Global Confinement Research Articles

Understanding the influence of configurations and intermolecular interaction on thermomechanical and dynamics properties of polymer–clay nanocomposites via molecular dynamics simulations

AbstractPolymer‐clay nanocomposites (PCNs) have emerged as highly versatile structural materials that possess exceptional thermomechanical and dynamic properties, all the while retaining their inherent attributes of being lightweight and optically clear. The fabrication of nanocomposites involves the incorporation of carefully calibrated quantities of clay nanofillers into polymer matrixes. Current research expands upon existing coarse‐grained (CG) models of nanoclay and poly (methyl methacrylate) (PMMA) and utilize molecular dynamics simulations to methodically explore the thermomechanical characteristics of PCNs. Specifically, the effects of exfoliated and stacked configurations of nanoclays, as well as variations in intermolecular interactions between the nanoclay and polymer constituents were tested. Tensile and shear simulations, as well as interfacial behaviors, are conducted. The intermolecular interaction could have significant influences on Shear Modulus and Young's Modulus, and those influences have their characteristics due to different configurations and different force directions, such as in most cases, exfoliated structures exhibit higher mechanical modulus compared with stacked configurations at varying interaction strengths. Additionally, in the in‐plane direction, they demonstrate stronger resistance effects compared with the out‐of‐plane direction. The interaction between PMMA and nanoclay slows down the global dynamics of PMMA, with a stronger effect observed for higher interaction strength. The impact of nanoclay on the segmental dynamics of PMMA decreases as we move away from the nanoclay layers toward the pure PMMA matrix. These findings provide molecular insights into the arrangement of components in PCNs during deformation and highlight the significance of nanoclay and the interface in determining their mechanical and dynamic properties.Highlights Variation patterns of mechanical modulus with interactions and configurations. The property difference in mechanical modulus due to configurations. Positive correlation between polymer Tg and intermolecular interaction. Global and local confinement effects on molecular stiffness during tension. Dynamical heterogeneity behavior on different interactions and temperatures.

Impurity study in the dimensionless and dimensional isotope identity experiment between JET Deuterium and Tritium L-mode plasmas

Abstract The behaviour of impurities in fusion plasmas is of crucial importance for achieving sustained fusion reactions, and understanding similarities and differences between Deuterium (D) and Tritium (T) plasmas is needed to assess potential changes from DD to DT in ITER and future reactors. The first dimensionless and dimensional isotope identity experiments between Deuterium (D) and Tritium (T) L-mode plasmas were conducted at the JET W/Be wall. In the first approach, the discharges with matched ρ∗, ν∗, βn, q, and Te/Ti were compared to emphasize direct isotope effects, while in the dimensional approach engineering parameters such as toroidal magnetic field BT, plasma current Ip, plasma electron density and NBI power PNBI were matched. The dimensionless isotope scaling showed an improvement in global confinement and local transport in T plasmas in comparison to the matched D one [1]. Detailed impurity analyses using VUV, visible spectroscopy, SXR cameras, and bolometry revealed that T plasmas exhibited higher radiation and impurity content, particularly Ni and W, compared to D plasmas. Understanding the origin of the increased impurity content is addressed in this paper. The dimensionless experiments showed differences in impurity transport. The Be source behaviour varied: D plasmas had higher Be influx in the dimensionless approach due to lower electron density and enhanced sputtering [2], while T plasmas showed a higher Be source in the dimensional experiments, highlighting isotope mass effects. W in the divertor region was not sputtered by hydrogen isotopes. W in the divertor region was not sputtered by hydrogen isotopes. In the dimensionless experiments, W sputtering was primarily influenced by Ni in T plasmas and by Be in D plasmas. However, in the dimensional approach, Be played a more significant role in W sputtering within T plasmas. MHD instabilities, including sawtooth oscillations, were present in all cases other ones were correlated with NBI power levels; higher NBI power led to elevated levels of Be, Ni, and W impurities. The comprehensive comparison underscores the necessity of accounting for isotope mass effects in predictive modelling and optimization of plasma performance in fusion reactors.

