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| 2. |
- Castello, Federico, et al.
(författare)
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Structure and thermodynamics of two dimensional Yukawa liquids
- 2021
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - : American Physical Society (APS). - 1063-651X .- 1095-3787. ; 103:063205
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Tidskriftsartikel (refereegranskat)abstract
- The thermodynamic and structural properties of two dimensional dense Yukawa liquids are studied with molecular dynamics simulations. The "exact" thermodynamic properties are simultaneously employed in an advanced scheme for the determination of an equation of state that shows an unprecedented level of accuracy for the internal energy, pressure and isothermal compressibility. The "exact" structural properties are utilized to formulate a novel empirical correction to the hypernetted-chain approach that leads to a very high accuracy level in terms of static correlations and thermodynamics.
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| 3. |
- Castello Lucco, Federico
(författare)
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Bridge functions in strongly coupled plasmas : theory, simulations and applications
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Strongly coupled or non-ideal plasmas are multi-component charged systems in which at least one species possesses an average interaction energy that is comparable or larger than its thermal energy. Non-ideal plasmas are naturally occurring in dense astrophysical objects (e.g. giant planet interiors) but also engineered in the laboratory (e.g. plasma discharges seeded with solid particulates). They are typically encountered in the liquid state, whose theoretical description is particularly challenging due to the lack of small parameters. This thesis is focused on the development of a novel theoretical approach for the accurate calculation of the structural and thermodynamic properties of plasma liquids. Apart from their inherent significance, these properties also constitute necessary input to advanced theories of dynamical correlations, collective excitations and transport coefficients. The theoretical approach is based on the integral equation theory framework, whose central quantity is the bridge function; an abstract object of diagrammatic analysis that is impossible to calculate or even approximate through virial-type expansions. Here the bridge function is accurately determined by combining elements of the isomorph theory of R-simple liquids with indirect extractions from computer simulations. The unprecedented level of accuracy in both the structural and thermodynamic properties and the very low computational cost, render the approach the most efficient alternative to computer simulations of classical and quantum plasma liquids. Applications to collective modes and metastable properties are also discussed.
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| 4. |
- Coburn, J., et al.
(författare)
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First wall energy deposition during vertical displacement events on ITER
- 2020
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Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; T171:1
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Tidskriftsartikel (refereegranskat)abstract
- The beryllium (Be) first wall energy deposition and melt damage profiles resulting from the current quench phase of an unmitigated, 5 MA/1.8 T upward vertical displacement event for ITER are investigated. Time dependent 2D magnetic flux profiles are calculated with the DINA code and used as input for the SMITER 3D field line tracing software. 3D maps of the wetted area and perpendicular heat flux q(perpendicular to) show that the majority of the energy deposition occurs on the upper first wall panels #8 and #9 SMITER simulations predict q(perpendicular to,peak) approximate to 190 MW m(-2) on the surfaces of upper FWPs #8 and #9 at the end of the similar to 450 ms current quench. The surface heat flux maps generated by SMITER are used as input in the MEMOS-U code, which models Be melt formation and dynamics. Simulations reveal peak surface temperatures of similar to 2200 K, inward surface damage of similar to 0.5 mm in depth, and average melt velocities of similar to 2 m s(-1). Although VDEs are in principle the easiest disruptive instability to avoid, the analysis demonstrates that any non-mitigated events or intentional VDEs taking place during low I-p, early operational phases of ITER for the purposes of estimating disruption forces, must be kept to a low number.
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| 5. |
- Corre, Y., et al.
(författare)
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Sustained W-melting experiments on actively cooled ITER-like plasma facing unit in WEST
- 2021
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Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 96:12
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Tidskriftsartikel (refereegranskat)abstract
- The consequences of tungsten (W) melting on divertor lifetime and plasma operation are high priority issues for ITER. Sustained and controlled W-melting experiment has been achieved for the first time in WEST on a poloidal sharp leading edge of an actively cooled ITER-like plasma facing unit (PFU). A series of dedicated high power steady state plasma discharges were performed to reach the melting point of tungsten. The leading edge was exposed to a parallel heat flux of about 100 MW.m(-2) for up to 5 s providing a melt phase of about 2 s without noticeable impact of melting on plasma operation (radiated power and tungsten impurity content remained stable at constant input power) and no melt ejection were observed. The surface temperature of the MB was monitored by a high spatial resolution (0.1 mm/pixel) infrared camera viewing the melt zone from the top of the machine. The melting discharge was repeated three times resulting in about 6 s accumulated melting duration leading to material displacement from three similar pools. Cumulated on the overall sustained melting periods, this leads to excavation depth of about 230 mu m followed by a re-solidified tungsten bump of 200 mu m in the JxB direction.
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| 6. |
- De Angeli, M., et al.
