Current Density Profile Research Articles

Deep learning approaches to recover the plasma current density profile from the safety factor based on Grad–Shafranov solutions across multiple tokamaks

Many magnetohydrodynamic stability analyses require generation of a set of equilibria with a fixed safety factor q-profile while varying other plasma parameters. A neural network (NN)-based approach is investigated that facilitates such a process. Both multilayer perceptron (MLP)-based NN and convolutional neural network (CNN) models are trained to map the q-profile to the plasma current density J-profile, and vice versa, while satisfying the Grad–Shafranov radial force balance constraint. When the initial target models are trained, using a database of semi-analytically constructed numerical equilibria, an initial CNN with one convolutional layer is found to perform better than an initial MLP model. In particular, a trained initial CNN model can also predict the q- or J-profile for experimental tokamak equilibria. The performance of both initial target models is further improved by fine-tuning the training database, i.e. by adding realistic experimental equilibria with Gaussian noise. The fine-tuned target models, referred to as fine-tuned MLP and fine-tuned CNN, well reproduce the target q- or J-profile across multiple tokamak devices. As an important application, these NN-based equilibrium profile convertors can be utilized to provide a good initial guess for iterative equilibrium solvers, where the desired input quantity is the safety factor instead of the plasma current density.

Systematic numerical analysis of ECCD exploring injection conditions with high CD efficiency and current profile controllability in JA DEMO

Systematic Electron Cyclotron Current Drive (ECCD) simulations were performed in JA DEMO plasma (Te=34keV and ne=1.0×1020m−3 at the center) for various injection conditions of EC waves, including wave frequency, injection direction and injection position. Different injection positions surrounding the plasma are comprehensively scanned, including midplane and upper launch on the high/low field side (HFS/LFS) of the plasma. Numerical results indicated that higher harmonic absorptions deteriorate the ECCD efficiency regardless of injection positions. High ECCD efficiencies for each injection position were obtained when avoiding higher harmonic absorptions. The maximum ECCD efficiency of 46kA/MW was obtained for upper LFS launch with an optimal frequency and direction. An important finding from the systematic analysis is that such an efficient ECCD exceeding 40kA/MW is expected for a wide range of injection positions of upper and midplane LFS launch. This result is favorable for fusion reactor design, indicating flexibility in EC port arrangement for efficient ECCD. Current profile controllability in JA DEMO was also discussed in two injection cases: the upper LFS launch and the conventional midplane LFS launch. Driven current density profiles with various injection angles from each injection position successfully cover the regions from the center to mid-radius of the plasma, where external current drive is required to achieve a weak reversed shear. Furthermore, sufficient ECCD efficiencies of 35–46kA/MW at the upper LFS launch and of 35–43kA/MW at the midplane LFS launch are obtained.

Electron ITB formation in EAST high poloidal beta plasmas under dominant electron heating

Plasma confinement and transport in tokamaks play a crucial role in the development of high poloidal beta steady-state operation scenarios. Therefore, it is very important to study the relevant mechanism of internal transport barriers (ITBs), which can help plasmas to obtain better confinement in order to achieve higher fusion gain. This paper mainly introduces the analysis of the characteristics of electron heat transport of discharges with ITB in high βP operation regime in Experimental Advanced Superconducting Tokamak (EAST). Based on the statistical analysis of stable discharges with βP > 1.5, it is found that there is an obvious bifurcation of the normalised electron temperature gradient (ETG) ( R/LTe ) in the range of βP = 2–2.2. Then the discharges of lower βP ( βP < 2, where the value of βP is below the bifurcation threshold) and of higher βP ( βP > 2.2, where the value of βP is above the threshold) were selected for analysis. The diagnostic data provided by Thomson scattering, x-ray crystal spectrometry and charge exchange recombination spectroscopy are used to provide reliable parameter profiles and then combined with the data of external magnetic probe measurements and the polarisation interferometer diagnosis system to fully reconstruct the balance. A relevant plasma current calculation model is used to calculate and analyse the current density profiles and power deposition, and then the transport analysis is carried out. Interestingly, in the higher βP discharges, it is found that the turbulence intensity provided by the CO2 laser collective scattering system gradually decreases and the normalised ETG R/LTe gradually increases. It is also found that the electron heat transport coefficient decreases in the discharge with higher βP and the growth rate of the electron-scale turbulence calculated by transport gyro-Landau fluid (TGLF) is significantly reduced. Meanwhile, similar conclusions are also obtained in the discharges when the βP is further increased.