Integrated analysis of plasma rotation effect on HL-3 hybrid scenario

Abstract The hybrid scenario, which has good confinement and moderate MHD instabilities, is a proposed operation scenario for international thermonuclear experimental reactor (ITER). In this work, the effect of plasma rotation on the HL-3 hybrid scenario is analyzed with the integrated modeling framework OMFIT. The results show that toroidal rotation has no obvious effect on confinement with a high line averaged density of n bar ∼ 7 × 1019 m−3. In this case, the ion temperature only changes from 4.7 keV to 4.4 keV with the rotation decreasing from 105 rad/s to 103 rad/s, which means that the turbulent heat transport is not dominant. While in the scenarios characterized by lower densities, such as n bar ∼ 4 × 1019 m−3, turbulent transport becomes dominant in determining heat transport. The ion temperature rises from 3.8 keV to 6.1 keV in the core as the rotation velocity increases from 103 rad/s to 105 rad/s. Despite the ion temperature rising, the rotation velocity does not obviously affect electron temperature or density. Additionally, it is noteworthy that the variation in rotation velocity does not significantly affect the global confinement of plasma in scenarios with low density or with high density.

Environmental Taxation and Sustainable Development in Digital Pollution in México

Environmental taxation represents an opportunity to encourage technological changes between society and the government, to avoid damage to climate change. The main objective of this work is to contribute to the care of the environment through environmental education, although environmental taxes represent an opportunity to reduce pollution, and some countries are committed to labeling environmental taxes, it would give them greater transparency about the destination of that money raised. Digital pollution has been increasing in recent years, and as a result of the global confinement and isolation of the COVID-19 pandemic, so the UN 2030 Agenda represents a great opportunity to analyze the importance of implementing a fiscal policy environment as a basis for the development of all countries in the care of the environment and sustainable development. The synthetic method was used to analyze the different bibliography in addition to the analytical and documentary method of the proposals of International Organizations and Mexican Laws on the environment. Green taxes must be on the agenda, their implementation and evaluation by governments that translate into federal, state and municipal public policies to advance care for the environment in the future.

Impact of divertor neutral pressure on confinement degradation of advanced tokamak scenarios at ASDEX Upgrade

Over previous campaigns, an intense experimental program on advanced tokamak (AT) scenarios, has been carried out at the ASDEX Upgrade tokamak with full-tungsten wall. These discharges have been executed shortly after the boronization of the first wall to reduce the density and the impurity influx. The confinement level of such AT discharges was found to vary considerably, even when discharges with similar, if not identical, engineering parameters were carried out. This work investigates the causes of such confinement variations. Among all plasma quantities analyzed, confinement quality of AT scenarios correlates best with divertor neutral pressure, highlighting the key role of edge and scrape-off layer physics in determining global plasma confinement. In particular, it is found that the main cause of confinement degradation is the reduction of pedestal stability, which is in turn caused by the outward shift of the maximum density gradient position typically observed when the divertor neutral pressure increases. Owing to the low density of AT discharges under analysis, the movement of the maximum density gradient position can be caused entirely by changes in deuterium outgassing from the wall, which is strongly influenced by the boron layer deposited on the plasma-facing components and by the deuterium wall inventory. Finally, the predictive capability of confinement quality with the integrated model IMEP [Luda et al., Nucl. Fusion 60, 036023 (2020)] is tested on these discharges and shows promising results.

Teacher Education and Gender Equality in Greece: A case study

In the sociology of education, a great debate on the issue of gender has been created. Nowadays, educating teachers about gender equality (GE) is a matter of sustainable development especially after the COVID-19 pandemic. The special living conditions of the global social confinement as a measure to eradicate the virus disclosed a worrying outbreakof domestic and gender-based violence in all social categories. After the pandemic, the educational community has been engaged in GE and gender issues with the development of schools’ action plans as reflected in relevant studies in Greece and all over the world. The present study attempts to examine the teachers’ self-efficacy and needs concerning their training for a sustainable GE practice. The importance of the study originates from the necessity to highlight the teachers’ attitudes towards the issues of GE as Greece ranks last in the European Union on the GE Index. For this research, the tool, a validated questionnaire of teacher efficacy for GE practice is administered to secondary education teachers in Greece. Teachers are asked to assess their confidence in gender knowledge, skills, and awareness. The findings of the research showed that the majority of the teachers express their moderate perceptions, great concern, and need for training in developing practices on GE issues at school. However, there are findings that show that patriarchal values are firm in pedagogical practices. This study will create awareness of the necessity of integrating practices of GE in teacher training and education and give the initiative for further studies on the local or national level concerning the attitudes towards GE in education. Integrating GE in the national curricula through suitable teacher interventions could bridge gender inequalities and lead to a more balanced living for future generations.

