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The correlation between the bifurcation of resonant magnetic perturbations (RMPs) to the unshielded state and edge localized mode (ELM) suppression in ASDEX Upgrade is studied using a kinetic plasma response model numerically and analytically. For the numerical studies, the linear kinetic Maxwell solver KiLCA for cylindrical geometry and the quasilinear transport code QL-Balance are used in combination with the ideal MHD solver GPEC to account for realistic tokamak geometry. Based on this modelling, a numerical local bifurcation criterion is introduced which estimates the effect of RMP-induced temperature plateau formation in the resonant layer. Its analytical form is derived in constant-psi approximation. The kinetic model reproduces the known gyrocenter resonance, E r = 0 , and the electron fluid resonance. In contrast to MHD theory, the latter is located at the zero of the perpendicular electron fluid velocity computed only with half of the electron temperature gradient. The application of the criterion to experimental data shows a correlation between bifurcation and the ELM suppression phase. Moreover, an electron density limit is found resembling the one observed in experiments. [ABSTRACT FROM AUTHOR]

According to recent DIII-D experiments (Logan et al 2024 Nucl. Fusion 64 014003), injecting edge localized electron cyclotron current drive (ECCD) in the counter-plasma-current (counter- I _p ) direction reduces the n = 3 resonant magnetic perturbation (RMP) current threshold for edge-localized mode (ELM) suppression, while co- I _p ECCD during the suppressed ELM phase causes a back transition to ELMing. This paper presents nonlinear two-fluid simulations on the ECCD manipulation of edge magnetic islands induced by RMP using the TM1 code. In the presence of a magnetic island chain at the pedestal-top, co- I _p ECCD is found to decrease the island width and restore the initially degraded pedestal pressure when its radial deposition location is close to the rational surface of the island. With a sufficiently strong co- I _p ECCD current, the RMP-driven magnetic island can be healed, and the pedestal pressure fully recovers to its initial ELMing state. On the contrary, counter- I _p ECCD is found to increase the island width and further reduce the pedestal pressure to levels significantly below the peeling-ballooning-mode limited height, leading to even stationary ELM suppression. These simulations align with the results from DIII-D experiments. However, when multiple magnetic island chains are present at the pedestal-top, the ECCD current experiences substantial broadening, and its effects on the island width and pedestal pressure become negligible. Further simulations reveal that counter- I _p ECCD enhances RMP penetration by lowering the penetration threshold, with the degree of reduction proportional to the amplitude of ECCD current. For the ∼1 MW ECCD in DIII-D, the predicted decrease in the RMP penetration threshold for ELM suppression is approximately 20%, consistent with experimental observations. These simulations indicate that edge-localized ECCD can be used to either facilitate RMP-driven ELM suppression or optimize the confinement degradation.

Integration of transient and steady-state divertor heat fluxes control with a high-performance core is necessary for future fusion reactors. In recent DIII-D high- ${\beta _{\text{p}}}$ experiments, divertor detachment and simultaneous edge localized mode (ELM) suppression are demonstrated while the plasma confinement quality is maintained high in ITER-similar shape. By optimizing the neon injection in high- ${\beta _{\text{p}}}$ scenario with ITER-similar shape, deep detachment and ELM suppression are achieved with a high-performance core ( ${\beta _{\text{N}}}$ ∼ 2.8, ${\beta _{\text{p}}}$ ∼ 2.3) at ${q_{95}}$ ∼ 7.5. Partial divertor detachment and suppression of large ELMs are achieved at ${q_{95}}$ ∼ 6. The stability analyses suggest that with low neon injection, the density pedestal becomes higher and steeper and the ${T_{\text{i}}}$ profile also increases, therefore the increased edge pressure and higher current density destabilize the Peeling-Ballooning mode (PBM), which would lead to a large ELM collapse. With strong neon gas puffing, the significantly reduced pedestal pressure and current density, due to the degraded ${T_{\text{e}}}$ pedestal, lead to the stabilization of PBM and ELMs are suppressed. For both cases, the coupling between the large radius internal transport barrier (ITB) and edge pedestal is the key reason for maintaining high global performance. The formation of large radius ITB compensates for pedestal degradation. Such results could provide an attractive scenario to well control the transient and steady-state heat flux onto the divertor plates while maintaining good plasma performance, which is an important step toward the steady-state operation of future fusion reactors.