Exploring the sustainability of serpentine flow-field fuel cell, straight channel PEM fuel cells hight temperature through numerical analysis

This study focuses on investigating the performance dynamics of high-temperature Proton Exchange Membrane fuel cells, with an emphasis on critical design parameters. Utilizing a comprehensive mathematical model, the research explores concentration profiles, current density profiles, and polarization curves within a three-dimensional, isothermal, steady-state PEM fuel cell.The model incorporates the intricate processes of gas transport in anode and cathode channels, diffusion in catalyst layers, and the transport of water and hydronium ions in both the polymer electrolyte and catalyst layers. Additionally, it accounts for electrical current transport in the solid phase. Simulations conducted with Comsol Multiphysics 6.1 demonstrate a robust alignment between model results and experimental polarization data obtained at 180 °C. Optimal conditions for performance are outlined, specifying an inlet hydrogen gas velocity of 0.12 m/s and an inlet air velocity of 1.2 m/s, with consideration for a proton conductivity of 9.825 S/m.In a parallel investigation, numerical analysis assesses the sustainability of Serpentine Flow-Field PEM fuel cells, using critical parameters. The model applied in this research considers gas, water, and electrical current transport across various layers of the fuel cell, with a crucial focus on optimizing the membrane electrode assembly's design. The finite element method and ANSYS Fluent are employed for model solution.This study contributes significantly to the understanding of HT-PEM fuel cell dynamics, providing insights into the interdependencies of design parameters and their impact on system performance. The study emphasizes the pivotal roles of air and hydrogen inlet velocities in shaping fuel cell performance, elucidating the intricate dynamics dictating reactant distributions within diverse cell components.

Distinct potassium channel types in brain capillary pericytes

Capillaries, composed of electrically coupled endothelial cells and overlying pericytes, constitute the vast majority of blood vessels in the brain. The most arteriole-proximate three to four branches of the capillary bed are covered by α-actin-expressing, contractile pericytes. These mural cells have a distinctive morphology and express different markers compared with their smooth muscle cell (SMC) cousins but share similar excitation-coupling contraction machinery. Despite this similarity, pericytes are considerably more depolarized than SMCs at low intravascular pressures. We have recently shown that pericytes, such as SMCs, possess functional voltage-dependent Ca2+ channels and ATP-sensitive K+ channels. Here, we further investigate the complement of pericyte ion channels, focusing on members of the K+ channel superfamily. Using NG2-DsRed-transgenic mice and diverse configurations of the patch-clamp technique, we demonstrate that pericytes display robust inward-rectifier K+ currents that are primarily mediated by the Kir2 family, based on their unique biophysical characteristics and sensitivity to micromolar concentrations of Ba2+. Moreover, multiple lines of evidence, including characteristic kinetics, sensitivity to specific blockers, biophysical attributes, and distinctive single-channel properties, established the functional expression of two voltage-dependent K+ channels: KV1 and BKCa. Although these three types of channels are also present in SMCs, they exhibit distinctive current density and kinetics profiles in pericytes. Collectively, these findings underscore differences in the operation of shared molecular features between pericytes and SMCs and highlight the potential contribution of these three K+ ion channels in setting pericyte membrane potential, modulating capillary hemodynamics, and regulating cerebral blood flow.

Faraday angle prediction based on 1-D CNN on the J-TEXT tokamak

The Faraday angle is an indispensable physical parameter to evaluate and reconstruct the current density profile which is imperative for advanced tokamak operation and physics study. The POLARIS system has been implemented on J-TEXT since 2012 for the measurement of the Faraday angle and this system occasionally encounters operational failures that result in the inability to provide measurements. So a deep learning model is trained to predict the Faraday angle when the POLARIS is unable to provide the measurement. The model is primarily based on a 1-D convolutional neural network (CNN) and is equipped with multiple convolutional paths that can accommodate various lengths of diagnostic data. The data of 100 shots are used to train the 1-D CNN model, and 30 shots are used to optimize the hyperparameters and select the model which performs best during the training process. The results on a test set of 30 shots show that the model obtains a satisfactory fitting effect.

