Sabina Markelj | Jožef Stefan Institute (original) (raw)
Papers by Sabina Markelj
In this work we studied the effect of grain size on retention and transport of deuterium in tungs... more In this work we studied the effect of grain size on retention and transport of deuterium in tungsten. Tungsten consists of grains with distinct crystal structure that are separated by grain boundaries. These grain boundaries can act as weak trapping sites for hydrogen isotopes and also act as a faster way for deuterium diffusion into the bulk of the material [1]. From the results of this study we can extrapolate the influence of grain size on tritium retention and transport in the walls of future fusion reactors made of tungsten. We carried out the experiment on three polycrystalline samples of tungsten that have different average grain sizes and a monocrystalline sample with surface orientation (100). In tungsten, native defects in the crystal mesh are present which act as strong trapping sites for hydrogen isotopes. Additional defects are created when the material is bombarded by particles from the hydrogen plasma and by neutron bombardment. In experiments samples were bombarded b...
EPJ Web of Conferences
For nucleosynthesis calculations, precise reaction rates should be known at energies within the G... more For nucleosynthesis calculations, precise reaction rates should be known at energies within the Gamow window. At these energies, electron screening cannot be neglected. Despite the significance of the effect, a huge disagreement between experimental data and theoretical predictions is still not understood. In order to address to this problem, we investigated the dependence of the electron screening potential on the target host lattice structure by measuring the rate of the 2H(19F,p)20F reaction in zirconium, titanium and palladium targets containing deuterium.
18th International Conference on Plasma-Facing Materials and Components for Fusion Applications (PFMC-18), 2021
18th International Conference on Plasma-Facing Materials and Components for Fusion Applications (PFMC-18), 2021
28th IAEA Fusion Energy Conference (FEC 2020), 2020
5th International Workshop Models and Data for Plasma-Material Interaction in Fusion Devices (MoD-PMI 2021) (virtual), 2021
30th International Conference Nuclear Energy for New Europe (NENE 2021), 2021
European Physical Journal A, 2010
We have measured the cross-section for the 1 H( 7 Li,[FORMULA]) 4 He reaction at lithium beam ene... more We have measured the cross-section for the 1 H( 7 Li,[FORMULA]) 4 He reaction at lithium beam energies from 0.34 to 1.05MeV. Hydrogen was forced by diffusion into Pd and PdAg alloy foils. A large electron screening effect was observed only when foils were under tensile stress. A dependence of the screening potential on hydrogen concentration or Hall coefficient of the metallic host could not be established.
Detailed knowledge of surface processes on plasma facing components is of high importance for und... more Detailed knowledge of surface processes on plasma facing components is of high importance for understanding and modelling of the edge plasma in tokamaks. This requires information on the kind of emitted particles as well as their state of excitation. While this was to more extent studied for carbon materials much less is known for metals (ITER relevant W) and especially at higher temperatures relevant to divertor operation and transient heat load phenomena. The production of vibrationally excited molecules by hydrogen atom (H and D) recombination is a subject of a present studies. A vibrational spectrometer is used for determination of vibrational excitation of hydrogen molecules. It was recently upgraded by single-stage differential pumping thus separating the detector and the reaction chamber. Recent results with new experimental arrangement are presented and compared to the results obtained with the old experimental set-up.
Journal of Nuclear Materials, 2021
Abstract Bulk tungsten samples were irradiated sequentially with 20 MeV tungsten ions and exposed... more Abstract Bulk tungsten samples were irradiated sequentially with 20 MeV tungsten ions and exposed to deuterium plasma. The experiments were performed in order to simulate the displacement damage that fusion neutrons will cause in a tungsten plasma-facing component of a future fusion device. To study the influence of the presence of hydrogen isotopes during the creation of displacement damage on the final defect density, tungsten irradiation and deuterium decoration cycles were performed up to three times. Deuterium depth profiling with 3He Nuclear Reaction Analysis and Thermal Desorption Spectroscopy showed that the deuterium concentration increased after each additional tungsten irradiation and deuterium exposure. After the third cycle, the deuterium concentration reached a maximum of 3.6 at.% at the given plasma exposure temperature of 370 K. We attribute this increase in retention to the stabilization of the displacement damage during the tungsten irradiation by the presence of deuterium. The experimental results were simulated using the MHIMS-R macroscopic rate-equation code, which was recently upgraded with a damage stabilization term to describe experiments where tungsten was irradiated with MeV tungsten ions and simultaneously exposed to low-energy deuterium ions. Using this novel model, it was possible to quantitatively describe also the present results for the sequential irradiation/exposure scheme, with model parameters that were congruent with parameters derived from the simultaneous experiment. Modelling shows that kinetic de-trapping of trapped deuterium takes place during irradiation However, it is not the dominant process that explains defect stabilization. In addition, the model facilitates the extrapolation of present experimental results to an even larger number of sequential tungsten irradiation and deuterium exposure cycles. The model predicts that after about five sequential irradiation and plasma exposure cycles, a stationary state is reached with an associated maximum trapped D concentration of 4.2 at.% for the given exposure temperature of 370 K.
