Low-density Vapor Research Articles

RACLETTE: a model for evaluating the thermal response of plasma facing components to slow high power plasma transients. Part II: Analysis of ITER plasma facing components

The transient thermal model RACLETTE (acronym of Rate Analysis Code for pLasma Energy Transfer Transient Evaluation) described in part I of this paper is applied here to analyse the heat transfer and erosion effects of various slow (100 ms-10 s) high power energy transients on the actively cooled plasma facing components (PFCs) of the International Thermonuclear Experimental Reactor (ITER). These have a strong bearing on the PFC design and need careful analysis. The relevant parameters affecting the heat transfer during the plasma excursions are established. The temperature variation with time and space is evaluated together with the extent of vaporisation and melting (the latter only for metals) for the different candidate armour materials considered for the design (i.e., Be for the primary first wall, Be and CFCs for the limiter, Be, W, and CFCs for the divertor plates) and including for certain cases low-density vapour shielding effects. The critical heat flux, the change of the coolant parameters and the possible severe degradation of the coolant heat removal capability that could result under certain conditions during these transients, for example for the limiter, are also evaluated. Based on the results, the design implications on the heat removal performance and erosion damage of the variuos ITER PFCs are critically discussed and some recommendations are made for the selection of the most adequate protection materials and optimum armour thickness.

Dynamic Selective Reflection from a Low-Density Atomic Vapor

The dynamics of selective reflection when atomic vapor density is modulated are studied. In our theoretical work, we found a new type of light emission in selectively reflected light, which differs from that of ordinary selective reflection. It is understood to be backscattering from a moving dynamic grating created in density-modulated atomic vapor. Experimentally, the dynamics of the selective reflection are studied by analyzing the intensity spectrum of the reflected light intensity.

Erosion lifetime of ITER divertor plates

For ITER divertor operation in the detached regime, erosion of divertor plates made of beryllium, carbon fibre composites and tungsten-rhenium alloys is evaluated. Erosion due to (a) physical and, for CFC, chemical sputtering (including surface temperature variation over the lifetime because of neutron irradiation), (b) disruption thermal quench using published data and (c) evaporation and melt layer loss (metals) for infrequent high-power transients (20 MW/m 2, up to 10 s) is evaluated both with and without the reduction of net incident power by radiation from the evaporated impurities (‘low density vapour shield’). The composite lifetime is calculated for normal operation (detached, 10% transients, 10% disruptions); the effect of an increase in transient frequency and in incident power (semi-attached operation) is determined. The resulting erosion lifetime excludes beryllium, whereas both CFC and W-3%Re yield acceptable lifetimes.

Lorentz-Lorenz shift in an inhomogeneously broadened medium

A simple calculation shows that the Lorentz-Lorenz shift due to the local field correction remains significant in situations where the inhomogeneous broadening of a medium exceeds the homogeneous broadening. As an illustration, the calculated selective reflection signals of a low-density atomic vapor are presented, and it is shown that the Lorentz-Lorenz shift persists in the case where the line width is predominantly determined by the inhomogeneous Doppler width.

Stochastic equations of motion for epitaxial growth.

We report an analytic derivation of the Langevin equations of motion for the surface of a solid that evolves under typical epitaxial-growth conditions. Our treatment begins with a master-equation description of the microscopic dynamics of a solid-on-solid model and presumes that all surface processes obey Arrhenius-type rate laws. Our basic model takes account of atomic deposition from a low-density vapor, thermal desorption, and surface diffusion. Refinements to the model include the effects of hot-atom knockout processes and asymmetric energy barriers near step edges. A regularization scheme is described that permits a (nonrigorous) passage to the continuum limit when the surface is rough. The resulting stochastic differential equation for the surface-height profile generically leads to the behavior at long length and time scales first described by Kardar, Parisi, and Zhang [Phys. Rev. Lett. 56, 889 (1986)] (due to desorption). If evaporation is negligible, the asymptotic behavior is characteristic of a linear model introduced by Edwards and Wilkinson [Proc. R. Soc. London, Ser. A 381, 17 (1982)] (due to asymmetric step barriers and/or knockout events). If the latter are absent as well, the surface roughness is determined by an equation independently analyzed by Villain [J. Phys. I 1, 19 (1991)] and Lai and Das Sarma [Phys. Rev. Lett. 66, 2348 (1991)] (which includes only deposition and site-to-site hopping). The consequences of reflection-symmetry breaking in the basic microscopic processes are discussed in connection with step-barrier asymmetry and Metropolis kinetic algorithms.

