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Warm dense matter (WDM)

  1. Feb 12, 2008 #1

    jal

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    “warm dense matter” (WDM)

    I have just read, National Task Force on High Energy Density Physics.
    I would like to get a clarification on “warm dense matter” (WDM).
    Are there models with the electrons in the lattice and/or outside the lattice for “warm dense matter” (WDM).

    I expect that the experiments on “warm dense matter” (WDM) will have impact on astrophysics, which leads to my second question.
    Prior to the CMB, the universe was mainly 10^80 hydrogens that would have cooled from plasma and gone through the “warm dense matter” (WDM) phase:
    Where are the neutrons in the “warm dense matter” (WDM) phase of hydrogen?
    Where did they come from?
    ------------
    references:
    http://www.ofes.fusion.doe.gov/News/HEDPReport.pdf
    Ronald C. Davidson
    Chair
    National Task Force on High Energy Density Physics
    July 20, 2004
    p. 60 - 51 -
    Experimentally, the study of warm dense matter has proven difficult, as the isolation of samples in this regime is complicated. Indeed, although every density-temperature time history that starts from the solid phase on the way to becoming a plasma goes through this regime, attempts to isolate warm dense
    matter for study have proven to be a major challenge.
    New metastable states possible with high energy density materials, such as the long-sought metallic atomic hydrogen, are achievable goals of HED physics.

    p. 61
    At the extreme densities of the stellar interior, the number of hydrogen atoms per cm3 is 6x10^25, so that on average there is only 0.25 Å (1 Å is 10 billionths of a cm) between atoms, which is smaller than the distance from the hydrogen's proton to the first stable electron orbit.
    Clearly the electron could not remain in a stable bound orbit around the proton,
    independent of temperature.


    The difficulty presented by warm dense matter arises theoretically from the fact that in this regime there are no obvious expansion parameters, as the usual perturbation expansions in small parameters used in either condensed matter studies [= temperature/(Fermi energy)] or plasma kinetic theories [
    = (potential energy)/(kinetic energy)] are no longer valid. Furthermore, density dependent effects, e.g., pressure ionization, become increasingly important as the environment surrounding the ion or atom starts to impinge on internal lattice or atomic structure.
    p.89
    Super-intense, relativistic laser beams carry light waves with electric field strengths far greater than the internal fields binding electrons to the nucleus. At sufficiently high intensity, not only are atoms literally ripped apart by the huge forces of the light beam, but the liberated electrons themselves acquire an energy which approaches or exceeds their rest energy. Unlike our usual way of describing matter irradiated by light, at these intensities, special relativity must be accounted for in describing the interaction. Exotic relativistic issues come into play including retardation effects, the production of enormous magnetic fields, and plasmas with electrons whose mass varies with time.

    At high intensities, where free electrons can be accelerated to relativistic energies in one optical cycle, the orbits of bound electrons in ions will be distorted severely, and the magnetic field of the light will participate in the electron and ion dynamics. Furthermore light-light scattering will become important. As a result, we expect that atomic physics will take on very different character to what we usually think of how an atom acts.
    Indeed, the optics of such relativistic matter will differ from traditional optics as the change of mass of an electron oscillating at these relativistic velocities introduces a nonlinearity, akin to that usually found only in specially designed nonlinear optical media. This phenomena represents a new era of “relativistic nonlinear optics” with applications that could be a widespread as traditional nonlinear optics has demonstrated over the previous 30 years. Furthermore, the acceleration of many electrons to such high velocity results in the production of truly enormous magnetic fields, with strengths perhaps as mush as a million times higher than a typical household refrigerator magnet.

    p.94 The frontier in ultra-fast spectroscopy is the study of the motion of electrons bound inside the atom, in orbits close to the nucleus. This new scale is defined by the time it takes the electron in the first Bohr (innermost) orbit of the hydrogen atom to complete one turn around the proton. The period of this orbit — 24 10_18 s, or 24 attoseconds — is at least a factor of a hundred shorter than the duration of the shortest laser pulse.

