Recent Publications

Revisit two-mode couplings of the ablative Rayleigh-Taylor instability in inertial confinement fusion

Xian Jiang, Shenming Xu, Dehua Zhang, Tao Tao, Jingfei Xin, Rui Yan, Hang Ding, Jian Zheng

University of Science and Technology of China, BYD Automobile Industry Co. Ltd

Two-dimensional two-mode couplings of the ablative Rayleigh-Taylor instability (ARTI) under inertial-confinement-fusion (ICF) relevant parameters are revisited via numerical simulations, with a focus on the regimes where the wavenumbers of the initial modes are close to the cutoff wavenumber. In the quasi-linear stage in which the generated modes approximately grow exponentially with time, both the self-growth of the generated mode (as if in the single-mode regime) and the driven-growth due to mode couplings are found to be important. A series of linearly unstable modes are found to be generated by coupling of two linearly stable initial modes, and then compete for the dominant mode according to a proposed criterion. A model including the contribution of both the self-growth and the driven-growth with an empirically modified coupling coefficient is proposed and shown to accurately predict the growth of the generated mode. The findings have implications for assessing the impact of ARTI in ICF designs.

A theoretical model for quantifying the imprinting sensitivity of direct-drive inertial confinement fusion implosions

Dongxue Liu, Jiaqin Dong, Yunxing Liu, Zhiyu HE He, Wei Wang, Yuqiu Gu, Xiuguang Huang, Jian Zheng

China Academy of Engineering Physics Shanghai Institute of Laser Plasma, China University of Mining and Technology, University of Science and Technology of China

To quantify the sensitivity of diverse implosion designs to laser imprinting, we developed an equivalent perturbation model that maps laser imprinting as the initial target surface perturbation. By incorporating imperfections in target fabrication and thermal smoothing in the plasma, the model shows a reduced implosion sensitivity to laser imprinting, extending the analysis beyond geometric irradiation. The imprinting sensitivity threshold is defined as δh_{proxy}/δh{tar}(0)= 0.1, where δh_{proxy} is the imprinting amplitude and δh{tar}(0) is the initial target perturbation amplitude. Radiation-hydrodynamics simulations confirm that whenδh_{proxy}/δh{tar}(0)< 0.1, variations in nonlinear onset time and adiabat remain within 12\% of that with δh{tar}(0) alone. Moreover, the imprinting sensitivity is supported by OMEGA experiments. Overall, for linear perturbations of medium-to-high modes in direct-drive, the model enhances our physical understanding of how laser and target perturbations evolve and serves as a simplified tool to optimize implosion performance.

Direct Optimization of Stellarator Omnigenity from the Second Adiabatic Invariant

Hanlin Chen, Zhiyuan Lu, Guosheng Xu, Shuai Cao, Yang Han, Dehong Chen, Baonian Wan

Institute of Plasma Physics, Chinese Academy of Sciences, University of Science and Technology of China

Stellarators offer a steady-state, disruption-free path to fusion energy but suffer from enhanced particle losses due to their three-dimensional geometry. Existing optimization methods rely on geometric proxies rather than the actual trapped-particle orbit condition. We present a differentiable framework that directly optimizes the fundamental orbit action governing particle confinement. The approach yields compact stellarator designs with excellent fast-ion confinement, finite-pressure stability, and coil compatibility, demonstrating that first-principles orbit optimization can be integrated with engineering constraints in a single computational workflow for fusion reactor design.