Equation of state of compressed liquids: statistical-mechanical basis

Abstract Recent advances in the statistical-mechanical theory of equilibrium fluids can be used to obtain an equation of state for compressed liquids, thereby supplying a theoretical basis for a century of empiricism. The empirical results, dating back to P.G. Tait, essentially state that the isothermal bulk modulus (reciprocal of the isothermal compressibility) of a liquid is nearly linear in the pressure, with the slope being a function of temperature only. The present theory includes supercritical fluids and low-density vapors, and so gives more complicated mathematical expressions than the empirical formulas, but the numerical results are almost the same. This point is illustrated for both computer simulations and real fluids. The theory shows that supercritical fluids do not approach liquid-like behavior until the pressure is roughly 50 times the critical pressure.

EXAFS Measurements for Dense Vapors of Chalcogens and Chalcogenides

We have measured the EXAFS spectra of dense Se vapor in the temperature-pressure range up to 1600°C and 150 bar. For the measurements we have developed a high-pressure vessel and a polycrystalline sapphire cell of our own design. We have found that dense Se vapor under the present experimental condition consists mainly of Se2. The bond length is much shorter than that of liquid Se, and nearly the same as the data for Se2 in low-density vapor Se obtained by the recent spectroscopic study. When the saturated vapor-pressure curve is approached, the bond is elongated. We have also measured the EXAFS spectra of vapor Te and AsS. We have found the bond length of the molecule in vapor Te is nearly equal to that for Te2 obtained from the spectroscopic data. The structural parameters of the molecules in vapor AsS is similar to those of cagelike AS4S4 molecules in the crystal with a monoclinic form.

Statistical-mechanical basis for accurate analytical equations of state for fluids

Abstract Theories of liquids have been developed over the past twenty years based on the recognition that the structure of a liquid is determined primarily by repulsive forces, so that fluids of hard bodies (spherical or nonspherical) can serve as useful reference states for perturbation theories. We show how these results can be extended to obtain simple analytical equations of state for real fluids, which include the low-density vapor and the supercritical fluid as well as the true liquid. These equations are quintic in the density (the van der Waals equation is cubic), and are very accurate (parts per thousand to a few percent in the density for nonpolar fluids). They are first-principles equations in the sense that the entire fluid p-v-T surface can be calculated if the intermolecular potential is known, but they can be used with much less input information. Because the parameters of the equations of state that depend only on the repulsion are insensitive to the detailed shape of the potential, knowledege of just the second virial coefficient as a function of temperature is sufficient to construct the p-v-T surface. Examples are given for a selection of fluids, including Ne, CH4 CO2, and H2O.

Transverse optical bistability and formation of transverse structures in a sodium-filled Fabry-Pérot resonator.

We report the observation of transverse optical bistability (TOB) in a sodium-filled Fabry-P\'erot resonator, pumped by circularly polarized light, nearly resonant with the ${\mathit{D}}_{1}$ line, in the presence of a buffer gas, for low vapor density. A sequence of circularly symmetric patterns, ascribable to superpositions of resonator modes, is obtained. The appearance of TOB can be explained in terms of a self-induced intensity-dependent lens formed in the medium by the interaction with the laser light. A simple model that considers the transverse diffusion of the atoms inside the cell provides predictions in good qualitative agreement with the observations.

Hydrocarbon-bearing fluid inclusions in fluorite associated with the Windy Knoll bitumen deposit, UK

