External Current Research Articles

Control-Oriented Free-Boundary Equilibrium Solver for Tokamaks

A free-boundary equilibrium solver for an axisymmetric tokamak geometry was developed based on the finite difference method and Picard iteration in a rectangular computational area. The solver can run either in forward mode, where external coil currents are prescribed until the converged magnetic flux function ψ(R,Z) map is achieved, or in inverse mode, where the desired plasma boundary, with or without an X-point, is prescribed to determine the required coil currents. The equilibrium solutions are made consistent with prescribed plasma parameters, such as the total plasma current, poloidal beta, or safety factor at a specified flux surface. To verify the mathematical correctness and accuracy of the solver, the solution obtained using this numerical solver was compared with that from an analytic fixed-boundary equilibrium solver based on the EAST geometry. Additionally, the proposed solver was benchmarked against another numerical solver based on the finite-element and Newton-iteration methods in a triangular-based mesh. Finally, the proposed solver was compared with equilibrium reconstruction results in DIII-D experiments.

Transprosthetic Fenestration With Electrified Wires. Experimental Evaluation of Three Multifilament Endografts.

In situ fenestration of aortic endografts is an alternative endovascular technique for treatment of complex aortic aneurysms. While this technique has been carried out also to pass stent-grafts in individual cases, its feasibility and safety using different stent-grafts needs to be evaluated. In a saline bath at water temperature of 37°C, a 0.018" Astato 30 guidewire was advanced through 3 different stent-grafts (RelayPro, Zenith and Endurant II) by applying external current of 180 W via an electrosurgery pencil. Puncture efficacy and quality of the fenestration after ballooning with a 6 mm percutaneous transluminal angioplasty (PTA) catheter were assessed. Then, balloon-expandable covered stents were deployed in the fenestrations and evaluated for stenosis, using microscopy and radiography. Crossing of the electrified guidewire was instantaneous in the Zenith (n:10) and RelayPro (n:10) groups but not in 3 of 10 punctures in the Endurant group (p<.05). The fenestration area created after PTA was significantly larger in the RelayPro (5.3 mm2 ± 1.8, interquartile range [IQR] 1.6) and Zenith group (6.7 mm2 ± 0.7, IQR 0.5) compared to Endurant (2.3 mm2 ± 0.4, IQR 0.5, p<.001). Fraying was observed in all groups while graft shredding was found in 8 cases after PTA of the Zenith and Endurant endografts and in 5 of the RelayPro group, but the difference was not significant. Vertical tearing was detected after RelayPro (2 out of 10) and Zenith (6 out of 10) fenestrations, no damage was found in the Endurant group (p<.01). Residual stenosis at the level of the fenestration after implantation of a 6 × 79 mm VBX stent had to be corrected in all Endurant cases with a high-pressure PTA catheter. No stenosis was found in the RelayPro and Zenith groups before and after flaring. The "electrified wire" technique is a feasible tool that can be used to perform in situ fenestration by perforation of the endograft fabric. Based on this experimental evaluation the "ideal graft" for this technique could not be identified. Long-term fatigue tests and comparison with other fenestration techniques are required. In situ endograft fenestration can be a useful technique in emergent aortic repair. Recently, the electrified wire technique has been proposed as alternative option to laser, radiofrequency and needle-based techniques. In comparison to these methods, the use of electrified wires can be performed without modifications of routine equipment. Additionally, the material costs can be substantially reduced. However, the effectiveness of this approach for fenestration of different prosthetic grafts is unknown. Based on our experimental studies, the electrified wire technique is feasible but the Endurant endograft requires more attempts, and the placement of a bridging stent should be completed with high-pressure balloons.

