ITER Scenarios Research Articles

JINTRAC integrated simulations of ITER scenarios including fuelling and divertor power flux control for H, He and DT plasmas

We have modelled self-consistently how to most efficiently fuel ITER hydrogen (H), helium (He) and deuterium–tritium (DT) plasmas with gas and/or pellets with the integrated core and 2D SOL/divertor suite of codes JINTRAC. This paper presents the first overview of full integrated simulations from core to divertor of ITER scenarios following their evolution from X-point formation, through L-mode, L–H transition, steady-state H-mode, H–L transition and current ramp-down. Our simulations respect all ITER operational limits, maintaining the target power loads below 10 MW m−2 by timely gas fuelling or Ne seeding. For the pre-fusion plasma operation (PFPO) phase our aim was to develop robust scenarios and our simulations show that commissioning and operation of the ITER neutral beam (NB) to full power should be possible in 15 MA/5.3 T L-mode H plasmas with pellet fuelling and 20 MW of ECRH. For He plasmas gas fuelling alone allows access to H-mode at 7.5 MA/2.65 T with 53–73 MW of additional heating, since after application of NB and during the L–H transition, the modelled density build-up quickly reduces the NB shine-through losses to acceptable levels. This should allow the characterisation of ITER H-mode plasmas and the demonstration of ELM control schemes in PFPO-2. In ITER DT plasmas we varied the fuelling and heating schemes to achieve a target fusion gain of Q = 10 and to exit the plasma from such conditions with acceptable divertor loads. The use of pellets in DT can provide a faster increase of the density in L-modes, but it is not essential for unrestricted NB operation due to the lower shine-through losses compared to H. During the H–L transition and current ramp-down, gas fuelling and Ne seeding are required to keep the divertor power loads under the engineering limits but accurate control over radiation is crucial to prevent the plasma becoming thermally unstable.

Quasi-linear toroidal simulations of resonant magnetic perturbations in eight ITER H-mode scenarios

Both linear and quasi-linear aspects of the plasma response to the resonant magnetic perturbation (RMP) field are numerically investigated for various H-mode scenarios in ITER, covering the pre-fusion power operation and the fusion power operation phases. Linear response computations for eight ITER scenarios, with varying plasma current and toroidal magnetic field, reveal that the best coil current phasing for controlling the type-I edge localized modes (ELMs) scales roughly linearly with the edge safety factor. The coil phasing is defined as the relative toroidal phase of the coil currents between different rows, for a given toroidal harmonic. Quasi-linear initial value simulation, which is the focus of the present study, shows that application of the n = 3 (n is the toroidal mode number) RMP field has a minimum side effect on the plasma core momentum confinement but potentially a large effect on the global particle transport. Generally, the RMP field with the best (worst) coil phasing for ELM control produces the strongest (weakest) effect on the plasma edge flow and the overall density. This robustly holds for all eight ITER scenarios. Consequently, in order to minimize the RMP induced side effects while achieving ELM control (suppression) in ITER, a compromise is necessary in choosing the coil current configuration.

Priority inheritance with backtracking for iterative multi-agent path finding

In the Multi-Agent Path Finding (MAPF) problem, a set of agents moving on a graph must reach their own respective destinations without inter-agent collisions. In practical MAPF applications such as navigation in automated warehouses, where occasionally there are hundreds or more agents, MAPF must be solved iteratively online on a lifelong basis. Such scenarios rule out simple adaptations of offline compute-intensive optimal approaches; and scalable sub-optimal algorithms are hence appealing for such settings. Ideal algorithms are scalable, applicable to iterative scenarios, and output plausible solutions in predictable computation time.For the aforementioned purpose, this study presents Priority Inheritance with Backtracking (PIBT), a novel sub-optimal algorithm to solve MAPF iteratively. PIBT relies on an adaptive prioritization scheme to focus on the adjacent movements of multiple agents; hence it can be applied to several domains. We prove that, regardless of their number, all agents are guaranteed to reach their destination within finite time when the environment is a graph such that all pairs of adjacent nodes belong to a simple cycle (e.g., biconnected). Experimental results covering various scenarios, including a demonstration with real robots, reveal the benefits of the proposed method. Even with hundreds of agents, PIBT yields acceptable solutions almost immediately and can solve large instances that other established MAPF methods cannot. In addition, PIBT outperforms an existing approach on an iterative scenario of conveying packages in an automated warehouse in both runtime and solution quality.

