Kinetic Transport Research Articles

Extended-magnetohydrodynamics in under-dense plasmas

Extended-magnetohydrodynamics (MHD) transports magnetic flux and electron energy in high-energy-density experiments, but individual transport effects remain unobserved experimentally. Two factors are responsible in defining the transport: electron temperature and electron current. Each electron energy transport term has a direct analog in magnetic flux transport. To measure the thermally driven transport of magnetic flux and electron energy, a simple experimental configuration is explored computationally using a laser-heated pre-magnetized under-dense plasma. Changes to the laser heating profile precipitate clear diagnostic signatures from the Nernst, cross-gradient-Nernst, anisotropic conduction, and Righi-Leduc heat-flow. With a wide operating parameter range, this configuration can be used in both small and large scale facilities to benchmark MHD and kinetic transport in collisional/semi-collisional, local/non-local, and magnetized/unmagnetized regimes.

Unravelling the Contribution of Kinetics and Mass Transport Phenomena to Impedance Spectra in Vanadium Redox Flow Batteries: Development and Validation of a 1D Physics-Based Analytical Model

Vanadium redox flow battery technology can support the spread of energy storage in stationary applications and allow higher penetration of renewables in the electric grid. Currently, its market competitiveness is hindered by low power density, which stems from complex interplay between kinetic and mass transport losses. The quantitative interpretation of experimental observations should rely on physics-based models, which allow a consistent comparison of different operative conditions. In this work, a fast analytical physics-based 1D model of the impedance of vanadium flow battery is presented and validated with respect to experimental data. The model, made available online at http://mrtfuelcell.polimi.it, employs a macro-homogeneous approach and considers losses due to kinetics, reactant distribution within the electrode (Sigracet® SGL 39 AA carbon paper), convection in flow channel and vanadium transport to electrode surface. Additionally, analytical expressions of contributions to impedance of single physical phenomena are derived through an asymptotical analysis. The results show that, at negative electrode, transport of ions to active surface is the limiting phenomenon at lower flow rates, while at higher flow rates depletion of reactants within electrode becomes critical together with charge transfer processes. At positive electrode, the main contribution to performance loss is the vanadium transport to electrode surface.

Integration of kinetic ions in a three‐dimensional Monte‐Carlo neutral transport code

AbstractCharged particles of species different from the major constituents of a plasma might not reach local thermodynamic equilibrium during their lifespan. Such low collisional ions render the often‐used fluid description, assuming Maxwellian velocity distribution, as insufficient. Hence, kinetic treatment of such minorities becomes inevitable. The three‐dimensional kinetic neutral particle Monte‐Carlo code EIRENE [D. Reiter et al., Fusion Science and Technology, 47 (2), 172 (2005)] possesses a model for ion transport reduced in physics, consisting of field‐line tracing and energy relaxation of particles. The trajectory integration is now extended to account for first‐order particle drifts, anomalous cross‐field diffusion denoting for turbulence effects, and the consideration of the magnetic mirror force. The technical implementation, as well as the verification of the enhanced kinetic ion transport is being reported.

Code/Code comparison of impurity transport in EMC3 and DIVIMP**Poster PB029.

Recently, the global impurity migration code WallDYN was coupled to the 3D edge transport code EMC3-Eirene in order to make WallDYN applicable to 3D, non-toroidally symmetric, geometries. As part of the coupling, a new impurity transport module was implemented, which, in contrast to the existing impurity module, takes the inertia of the impurity into account, making it more suitable for heavy impurities like W. This new ‘kinetic’ impurity transport module uses the same physics as the 2D trace impurity transport code DIVIMP and therefore, to check the correctness of the implementation, a code/code benchmark was performed comparing the transport of Be- and W-impurities in EMC3 and DIVIMP. The comparison was performed for toroidally symmetric plasma that could be handled both by EMC3 and DIVIMP. Both codes were setup such that they would treat the transport of the impurities as similar as possible. Then the re-distribution of Be and W launched from different positions around the poloidal circumference of the first wall was calculated in both codes. To compare the resulting material re-distribution data () and judge the significance of any differences, was used in WallDYN calculations that model the evolution of the first wall due to erosion, deposition, re-erosion and re-deposition. These WallDYN calculations, performed using the from EMC3 or DIVIMP, showed the same major erosion and deposition areas and it can therefore be concluded that the new kinetic impurity transport module is implemented correctly and now allows us to make DIVIMP-like transport calculations using EMC3 in 3D.