Evaluating the Viability and Optimization of Plasma Pilot Plants

Nuclear fusion stands as a promising avenue for achieving a sustainable and abundant energy source. Central to this endeavor is the development of effective pilot plants capable of demonstrating the feasibility of fusion power on a commercial scale. This paper provides a comprehensive evaluation of three leading magnetic confinement fusion configurations: the Advanced Tokamak (AT), Spherical Tokamak (ST), and Compact Stellarator (CS).The Tokamak, characterized by its toroidal shape and strong magnetic fields, has been the most researched and developed fusion device. The analysis focuses on the challenges related to maintaining stability and minimizing disruptions. Furthermore, the optimization strategies involving advanced materials, superconducting magnets, and innovative plasma control techniques are discussed to enhance the Tokamak's viability. In contrast, the Spherical Tokamak, a variant with a more compact and spherical design, promises improved current advancements including the handling of higher heat loads and magnetic field configurations. The Stellarator, with its complex, twisted magnetic field structure, eliminates the need for continuous external current drive, addressing some intrinsic issues of the Tokamak. By comparing these configurations, the paper identifies the relative strengths and weaknesses of each approach in terms of confinement efficiency, operational stability, and engineering feasibility. The evaluation is supported by recent experimental data, simulation results, and technological advancements. Finally, the paper proposes a roadmap for the future development of fusion pilot plants, highlighting the need for an integrated approach that leverages the strengths of each configuration while addressing their individual challenges. The synthesis of this evaluation underscores the importance of continued research, cross-collaboration, and investment in advanced technologies to realize the goal of practical and economically viable fusion energy. This comparative analysis aims to provide a strategic framework for policymakers, researchers, and engineers in the fusion community, fostering informed decisions and prioritizing research efforts towards the most promising fusion energy configurations.

Heavy-to-light form factors to three loops

We compute three-loop corrections of O(αs3) to form factors with one massive and one massless quark coupling to an external vector, axialvector, scalar, pseudoscalar, or tensor current. We obtain analytic results for the color-planar contributions, for the contributions of light-quark loops, and the contributions with two heavy-quark loops. For the computation of the remaining master integrals we use the “expand and match” approach which leads to semianalytic results for the form factors. We implement our results in a and a ortran code which allows for fast and precise numerical evaluations in the physically relevant phase space. The form factors are used to compute the hard matching coefficients in Soft-Collinear Effective Theory for all currents. The tensor coefficients at lightlike momentum transfer are used to extract the hard function in B¯→Xsγ to three loops. Published by the American Physical Society 2024

Failure mechanism and model study of Link16 data link limiters caused by the electromagnetic pulse

Abstract Electromagnetic pulse can easily cause interference or damage to the circuit. This study used TCAD device-level modeling and device-circuit mixed simulation methods to investigate the impact of high-power microwaves on the radar front-end limiter. In addition, the variations of the electron concentration, the hole concentration, and the external drain current of the limiter with the electromagnetic pulse radiation are given by establishing a simulation model, and the damage mechanism of the limiter under the electromagnetic pulses (HPM) radiation is revealed. This study provides an important theoretical basis for the protection and reinforcement of PIN limiters.

Influence of sinusoidal forcing on the master FitzHugh–Nagumo neuron model and global dynamics of a unidirectionally coupled two-neuron system

In this paper, we investigate a seven-parameter, five-dimensional dynamical system, specifically a unidirectional coupling of two FitzHugh–Nagumo neuron models, with one neuron being sinusoidally driven. This master–slave configuration features neuron N1 as the master, subjected to an external sinusoidal electrical current, and neuron N2 as the slave, interacting with N1 through an electrical force. We report numerical results for three distinct scenarios where N1 operates in (i) periodic, (ii) quasiperiodic, and (iii) chaotic regimes. The primary objective is to explore how the dynamics of the master neuron N1 influence the coupled system’s behavior. To achieve this, we generated cross sections of the seven-dimensional parameter space, known as parameter planes. Our findings reveal that in the periodic regime of N1, the coupled system exhibits period-adding sequences of Arnold tongue-like structures in the parameter planes. Furthermore, regions of multistability can also be identified in these parameter planes of the coupled system. In the quasiperiodic regime, regions of periodic motion are absent, with only regions of quasiperiodic and chaotic dynamics present. In the chaotic regime of N1, the parameter planes display regions of chaos, hyperchaos, and transient hyperchaos.

