Steady-state Scenarios Research Articles

A study of the heating and current drive options and confinement requirements to access steady-state plasmas at Q ∼ 5 in ITER and associated operational scenario development

Access to steady-state (SS) plasma scenarios that can be potentially achieved in ITER by the exploitation of the neutral beam (NB) and electron cyclotron (EC) heating and current drive capabilities, including their foreseen upgrades, has been assessed and development of the Q ∼ 5 ITER SS operation (SSO) scenario has been carried out by combining all the necessary physics and engineering components. A set of modelling codes including 0.5D/1.5D transport and source modelling suites (METIS, ASTRA and CORSICA) and ideal MHD stability analysis codes (KINX and MISHKA) are applied to combined analysis and scenario development. Operating the plasma with a moderate density peaking factor (n e0/<n e> ∼ 1.3) for sufficient fusion gain (Q up to 5) at a low density (f GW = 0.6–0.8) and the required current drive efficiency produced an internal inductance (l i(3) ∼ 0.8–0 9) which improves the stability margin for low-n external ideal MHD modes. Based on this first observation, a combined operational space and ideal MHD stability analysis has recently identified Q ∼ 5 ITER SS target plasmas (Polevoi et al 2020 Nucl. Fusion 60 096024), and then the CORSICA scenario modelling suite has been applied to study access to the target plasmas as well as to develop a candidate operation scenario. Ideal MHD stability analysis on the SS plasmas has been performed using DCON embedded in the CORSICA scenario modelling suite. The use of off-axis electron cyclotron current drive (ECCD) with a power level of 20–30 MW from the equatorial and upper launchers was essential for the tailoring of the current profile to maintain ideal MHD stability of SS plasmas in ITER. Upgrading the NBI power from the baseline 33 MW to 49.5 MW provided the necessary current drive capability to allow fully non-inductive Q ∼ 5 operation with an energy confinement enhancement requirement (H 98 ≲ 1.6) similar to that achieved in some experiments in present tokamaks (Petty et al 2020 62nd Annual Meeting of the APS Division of Plasma Physics, Virtual Meeting (USA, 9–13 November 2020); Snyder et al 2019 Nucl. Fusion 59 086017; Solomon et al 2013 Nucl. Fusion 53 093033). The CORSICA simulations of the access to the Q ∼ 5 ITER SS target plasmas show that, provided that the enhancement of the energy confinement (H 98 ∼ 1.5–1.6) is achieved, it is possible for ITER to demonstrate the Q ∼ 5 SSO with NB and EC heating and current drive within the limits of the ITER Central Solenoid (CS)/Poloidal Field (PF) coil systems.

Early-Stage Naval Ship Distributed System Design Using Architecture Flow Optimization

This article describes an architecture flow optimization (AFO) method for naval ship system design. AFO is a network-based method. It is used to design and analyze naval ship Mission, Power, and Energy Systems (MPES) in a naval ship Concept and Requirements Exploration (C&amp;RE) process at a sufficient level of detail to better understand system energy flow, define MPES architecture and sizing, reduce system vulnerability, and improve system reliability. This method decomposes MPES into three architectures: logical, physical, and operational which describe the system’s spatial, functional, and temporal characteristics, respectively. Using this framework, the AFO incorporates system topologies, input/output energy coefficient component models, preliminary arrangements, and (nominal and damaged) steady-state operational scenarios into a linear optimization method to minimize the energy flow cost required to satisfy all operational scenario demands and constraints. AFO results are used to inform system topology design and assess the feasibly and survivability of representative designs in the C&amp;RE process. AFO results may also be used in physics-based vital component sizing, calculation of vulnerability/effectiveness metrics in the C&amp;RE process, and subsequent linear optimization formulations to assess recoverability and operational effectiveness in the time domain.

Integrated Control and Actuator Management Strategies for Internal Inductance and Normalized Beta Regulation

