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Radiation Losses (radiation + loss)
Selected AbstractsStabilization of Radiation-Condensation Instability by Light Impurity InjectionCONTRIBUTIONS TO PLASMA PHYSICS, Issue 3-5 2010A. A. Pshenov Abstract As it has been shown in [1,2], Radiation-Condensation Instability (RCI) may initiate Microfaceted Asymmetric Radiation from the Edge (MARFE) in tokamaks (see also review papers [3-5]). Nevertheless, experiments demonstrate the stable regimes with strongly radiated edge plasmas after Ne injection [6-8] or in siliconized discharges. Two effects destabilize radiative plasmas, the decrease of radiation losses Q with the electron temperature Te increase, and the increase of Q with electron and impurity densities rise. The finite relaxation time of impurity distribution over ionization states [6] as well as the thermal force acting on the growth rate doesn't shift the instability margin. Hence, one can examine the stability margin using the approximation of the coronal equilibrium. Radiation losses of intrinsic impurities like beryllium, carbon and nitrogen usually decrease with the temperature increase at the temperature range typical for the edge (see Fig. 1, curve 1). The situation may be significantly different for impurity mixtures. Radiation losses L , Q /(nenI)normalized by electron and impurity densities ne and nI for the mixture of carbon and neon are shown in Fig. 1, curves 2-5. One can see that ,Q/,T > 0 for practically any temperature at the edge if the concentration ratio nNe/nC , 5. Hence, one can expect the stabilization of RCI by injection of additional impurity and achievement of stable regime with the strongly radiated edge plasmas. The stability of plasmas with few impurity mixtures is examined in the present paper numerically (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Meta-structured one-unit-cell epsilon negative antennaMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 12 2009Seongnam Jang Abstract This Letter presents a metamaterial-based compact one-unit-cell epsilon negative zeroth-order resonant antenna designed on a microstrip line. The size of the proposed antenna is only 7.85 mm × 18 mm (or 0.05,0 × 0.12,0) at 1.79 GHz owing to zeroth-order resonance. Closed-form design equations for the proposed antenna are provided based on the equivalent circuit employing transmission line theory considering radiation loss. The return losses based on circuit/EM simulations and measurement are in excellent agreement. The measured antenna bandwidth is 17 MHz (about 1%) and total gain is 2.6 dBi. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2991,2994, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24751 [source] Turbulent Dynamics of Beryllium Seeded Plasmas at the Edge of TokamaksCONTRIBUTIONS TO PLASMA PHYSICS, Issue 3-5 2010R.V. Shurygin Abstract Numerical simulation of turbulent MHD dynamics of beryllium seeded plasmas at the edge of tokamaks is performed. The model is based on the 4-fluid {,, n, pe, pi } reduced nonlinear Braginsky's MHD equations. Neutral hydrogen flow from the wall is described with a diffusion model. Beryllium line radiation is taken into consideration. The Be ion distribution over ionization states is calculated using the reduced model. Electron impact ionization, three body, photo- and dielectronic recombination and charge-exchange with neutral hydrogen are taken into account. Coronal equilibrium is not supposed. Simulations are performed for T-10 parameters. Radial distributions of averaged temperatures and their fluctuation levels, species flows, impurity radiation power, and impurity ions concentrations are obtained as functions of the Be concentration at the wall. The impurity radiation is shown to act on the turbulent oscillation level significantly if the total Be concentration at the wall exceeds 3 · 1011cm,3. The impurity turbulent transversal flow is directed inward and exceeds neoclassical flow significantly. The parallel conductivity and, as a consequence, turbulent transport are increased significantly by impurity radiation. The radiation loss dependence on the neutral Hydrogen concentration at the wall is also examined. The hydrogen concentration increasing the plasma density also rises. The relative beryllium concentration decreases. In total, these two effects are compensated, and the level of radiation losses is changed insignificantly (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Reduced Models of Impurity Seeded Edge PlasmasCONTRIBUTIONS TO PLASMA PHYSICS, Issue 1-3 2008D. Kh. Abstract The reduced descriptions of the distribution of impurities over ionization states, radiation losses and plasma dynamics are reviewed. Two and three most important ion approximation for light impurities and continuous descriptions of heavy impurities are discussed. Reduced descriptions of atomic processes like ionization, photo- and dielectronic recombination rates as well as of radiation abilities are proposed. As it shown, thermal forces, final relaxation times of impurity distributions over ionization states, charge-exchange and opacity effects must be taken into account in reduced models, especially for ITER problems. Linear and nonlinear stages of the radiation-condensation mode as well as some aspects of disruptions and noble gas injection into tokamak plasmas are analyzed with the reduced models. