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Evidence for a glassy state in strongly driven carbon.

Brown CR, Gericke DO, Cammarata M, Cho BI, Döppner T, Engelhorn K, Förster E, Fortmann C, Fritz D, Galtier E, Glenzer SH, Harmand M, Heimann P, Kugland NL, Lamb DQ, Lee HJ, Lee RW, Lemke H, Makita M, Moinard A, Murphy CD, Nagler B, Neumayer P, Plagemann KU, Redmer R, Riley D, Rosmej FB, Sperling P, Toleikis S, Vinko SM, Vorberger J, White S, White TG, Wünsch K, Zastrau U, Zhu D, Tschentscher T, Gregori G - Sci Rep (2014)

Bottom Line: Here, we report results of an experiment creating a transient, highly correlated carbon state using a combination of optical and x-ray lasers.Scattered x-rays reveal a highly ordered state with an electrostatic energy significantly exceeding the thermal energy of the ions.The experiment suggests a much slower nucleation and points to an intermediate glassy state where the ions are frozen close to their original positions in the fluid.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, UK [2] Plasma Physics Department, AWE plc., Aldermaston, Reading RG7 4PR, UK [3] Plasma Physics Group, Blackett Laboratory, Imperial College London, Prince Consort Road, London SW7 2AZ, UK.

ABSTRACT
Here, we report results of an experiment creating a transient, highly correlated carbon state using a combination of optical and x-ray lasers. Scattered x-rays reveal a highly ordered state with an electrostatic energy significantly exceeding the thermal energy of the ions. Strong Coulomb forces are predicted to induce nucleation into a crystalline ion structure within a few picoseconds. However, we observe no evidence of such phase transition after several tens of picoseconds but strong indications for an over-correlated fluid state. The experiment suggests a much slower nucleation and points to an intermediate glassy state where the ions are frozen close to their original positions in the fluid.

No MeSH data available.


Related in: MedlinePlus

Ion-ion structure factor calculations.A comparison between DFT-MD and MSA predictions for the ion-ion structure factor. In density functional simulations both electrons and ions are handled as elementary particles. Properties of the electrons are calculated via density functional theory using a Mermin functional that accounts for temperature effects within the electron subsystem in a statistical sense. The ions instead are treated by classical molecular dynamics simulations. This is possible because the dynamics of ions and electrons is effectively decoupled with the Born-Oppenheimer approximation. By taking snapshots of the ions positions, the ion-ion structure factor can be thus calculated. Our ab initio calculations are performed with ρ = 3 g/cm3 and T = 30, 000 K. MSA calculations27 instead use the ionization state (Z) as an additional input.
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f4: Ion-ion structure factor calculations.A comparison between DFT-MD and MSA predictions for the ion-ion structure factor. In density functional simulations both electrons and ions are handled as elementary particles. Properties of the electrons are calculated via density functional theory using a Mermin functional that accounts for temperature effects within the electron subsystem in a statistical sense. The ions instead are treated by classical molecular dynamics simulations. This is possible because the dynamics of ions and electrons is effectively decoupled with the Born-Oppenheimer approximation. By taking snapshots of the ions positions, the ion-ion structure factor can be thus calculated. Our ab initio calculations are performed with ρ = 3 g/cm3 and T = 30, 000 K. MSA calculations27 instead use the ionization state (Z) as an additional input.

Mentions: In the case of a plasma in thermodynamic equilibrium, density functional theory coupled to molecular dynamics (DFT-MD) simulations represent an ab initio method to calculate the ion-ion structure factor26. The result of such simulations is shown in Figure 4. We notice that for the conditions of our experiment, DFT-MD gives an ion-ion structure factor which is relatively flat in the region of indicating a moderately coupled system only. By comparing the DFT-MD results with the experimental data (Figure 3), we see that the agreement is rather poor, particularly in the region of the first peak of the structure factor. This is due to the fact that an equilibrium calculation only predicts a moderate ionization for carbon (Z ~ 2), whereas in our experiment, additional ionization is driven by supra-thermal electrons while keeping the initial density and ion temperature almost unaffected. Hence, the plasma state created in our experiment is better described in terms of positively charged ions with a much higher charge state embedded in a polarisable background of electrons27. This situation can often be described by the mean spherical approximation (MSA) making the problem of the ion structure analytically solvable. The best fit with the experimental data is obtained for an ion charge state of Z = 4.5 (Figure 3). The calculations shown in Figure 4 clearly indicate that as the ionization increases there is the emergence of a strong correlation peak. The position of the peak depends on the density, thus the crystal analyzer placed at ~ 3.4 Å−1 (θ = 50°) primarily selects scattering coming from region in the sample where ρ = 2.5 g/cm3. On the other hand, different densities are equally weighted in the scattering signal, when the crystal analyzer selects ~ 7.4 Å−1 at a scattering angle of θ = 130°.