The operational space and global performance of plasmas with edge-localized modes (ELMs) suppressed by resonant magnetic perturbations (RMPs) are surveyed by comparing AUG, DIII-D, EAST, and KSTAR stationary operating points. RMP-ELM suppression is achieved over a range of plasma currents, toroidal fields, and RMP toroidal mode numbers. Consistent operational windows in edge safety factor are found across devices, while windows in plasma shaping parameters are distinct. Accessed pedestal parameters reveal a quantitatively similar pedestal-top density limit for RMP-ELM suppression in all devices of just over $3\times 10^{19}$ m ^−3 . This is surprising given the wide variance of many engineering parameters and edge collisionalities, and poses a challenge to extrapolation of the regime. Wide ranges in input power, confinement time, and stored energy are observed, with the achieved triple product found to scale like the product of current, field, and radius. Observed energy confinement scaling with engineering parameters for RMP-ELM suppressed plasmas are presented and compared with expectations from established H and L-mode scalings, including treatment of uncertainty analysis. Different scaling exponents for individual engineering parameters are found as compared to the established scalings. However, extrapolation to next-step tokamaks ITER and SPARC find overall consistency within uncertainties with the established scalings, finding no obvious performance penalty when extrapolating from the assembled multi-device RMP-ELM suppressed database. Overall this work identifies common physics for RMP-ELM suppression and highlights the need to pursue this no-ELM regime at higher magnetic field and different plasma physical size.

The q _95 window for Type-I edge localized modes (ELMs) suppression using n = 4 even parity resonant magnetic perturbations (RMPs) has been significantly expanded to the ranges [3.9, 4.1] and [4.2, 4.8] in EAST while maintaining good confinement, which is demonstrated to be reliable and repeatable over the last two years. This window is significantly wider than the previous one achieved using n = 4 odd parity RMPs, which is around $q_{95} = 3.7\pm0.1$ . Here, n represents the toroidal mode number of the applied RMPs and q _95 is the safety factor at $95\%$ of the normalized poloidal magnetic flux. During ELM suppression, there is only a slight drop in the plasma stored energy and density ( ${\leqslant}10\%$ ). The comparison of changes in the pedestal profiles suggests that ELM suppression is achieved when the pedestal gradient is kept lower than a threshold. This wide q _95 window for ELM suppression is consistent with the prediction made by MARS-F modeling prior to the experiment, which located it at one of the resonant q _95 windows for plasma response. The Chirikov parameter taking into account plasma response near the pedestal top, which measures plasma edge stochasticity, significantly increases when q _95 exceeds 4, mainly due to the denser neighboring rational surfaces. The modeling of plasma response reveals a strong coupling between resonant and non-resonant components across the pedestal region, which is a characteristic of the kink-peeling like response observed during RMP-ELM suppression in previous studies on EAST. These promising results demonstrate the reliability of ELM suppression using the n = 4 RMPs in EAST and expand the physical understanding on ELM suppression mechanism.

Nonlinear 3D MHD simulations and validations reveal that the hybrid particle-MHD transport is a key process for driving the pump-out in the presence of Resonant Magnetic Perturbations (RMPs) in the KSTAR tokamak. Particle transport and the resulting density pump-out by RMPs are shown to be composed of not only the classical flow convection near magnetic islands due to polarization but also the neoclassical ion diffusion across perturbed magnetic surfaces. The latter is known as the Neoclassical Toroidal Viscosity (NTV) and is integrated into nonlinear MHD simulations here for the first time, revealing that the two-stage pump-outs observed in KSTAR experiments are reproduced only with such integrated nonlinear MHD and transport evolution. Near-resonant responses, which have received less attention than the resonant response, play distinct roles in the pump-out along with the island formation. In addition, this modeling is used to investigate the pump-outs in double-null-like plasmas and numerically capture the effect of the double-null shape on the pump-outs, which may explain the difficulty of Edge Localized Mode (ELM) suppression access in double-like plasmas. This reveals new aspects of the impact toroidal geometry and mode coupling have on 3D physics and reveals the importance of near-resonant components in suppressing ELMs.