Confinement controls the creep rate in soft granular packings.

Flow in soft materials encompasses a wide range of viscous, plastic and elastic phenomena which provide challenges to modelling at the microscopic level. To create a controlled flow, we perform falling ball viscometry tests on packings of soft, frictionless hydrogel spheres. Systematic creep flow is found when a controlled driving stress is applied to a sinking sphere embedded in a packing. Here, we take the novel approach of applying an additional global confinement stress to the packing using an external load. This has enabled us to identify two distinct creep regimes. When confinement stress is small, the creep rate is independent of the load imposed. For larger confinement stresses, we find that the creep rate is set by the mechanical load acting on the packing. In the latter regime, the creep rate depends exponentially on the imposed stress. We can combine the two regimes via a rescaling onto a master curve, capturing the creep rate over five orders of magnitude. Our results indicate that bulk creep phenomena in these soft materials can be subtly controlled using an external mechanical force.

Study of fast-ion-driven toroidal Alfvén eigenmodes impacting on the global confinement in TCV L-mode plasmas

Following recent observations of unstable Toroidal Alfvén Eigenmodes (TAEs) in a counter-current Neutral Beam Injection (NBI) scenario developed in TCV, an in-depth analysis of the impact of such modes on the global confinement and performance is carried out. The study shows experimental evidence of non-degradation of ion thermal confinement despite the increasing of auxiliary power. During such an improved confinement period, Toroidal Alfvén Eigenmodes (TAEs) driven by fast ions generated through Neutral Beam Injection (NBI) are found unstable. Together with the TAEs, various instabilities associated with the injection of the fast neutrals are observed by multiple diagnostics, and a first characterization is given. Nonlinear wave-wave couplings are also detected through multi-mode analysis, revealing a complex picture of the stability dynamics of the TCV scenario at hand. The measurements provided by a short-pulse reflectometer corroborate the identification and radial localization of the instabilities. A preliminary, but not conclusive, analysis of the impact of TAEs on the amplitude of the electron density fluctuations is carried out. Local flux-tube gyrokinetic simulations show that the dominant underlying instabilities in the absence of fast ions are Trapped Electron Modes (TEM), and that these modes are effectively suppressed by zonal flows. Attempts to simulate the simultaneous presence of fast-ion driven TAEs and TEM turbulence show that elongated streamers develop up to the full radial extent of the flux-tube domain, thereby invalidating the local assumption and indicating that a global approach is mandatory in these TCV plasmas.

Elevating zero dimensional global scaling predictions to self-consistent theory-based simulations

We have developed an innovative workflow, Stability, Transport, Equilibrium, and Pedestal (STEP)-zero-dimensional (0D), within the OMFIT integrated modeling framework. Through systematic validation against the International Tokamak Physics Activity global H-mode confinement database, we demonstrated that STEP-0D, on average, predicts the energy confinement time with a mean relative error of less than 19%. Moreover, this workflow showed promising potential in predicting plasmas for proposed fusion reactors such as the affordable, robust, compact (ARC) reactor, the European demonstration power plant (EU-DEMO), and the China fusion engineering test reactor (CFETR) indicating moderate H-factors between 0.9 and 1.2. STEP-0D allows theory-based prediction of tokamak scenarios, beginning with 0D quantities. The workflow initiates with the PRO-create module, generating physically consistent plasma profiles and equilibrium using the same 0D quantities as the IPB98(y,2) confinement scaling. This sets the starting point for the STEP module, which further iterates between theory-based physics models of equilibrium, core transport, and pedestal to yield a self-consistent solution. Given these attributes, STEP-0D not only improves the accuracy of predicting plasma performance but also provides a path toward a novel fusion power plant design workflow. When integrated with engineering and costing models within an optimization, this new approach could eliminate the iterative reconciliation between plasma models of varying fidelity. This potential for a more efficient design process underpins STEP-0D's significant contribution to future fusion power plant development.

