arXiv subjects

P. Tolias

Publications and source records attributed to P. Tolias.

At least 19 recordsLinked to original sources

arXiv2026

Runaway electron induced explosions of graphite; modeling versus controlled DIII-D experiments

The state-of-the-art concerning the modeling of the thermomechanical response of graphite to runaway electron (RE) impact is based on one-way coupled linear thermoelasticity combined with Rankine's strength-based failure criterion and limited to the onset of material failure. Here, the predictive capabilities are extended to the nonlinear damage phase characterized by material fragmentation and debris expulsion. This is achieved by introducing plasticity via the Johnson-Holmquist constitutive model, adopting an effective plastic strain-based failure criterion and coupling finite element analysis with smoothed-particle hydrodynamics. The extended thermomechanical model is successfully benchmarked against the results of two controlled RE-induced damage experiments recently carried out in DIII-D. This constitutes an important step towards the final objective of quantitatively describing the thermomechanical response of tungsten to REs.

physics.plasm-ph↗

arXiv2026

Thermal modeling of runaway electron induced damage in the SPARC tokamak

The integrity of plasma-facing components (PFCs) in tokamaks is critically challenged by transient events such as runaway electron (RE) impacts. We report the first systematic analysis of the thermal damage to tungsten-based PFC tiles comprising the SPARC outboard off-midplane limiters that is induced by RE beams formed during vertical displacement events. Parametric scans in RE impacting characteristics as well as energy-pitch distribution functions from the Dream code are employed for calculations of the volumetric heat loads. A realistic panel design is adopted to enhance the fidelity of the thermal analysis. The PFC thermal responses are compared in terms of in-depth temperature profiles and damage characteristics, such as melt depth and vaporization losses.

physics.plasm-ph↗

arXiv2025

Thermal resilience of the ITER tungsten first wall to runaway electron impact

The fast volumetric deposition of multi-MeV high current runaway electron (RE) beams constitutes the most critical issue for the ITER tungsten (W) first wall (FW) longevity. Such relativistic electron beams could generate extreme volumetric power densities inside the FW armour which lead to significant vaporization, deep melting and even material explosions, as well as to elevated temperatures at the bond interface with the cooling substrate that could cause rupture and water leaks. Here the thermal response of the ITER FW is modeled with a three-stage, one-way coupled workflow focusing on assessments of the extent of the wall damage and the increase of the bond interface temperature for varying W thickness. Increased W thickness is found to be essential for wall protection against intense RE dissipation events in terms of both W tile damage and cooling system integrity.

physics.plasm-ph↗

arXiv2025

Runaway electron-induced plasma facing component damage in tokamaks

This Roadmap article addresses the critical and multifaceted challenge of plasma-facing component (PFC) damage caused by runaway electrons (REs) in tokamaks, a phenomenon that poses a significant threat to the viability and longevity of future fusion reactors such as ITER and DEMO. The dramatically increased RE production expected in future high-current tokamaks makes it difficult to avoid or mitigate REs when a plasma discharge terminates abnormally. Preventing damage from the intense localised heat loads REs can cause requires a holistic approach that considers plasma, REs and PFC damage. Despite decades of progress in understanding the physics of REs and the thermomechanical response of PFCs, their complex interplay remains poorly understood. This document aims to initiate a coordinated, interdisciplinary approach to bridge this gap by reviewing experimental evidence, advancing diagnostic capabilities, and improving modelling tools across different scales, dimensionalities and fidelities. Key topics include RE beam formation and transport, damage mechanisms in brittle and metallic PFCs, and observations in major facilities such as JET, DIII-D, WEST and EAST. The Roadmap emphasises the urgency of predictive, high-fidelity modelling validated against well-diagnosed controlled experiments, particularly in the light of recent changes in ITER's wall material strategy and the growing importance of private sector initiatives. Each section of the article is written to provide a concise overview of one area of this multidisciplinary subject, with an assessment of the status, a look at current and future challenges, and a brief summary. The ultimate goal of this initiative is to guide future mitigation strategies and design resilient components that can withstand the loads imposed by REs, thus ensuring the safe and sustainable operation of the next generation of fusion power plants.

physics.plasm-ph↗

arXiv2024

Impact of repetitive ELM transients on ITER divertor tungsten monoblock top surfaces