(författare)
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Cross machine investigation of magnetic tokamak dust : Morphological and elemental analysis
- 2021
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Ingår i: Fusion engineering and design. - : Elsevier BV. - 0920-3796 .- 1873-7196. ; 166
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Tidskriftsartikel (refereegranskat)abstract
- The presence of magnetic dust can be an important issue for future fusion reactors where plasma breakdown is critical. Magnetic dust has been collected from contemporary fusion devices (FTU, Alcator C-Mod, COMPASS and DIII-D) that feature different plasma facing components. The results of morphological and elemental analysis are presented. Magnetic dust is based on steel or nickel alloys and its magnetism is generated by intense plasma material interactions. In spite of the strong similarities in terms of morphology and composition, X-ray diffraction analysis revealed differences in the structural evolution that leads to non-trivial magnetic responses.
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| 7. |
- De Angeli, M., et al.
(författare)
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Cross machine investigation of magnetic tokamak dust; structural and magnetic analysis
- 2021
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Ingår i: Nuclear Materials and Energy. - : Elsevier BV. - 2352-1791. ; 28
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic dust collected from multiple fusion devices (FTU, Alcator C-Mod, COMPASS) that feature different plasma-facing components (PFCs) and toroidal magnetic fields has been analyzed by means of the X-ray diffraction technique aiming to investigate the nature and origin of dust magnetism. Analysis led to the conclusion that the main mechanism of ferromagnetic dust formation is the change of iron crystalline phase from austenitic to ferritic during the re-solidification of stainless steel droplets. Analysis also revealed differences in the collected dust structure and an unexpectedly high amount of stainless steel based dust in its native austenitic phase. Theoretical estimates showed that the magnetic moment force can also mobilize strongly paramagnetic adhered dust prior to the establishment of proper tokamak discharges. The post-mortem analysis of dust collected during pure magnetic discharges in FTU confirmed these estimates.
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| 8. |
- Dornheim, Tobias, et al.
(författare)
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Analytical representation of the local field correction of the uniform electron gas within the effective static approximation
- 2021
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Ingår i: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 103:16
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Tidskriftsartikel (refereegranskat)abstract
- The description of electronic exchange-correlation effects is of paramount importance for many applications in physics, chemistry, and beyond. In a recent paper, Dornheim et al. [Phys. Rev. Lett. 125, 235001 (2020)] have presented the effective static approximation (ESA) to the local field correction (LFC), which allows for the highly accurate estimation of electronic properties such as the interaction energy and the static structure factor. In this work, we give an analytical parametrization of the LFC within ESA that is valid for any wave number, and available for the entire range of densities (0.7 <= r(s) <= 20) and temperatures (0 <= theta <= 4) that are relevant for applications both in the ground state and in the warm dense matter regime. A short implementation in PYTHON is provided, which can easily be incorporated into existing codes. In addition, we present an extensive analysis of the performance of ESA regarding the estimation of various quantities like the dynamic structure factor, static dielectric function, the electronically screened ion potential, and also the stopping power in an electronic medium. In summary, we find that the ESA gives an excellent description of all these quantities in the warm dense matter regime, and only becomes inaccurate when the electrons start to form a strongly correlated electron liquid (r(s) similar to 20). Moreover, we note that the exact incorporation of exact asymptotic limits often leads to a superior accuracy compared to the neural-net representation of the static LFC [T. Dornheim et al., J. Chem. Phys. 151, 194104 (2019)].
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| 9. |
- Komm, M., et al.
(författare)
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Space-charge limited thermionic sheaths in magnetized fusion plasmas
- 2020
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 60:5
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Tidskriftsartikel (refereegranskat)abstract
- A systematic particle-in-cell investigation is reported focusing on the sheaths surrounding hot planar surfaces that are embedded in fusion plasmas with an arbitrary magnetic field inclination angle. The transition to the space-charge limited regime and the subsequent strict limitation of the escaping thermionic current density are demonstrated to be global characteristics of strongly emitting sheaths also in the presence of inclined magnetic fields. A physically transparent semi-empirical expression has been identified for the limited thermionic current as a function of the plasma conditions and inclination angle that is accurate for both the inter-and intra-ELM plasmas of present-day tokamaks.
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| 10. |
- Lucco Castello, Federico, et al.
(författare)
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On the advanced integral equation theory description of dense Yukawa one-component plasma liquids
- 2020
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Ingår i: Contributions to Plasma Physics. - : Wiley-VCH Verlag. - 0863-1042 .- 1521-3986.
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Tidskriftsartikel (refereegranskat)abstract
- Different advanced bridge function closures are utilized to investigate the structural and thermodynamic properties of dense Yukawa one-component plasma liquids within the framework of integral equation theory. The isomorph-based empirically modified hypernetted-chain, the variational modified hypernetted-chain, the Rogers-Young, and the Ballone-Pastore-Gall-Gazzillo approaches are compared at the level of thermodynamic properties, radial distribution functions, and bridge functions. The comparison, based on accuracy and computational speed, concludes that the two modified hypernetted-chain approaches are superior and singles out the isomorph-based variant as the most promising alternative to computer simulations of structural properties of dense Yukawa liquids. The possibility of further improvement through artificial crossover to exact asymptotic limits is studied.
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