Degradation of Sb-Doped SnO2 Supported IrRu-Based Electrocatalysts for PEM Water Electrolysis Via Accelerated Stress Protocols

Proton exchange membrane (PEM) water electrolyzers offer a very promising option to offset the environmental burden of conventional hydrogen production by splitting water into high purity hydrogen and oxygen without releasing carbon dioxide as by-product. However, the corrosive nature of the process makes it dependent on expensive materials, such as iridium (Ir), ruthenium (Ru) or titanium (Ti), which makes the upscaling of the technology considerably more difficult [1, 2]. To ensure industrial success of this technology, the study of the mechanisms involved in the degradation of the cell components is of great importance. Particularly, the development of accelerated stress test protocols has attracted attention in recent years, due to their potential to yield representative data pertaining degradation without incurring long testing times that would meet the typical industrial standards of 20,000 to up to 50,000 hours [3].Several strategies to investigate the various degradation mechanisms have been discussed in recent years in the literature. Particularly, Spöri pointed out the difference between transient and static operation and the degradation mechanisms triggered by each of these modes, while also investigating the intrinsic mechanisms of the catalyst via rotating disk electrode analysis [3]. Meanwhile, Frensch explored in their work the relation of cathodic fluoride release with different current density profiles and different temperatures [4]. Furthermore, attempts have been made to increase the electrochemical stability of oxygen evolution reaction (OER) electrocatalysts by adding a support material to the catalyst layer. This was described by Saveleva in their work, as they found evidence that supporting Ir on antimony-doped tin oxide (Sb-doped SnO2) resulted in a preferential dissolution of Sb and Sn, thus noticeably reducing the dissolution rate of Ir [2].In this work, the electrochemical activity and stability of newly developed IrRu OER catalysts supported on Sb-doped SnO2 is studied in a single cell setup. The catalyst and support materials were synthetized as part of the study. For the preparation of the MEAs the fabricated materials were used with membranes and ionomers which are commercially available. The prepared MEAs were analyzed using both static and dynamic current profiles with a current range of up to 4 A cm-2. To understand the different mechanisms and material dependencies at play during characterization, the MEA configuration (membrane type, material ratios, ionomer) was varied. The first screenings with different MEA configurations not only suggest a strong stability with the catalyst loading, as it was previously observed by Alia [5], but also a strong dependence on the anodic ionomer content, which reflects in the degradation rate in the first hundred hours of test.

Intercalation Pathway in Graphite Particles Analyzed with a Multi-Layer Phase Field Model