Hydrocarbon-bearing fluid inclusions in fluorite, associated with an outcropping bitumen deposit at Windy Knoll, Derbyshire, have been analysed in situ using a combination of microthermometry, Fourier transform infrared (FTIR) microspectrometry, and ultraviolet (UV) microscopy. The inclusions in these samples can be considered as a series with two endmembers: aqueous inclusions containing a low-density vapour phase and inclusions containing liquid “oil” with no detectable aqueous phase. The majority of the inclusions are mixed types containing both aqueous and liquid hydrocarbon phases. Although microthermometry distinguishes at least two different aqueous fluids with varying homogenization temperatures and salinities, the oil fraction is cogenetic and trapped together with just one fluid, a low-salinity, low-calcium brine with an average homogenization temperature of 134°C. The majority of the liquid hydrocarbon-bearing inclusions fluoresce bright blue under UV illumination with peaks around 475 nm, characteristic of paraffinic oils. The FTIR spectra of these inclusions are dominated by peaks assigned to aliphatic C—H bonding. However, inclusions have also been found which display a fluorescence typical of the red-shift associated with less mature oils. The FTIR spectra display peaks assigned to CO, C—O, and O—CH 2 bonding. This study presents new data on the in-situ analysis of hydrocarbon-bearing fluid inclusions from this important area of natural petroleum seepage and ore mineralization. The results suggest a direct link between the fluid inclusion populations, the outcropping bitumens, and fluorite deposition.

An infrared study of water vapour in the temperature range 573–723 K. Dimerization enthalpy and absorption intensities for monomer and dimer

A high-temperature high pressure cell with changeable path length was used to obtain the integrated intensities of the low density vapour in the spectral region λ = 2·7 μm along four isotherms in the range from 573 to 723 K. A linear dependence of the intensity was observed and interpreted in terms of the ‘monomer-dimer’ equilibrium. A dimerization enthalpy of 16·65 ± 3·77 kJ mol-1 has been found using the Arrhenius behaviour of the intensity isotherms. All isotherms intersect at zero pressure giving the total integrated intensity 54·92 ± 0·5 km mol-1. Rough estimation of the total intensity for the water dimer gives 318 ± 120 km mol-1.

Compressibility of liquids: Theoretical basis for a century of empiricism

We show how the successful empirical results of the past century for the compressibility of liquids can be obtained from a recent statistical-mechanical theory that includes dense fluids as well as low-density gases and vapors. The theory also shows to what extent the results for liquids can be extended to dense supercritical fluids and how they can be generalized to any number of dimensions. For simplicity only argon and a Lennard-Jones (12,6) fluid are examined in detail, but the results can probably be extended to real molecular fluids.

The role of metamorphic fluids in the development of the Cornubian orefield: fluid inclusion evidence from south Cornwall

AbstractVeins developed during contact metamorphism associated with the emplacement of the Cornubian granite batholith contain both H2O-rich and CO2-rich fluid inclusions. Microthermometric data indicate that unmixing of a low-CO2, low-salinity fluid occurred at 400–200°C and 1000–500 bars to produce low-density CO2-rich vapour and saline aqueous fluids (8–42 wt. % NaCl equivalent). Decrepitation-linked ICP analyses show that the cation composition of the brines is dominated by Na, K and Ca, but that significant amounts of Li, Sr, Ba, Fe, Mn, Zn and B are also present. Bulk volatile analyses confirm the dominance of CO2 over N2 and CH4 in the vapour phase, with CO2/N2 molar ratios of 15.3–28.7 and CO2/CH4 molar ratios of 66.9–292. The relative abundance of nitrogen suggests an aureole-derived ‘organic’ component is present.The source of the fluids is ambiguous as they are intermediate in composition between ideal ‘magmatic’ and ‘metamorphic’ end-members. It is proposed that this is due to mixing of the two types of fluid in the contact aureole during granite intrusion. A model is suggested in which magmatic-metamorphic circulation occurred synchronously with granite emplacement and subsequently evolved to a meteoric-dominated system with the bulk of the ore deposits forming in response to the influx of meteoric fluids.

Wall and aerosol condensation during cooled laminar tube flows

The equations for heat and mass transfer in laminar flow are presented and their solutions are considered in the limit of low vapor density and constant thermodynamic properties. Simple ways of determining the maximum and minimum possible wall condensation are discussed. Numerical calculations between these limits are performed by orthogonal collocation. For dibutyl phthalate vapor in air, latent heat release is negligible and most of the vapor condenses das aerosol. New results are presented for water vapor, including the effects of latent heat. Water aerosol growth is inhibited due to latent heat release and most of the vapor condenses on the wall. Also, water droplets near the tube axis may evaporate, due to the large diffusion rate of water molecules to the wall.