    p. 89
    Modern ultra-intense, ultra short laser can create extreme material states, corresponding to solid density materials at a few eV energy and 10-100
    G’s of pressures. Creation of materials in this “warm dense matter” (WDM) regime is of fundamental interest since materials in this regime falls in between “standard” condensed matter and “plasma” descriptions of mater. The creation of WDM material, together with the use of ultra-short x-rays to probe their initial properties, will provide important experimental data for developing “equation-of-state” description of highly excited materials. Importantly, the subsequent evolution of WDM material (which occur upon expansion of these states as associated with ablation) will provide an important opportunity for studying phase transitions kinetics. WDM states typically correspond to materials driven to the “supercritical fluid” regime of a phase diagram.
    -----------
    A more recent link

    http://hifweb.lbl.gov/public/AcceleratorWDM/TableOfContents.html
    Workshop on Accelerator Driven Warm Dense Matter Physics
    Four Point Sheraton Hotel
    Pleasanton, California
    February 22-24, 2006
    --------
    Latest link

    http://hifweb.lbl.gov/wdmschool/
    2008 Warm Dense Matter Winter School
    The lectures will be tutorials intended for students beginning research work in the field of WDM; they will start from the basics, give clear definitions of the specialized terms, and describe the principal diagnostics and experimental techniques.
    (See their presentations)
    --------
    “warm dense matter” (WDM) seems like a promission area of research.
    jal
     
  2. jcsd
  3. Feb 14, 2008 #2

    jal

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    Is the work on “warm dense matter” (WDM) classified?
     
  4. Feb 15, 2008 #3

    jal

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    I found with my quick search into “warm dense matter” (WDM) that the experimental results of protons under pressure puts a lot present models into question and opens up the possibility of investigating NEW models. (1)

    Under pressure (which we can achieve in experiments in the lab.), it appears that the distance within a nucleon is shorten and that electrons and neutrons cannot occupy the interior of the lattice. (see previous post) Ionized might be a good word to describe the universe prior decoupling.
    Perhaps ZapperZ could give me some links to some of those models.
    Even John Baez gave some tantalizing clues (2) that these models could exist and would change our understanding of the universe prior to decoupling.
    --------
    reference
    1)
    http://query.nytimes.com/gst/fullpage.html?res=9800E5D61439F935A15750C0A960958260
    Big Gun Makes Hydrogen Into a Metal
    By MALCOLM W. BROWNE
    Published: March 26, 1996
    USING a 60-foot-long gun, physicists at Lawrence Livermore Laboratory have created a metallic form of hydrogen

    2)
    http://math.ucr.edu/home/baez/lengths.html#bohr_radius
    Length Scales in Physics
    John Baez
    December 23, 2005


    .. quantum field theory effects start really mattering for electrons on a distance scale 1/137 the size of the hydrogen atom.
    We can derive the classical electron radius by working out the electric field outside of a ball having charge equal to that of the electron, e, and radius L, then working out the energy of this electric field, and then setting that energy equal to the electron mass m. Solving for L we get a formula for the electron radius re. In other words, the classical electron radius is the radius the electron would have to have for all of its mass to be due to the electric field it produced, assuming it was a charged shell.
    But we want some understanding at a gut level why making the electron heavier would make the hydrogen atom smaller! It's known that this is true, by the way, because one can take a muon, which is just like an electron but 206.77 times heavier (and decays rapidly), and make muonic hydrogen which is about 206.77 times smaller. But WHY?
    We see at any rate that the Bohr radius can be guessed by essentially classical reasoning together with the uncertainty principle, and this length scale is naturally proportional to an inverse mass scale - the inverse of the electron mass!
    =========
     
  5. Feb 17, 2008 #4
    could metastable metalllic hydrogen be achieved, either by using the muons to get hydrogen nuclei closer together, or else by some powerful electrostatic field to shove electrons out of a mass of compressed hydrogen?

    why would metallic hydrogen be metastable anyway?

    what are the applications for such a material? I'd read about possible compact rocket fuel, and even as a superconductor, but wouldn't the stuff be catastrophically explosive? what about as a radiation shield/absorber? Wouldn't such dense/degenerate nuclear/nucleonic matter present a much better radiation absorption cross-section?
     