Graphite is today the most common negative electrode material in commercial cells, alone or blended with silicon, thanks to its relatively high specific capacity of 372 mAh·g−1, its excellent cycling stability, its low thermodynamic potential, and relatively low cost compared to alternative materials. The increase in the energy densities, power capabilities, and durability of lithium-ion batteries using this conventional cost-effective active material is possible through an optimization of the electrode and material designs. Such optimization requires, however, knowledge of the fundamental mechanisms that govern both the lithium transport inside graphite particles and the electrochemical transfer at the electrolyte / active material interface.Graphite has an ideal lamellar structure made of graphene sheets. During intercalation, the lithium atoms insert between the graphene planes, with almost no lithium transport across the graphene sheets. The interactions between lithium atoms in adjacent galleries leads to the formation of structures with filled layers separated by a number of empty layers, known as stages. Given this phenomenon, graphite active material undergoes phase separation between successions of several stable phases during lithium intercalation. This staging phenomenon influences the critical properties of graphite like its equilibrium potential, lithium diffusion or lithium insertion kinetics.In the present work, we use a Cahn-Hilliard type model, adapted to multi-layered materials1 and study the influence of the parameters in the underlying free-energy models. We focus first on the intra-layer and inter-layer lithium interaction contributions. Free-energy models with increasing complexity of inter-layer interactions are introduced and discussed based on their corresponding phase diagrams. In particular, we show that occurrence of fractional 3/2 stage, observed for potassium or rubidium intercalation in graphite at high pressure, requires an interlayer interaction effective at second neighbor, while a continuous screening effect of the intercalant is necessary to predict the occurrence of stages greater than 2 without the occurrence of the fractional 3/2 stage, as observed for lithium2.The kinetics of stage formation and evolution is also greatly affected by the interaction parameters of the free-energy model. A linear stability analysis (LSA) is performed to investigate the impact of the free energy model parameters on the stage formation dynamics and growth rates. In particular, the LSA shows that stage 2 grows the fastest, even for low lithium filling fraction. In accordance with this result, simulations of spinodal decomposition from moderate homogeneous lithium filling fraction (c=0.3) shows the formation of stage 2 at early times before an evolution towards stage 3 (See figure 1). This higher growth rate of stage 2 seems to have an impact on lithium intercalation pathway. Indeed, during simulations of lithium intercalation in a graphite particle at different C-rates, stage 2 tends to form very early at the electrolyte/particle interface, even when stage 3 and dilute stage 1 dominates inside the particle. The simulation of lithium intercalation also provides access to the effective exchange current density as function of the averaged surface concentration. The presence of the stages at the surface of the particles directly affects this averaged exchange current density. It results in non-symmetric exchange current density profiles, in coherence with operando X-ray micro-diffraction measurement in thick graphite electrodes3.Figure 1: Snapshots of a spinodal decomposition at different times. The initial average filling fraction is c=0.3 and the system has six layers. For each subfigure, top: lithium content in each layer, bottom: coefficients of the Fourier transform used to track the stages Smith, R. B. et al. Intercalation Kinetics in Multiphase-Layered Materials. J. Phys. Chem. C 121, 12505–12523 (2017).Chandesris, M., et al. Thermodynamics and Related Kinetics of Staging in Intercalation Compounds. J. Phys. Chem. C 123, 23711–23720 (2019)Tardif, S. et al. Combining operando X-ray experiments and modelling to understand the heterogeneous lithiation of graphite electrodes. J. Mater. A 9, 4281–4290 (2021) Figure 1

F-region drift current and magnetic perturbation distribution by the X-wave heating ionosphere

Abstract. We present a theoretical and numerical study of the drift current and magnetic perturbation model in the ionosphere by incorporating the ohmic heating model and the magnetohydrodynamic (MHD) momentum equation. Based on these equations, the ionospheric electron temperature and drift current are investigated. The results indicate that the maximum change in electron temperature ΔTe is about 570 K, and the ratio is ΔTe/Te ∼ 48 %. The maximum drift current density is 8×10-10 A m−2, and its surface integral is 5.76 A. Diamagnetic drift current is the main form of current. The low collision frequency between charged particles and neutral particles has little effect on the current, and the collision frequency of electrons and ions is independent of the drift current. The current density profile is a flow ring. We present the effective conductivity as a function of the angle between the geomagnetic field and the radio wave; the model explains why the radiation efficiency was strongest when the X wave is heating along the magnetic dip angle, as reported in recent observations by Kotik et al. (2013). We calculate the magnetic field variation in the heating region based on the MHD theory: the results show that the maximum magnetic field perturbation in the heating area is 48 pT.

Design of line array detection scheme for Polarimeter-Interferometer system on EAST