Activation analysis and radioactive waste assessment for COOL blanket in CFETR

Xiaokang Zhang, Qiuran Wu, Lin Kong, Xilong Tong, Shanliang Zheng

Hefei Institutes of Physical Science, Chinese Academy of Sciences, University of Science and Technology of China

Hybrid simulation of transition from Beta induced Alfv'en Eigenmode to Reverse Shear Alfv'en Eigenmode on EAST

Andong Xu, Yiqi Liu, Wei Shen, Ming Xu, Baonian Wan

Institute of Plasma Physics, Chinese Academy of Science, University of Science and Technology of China, State Key Laboratory of Nuclear Physics and Technology

Kinetic-magnetohydrodynamic (MHD) hybrid simulations have been carried out to investigation the transition of different types of Alfv'en eigenmode based on Experimental Advanced Superconducting Tokamak(EAST). Two evolution processes of q profile starting with a reverse shear q profile with minimum $q_{min} < 2$ have been analyzed: ascending one based on magnetic diffusion effect and descending one inferred from coexistence of double tearing mode. The experimental phenomenon that type of Alfv'en eigenmode transit from Beta induced Alfv'en Eigenmode (BAE) to Reverse Shear Alfv'en Eigenmode (RSAE) and up-sweeping of RSAE frequency with multiple toroidal number n is reproduced in both processes. In the ascending process, transition from BAE to RSAE happens at $q_{min} = 2$ when rational surface of $q = 2$ vanishes. In the descending process, transition happens at $q_{min} = 1.92$ without vanishing of $q = 2$ rational surface and is accompanied by a sudden shift in mode location. Comparing frequency and growth rate pattern with experimental observation during mode transition, the descending process satisfies experiment better. In addition, different physical factors to affect the mode transition have been investigated including q profile shape and energetic particle pressure. It is found that smaller magnetic shear at rational surface is in favor of excitation of BAE, and RSAE frequency is influenced by second order derivative of q profile at its minimum. Moreover, the excitation of BAE is not sensitive to the peak location of energetic particle pressure gradient, but radial phase variance of mode structure is positively linked to distance between energetic particle drive location and mode location, which is also influenced by local magnetic shear. These systematical study on the effect of different physical factors on Alfv'en eigenmodes can provide guidance for controlling Alfv'en instabilities in future.

The Verification, Validation, and Uncertainty Quantification Framework of the EAST Tokamak Diagnostic System

Shuzhi Yuan, Haiqing Liu, Kazuaki Hanada, Mitsutaka Isobe, Yang Zhang, Ting Lan, Xiang Liu, Hui Lian, YuQi Chu, Shouxin Wang, et al.

Hefei Institutes of Physical Science, Chinese Academy of Sciences, University of Science and Technology of China, Kyushu University, Mahasakham University, National Institutes of Natural Sciences

The diagnostic system in a tokamak serves as the foundation for research in plasma physics, plasma operation control, and device protection. The accuracy and reliability of diagnostic data have long been critical considerations in tokamak data analysis and processing. To achieve systematic error assessment, optimized design, and coupling with other systems or simulation modules, the development of a digital diagnostic system module, digital twin, can significantly reduce labor and time costs. Based on a digital diagnostic model, uncertainty quantification and sensitivity analysis are conducted for the diagnostic system, providing a basis for its upgrade. Meanwhile, the engineering design, system hardware, and data processing system of the actual diagnostic system are hierarchically validated to identify uncertainty sources, which are then compared with those of the digital system. This enables complementary validation between the real system and its digital twin. By analyzing uncertainty sources and conducting sensitivity analysis, high-impact uncertainty sources are prioritized for optimization, thereby enhancing the accuracy and reliability of the diagnostic system. This paper quantifies uncertainties and sensitivities of the POINT system and its digital module. The VVUQ analysis yields a total uncertainty of 6.17% and a high confidence coefficient of 0.995. The agreement between experiment and digital module exceeds 97.5% except in the boundary region (≈82.5% due to missing chords). Sensitivity analysis shows that laser frequency stability (≈30%), core channel position (≈23%), and ion mass (≈11%) are the dominant factors. Future devices should improve frequency stabilization, core chord coverage, and fuel calibration to reduce density inversion uncertainty.