Analytic smoothing effect for the nonlinear Landau equation of Maxwellian molecules

We consider the Cauchy problem of the nonlinear Landau equation of Maxwellian molecules, under the perturbation frame work to global equilibrium. We show that if $H^r_x(L^2_v), r >3/2$ norm of the initial perturbation is small enough, then the Cauchy problem of the nonlinear Landau equation admits a unique global solution which becomes analytic with respect to both position $x$ and velocity $v$ variables for any time $t>0$. This is the first result of analytic smoothing effect for the spatially inhomogeneous nonlinear kinetic equation. The method used here is microlocal analysis and energy estimates. The key point is adopting a time integral weight associated with the kinetic transport operator.

Wellbore cement alteration during decades of abandonment and following CO2 attack – A geochemical modelling study in the area of potential CO2 reservoirs in the Pannonian Basin

In East-Central Europe, the sedimentary rocks and saline reservoirs of the Pannonian Basin provide the greatest potential for geological sequestration of CO2. However, there is no knowledge about the integrity of cement casing and plugs in abandoned wellbores drilled in the last century, which surround the potential CO2 geological storage sites. Thermodynamic and kinetic batch, and 1D kinetic reactive transport models have been built up in PHREEQC to estimate the present composition of hydrated cement in different depths (106, 1478, 2136 and 2718 m) of these abandoned wellbores and, to access cement reactivity for the effect of potentially injected CO2. The wellbore cements are all predicted to presently consist of mainly calcium silicate hydrate (CSH) and portlandite but differences occur due to the stability of ettringite connected to the temperature of the geological environment. With the depth, the amount of potentially dissolved CO2 increases which induces the breakdown of portlandite and CSH in the cement, and the major precipitation of calcite and amorphous silica. The transformation affects the whole width of the cement casing after about 2–3 years in most of the depths. However, the calculated mass transfer among minerals indicate a 2–6% porosity drop, which raises the attention to potential pore clogging. This process significantly reduces the risks of abandoned wellbores when implementing CO2 geological storage.

ACR Proton Acceleration Associated with Reconnection Processes beyond the Heliospheric Termination Shock

Abstract One of the curious observations from the Voyagers is that the intensity of anomalous cosmic rays (ACRs) did not peak at the heliospheric termination shock (HTS) but instead a short distance (within ∼1 au) downstream of the HTS. One possible explanation is that the interaction of the wavy heliospheric current sheet with the HTS enhances magnetic reconnection and generates numerous small-scale magnetic flux ropes in the heliosheath immediately downstream of the HTS. Charged particles are accelerated in this region due to Fermi acceleration and the reconnection electric field. In this work, we provide observational evidence of the presence of magnetic flux ropes in the heliosheath region just downstream of the HTS using a wavelet analysis of the reduced magnetic helicity and Grad–Shafranov reconstruction techniques. The Zank et al. kinetic transport theory for particles propagating through the magnetic islands region is employed to fit the observed energetic proton intensities in the post-HTS region. Our modeling results agree reasonably well with the observations, which suggests that stochastic acceleration via reconnection processes can explain the ACR proton peak beyond the HTS.

Axial kinetic theory and spin transport for fermions with arbitrary mass

We derive the quantum kinetic theory for fermions with arbitrary mass in a background electromagnetic field from the Wigner-function approach. Since spin of massive fermions is a dynamical degree of freedom, the kinetic equations with the leading-order quantum corrections describe entangled dynamics of not only the vector- and axial-charge distributions but also of the spin polarization. Therefore, we obtain one scalar and one axial-vector kinetic equations with magnetization currents pertinent to the spin-orbit interaction. We show that our results smoothly reduce to the massless limit where the spin of massless fermions is no longer an independent dynamical degree of freedom but is enslaved by the chirality and momentum and the accordingly kinetic equations turn into the chiral kinetic theory for Weyl fermions. We provide a kinetic theory covering both the massive and massless cases, and hence resolves the problem in constructing the bridge between them. Such generalization may be crucial for applications to various physical systems. Based on our kinetic equations, we discuss the anomalous currents transported by massive fermions in thermal equilibrium.