A multi-channel POlarimeter-INTerferometer (POINT) system has been constructed in the core region of Experimental Advanced Superconducting Tokamak (EAST) plasma for electron density profile and current density profile measurements, with a spatial resolution of 8.5 cm. To explore the small spatial scale density fluctuation phenomena in the core plasma induced by MHD instabilities effects, a higher spatial resolution and higher responsivity detection is required.A novel line array detection scheme of POINT is proposed. By replacing the single Schottky mixer with a highly integrated line array HEMT detector at the central channel position, the existing single channel can be extended to 5 channels for spatial continuous measurement in the core plasma, which has a significantly simplified structure design compared with the discrete upgrade scheme. Related optical design, component selection, and bench tests have been carried out to validate the feasibility and reliability of the novel scheme.The IF signals are detected by an AlGaN/GaN line array high electron mobility transistors (HEMT) detector based on five silicon lenses integrated. The average responsivity of the line array detector elements is 40 kV/W. Compared with the existing planar diode Schottky mixer with a sensitivity of 750 V/W, the line array detector can also meet the essential requirements of coherent signal measurement. Benefiting from the highly integrated array detector, the spatial resolution will be improved to 4.5 mm in the novel scheme. Additionally, a circular Plano cylindrical lens is designed as a beam-shaping component to compress the Gaussian beam into a stripe. Bench test results displayed the excellent performance of the cylindrical lens, which is consistent with the simulation results. Furthermore, normalized responsivity coefficients of array elements are determined by test results.

Characterization of early current quench time during massive impurity injection in JT-60SA

Characteristics of the early current quench (CQ) time in mitigated disruptions are studied for a full-current (5.5 MA) scenario in the JT-60SA superconducting tokamak. Self-consistent evolution of the plasma temperature and current density profiles during the early CQ phase before the plasma moves vertically is simulated using the axisymmetric disruption code INDEX for given impurity source profiles. It is shown that the hollow (flat) impurity density profiles peaks (flattens) the current density, and it causes a temporal change in the internal inductance in this phase. However the resultant CQ time is found to be insensitive to the impurity source profile for the same assimilated quantity. The simulation results are interpreted by the L/R model including the temporal change in the internal inductance as well as the effect of a gap between the plasma and the conducting vessel structures and stabilizing plates. This results will improve the accuracy to estimate the amount of impurity assimilated into plasma from the observed CQ rate in the massive gas injection (MGI) experiment planned in JT-60SA. The accessible range in which the CQ time can be scanned as well as the electron densities to suppress runaway electrons is also shown for different injected amounts of neon, argon, and their deuterium mixture under the limitation of the MGI gas amount. Mitigated disruptions in JT-60SA typically lead to the CQ time shorter than the vessel wall time, which is expected to produce relevant contributions to disruption mitigation in ITER and future reactors.

Effects of toroidally-distributed-divertor biasing on scrape-off-layer (SOL) current drive, divertor particle flux and fast electron confinement in the QUEST spherical tokamak

A novel divertor biasing by four biasing plates distributed toroidally (TDDB) on the upper divertor target plate is applied to low density tokamak plasmas started-up by 28 GHz 2nd harmonic electron cyclotron current drive (ECCD) in a quasi-double null configuration of the QUEST spherical tokamak (ST). In the ST plasmas of line averaged electron density < ne > ∼0.7–1 × 1018 m−3, about 20%–40% of the current Ibias driven by ∼85 V sawtooth bias voltage reaches the lower divertor plate along the biased scrape-off-layer (SOL) flux tube as the SOL current ISOL . The fact ISOL is noticeably lower than Ibias indicates an appreciable leakage of parallel current from the biased SOL flux tube. The leakage currents in the toroidal and radial directions are confirmed by detection of them using the unbiased plates in the TDDB experiments. From the ion saturation current density profile obtained by a divertor Langmuir probe array, the fall-off lengths of divertor particle flux are estimated together with the strike line position. Total particle flux to the upper divertor, evaluated by the integrated ion saturation current density profile is reduced by up to 45% during positive biasing of the TDDB, depending on the position of the strike line to the biased plate. In addition, the TDDB also induces a noticeable loss of fast electrons produced by ECCD, leading to an ∼2% reduction in the maximum toroidal current of the ST plasma compared to a shot without the TDDB. Reduction of the divertor particle flux and enhancement of the fast electron losses are thought to be dominantly caused by E ×B drift induced by the TDDB. In the present experimental conditions, the effects of magnetic perturbations produced by the SOL currents on the fast electron losses can be neglected because of a too small SOL current.