An integrated-control architecture for simultaneous regulation of the plasma internal inductance and normalized beta has been designed and tested in simulations using COTSIM (Control-Oriented Transport SIMulator). As present-day tokamaks evolve into nuclear-fusion reactors capable of producing net energy, a significant control-engineering challenge must be solved: regulating a wide variety of plasma variables, often simultaneously, by employing only a reduced number of actuators. As a contribution towards this objective, the present work tackles the problem of controlling the plasma internal inductance, which is a proxy for the broadness of the current-density profile, simultaneously with the plasma normalized beta. Based on zero-dimensional, control-oriented models of the plasma dynamics, individual Lyapunov-theory-based controllers for the internal inductance and normalized beta have been developed. These controllers are integrated by means of an actuator manager that decides, in real time, how the available actuators are utilized in order to fulfill as many control objectives as possible. In addition, the actuator manager is designed to achieve a particular performance metric defined by the control engineer. This metric could be, for example, prioritizing a particular control task over the others and/or minimizing the use of a particular actuator during certain phases of the plasma discharge. Using COTSIM, which includes one-dimensional models of the plasma current-density and electron-temperature dynamics, the performance of the integrated-control framework has been tested in a steady-state scenario for the DIII-D tokamak. These simulation results yield illustrative insights into the plasma current-density and electron-temperature controllability with the current actuation capabilities in DIII-D. Moreover, these simulations show that the way in which the different actuators are employed during the discharge (based on the choice of the aforementioned actuator-manager performance metric) highly determines the value of internal inductance and normalized beta achieved in steady-state conditions, and therefore, the final current-profile shape.

Design and Analysis of the Fractional-Order Complex Least Mean Square (FoCLMS) Algorithm

In this work, a new class of stochastic gradient algorithm is developed based on fractional calculus. Unlike the existing algorithms, the concept of complex fractional gradient is introduced by employing Caputo’s fractional derivative which results in a fractional steepest descent algorithm and a fractional-order complex LMS (FoCLMS) algorithm. We demonstrate that with the Caputo’s fractional gradient definition, the Weiner solution remains invariant. Convergence analysis of the proposed FoCLMS algorithm is presented for both transient and steady state scenarios. Consequently, expressions for the learning curves and steady state EMSE are derived. Our theoretical developments are validated by simulation experiments. Extensive simulations are presented to investigate all possible scenarios: channel with negative weights and real input data, channel with positive weights and complex input data, and channel with complex weights and complex input data.

Energetic Particle Transport Prediction for CFETR Steady State Scenario Based on Critical Gradient ModelSupported by the National Key R&D Program of China (Grant No. 2019TFE03020000), the National Natural Science Foundation of China (Grant Nos. 11875021, 12005054, and 12005055), the Sichuan Science and Technology Program (Grant No. 2020jqqn0070).

The critical gradient mode (CGM) is employed to predict the energetic particle (EP) transport induced by the Alfvén eigenmode (AE). To improve the model, the normalized critical density gradient is set as an inverse proportional function of energetic particle density; consequently, the threshold evolves during EP transport. Moreover, in order to consider the EP orbit loss mechanism in CGM, ORBIT code is employed to calculate the EP loss cone in phase space. With these improvements, the AE enhances EPs radial transport, pushing the particles into the loss cone. The combination of the two mechanisms raises the lost fraction to 6.6%, which is higher than the linear superposition of the two mechanisms. However, the loss is still far lower than that observed in current experiments. Avoiding significant overlap between the AE unstable region and the loss cone is a key factor in minimizing EP loss.

Advances in physics understanding of high poloidal beta regime toward steady-state operation of CFETR

Experimental and modeling investigations of high βp scenarios on DIII-D and EAST tokamaks show advantages in high energy confinement, avoidance of n = 1 MHD, and core-edge integration with reduced heat flux, making this scenario an attractive option for China Fusion Engineering Test Reactor steady-state operation. Experiments show that plasmas with high confinement and high density can be achieved with neutral beam injection on DIII-D (βp ∼ 2.2, βN ∼ 3.5, fBS ∼ 50%, fGw ∼ 1.0, and H98y2 ∼ 1.5) and pure RF power on EAST (βP ∼ 2.0, βN ∼ 1.6, fBS ∼ 50%, fGw ∼ 0.8, and H98y2 &amp;gt; 1.3). By tailoring the current density profile, a q-profile with local (off-axis) negative shear is achieved, which yields improved confinement and MHD stability. Transport analysis and simulation suggest that the combination of a high density gradient and high Shafranov shift allows turbulence stabilization and higher confinement. Using on-axis Electron Cyclotron Heating injection, tungsten accumulation is avoided on EAST, and this is reproduced in modeling. Reduced heat flux (by &amp;gt; 40%) and maintenance of high core confinement is achieved with active feedback control of the radiated divertor, an important result for long pulse operation in tokamaks. The improved physics understanding and validated modeling tools are used to design a 1 GW steady-state scenario for CFETR.

