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Y A Omarbakiyeva - One of the best experts on this subject based on the ideXlab platform.
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cluster virial expansion of the equation of state for Hydrogen Plasma with e h 2 contributions
Physical Review E, 2015Co-Authors: Y A Omarbakiyeva, H Reinholz, G RopkeAbstract:The equation of state of partially ionized Hydrogen Plasma is considered with special focus on the contribution of the $e\text{\ensuremath{-}}{\mathrm{H}}_{2}$ interaction. Traditional semiempirical concepts such as the excluded volume are improved using microscopic approaches to treat the $e\text{\ensuremath{-}}{\mathrm{H}}_{2}$ problem. Within a cluster virial expansion, the Beth-Uhlenbeck formula is applied to infer the contribution of bound and scattering states to the temperature-dependent second virial coefficient. The scattering states are calculated using the phase expansion method for the polarization interaction that incorporates experimental data for the $e\text{\ensuremath{-}}{\mathrm{H}}_{2}$ scattering cross section. We present results for the scattering phase shifts, differential scattering cross sections, and the second virial coefficient due to the $e\text{\ensuremath{-}}{\mathrm{H}}_{2}$ interaction. The influence of this interaction on the composition of the partially ionized Hydrogen Plasma is confined to the parameter range where both the ${\mathrm{H}}_{2}$ and the free-electron components are abundant.
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cluster virial expansion for the equation of state of partially ionized Hydrogen Plasma
Physical Review E, 2010Co-Authors: Y A Omarbakiyeva, C Fortmann, T S Ramazanov, G RopkeAbstract:We study the contribution of electron-atom interaction to the equation of state for partially ionized Hydrogen Plasma using the cluster-virial expansion. We use the Beth-Uhlenbeck approach to calculate the second virial coefficient for the electron-atom (bound cluster) pair from the corresponding scattering phase shifts and binding energies. Experimental scattering cross-sections as well as phase shifts calculated on the basis of different pseudopotential models are used as an input for the Beth-Uhlenbeck formula. By including Pauli blocking and screening in the phase shift calculation, we generalize the cluster-virial expansion in order to cover also near solid density Plasmas. We present results for the electron-atom contribution to the virial expansion and the corresponding equation of state, i.e. pressure, composition, and chemical potential as a function of density and temperature. These results are compared with semiempirical approaches to the thermodynamics of partially ionized Plasmas. Avoiding any ill-founded input quantities, the Beth-Uhlenbeck second virial coefficient for the electron-atom interaction represents a benchmark for other, semiempirical approaches.
D Daan C Schram - One of the best experts on this subject based on the ideXlab platform.
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optimization of the output and efficiency of a high power cascaded arc Hydrogen Plasma source
Physics of Plasmas, 2008Co-Authors: W A J Vijvers, D Daan C Schram, W J Goedheer, V P Veremiyenko, C A J Van Gils, H J Van Der Meiden, J Westerhout, N Lopes J Cardozo, G J Van RooijAbstract:The operation of a cascaded arc Hydrogen Plasma source was experimentally investigated to provide an empirical basis for the scaling of this source to higher Plasma fluxes and efficiencies. The flux and efficiency were determined as a function of the input power, discharge channel diameter, and Hydrogen gas flow rate. Measurements of the pressure in the arc channel show that the flow is well described by Poiseuille flow and that the effective heavy particle temperature is approximately 0.8eV. Interpretation of the measured I-V data in terms of a one-parameter model shows that the Plasma production is proportional to the input power, to the square root of the Hydrogen flow rate, and is independent of the channel diameter. The observed scaling shows that the dominant power loss mechanism inside the arc channel is one that scales with the effective volume of the Plasma in the discharge channel. Measurements on the Plasma output with Thomson scattering confirm the linear dependence of the Plasma production on...