Design and Experimental Investigation of Temperature Control for a 10 kW SOFC System Based on an Artificial Neuronal Network

For a future carbon-neutral energy economy, fuel cells play an important role due their high efficiency. Especially the Solid Oxide Fuel Cell (SOFC) with demonstrated efficiencies beyond 60 % 1 can contribute to reasonable roundtrip efficiencies for hydrogen and e-fuels 2.To match the fluctuating electricity demand in a future electricity grid, dominated by renewable energy sources like wind and photovoltaic, dynamic operation of fuel cells is required. The research has shown that the degradation und therefore the lifespan of Solid Oxide Cell (SOC) stacks shows a significant dependency on the operating conditions and dynamic load changes 3. However, some research suggests that the degradation is not caused by the load changes itself but spatial temperature gradients during load changes 4–6.Therefore, controlling the temperature gradients in the stack during load changes can have a significant impact on the lifespan of SOC stacks. This is typically more dramatically for stacks with larger cell sizes or multiple cells per layer. Furthermore, a tight temperature control allows for running the stack at maximum efficiency without the risk of stack damage due to exceeding temperature limits.In this work the authors designed and experimentally evaluated different controller topologies for fuel cell operation (SOFC) of a reversible solid oxide cell (rSOC) system described previously 7. The controller design incorporates an artificial neuronal network (ANN) for real time state predictions. The training data for the ANN was generated by a dynamic model of this system. This model is implemented in Matlab Simulink and was validated against experimental data. The generated training data consists of about 1,000 simulated days of dynamic system operation with a sample interval of 10 s. Additionally, data for 16,000 different steady state operating conditions of the system were generated.One focus of this work is the robustness of the controller under real world conditions despite inaccuracies of the underlying model and SOC degradation effects over time. To compensate the aging of the stack, the ANN is trained on variable degradation states. The degradation state is then tracked by the controller during operation to maintain an accurate prediction. First system experiments showed promising results in this respect (Fig. 1).Fig 1. Maximum temperature (red) and its setpoint (red, dashed) as well as 8 other temperatures distributed over the stack (black) in response to a given current density profile (green) and the air flow (blue) set by the controller AcknowledgmentsThe authors would like to thank their colleagues at the Forschungszentrum Jülich GmbH, who helped realize this work, and the Helmholtz Society for financing these activities as part of the Living Lab Energy Campus. References(1) Peters, Ro.; Frank, M.; Tiedemann, W.; Hoven, I.; Deja, R.; Kruse, N.; Fang, Q.; Blum, L.; Peters, R. Long-Term Experience with a 5/15kW-Class Reversible Solid Oxide Cell System. J. Electrochem. Soc. 2021, 168 (1), 014508. https://doi.org/10.1149/1945-7111/abdc79.(2) Heydarzadeh, Z.; McVay, D.; Flores, R.; Thai, C.; Brouwer, J. Dynamic Modeling of California Grid-Scale Hydrogen Energy Storage. ECS Trans. 2018, 86 (13), 245–258. https://doi.org/10.1149/08613.0245ecst.(3) Kim, Y.-D.; Lee, J.-I.; Saqib, M.; Park, K.-Y.; Hong, J.; Yoon, K. J.; Lee, I.; Park, J.-Y. Degradation of Anode-Supported Solid Oxide Fuel Cells under Load Trip and Cycle Conditions and Their Degradation Prevention Operating Logic. J. Electrochem. Soc. 2018, 165 (9), F728–F735. https://doi.org/10.1149/2.1391809jes.(4) Hagen, A.; Høgh, J. V. T.; Barfod, R. Accelerated Testing of Solid Oxide Fuel Cell Stacks for Micro Combined Heat and Power Application. Journal of Power Sources 2015, 300, 223–228. https://doi.org/10.1016/j.jpowsour.2015.09.054.(5) Nakajo, A.; Wuillemin, Z.; Van herle, J.; Favrat, D. Simulation of Thermal Stresses in Anode-Supported Solid Oxide Fuel Cell Stacks. Part I: Probability of Failure of the Cells. Journal of Power Sources 2009, 193 (1), 203–215. https://doi.org/10.1016/j.jpowsour.2008.12.050.(6) Jiang, W.; Luo, Y.; Zhang, W.; Woo, W.; Tu, S. T. Effect of Temperature Fluctuation on Creep and Failure Probability for Planar Solid Oxide Fuel Cell. Journal of Fuel Cell Science and Technology 2015, 12 (5), 051004. https://doi.org/10.1115/1.4031697.(7) Peters, R.; Tiedemann, W.; Hoven, I.; Deja, R.; Kruse, N.; Fang, Q.; Blum, L.; Peters, R. Development of a 10/40kW-Class Reversible Solid Oxide Cell System at Forschungszentrum Jülich. ECS Trans. 2021, 103 (1), 289–297. https://doi.org/10.1149/10301.0289ecst. Figure 1