A fluid inclusion and stable isotope study of synmetamorphic copper ore formation at Mount Isa, Australia

Earlier structural studies indicate that the dolomitic and siliceous breccias and contained copper mineralization at Mount Isa (Queensland, Australia) formed during regional deformation and greenschist facies metamorphism of their host mid-Proterozoic metasediments. The metasomatic breccia body (locally called silica dolomite) is zoned, with an outer halo of sparry dolomitic alteration replacing finely laminated dolomitic-pyritic metasediments. The core of the dolomitic breccia next to the underlying altered greenstones is overprinted by siliceous breccia containing the bulk of the chalcopyrite ore.Fluid inclusions in quartz and dolomite were studied by microthermometry, micro-Raman spectrometry, and semiquantitative electron microprobe analysis of inclusion salts. Two types of aqueous inclusions are restricted to dolomitic breccia: CaCl 2 -rich (group 1) with a cation ratio Na/Ca/K/Mg nearly equal 30:10:3:1 and salinity ( approximately 25 wt %) similar to recent Salton Sea geothermal brines; and low-salinity with 10 to 20 mole percent CO 2 (CO 2 -rich, group 2). These two aqueous inclusion types are intimately associated in the same crystals and have probably both been trapped during dolomitic alteration.Siliceous alteration superimposed on dolomitic breccia contains NaCl-rich fluid inclusions (group 3: Na/Ca/K/Mg nearly equal 300:10:30:1, minor CH 4 ). Microstructures suggest that earlier higher salinity (10-20 wt %) and later lower salinity (4-9 wt %) variants of this NaCl-rich fluid bracket the main stage of chalcopyrite introduction. There are no low-density vapor inclusions indicative of any stage of fluid boiling. Rare high-density CH 4 (+ or -CO 2 )-rich carbonic inclusions are associated with NaCl-rich aqueous inclusions in a few samples. Secondary inclusions of a highly calcic low-temperature brine (group 4) occur along late healed cracks and postdate all major stages of mineral precipitation.The C, O, and H isotope compositions of dolomites, quartz, and hydrous silicates and of fluid inclusion extracts from samples of the siliceous alteration zone were imposed by the externally derived, weakly CH 4 + CO 2 -bearing, NaCl-rich fluid at high fluid/rock ratios and over a small range of temperatures. This fluid may have originated as a highly evolved basin brine or an evaporite-derived metamorphic fluid. The early CaCl 2 -rich fluid may have had an origin similar to the NaCl-rich ore fluid, but its different delta D and the mass balance constraints arising from its chemical composition suggest that it has not been derived from the NaCl-rich fluid by progressive rock interaction within the zoned alteration system. Similarly, an independent source is likely for the CO 2 -rich fluid.The absolute pressure-temperature ranges for the two alteration processes seem to be slightly different, but it is uncertain whether the quartz-chalcopyrite mineralization occurred at slightly lower temperature or higher pressure compared with the dolomitic alteration. The latter is confined to 270 degrees to 350 degrees C and 700 to 1,500 bars by isochore and mineral stability data.The following working hypothesis for the syntectonic and synmetamorphic fluid-rock interaction and copper ore formation at Mount Isa is proposed. In an initial stage, dolomitic alteration occurred by chemical interaction between the Urquhart Shale and moderate amounts of two fluids of different chemical and hydrological origin, represented by the CaCl 2 -rich and the CO 2 -rich fluid inclusions. Fluid mixing may have been aided by extension on the limb of a regional fold which temporarily lowered fluid pressures, thus leading to hydraulic brecciation and fluid influx from two fluid regimes, above and below. The CO 2 -rich fluid probably represents the local metamorphic fluid of the Urquhart Shale, whereas the CaCl 2 -rich brine was introduced from the underlying altered greenstones. The initial stage of brecciation and dolomitic alteration was followed by the main stage of silicification and copper introduction by the much more copious NaCl-rich fluid, probably at near-lithostatic fluid pressure. Quartz and chalcopyrite precipitation occurred by a combination of slight cooling, a pH increase, and possibly an increase in sulfur activity, as the initially reduced, acid, and possibly S-deficient, NaCl-rich fluids reacted with the previously dolomitized pyritic and dolomitic Urquhart Shale.