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extreme Hydrogen Plasma densities achieved in a linear Plasma generator
Applied Physics Letters, 2007Co-Authors: G J Van Rooij, W J Goedheer, Richard Engeln, Aart W Kleyn, V P Veremiyenko, B De Groot, P H M Smeets, T W Versloot, D G Whyte, D Daan C SchramAbstract:A magnetized Hydrogen Plasma beam was generated with a cascaded arc, expanding in a vacuum vessel at an axial magnetic field of up to 1.6T. Its characteristics were measured at a distance of 4cm from the nozzle: up to a 2cm beam diameter, 7.5×1020m−3 electron density, ∼2eV electron and ion temperatures, and 3.5km∕s axial Plasma velocity. This gives a 2.6×1024H+m−2s−1 peak ion flux density, which is unprecedented in linear Plasma generators. The high efficiency of the source is obtained by the combined action of the magnetic field and an optimized nozzle geometry. This is interpreted as a cross-field return current that leads to power dissipation in the beam just outside the source.
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behavior of the h atom velocity distribution function within the shock wave of a Hydrogen Plasma jet
Physical Review E, 2001Co-Authors: St Ephane Mazouffre, Pjw Peter Vankan, Rah Richard Engeln, D Daan C SchramAbstract:The evolution of the ground-state Hydrogen atom velocity distribution function throughout the stationary shock wave of a supersonic Hydrogen Plasma jet (3
velocity distribution function may be decomposed into two Maxwellian distributions. The fast component of the distribution corresponds to the unhampered supersonic conditions. The slow component corresponds to the conditions in the shock region, i.e., within the shock front, the mean velocity and the temperature of this atom group vary. Across the shock wave, the H atom population is gradually transferred from the fast to the slow component by means of collisions. The development of the mean axial velocity is modeled using the Mott-Smith approach. Departure from the theoretical shock profile is interpreted in terms of the nonconservation of both the H atom forward flux and momentum across the shock wave. -
influence of surface chemistry on the transport of h atoms in a supersonic Hydrogen Plasma jet
Physics of Plasmas, 2001Co-Authors: St Ephane Mazouffre, Pjw Peter Vankan, Rah Richard Engeln, D Daan C SchramAbstract:The transport of ground-state Hydrogen atoms in the expansion of a thermal Hydrogen Plasma created by a cascaded arc is studied by means of two-photon absorption laser induced fluorescence. The low-dissociation degree measured at the source exit implies that H atoms flow in a H2 environment. It is shown that the H atom expansion pattern is in disagreement with the neutral gas supersonic expansion theory. Indeed the transport of H atoms in the Plasma jet is strongly influenced by surface-recombination processes. Because of the large density gradients between the core of the jet and its surroundings induced by the recombination of H atoms at the reactor walls, Hydrogen atoms diffuse out of the Plasma jet in the course of the expansion. When the surface loss probability is high, i.e., the combination of a large wall-recombination probability with a long residence time, the losses of radicals by diffusion cannot be avoided even when the mass of the carrier gas is close to the mass of the radical.
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diagnostics of the magnetized low pressure Hydrogen Plasma jet molecular regime
Journal of Applied Physics, 1996Co-Authors: Zhou Z Qing, D K Otorbaev, Gjh Seth Brussaard, Van De Mcm Richard Sanden, D Daan C SchramAbstract:rotational temperature of the excited state H 2~d 2 P u) has been determined by analyzing the intensity distribution of the spectral lines of the Fulcher- a system of H 2 . The gas temperature in the Plasma, which is twice the value of the rotational temperature is equal to . 520 K. Several clear indications of presence of the ‘‘hot’’ electrons have been observed in the Plasma: ~1! Langmuir probe measurements ~T e .1.4 eV!, ~2! appearance of the Fulcher-a system of H 2 ~excitation potential DE513.87 eV!, ~3! low rotational temperature ~T rot .260 K! of the excited H 2 ~d 3 P u ) molecules, ~4! local excitation in the Plasma of Ar I~DE515.45 eV!, and Ar II~DE519.68 eV! spectral lines, ~5! local excitation in the Plasma of He I~DE523.07 eV and DE524.04 eV! spectral lines. Optical actinometry has been applied to measure the absolute density of Hydrogen atoms and Hydrogen dissociation degree in the Plasma. The measured absolute density of Hydrogen atoms are in the ~1‐1.4!310 20 m 23 range, and the corresponding dissociation degree of the Hydrogen Plasma is in the range of 8%‐13%. © 1996 American Institute of Physics.@S0021-8979~96!01914-7#
G Ropke - One of the best experts on this subject based on the ideXlab platform.