Current density profiles at thin layer electrochemical cells under laminar and turbulent regimes

The transition of laminar to turbulent regimes on smooth electrocatalysts in thin-film electrochemical cells is a subject of study with the aim of predicting current density profiles. Analytical solutions are obtained for velocity profiles under steady state conditions for both hydrodynamic conditions applying a proper velocity contour condition on the catalyst surface. This state is necessary to describe electrochemical cell performances since in these cases, electrode reactions occur at the surface and not in the bulk of the electrolyte. The obtained equations for linear momentum under asymptotic conditions reduce to the solutions obtained by classical Power Series methods years ago. Concentration and current density profiles are also solved accordingly and compared with experimental data of fast redox and dissolved gas reactions on smooth noble metal electrocatalysts.

Exploring the Impact of Concentration and Temperature Variations on Transient Natural Convection in Metal Electrodeposition: A Finite Volume Method Analysis

A mathematical model was developed to accurately determine the current density, concentration, and velocity profiles in electrochemical reactors operating under natural convection conditions. The model considers the interplay of key variables, such as potential, concentration, and temperature linked to the hydrodynamics through the density field using the Boussinesq approximation. Thus, a comprehensive analysis under both laminar and turbulent flow conditions is provided. The computational algorithm that represents the model is implemented in OpenFOAM and it offers the ability to operate the reactor at a fixed cell potential difference or under potentiostatic and galvanostatic control. The model’s accuracy was verified in different parallel-plate reactors using copper deposition as a test reaction from dilute and concentrated solutions, showing a strong agreement with the experimental results. This tool can be leveraged to optimize cell design and operating conditions in electrochemical systems that involve significant natural convection, such as in the electrowinning and electrorefining industries.

Computing the Non-Uniform Current Effects on the Magnetic Field in Sector Coil Dipoles

In this study, we extend the previous ‘Segmentation method’, which was originally suggested to calculate harmonic coefficients of solenoid magnets, to apply to high temperature superconductor (HTS) accelerator dipole magnets. The key idea of the segmentation method is to divide the current flowing domain into several segments to find its equivalent loop currents, by whose magnetic fields or corresponding field quality can be analytically calculated. This paper formulates an equation to calculate the multipole coefficients by segmented loop currents which represents the current densities of a sector-coil dipole magnet. The extended segmentation method is validated by comparison with analytic and inverse method through the multipole coefficient calculation. Second, the segmentation method is applied on an example model of a dipole magnet whose non-uniform current densities which are calculated by using the H-formulation based finite element method. The multipole coefficient calculation results and magnetic field are compared between the uniform and non-uniform current density using the segmentation method. Finally, a case study of extending the obtained 2D current density profile to 3D space is conducted with several assumptions.

The Formation and Stationary Maintenance of Peaked Pressure Profiles in Turbulent Tokamak Plasmas

The theoretical model for increasing peaking of radial distribution of plasma thermal energy and plasma energy confinement time improvement due to the formation of current profiles those provide the increased value of the safety factor qb at the outer plasma boundary is considered. The model for the formation and stationary maintenance of the peaked current density profiles those ensure the maintenance of plasma column equilibrium state with increased qb value and conservation of q0=1 at the magnetic axis is developed. The model is based on the significant ramp down of the Iind current maintained by the inductor with simultaneous central ECR heating and electron cyclotron current drive (ECCD) switching on. It is shown by the computer simulations of the self-consistent time evolution of turbulent plasma for the conditions of T-10 and T-15MD tokamaks that in the shot scenarios with three- or four-fold decrease in the Iind current at the ECRH stage of shots it was achieved an approximately two-fold enhancement of the electron and ion temperatures at the axis of the plasma column as compared to the standard shots with the same heating powers.