High-frequency current monitoring system for superconducting magnet insulation assessment and preliminary experimental verification

Shuliang Ma, Yezheng Xiao, Liang Guo, Jianhua Yang, Yuanyuan Ma, Xiaofeng Han, Shuqing Zhang, Tuo Wu, Yanlan Hu, Huajun Liu

Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei International Applied Superconductivity Center, University of Science and Technology of China

Numerical investigation of helium ash transport in CFETR steady state scenario

Zhihong Kuang, Wei Shen, Jiale Chen

Hefei Institutes of Physical Science, Chinese Academy of Science, University of Science and Technology of China

In magnetic confinement fusion plasmas, the main product of deuterium-tritium fusion is energetic alpha particles, which transfer energy to the background plasma by collisions and become thermalized helium ash. Helium ash accumulation would cause fuel dilution and reduce plasma confinement performance and fusion gain. In this work, the transport of helium ash in CFETR is simulated by the advanced transport solver TGYRO, which invokes the NEO and TGLF codes to compute neoclassical and turbulent transport, respectively. By analyzing the neoclassical and turbulent transport of helium ash, it is found that ITG turbulence is dominant for helium ash transport in CFETR. In addition, with low helium ash fractions, the redistributed helium ash density is larger than the initial setting profile because the source rate exceeds the outward transport, while the helium ash density is smaller than the initial density with high helium ash fractions. Inside the ITB, ITG turbulence is suppressed, leading to a significant reduction in the outward transport of helium ash. The transport process of helium ash can have some influences on micro-instabilities. In particular, an increase in helium ash concentration may stabilize ITG turbulence. Redistributed energetic alpha particles due to Alfvén eigenmodes affect the helium ash transport by changing its source, but they do not significantly alter the helium ash distribution. Our work advances the understanding of the dominant physical mechanism governing helium ash transport in future fusion devices.

Hybrid simulations of fishbones with high order harmonics in EAST tokamak

Shengfa Wu, Wei Shen, Zhiyong Qiu, Liqing Xu

Chinese Academy of Science, University of Science and Technology of China

The linear stability and nonlinear dynamics of fishbones with high order harmonics have been investigated by the global kinetic-magnetohydrodynamic (MHD) code M3D-K in the Experimental Advanced Superconducting Tokamak (EAST). Based on EAST discharge parameters with Neutral Beam Injection (NBI) heating, linear simulations show that the modes with different toroidal mode numbers are primarily driven by trapped energetic particles through toroidal precession resonance. The n=1 mode is the typical fishbone, while there exists a transition for n=2 mode from fishbone-like mode to Energetic Particle Mode (EPM) when the energetic particle pressure exceeds a critical value. For the n=3 mode, the mode frequency remains almost unchanged with different energetic particle pressures. Nonlinear simulations show that with weak energetic particle drive, the m/n=2/2 mode is driven by the MHD nonlinear coupling of the fundamental m/n=1/1 mode. In this regime, the frequency of the m/n=2/2 harmonic is twice that of the m/n=1/1 mode, with both modes exhibiting downward frequency chirping. With strong energetic particle drive, beta-induced Alfvén eigenmodes (BAEs) with higher mode frequencies emerge for both m/n=1/1 and m/n=2/2 components, and the m/n=3/3 component is driven unstable with frequency chirping up. These simulation results highlight that nonlinear MHD coupling and fast ion redistribution are critical for understanding the dynamics of fishbones with high order harmonics.

Combination of quasi-isodynamic and piecewise omnigenous magnetic fields

Jose Luis Velasco, Ivan Calvo, Víctor Fernández-Pacheco, Hengqian Liu, Misha Padidar, Edilberto Sanchez, Guodong Yu, Caoxiang Zhu

CIEMAT, University of Science and Technology of China, Flatiron Institute

Due to their simultaneous optimization for radial and parallel neoclassical transport, quasi- isodynamic fields have been the main choice of stellarator magnetic configuration for most fusion reactor candidates in recent years. However, achieving a high degree of quasi-isodynamicity often comes at the cost of a strong shaping of the flux surfaces of the stellarator and complex coil geometries. In this work, the concepts of quasi-isodynamicity and piecewise omnigenity are combined to form QI-pwO fields. These fields are quasi-isodynamic in the low-field region of the magnetic surface, whereas they significantly depart from quasi-isodynamicity in the high-field region without sacrificing the neoclassical transport properties of quasi-isodynamic fields. This departure could make it easier to integrate the optimization of neoclassical transport with other physical and technological aspects of a stellarator reactor.