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cluster virial expansion of the equation of state for Hydrogen Plasma with e h 2 contributions
Physical Review E, 2015Co-Authors: Y A Omarbakiyeva, H Reinholz, G RopkeAbstract:The equation of state of partially ionized Hydrogen Plasma is considered with special focus on the contribution of the $e\text{\ensuremath{-}}{\mathrm{H}}_{2}$ interaction. Traditional semiempirical concepts such as the excluded volume are improved using microscopic approaches to treat the $e\text{\ensuremath{-}}{\mathrm{H}}_{2}$ problem. Within a cluster virial expansion, the Beth-Uhlenbeck formula is applied to infer the contribution of bound and scattering states to the temperature-dependent second virial coefficient. The scattering states are calculated using the phase expansion method for the polarization interaction that incorporates experimental data for the $e\text{\ensuremath{-}}{\mathrm{H}}_{2}$ scattering cross section. We present results for the scattering phase shifts, differential scattering cross sections, and the second virial coefficient due to the $e\text{\ensuremath{-}}{\mathrm{H}}_{2}$ interaction. The influence of this interaction on the composition of the partially ionized Hydrogen Plasma is confined to the parameter range where both the ${\mathrm{H}}_{2}$ and the free-electron components are abundant.
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cluster virial expansion for the equation of state of partially ionized Hydrogen Plasma
Physical Review E, 2010Co-Authors: Y A Omarbakiyeva, C Fortmann, T S Ramazanov, G RopkeAbstract:We study the contribution of electron-atom interaction to the equation of state for partially ionized Hydrogen Plasma using the cluster-virial expansion. We use the Beth-Uhlenbeck approach to calculate the second virial coefficient for the electron-atom (bound cluster) pair from the corresponding scattering phase shifts and binding energies. Experimental scattering cross-sections as well as phase shifts calculated on the basis of different pseudopotential models are used as an input for the Beth-Uhlenbeck formula. By including Pauli blocking and screening in the phase shift calculation, we generalize the cluster-virial expansion in order to cover also near solid density Plasmas. We present results for the electron-atom contribution to the virial expansion and the corresponding equation of state, i.e. pressure, composition, and chemical potential as a function of density and temperature. These results are compared with semiempirical approaches to the thermodynamics of partially ionized Plasmas. Avoiding any ill-founded input quantities, the Beth-Uhlenbeck second virial coefficient for the electron-atom interaction represents a benchmark for other, semiempirical approaches.
T.w. Morgan - One of the best experts on this subject based on the ideXlab platform.
