| 1. |
- Holmlid, Leif, 1942, et al.
(author)
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Laser-induced annihilation: Relativistic particles from ultra-dense hydrogen H(0)
- 2021
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In: High Energy Density Physics. - : Elsevier BV. - 1574-1818. ; 40
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Journal article (peer-reviewed)abstract
- Particle annihilation means that nuclear particles annihilate each other (for example nucleons like a neutron and an anti-neutron) and generate showers of mesons (mainly kaons and pions) at high energy. The kaons decay via pions and muons to electrons, positrons, neutrinos and photons. The energy which can be extracted from the very fast particles is of the order of 50% of the total energy of the nucleon masses involved or 500 MeV per mass unit. Several reports have been published recently on the meson showers ejected by pulsed-laser impact on ultra-dense hydrogen H(0). Since the particle velocities often are relativistic at >100 MeVu 1 it is clear that a much more efficient nuclear process is responsible than in a normal hydrogen isotope fusion process (which can give only 3 and 15 MeV per mass unit out). The first experiment showing heat production above break-even in a laser-induced nuclear process in H(0) was published in AIP Avances as early as 2015. Here, we use a standard method for relativistic particle detection to show that the particles ejected by the laser pulse from D(0) are charged (thus not photons), and in fact positive, and that the signals decay with the characteristic decay times of kaons and pions with uncertainty < 1%. Using the measured kinetic energies of the mesons gives exact energy conservation. We conclude that annihilation of nucleons in H(0) is observed. This may have profound effects on future energy production, since the efficiency of the fuel in annihilation is roughly a factor of 100 higher than in a nuclear fusion process. Ordinary hydrogen (protium and deuterium) can be used as fuel instead of radioactive tritium. This means that energy is generated at low cost and with very little harmful radiation both for terrestrial and space applications (Acta Astronautica 2020).
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| 2. |
- Iwan, Bianca S, et al.
(author)
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TOF-OFF : A method for determining focal positions in tightly focused free-electron laser experiments by measurement of ejected ions
- 2011
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In: High Energy Density Physics. - : Elsevier BV. - 1574-1818. ; 7:4, s. 336-342
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Journal article (peer-reviewed)abstract
- Pulse intensities greater than 1017 Watt/cm2 were reached at the FLASH soft X-ray laser in Hamburg, Germany, using an off-axis parabolic mirror to focus 15 fs pulses of 5–70 μJ energy at 13.5 nm wavelength to a micron-sized spot. We describe the interaction of such pulses with niobium and vanadium targets and their deuterides. The beam produced craters in the solid targets, and we measured the kinetic energy of ions ejected from these craters. Ions with several keV kinetic energy were observed from craters approaching 5 μm in depth when the sample was at best focus. We also observed the onset of saturation in both ion acceleration and ablation with pulse intensities exceeding 1016 W/cm2, when the highest detected ion energies and the crater depths tend to saturate with increasing intensity. A general difficulty in working with micron and sub-micron focusing optics is finding the exact focus of the beam inside a vacuum chamber. Here we propose a direct method to measure the focal position to a resolution better than the Rayleigh length. The method is based on the correlation between the energies of ejected ions and the physical dimensions of the craters. We find that the focus position can be quickly determined from the ion time-of-flight (TOF) data as the target is scanned through the expected focal region. The method does not require external access to the sample or venting the vacuum chamber. Profile fitting employed to analyze the TOF data can extend resolution beyond the actual scanning step size.
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| 3. |
- Jönsson, Olof, et al.
(author)
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FreeDam – A Webtool for Free-Electron Laser-Induced Damage in Femtosecond X-ray Crystallography
- 2018
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In: High Energy Density Physics. - : Elsevier. - 1574-1818. ; 26, s. 93-98
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Journal article (peer-reviewed)abstract
- Over the last decade X-ray free-electron laser (XFEL) sources have been made available to the scientific community. One of the most successful uses of these new machines has been protein crystallography. When samples are exposed to the intense short X-ray pulses provided by the XFELs, the sample quickly becomes highly ionized and the atomic structure is affected. Here we present a webtool dubbed FreeDam based on non-thermal plasma simulations, for estimation of radiation damage in free-electron laser experiments in terms of ionization, temperatures and atomic displacements. The aim is to make this tool easily accessible to scientists who are planning and performing experiments at XFELs.
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| 4. |
- Nazir, Sadia, et al.
(author)
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Ab-initio simulations of MgTiO3 oxide at different pressure
- 2019
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In: High Energy Density Physics. - : Elsevier. - 1574-1818. ; 33
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Journal article (peer-reviewed)abstract
- We employ Wien2k code, an all-electron scheme based on density functional theory (DFT) to explore the structural, thermodynamic, mechanical and opto-electronic behavior of MgTiO3 (MTO) oxide in the pressure range 0-200GPa. The structural, mechanical and thermodynamic stabilities of MTO are discussed in terms of Goldschmidt's tolerance factor, enthalpy of formation and Born stability criteria, respectively. Mechanical nature is further discussed by calculating the Debye temperature, wave velocity, Pugh's and Poisson's ratios. The electron density (n) and specific heat capacity (Cv) of electrons are explained in details. The pressure up to 200 GPa, with the step of 50 GPa, is implemented in order to tune the electronic properties where a direct to indirect band gap transition is observed. We further explored the refraction of light (ultraviolet region), dielectric constant and the optical behavior of MTO.
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| 5. |
- Tramontina, Diego, et al.
(author)
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Molecular dynamics simulations of shock-induced plasticity in tantalum
- 2014
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In: High Energy Density Physics. - : Elsevier BV. - 1574-1818. ; 10:3, s. 9-15
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Journal article (peer-reviewed)abstract
- We present Non-Equilibrium Molecular Dynamics (NEMD) simulations of shock wave compression along the [001] direction in monocrystalline Tantalum, including pre-existing defects which act as dislocation sources. We use a new Embedded Atom Model (EAM) potential and study the nucleation and evolution of dislocations as a function of shock pressure and loading rise time. We find that the flow stress and dislocation density behind the shock front depend on strain rate. We find excellent agreement with recent experimental results on strength and recovered microstructure, which goes from dislocations to a mixture of dislocations and twins, to twinning dominated response, as the shock pressure increases.
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