Plasma burn-mind the gap.

The programme to design plasma scenarios for the Spherical Tokamak for Energy Production (STEP), a reactor concept aiming at net electricity production, seeks to exploit the inherent advantages of the spherical tokamak (ST) while making conservative assumptions about plasma performance. This approach is motivated by the large gap between present-day STs and future burning plasmas based on this concept. It is concluded that plasma exhaust in such a device is most likely to be manageable in a double null (DN) configuration, and that high core performance is favoured by positive triangularity (PT) plasmas with an elevated central safety factor. Based on a full technical and physics assessment of external heating and current drive (CD) systems, it was decided that the external CD is provided most effectively by microwaves. Operation with active resistive wall mode (RWM) stabilization as well as high elongation is needed for the most compact solution. The gap between existing devices and STEP is most pronounced in the area of core transport, owing to high normalized plasma pressure in the latter which changes qualitatively the nature of the turbulence controlling transport. Plugging this gap will require dedicated experiments, particularly on high-performance STs, and the development of reduced models that faithfully represent turbulent transport at high normalized pressure. Plasma scenarios in STEP will also need to be such that edge localized modes (ELMs) either do not occur or are small enough to be compatible with material lifetime limits. The high current needed for a power plant-relevant plasma leads to the unavoidable generation of high runaway electron beam current during a disruption, where novel mitigation techniques may be needed. This article is part of the theme issue 'Delivering Fusion Energy - The Spherical Tokamak for Energy Production (STEP)'.

Fractional-order heterogeneous neuron network based on coupled locally-active memristors and its application in image encryption and hiding

Synaptic crosstalk significantly influences neural firing in the brain. Locally-active memristors can effectively emulate neural network synapses and have a significant importance in neural network research. This paper designs a tristable locally-active memristive model and presents a novel fractional-order (FO) heterogeneous neuron network. This neural network consists of Hindmarsh-Rose (HR) neuron and FitzHugh-Nagumo (FHN) neuron, which are connected by coupling FO locally-active memristors. The research found that changes in the order of different dimensions have a significant effect on the neural network firing through the three-parameter bifurcation diagram. Moreover, it is found that the locally-active memristor as a synapse can affect the coexistence firing behavior of the network. The complex dynamics have been studied numerically by using phase diagrams, Lyapunov exponent spectrum, bifurcation diagram and extreme multistability can be found. In particular, the system can generate a complex bursting behavior in the presence of an external current. In order to verify the accuracy of the simulation, the phase diagram of FO heterogeneous neuron network is implemented by STM32 microcontroller, and results of the experiments are in great agreement with results of the numerical simulations. Finally, an image encryption and hiding method based on FO heterogeneous neuron network and discrete wavelet transform (DWT) is proposed. The experimental results demonstrate that the encryption and hiding scheme has excellent security and strong robustness.

Dynamical behavior of memristive Hopfield neural network under pulsed current excitation

This paper investigates the effect of pulsed currents and multi-piecewise memristor on dynamic behavior of memristive Hopfield neural network (HNN). Firstly, a four-neuron HNN model is constructed by using the traditional memristor as the connecting synapse and its dynamic behavior is analyzed. Secondly, the traditional memristor in the HNN is replaced with a multi-piecewise memristor, and external pulse currents are applied to the model. The system exhibits rich dynamical behavior by introducing varying numbers of pulse current stimuli and adjusting the parameters of the multi-piecewise memristor. Experimental results demonstrate that the number of attractors in the system changes when pulse currents are applied, and after a period of chaotic behavior, the system eventually exhibits periodic activity. Furthermore, adjusting the parameters of the multi-piecewise memristor can generate multiple scroll attractors in the system. Finally, the experimental results were verified by Multisim.