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Recrystallization-mediated crack initiation in tungsten under simultaneous high-flux Hydrogen Plasma loads and high-cycle transient heating
Nuclear Fusion 61 046018, 2021Co-Authors: T.w. Morgan, M Wirtz, T. Vermeij, J.w. M. Vernimmen, T. Loewenhoff, J.p. M. Hoefnagels, J.a. W. Van Dommelen, G. De Temmerman, K. VerbekenAbstract:Tungsten and tungsten-based alloys are the leading material choices for the divertor Plasma facing components (PFCs) in future fusion reactors. Recrystallization may occur when they undergo high heat loads, drastically modifying the predesigned grain structures and the associated desired mechanical properties. However, the influence of recrystallization on the thermal fatigue behavior of tungsten PFCs still remains unclear. In this study, ITER-grade tungsten was simultaneously exposed to a high-flux Hydrogen Plasma (~5×1024 m-2s-1) and high-cycle (104-105) transient heat loads in the linear Plasma device Magnum-PSI. By correlating the surface temperature distribution, obtained by analyzing temperature-, wavelength-, and surface-dependent emissivity, and the surface modifications of the Plasma exposed specimens, the crack initiation heat flux factor threshold was found to be ~2 MWm-2s0.5 (equivalently, ~0.07 MJm-2 for a 1 ms pulse), which slightly decreases with increasing surface temperature (~1550 K) and increasing pulse number. Based on electron backscatter diffraction (EBSD) analyses of cross-sections near the crack initiation sites, faster recrystallization kinetics near the surface compared to literature was observed and the surface cracks preferentially initiated at high angle grains boundaries (HAGBs). Upon recrystallization, the yield strength decreases which entails increasing cyclic plastic strains. The HAGBs fraction is increased, which constrains the transfer of plastic strains at grain boundaries. The recrystallization decreases the dislocation density, which promotes heterogeneous deformation. All these mechanisms explain the reduced crack initiation threshold of recrystallized tungsten compared to its as-received counterpart. The results provide new insights into the structural failure mechanisms in tungsten PFCs exposed to extreme fusion Plasmas
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Recrystallization behaviour of high-flux Hydrogen Plasma exposed tungsten
Journal of Nuclear Materials 545 152748, 2021Co-Authors: V. Shah, M Wirtz, T.w. Morgan, T. Loewenhoff, J.t. S. Beune, J.a. W. Van DommelenAbstract:Knowledge of a material’s thermal stability under extreme synergistic particle and heat loads is crucial for developing high performance reactor materials. In this work, the recrystallization behaviour of tungsten under the influence of Hydrogen is investigated by low energy high flux Hydrogen Plasma exposure for various lengths of time. The microstructural changes following exposure are probed by micro-indentation, electron back-scatter diffraction measurements and the characteristic time for recrystallization is assessed using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) model. A recrystallization activation energy in the range of 425 to 440 kJ.mol-1_ is determined, identical to that of oven annealed samples, thereby indicating an insignificant influence of Hydrogen Plasma on the recrystallization kinetics of tungsten
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Power deposition behavior of high-density transient Hydrogen Plasma on tungsten in Magnum-PSI
Plasma Physics and Controlled Fusion 63 085016, 2021Co-Authors: T.w. Morgan, J.p. M. Hoefnagels, J.a. W. Van Dommelen, G. De Temmerman, K. Verbeken, J. Van Den Berg, J.w. Genuit, M.g. D. GeersAbstract:The lifetime of Plasma-facing components (PFCs) will have a strong influence on the efficiency and viability of future fusion power plants. However, the PFCs suffer from thermal stresses and physical sputtering induced by edge-localized modes (ELMs). ELMs in future fusion devices are expected to occur with a high Plasma density compared to current day devices such that coupling of recycling neutrals and Plasma ions will be strong. Because of the scale hierarchy of future fusion devices compared to the present ones, the influence of this coupling is difficult to predict. Here, we investigate the ELM-like Hydrogen Plasma induced heat loads on tungsten in the linear device Magnum-PSI, producing similar to 1 ms Plasma pulses with electron densities up to 3.5 x 10(21) m(-3). A combination of time-resolved Thomson scattering and coherent Thomson scattering was used to acquire Plasma parameters in front of the target. Moreover, a fast infrared camera coupled to finite element thermal analyses allowed to determine the deposited heat loads on the target. We found a significant inconsistency between the Plasma power calculated with a conventional collisionless sheath model and the absorbed power by the target. Moreover, Plasma stagnation upstream and Plasma cooling downstream were observed during the pulses. The observations are explained based on ionization and elastic collisions between the recycling neutrals and Plasma ions. The results highlight the impact of Plasma-neutral interaction on the power deposition behavior of ELM-like Hydrogen Plasma on tungsten