Evidence for a glassy state in strongly driven carbon.

Brown CR, Gericke DO, Cammarata M, Cho BI, Döppner T, Engelhorn K, Förster E, Fortmann C, Fritz D, Galtier E, Glenzer SH, Harmand M, Heimann P, Kugland NL, Lamb DQ, Lee HJ, Lee RW, Lemke H, Makita M, Moinard A, Murphy CD, Nagler B, Neumayer P, Plagemann KU, Redmer R, Riley D, Rosmej FB, Sperling P, Toleikis S, Vinko SM, Vorberger J, White S, White TG, Wünsch K, Zastrau U, Zhu D, Tschentscher T, Gregori G - Sci Rep (2014)

Ion-ion structure factor calculations.A comparison between DFT-MD and MSA predictions for the ion-ion structure factor. In density functional simulations both electrons and ions are handled as elementary particles. Properties of the electrons are calculated via density functional theory using a Mermin functional that accounts for temperature effects within the electron subsystem in a statistical sense. The ions instead are treated by classical molecular dynamics simulations. This is possible because the dynamics of ions and electrons is effectively decoupled with the Born-Oppenheimer approximation. By taking snapshots of the ions positions, the ion-ion structure factor can be thus calculated. Our ab initio calculations are performed with ρ = 3 g/cm3 and T = 30, 000 K. MSA calculations27 instead use the ionization state (Z) as an additional input.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4048912&req=5

f4: Ion-ion structure factor calculations.A comparison between DFT-MD and MSA predictions for the ion-ion structure factor. In density functional simulations both electrons and ions are handled as elementary particles. Properties of the electrons are calculated via density functional theory using a Mermin functional that accounts for temperature effects within the electron subsystem in a statistical sense. The ions instead are treated by classical molecular dynamics simulations. This is possible because the dynamics of ions and electrons is effectively decoupled with the Born-Oppenheimer approximation. By taking snapshots of the ions positions, the ion-ion structure factor can be thus calculated. Our ab initio calculations are performed with ρ = 3 g/cm3 and T = 30, 000 K. MSA calculations27 instead use the ionization state (Z) as an additional input.
Mentions: In the case of a plasma in thermodynamic equilibrium, density functional theory coupled to molecular dynamics (DFT-MD) simulations represent an ab initio method to calculate the ion-ion structure factor26. The result of such simulations is shown in Figure 4. We notice that for the conditions of our experiment, DFT-MD gives an ion-ion structure factor which is relatively flat in the region of indicating a moderately coupled system only. By comparing the DFT-MD results with the experimental data (Figure 3), we see that the agreement is rather poor, particularly in the region of the first peak of the structure factor. This is due to the fact that an equilibrium calculation only predicts a moderate ionization for carbon (Z ~ 2), whereas in our experiment, additional ionization is driven by supra-thermal electrons while keeping the initial density and ion temperature almost unaffected. Hence, the plasma state created in our experiment is better described in terms of positively charged ions with a much higher charge state embedded in a polarisable background of electrons27. This situation can often be described by the mean spherical approximation (MSA) making the problem of the ion structure analytically solvable. The best fit with the experimental data is obtained for an ion charge state of Z = 4.5 (Figure 3). The calculations shown in Figure 4 clearly indicate that as the ionization increases there is the emergence of a strong correlation peak. The position of the peak depends on the density, thus the crystal analyzer placed at ~ 3.4 Å−1 (θ = 50°) primarily selects scattering coming from region in the sample where ρ = 2.5 g/cm3. On the other hand, different densities are equally weighted in the scattering signal, when the crystal analyzer selects ~ 7.4 Å−1 at a scattering angle of θ = 130°.

Bottom Line: Here, we report results of an experiment creating a transient, highly correlated carbon state using a combination of optical and x-ray lasers.Scattered x-rays reveal a highly ordered state with an electrostatic energy significantly exceeding the thermal energy of the ions.The experiment suggests a much slower nucleation and points to an intermediate glassy state where the ions are frozen close to their original positions in the fluid.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, UK [2] Plasma Physics Department, AWE plc., Aldermaston, Reading RG7 4PR, UK [3] Plasma Physics Group, Blackett Laboratory, Imperial College London, Prince Consort Road, London SW7 2AZ, UK.

ABSTRACT
Here, we report results of an experiment creating a transient, highly correlated carbon state using a combination of optical and x-ray lasers. Scattered x-rays reveal a highly ordered state with an electrostatic energy significantly exceeding the thermal energy of the ions. Strong Coulomb forces are predicted to induce nucleation into a crystalline ion structure within a few picoseconds. However, we observe no evidence of such phase transition after several tens of picoseconds but strong indications for an over-correlated fluid state. The experiment suggests a much slower nucleation and points to an intermediate glassy state where the ions are frozen close to their original positions in the fluid.

No MeSH data available.


Related in: MedlinePlus