Exploration of microscopic physical processes of Z-pinch by a modified electrostatic direct implicit particle-in-cell algorithm

Abstract For investigating efficiently the stagnation kinetic-process of Z-pinch, we develop a novel modified electrostatic implicit particle-in-cell algorithm in radial one-dimension for Z-pinch simulation in which a small-angle cumulative binary collision algorithm is used. In our algorithm, the electric field in z-direction is solved by a parallel electrode-plate model, the azimuthal magnetic field is obtained by Ampere’s law, and the term for charged particle gyromotion is approximated by the cross product of the averaged velocity and magnetic field. In simulation results of 2 MA deuterium plasma shell Z-pinch, the mass-center implosion trajectory agrees generally with that obtained by one-dimensional MHD simulation, and the plasma current also closely aligns with the external current. The phase space diagrams and radial-velocity probability distributions of ions and electrons are obtained. The main kinetic characteristic of electron motion is thermal equilibrium and oscillation, which should be oscillated around the ions, while that of ion motion is implosion inwards. In the region of stagnation radius, the radial-velocity probability distribution of ions transits from the non-equilibrium to equilibrium state with the current increasing, while of electrons is basically the equilibrium state. When the initial ion density and current peak are not high enough, the ions may not reach their thermal equilibrium state through collisions even in its stagnation phase.

Encoding of linear kinetic plasma problems in quantum circuits via data compression

We propose an algorithm for encoding linear kinetic plasma problems in quantum circuits. The focus is on modelling electrostatic linear waves in a one-dimensional Maxwellian electron plasma. The waves are described by the linearized Vlasov–Ampère system with a spatially localized external current that drives plasma oscillations. This system is formulated as a boundary-value problem and cast in the form of a linear vector equation $\boldsymbol {A}{\boldsymbol{\psi} } = \boldsymbol {b}$ to be solved by using the quantum signal processing algorithm. The latter requires encoding of matrix $\boldsymbol {A}$ in a quantum circuit as a sub-block of a unitary matrix. We propose how to encode $\boldsymbol {A}$ in a circuit in a compressed form and discuss how the resulting circuit scales with the problem size and the desired precision.

A Novel Coupled Memristive Izhikevich Neuron Model and Its Complex Dynamics

This paper proposes a novel, five-dimensional memristor synapse-coupled Izhikevich neuron model under electromagnetic induction. Firstly, we analyze the global exponential stability of the presented system by constructing an appropriate Lyapunov function. Furthermore, the Hamilton energy functions of the model and its corresponding error system are derived by using Helmholtz’s theorem. In addition, the influence of external current and system parameters on the dynamical behavior are investigated. The numerical simulation results indicate that the discharge pattern of excitatory and inhibitory neurons changes significantly when the amplitude and frequency of the external stimulus current are applied at different degrees. And the crucial dynamical behavior of the neuronal system is determined by the intensity of modulation of the induced current and the gain in the electromagnetic induction. Moreover, the amount of Hamilton energy released by the model could be evaluated during the conversion between the distinct dynamical behaviors.

Probing the Spin-Momentum Locking on Rashba Surfaces via Spin Current.

In this study, we investigate the spin-momentum locking phenomenon on Rashba states of antimony (Sb) films. Utilizing spin pumping in conjunction with an external charge current, we uncover the topological properties of Sb surface states. Our key finding is the precise manipulation of the direction and magnitude of the charge current generated by the inverse Rashba-Edelstein effect. This control is achieved through the dynamic interaction between out-of-equilibrium pumped spins and spin-momentum-locked flowing spins, which are perpendicular to the charge current. Our results highlight Sb as a promising material for both fundamental and applied spintronics research. The studied Sb nanostructures demonstrate potential for the development of low-power logic gates operating with currents in the microampere range, paving the way for advanced spintronic applications.