Dissolution kinetics of alumina in molten CaO–Al2O3–FetO–MgO–SiO2 oxide representing the RH slag in steelmaking process

AbstractIn order to effectively remove alumina inclusions suspending in ultra‐low C steel during RH process, the dissolution kinetics of alumina in molten CaO–Al2O3–FetO–MgO–SiO2 oxide was investigated. A crucible dissolution technique was used where the alumina crucible was allowed to dissolve in the slag of various conditions ((% CaO)/(% Al2O3), (% FetO), temperature). The obtained data were interpreted using a kinetic mass transport equation to obtain the mass transport coefficient (km) in each condition. Increasing (% CaO)/(% Al2O3), (% FetO), and temperature increased the dissolution rate as well as the km provided that the slag composition is not close to its saturation composition by alumina. In order to simulate the dissolution of alumina inclusion in the RH slag, which cannot be measured by a confocal scanning laser microscopy (CSLM) at present due to the opaqueness of the slag, the modified invariant interface approximation was employed. Along with the obtained km, the viscosity of slag, and a reference experiment using the CSLM, the dissolution kinetics of alumina inclusion in the FetO‐containing RH slag was predicted. The time required for the dissolution of alumina inclusions from liquid steel to RH slag was discussed.

Operando probing ion and electron transport in porous electrodes

Utilization of thick and densified electrodes can efficiently increase battery energy density, which is critical for electrical transportation. However, the penalty from ion and electron transport significantly reduces the usable capacity of the electrode and limites the cell level energy density. Mechanistic understanding thus is required to improve electrode design. At present, no experimental method is capable of fully characterizing the kinetic processes, especially ion and electron transport, in porous electrode during dynamic charge and discharge. Here we for the first time measure the potential drops for ion and electron transport in a thick porous electrode during charge/discharge with pulse current cessation in a modified three-electrode cell. Our measurement suggests that capacity loss of a thick electrode at a high rate is highly related to both ion and electron transport potential drops. The potential drops caused by ion and electron transport disintegrates the chemical potential of the active materials in the electrode, thus stop or delay lithiation process of the active materials in the porous electrolde. Electrode capacity with phase transformation materials showed higher sensitivities to ion and electron transport potential drops compared to solid solution materials due to different chemical potential profiles upon lithiation.

Flow in AA and pA as an interplay of fluid-like and non-fluid like excitations

To study the microscopic structure of quark–gluon plasma, data from hadronic collisions must be confronted with models that go beyond fluid dynamics. Here, we study a simple kinetic theory model that encompasses fluid dynamics but contains also particle-like excitations in a boost invariant setting with no symmetries in the transverse plane and with large initial momentum asymmetries. We determine the relative weight of fluid dynamical and particle like excitations as a function of system size and energy density by comparing kinetic transport to results from the 0th, 1st and 2nd order gradient expansion of viscous fluid dynamics. We then confront this kinetic theory with data on azimuthal flow coefficients over a wide centrality range in PbPb collisions at the LHC, in AuAu collisions at RHIC, and in pPb collisions at the LHC. Evidence is presented that non-hydrodynamic excitations make the dominant contribution to collective flow signals in pPb collisions at the LHC and contribute significantly to flow in peripheral nucleus–nucleus collisions, while fluid-like excitations dominate collectivity in central nucleus–nucleus collisions at collider energies.