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Plasma Edge Physics with B2-EireneCONTRIBUTIONS TO PLASMA PHYSICS, Issue 1-2 2006R. Schneider Abstract The B2-Eirene code package was developed to give better insight into the physics in the scrape-off layer (SOL), which is defined as the region of open field-lines intersecting walls. The SOL is characterised by the competition of parallel and perpendicular transport defining by this a 2D system. The description of the plasma-wall interaction due to the existence of walls and atomic processes are necessary ingredients for an understanding of the scrape-off layer. This paper concentrates on understanding the basic physics by combining the results of the code with experiments and analytical models or estimates. This work will mainly focus on divertor tokamaks, but most of the arguments and principles can be easily adapted also to other concepts like island divertors in stellarators or limiter devices. The paper presents the basic equations for the plasma transport and the basic models for the neutral transport. This defines the basic ingredients for the SOLPS (Scrape-Off Layer Plasma Simulator) code package. A first level of understanding is approached for pure hydrogenic plasmas based both on simple models and simulations with B2-Eirene neglecting drifts and currents. The influence of neutral transport on the different operation regimes is here the main topic. This will finish with time-dependent phenomena for the pure plasma, so-called Edge Localised Modes (ELMs). Then, the influence of impurities on the SOL plasma is discussed. For the understanding of impurity physics in the SOL one needs a rather complex combination of different aspects. The impurity production process has to be understood, then the effects of impurities in terms of radiation losses have to be included and finally impurity transport is necessary. This will be introduced with rising complexity starting with simple estimates, analysing then the detailed parallel force balance and the flow pattern of impurities. Using this, impurity compression and radiation instabilities will be studied. This part ends, combining all the elements introduced before, with specific, detailed results from different machines. Then, the effect of drifts and currents is introduced and their consequences presented. Finally, some work on deriving scaling laws for the anomalous turbulent transport based on automatic edge transport code fitting procedures will be described. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] J-aggregation visualized with two-photon-resonant third-harmonic generationJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2003D. A. Akimov Abstract Third-harmonic generation (THG) with a two-photon-absorption (TPA) type resonance was used to monitor the J-aggregation of ethyl thiacarbocyanine in aqueous solution. Correlations between TPA-resonant THG and two-photon-excited photoluminescence are revealed, indicating the significance of excited states for non-linear-optical processes in J-aggregating solutions. Similar to Raman resonances in coherent anti-Stokes Raman scattering, TPA resonances in THG allow THG enhancement to be effectively decoupled from the growth of radiation losses. Copyright © 2003 John Wiley & Sons, Ltd. [source] Non-local thermodynamic equilibrium dust nucleation in subsaturated vapoursMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008Davide Lazzati ABSTRACT We use the kinetic theory of nucleation to explore the properties of dust nucleation in subsaturated vapours. Due to radiation losses, the subcritical clusters have a smaller temperature compared to their vapour. This alters the dynamical balance between the attachment and detachment of monomers, allowing for stable nucleation of grains in vapours that are subsaturated for their temperature. We find this effect particularly important at low densities and in the absence of a strong background radiation field. We find new conditions for stable nucleation in the n,T phase diagram. The nucleation in the non-local thermodynamic equilibrium (non-LTE) regions is likely to be at much slower rate than in the supersaturated vapours. We evaluate the nucleation rate, warning the reader that it does depend on poorly substantiated properties of the macro-molecules assumed in the computation. On the other hand, the conditions for nucleation depend only on the properties of the large stable grains and are more robust. We finally point out that this mechanism may be relevant in the early Universe as an initial dust pollution mechanism, since once the interstellar medium is polluted with dust, mantle growth is likely to be dominant over non-LTE nucleation in the diffuse medium. [source] The white dwarf in AE Aqr brakes harderMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006Christopher W. Mauche ABSTRACT Taking advantage of the very precise de Jager et al. optical white dwarf orbit and spin ephemerides; ASCA, XMM,Newton and Chandra X-ray observations spread over 10 yr; and a cumulative 27-yr baseline, we have found that in recent years the white dwarf in AE Aqr is spinning down at a rate that is slightly faster than predicted by the de Jager et al. spin ephemeris. At the present time, the observed period evolution is consistent with either a cubic term in the spin ephemeris with , which is inconsistent in sign and magnitude with magnetic dipole radiation losses, or an additional quadratic term with , which is consistent with a modest increase in the accretion torques spinning down the white dwarf. Regular monitoring, in the optical, ultraviolet and/or X-rays, is required to track the evolution of the spin period of the white dwarf in AE Aqr. 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