Hua Yang

In magnetically confined plasmas, energetic-particle (EP)-driven instabilities can induce redistribution and losses of energetic ions, thereby affecting plasma heating and confinement. In this work, fast-ion-driven beta-induced Alfvén eigenmode (BAE) excited by ion cyclotron resonance heating (ICRH) was investigated in low-density EAST plasmas using experimentally reconstructed equilibria and profiles. Experimentally, strong ICRH led to a significant increase in ion temperature and plasma stored energy, accompanied by the excitation of an Alfvén eigenmode at 64kHz under 1.6 MW heating power, while no such mode was observed at reduced power. Continuum analysis identified this mode as a core-localized BAE. To interpret these observations, integrated simulations combining TORIC, ASCOT, and GTC were performed. A modified fast-ion distribution function was implemented to capture the strong velocity-space anisotropy of ICRH-generated fast ions. Linear gyrokinetic simulations reproduced the observed BAE frequency and identified a threshold in fast-ion pressure for mode excitation. Orbit-following simulations with realistic wall geometry demonstrated that the BAE induces significant phase-space redistribution and enhances the loss of high-energy fast ions (energy >600keV). Separately, the ASCOT power-deposition analysis shows that the strong BAE reduces the collisional power transferred from fast ions to thermal ions, thereby suppressing the fast-ion contribution to ion heating and limiting the increase in ion temperature. As the measured BAE activity decreases in Phase B, recovery of this ion-heating channel explains the subsequent rise in ion temperature. These results clarify the interplay between ICRH-generated fast ions, BAE activity, and ion heating, and provide insights into optimizing fast-ion confinement and heating efficiency in future burning plasma devices.

A novel multichannel X-mode reflectometer has been developed for density measurements near the ion cyclotron resonance heating antennas on the Experimental Advanced Superconducting Tokamak. This system enables direct measurement of the edge density profile in the immediate vicinity of the antennas. Key challenges associated with long fundamental rectangular waveguides—significant attenuation and dispersion—are addressed through a combination of watt-level amplifiers and a digital mixing method calibrated via a closed-loop waveguide test. Furthermore, a dedicated peak-seeking algorithm is implemented to robustly determine the zero-density starting position (Rstart) under conditions of harmonic interference. Finally, a corrected reconstruction formula accounting for the dual-horn geometry confirms its negligible influence (≲0.5mm) on profile accuracy.

During the 2025 campaign, helium-3 ( 3 He) minority heating with waves in the ion cyclotron range of frequencies (ICRF) was investigated for the first time on the Experimental Advanced Superconducting Tokamak (EAST). With the lowest available ICRF frequency of f IC = 27 MHz, experiments were conducted at a high toroidal magnetic field of B t = 2.8 T and plasma current I p = 450 kA. To optimize 3 He minority heating, the variation of 3 He concentration was systematically explored. Real-time feedback control of the 3 He concentration was successfully implemented through spectroscopic measurement and closed-loop regulation of the 3 He gas injection, demonstrating the feasibility of the control system functions. The ICRF heating efficiency reached a maximum at a minority concentration of ∼ 8%–9%, with the core electron temperature increasing from approximately 5.0–7.0 keV and the ion temperature from approximately 1.3–1.9 keV under 2.9 MW of ICRF power. These results are in good agreement with simulations from the two-dimensional full-wave code TORIC. Experiments further indicate that higher plasma density enhances 3 He heating efficiency. We also briefly discuss the strategy for future 3 He ICRF experiments on EAST.

Neoclassical tearing modes (NTMs) in high-beta plasmas can degrade confinement and trigger disruptions. Experiments were conducted on EAST to investigate the effects of ion cyclotron range of frequency (ICRF) heating on NTMs through controlled variation of the power deposition location and fast-ion distribution. Using hydrogen minority heating, on-axis and off-axis ICRF heating scenarios were achieved by varying the toroidal magnetic field, together with additional ICRF power modulation. The results show that on-axis ICRF heating effectively suppresses the m / n = 3 / 2 tearing mode, while off-axis heating tends to enhance the m / n = 4 / 3 mode. On-axis heating also improves plasma confinement and increases the neutron yield. TROIC-TRANSP simulations confirm the distinct power deposition locations, while ASCOT calculations indicate that the fast-ion energy reaches up to 800 keV during on-axis heating, which is substantially higher than that in the off-axis cases. A modified Rutherford equation (MRE) incorporating fast-ion effects suggests that the fast-ion-driven uncompensated cross-field current term is responsible for the observed NTM behaviors. These results demonstrate that controlling the ICRF resonance position is a feasible approach for NTM suppression and improved plasma performance.

Ion cyclotron resonance heating (ICRH) is one of the common auxiliary heating methods employed in tokamaks. Therefore, optimizing the ICRH scheme for tokamaks is of great importance. In this study, the two-dimensional full-wave code Interative fluid-kinetics (INTFLUK) is employed to systematically investigate ICRH scenarios for the China Fusion Engineering Demonstration Reactor (CFEDR). A comparative analysis is conducted between the D–T– ⁷ Li three-ion heating scheme and the conventional D–T– ³ He minority scheme. Both the D–T– ⁷ Li and D–T– ³ He scenarios exhibit a relatively high target ion absorption fraction. For the D–T– ⁷ Li scheme, increasing the ⁷ Li ion concentration while reducing the T ion concentration effectively minimizes collisional energy transfer to electrons Furthermore, results indicate that the target ion absorption fraction in the D–T– ⁷ Li scenario is superior to that of other three-ion alternatives. Finally, an assessment of alpha particle effects under the optimized scheme reveals that when the alpha particle concentration reaches 3%, its power absorption fraction exceeds 50%. However, assuming an equivalent Maxwellian distribution slightlyoverestimates the alpha particle power absorption fraction compared to a conventional slowing-down distribution.