Continuous reactor network design for multi‐product rigid polyols under uncertainty

AbstractDifferential‐algebraic optimization models for rigid polyol production from our previous work are able to generate optimal reactor configurations along with the optimal operation recipe. However, their performance could degenerate when uncertainty comes into play. In this study, we apply a multi‐scenario (MS) strategy to analyze the impact of kinetic uncertainty on reactor network design. Our approach first identifies scenarios that are worst‐case violations of inequality constraints. Then, we solve the MS problem with current number of scenarios and obtain the optimal common (or first‐stage) decision profiles (q). Next, we apply an iterative scenario sampling and updating strategy, where the uncertainty range is sampled for fixed q to discover constraint violations that determine the need for additional scenarios. This process continues until no further violations are detected. We adopt the MS method to three continuous reactor networks that were optimized in our previous work: CSTR in series, single differential sidestream reactor (DSR) and CSTR followed by a DSR. Among these, the DSR reactor is found to be the most economical and robust with respect to uncertainties.

Effect of inclusion of pitch-angle dependence on a simplified model of RF deposition in tokamak plasma

Using the PION ICRH modelling code and comparisons against JET tokamak experiments, the effect of including pitch angle dependence within the RF diffusion operator on the fast ion particle distribution functions is quantified. It is found to be of greatest importance in cases of higher harmonic heating and lower heating ion mass, resulting in faster drop-off of the distribution’s high energy tail. We see differences of several orders of magnitude in the high-energy range and significant non-linear alterations by several tens of percent to ion species power partition. ITER scenario operational parameters are also considered, and this improved treatment is shown to benefit anticipated ITER scenarios with second harmonic hydrogen heating, according to our predictions. PION’s combination of benchmarked simplified wave physics and Fokker-Planck treatment offers modelling advantages. Since including the pitch angle dependence in the RF diffusion operator has not led to a significant increase in the required computing time when modelling different ICRF schemes in JET discharges, it has been made available within the production code.

Prediction of divertor heat flux width for ITER pre-fusion power operation using BOUT++ transport code

Prediction of divertor heat flux width is performed for the first and the second pre-fusion power operation (PFPO) phases specified in the new ITER research plan using BOUT++ transport code (Li et al 2018 Comput. Phys. Commun. 228 69–82). The initial plasma profiles inside the separatrix are taken from CORSICA scenario studies. Transport coefficients in transport code are calculated by inverting the plasma profiles inside the separatrix and are assumed to be constants in the scrape-off-layer. An anomalous thermal diffusivity scan is performed with E × B and magnetic drifts. The results in two scenarios identifying two distinct regimes: a drift-dominant regime when diffusivity is smaller than the respective critical thermal diffusivity χ c and a turbulence-dominant regime when diffusivity is larger than it. The Goldston heuristic drift model and the ITPA multi-machine experimental scaling yield a lower limit of the width λ q . From transport simulations, we obtain the critical thermal diffusivity χ c = 0.5 m2 s−1 for the PFPO-1 scenario with toroidal magnetic field B = 1.77 T and plasma current I p = 5 MA, and χ c = 0.3 m2 s−1 for the PFPO-2 scenario with toroidal magnetic field B = 2.65 T and plasma current I p = 7.5 MA. Separatrix temperature and collisionality also have a significant impact on the heat flux width in the drift-dominant regime. The investigation clearly yields a scaling for critical thermal diffusivity using ITER scenarios with fixed safety factor q 95, major radius R, aspect ratio R/a, and the separatrix temperature T sep, and establishes the connection with CFETR and C-Mod discharges. This scaling implies that for a given tokamak device with q 95, R, R/a, and T sep fixed, a reduction of poloidal magnetic field by a factor of 3 leads to a 9 times higher critical value of thermal diffusivity χ c, possibly yielding a transition from turbulence- to drift-dominant regime.