Effects of social confinement during the first wave of COVID-19 in Mexico City.

The COVID-19 pandemic led to global social confinement that had a significant impact on people's lives. This includes changes such as increased loneliness and isolation, changes in sleep patterns and social habits, increased substance use and domestic violence, and decreased physical activities. In some cases, it has increased mental health problems, such as anxiety, depression, and post-traumatic stress disorder. The objective of this study is to analyze the living conditions that arose during social confinement in the first wave of COVID-19 within a group of volunteers in Mexico City. This is a descriptive and cross-sectional analysis of the experiences of volunteers during social confinement from 20 March 2020 to 20 December 2020. The study analyzes the impact of confinement on family life, work, mental health, physical activity, social life, and domestic violence. A maximum likelihood generalized linear model is used to determine the association between domestic violence and demographic and health-related factors. The findings indicate that social confinement had a significant impact on the participants, resulting in difficulties within families and vulnerable conditions for individuals. Gender and social level differences were observed in work and mental health. Physical activity and social life were also modified. We found that suffering from domestic violence was significantly associated with being unmarried (OR = 1.4454, p-value = 0.0479), lack of self-care in feeding habits (OR = 2.3159, p-value = 0.0084), and most notably, having suffered from a symptomatic COVID-19 infection (OR = 4.0099, p-value = 0.0009). Despite public policy to support vulnerable populations during confinement, only a small proportion of the studied population reported benefiting from it, suggesting areas for improvement in policy. The findings of this study suggest that social confinement during the COVID-19 pandemic had a significant impact on the living conditions of people in Mexico City. Modified circumstances on families and individuals, included increased domestic violence. The results can inform policy decisions to improve the living conditions of vulnerable populations during times of social confinement.

The dependence of tokamak L-mode confinement on magnetic field and plasma size, from a magnetic field scan experiment at ASDEX Upgrade to full-radius integrated modelling and fusion reactor predictions

The dependence of the confinement of a tokamak plasma in L-mode on the magnetic field is explored with a set of dedicated experiments in ASDEX Upgrade and with a theory-based full-radius modelling approach, based on the ASTRA transport code and the TGLF-SAT2 transport model and only using engineering parameters in input, like those adopted in scaling laws for the confinement time. The experimental results confirm the weak dependence of the global confinement on the magnetic field, consistent with the scaling laws for L-mode plasmas and in agreement with the full-radius TGLF-SAT2 predictions. The modelling approach is then extended to numerically investigate the confinement dependence on magnetic field, plasma current and plasma size. The weak dependence of the L-mode confinement on the magnetic field at constant plasma current and plasma size is shown to be produced by a balance between the decrease of confinement mainly produced by the reduction of the E×B shearing rate and the increase of confinement provided by the reduced gyro-Bohm factor, when the magnetic field is increased. The ASTRA/TGLF-SAT2 predicted increase of confinement with increasing plasma size is investigated in comparison with the predictions of the global confinement scaling laws for L-mode plasmas and the Bohm and gyro-Bohm dependencies of confinement, highlighting interesting similarities and important differences. Full-radius TGLF-SAT2 simulations with increasing plasma size are then extended to dimensions which are compatible with reactor relevant fusion power production, using ITER and the European DEMO as references. ASTRA/TGLF-SAT2 predictions of fusion power and confinement of an L-mode fusion reactor are presented at both 5.7 T and 10 T of magnetic field on the magnetic axis.