A molecular dynamics study of the structure of a model Langmuir monolayer of amphiphile molecules

We study the thermodynamics and structure of a model monomolecular film of pentadecanoic acid on water. In this model the water is treated as a uniform polarizable continuum and the pentadecanoic acid molecules as chains of 15 pseudoatom with internal bond constraints, angle bending and torsional intramolecular interactions, and Lennard-Jones atom–atom intermolecular interactions. The only low pressure phases exhibited by this model at temperatures between 300 and 400 K are the very low density vapor phase and a well ordered condensed phase with a reciprocal density ≤23 Å2 per molecule. This is in sharp contrast with experimental studies which show the existence of a stable liquid-expanded phase with a density of about 35 Å2 per molecule at pressures <15 dyn cm−1.

Electron mobility in low-density saturated acetonitrile vapour

Electron mobilities in saturated acetonitrile vapour are reported for the temperature range 313<or=T<or=353 K which show very strong deviations from the Lorentz behaviour. The results can be partially explained by density corrections of quantum character proposed by Polischuk (1985).

Fluid inclusion studies in the polymetallic ores of Gyöngyösoroszi (north Hungary) — Spatial and temporal evolution of ore-forming fluids

The PbZnCu-bearing vein-like poly-ascendent occurrence of Gyöngyösoroszi is related to Neogene volcanic formations. The characteristic curved veins occur in the so-called “middle varying andesite” sequence accompanied by typical rock alterations (potash metasomatism, silicification, clay mineralization). Fluid inclusion studies were carried out on quartz, barite, sphalerite and calcite. The identified inclusion types are as follows: (1) vapor (low-density vapor); (2) monophase liquid (high-density liquid); (3) two-phase (l + v) hydrous inclusions; (4) three-phase (l + v + s) inclusions; (5) hydrocarbon-bearing (often oil-rich) inclusions. Based on the homogenization measurement data the occurrence was formed under epi-mesothermal conditions, concordant with the mineral paragenesis and textural-structural features of the locality. Based on the aqueous leaching data and the cryoscopic measurements two types of fluid can be identified: 1. (a) the alkali-bicarbonate type in the veinlets with druses of the wall-rock in the early phase of mineralization; 2. (b) NaCaCl type in the main (vein forming) phase of mineralization. Fluids are often accompanied by CO 2 in minor quantities being of heterogeneous distribution and occasionally by hydrocarbon derivates. The salt concentration, density and vapor pressure data of the ore-forming fluids are characteristic of the young volcanic and subvolcanic vein-like mineralizations. By means of the dynamic interpretation of the physico-chemical data the spatial and temporal evolution of fluids can be followed. The spatial evolution is reflected by isotherm maps constructed from the fluid data and by gradient determinations, the temporal evolution can be followed by the fluid control of the mineral paragenesis.

Complete Doppler coverage in laser optical pumping by wall-induced velocity-changing collisions.

Enhanced Doppler coverage has been observed in the laser-induced optical pumping of low-density rubidium vapor in the absence of any buffer gas. Transient and steady-state measurements show that this enhancement arises from velocity-changing collisions (VCC's) of rubidium atoms with the walls of the cell containing the vapor. Wall-induced VCC's offer a possible mechanism for increasing the efficiency with which atomic and nuclear polarization may be produced with lasers.

Bubble Growth Following a Localized Electrical Discharge and its Relationship to the Breakdown of Triggered Spark Gaps in Liquids

In order to investigate the mechanism of breakdown of the liquid-filled, triggered spark gap, a flash-illuminated, shadowgraph optical system has been used to photograph the pre-breakdown events in a triggered gap. Photographs indicate that in all cases the trigger spark is followed by the growth of a hemispherical bubble, or vapor cavity, and this bubble appears to be the precursor of the main gap breakdown. A theoretical investigation shows that the expansion and collapse of the cavity in the low-viscosity limit, follows a simple hydrodynamic model. We find that only about 1% of the circuit energy is transferred to kinetic energy of the liquid surrounding the expanding cavity. The time required for an expanding bubble to fill a 1 mm gap is of the same order as the breakdown time lag for the triggered gap. It is concluded that the bubble generated by the trigger spark clears the gap of liquid, leaving a low-density gas or vapor between the electrodes, so that the actual process of electrical breakdown takes place through the low strength gas, not through the liquid. In the case of longer gaps, of 2 mm and above, the bubble may have time to expand across the entire gap and it is suggested that an electrohydrodynamic instability may cause the bubble surface to breakup into streamers, which cross the gap and cause breakdown.