatryan A. A., Chrzanowski J., Kirkiewicz J.
Optica Applicata
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2003
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Vol. 33, nr 2-3
293-305
EN
The phenomenon of range dependent radiation leakage from thin random columns caused by small angle multiple scatter is analysed. On the basis of modified Born approximation (Ishimaru, 1978; Apresyan and Kravtsov, 1996), it is shown that extinction coefficient, describing energy leakage due to multiple scatter on large (as compared to wavelength) inhomogeneities, first increases proportionally to distance z1/2 and then saturates on the level which might significantly exceed conventional extinction coefficient, connected with large angle light scatter on small inhomogeneities. The effect might be observed in many physical systems, for example, in a tube filled with water emulsion or suspension, containing small and large particles. The phenomenon may be helpful in distinguishing the contribution of small and large inhomogeneities to total extinction
12
Content available remote Rola rezonansowego i nierezonansowego odbicia mikrofal od powierzchni morza w tworzeniu obrazów radarowych
Kravtsov Y. A.
Zeszyty Naukowe / Wyższa Szkoła Morska w Szczecinie
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2002
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nr 67
97-107
PL
Opisano główne mechanizmy odbicia mikrofal od powierzchni morza: tradycyjny rezonansowy (braggowski) mechanizm, leżący w gruncie ogólnie uznanego dwuskalowego modelu powierzchni morskiej I niedawno opracowany nierezonansowy mechanizm, związany z istnieniem na powierzchni morza stromych spadających fal mezoskalowej długości. W połączeniu z dwuskalowym modelem nierezonansowy mechanizm doprowadza do trójskalowego modelu powierzchni morskiej, który zdoła wyjaśnić znacznie większy zakres zjawisk, niż dwuskalowy model.
EN
The basic mechanisms for microwave scattering at the sea surface are described: traditional resonant (Bragg) mechanism underlying commonly accepted two-scale model of the sea surface, and recently revealed nonresonant mechanism connected with steep and breaking waves of mesoscale spectrum. Being combined with two-scale model nonresonant mechanism leads to three-scale model of the sea surface which is able to uniformly explain much more wide circle of phenomena than two-scale one.
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