Coherent mode induced by supersonic molecular beam injection in EAST Ohmic plasmas

A coherent mode (CM) induced by the supersonic molecular beam injection (SMBI) was observed in Ohmic plasmas of EAST tokamak. The CM existed in the spectra of the electron temperature fluctuation and density fluctuation, but not in the spectrum of Mirnov fluctuation. The radial location of the CM was about 10 cm inside the separatrix (normalized minor radius ). In most cases, the CM has multiple discrete frequencies between with an interval of ∼1 kHz. Occasionally, there is only one dominant frequency. The poloidal scale of the CM (poloidal wavenumber , poloidal mode number ) is between that of typical ion turbulence and macroscopic magnetohydrodynamic activities. Statistical analysis results suggest that the onset of the CM requires a high temperature gradient and a relatively low density gradient. Furthermore, the transport analysis shows that the SMBI-caused perturbation propagates inward faster in plasmas with stronger CM, which implies that the CM might be correlated to a high local transport level. However, the impact of the CM on macroscopic plasma parameters including stored energy, energy confinement time, and SMBI-caused mean density fluctuation is too weak to be found in comparison with the random fluctuation and the measurement errors, which suggests that the CM does not have a clear influence on the global confinement.

Analysis of edge transport in L-mode negative triangularity TCV discharges

One of the major problems for future tokamak devices are ELMs (Edge Localized Modes) as they can lead to large, uncontrolled heat fluxes at the machine targets. For this reason, different techniques and alternative magnetic configurations are under study to mitigate or avoid these phenomena. One of the most promising among these studies is the Negative Triangularity (NT) configuration, which exhibits a global confinement comparable with H-Mode operation and, staying in L-mode, could enable an easier power exhaust dissipation due to a possible bigger heat flux decay length with respect to the conventional Positive triangularity (PT) H-mode. In this work, the fluid code SOLEDGE2D-EIRENE is used to study edge transport. Studies are made on discharges performed in the TCV device (Tokamak à configuration variable), which can create a variety of different plasma geometries thanks to 16 independently powered poloidal field coils and its open vacuum vessel. In order to understand if and how power and particle exhaust in NT differs with respect to those of the PT shape, four discharges in single null magnetic divertor configuration with fixed lower triangularity (δbot=+0.5) but with different upper triangularity (from δup=-0.28 to δup=+0.45) have been modelled. All of them are ohmically heated, L-mode deuterium plasmas, and in the high recycling regime. Moreover, these discharges were previously used in [4] to measure the heat flux decay length by IRT (Infrared Thermography), allowing us to make comparisons with modelling results.

Validation of IMEP on Alcator C-Mod and JET-ILW ELMy H-mode plasmas

The recently developed integrated model based on engineering parameters (IMEP) (Luda et al 2020 Nucl. Fusion 61 126048; Luda et al 2021 Nucl. Fusion 60 036023), so far validated on ASDEX Upgrade, has been tested on a database of 3 Alcator C-Mod and 55 JET-ILW ELMy (type I) H-mode stationary phases. The empirical pedestal transport model included in IMEP, consisting now of imposing a fixed value of , allows an accurate prediction of the pedestal top temperature (when the pedestal top density is fixed to the experimental measurements) across these three machines with different sizes, when the pedestal is peeling–ballooning (PB) limited. Cases far from the ideal PB boundary, corresponding to high edge Spitzer resistivity, are instead strongly overpredicted by IMEP. A comparison between the predictions of Europed and IMEP for a subset of JET-ILW cases shows that IMEP can more accurately reproduce the experimental pedestal width. This allows IMEP to better capture profile effects on the pedestal stability, and therefore to correctly describe the negative effect of fueling on the pedestal pressure for PB limited cases. A strong correlation between the separatrix density and the fueling rate has been identified for a subset of JET-ILW cases, when taking into account different divertor configurations. Overall, these promising results encourage further developments of integrated models to obtain reliable predictions of pedestal and global confinement using only engineering parameters for present and future machines.

