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Author: Publisher: ISBN: Category : Languages : en Pages : 27
Book Description
The authors present analytical expressions for the dynamic structure factor, or form factor S(k, [omega]), which is the quantity describing the inelastic x-ray cross section from a dense plasma or a simple liquid. The results, based on the random phase approximation (RPA) for the treatment on the charged particle coupling, can be applied to describe scattering from either weakly coupled classical plasmas or degenerate electron liquids. The form factor correctly reproduces the Compton energy downshift and the usual Fermi-Dirac electron velocity distribution for S(k, [omega]) in the case of a cold degenerate plasma. the usual concept of scattering parameter is also reinterpreted for the degenerate case in order to include the effect of the Thomas-Fermi screening. The results shown in this work can be applied to interpreting x-ray scattering in warm dense plasmas occurring in inertial confinement fusion experiments or inside the interior of planets.
Author: Publisher: ISBN: Category : Languages : en Pages : 27
Book Description
The authors present analytical expressions for the dynamic structure factor, or form factor S(k, [omega]), which is the quantity describing the inelastic x-ray cross section from a dense plasma or a simple liquid. The results, based on the random phase approximation (RPA) for the treatment on the charged particle coupling, can be applied to describe scattering from either weakly coupled classical plasmas or degenerate electron liquids. The form factor correctly reproduces the Compton energy downshift and the usual Fermi-Dirac electron velocity distribution for S(k, [omega]) in the case of a cold degenerate plasma. the usual concept of scattering parameter is also reinterpreted for the degenerate case in order to include the effect of the Thomas-Fermi screening. The results shown in this work can be applied to interpreting x-ray scattering in warm dense plasmas occurring in inertial confinement fusion experiments or inside the interior of planets.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
In this paper the authors demonstrate through calculations and theoretical analysis the first application of a x-ray laser for probing hot, high-density plasmas (n[sub e][ge] 10[sup 23] cm[sup -3]) using a Ni-like transient collisional excitation x-ray laser as a probe. Theoretical predictions are used to diagnose the electron temperature in short pulse (500 fs) laser produced plasmas. The threshold power of the x-ray probe is estimated by comparing theoretical scattering levels with plasma thermal emission. The necessary spectral resolution of the instrument sufficient for resolving electron temperature is given.
Author: Kathrin Wünsch Publisher: ISBN: Category : Languages : en Pages :
Book Description
This thesis presents the theoretical framework required to apply spectrally resolved x-ray Thomson scattering (XRTS) as a diagnostic method for warm dense matter. In particular, the theory is generalised to allow for the description of systems with multiple ion species where all mutual correlations are taken into account within the new approach. Supplemented with the theory presented, XRTS is now a promising diagnostics for high-energy-density matter containing different chemical elements or mixtures of different materials. The signal measured at XRTS contains the unshifted Rayleigh peak and frequency-shifted features. The first is related to elastic scattering from electrons co-moving with the ions whilst the second occurs due to scattering from free electrons and excitation/ionisation events. The focus of this thesis lies on the elastic scattering feature which requires the ion structure and the electron density around the ion as input for the theoretical modelling. The ion structure is obtained from quantum simulations (DFT-MD) and classical hypernetted-chain (HNC) equations. The analysis of the DTF-MD simulation data reveals that partial ionisation yields strong modifications of the ion-ion interactions. Similar effects are found for the form of the electron screening cloud around an ion. On the basis of the newly developed theory and structural models, multicomponent effects on the XRTS signal are studied. It is shown that the Rayleigh feature is very sensitive to the ratio of the elements in the scattering volume and their mutual correlations. These results indicate that XRTS is well-suited to probe the properties of complex materials and the process of mixing in the WDM regime. The advanced theories are finally applied to experimental spectra. The procedure allows for both extracting the basic plasma parameters and assessing the quality of the theoretical models applied. Comparisons with several experiments demonstrated that the non-collective regime (large scattering angle) is reasonably well understood whereas the collective regime (small scattering angle/long wavelength limit) still holds challenges. The collective regime is problematic as here strong correlations and screening are highly relevant and, thus, a yet unknown description for fully coupled quantum systems needs to be applied.
