Prediction of multifaceted asymmetric radiation from the edge movement in density-limit disruptive plasmas on Experimental Advanced Superconducting Tokamak using random forest

Hu, Wenhui; Hou, Jilei; Luo, Zhaohua; Huang, Yao; Chen, Dalong; Xiao, Bingjia; Yuan, Q.P.; Duan, Yanmin; Hu, Jiansheng; Zuo, Guizhong; Li, Jiangang

doi:10.1088/1674-1056/acd2b0

Cited by 2 publications

(1 citation statement)

References 50 publications

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“…The density limit is commonly accompanied by a radiative phenomenon, the so-called MARFE [30][31][32][33][34]. The evolution of such a MARFE, in diverted plasmas, is illustrated in figure 1.…”

Section: Density Limitmentioning

confidence: 99%

Disruption avoidance and investigation of the H-Mode density limit in ASDEX Upgrade

Sieglin,

Maraschek,

Gude

et al. 2023

Plasma Phys. Control. Fusion

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In recent years a strong effort has been made to investigate disruption avoidance schemes in order to aid the development of integrated operational scenarios for ITER. Within the EUROfusion programme the disruptive H-mode density limit (HDL) has been studied on the WPTE (Work Package Tokamak Exploitation) devices ASDEX Upgrade, TCV and JET. Advanced real-time control coupled with improved real-time diagnostics has enabled the routine disruption avoidance of the HDL. This allowed the systematic study of the influence of various plasma parameters on the onset and behavior of the HDL in regimes not easily accessible otherwise. The upper triangularity δ t o p is found to have a significant influence on the x-point radiator (XPR), which plays a major role for the evolution of the disruptive HDL. At high δ t o p the gas flow rate at which the onset of the XPR occurs is strongly reduced compared to low δ t o p . The reduction of δ t o p has proven to be an effective actuator for the HDL disruption avoidance on ASDEX Upgrade for highly shaped scenarios ( δ t o p > 0.25 ). It is observed that the occurrence of the XPR and the H–L transition at the density limit are two separate events, the order of which depends on the applied auxiliary heating power. At sufficiently high heating power the XPR occurs before the H–L transition. Impurity seeding, used for divertor detachment, influences the onset and the dynamics of the XPR and the behavior of the HDL. The stable existence of the XPR, which is thought to be a requirement for detachment control in future devices, has also been observed without impurity seeding. The implementation of a robust and sustainable operational scenario, e.g. for ITER, requires the combination of continuous control and exception handling. For each disruption path the appropriate observers and actuators have to be validated in present devices. Automation of the dynamic pulse schedule has proven successful to scan the operational space of the HDL without disruption. Applying such a technique to ITER could reduce the machine risk induced by disruptions during commissioning. The methodology to develop physics-based observers, which indicate the entry into a disruption path well in time, and applying the appropriate action before the discharge becomes unstable has proven successful.

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Section: Density Limitmentioning

confidence: 99%

Disruption avoidance and investigation of the H-Mode density limit in ASDEX Upgrade

Sieglin,

Maraschek,

Gude

et al. 2023

Plasma Phys. Control. Fusion

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Correlation of the L-mode density limit with edge collisionality

Maris,

Rea,

Pau

et al. 2024

Nucl. Fusion

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The ``density limit'' is one of the fundamental bounds on tokamak operating space, and is commonly estimated via the empirical Greenwald scaling. This limit has garnered renewed interest in recent years as it has become clear that ITER and many tokamak pilot plant concepts must operate near or above the widely-used Greenwald limit to achieve their objectives. Evidence has also grown that the Greenwald scaling - in its remarkable simplicity - may not capture the full complexity of the disruptive density limit. In this study, we assemble a multi-machine database to quantify the effectiveness of the Greenwald limit as a predictor of the L-mode density limit and identify alternative stability metrics. We find that a two-parameter dimensionless boundary in the plasma edge, $\nu_{*\rm, edge}^{\rm limit} = 3.0 \beta_{T,{\rm edge}}^{-0.4}$, achieves significantly higher accuracy (true negative rate of 97.7\% at a true positive rate of 95\%) than the Greenwald limit (true negative rate 86.1\% at a true positive rate of 95\%) across a multi-machine dataset including metal- and carbon-wall tokamaks (AUG, C-Mod, DIII-D, and TCV). The collisionality boundary presented here can be applied for density limit avoidance in current devices and in ITER, where it can be measured and responded to in real time.

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Prediction of multifaceted asymmetric radiation from the edge movement in density-limit disruptive plasmas on Experimental Advanced Superconducting Tokamak using random forest

Cited by 2 publications

References 50 publications

Disruption avoidance and investigation of the H-Mode density limit in ASDEX Upgrade

Disruption avoidance and investigation of the H-Mode density limit in ASDEX Upgrade

Correlation of the L-mode density limit with edge collisionality

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