The correlation between the bifurcation of resonant magnetic perturbations (RMPs) to the unshielded state and edge localized mode (ELM) suppression in ASDEX Upgrade is studied using a kinetic plasma response model numerically and analytically. For the numerical studies, the linear kinetic Maxwell solver KiLCA for cylindrical geometry and the quasilinear transport code QL-Balance are used in combination with the ideal MHD solver GPEC to account for realistic tokamak geometry. Based on this modelling, a numerical local bifurcation criterion is introduced which estimates the effect of RMP-induced temperature plateau formation in the resonant layer. Its analytical form is derived in constant-psi approximation. The kinetic model reproduces the known gyrocenter resonance, $E_r = 0$ , and the electron fluid resonance. In contrast to MHD theory, the latter is located at the zero of the perpendicular electron fluid velocity computed only with half of the electron temperature gradient. The application of the criterion to experimental data shows a correlation between bifurcation and the ELM suppression phase. Moreover, an electron density limit is found resembling the one observed in experiments.

Experiments on the DIII-D tokamak demonstrate that edge localized mode (ELM) stability can be manipulated using localized electron cyclotron current drive (ECCD) in conjunction with resonant magnetic perturbations (RMPs). The injection of counter-plasma-current edge ECCD reduces the RMP amplitude required to suppress ELMs and bifurcates the pedestal into a high-confinement regime with 7 kPA pedestal pressure. This is the first time such a high confinement regime has been accessed through the bifurcation from the ballooning stability branch predicted by existing models. These observations are consistent with modeled ECCD manipulation of magnetic islands induced by the RMPs.

Full suppression of type-I edge localized modes (ELMs) using n = 4 resonant magnetic perturbations (RMPs) as planned for ITER has been demonstrated for the first time (n is the toroidal mode number of the applied RMP). This is achieved in EAST plasmas with low input torque and tungsten divertor, and the target plasma for these experiments in EAST is chosen to be relevant to the ITER Q = 10 operational scenario, thus also addressing significant scenario issues for ITER. In these experiments the lowest neutral beam injection (NBI) input torque is around T NBI ∼ 0.44 Nm, which extrapolates to around 14 Nm in ITER (compared to a total torque input of 35 Nm when 33 MW of NBI are used for heating). The q 95 is around 3.6 and normalized plasma beta β N ∼ 1.5â€"1.8, similar to that in the ITER Q = 10 scenario. Suppression windows in both q 95 and plasma density are observed; in addition, lower plasma rotation is found to be favourabe to access ELM suppression. ELM suppression is maintained with line averaged density up to 60% n GW (Greenwald density limit) by feedforward gas fuelling after suppression is achieved. It is interesting to note that in addition to an upper density, a low density threshold for ELM suppression of 40% n GW is also observed. In these conditions energy confinement does not significantly drop (<10%) during ELM suppression when compared to the ELM y H-mode conditions, which is much better than previous results using low n (n = 1 and 2) RMPs in higher q 95 regimes. In addition, the core plasma tungsten concentration is clearly reduced during ELM suppression demonstrating an effective impurity exhaust. MHD response modelling using the MARS-F code shows that edge magnetic field stochasticity has a peak at q 95 ∼ 3.65 for the odd parity configuration, which is consistent to the observed suppression window around 3.6â€"3.75. These results expand the physical understanding of ELM suppression and demonstrate the effectiveness of n = 4 RMPs for reliable control ELMs in future ITER high Q plasma scenarios with minimum detrimental effects on plasma confinement. [ABSTRACT FROM AUTHOR]