An analytical model for coupling losses in large conductors for magnetic fusion

During the operation scenarios of large superconducting tokamaks such as JT-60SA or ITER, disruptions or VDE (Vertical Displacement Events), AC losses are deposited in the superconducting magnets. Due to these AC losses, the temperatures of the Cable in Conduit Conductors (CICC) increase, reducing the temperature margins. It is of highest importance for the operation to correctly estimate AC losses and conductor temperatures. Due to the fast transient nature of those events, an important component of the losses is the coupling losses.The approach for coupling losses estimation, using a unique effective time constant “nτ” is not completely adequate to calculate these losses.For this purpose, since 2010, a heuristic analytical model called MPAS (Multizone PArtial Shielding), has been proposed. It is now currently used by several teams.For each conductor of the coils of a tokamak, the parameters of the MPAS model and nτ are estimated based on the characterization of the conductor AC losses under a sinusoidal excitation at different frequencies. This process is extensively conducted in existing facilities such as the SULTAN test facility at SPC (Swiss Plasma Center), on the dipole and press of Twente University or on JOSEFA dipole test facility at IRFM (Research Institute for Magnetic Confinement) at Cadarache.This characterisation leads to the constitution of a database for the different conductors used in the tokamak. This has been pushed to the uttermost within the ITER qualification and QA/QC (Quality Assurance, Quality Control).The methodology for estimating the MPAS parameters in relation with the measured AC losses is described in details and illustrated for two conductors. Using this database, it is then possible to calculate the coupling losses during ITER module discharges and scenarios. Estimation of coupling losses are compared to experimental results in recent experiments on ITER CS (Central Solenoid) modules.

Progress on performance tests of ITER gyrotrons and design of dual-frequency gyrotrons for ITER staged operation plan

This paper presents the progress of performance tests of ITER gyrotrons developed at QST and the design of dual-frequency (170 GHz and 104 GHz) gyrotrons to enhance various operation scenarios in ITER, such as characteristics studies of H-mode/ELM at low magnetic fields. The major achievements in developing the ITER gyrotrons are as follows: (i) manufacturing of eight ITER gyrotrons and their auxiliary components has been completed. Performance tests at QST have been progressing and four of the eight gyrotrons achieved the required test criteria—1 MW/300 s/50%, 5 kHz modulation with ⩾0.8 MW. Excitation of LP01 mode having a purity of ⩾95% was also successfully demonstrated using a 50 mm-diameter waveguide transmission line, satisfying the specification. (ii) The design of dual-frequency gyrotrons capable of 1 MW continuous-wave operation, was successfully completed.

Fore-sighting autonomous driving - An Ethnographic approach

A growing body of Human-Computer-Interaction research and the automotive industry has identified that understanding user needs and creating positive user experience (UX) is crucial in order to successfully introduce Autonomous Driving (AD) vehicles to the market. AD research is commonly undertaken to provide user insights by studying the individual-technology experiences in lab settings or by forecasting attitudes and acceptability through large surveys. However, these approaches base their knowledge on people's past or present expectations and limited real life experiences of AD. To better understand upcoming individual user needs and to enable new innovations beyond acceptability forecasts and UX lab tests, we need to identify new concepts through alternative methodologies that can generate user foresights based on users’ evolving anticipations of AD in their everyday lives. We propose an ethnographic approach with iterative speculative scenarios, which we demonstrate through a study undertaken with participants from five families who were introduced to evolving levels of AD, in real-life situations. To demonstrate the methodology, we draw on empirical findings which reveal anticipatory experiences, which we abstract through the concepts of confidence, hope and being-in-the-moment. We show how these concepts structured our user foresights, and outline the implications of engaging them in innovation processes.