Interplay between beam-driven chirping modes and plasma confinement transitions in spherical tokamak ST40

Experiments on the high field spherical tokamak ST40 have led to the recent observation of interplay between beam-driven modes of sweeping frequency (chirping modes) and transitions to the enhanced global confinement regime (H-mode) and back to the low confinement regime (L-mode). The H-modes of plasma confinement are identified from decreased intensity of Dα signal and from clear distinctions in the edge gradients of the visible plasma boundary (observed as a sharp plasma edge in camera images). The beam-driven chirping modes, identified as ideal magnetohydrodynamics beta-induced Alfvén acoustic eigenmodes modes, are observed in Mirnov coil signals, interferometry, and soft x-ray diagnostics. A moderate amplitude ‘primer’ chirping mode usually precedes an H–L transition. This is followed by a ‘dominant’ chirping mode with higher amplitude during the L-mode. The L–H transition back to the improved confinement occurs on a longer time scale of tens of ms, consistent with the slowing down time scale of fast beam ions. A dramatic decrease in toroidal plasma rotation is systematically observed associated with chirping modes sweeping down to zero frequency. Resonance maps built for the beam-driven chirping modes with the ASCOT (accelerated simulation of charged particle orbits in torodoial devices) code show that the resonant beam ions have orbits near the trapped-passing boundary. The ASCOT modelling assesses how losses of the resonant fast ions caused by the chirping modes with high enough amplitude modify the torque, potentially affecting the plasma rotation.

Neural Network-Based Confinement Mode Prediction for Real-Time Disruption Avoidance

Reliable disruption avoidance techniques are critical for the development of safe and economically viable fusion reactors. This incipient need has driven the fusion community to spend substantial effort to develop machine learning (ML) models that aim to assist in this area. One area of concern is a sudden loss in global confinement associated with an unintended back-transition from H-mode confinement to L-mode confinement (“H–L back-transition”), which can sometimes lead to a disruption and increased risk of damage to a reactor-grade fusion device. A recent experiment on DIII-D demonstrated a real-time control method able to steer away from such unwanted back transitions. The present confinement mode of the plasma was inferred in real-time using a temporal convolutional neural network that outputs a continuous scalar estimate suitable for input to a closed-loop controller. This scalar estimate was then regulated to a value consistent with H-mode by adjusting power associated with the ratio of the plasma pressure to magnetic pressure ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta _{N}$ </tex-math></inline-formula> ). The model was trained on hundreds of thousands of discrete time steps of expert-labeled data of periods of H-mode and L-mode confinement, taken from hundreds of DIII-D tokamak discharges. This work presents these experimental results, including the method of collecting expert-labeled H- and L-mode confinement data, and the ML model performance and efficacy on the mode prediction task. In addition, the first application of this tool for H–L back-transition prevention is demonstrated in this experiment. Details are presented on the training of the neural network model, including concerns such as hyperparameter tuning and the network architecture. In addition, the methodology for embedding the neural network into the control system for real-time inference and closed-loop control is discussed.

Edge turbulence measurements in L-mode and I-mode at ASDEX Upgrade

The I-mode confinement regime is promising for future reactor operation due to high energy confinement without high particle confinement. However, the role of edge turbulence in creating I-mode's beneficial transport properties is still unknown. New measurements of edge turbulence (ρpol=0.9−1.0) in L-modes and I-modes at low and high densities at ASDEX Upgrade are presented in this paper. A high radial resolution correlation electron cyclotron emission radiometer measures the broadband turbulence throughout the L-mode and I-mode edge and pedestal. The weakly coherent mode (WCM) is measured in both L-mode and I-mode near the last closed flux surface with Te fluctuation levels of 2.3%–4.2%, with a frequency shift between the two phases related to a deeper Er well in I-mode. An neTe phase diagnostic captures a change of the WCM neTe phase between L-mode and I-mode from −171° to −143°. The thermal He beam diagnostic measures a WCM wavenumber range of −0.5 to −1.0 cm−1. A low-frequency edge oscillation (LFEO) appears in the I-mode phase of these discharges and displays coupling to the WCM, but the LFEO does not appear in the L-mode phase. Linear gyrokinetic simulations of the outer core and pedestal top turbulence indicate that while the dominant turbulent modes in the outer core are ion directed and electrostatic, the turbulence becomes increasingly electron directed and electromagnetic with increasing radius. Collisionality is not found to impact characteristics of the L-mode and I-mode edge turbulence with respect to the presence of the WCM; however, the quality of global confinement decreases with collisionality.