Author: Alison Marie-Anne Saunders Publisher: ISBN: Category : Languages : en Pages : 143
Book Description
High energy density physics (HEDP) is an emerging field that seeks to investigate the properties of matter at extreme conditions. High energy density conditions occur in materials with pressures exceeding 1 Mbar, or pressures that exceed Earth’s atmospheric pressure by a factor of more than a million. A regime of HEDP of particular interest is warm dense matter (WDM) physics, which describes the behavior of materials at near solid densities and 10’s of eV temperatures. WDM occurs in astrophysical objects, such as giant planets and brown dwarfs, and is also generated in inertial confinement fusion (ICF) experiments. X-ray Thomson scattering (XRTS) offers a powerful tool to probe the equation of state of WDM. XRTS spectra consist of two components: elastically scattered photons with the frequency of the original x-ray source and inelastically scattered photons that are down- shifted in frequency. The Compton-shifted profile of inelastically scattered x-rays can be analyzed to return the sample’s electron density and electron temperature. The ratio of elastically to inelastically scattered x-rays relates to the number of tightly bound versus free electrons, and thus reflects the ionization state. This thesis discusses the results of XRTS experiments on WDM performed at the OMEGA Laser facility. The first experiment presents and discusses XRTS results from 1 mm diamond spheres. The scattering spectra show evidence of higher ionization than predicted by several commonly-applied ionization models. A second experiment analyzed the contributions to elastic scattering from a small argon impurity in imploding beryllium capsules. The exper- iment found that less than 1 at.% of argon significantly affects the elastic scattering signal strength, and concluded that impurities in a sample should be considered before drawing conclusions from elastic scattering signals. The final experiment uses XRTS to measure the electron temperature and ionization state in isochorically heated materials used in ion stopping power experiments. The results from these experiments demonstrate the power of XRTS to measure ionization in WDM to benchmark theoretical modeling.
Author: Publisher: ISBN: Category : Languages : en Pages : 12
Book Description
We have developed accurate x-ray scattering techniques to measure the physical properties of dense plasmas. Temperature and density are inferred from inelastic x-ray scattering data whose interpretation is model-independent for low to moderately coupled systems. Specifically, the spectral shape of the non-collective Compton scattering spectrum directly reflects the electron velocity distribution. In partially Fermi degenerate systems that have been investigated experimentally in laser shock-compressed beryllium, the Compton scattering spectrum provides the Fermi energy and hence the electron density. We show that forward scattering spectra that observe collective plasmon oscillations yield densities in agreement with Compton scattering. In addition, electron temperatures inferred from the dispersion of the plasmon feature are consistent with the ion temperature sensitive elastic scattering feature. Hence, theoretical models of the static ion-ion structure factor and consequently the equation of state of dense matter can be directly tested.
Author: John Sheffield Publisher: Academic Press ISBN: 0080952038 Category : Science Languages : en Pages : 512
Book Description
This work presents one of the most powerful methods of plasma diagnosis in exquisite detail, to guide researchers in the theory and measurement techniques of light scattering in plasmas. Light scattering in plasmas is essential in the research and development of fusion energy, environmental solutions, and electronics. Referred to as the "Bible" by researchers, the work encompasses fusion and industrial applications essential in plasma research. It is the only comprehensive resource specific to the plasma scattering technique. It provides a wide-range of experimental examples and discussion of their principles with worked examples to assist researchers in applying the theory. Computing techniques for solving basic equations helps researchers compare data to the actual experiment New material on advances on the experimental side, such as the application of high density plasmas of inertial fusion Worked out examples of the scattering technique for easier comprehension of theory
Author: Publisher: ISBN: Category : Languages : en Pages : 11
Book Description
Collective x-ray Thomson scattering allows measuring plasmons, i.e electron plasma oscillations (Langmuir waves). This is manifest in the appearance of spectrally up- and down-shifted spectral features in addition to the Rayleigh signal. The ratio of the up- and down-shifted signals is directly related to detailed balance, allowing to determine the plasma temperature from first principles. The spectral shift of the plasmon signals is sensitive to temperature and electron density. We discuss the experimental considerations that have to be fulfilled to observe plasmon signals with x-ray Thomson scattering. As an example, we describe an experiment that used the Cl Ly-[alpha] x-ray line at 2.96 keV to measure collective Thomson scattering from solid beryllium, isochorically heated to 18 eV. Since temperature measurement based on detailed balance is based on first principles, this method is important to validate models that, for example, calculate the static ion-ion structure factor S{sub ii}(k).
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Author: Kathrin Wünsch
Author: Alison Marie-Anne Saunders
Author: Hideaki Takabe
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Author: John Sheffield
Author: Richard G. Seasholtz
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