NNBI for ITER: status of long pulses in deuterium at the test facilities BATMAN Upgrade and ELISE

For the D-T operational phase of the international fusion experiment ITER, starting in 2035, pulses are planned with Q > 10 and a duration of 400 s and pulses with Q = 5 for up to 3600 s. The two neutral beam injection (NBI) systems will deliver 33.3 MW of heating power to the plasma and will also be an important source for non-inductive current drive. An essential part of the NBI systems is a large RF driven source for negative hydrogen or deuterium ions. In order to fulfil the requirements imposed to the NBI system, the ion source has to deliver an intense, stable and homogeneous large negative ion beam over pulse lengths of 400 s or 3600 s. Till now, long pulses in deuterium at the extracted negative ion current density required for ITER could not be demonstrated. The achievable performance is limited by a high current and a pronounced vertical asymmetry of the co-extracted electrons, both strongly increasing with time, whereas the stability of the negative deuterium ions is not an issue. For reduced performance, i.e. reduced negative ion current, lower and more stable co-extracted electron currents are observed, making possible pulses up to 3600 s (using pulsed extraction). One main aim of ongoing investigations at the two test facilities BATMAN Upgrade (Bavarian test machine for negative ions) and ELISE (extraction from a large ion source experiment) is the development of scenarios stabilizing and symmetrizing the co-extracted electron current in deuterium. These investigations are discussed and the current status of hardware upgrades ongoing at BATMAN Upgrade and ELISE towards the ITER scenario of one-hour steady state extraction is presented.

Modelling tritium adsorption and desorption from tungsten dust particles with a surface kinetic model

A kinetic surface model is presented and used to explain the loading and desorption kinetics of tritium retained in micrometre-sized tungsten (W) dust particles. The model describes the sticking of hydrogen isotopes from the gas phase to W surfaces and the desorption from W surfaces. The initial sticking coefficient is set to one and independent of the temperature. The activation energy for desorption depends on the hydrogen coverage of the surface and is parameterised with density functional theory (DFT) calculations for W(100), W(110) and W(111) surfaces. The DFT-parameterised model is successfully compared to experimental results showing that the amount of measured tritium as well as the desorption kinetic can be modelled with only tritium adsorbed on the surface of W dust particles. Then, the model is used to explore possible scenarios to remove the tritium from the W surfaces by exposing the tritiated surfaces to either deuterium and hydrogen. The simulations suggest that it can be possible to remove all the tritium trapped on the W surfaces even at room temperature as soon as the hydrogen or deuterium pressure is higher than the tritium pressure. This gives opportunity to build tritium removal scenarios for ITER.

A bi-objective stochastic order planning problem in make-to-order multi-site textile manufacturing

This study addresses a multi-site stochastic order planning problem with real-world features existing in make-to-order textile manufacturing supply chains widely. A mathematical model of the problem is presented with the consideration of uncertain orders and heterogeneous carbon emission levels of different plants. The problem aims at minimizing the total tardiness and the excessive carbon emissions. By combining a single-objective-guided multi-objective evolution algorithm and a scenario generation technique, a multi-objective evolutionary stochastic optimization approach is proposed to solve this problem. For the first time, the single-objective-guided multi-objective evolutionary algorithm is adapted to handle discrete optimization problems. The iterative scenario selection-based scenario generation approach is used in evaluating the candidate solutions to the problem with uncertain orders. Extensive experimental results demonstrate the effectiveness of the proposed approach and the necessity of considering uncertain orders in real-world production planning.