Investigation of Dynamic Radiation Belt Characteristics and Mechanisms in EAST Tokamak

Bingcheng Qi, Fang Ding, Qing Zhang, Tonghui Shi, Yue Yu, Jinju Yang, Jingsheng Yuan, Lin Yu, Lifeng Yang, Minrui Wang, et al.

Institute of Plasma Physics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, University of Science and Technology of China, Anhui University, Anhui University of Science and Technology

A dynamic radiation belt—exhibiting characteristics of intense radiation, high density, and low electron temperature, akin to multifaceted asymmetric radiation from the edge (MARFE)—was observed and investigated in the Experimental Advanced Superconducting Tokamak (EAST). This belt forms in the divertor region with impurity injection and subsequently migrates towards the X-point and the high-field side (HFS) of the plasma boundary after the transition from H mode to L mode (H-L transition) or confinement degradation. The belt traverses the inner mid-plane, reaches the opposite divertor, and subsequently retreats back to its initial divertor location. This migration is accompanied by a concurrent evolution of poloidal asymmetry in key plasma parameters, including electron density, radiation profiles, neutral pressure, and wall heat load distribution. The migration of the radiation belt is closely related to the evolution of the edge neutral pressure. Reversing the toroidal magnetic field (BT) direction inverts both the initial position of the radiation belt and its trajectory. The reversal of neutral pressure asymmetry between upper and lower divertors following BT direction change demonstrates the role of B-direction-dependent drift effects. Furthermore, the migration of the radiation belt is consistently accompanied by localized fluctuations with frequencies up to 10 kHz in both plasma radiation and density signals. During belt migration, the magnetic oscillations transition from a broadband spectrum to a coherent narrowband emission, identified as an m/n=2/1 magnetohydrodynamic (MHD) instability mode. The frequency of the mode is positively correlated with the distance of the radiation belt from its initial position. Excessive increases in the magnetic oscillation frequency typically precede plasma disruptions, which may suggest a critical link between oscillation spectral characteristics and disruption onset mechanisms.

Optimization of stellarator configurations combining omnigenity and piecewise omnigenity

Hengqian Liu, Guodong Yu, José Luis Velasco, Caoxiang Zhu

University of Science and Technology of China, Laboratorio Nacional de Fusión, CIEMAT

We present a method for optimizing stellarator configurations that combine omnigenity and piecewise omnigenity (pwO). Within the OOPS optimization framework (Liu et al 2025 2502.09350 ), we introduce a mapping technique that can ‘squeeze’ general omnigenous fields to approximate pwO on the high-field side. Using this approach, we obtain a range of optimized configurations that combine poloidal omnigenity (PO) and pwO, spanning different field periods and aspect ratios. We further show that these configurations are compatible with a magnetic well. The resulting configurations exhibit favorable neoclassical transport and bootstrap current properties while partially relaxing the strict constraints of omnigenity. These results suggest that such configurations are promising candidates for future stellarator reactors.

Boronization-enabled I-mode on EAST tokamak with an expanded density window and favorable-configuration access

X. M. Zhong, X. L. Zou, A. D. Liu, L. Q. Xu, B. Zhang, C. Zhou, J. P. Qian, X. Z. Gong, Y. T. Song, G. Zhuang, et al.

Institute of Plasma Physics, Chinese Academy of Sciences, University of Science and Technology of China, CEA