Owing to the high stored energy of ITER plasmas, the heat pulses due to uncontrolled Type I edge localized modes (ELMs) can be sufficient to melt the top surface of several poloidal rows of tungsten monoblocks in the divertor strike point regions. Coupled with the melt motion associated with tungsten in the strong tokamak magnetic fields, the resulting surface damage after even a comparatively small number of such repetitive transients may have a significant impact on long-term stationary power handling capability. The permissible numbers set important boundaries on operation and on the performance required from the plasma control system. Modelling is carried out with the recently updated MEMENTO melt dynamics code, which is tailored to tackle melt motion problems characterized by a vast spatio-temporal scale separation. The crucial role of coupling between surface deformation and shallow angle heat loading in aggravating melt damage is highlighted. As a consequence, the allowable operational space in terms of ELM-induced transient heat loads is history-dependent and once deformation has occurred, weaker heat loads, incapable of melting a pristine surface, can further extend the damage.

physics.plasm-ph↗

arXiv2024

The MEMENTO code for modelling of macroscopic melt motion in fusion devices

The MEMENTO (MEtallic Melt Evolution in Next-step TOkamaks) code is a new numerical implementation of the physics model originally developed for the MEMOS-U code with the objective to self-consistently describe the generation of melt and its subsequent large scale dynamics in fusion devices and to assess the damage of metallic reactor armor under powerful normal and off-normal plasma events. The model has been validated in multiple dedicated EUROfusion experiments. MEMENTO solves the heat and phase transfer problem coupled with the incompressible Navier-Stokes equations in the shallow water approximation for the thin liquid film over the solid metal and with the current propagation equations on a domain that features a time-evolving deforming metal-plasma interface. The code utilizes non-uniform and adaptive meshing along with sub-cycling in time facilitated by the AMReX open-source framework as well as AMReX's built-in parallelization capabilities.

physics.plasm-ph↗

arXiv2022

On the Klimontovich description of complex (dusty) plasmas

The numerous idealizations that are involved in the exact microscopic statistical description of complex (dusty) plasmas are discussed in detail. The two prevailing approaches in the Klimontovich description of dusty plasmas are reviewed in a pedagogical manner. The continuous phase space approximation is introduced, within which the more rigorous treatment should collapse to the more heuristic treatment. The plasma Klimontovich equations are shown to be identical, but there are marked differences in the dust Klimontovich equations whose origin is analyzed in depth.

physics.plasm-ph↗

arXiv2022

Evidence for high-velocity solid dust generation induced by runaway electron impact in FTU

Post-mortem and in-situ evidence is presented in favor of the generation of high-velocity solid dust during the explosion-like interaction of runaway electrons with metallic plasma-facing components in FTU. The freshly-produced solid dust is the source of secondary de-localized wall damage through high-velocity impacts that lead to the formation of craters, which have been reproduced in dedicated light gas gun impact tests. This novel mechanism, of potential importance for ITER and DEMO, is further supported by surface analysis, multiple theoretical arguments and dust dynamics modelling.

physics.plasm-ph↗

arXiv2022

Classical bridge functions in classical and quantum plasma liquids

Bridge functions, the missing link in the exact description of strong correlations, are indirectly extracted from specially designed molecular dynamics simulations of classical one-component plasma liquids and accurately parameterized. Their incorporation into an advanced integral equation theory description of Yukawa one-component plasma liquids and a novel dielectric formalism scheme for quantum one-component plasma liquids leads to an unprecedented agreement with available molecular dynamics simulations and new ab initio path integral Monte Carlo simulations, respectively.

physics.plasm-ph↗

arXiv2022

Retarded room temperature Hamaker coefficients between bulk elemental metals

The exact Lifshitz theory is utilized for the systematic calculation of the retarded room temperature Hamaker coefficients between 26 identical isotropic elemental metals embedded in vacuum or pure water. The full spectral method, complemented with a Drude model low frequency extrapolation, is employed for metals with input from extended-in-frequency dielectric data, while the simple spectral method is employed for water with input from three dielectric representations. The accuracy of common Lifshitz approximations is quantified. A novel compact semi-empirical expression is proposed for the separation-dependence of the Hamaker coefficient that is demonstrated to be very accurate for all combinations.

physics.chem-ph↗

arXiv2022

Analytical expressions for thermophysical properties of solid and liquid beryllium relevant for fusion applications