A combined morphological and electrochemical characterization of carbon electrodes in vanadium redox flow batteries: Insights into positive and negative electrode performance

Reduced power density is one of the main critical issues of vanadium redox flow batteries and it is mainly due to critical electrolyte distribution over the porous electrodes and sluggish kinetics. Therefore, it is crucial to elucidate the interplay between morphological and electrochemical features of carbon electrodes and their influence on battery performance. In this work, three considerably different carbon electrodes were characterized in order to highlight the most relevant electrode properties governing system operation, distinguishing between positive and negative electrode performance, that are differently affected by kinetic and mass transport losses, especially at local level. Scanning electron microscopy and Raman spectroscopy provided insights on the electrodes structure, while mercury intrusion porosimetry and thermogravimetric analyses permitted to evaluate porous volume, surface area, skeletal density and pores diameter. Local electrochemical characterization was performed by means of through-plate hydrogen reference electrodes: innovative in-situ cyclic voltammetry allowed to decouple electrode operation from fluid-dynamic phenomena, whose influence on battery performance was evaluated with polarization curves at different flow rates. The best electrode design is the result of a proper combination between high surface area and pores diameter, that on one hand has to be sufficiently large to promote electrolyte permeation from distribution channel, but on the other hand has to be small to reduce mass transport losses at pore scale. The negative electrode performance is strongly affected by kinetic losses, while the operation of positive electrode is mainly influenced by mass transport phenomena.

Computational Modeling of Electrochemical Systems: Activation-Control vs. Mass-Transport-Control Analysis

The computational modeling of two generic heterogeneous reactions within an electrochemical cell formed by two planar electrodes in contact with an aqueous electrolyte was carried out with the FlexPDE 6 software. Both Red-Ox reactions were initially given identical kinetic and mass transport parameters to corroborate the functionality of the model. The derived steady-state current/overpotential curves, under mass transport control, were compared to the analytical model for Nernstian reactions (1). A very good match was found. The diffusion coefficients and standard reaction-rate-constants were afterwards varied. Inspecting the current/overpotential curve shape helped to rapidly identify the reaction-rate control-mechanism: either mass transport or activation. However, if the current density at each given potential is recorded before a steady-state value is attained, the correct identification of the reaction-rate control-mechanism may be hindered.

Compressibility effects on the transition to turbulence in a spatially developing plane free shear layer

The compressibility effects on the transition to turbulence in a spatially developing, compressible plane free shear layer are investigated via direct numerical simulation using a high-order discontinuous spectral element method for three different convective Mach numbers of 0.3, 0.5, and 0.7. The location of the laminar–turbulent transition zone is predicted by the analyses of vorticities, Reynolds stresses, and the turbulent dissipation rate. In the turbulence transition and self-similar turbulence regions, the effects of compressibility on the flow properties, such as the velocity autocorrelation function, integral time scale, momentum thickness, Reynolds stress, and turbulent kinetic energy budget, are investigated. The compressibility effects on the onset and length of the turbulence transition zone are studied based on the analyses of such flow properties. The mean velocity, momentum thickness, and Reynolds stress profiles compare well with published experimental data. Vorticity contours and iso-surface of the second invariant of velocity gradient tensor identify the characteristic of flow structures. The two-point correlation functions of velocity components, the one-dimensional (1D) spanwise energy spectrum, and the balance of the turbulent kinetic energy transport equation validate the domain size and resolution of the adopted grid for turbulence simulation. An increase in the convective Mach number leads to a reduction in the sizes of the largest-scale structures, resulting in a significant decrease in Reynolds stresses and turbulence production. The onset of turbulence transition and the location where the transition completes shift downstream, while the length of the transition zone increases with increasing convective Mach number.

Radiation Dose Analysis in Criticality Accident of Fuel Debris in Water

Removal of fuel debris is regarded as one of the most important operations in the decommissioning of the Fukushima Daiichi nuclear power station (1F-NPS) to decrease long-term risk. To begin the operation, the consequences of possible criticality accidents must be evaluated in advance. In this work, we evaluated radiation doses during possible criticality accidents at 1F-NPS in assumptive fuel debris systems. In particular, the relationship between the water level surrounding the fuel debris and the radiation dose was investigated. This is because the water level surrounding the fuel debris is thought to have an impact on radiation dose during accidents as it affects both the reactivity and shielding of radiation. A combination of space-dependent kinetic analysis and radiation transport analysis was carried out in order to consider the special characteristics of fuel debris systems in water. Instead of traditional point-kinetics analysis, we used the Multi-region Integral Kinetic (MIK) code, which is a unique method based on Monte Carlo neutron transport calculations. The radiation transport calculation code Particle and Heavy Ion Transport Code System (PHITS) was used as well. The analyses revealed that the dose caused by criticality accidents may be the largest in systems in which part of the fuel debris is exposed to the air.