I-mode is a promising confinement regime for future fusion reactors because it combines enhanced energy confinement with L-mode-like particle transport and naturally ELM-free operation. Previous EAST I-mode studies were performed exclusively under lithium-conditioned wall conditions. Here we report the first systematic experimental investigation of I-mode under boronized wall conditions on EAST and compare it with an existing lithium-conditioned I-mode database at the same toroidal field, $B_t = 2.47$\,T. The boronized-wall dataset exhibits a substantially broader accessible density range, with the Greenwald fraction extending from $f_{\mathrm{GW}} = 0.26 - 0.77$ , compared with $f_{\mathrm{GW}} = 0.35 - 0.54$ under lithiation. A higher normalized $\mathrm{D}_α$ emission suggests that enhanced edge recycling may contribute to this density extension. A striking increase in favorable-configuration I-mode is also observed: $51\%$ boronized-wall discharges are obtained in favorable-configuration, compared with only $8\%$ lithium-conditioned discharges. These favorable-configuration cases are concentrated at high density and exhibit a deeper radial electric-field($E_r$) well and stronger $\mathbf{E_r}\times\mathbf{B}$ velocity shear. When ETRO is present, the associated transition between electron and ion turbulence is similar under the two wall conditions, although ETRO occurs less frequently ($15\%$) under boronization. An empirical EAST I-mode energy confinement scaling at fixed $B_t$ is obtained, $τ_E = 3.29 I_p^{0.51 \pm 0.10} P_{\mathrm{loss}}^{-0.53 \pm 0.05} \bar{n}_e^{0.08 \pm 0.07}$, indicating weaker power degradation than IPB98(y,2) H-mode scaling and a weak density dependence. These results show that boronization can broaden the operational space of EAST I-mode and support the development of reactor-relevant ELM-free scenarios.

Effect of surface roughness on corrosion behavior of CLF-1 steel in magnetic field environments: increased surface roughness accelerates corrosion

Ye Li, Yi-Ming Lyu, Shufeng Zhang, Ning Liu, Jiejie Li, Yuxin Xiao, Guoping Yang, Shanliang Zheng

Hefei Comprehensive National Science Center (Anhui Energy Laboratory), Hefei Institutes of Physical Science, Chinese Academy of Sciences, University of Science and Technology of China, Southwestern Institute of Physics

Tokamak discharge simulation for EAST by coupling METIS and free-boundary equilibrium code FBT

Wenyi Lu, Wenbin Liu, Jinping Qian, Miaohui Li, Ye Tao, Zhengping Luo, Dehong Chen, Rundu Hu, Feifei Long, Jian Liu, et al.

Chinese Academy of Sciences, University of Science and Technology of China, Dalian University of Technology, Shandong University

Fast and reliable discharge modeling is an essential tool for tokamak scenario development, as extensive simulations are required to explore the feasible operational space and translate physical targets into implementable actuator waveforms. In this work, a fast discharge simulator for Experimental Advanced Superconducting Tokamak (EAST) was developed by coupling the fast integrated tokamak modeling tool METIS with the free-boundary equilibrium code FBT from the MEQ (Matlab EQuilibrium) suite. METIS provides the evolution of the plasma profiles by self-consistently solving heat and particle transport with source profiles. The generated outputs are then used directly in FBT to computes the poloidal field (PF) coils currents needed in order to obtain a given plasma shape. The coupling strategy is based either on matching the free functions ( p ′ ( ψ ) and F F ′ ( ψ ) ) on the right-hand side of the Grad–Shafranov equation, or on matching global quantities such as the plasma current I p and stored energy W MHD . Both approaches are effective in ensuring consistency of the pressure and current-density profiles between the two codes. The last closed flux surface (LCFS) curve computed by FBT is fed back into METIS to update the LCFS, and METIS is then run again. The METIS – FBT iteration is repeated until convergence is reached. The results obtained with the equilibrium code FBT are first benchmarked against experimental data and reconstruction results available on EAST. The coupled METIS-FBT workflow is then assessed through a post-shot simulation of an radio-frequency heated EAST discharge, showing its ability to reproduce the main plasma evolution and generate inverse free-boundary PF-coil current trajectories consistent with experimental references. Its predictive scenario-design capability is further demonstrated through the design of a synthetic discharge scenario.