On the Development of Triple Homogeneously Weighted Moving Average Control Chart

To detect sustainable changes in the manufacturing processes, memory-type charting schemes are frequently functioning. The recently designed, homogenously weighted moving average (HWMA) technique is effective for identifying substantial changes in the processes. To make the HWMA chart more effective for persistent shifts in the industrial processes, a double HWMA (DHWMA) chart has been proposed recently. This study intends to develop a triple HWMA (THWMA) chart for efficient monitoring of the process mean under zero- and steady-state scenarios. The non-normal effects of monitoring characteristics under in-control situations for heavy-tailed highly skewed and contaminated normal environments are computed under both states. The relative efficiency of the proposed structure is compared with HWMA, DHWMA, exponentially weighted moving average (EWMA), double EWMA, and the more effective triple EWMA control charting schemes. The relative analysis reveals that the proposed THWMA design performs more efficiently than the existing counterparts. An illustrative application related to substrate manufacturing is also incorporated to demonstrate the proposal.

Numerical experiments on firn isotope diffusion with the Community Firn Model

AbstractAdvances in analytical methods have made it possible to obtain high-resolution water isotopic data from ice cores. Their spectral signature contains information on the diffusion process that attenuated the isotopic signal during the firn densification process. Here, we provide a tool for estimating firn-diffusion rates that builds on the Community Firn Model. Our model requires two main inputs, temperature and accumulation, and it calculates the diffusion lengths for δ17O, δ18O and δD. Prior information on the isotopic signal of the precipitation is not a requirement. In combination with deconvolution techniques, diffusion lengths can be used in order reconstruct the pre-diffusion isotopic signal. Furthermore, the temperature dependence of the isotope diffusion and firn densification makes the diffusion length an interesting candidate as a temperature proxy. We test the model under steady state and transient scenarios and compare four densification models. Comparisons with ice core data provide an evaluation of the four models and indicate that there are differences in their performance. Combining data-based diffusion length estimates with information on past accumulation rates and ice flow thinning, we reconstruct absolute temperatures from three Antarctic ice core sites.

Determination of single-phase transformer saturation characteristic by using Nelder–Mead optimization method

Correctly modelling the nonlinear saturation characteristics of the transformer iron core is of great importance in steady-state calculations (harmonics and power quality) and calculations of the electromagnetic transients (inrush current, ferroresonance, temporary overvoltages). Thus, this paper presents an original estimation algorithm for determining the transformer nonlinear saturation characteristic from the measured inrush and steady-state current waveforms in entire windows of occurrences. The proposed algorithm is based on the minimization of a specifically defined cost function by applying the Nelder–Mead method, which was used to create a balance between the transformer steady-state current and the inrush current at zero residual flux. The algorithm uses the BDF numerical method in the background to solve the stiff differential equation system. By applying the appropriate indexes of quality estimation, it was demonstrated that, out of a total of twelve proposed analytical functions, the best optimization results were achieved with three proposed functions (the Frolich extended, three-term polynomial and special hyperbolic function). Detailed performances and accuracy suggested that the estimation algorithm has been verified by a very close agreement between the simulation results and measured transformer current waveforms in the steady-state and different inrush current scenarios.

Integrated simulation of plasma current profile in HL-2A high confinement mode(H mode)

The plasma current (&lt;i&gt;I&lt;/i&gt;&lt;sub&gt;p&lt;/sub&gt;&lt;italic/&gt;), magnetic field (&lt;i&gt;B&lt;/i&gt;), and safety factor distribution (&lt;i&gt;q&lt;/i&gt; profile) of the HL-2A tokamak device are crucial to monitoring the steady-state operational scenarios (in high confinement mode, H mode). Based on real experimental data and integrated modeling simulation method (OMFIT), the plasma parameters’ profiles such as magnetic field configuration and current density profiles in H mode were reconstructed. By building up an integrated simulation platform for dynamic equilibrium configuration, and combining the rapid workflow processing method and experimental data with integrated simulation models, the ion and electron temperature, density, and current density profiles were obtained. The integration simulation platform was established to reconstruct the internal magnetic surface configuration, the plasma boundary parameter distribution, the ion/electron temperature, current density, and the &lt;i&gt;q&lt;/i&gt; profile. The Ohmic current, bootstrap current, and radio-frequency current profiles with its fractions were calculated. The width of the pedestal region was about 7.52 cm according to our simulation results. It was found that the pressure gradient changes its direction at radial coordinate &lt;i&gt;ρ&lt;/i&gt;(&lt;i&gt;r/a&lt;/i&gt;) = 0.1 and reaches its maximum value near &lt;i&gt;ρ&lt;/i&gt; = 0.7, which may be the internal transport barrier (ITB) configuration caused by negative shear. The profile reconstruction and real-time monitoring of the physical parameters are conducive to evaluating the quality of H mode discharge experiment and can assist in the steady-state operation of advanced operating modes such as HL-2M high normalized beta (&lt;i&gt;β&lt;sub&gt;n&lt;/sub&gt;&lt;/i&gt;) discharge.

