arXiv subjects

Q. Zang

Publications and source records attributed to Q. Zang.

6 recordsLinked to original sources

arXiv2026

Self-organized hybrid scenario mediated by fishbone modes in the EAST tokamak

Self-organized hybrid scenario mediated by fishbone modes in the Experimental Advanced Superconducting Tokamak (EAST) is reported in this work. In this regime, internal transport barriers(ITBs) and a flat core safety factor profile were maintained simultaneously by fishbone modes. First,the drive of low-frequency flows by fishbone modes is clarified, which subsequently suppresses turbulence transport. Besides, fishbone-induced poloidally symmetric (m = 0) toroidal current sheets were first reported experimentally, which drive outward current redistribution that mitigates core current peaking. Together, these effects enable hybrid operation with stable ITBs and robust magnetohydrodynamic (MHD) stability, revealing a self-organized pathway for sustaining hybrid scenario for fusion reactors.

physics.plasm-ph↗

arXiv2026

Experimental evidence of forward energy transfer induced by core-edge coupling in multiscale tokamak turbulence

Turbulence in magnetically confined plasmas is inherently quasi-two-dimensional and can exhibit both inverse and forward energy transfer across scales. Experimental evidence for cross-scale energy transfer in the hot plasma core has, however, remained scarce. Understanding such energy transfer is crucial because it governs turbulent transport, which directly impacts confinement quality of fusion plasmas. Here we report experimental evidence consistent with forward energy transfer associated with core-edge coupling in tokamak turbulence. We combined multichannel collective Thomson scattering (CTS) and radially localized Doppler backscattering (DBS) to resolve cross-scale fluctuation dynamics. The results reveal that a quasi-coherent mode (QCM) originating from the edge is also present in the core and resonantly couples with broadband turbulence, producing significant forward energy transfer and characteristic secondary instabilities. These combined measurements indicate that quasi-two-dimensional tokamak turbulence can support a net energy transfer from ion to electron scales through cross-scale wave-wave interactions, contrary to the inverse cascade paradigm of idealized two-dimensional turbulence. Such a plasma regime is attractive for fusion reactors, as it avoids large edge-localized modes (ELMs) that damage first-wall components and maintains high confinement quality even in the presence of high-Z impurities.

physics.plasm-ph↗

arXiv2024

Suppression of Edge Localized Modes in ITER Baseline Scenario in EAST using Edge Localized Magnetic Perturbations

We report the suppression of Type-I Edge Localized Modes (ELMs) in the EAST tokamak under ITER baseline conditions using $n = 4$ Resonant Magnetic Perturbations (RMPs), while maintaining energy confinement. Achieving RMP-ELM suppression requires a normalized plasma beta ($β_N$) exceeding 1.8 in a target plasma with $q_{95}\approx 3.1$ and tungsten divertors. Quasi-linear modeling shows high plasma beta enhances RMP-driven neoclassical toroidal viscosity torque, reducing field penetration thresholds. These findings demonstrate the feasibility and efficiency of high $n$ RMPs for ELM suppression in ITER.

physics.plasm-ph↗

arXiv2024

I-mode Plasma Confinement Improvement by Real-time Lithium Injection and its Classification on EAST Tokamak

I-mode is a promising regime for future fusion reactors due to the high energy confinement and the moderate particle confinement. However, the effect of lithium, which has been widely applied for particle recycling and impurity control, on I-mode plasma is still unclear. Recently, experiments of real-time lithium powder injection on I-mode plasma have been carried out in EAST Tokamak. It was found that the confinement performance of the I-mode can be improved by the lithium powder injection, which can strongly reduce electron turbulence (ET) and then trigger ion turbulence (IT). Four different regimes of I-mode have been identified in EAST. The Type I I-mode plasma is characterized by the weakly coherent mode (WCM) and the geodesic-acoustic mode (GAM). The Type II I-mode is featured as the WCM and the edge temperature ring oscillation (ETRO). The Type III I-mode corresponds to the plasma with the co-existence of ETRO, GAM, and WCM. The Type IV I-mode denotes the plasma with only WCM but without ETRO and GAM. It has been observed that WCM and ETRO are increased with lithium powder injection due to the reduction of ion and electron turbulence, and the enhancement of the pedestal electron temperature gradient. EAST experiments demonstrate that lithium powder injection is an effective tool for real-time control and confinement improvement of I-mode plasma.

physics.plasm-ph↗

arXiv2023

Extension of ELM suppression window using n=4 RMPs in EAST

The q95 window for Type-I Edge Localized Modes (ELMs) suppression using n=4 even parity Resonant Magnetic Perturbations (RMPs) has been significantly expanded to a range from 3.9 to 4.8, which is demonstrated to be reliable and repeatable in EAST over the last two years. This window is significantly wider than the previous one, which is around q95=3.7pm0.1, and is achieved using n=4 odd parity RMPs. Here, n represents the toroidal mode number of the applied RMPs and q95 is the safety factor at the 95% normalized poloidal magnetic flux. During ELM suppression, there is only a slight drop in the stored energy (<=10%). The comparison of pedestal density profiles suggests that ELM suppression is achieved when the pedestal gradient is kept lower than a threshold. This wide q95 window for ELM suppression is consistent with the prediction made by MARS-F modeling prior to the experiment, in which it is located at one of the resonant q95 windows for plasma response. The Chirikov parameter taking into account plasma response near the pedestal top, which measures the plasma edge stochasticity, significantly increases when q95 exceeds 4, mainly due to denser neighboring rational surfaces. Modeling of plasma response by the MARS-F code shows a strong coupling between resonant and non-resonant components across the pedestal region, which is characteristic of the kink-peeling like response observed during RMP-ELM suppression in previous studies on EAST. These promising results show the reliability of ELM suppression using the n=4 RMPs and expand the physical understanding on ELM suppression mechanism.

physics.plasm-ph↗

arXiv2022

An auto-locking ultra-stable laser with sub-hertz linewidth

We report in detail the design process and performance of an auto-locking ultra-stable laser with sub-hertz linewidth at the first time. The laser frequency is automatically stabilized to an optical reference cavity with a home-made controller, which is based on a combination of digital circuit and analog circuit. The digital circuit is used for diagnosing and manipulating the state of the ultra-stable laser, and the analog circuit is used for demodulating the discriminate signal and servo control. A method of searching the transmission signal in the closed-loop state instead of the open-loop state is proposed to reduce the locking time and improve the reliable of the auto-locking ultra-stable laser. The median time of 16.6s is obtained after 157 times of relocking, and the probability of less than 20 s is more than 86%. The median linewidth of 1.08 Hz is obtained, and the fractional frequency instability is less than 3.4E-15 at integration time between 0.1 and 100 s. The performance of this system demonstrates that will be used as an important subsystem to transfer the optical clock signal.

physics.ins-det↗