ESR2D: a two-dimensional Fourier-space global gyrokinetic eigenvalue code for the ion-temperature-gradient modes in tokamaks

Haochuan Wang, Jie Wang, Yuefeng Qiu, Shaojie Wang, Zihao Wang, Tiannan Wu, Yuesong Li, Yicheng Cai, Shiqi Xiao

University of Science and Technology of China, Chinese Academy of Sciences

A two-dimensional (2D) Fourier-space global gyrokinetic eigenvalue solver, ESR2D, has been developed to solve the 2D gyrokinetic eigenvalue problem for the ion-temperature-gradient (ITG) modes in tokamaks. With no simplifying assumptions made for passing or trapped ions, the 2D gyrokinetic eigenvalue equations in the poloidal Fourier space have been derived and numerically solved in the ESR2D code. In the linear ITG Cyclone test with adiabatic electrons, the ESR2D code benchmarks well against the gyrokinetic initial-value codes GENE, NLT and ORB5. It is found that two toroidal branches of ITG modes coexist in the system.

Investigation on the high-temperature creep and irradiated damage behaviours of plasma-facing components material fabricated by selective laser melting

Zhihong Liu, Zhiyong Wang, Jianguo Ma, Huapeng Wu, Nengtao Zhou, Wangqi Shi, Tao Zhu, Yudong Su, Jiefeng Wu

Chinese Academy of Sciences, Anhui Province Key Laboratory of Special Welding Technology, Lappeenranta University of Technology, University of Science and Technology of China

Oxide dispersion-strengthened (ODS) steel is a promising structural material in fusion reactors, nanoparticles in matrix pin grain boundaries, and capture point defects and they delay the performance degradation caused by creep and irradiation. In this paper, RAFM steel with Y 2 O 3 was formed by selective laser melting (SLM) and the microstructural evolution under creep and irradiation were closely studied. SLM-formed ODS-RAFM steel had a longer high-temperature creep life than RAFM steel at the same stress and temperature, the fined grains were closely related to recrystallisation and pinning of oxide. The ODS-RAFM steel exhibited great irradiation stability, the lath width slightly increased, and the hardening rate was smaller than RAFM steel. During the irradiation process, continuously precipitated new MX carbides and Y–Ta–O oxide occurred in ODS-RAFM steel, which resisted the growth of grains. The above research results explained the microstructural evolution of RAFM steel and the change of performance under high temperature and an irradiation environment of fusion reactors, which verified the significant role of Y 2 O 3 nanoparticles in maintaining high temperature stability and irradiation resistance, hence providing a strong theoretical basis for the ODS-RAFM steel of the future to be fully used as the blanket structural material of nuclear fusion reactors.

Isoflux plasma shape control under large transient disturbances on EAST via reinforcement learning

Y.C. Zhang, Y.H. Wang, Z.M. Huang, Q.P. Yuan, Y. Huang, J.Q. Zhu, W.Y. Rui, H.R. Guo, B.J. Xiao

Institute of Plasma Physics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, University of Science and Technology of China, Institute of Energy, Hefei Comprehensive National Science Center

Magnetic shape control is fundamental to stable tokamak operation, where the plasma boundary must be maintained with high accuracy and robustness against external disturbances. Experimental observations on EAST indicate that, under large transient-error conditions, a fixed-parameter PID-based controller may drive the actuators into saturation, degrading regulation performance and potentially leading to loss of shape control. To address this limitation, this work develops a deep reinforcement learning plasma shape controller for EAST within the existing Isoflux control scheme. The controller is trained in a disturbance-rich simulation environment designed to reproduce large transient-error conditions, and employs a tailored reward design that explicitly targets large-disturbance robustness while improving early-stage learning stability under actuator constraints. Simulation results show that the learned policy achieves improved disturbance rejection and higher control accuracy in regimes where PID control tends to saturate and recover slowly. The controller is further deployed and experimentally validated on EAST, demonstrating stable plasma shape regulation with acceptable accuracy and enhanced robustness during long-pulse operation.