Open Chance and Risk Management Process Supported by a Software Tool for Improving Urban Security

By now the 5-step risk and chance management process according to the generic ISO 31000 standard has been applied to a wide range of domains including organizational risk management, business continuity, safety and IT security management, as well as occupational safety. The paper motivates the context and need for an open, scalable and flexible urban (perceived) security and safety assessment and improvement process, showing that it should be applicable also at local community level. The basic ideas of the process include the division of risk and chance analysis and management (treatment) into defined phases which are addressed iteratively: (1) within a framing context, stakeholders and their objectives are identified; (2) chance events for reaching objectives or, as often more straightforward, risk events opposing objectives are identified; (3) these chances and risks on objectives are quantified in terms of probability and consequences on the identified objectives; (4) they are assessed regarding their context-sensitive societal acceptability; (5) improvement measures are selected and implemented. The process is iterated until all risks on objectives are sufficiently controlled, also the combination of risks. Concerning the methodology, a semi-formal modelling of the static and dynamic requirements of a tailored process based on ISO 31000 is provided, which in addition allows the formulation of minimum consistency and completeness requirements, e.g. for each objective at least one stakeholder and risk should be identified. For the urban domain, a classification of risk assessment techniques regarding their suitability for supporting the process is presented. A further focus is the efficient provision of best practice options for urban security enhancement. Based on the insights gained by the systematic modelling of the risk management process, a software tool was developed to facilitate the application of the process in participatory settings like round table discussions with stakeholders. The paper presents as use case the application of the tool-supported methodology in several discussion rounds within a residential district in a medium sized university town in Germany along with the discussion of the evaluations and findings. Thus, the applicability of the software-supported urban security risk management to the novel urban security domain is demonstrated. In summary, the approach is sufficiently transparent and flexible for fast summaries of round table discussions up to complex iterative decision and participatory scenarios, which have to consider multiple stakeholders and a large variety of possible urban security and safety enhancement options with a given urban context.

Iterative scenarios for social-ecological systems.

Managing social-ecological systems toward desirable regimes requires learning about the system being managed while preparing for many possible futures. Adaptive management (AM) and scenario planning (SP) are two systems management approaches that separately use learning to reduce uncertainties and employ planning to manage irreducible uncertainties, respectively. However, each of these approaches have limitations that confound management of social-ecological systems. Here, we introduce iterative scenarios (IS), a systems management approach that is a hybrid of the scopes and relationships to uncertainty and controllability of AM and SP that combines the "iterativeness" of AM and futures planning of SP. Iterative scenarios is appropriate for situations with high uncertainty about whether a management action will lead to intended outcomes, the desired benefits are numerous and cross-scale, and it is difficult to account for the social implications around the natural resource management options. The value of iterative scenarios is demonstrated by applying the approach to green infrastructure futures for a neighborhood in the city of Cleveland, Ohio, U.S., that had experienced long-term, systemic disinvestment. The Cleveland green infrastructure project was particularly well suited to the IS approach given that learning about environmental factors was necessary and achievable, but what would be socially desirable and possible was unknown. However, iterative scenarios is appropriate for many social-ecological systems where uncertainty is high as IS accommodates real-world complexity faced by management.

Management tools in the context of NBIC convergence

In view of the potential global human factors threats, NBIC convergence in manufacturing systems requires new, sustainable approaches to HR management. The proposed methodology is based on the systems paradigm of Janos Kornai, which is used in the framework of BigData technologies, artificial intelligence, and blockchain. The problem of control, optimization and evolution of the human factor in NBIC-production cyber-physical systems is solved by means of the developed human-oriented concept of HR-resources management, the development of which occurs in a spiral, involving exit from the system to form new meanings and concepts. Each turn of the spiral is a self-organizing system. For the current stage of development, a cyber-physical system of interaction “Man” - “Machine” is proposed, based on global and double iterative connections, parallel analysis, scenario forecasting, machine learning, cognitive component and collective decision making. The developed human-oriented concept of HR-resources management allows you to control, optimize and develop human production activities, ensure iterative self-development and self-improvement of the system, guarantee the stability and safety of the system, maximize the percentage of return on human resources and reduce the level of opportunistic human behavior.