The status of the literature is reviewed for thermophysical properties of pure polycrystalline solid and liquid beryllium which constitute input for the modelling of intense plasma-surface interaction phenomena that are important for fusion applications (thermal analysis, vapor shielding, melt motion, arcing, dust generation, dust transport). Reliable experimental data are analyzed for the latent heats, specific isobaric heat capacity, electrical resistivity, thermal conductivity, mass density, vapor pressure, work function, total hemispherical emissivity and absolute thermoelectric power from the room temperature up to the normal boiling point of beryllium as well as for the surface tension and the dynamic viscosity across the liquid state. Analytical expressions are recommended for the temperature dependence of these thermophysical properties, which involve high temperature extrapolations given the absence of extended liquid beryllium measurements.

physics.plasm-ph↗

arXiv2021

Bridge functions of classical one-component plasmas

In a recent paper, Lucco Castello et al. [arXiv:2107.03537] performed systematic extractions of classical one-component plasma bridge functions from molecular dynamics simulations and provided an accurate parametrization that was incorporated in the novel isomorph-based empirically modified hypernetted chain approach for Yukawa one-component plasmas. Here, the extraction technique and parametrization strategy are described in detail, while the deficiencies of earlier efforts are discussed. The structural and thermodynamic predictions of the updated version of the integral equation theory approach are compared with extensive available simulation results revealing a truly unprecedented level of accuracy in the entire dense liquid region of the Yukawa phase diagram.

physics.plasm-ph↗

arXiv2021

Integral equation theory based dielectric scheme for strongly coupled electron liquids

In a recent paper, Lucco Castello et al. [arXiv:2107.03537] provided an accurate parametrization of classical one-component plasma bridge functions that was embedded in a novel dielectric scheme for strongly coupled electron liquids. Here, this approach is rigorously formulated, its set of equations is formally derived and its numerical algorithm is scrutinized. Systematic comparison with available and new path integral Monte Carlo simulations reveals a rather unprecedented agreement especially in terms of the interaction energy and the long wavelength limit of the static local field correction.

cond-mat.stat-mech↗

arXiv2021

Structure and thermodynamics of two dimensional Yukawa liquids

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.

cond-mat.soft↗

arXiv2021

Description of longitudinal modes in moderately coupled Yukawa systems with the static local field correction

In moderately coupled Yukawa fluids, longitudinal mode dispersion is determined by the competition between kinetic and potential effects. In a recent paper [Khrapak and Couëdel, Phys. Rev. E 102, 033207 (2020)], a semi-phenomenological dispersion relation was constructed by the ad-hoc addition of the Bohm-Gross kinetic term to the generalized instantaneous excess bulk modulus, which showed very good agreement with simulations. In this paper, a nearly identical dispersion relation is derived in a rigorous manner based on a dielectric formulation with static local field corrections. At moderate coupling, this formalism is revealed to be more accurate than other successful theoretical approaches.

cond-mat.soft↗

arXiv2020

Testing the isomorph invariance of the bridge functions of Yukawa one-component plasmas. I. Intermediate and long range

It has been recently conjectured that bridge functions remain nearly invariant along phase diagram lines of constant excess entropy for the broad class of R-simple liquids. To test this hypothesis, the bridge functions of Yukawa systems are computed outside the correlation void with the Ornstein-Zernike inversion method and structural input from ultra-accurate molecular dynamics simulations. The effect of statistical, grid, finite-size, tail and isomorphic errors is quantified. Uncertainty propagation analysis is complemented with a detailed investigation of the sensitivity of the bridge function to periodic and aperiodic multiplicative perturbations in the radial distribution function. In the long and intermediate range, bridge functions are demonstrated to be approximately isomorph invariant.

cond-mat.soft↗

arXiv2020

On the advanced integral equation theory description of dense Yukawa one-component plasma liquids

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-Galli-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 cross-over to exact asymptotic limits is studied.

cond-mat.soft↗

arXiv2020

Non-retarded room temperature Hamaker constants between elemental metals

The Lifshitz theory of van der Waals forces is utilized for the systematic calculation of the non-retarded room temperature Hamaker constants between 26 identical isotropic elemental metals that are embedded in vacuum or in pure water. The full spectral method, complemented with a Drude-like low frequency extrapolation, is employed for the elemental metals benefitting from the availability of extended-in-frequency reliable dielectric data. The simple spectral method is employed for pure water and three dielectric representations are explored. Numerical truncation and low frequency extrapolation effects are shown to be negligible. The accuracy of common Lifshitz approximations is quantified. The Hamaker constants for 100 metal combinations are reported; the geometric mixing rule is revealed to be highly accurate in vacuum and water.

physics.chem-ph↗