Alfvén wave instabilities driven by energetic particles are common in fusion devices. Understanding their behavior is essential for the good confinement of fusion plasma. For this purpose, a series of experiments are performed on EAST to investigate the excitation of toroidal Alfvén eigenmodes (TAEs). Experimentally, it was found that AEs with frequencies around 80, 134, 157 kHz are excited by ion cyclotron resonance heating (ICRH) hydrogen minority heating scenario. Moreover, the excitation of AEs is independent of the wall-coating materials, but determined with the generation and confinement of the fast ions. Statistical analysis suggests that the TAEs can only be excited when the ICRH power is larger than 2 MW and the H ₉₈ factor is larger than 1.15. In line with the experiments, a set of simulations using TORIC, ASCOT, and NOVA-C is performed. The simulation results show that with the experimental density profile and safety factor, the measured TAE with frequency of 134 kHz is well reproduced by taking into account the plasma toroidal rotation frequency. However, the appearance of the 80 kHz mode cannot be captured in the simulations. The ICRH-generated fast hydrogen ions mainly have banana orbits and that their perpendicular velocity is much larger than that of the parallel ions. The stability analysis with NOVA-C suggests that the radial gradient of the fast H ion distribution is the only driving source of TAEs. For TAEs locate in the center of Alfvén continuum, the D ion Landau damping is the dominant damping term; For most other TAEs which have intersections with the continuum boundary, the continuum damping becomes the dominant damping mechanism.

Although ion cyclotron resonance heating plasma has succeeded in tokamaks, it also faces the problem of wave-related impurities, especially in the future operation environment with an all-metal first wall. By controlling the antenna wave spectrum, we experimentally observed the behavior of impurities and the floating potential on the Experimental Advanced Superconducting Tokamak (EAST) and used the finite element code to calculate the wave propagation at the plasma edge. The results demonstrate that the floating potential is relatively high in the region in the monopole phase is higher than in other phases. Although particular floating potential strength was observed in the low hybrid resonance region, the floating potential was not too high. The simulation results tend to support that under low k _// of antenna, the high potential in front of the ion cyclotron range of frequency antenna drives E× B ₀ drift, which increases the asymmetry of the poloidal plasma distribution near the antenna and locally enhances the radio frequency sheath and heat load.

Significant advancements have been achieved in facilitating high-power and long-pulse operation up to 310 seconds by developing novel techniques for Ion Cyclotron Range of Frequency (ICRF) wave heating systems on EAST. This paper presents an overview of the current status of the ICRF facility, spotlighting the principal modifications implemented on the original installation and the corresponding results. A new ICRF antenna has been devised, featuring an increased toroidal distance between the straps. This design reduces the parallel wave number, augments wave coupling efficiency, and boosts plasma heating performance. A novel active water-cooling mechanism for the Faraday Screen has been introduced to ensure the FS temperature remains within a safe range during long-pulse and high-power operations. An Impedance Transformer has also been developed to diminish the voltage in the transmission line. A load-tolerant matching network with a conjugate-T configuration guarantees stable operation by maintaining low reflection across a broad spectrum of antenna loads. Moreover, a rapid and real-time impedance matching methodology has been successfully incorporated, empowering the system to adapt the matching system to the fluctuating antenna load dynamically. Thanks to these optimizations and upgrades, during the EAST experiments, we attained 2.2 MW of ICRF power for 2 seconds and maintained 1.2 MW for 310 seconds.

Ion cyclotron resonance heating (ICRH) plays a crucial role in magnetic confinement nuclear fusion, enhancing plasma temperature and enabling sustained fusion reactions. Full wave simulations in the ion cyclotron range of frequency are essential for exploring heating mechanisms and guiding experiments. This paper focuses on the development and application of a finite element method (FEM) based full wave simulation code, INTFLUK, which incorporates the poloidal magnetic field to account for the up and down shift effect of the parallel wave number. The code’s superiority lies in its ability to handle complex antenna structures and irregular boundaries, saving computational resources and reducing calculation time. The paper presents the physical model of INTFLUK, including the poloidal magnetic field, and demonstrates its application through tests on the EAST and China Fusion Engineering Test Reactor tokamak. The results show that INTFLUK effectively captures the up–down asymmetry of the electric field and the mode conversion between fast waves and slow ion cyclotron waves. Comparisons with the TORIC code validate the accuracy of INTFLUK in simulating these effects, with integral power partition errors less than 10%. The findings highlight the importance of considering the poloidal magnetic field and spatial dispersion effects in FEM based full wave simulation code for ICRH, advancing the understanding and application of ICRH in fusion research.

Efficient ion cyclotron range of frequencies (ICRF) wave heating requires good wave coupling at the plasma edge and good radio frequency power absorption in the plasma core. This study reviews recent progress in improving these two aspects of ICRF heating with the new two-strap antennas through various experiments and simulations on the Experimental Advanced Superconducting Tokamak (EAST). Our study shows that the ICRF coupling can be significantly improved by decreasing the parallel wave number, increasing the local scrape-off layer (SOL) density by midplane gas puffing, and increasing the global SOL density by decreasing the separatrix–antenna distance. It can also be improved by increasing the core plasma density, changing the divertor strike point position, and optimizing the antenna phasing. The core ICRF power absorption can be increased by optimizing the cyclotron resonance position and minority ion concentration and by applying new heating schemes such as three-ion heating. Although some of the methods have been previously studied on other devices, improving ICRF coupling by shifting the divertor strike point was tested on EAST for the first time. Quantitative characterization of these methods and the conclusions drawn from this study can provide important insights for achieving more efficient ICRF heating in current and future fusion machines.