The Formation and Stationary Maintenance of Peaked Pressure Profiles in Turbulent Tokamak Plasmas

The theoretical model for increasing peaking of radial distribution of plasma thermal energy and plasma energy confinement time improvement due to the formation of current profiles those provide the increased value of the safety factor {{q}_{b}} at the outer plasma boundary is considered. The model for the formation and stationary maintenance of the peaked current density profiles those ensure the maintenance of plasma column equilibrium state with increased {{q}_{b}} value and conservation of {{q}_{0}} approx 1 at the magnetic axis is developed. The model is based on the significant ramp down of the {{I}_{{{text{ind}}}}} current maintained by the inductor with simultaneous central ECR heating and electron cyclotron current drive (ECCD) switching on. It is shown by the computer simulations of the self-consistent time evolution of turbulent plasma for the conditions of T-10 and T-15MD tokamaks that in the shot scenarios with three- or four-fold decrease in the {{I}_{{{text{ind}}}}} current at the ECRH stage of shots it was achieved an approximately two-fold enhancement of the electron and ion temperatures at the axis of the plasma column as compared to the standard shots with the same heating powers.

Spatiotemporal dynamics across visual cortical laminae support a predictive coding framework for interpreting mismatch responses.

Context modulates neocortical processing of sensory data. Unexpected visual stimuli elicit large responses in primary visual cortex (V1)-a phenomenon known as deviance detection (DD) at the neural level, or "mismatch negativity" (MMN) when measured with EEG. It remains unclear how visual DD/MMN signals emerge across cortical layers, in temporal relation to the onset of deviant stimuli, and with respect to brain oscillations. Here we employed a visual "oddball" sequence-a classic paradigm for studying aberrant DD/MMN in neuropsychiatric populations-and recorded local field potentials in V1 of awake mice with 16-channel multielectrode arrays. Multiunit activity and current source density profiles showed that although basic adaptation to redundant stimuli was present early (50ms) in layer 4 responses, DD emerged later (150-230ms) in supragranular layers (L2/3). This DD signal coincided with increased delta/theta (2-7Hz) and high-gamma (70-80Hz) oscillations in L2/3 and decreased beta oscillations (26-36Hz) in L1. These results clarify the neocortical dynamics elicited during an oddball paradigm at a microcircuit level. They are consistent with a predictive coding framework, which posits that predictive suppression is present in cortical feed-back circuits, which synapse in L1, whereas "prediction errors" engage cortical feed-forward processing streams, which emanate from L2/3.

Nonlinear Equilibrium Structure of Super Thin Current Sheets: Influence of Quasi‐Adiabatic Electron Population

AbstractRecent MMS observations confirmed the existence of the quasi‐stationary electron‐scale super‐thin current sheets (STCSs) with a half‐thickness of few electron gyroradii. STCSs contain the electron population consisting of magnetized and demagnetized particles. To study the role of the demagnetized electrons, we developed a self‐consistent combined model of a STCS in which the dynamics of a part of the electron population is described by the quasi‐adiabatic approximation, while the motion of the other part is described by the guiding center approximation. Demagnetized ion population can be described in a frame of quasi‐adiabatic approach. In the presented model we introduced the weight coefficient of the demagnetized electron plasma density χ depending on the magnetic field normal component Bn/B0 and compared the characteristic profiles of two STCSs differing by the presence (χ ≠ 0) and absence (χ = 0) of demagnetized electrons. It is shown that the presence of demagnetized electrons makes the current density profile of STCS significantly more intense and narrower. The thickness and intensity of STCS depend on the anisotropy coefficient of magnetized electrons and the incoming drift velocity of demagnetized electrons. The maximum current density continuously increases with the growth of the demagnetized electron population and is controlled by the ratio of the thermal to the incoming drift electron velocities. Thus intense current sheets can be formed even in the absence of strong electron anisotropy, which is confirmed by MMS observations.