Nuclear Fusion, 2021
Gross and net erosion of tungsten (W) and other plasma-facing materials in the divertor region ha... more Gross and net erosion of tungsten (W) and other plasma-facing materials in the divertor region have been investigated in deuterium (D) and helium (He) plasmas during dedicated experiments in L- and H-mode on ASDEX Upgrade and after full-length experimental campaigns on the WEST tokamak. Net erosion was determined via post-exposure analyses of plasma-exposed samples and full-size wall components, and we conclude that the same approach is applicable to gross erosion if marker structures with sub-millimeter dimensions are used to eliminate the contribution of prompt re-deposition. In H-mode plasmas, gross erosion during ELMs may exceed the situation in inter-ELM conditions by 1–2 orders of magnitude while net erosion is typically higher by a factor of 2–3. The largest impact on net erosion is attributed to the electron temperature while the role of the impurity mixtures is weaker, even though both on ASDEX Upgrade and WEST significant amounts of impurities are present in the edge plasmas. Impurities, on the other hand, will lead to the formation of thick co-deposited layers. We have also noted that with increasing surface roughness, net erosion is strongly suppressed and the growth of co-deposited layers is enhanced. In He plasmas, gross erosion is increased compared to D due to the higher mass and charge states of the plasma particles, resulting from larger energies due to sheath acceleration, but strong impurity fluxes can result in apparent net deposition in the divertor. Our results from ASDEX Upgrade and WEST are comparable and indicate typical net-erosion rates of 0.1–0.4 nm s−1, excluding the immediate vicinity of the strike-point regions.
In this work we studied the effect of grain size on retention and transport of deuterium in tungs... more In this work we studied the effect of grain size on retention and transport of deuterium in tungsten. Tungsten consists of grains with distinct crystal structure that are separated by grain boundaries. These grain boundaries can act as weak trapping sites for hydrogen isotopes and also act as a faster way for deuterium diffusion into the bulk of the material [1]. From the results of this study we can extrapolate the influence of grain size on tritium retention and transport in the walls of future fusion reactors made of tungsten. We carried out the experiment on three polycrystalline samples of tungsten that have different average grain sizes and a monocrystalline sample with surface orientation (100). In tungsten, native defects in the crystal mesh are present which act as strong trapping sites for hydrogen isotopes. Additional defects are created when the material is bombarded by particles from the hydrogen plasma and by neutron bombardment. In experiments samples were bombarded b...
EPJ Web of Conferences
For nucleosynthesis calculations, precise reaction rates should be known at energies within the G... more For nucleosynthesis calculations, precise reaction rates should be known at energies within the Gamow window. At these energies, electron screening cannot be neglected. Despite the significance of the effect, a huge disagreement between experimental data and theoretical predictions is still not understood. In order to address to this problem, we investigated the dependence of the electron screening potential on the target host lattice structure by measuring the rate of the 2H(19F,p)20F reaction in zirconium, titanium and palladium targets containing deuterium.
18th International Conference on Plasma-Facing Materials and Components for Fusion Applications (PFMC-18), 2021
18th International Conference on Plasma-Facing Materials and Components for Fusion Applications (PFMC-18), 2021
28th IAEA Fusion Energy Conference (FEC 2020), 2020
5th International Workshop Models and Data for Plasma-Material Interaction in Fusion Devices (MoD-PMI 2021) (virtual), 2021
30th International Conference Nuclear Energy for New Europe (NENE 2021), 2021
European Physical Journal A, 2010
We have measured the cross-section for the 1 H( 7 Li,[FORMULA]) 4 He reaction at lithium beam ene... more We have measured the cross-section for the 1 H( 7 Li,[FORMULA]) 4 He reaction at lithium beam energies from 0.34 to 1.05MeV. Hydrogen was forced by diffusion into Pd and PdAg alloy foils. A large electron screening effect was observed only when foils were under tensile stress. A dependence of the screening potential on hydrogen concentration or Hall coefficient of the metallic host could not be established.
