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Dense Plasma (dense + plasma)
Selected AbstractsQuantum-Statistical Equation-of-State Models of Dense Plasmas: High-Pressure Hugoniot Shock AdiabatsCONTRIBUTIONS TO PLASMA PHYSICS, Issue 6 2007J. C. Pain Abstract We present a detailed comparison of two self-consistent equation-of-state models which differ from their electronic contribution: the atom in a spherical cell and the atom in a jellium of charges. It is shown that both models are well suited for the calculation of Hugoniot shock adiabats in the high pressure range (1 Mbar-10 Gbar), and that the atom-in-a-jellium model provides a better treatment of pressure ionization. Comparisons with experimental data are also presented. Shell effects on shock adiabats are reviewed in the light of these models. They lead to additional features not only in the variations of pressure versus density, but also in the variations of shock velocity versus particle velocity. Moreover, such effects are found to be responsible for enhancement of the electronic specific heat. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magnetohydrodynamic Simulation of Tungsten Wire in Wire-Array Z PinchCONTRIBUTIONS TO PLASMA PHYSICS, Issue 2 2010D.-K. Kim Abstract The magnetohydrodynamic behavior of tungsten wire ablating in wire-array Z pinch discharge on MAGPIE is simulated in a two-dimensional fine-grid domain using the GORGON code. A nonideal resistivity model has been implemented in the simulation to obtain plasma transport coefficients in the high density regime along with a screened hydrogenic model to calculate the radiative cooling. Starting from the initial state of warm dense plasma, the evolution of ablated wire is demonstrated to show its explosion and implosion dynamics as a function of discharge time and then the computed profile of electron density is compared with the contour lines reproduced from the measurement by a laser interferometer during the early stage of discharge. The comparison overall shows a fair agreement in terms of the magnitude and the profile shape while some discrepancies can be attributed to the simplified description of the internal wire core physics (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Blob Transport in the Tokamak Scrape-off-LayerCONTRIBUTIONS TO PLASMA PHYSICS, Issue 1-3 2004D. A. D'Ippolito Abstract Recent experimental evidence suggests the importance of fast radial plasma transport in the scrape-off-layer (SOL) of tokamaks. The outward transport appears to be convective rather than diffusive, extends into the far SOL, and can produce significant recycling from the main-chamber walls, partially bypassing the divertor. A plausible theoretical mechanism to explain this phenomenon is the radial transport of "blobs" of locally dense plasma created by turbulent processes. A related process is the inward transport of "holes" of reduced density plasma, which provides a mechanism for rapid inward transport of impurities. The blob model is also consistent with the spatial and temporal intermittency and the non-Gaussian statistics observed in the SOL plasma. This paper reviews the present status of blob theory, including analytic models and simulations, and discusses the preliminary comparisons of the blob model with experimental data. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A high-resolution radio survey of Class I protostarsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2000P. W. Lucas We report the results of a survey of low-mass Class I protostars in the cm continuum. In the initial survey, seven sources in the Taurus star formation region were observed with the VLA at 0.25-arcsec resolution. All seven sources drive CO outflows and display Herbig,Haro flows in the optical or near-infrared (NIR) wavebands. Four out of seven sources were detected, two of which are new discoveries in systems of very low luminosity, one being the lowest luminosity system detected to date in the cm continuum. Notably, three sources were not detected to a 3, limit of 0.10 mJy/beam, which indicates that significant cm continuum emission is not a universal feature of Class I systems with outflow activity. Subsequent observations of HH30, a more evolved Class II system, found no emission to a 3, limit of 0.03 mJy/beam. After comparison with near infrared data, we suggest that the discriminating feature of the detected systems is a relatively high ionization fraction in the stellar wind. Temporal variability of the outflow may also play a role: only recently ejected knots may have sufficiently dense plasma to be optically thick to free,free emission, and hence produce detectable flux. The one relatively bright source, IRAS 04016+2610 (L1489 IRS), is clearly resolved on a 0.4-arcsec scale at 2 and 3.5 cm. Additional imaging with MERLIN did not detect this source with a 0.04-arcsec beam, indicating that the radio emission is generated in a region with a radius of ,25 au, which is broadly similar to the radius of the bipolar cavities inferred from models of NIR data. Interpretation of this system is complicated by the existence of a quadrupolar outflow, i.e. two bipolar outflows along roughly perpendicular axes, which we originally detected through polarimetric imaging. We present an NIR H2 image in which a bow shock in the secondary outflow is clearly seen. This complicated structure may have been caused by a gravitational interaction between two protostars. [source] Composition of Partially Ionized Systems Using the PlanckLarkin Partition Function of Mid-Z ionsCONTRIBUTIONS TO PLASMA PHYSICS, Issue 10 2009A. Sengebusch Abstract We report on the composition of warm, dense plasmas of M-shell ions. Assuming local thermal equilibrium, the abundance of different ionization stages is given by a set of coupled Saha-equations. In order to avoid discontinuities at the Mott density, the partition functions have to account for pressure ionization due to continuum lowering consistently. The Planck-Larkin renormalization of bound and scattering states is well elaborated for hydrogenic systems. This paper shows the consistent extension to moderately ionized Mid-Z elements. We present results for solid-density polymere and titanium plasmas (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Density Diagnostic Using Stark Broadening of He I Spectral Line Emission from Rydberg LevelsCONTRIBUTIONS TO PLASMA PHYSICS, Issue 7-9 2006M. Koubiti Abstract Neutral helium line spectra of the diffuse series observed under recombining plasma conditions, are used for electron density diagnostics. The method is similar to that using high members of the Balmer series of hydrogen or its isotopes. It is based on the comparison of experimental line spectra to calculated Stark profiles obtained with the Stark line shape code PPP. Among the required atomic data, the dipole reduced matrix elements have been calculated using a hydrogenic approximation. A good agreement was found between the behaviors of the Einstein coefficients calculated using this approximation and the available corresponding values found in the literature. It is demonstrated here through its application to JET data that for relatively dense plasmas this method gives promising results which are consistent with other measurements. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Pressure Ionization and Transitions in Dense HydrogenCONTRIBUTIONS TO PLASMA PHYSICS, Issue 3-4 2005W. Ebeling Abstract Shock experiments with fluid hydrogen have shown that a transition from insulating behavior to metal-like conductivity occurs at pressures beyond 100 GPa. This requires the development of new methods to describe the transition region of dense plasmas. The traditional approach due to Saha is based on the assumption of chemical equilibrium between charged and neutral components. This is equivalent to minimizing the free energy with respect to the composition. Here we improve an expression for the free energy developed recently to determine Hugoniot curves and isentropes in dense hydrogen and deuterium plasma in the regions of partial dissociation and partial ionization. We show that at high pressures the influence of the excluded volume occupied by neutral species is crucial for the transition to full ionization. We present curves for several thermodynamic functions for the region 5000 K < T < 20000 K and 0.6 g/cm3 < , < 1 g/cm3. The influence of the effective radii of the neutral species is crucial in the transition region. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||