IMPGYRO: The full-orbit impurity transport code for SOL/divertor and its successful application to tungsten impurities

In future fusion reactors, tungsten (W) is currently regarded as one of the most feasible candidates for the plasma-facing components (PFCs). Once the W impurities sputtered from the PFCs penetrate into the core plasma, the large radiation cooling and fuel dilution, which leads to the deterioration of the core plasma performance, take place. To understand and to control W impurity transport are indispensable for future fusion reactors. In order to understand W transport, we are continuing to develop the kinetic impurity transport code IMPGYRO for SOL/divertor in fusion reactors. The IMPGYRO has obtained following unique features compared to other existing kinetic impurity transport codes through the 15-years development activity; (i) the exact Larmor motion of impurity ions are computed so that the effects of drifts are automatically taken into account, (ii) the Coulomb collision between impurities and background plasma ions are modelled by the Binary Collision Method which kinetically calculates more precise friction and thermal forces, and (iii) the background plasma transport and impurity transport are computed self-consistently by the coupled calculation with SOL/divertor plasma transport code such as SOLPS-ITER. Although the IMPGYRO transport model has significantly improved from the initial development phase, the modelling improvement of the IMPGYRO has never been described in detail. In this paper, (a) the current W generation/transport model, and (b) the coupling strategy between the SOLPS-ITER and the IMPGYRO are summarized. The new results (c) the check of the prompt re-deposition model of the IMPGYRO, and (d) the further extension of the Coulomb collision modelling of the IMPGYRO towards the neoclassical (NC) transport handling capability has been performed. The effects of the NC transport processes on a simple circular tokamak geometry are compared with the anomalous diffusion by means of the extended IMPGYRO to obtain better understanding of cross-field transport process of W. The results show that the NC transport process may become non-negligible compared to the anomalous diffusion at least in this configuration. Based on these recent improvements, the present version of the IMPGYRO is very useful tool for understanding and prediction of W transport in SOL/divertor regions of fusion devices.

Statistical behavior of turbulent kinetic energy transport in boundary layer flashback of hydrogen-rich premixed combustion

Statistical behavior of turbulent kinetic energy (TKE) transport in boundary layer flashback of hydrogen-rich premixed combustion is analyzed for the first time. Flame alters the structure of the turbulent boundary layer, which is evident from the changes in the budget of the TKE transport equation.

In-Situ Electrochemical Techniques to Determine Ionomer Coverage in PEFC Electrodes

Many electrochemical devices such as low temperature fuels utilize ionomers to improve efficiency and overall performance. In polymer electrolyte fuel cells (PEFCs), perflurosulfonic acid ionomers improve ionic (protonic) conductivity and Pt utilization within the catalyst layer. However, the strong interaction between sulfonate (-SO3 -) functional groups and Pt nanoparticles have been linked lower catalytic rates and higher O2 transport resistances.1,2 There have been numerous strategies implemented to control the local distribution of ionomer and Pt/C catalyst particles, but limitations in the resolution of state-of-the-art characterization techniques make it difficult to assess how ink formulations and/or electrode fabrication techniques control ionomer-catalyst interactions and its impact device performance.3–5 Herein, the development and utilization of in situ electrochemical techniques designed to probe the local ionomer interactions will be utilized in conjunction with established testing protocols to relate ionomer coverage (on Pt and/or C support) with kinetic performance and O2 transport resistance of fully-conditioned PEFC electrodes. Specifically, CO displacement chronoamperometry and electrochemical impedance spectroscopy techniques will be described to determine local ionomer coverages across a series of Pt/C MEAs. These results will promote a deeper understanding of ionomer-catalyst interactions which in turn will inform future materials development and integration necessary to achieve high performance PGM (e.g. Pt/C and Pt alloy/C) electrocatalyst-based electrodes. Schuler, T. et al. Fuel-Cell Catalyst-Layer Resistance via Hydrogen Limiting-Current Measurements. J. Electrochem. Soc. 166, F3020–F3031 (2019).Subbaraman, R., Strmcnik, D., Paulikas, A. P., Stamenkovic, V. R. & Markovic, N. M. Oxygen Reduction Reaction at Three-Phase Interfaces. ChemPhysChem 11, 2825–2833 (2010).Berlinger, S. A., McCloskey, B. D. & Weber, A. Z. Inherent Acidity of Perfluorosulfonic Acid Ionomer Dispersions and Implications for Ink Aggregation. J. Phys. Chem. B 122, 7790–7796 (2018).Orfanidi, A., Rheinländer, P. J., Schulte, N. & Gasteiger, H. A. Ink Solvent Dependence of the Ionomer Distribution in the Catalyst Layer of a PEMFC. J. Electrochem. Soc. (2018). doi:10.1149/2.1251814jesKhandavalli, S. et al. Rheological Investigation on the Microstructure of Fuel Cell Catalyst Inks. ACS Appl. Mater. Interfaces (2018). doi:10.1021/acsami.8b15039