    Last edited: Feb 17, 2008
  6. Feb 17, 2008 #5
    From reading the below:

    http://physci.llnl.gov/Organization/HDivision/Research/GasGun/Nellis.html

    It's said that diamond anvils cannot contain the compressed hydrogen as its temperature passes over 500K. The 1996 detection briefly of metallic hydrogen by Livermore was done by a gunshot experiment. So why not compress it slowly/isothermally under very cold conditions? Wouldn't liquid hydrogen have much more difficulty in diffusing/escaping?
     
  7. Feb 17, 2008 #6

    jal

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    An interesting link of information.
    I made some quotes for the other readers.

    http://physci.llnl.gov/Organization/HDivision/Research/GasGun/Nellis.html
    Last Changed Date: 01/21/00
    Quest for Metallic Hydrogen
    Under normal conditions on our planet, molecular hydrogen functions as an insulator, blocking electrical flow. Apply sufficient pressure, theory said, and hydrogen turns metallic, becoming an exceptional conductor of electricity. Theory predicted that metallization would occur when the insulating molecular solid would transform to a metallic monatomic solid at absolute zero--0 degrees kelvin (K) or -460°F. For early metallic hydrogen theorists, "sufficient pressure" was thought to be 0.2 megabars (1 bar is atmospheric pressure at sea level; a megabar, or Mbar, is a million times atmospheric pressure at sea level). Subsequent predictions pushed metallization pressure to as high as 20 Mbar. At the time our experiments were conducted, the prevailing theory predicted 3 Mbar for solid hydrogen at 0 K.
    Our Approach
    In 1991, we began a series of experiments to determine how compression affected the electrical properties of diatomic or molecular hydrogen and deuterium both of which are insulators at ambient temperatures and pressures.
    Evidence of actual metallization was an unanticipated result of our experiments. It was unexpected for several reasons: (1) we used liquid hydrogen, rather than solid hydrogen that conventional wisdom indicated was required; (2) we applied a methodology--shock compression--that had never before been tried in order to metallize hydrogen; and (3) we were working at higher temperatures (3,000 K) than metallization theory specified.
    Our Results
    As shown in Figure 2, we found that from 0.9 to 1.4 Mbar, resistivity in the shocked fluid decreases almost four orders of magnitude (i.e., conductivity increases); from 1.4 to 1.8 Mbar, resistivity is essentially constant at a value typical of that of liquid metals. Our data indicate a continuous transition from a semiconducting to metallic diatomic fluid at 1.4 Mbar, nine-fold compression of initial liquid density, and 3,000 K.
    Some theorists have speculated that metallic hydrogen produced under laboratory conditions might remain in that state after the enormous pressures required to create it are removed.
    At metallization, we calculate that only about 5% of the original molecules have separated into individual atoms of hydrogen, which means that our metallic hydrogen is primarily a molecular fluid. (Observation of this molecular metallic state in our experiments was unexpected. Only the monatomic metallic state was predicted by theory.)

    Speculations about possibilities for metastable solid metallic hydrogen (MSMH) are discussed below. ( hehehe …You will have to go and read the article.)

    At high presures metallic fluid hydrogen exists at ~10 times molecular-solid density, or ~0.7 g/cm3 . So, we assume that MSMH will have a comparable density. Thus, its density is comparable to the density of water, is ~3 times lighter than Al and ~10 times lighter than iron.

    jal
     
  8. Feb 17, 2008 #7
    Well, that article mentions that MSMH could be a highly compact and energetic rocket fuel that could greatly aid space travel. But why would hydrogen remain metastably in such a state at STP, in the face of entropy pressures to revert to its normal diatomic gaseous state? What barrier would be there to prevent/impede the reversion?

    What is the state of ongoing research to achieve metastable metallic hydrogen? Any known planned experiments in the future coming up?
     
  9. Feb 18, 2008 #8

    jal

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    If you have access to http://publish.aps.org/ then you should be able to read the latest published data.

    I’ll make a “Warm Dense Matter (WDM) = solid hydrogen /crystal” blog and go look into astrophysic to see what they have to say about Solid hydrogen.
     
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