Active control of ion-ITB using RMP in the EAST tokamak

H. Sheng, Y.W. Sun, T.H. Shi, S. Gu, H.H. Wang, X. Jian, C. Ye, Y.Y. Li, M.N. Jia, Y.Q. Liu, et al.

Institute of Plasma Physics, Chinese Academy of Sciences, University of Science and Technology of China, Enn Science and Technology Development Co., Ltd, General Atomics

Resonant magnetic perturbations (RMPs) have been demonstrated to trigger sustainable internal transport barriers in the ion temperature channel (ion-ITB) in the EAST tokamak (Sheng et al 2025 PRX Energy 4 043012). This paper further examines the diverse effects of RMPs on ion-ITB. In addition to triggering and sustaining ion-ITB using RMPs, the barrier can also be actively controlled by adjusting the phasing, toroidal mode number ( n ), and current of the RMP coils. The formation of ion-ITBs exhibits robust reproducibility, achievable solely by adjusting the RMP coil configuration with all other discharge settings held fixed. Comparative results indicate that high- n RMPs are more favorable for ion-ITB formation than low- n RMPs. Both experimental and modeling results demonstrate that strong magnetic perturbations in the core region suppress the formation of the ion-ITB in these cases. Preliminary results from RMP-modulated ITB experiments reveal that fishbone is not essential for ion-ITB formation, nor is sawtooth essential for its collapse, whereas the plasma current profile appears likely to play an important role. Overall, these results demonstrate that RMPs can serve as an effective method for controlling ITBs and investigating their underlying physics.

A surrogate-based thermo-mechanical optimization framework using NSGA-II for the first wall of CFETR COOL blanket

Hongyu Wang, Kecheng Jiang, Lei Chen, Songlin Liu

Chinese Academy of Sciences, University of Science and Technology of China

The supercritical carbon dioxide (S-CO2) cOoled Lithium-Lead (COOL) blanket is under development for China Fusion Engineering Test Reactor (CFETR). As a key component of the blanket, the First Wall (FW) is subjected to high heat flux and plasma sputtering, requiring the simultaneous satisfaction of stringent thermal and structural requirements. To reduce the prohibitive computational cost of high-fidelity simulations when exploring vast design spaces, a thermo-mechanical coupled surrogate model is developed, which integrates the FW geometry, heat loads and boundary conditions as parametric inputs. By combining thermal balance theory, empirical correlations and 1D/2D hybrid analytical heat conduction model, the surrogate model enables the rapid prediction of key thermal-hydraulic responses, including coolant outlet temperature, pressure drop and temperature distribution of RAFM steel. Based on the temperature distribution, the corresponding stress quantities are evaluated using generalized Hooke’s law, beam theory and plate theory. To improve the consistency of thermo-mechanical stress prediction, FEM-derived stress linearization results are further used to correct the analytical stress quantities, leading to a corrected thermo-mechanical surrogate model. Through consistency assessment against CFD/FEM simulations and FEM-based correction, the corrected surrogate model shows improved agreement with numerical results while retaining sub-second computational performance, making it suitable for rapid pre-design screening within the investigated parameter range. On this basis, a multi-objective optimization framework employing the Non-dominated Sorting Genetic Algorithm II (NSGA-II) for FW design is established. Taking the equatorial unit #3 of COOL blanket as an example, the framework is applied to optimize the coolant channel geometry and mass flow rate, with the objectives of maximizing outlet temperature and minimizing the flow-resistance power loss associated with the FW pressure drop to improve the thermal-to-electric conversion efficiency under multi-physics constraints. The optimization result is a nonlinear Pareto-Front curve describing the trade-off between these competing objectives. Two representative solutions on the curve are selected for detailed comparison with the baseline design: one design maintains a similar outlet temperature while reducing flow-resistance power loss by 22.67%, whereas the other maintains comparable flow-resistance power loss but increases the outlet temperature by 8.31 ℃. Moreover, all solutions between these two points on the Pareto-Front outperform the baseline design in both objectives. Overall, the proposed surrogate-based optimization framework demonstrates its capability to efficiently identify high-performance designs via balancing competing objectives and provides a flexible and systematic tool for thermo-mechanical pre-design screening and optimization of the CFETR COOL blanket FW.