The transport of tungsten impurities induced by the intrinsic carbon during upper-single null discharge on EAST tokamak

• SOLPS-DIVIMP modeling is applied to the production and transport of W impurities on EAST. • High n e , s e p OMP suppresses W impurity, while higher input power enhances W concentration. • Strong correlation between T e at the outer target and W ion density at core is observed. • T e < 20 eV is required to maintain W concentration at CEI < 10 −5 in steady-state scenarios. The transport as well as accumulation of tungsten (W) impurity is one of the critical issues for the W divertor operation. The EAST tokamak with W and graphite divertor targets, provides a good platform for the investigation of W impurity behaviors. In this work, the production, transport and accumulation of W impurities are simulated via the SOLPS-DIVIMP modeling. The plasma background is obtained by the SOLPS simulations, while the W sputtering yield is calculated via empirical formula, and the following W transport is traced using the DIVIMP code. The W impurity source is mainly contributed by the incidence of carbon (C) impurity in this simulation. The distribution of W ions with different charge states is obtained and the transport of the W ions is analyzed by the net forces. The dependences of W impurity on the n e , s e p OMP and P SOL are illustrated, which show the divertor plasma has great impact on the W impurity distribution. The increase of n e , s e p OMP can suppress the W impurity in the core region with the fixed P SOL , while higher input power can enhance the W concentration significantly. The W impurity can lead to sufficient power radiation due to strong impurity source and high radiation rate in the core region during low density discharge, while the influence becomes weaker as n e , s e p OMP raises. The effects of self-sputtering on the W impurity accumulation are also discussed. With the increment of P SOL , the sputtering and self-sputtering of W increase remarkably, leading to the W ions concentration exceed 10 −5 in the core–edge interface (CEI). Moreover, the strong correlation between T e at the outer target and W ion density at CEI is observed, showing that T e < 20 eV is required to maintain W concentration at CEI below the acceptable limitation (10 −5 ) in steady-state scenarios in EAST (without ELMs).

End-to-End Remote Field Testing of Phasor Measurement Units Using Phasor Measurement Unit Performance Analyzer Test Suite

Phasor measurement unit (PMU) testing is desired to ensure the continued power system monitoring and the maneuvering precision of synchrophasor-based control. IEEE Std C37.118 and IEEE synchrophasor measurement test suite specification (TSS) clarify the different requirements for both steady-state and dynamic test scenarios with varied error ranges. Existing PMU testing requires taking PMUs out of service and test in the lab typically manually. This article presents an architecture for remote PMU testing utilizing the PMU performance analyzer (PPA) test suite, which can considerably reduce the cost while achieving the substation automation. The proposed field-programmable gate array (FPGA) programming method is demonstrated to meet the TSS requirements for signal source generators (SSG). The accuracy of the frequency and harmonic distortion factors by SSG using the proposed method are compared with the built-in signal generation module of the national instruments (NI) cRIO system. The steady-state and dynamic test results of remote PMU testing based on the proposed architecture are presented in this article. The satisfactory performance test results demonstrate the feasibility of the architecture.

Nonparametric progressive sign chart for monitoring process location based on individual data

ABSTRACT Statistical process control (SPC) plays a vital role in the maintenances and improvements of quality outputs in manufacturing, industrial and service production processes. Control chart is an important SPC tool, used to detect noises and to improve process performance. When the underlying process distribution lacks the assumption of normality, nonparametric (NP) control charts become essential and particularly are useful because their in-control (IC) run length properties remain the same for every continuous distribution. This article develops the NP progressive mean sign (NPPM-SN) chart for monitoring the process target through 100% inspection by taking individual measurements from the process. The performance of the proposed NPPM-SN chart is examined under zero-state and steady-state scenarios. The IC and out-of-control run length properties of the proposed control chart are evaluated using Monte Carlo simulation. The proposed NPPM-SN chart is compared with traditional exponentially weighted moving average (EWMA), nonparametric EWMA sign (NPEWMA-SN) and traditional progressive mean (PM) control charts based on individual measurements using average run length and some other characteristics of the run-length distribution. The proposed NPPM-SN chart is found more robust (for all distributions) and efficient (for skewed distributions) as compared to its competitors. Along with a real-life example related to high voltage power supply, a simulated data example is also presented for the implementation of the proposed NPPM-SN chart.

