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   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Under pressure: Foundations of stellar physics and nuclear fusion   
   investigated    
      
     Date:   
         May 31, 2023   
     Source:   
         University of Warwick   
     Summary:   
         Research using the world's most energetic laser has shed light   
         on the properties of highly compressed matter -- essential to   
         understanding the structure of giant planets and stars, and to   
         develop controlled nuclear fusion, a process that could harvest   
         carbon-free energy.   
      
      
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   FULL STORY   
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   Research using the world's most energetic laser has shed light on the   
   properties of highly compressed matter -- essential to understanding the   
   structure of giant planets and stars, and to develop controlled nuclear   
   fusion, a process that could harvest carbon-free energy.   
      
   Matter in the interior of giant planets and some relatively cool stars   
   is highly compressed by the weight of the layers above. The extreme   
   pressures generated are strong enough to charge of atoms and generate   
   free electrons, in a process known as ionisation. The material properties   
   of such matter are mostly determined by the degree of ionisation of   
   the atoms. While ionisation in burning stars is primarily determined   
   by temperature, pressure-driven ionization dominates in cooler stellar   
   objects. However, this process is not well understood, and the extreme   
   states of matter required are very difficult to create in the laboratory   
   limiting the predictive power required to model celestial objects.   
      
   Extreme conditions also occur in laser-driven fusion experiments where   
   hydrogen atoms are fused under high pressures and temperatures to helium,   
   a heavier element. This process has been heralded as an unlimited,   
   carbon free energy source -- by using large excess energy generated by   
   the fusion reactions to generate electricity. Progress in this grand   
   scientific challenge relies heavily on numerical modelling and the   
   ionisation balance in high-pressure systems is of central importance.   
      
   The only way to study this complex process in the laboratory is   
   to dynamically compress matter to extreme densities which requires   
   very large energy inputs in a very short time. In a new experiment   
   published today in Nature, scientists have done just that using the   
   largest and most energetic laser in the world, the National Ignition   
   Facility (NIF). Through their research at the Lawrence Livermore   
   National Laboratory (LLNL), US, the team provide new insights on the   
   complex process of pressure-driven ionisation in giant planets and   
   stars. They investigated the properties and behaviour of matter under   
   extreme compression, offering important implications for astrophysics   
   and nuclear fusion research.   
      
   The international research team used NIF to generate the extreme   
   conditions necessary for pressure-driven ionisation. They focused 184   
   laser beams on a cavity, converting the laser energy into X-rays that   
   heated a 2mm metal shell placed in the centre. As the outside of the shell   
   rapidly expanded due to the heating, the inside was driven inwards --   
   reaching temperatures around two million kelvins (1.9m degrees Celsius)   
   and pressures up to three billion atmospheres -- creating a tiny piece   
   of matter as found in dwarf stars for just a few nanoseconds.   
      
   The highly compressed metal shell (made of beryllium) was then   
   analysed using X-rays to reveal its density, temperature, and   
   electron structure. The findings revealed that, following strong   
   heating and compression, at least three out of four electrons in   
   beryllium transitioned into conducting states, that is, they can move   
   independent from the nuclear cores of the atoms. Additionally, the study   
   uncovered unexpectedly weak elastic X-ray scattering, indicating reduced   
   localization of the remaining electron, that is a new stage shortly   
   before all electrons become free and thus revealing the pathways to a   
   fully ionised state.   
      
   LLNL physicist Tilo Do"ppner, who led the project, said: "By recreating   
   extreme conditions similar to those inside giant planets and stars,   
   we were able to observe changes in material properties and electron   
   structure that are not captured by current models. Our work opens new   
   avenues for studying and modeling the behavior of matter under extreme   
   compression. The ionization in dense plasmas is a key parameter as it   
   affects the equation of state, thermodynamic properties, and radiation   
   transport through opacity."  Associate Professor Dirk Gericke, University   
   of Warwick, Department of Physics, added: "Having created and diagnosed   
   these extreme pressures in the laboratory gives an invaluable benchmark   
   for our theoretical models. Improved predictive capabilities are urgently   
   needed not only for astrophysics but also for further progress toward   
   controlled nuclear fusion which would allow to harvest the energy source   
   of the stars for humanity."  The pioneering research was the result   
   of an international collaboration to develop x-ray Thomson scattering   
   at the NIF as part of LLNL's Discovery Science program. Collaborators   
   included scientists from University of Rostock (Germany), University of   
   Warwick (U.K.), GSI Helmholtz Center for Heavy Ion Research (Germany),   
   University of California Berkeley, SLAC National Accelerator Laboratory,   
   Helmholtz-Zentrum Dresden-Rossendorf (Germany), University of Lyon   
   (France), Los Alamos National Laboratory, Imperial College London (U.K.),   
   and First Light Fusion Ltd. (U.K.).   
      
       * RELATED_TOPICS   
             o Space_&_Time   
                   # Astrophysics # Dark_Matter # Stars   
             o Matter_&_Energy   
                   # Physics # Nuclear_Energy # Quantum_Physics   
             o Earth_&_Climate   
                   # Energy_and_the_Environment # Renewable_Energy # Weather   
       * RELATED_TERMS   
             o Nuclear_fusion o Stellar_nucleosynthesis o Nucleosynthesis   
             o Effects_of_nuclear_explosions o Nuclear_fission o Astronomy   
             o Supernova o Atom   
      
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   Story Source: Materials provided by University_of_Warwick. Note: Content   
   may be edited for style and length.   
      
      
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   Journal Reference:   
      1. T. Do"ppner, M. Bethkenhagen, D. Kraus, P. Neumayer, D. A. Chapman,   
      B.   
      
         Bachmann, R. A. Baggott, M. P. Bo"hme, L. Divol, R. W. Falcone,   
         L. B.   
      
         Fletcher, O. L. Landen, M. J. MacDonald, A. M. Saunders,   
         M. Scho"rner, P.   
      
         A. Sterne, J. Vorberger, B. B. L. Witte, A. Yi, R. Redmer,   
         S. H. Glenzer, D. O. Gericke. Observing the onset of   
         pressure-driven K-shell delocalization. Nature, 2023; DOI:   
         10.1038/s41586-023-05996-8   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/05/230531150055.htm   
      
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