Lithium Battery SoC Estimation Based on Improved Iterated Extended Kalman Filter

With the application of lithium batteries more and more widely, in order to accurately estimate the state of charge (SoC) of the battery, this paper uses the iterated extended Kalman filter (IEKF) algorithm to estimate the SoC. The Levenberg–Marquardt (LM) method is used to optimize the error covariance matrix of IKEF. Based on the hybrid pulse power characteristics experiment, a second-order Thevenin model with variable parameters is established on the MATLAB platform. The experimental results show that the proposed model is effective under the constant current discharge condition, the Federal Urban Driving Schedule (FUDS) condition, and the Beijing dynamic stress test (BJDST) condition. The results show that the simulation error of the improved LM-IEKF algorithm is less than 2% under different working conditions, which is lower than that of the IKEF algorithm. The improved algorithm has a fast convergence speed to the true value, and it has a good estimation accuracy in the case of large changes in external input current. Additionally, the fluctuation of error is relatively stable, which proves the reliability of the algorithm.

Implementation of external magnetic field to improve strength of St37 steel resistance spot weld

The magnetic assist technique involves the interaction between an external magnetic field and electrical current which produces Lorentz force that influences the flow pattern of molten metal and ultimately impacts the appearance and microstructure of the weld. Many parameters may influence on this process such as welding current, time, and force as well as the working magnet distance (MD). In this study, the effects of the distance between the permanent magnet’s MD on the heat-affected zone (HAZ) and weld nugget zone (NZ) were examined through mechanical and macro- and microstructural analyses. The results demonstrated that MD has a strong influence on the magnetic flux density which determines the joint appearance, quality, and microstructure of St37 steel. Results showed that with increasing MD, HAZ increased from 8 to 22 mm2 while NZ decreased from 26 to 19 mm2, and also, the grain size increased with increasing MD and reaching 48 µm at MD was set to 9 cm. Moreover, hardness decreased at both areas through increasing MD from (120–110) HV at HAZ and from (170–150) HV at NZ. Under the action of (electromagnetic filed) EMF, weld tensile shear strength and the cross tensile strength give the highest values equal to 172 MPa and 155 MPa, respectively, when MD is set to 4.5 cm. Besides, soundness joint was obtained at MD = 4.5 cm which confirms that this is the best distance between magnets.

Effect of external fields and currents on electronic nematic ordering with quadrupole moments

We theoretically investigate the effect of external fields and currents on electronic nematic orderings based on the concept of augmented multipoles consisting of electric, magnetic, magnetic toroidal, and electric toroidal multipoles. We show the relation between rank-2 electric quadrupoles and the other multipoles, the former of which corresponds to the microscopic order parameter for the nematic phases. The electric (magnetic) field induces the rank-1 and rank-3 electric (magnetic) multipoles and rank-2 electric toroidal (magnetic toroidal) quadrupoles, while the electric current induces the rank-1 and rank-3 magnetic toroidal multipoles and rank-2 magnetic quadrupoles. We classify the active multipoles under magnetic point groups, which will be a reference to explore cross-correlation and transport phenomena in nematic phases. As a demonstration, we show that unconventional symmetric and antisymmetric spin splittings are brought about by field-induced toroidal multipoles.

Efficient ECCD non-inductive plasma current start-up, ramp-up, and sustainment for an ST fusion reactor