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fracture behavior of tungsten based composites exposed to steady state transient Hydrogen Plasma
Nuclear Fusion, 2020Co-Authors: T.w. Morgan, J.p. M. Hoefnagels, J.a. W. Van Dommelen, G. De Temmerman, S Antusch, M Rieth, D Terentyev, Kim Verbeken, M.g. D. GeersAbstract:The fracture behavior of Plasma-facing components (PFCs) under extreme Plasma-material interaction conditions is of great concern to ITER and future fusion reactors. This was explored in the current study by exposing pure tungsten (W), W-1%TiC and W-2%Y2O3 composites to a combined steady-state/transient Hydrogen Plasma up to a base surface temperature of 2224 K, and up to 5000 transient pulses for 1000 seconds using the linear Plasma generator Magnum-PSI. The applied heat loads were characterized by combining sheath physics, thermographic information and finite element analyses, with which the thermal stress was evaluated. Combining microstructural investigation and thermo-mechanical numerical analyses, a physical picture of fracture is developed. The transient heat loads drive surface crack initiation, whose depth can be estimated by a simple analytical model for pure tungsten, while the cooling period following the steady-state heat load induces tensile stresses, opening existing surface cracks deeper. The fracture process is mediated by the microstructure whereby the ceramic particles stabilize the microstructure but promote surface crack initiation due to suppressed plasticity at the grain boundaries. The surface cracks relieve the subsequent cycles of transient thermal stress but intensify the steady-state thermal stress, therefore, promoting deep crack propagation. These results help to understand failure mechanisms in PFCs under extreme operation conditions which are valuable for developing advanced PFCs.
Lars Korte - One of the best experts on this subject based on the ideXlab platform.
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Hydrogen Plasma treatments for passivation of amorphous crystalline silicon heterojunctions on surfaces promoting epitaxy
Applied Physics Letters, 2013Co-Authors: Mathias Mews, T F Schulze, Nicola Mingirulli, Lars KorteAbstract:The impact of post-deposition Hydrogen Plasma treatment (HPT) on passivation in amorphous/crystalline silicon (a-Si:H/c-Si) interfaces is investigated. Combining low temperature a-Si:H deposition and successive HPT, a high minority carrier lifetime >8 ms is achieved on c-Si 〈100〉, which is otherwise prone to epitaxial growth and thus inferior passivation. It is shown that the passivation improvement stems from diffusion of Hydrogen atoms to the heterointerface and subsequent dangling bond passivation. Concomitantly, the a-Si:H Hydrogen density increases, leading to band gap widening and void formation, while the film disorder is not increased. Thus, HPT allows for a-Si:H band gap and a-Si:H/c-Si band offset engineering.The impact of post-deposition Hydrogen Plasma treatment (HPT) on passivation in amorphous/crystalline silicon (a-Si:H/c-Si) interfaces is investigated. Combining low temperature a-Si:H deposition and successive HPT, a high minority carrier lifetime >8 ms is achieved on c-Si 〈100〉, which is otherwise prone to epitaxial growth and thus inferior passivation. It is shown that the passivation improvement stems from diffusion of Hydrogen atoms to the heterointerface and subsequent dangling bond passivation. Concomitantly, the a-Si:H Hydrogen density increases, leading to band gap widening and void formation, while the film disorder is not increased. Thus, HPT allows for a-Si:H band gap and a-Si:H/c-Si band offset engineering.
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Hydrogen Plasma treatments for passivation of amorphous crystalline silicon heterojunctions on surfaces promoting epitaxy
Applied Physics Letters, 2013Co-Authors: Mathias Mews, T F Schulze, Nicola Mingirulli, Lars KorteAbstract:The impact of post-deposition Hydrogen Plasma treatment (HPT) on passivation in amorphous/crystalline silicon (a-Si:H/c-Si) interfaces is investigated. Combining low temperature a-Si:H deposition and successive HPT, a high minority carrier lifetime >8 ms is achieved on c-Si 〈100〉, which is otherwise prone to epitaxial growth and thus inferior passivation. It is shown that the passivation improvement stems from diffusion of Hydrogen atoms to the heterointerface and subsequent dangling bond passivation. Concomitantly, the a-Si:H Hydrogen density increases, leading to band gap widening and void formation, while the film disorder is not increased. Thus, HPT allows for a-Si:H band gap and a-Si:H/c-Si band offset engineering.