Parametric study of hydrogenic inventory in the ITER divertor based on machine learning

A parametric study is performed with the 2D FESTIM code for the ITER monoblock geometry. The influence of the monoblock surface temperature, the incident ion energy and particle flux on the monoblock hydrogen inventory is investigated. The simulated data is analysed with a Gaussian regression process and an inventory map as a function of ion energy and incident flux is given. Using this inventory map, the hydrogen inventory in the divertor is easily derived for any type of scenario. Here, the case of a detached ITER scenario with inputs from the SOLPS code is presented. For this scenario, the hydrogen inventory per monoblock is highly dependent of surface temperature and ranges from 10^{18} to 6 times 10^{19} H after a 10^{7} s exposure. The inventory evolves as a power law of time and is lower at strike points where the surface temperature is high. Hydrogen inventory in the whole divertor after a 10^{7} s exposure is estimated at approximately 8 g.

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.

The impact of anisotropy on ITER scenarios

We report on the impact of anisotropy to tokamak plasma configuration and stability. Our focus is on analysis of the impact of anisotropy on ITER pre-fusion power operation 5 MA, B = 1.8 T ICRH scenarios. To model ITER scenarios remapping tools are developed to distinguish the impact of pressure anisotropy from the change in magnetic geometry caused by an anisotropy-modified current profile. The remappings iterate the anisotropy-modified current-density profile to produce the same q profile with matched thermal energy. The analysis is a step toward equilibria that are kinetically self-consistent for a prescribed scenario. We find characteristic detachment of flux surfaces from pressure surfaces and an outboard (inboard) shift of peak density for ( ). Differences in the poloidal current profile are evident, albeit not as pronounced as for the spherical tokamak. We find that the incompressional continuum is largely unchanged in the presence of anisotropy and the mode structure of gap modes is largely unchanged. The compressional branch however exhibits significant differences in the continuum. We report on the implication of these modifications.

Stochastic AC optimal power flow: A data-driven approach

There is an emerging need for efficient solutions to stochastic AC Optimal Power Flow (AC-OPF) to ensure optimal and reliable grid operations in the presence of increasing demand and generation uncertainty. This paper presents a highly scalable data-driven algorithm for stochastic AC-OPF that has extremely low sample requirement. The novelty behind the algorithm’s performance involves an iterative scenario design approach that merges information regarding constraint violations in the system with data-driven sparse regression. Compared to conventional methods with random scenario sampling, our approach is able to provide feasible operating points for realistic systems with much lower sample requirements. Furthermore, multiple sub-tasks in our approach can be easily paralleled and based on historical data to enhance its performance and application. We demonstrate the computational improvements of our approach through simulations on different test cases in the IEEE PES PGLib-OPF benchmark library.

ELM control optimization for various ITER scenarios based on linear and quasi-linear figures of merit

For the purpose of better understanding type-I edge localized mode (ELM) control in ITER with resonant magnetic perturbation (RMP) fields, the plasma response to RMP is computed by a resistive full magneto-hydrodynamic model in toroidal geometry. Five scenarios designed for ITER are considered, ranging from the pre-nuclear to nuclear phases. The plasma response to RMP is quantified by the plasma surface displacement near the X-point of the divertor plasma and at the outboard mid-plane. The optimal coil configurations between two high-Q deuterium-tritium (DT) scenarios (at the same plasma current of 15 MA and the same magnetic field of 5.3 T but different fusion gains, Q = 5 and 10) are predicted to be similar. For the other ITER scenarios with similar edge safety factor q95 ∼ 3 to that of the baseline scenario, the optimal coil phasing is also similar. The optimization results are different for a half-current full-field (7.5 MA/5.3 T) scenario, largely due to the difference in q95. The RMP coil currents are also optimized to tailor the core vs edge toroidal torques exerted by the 3D RMP fields on the plasma column. Torque optimization, with various objective functions proposed in the study, is useful for minimizing the side effects of RMP on the plasma core flow in ITER, while still maintaining the ELM control capability. Full utilization of three rows of ELM control coils in ITER is found to be essential to ensure both flexibility and robustness of ELM control, in terms of both linear and quasi-linear plasma responses.