Detailed knowledge of surface processes on plasma facing components is of high importance for und... more Detailed knowledge of surface processes on plasma facing components is of high importance for understanding and modelling of the edge plasma in tokamaks. This requires information on the kind of emitted particles as well as their state of excitation. While this was to more extent studied for carbon materials much less is known for metals (ITER relevant W) and especially at higher temperatures relevant to divertor operation and transient heat load phenomena. The production of vibrationally excited molecules by hydrogen atom (H and D) recombination is a subject of a present studies. A vibrational spectrometer is used for determination of vibrational excitation of hydrogen molecules. It was recently upgraded by single-stage differential pumping thus separating the detector and the reaction chamber. Recent results with new experimental arrangement are presented and compared to the results obtained with the old experimental set-up.
Journal of Nuclear Materials, 2021
Abstract Bulk tungsten samples were irradiated sequentially with 20 MeV tungsten ions and exposed... more Abstract Bulk tungsten samples were irradiated sequentially with 20 MeV tungsten ions and exposed to deuterium plasma. The experiments were performed in order to simulate the displacement damage that fusion neutrons will cause in a tungsten plasma-facing component of a future fusion device. To study the influence of the presence of hydrogen isotopes during the creation of displacement damage on the final defect density, tungsten irradiation and deuterium decoration cycles were performed up to three times. Deuterium depth profiling with 3He Nuclear Reaction Analysis and Thermal Desorption Spectroscopy showed that the deuterium concentration increased after each additional tungsten irradiation and deuterium exposure. After the third cycle, the deuterium concentration reached a maximum of 3.6 at.% at the given plasma exposure temperature of 370 K. We attribute this increase in retention to the stabilization of the displacement damage during the tungsten irradiation by the presence of deuterium. The experimental results were simulated using the MHIMS-R macroscopic rate-equation code, which was recently upgraded with a damage stabilization term to describe experiments where tungsten was irradiated with MeV tungsten ions and simultaneously exposed to low-energy deuterium ions. Using this novel model, it was possible to quantitatively describe also the present results for the sequential irradiation/exposure scheme, with model parameters that were congruent with parameters derived from the simultaneous experiment. Modelling shows that kinetic de-trapping of trapped deuterium takes place during irradiation However, it is not the dominant process that explains defect stabilization. In addition, the model facilitates the extrapolation of present experimental results to an even larger number of sequential tungsten irradiation and deuterium exposure cycles. The model predicts that after about five sequential irradiation and plasma exposure cycles, a stationary state is reached with an associated maximum trapped D concentration of 4.2 at.% for the given exposure temperature of 370 K.
Nuclear Fusion, 2021
Gross and net erosion of tungsten (W) and other plasma-facing materials in the divertor region ha... more Gross and net erosion of tungsten (W) and other plasma-facing materials in the divertor region have been investigated in deuterium (D) and helium (He) plasmas during dedicated experiments in L- and H-mode on ASDEX Upgrade and after full-length experimental campaigns on the WEST tokamak. Net erosion was determined via post-exposure analyses of plasma-exposed samples and full-size wall components, and we conclude that the same approach is applicable to gross erosion if marker structures with sub-millimeter dimensions are used to eliminate the contribution of prompt re-deposition. In H-mode plasmas, gross erosion during ELMs may exceed the situation in inter-ELM conditions by 1–2 orders of magnitude while net erosion is typically higher by a factor of 2–3. The largest impact on net erosion is attributed to the electron temperature while the role of the impurity mixtures is weaker, even though both on ASDEX Upgrade and WEST significant amounts of impurities are present in the edge plasmas. Impurities, on the other hand, will lead to the formation of thick co-deposited layers. We have also noted that with increasing surface roughness, net erosion is strongly suppressed and the growth of co-deposited layers is enhanced. In He plasmas, gross erosion is increased compared to D due to the higher mass and charge states of the plasma particles, resulting from larger energies due to sheath acceleration, but strong impurity fluxes can result in apparent net deposition in the divertor. Our results from ASDEX Upgrade and WEST are comparable and indicate typical net-erosion rates of 0.1–0.4 nm s−1, excluding the immediate vicinity of the strike-point regions.