Alpha particle ripple loss in CFETR steady-state scenario

Confinement of alpha particles is one of the key issues of burning plasma in tokamaks. Due to the discreteness of the toroidal field (TF) coils, the loss alpha particles induced by TF ripple can cause a strong heat load on the first wall. In this work, by using the guiding center code ORBIT, we investigated alpha particle TF ripple loss in Chinese Fusion Engineering Test Reactor (CFETR) steady-state scenario (v20190422), in which both the initial distribution and classical steady-state slowing down distribution of alpha particles are considered. Effects of TF ripple on three particle loss mechanisms, namely prompt loss, ripple well trapping loss and stochastic diffusion loss, are analyzed in detail. Through comparison, it is found that the stochastic diffusion is the main mechanism of alpha particle ripple loss. Moreover, the toroidal and poloidal profiles of the heat load on the first wall are calculated and compared with the safety threshold of CFETR. In addition, a comparison study of alpha particle ripple loss in the hybrid scenario (v20190422) has been carried out. It is found that both total particle loss fraction and maximum heat load in the steady-state scenario are approximately 50% larger than those in the hybrid scenario.

Wheelset-rail mechanical model for a steady-state dynamic condition and prediction of rolling contact fatigue locci

In railway heavy haul transportation, the wheel-rail contact interaction has a strong influence on the performance of the entire system. According to the vehicle longitudinal movement conditions - straight/curved tracks and travel speed, contact interaction takes place on different portions along the wheel/rail geometric profiles. Determining wheel/rail contact patches is fundamental both for vehicle dynamics and to predict the locci prone to rolling contact fatigue (RCF), due to high contact pressures. This work presents a quasi-static model to determine the wheel-rail contact locations and pressures for a given steady-state scenario of straight or curved track. The model is able to consider generic wheel and rail profile geometries with several contact pointwise interactions. Each contact pair is solved by the called ‘master-master methodology’, developed generally for a 3D environment. A proposed simplification leads to a two-dimensional model, able to produce results in fast processing time and very low computational cost. The result gives predictions related to RCF-prone location. The model is motivated for application together with a methodology to quantify the accumulated contact pressure, considering a family of distinct wheelsets and their combined interactions with the rails. We present a case study considering real measured wheel and rail profiles.

Experimental progress of hybrid operational scenario on EAST tokamak

Extensive experiments of advanced scenario development, which contribute to the ITER hybrid operational scenario have been carried out on experimental advanced superconducting tokamak (EAST) tokamak recently with the ITER-like tungsten divertor. The in this operational scenario is intermediate up to 2.1 (EAST#78987, ∼ 2.1, I p ∼ 0.45 MA, q 95 = 3.7, ∼ 1.5 T, 3 MW neutron beam injection and 1 MW 4.6 GHz lower hybrid wave). In these hybrid H-mode plasmas, the internal transport barrier (ITB) has been frequently observed with central flat q profile and it is found that the fishbone mode (m/n = 1/1) can be beneficial to sustain the central flat (q(0) ∼ 1) q profile, thus a stable ITB can be obtained. In this case, better plasma performance is achieved. The formation of the ITB of the electron density is related to the fishbone activities. Energy transport analysis shows that the fishbone instabilities have a suppression on electron turbulent energy transport, while the ITB of ion temperature is due to the suppression of high-k modes (electron temperature gradient). The mechanism of turbulence suppression from fishbone instabilities in the EAST tokamak is not clear and needs more investigation. It is also observed that the power threshold for ITB formation is 3.5 MW, which is consistent with the scaling law for other tokamaks. The dimensionless parameter () obtained in the EAST reaches 0.3, but is still lower than the ITER hybrid scenario design (G ≥ 0.4) and needs more extension. Further investigation of extending the operational regimes, such as expanding the ITB foot outwards, would be important for the development of the hybrid and steady-state scenarios for next-step fusion devices like ITER and CFETR.