The elimination of the need for an Ohmic heating solenoid may be the most impactful design driver for the realization of economical compact fusion tokamak reactor systems. However, this would require fully non-inductive start-up and current ramp-up from zero plasma current and low electron temperature of sub-keV to the full plasma current of ∼10–15 MA at 20–30 keV electron temperature. To address this challenge, an efficient solenoid-free start-up and ramp-up scenario utilizing a low-field-side-launched extraordinary mode at the fundamental electron cyclotron harmonic frequency (X–I) is proposed, which has more than two orders of magnitude higher electron cyclotron current drive (ECCD) efficiency than the conventional ECCD for the sub-keV start-up regime. A time dependent model was developed to simulate the start-up scenarios. For the Spherical Tokamak Advanced Reactor (STAR) (Menard et al 2023 Next-Step Low-Aspect-Ratio Tokamak Design Studies (IAEA)), it was found that to fully non-inductively ramp-up to 15 MA, it would take about 25 MW of EC power at 170 GHz. Because of the relatively large plasma volume of STAR, radiation losses must be considered. It is important to make sure that high Z impurities are kept sufficiently low during the early current start-up phase where the temperature is sub-keV range. Since the initial current ramp up takes place at a factor of ten lower density compared to the sustained regimes, it is important to transition into a higher bootstrap fraction discharge at lower density to minimize the ECCD power requirement during the densification. For the sustainment phase an array of eight gyrotron launchers with a total of about 60 MW of fundamental O-mode was found to be sufficient to provide the required axis-peaked external current drive. High efficiencies between 19–57 kA MW−1 were found with optimal aiming, and these were resilient to small changes in aiming angles and density and temperature profiles.

Importance of the Rotational Transform for L–H Transitions in the TJ-II Stellarator

We study the effect of the rotational transform profile on the L–H confinement transitions in the neutral beam-heated plasmas in the TJ-II stellarator. The rotational transform profile in the vacuum is determined by the external coil currents but is modified by the plasma current, Ip. We find that L–H confinement transitions systematically occur when the configuration and plasma current are such that a low-order rational is placed in the plasma edge region, with a distribution centered around ρ=0.8±0.05. It is suggested that magnetohydrodynamic turbulence plays an important role in triggering the L–H transitions at TJ-II.

Comparison models of the operation of absorption machines using the characteristic equation

The integration of absorption machines in micro-trigeneration systems based on micro gas turbines is one of the most viable options for the use of waste gases from micro-turbines, increasing the energy efficiency of the systems, for which the analytical model proposed by the authors is used (Malinowski &amp; Lewandowska, 2013) and (Wang, Cai, &amp; Zhang, 2004), which was reproduced, tested, modified and extended to gas micro-turbines with different power ratings but of the same type, this model is used to heat the activation fluids of the absorption chillers used in these systems, directly influencing the behavior of the chillers according to the load and operating conditions of the micro-turbines, This makes it necessary to develop and apply models of the absorption chillers, with the aim of analyzing the degree of influence that micro-turbines operating at partial load have on the absorption chillers. For this reason, the model selected to obtain the performance of the chillers must be a simple model capable of predicting the behavior of the chillers based on the information from the external currents of the chillers. In the literature, there are a large number of studies focused on the development of absorption chiller models with experimental validation, which take into account specific characteristics of the machine with a greater or lesser degree of detail; this type of model and the literature review.

Controlling three-dimensional magnetic island appearance with external current drive in the Chinese first quasi-axisymmetric stellarator

In this study, the impact of a non-inductive current drive, such as electron cyclotron current drive, on three-dimensional (3D) magnetic islands in the high-β equilibrium of the Chinese First Quasi-axisymmetric Stellarator (CFQS) was investigated using the HINT code. In the case of a high-β equilibrium (volume-averaged plasma beta <β> ∼ 0.74% and bootstrap current I bs∼ 24.5 kA), two m/n = 4/2 rational surfaces with large magnetic islands develop (Wang et al 2021 Nucl. Fusion 61 036021). The islands can be effectively controlled using a constant or a Gaussian current density profile, depending on the direction and amplitude of the current. With a constant current density amounting to a total current of −6 kA, the rotational transform profile can be modified such that the m/n = 4/2 rational surface is eliminated and the island is suppressed. For the Gaussian current density profile, the magnetic island can also be suppressed using a smaller total current of ∼−2 kA to adjust the iota profile. These results suggest that in the CFQS stellarator, the external current drive might be an efficient approach for controlling 3D magnetic islands and consequently improving plasma confinement.