96 research outputs found
Conductivity and Dissociation in Metallic Hydrogen: Implications for Planetary Interiors
Liquid metallic hydrogen (LMH) was recently produced under static compression
and high temperatures in bench-top experiments. Here, we report a study of the
optical reflectance of LMH in the pressure region of 1.4-1.7 Mbar and use the
Drude free-electron model to determine its optical conductivity. We find static
electrical conductivity of metallic hydrogen to be 11,000-15,000 S/cm. A
substantial dissociation fraction is required to best fit the energy dependence
of the observed reflectance. LMH at our experimental conditions is largely
atomic and degenerate, not primarily molecular. We determine a plasma frequency
and the optical conductivity. Properties are used to analyze planetary
structure of hydrogen rich planets such as Jupiter
Finite element simulation of the liquid-liquid transition to metallic hydrogen
Hydrogen at high temperature and pressure undergoes a phase transition from a
liquid molecular phase to a conductive atomic state, or liquid metallic
hydrogen, sometimes referred to as the plasma phase transition (PPT). The PPT
phase line was observed in a recent experiment studying laser-pulse heated
hydrogen in a diamond anvil cell in the pressure range for temperatures up to . The experimental
signatures of the transition are (i) a negative pressure-temperature slope,
(ii) a plateau in the heating curve, assumed to be related to the latent heat
of transformation, and (iii) an abrupt increase in the reflectance of the
sample. We present a finite element simulation that accurately takes into
account the position and time dependence of the heat deposited by the laser
pulse. We calculate the heating curves and the sample reflectance and
transmittance. This simulation confirms that the observed plateaus are related
to the phase transition, however we find that large values of latent heat are
needed and may indicate that dynamics at the transition are more complex than
considered in current models. Finally, experiments are proposed that can
distinguish between a change in optical properties due to a transition to a
metallic state or due to closure of the bandgap in molecular hydrogen.Comment: 23 pages, 4 figure
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Pathways to Metallic Hydrogen
The traditional pathway that researchers have used in the goal of producing atomic metallic hydrogen is to compress samples with megabar pressures at low temperature. A number of phases have been observed in solid hydrogen and its isotopes, but all are in the insulating phase. The results of experiment and theory for this pathway are reviewed. In recent years a new pathway has become the focus of this challenge of producing metallic hydrogen, namely a path along the melting line. It has been predicted that the hydrogen melt line will have a peak and with increasing pressure the melt line may descend to zero Kelvin so that high pressure metallic hydrogen may be a quantum liquid. Even at lower pressures hydrogen may melt from a molecular solid to an atomic liquid. Earlier attempts to observe the peak in the melting line were thwarted by diffusion of hydrogen into the pressure cell components and other problems. In the second part of this paper we present a detailed description of our recent successful demonstration of a peak in the melting line of hydrogenPhysic
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The Melting Line of Hydrogen at High Pressures
The insulator to metal transition in solid hydrogen was predicted over 70 years ago but the demonstration of this transition remains a scientific challenge. In this regard, a peak in the temperature vs. pressure melting line of hydrogen may be a possible precursor for metallization. However, previous measurements of the fusion curve of hydrogen have been limited in pressure by diffusion of hydrogen into the gasket or diamonds. To overcome this limitation we have used an innovative technique of pulsed laser heating of the sample and final peak in the melting line at GPa and K.Physic
Electron Emission in Superfluid and Low-temperature Vapor Phase Helium
Tungsten filaments used as sources of electrons in a low temperature liquid
or gaseous helium environment have remarkable properties of operating at
thousands of degrees Kelvin in surroundings at temperatures of order 1 K. We
provide an explanation of this performance in terms of important changes in the
thermal transport mechanisms. The behavior can be cast as a first-order phase
transition.Comment: 12 pages, 3 figure
The Melting Line of Hydrogen at High Pressures
The insulator to metal transition in solid hydrogen was predicted over 70
years ago but the demonstration of this transition remains a scientific
challenge. In this regard, a peak in the temperature vs. pressure melting line
of hydrogen may be a possible precursor for metallization. However, previous
measurements of the fusion curve of hydrogen have been limited in pressure by
diffusion of hydrogen into the gasket or diamonds. To overcome this limitation
we have used an innovative technique of pulsed laser heating of the sample and
final peak in the melting line at P=64.7+-4GPa and T=1055+-20 K.Comment: 11 page
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Metallic Hydrogen: The Most Powerful Rocket Fuel Yet To Exist
Wigner and Huntington first predicted that pressures of order 25 GPa were required for the transition of solid molecular hydrogen to the atomic metallic phase. Later it was predicted that metallic hydrogen might be a metastable material so that it remains metallic when pressure is released. Experimental pressures achieved on hydrogen have been more than an order of magnitude higher than the predicted transition pressure and yet it remains an insulator. We discuss the applications of metastable metallic hydrogen to rocketry. Metastable metallic hydrogen would be a very light-weight, low volume, powerful rocket propellant. One of the characteristics of a propellant is its specific impulse, . Liquid (molecular) hydrogen-oxygen used in modern rockets has an Isp of ; metallic hydrogen has a theoretical of 1700s! Detailed analysis shows that such a fuel would allow single-stage rockets to enter into orbit or carry economical payloads to the moon. If pure metallic hydrogen is used as a propellant, the reaction chamber temperature is calculated to be greater than 6000 K, too high for currently known rocket engine materials. By diluting metallic hydrogen with liquid hydrogen or water, the reaction temperature can be reduced, yet there is still a significant performance improvement for the diluted mixture.Physic
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