Evaluation of core beta effects on pedestal MHD stability in ITER and consequences for energy confinement

The maximum stable pedestal pressure has been shown to increase with core pressure and, in combination with core transport effects, this can lead to a positive feedback mechanism. However, the effect is shown to saturate for a high β in ASDEX-Upgrade simulations [Wolfrum et al. “Impact of wall materials and seeding gases on the pedestal and on core plasma performance,” Nucl. Mater. Energy 12, 18 (2017)]. In this paper, it is numerically investigated whether this effect appears in ITER plasmas, using ideal MHD numerical codes HELENA and MISHKA for different ITER scenarios, in a range of plasma conditions: two inductive scenarios at 7.5 MA/2.65 T and 15 MA/5.3 T and one steady-state scenario at 10 MA/5.3 T. For all scenarios, reference cases for ITER plasmas were taken as a starting point. No pedestal pressure saturation is found for the inductive scenarios, gradually growing up to the global βN limit, which is determined by the Troyon limit. On the contrary, for the 10 MA/5.3 T steady-state scenario, the maximum stable pedestal pressure does not depend on the total β and it is limited by low-n kink-peeling modes, as opposed to high-n peeling-ballooning modes that limit the maximum attainable pedestal height in the inductive scenarios. This core-edge MHD stability feedback loop has been investigated for two assumptions regarding the scaling of the pedestal width with βp,ped¯, using either a constant pedestal width or when scaling it as ΔψN∝βp,ped¯1/2. A stronger core-edge MHD stability feedback is observed for the varying pedestal width for the inductive plasma scenarios, which is closer to the experimental results from JET [Challis et al. “Improved confinement in JET high plasmas with an ITER-like wall,” Nucl. Fusion 55(5), 053031 (2015)], but not for the steady-state one. Finally, the pressure achieved according to this core-edge feedback stability analysis is compared to the plasma pressure achievable on the basis of the energy confinement IPB98(y,2) scaling for various assumptions regarding the scaling of core plasma confinement with heating power.

A recursive harmonic current detection method without fictitious orthogonal components for single-phase system

Detecting the harmonic currents fast and precisely in non-linear loads are very important to suppress harmonics. Among different detection methods, the detection method based on instantaneous reactive power theory is considered as one of the simplest and most attractive techniques. However, the speed and accuracy of the detection method for single-phase system are seriously affected by the fluctuation of the output of low-pass filters (LPFs) and the correctness of fictitious orthogonal components. To address these issues, the inherent relations between the output of LPFs and the harmonic currents of the loads are discussed. A recursive module is proposed to suppress the fluctuation of the output of LPFs, which is mainly caused by the two dominant harmonic currents in non-linear loads. Based on recursive modules, a recursive harmonic current detection method, which is little affected by the two dominant harmonic currents, is presented in the paper. In addition, to eliminate the effects of inaccurate orthogonal current in traditional detection methods, coordinate transformation modules without the use of fictitious orthogonal components are adopted. Simulation and experimental results show that the proposed current detection method has high detection accuracy in steady-state scenarios and fast dynamic responses under load change, voltage sag and frequency variation can be achieved with the proposed detection method.

A steady-state model of microbial acclimation to substrate limitation.

Microbes acclimate to changes in substrate availability by altering the number of transporters on the cell surface, however there is some disagreement on just how. We revisit the physics of substrate uptake and consider the steady-state scenario whereby cells have acclimated to maximize fitness. Flux balance analysis of a stoichiometric model of Escherichia coli was used in conjunction with quantitative proteomics data and molecular modeling of membrane transporters to reconcile these opposing views. An emergent feature of the proposed model is a critical substrate concentration S*, which delineates two rate limits. At concentrations above S*, transporter abundance can be regulated to maintain uptake rates as demanded by maximal growth rates, whereas below S*, uptake rates are strictly diffusion limited. In certain scenarios, the proposed model can take on a qualitatively different shape from the familiar hyperbolic kinetics curves, instead resembling the long-forgotten Blackman kinetics.

Experimental Realization of Diffusion with Stochastic Resetting.

Stochastic resetting is prevalent in natural and man-made systems, giving rise to a long series of nonequilibrium phenomena. Diffusion with stochastic resetting serves as a paradigmatic model to study these phenomena, but the lack of a well-controlled platform by which this process can be studied experimentally has been a major impediment to research in the field. Here, we report the experimental realization of colloidal particle diffusion and resetting via holographic optical tweezers. We provide the first experimental corroboration of central theoretical results and go on to measure the energetic cost of resetting in steady-state and first-passage scenarios. In both cases, we show that this cost cannot be made arbitrarily small because of fundamental constraints on realistic resetting protocols. The methods developed herein open the door to future experimental study of resetting phenomena beyond diffusion.