On the role of density fluctuations in the core turbulent transport of Wendelstein 7-X

A recent characterization of core turbulence carried out with a Doppler reflectometer in the optimized stellarator Wendelstein 7-X (W7-X) found that discharges achieving high ion temperatures at the core featured an ITG-like suppression of density fluctuations driven by a reduction of the gradient ratio (Carralero et al 2021 Nucl. Fusion 61 096015). In order to confirm the role of ITG turbulence in this process, we set out to establish experimentally the relation between core density fluctuations, turbulent heat flux and global confinement. With this aim, we consider the scenarios found in the previous work and carry out power balance analysis for a number of representative ones, including some featuring high ion temperature. We also evaluate the global energy confinement time and discuss it in the context of the ISS04 inter-stellarator scaling. We find that when turbulence is suppressed as a result of a reduction of η i , there is a reduction of ion turbulent transport, and global performance is improved as a result. This is consistent with ITG turbulence limiting the ion temperature at the core of W7-X. In contrast, when turbulence is reduced following a decrease in collisionality, no changes are observed in transport or confinement. This could be explained by ITG modes being combined with TEM turbulence when the latter is destabilized at low collisionalities.

Confinement improvement during detached phase with RMP application in deuterium plasmas of LHD

In order to explore the compatibility of good core plasma performance with divertor heat load mitigation, the interaction between cold edge plasma and core plasma transport, including the edge transport barrier (ETB), has been analysed in the divertor detachment discharges of deuterium plasmas in LHD with resonant magnetic perturbation (RMP) field application. The RMP application introduces a widened edge stochastic layer and sharp boundary in the magnetic field structure between the confinement region and the edge stochastic layer. The widened edge stochastic layer enhances impurity radiation and provides stable detachment operation as compared with the case without RMP. It is found that ETB is formed at the confinement boundary at the onset of detachment transition. However, as the detachment deepens, the resistive pressure gradient-driven MHD mode is excited, which degrades the ETB. At the same time, however, the core transport decreases to keep global plasma stored energy (W p) unchanged, showing clear core-edge coupling. After a gradual increase of density fluctuation during the MHD activity, a spontaneous increase of W p and the recovery of ETB are observed while the detachment is maintained. Then, the coherent MHD mode ceases and ELM-like bursts appear. In the improved mode, impurity decontamination occurs, and the divertor heat load increases slightly. Key controlling physical processes in the interplay between core and cold edge plasma are discussed. A comparison between deuterium and hydrogen plasmas shows that hydrogen plasmas exhibit similar features to the deuterium ones in terms of density and magnetic fluctuations, impurity decontamination towards higher confinement, etc. But most of the features are modest in the hydrogen plasmas and thus no clear confinement mode transition with clear ETB formation is defined. Better global confinement is obtained in the deuterium plasmas than the hydrogen ones at a higher radiation level.

Optimization of 3D controlled ELM-free state with recovered global confinement for KSTAR with n = 1 resonant magnetic field perturbation

Mitigation of deleterious heat flux from edge-localized modes (ELMs) on fusion reactors is often attempted with 3D perturbations of the confining magnetic fields. However, the established technique of resonant magnetic perturbations (RMPs) also degrades plasma performance, complicating implementation on future fusion reactors. In this paper, we introduce an adaptive real-time control scheme on the KSTAR tokamak as a viable approach to achieve an ELM-free state and simultaneously recover high-confinement (β N ∼ 1.91, β p ∼ 1.53, and H 98 ∼ 0.9), demonstrating successful handling of a volatile complex system through adaptive measures. We show that, by exploiting a salient hysteresis process to adaptively minimize the RMP strength, stable ELM suppression can be achieved while actively encouraging confinement recovery. This is made possible by a self-organized transport response in the plasma edge which reinforces the confinement improvement through a widening of the ion temperature pedestal and promotes control stability, in contrast to the deteriorating effect on performance observed in standard RMP experiments. These results establish the real-time approach as an up-and-coming solution toward an optimized ELM-free state, which is an important step for the operation of ITER and reactor-grade tokamak plasmas.