Survey of the near wake of an axial-flow hydrokinetic turbine in the presence of waves

Flow field results are presented for the near-wake of an axial-flow hydrokinetic turbine in the presence of surface gravity waves. The turbine is a 1/25 scale, 0.8 m diameter, two bladed turbine based on the U.S. Department of Energy's Reference Model 1 tidal current turbine. Measurements were obtained in the large towing tank facility at the U.S. Naval Academy with the turbine towed at a constant carriage speed and a tip speed ratio selected to provide maximum power. The turbine has been shown to be nearly scale independent for these conditions. The selected wave form was intended to represent oceanic swell encountered off the U.S. eastern seaboard. The resulting model wave is a deep water wave, in terms of relative depth, traveling with the “current”, in the opposite direction of the towing carriage. Velocity measurements were obtained using a submersible, planar particle image velocimetry (PIV) system at streamwise distances of up to two diameters downstream of the rotor plane. PIV ensembles were obtained for phase locked conditions with the reference blade at the horizontal position. Phase averaged results for no-wave and wave conditions are presented for comparison showing further expansion of the wake and shear layer in the presence of waves as compared to the no-wave case. When ensembles are selectively sampled on the wave phase, a high degree of coherency is shown to remain and the wake width is shown to undulate with the passing of the wave, with the vertical displacement range on the same order as that of a particle under similar conditions. The impact of waves on turbine tip vortex helical structure is also examined. Waves are shown to change the location of adjacent helices. In the streamwise direction, this changes the pitch of the helix, shown in previous studies to affect the downstream wake recovery distance. In the vertical direction, depending on the wave-induced flow field at the time they were created, vortices are forced outward, into the mean flow or inward, into the wake core, potentially enhancing kinetic energy transport and accelerating the re-energization process.

Some features of semiclassical chiral transport in rotating frames

Semiclassical chiral kinetic theories in the presence of electromagnetic fields as well as vorticity can be constructed by means of some different relativistic or nonrelativistic approaches. To cover the noninertial features of rotating frames one can start from the modified quantum kinetic equation of Wigner function in Minkowski spacetime. It provides a relativistic chiral transport equation whose nonrelativistic limit yields a consistent three-dimensional kinetic theory which does not depend explicitly on spatial coordinates. Recently a chiral transport equation in curved spacetime has been proposed and its nonrelativistic limit in rotating coordinates was considered in the absence of electromagnetic fields. We show that the modified theory can be extended to curved spacetime. The related particle current density and chiral transport equation for an inertial observer in the rotating frame are derived. A novel three-dimensional chiral kinetic transport equation is established by inspecting the nonrelativistic limit of the curved spacetime approach in the rotating frame for a comoving observer in the presence of electromagnetic fields. It explicitly depends on spatial coordinates. We prove that it is consistent with the chiral anomaly, chiral magnetic and vortical effects.