arXiv subjects

Ping Zhu

Publications and source records attributed to Ping Zhu.

At least 37 records · Page 2Linked to original sources

arXiv2025

Visual Anomaly Detection for Reliable Robotic Implantation of Flexible Microelectrode Array

Flexible microelectrode (FME) implantation into brain cortex is challenging due to the deformable fiber-like structure of FME probe and the interaction with critical bio-tissue. To ensure reliability and safety, the implantation process should be monitored carefully. This paper develops an image-based anomaly detection framework based on the microscopic cameras of the robotic FME implantation system. The unified framework is utilized at four checkpoints to check the micro-needle, FME probe, hooking result, and implantation point, respectively. Exploiting the existing object localization results, the aligned regions of interest (ROIs) are extracted from raw image and input to a pretrained vision transformer (ViT). Considering the task specifications, we propose a progressive granularity patch feature sampling method to address the sensitivity-tolerance trade-off issue at different locations. Moreover, we select a part of feature channels with higher signal-to-noise ratios from the raw general ViT features, to provide better descriptors for each specific scene. The effectiveness of the proposed methods is validated with the image datasets collected from our implantation system.

cs.CV↗

arXiv2025

Effects of reversed magnetic shear on the plasma rotation stabilization of resistive wall modes in tokamaks

Effects of reversed magnetic shear on the plasma rotation stabilization of resistive wall modes in tokamaks are investigated using the AEGIS code. MHD equilibria in toroidal configuration from circular cross-sections to realistic CFETR-like scenarios with various magnetic shear profiles are considered. Two critical aspects of the $n=1$ RWM are examined: the influence of toroidal rotation on the unstable regime and the toroidal rotation frequency thresholds required for complete stabilization. It is found that strongly reversed magnetic shear consistently broadens the unstable $β_{\rm N}$ window in both circular and CFETR equilibria when toroidal rotation is included. Furthermore, reversed magnetic shear significantly reduces the rotational stabilization, resulting in narrower stability windows and notably higher toroidal rotation frequency thresholds required for complete RWM suppression compared to the cases with positive shear only. These results clearly demonstrate that the reversed magnetic shear in the advanced tokamak configuration imposes more stringent requirement for the effective toroidal rotation stabilization of the $n=1$ RWM.

physics.plasm-ph↗

arXiv2025

MHD simulation of tilt instability during the dynamic FRC magnetic compression process

The nonlinear evolution of the tilt instability in a field reversed configuration (FRC) during the dynamic magnetic compression process has been investigated using magnetohydrodynamic (MHD) simulations with the NIMROD code [C. R. Sovinec \textit{et al.}, J. Comput. Phys. \textbf{195}, 355 (2004)]. The tilt mode induces significant deformations in the linear growth phase and results in complete confinement loss of the FRC in the nonlinear phase, with no evidence of dynamic nonlinear stabilization. The growth rate of the tilt mode increases with the compression field ramping rate and approaches an asymptotic value. Toroidal flow can reduce both the growth rate and the nonlinear saturation amplitude of the tilt mode. The stabilizing effect of the toroidal rotation is enhanced with higher compression field ramping rates due to the spontaneous toroidal field generation and increased flow shear during compression. Although the tilt mode remains unstable with a toroidal rotation Mach number close to 0.5, the onset of tilt distortion can be delayed, allowing a magnetic compression ratio up to 5.3 before the compressional heating terminates.

physics.plasm-ph↗

arXiv2025

Dual Synchronization Effects in Light Scattering by Spherical Particle Systems

We report the discovery of a novel and fundamental dual synchronization relationship between the scattering efficiency (Q$_{\text{sca}}$) and a specifically formulated angular distribution complexity parameter ($\widetilde{C}_{\text{p}}$) in spherical particle systems. Through extensive numerical simulations using the rigorous Multiple Sphere T-Matrix (MSTM) method, we found that Q$_{\text{sca}}$ exhibits a strong positive correlation with (1-$\widetilde{C}_{\text{p}}$) when the real part of the refractive index is varied, while it synchronizes strongly and positively with $\widetilde{C}_{\text{p}}$ when the imaginary part is varied. Our analysis reveals that this duality arises from the distinct ways the real and imaginary parts of the refractive index \textbf{perturb vs.~dampen electromagnetic resonances} within the particles, leading to different coupled responses in the total scattered energy and the angular distribution. This discovery provides unprecedented insights into how phase contrast and absorption processes distinctly modulate scattering properties and the angular distribution of scattered light, particularly in regimes dominated by resonance. It establishes that the specific formulation of $\widetilde{C}_{\text{p}}$ used here is sensitive to the overall balance of multipole contributions, making it a valuable parameter for capturing refractive index-driven changes. }.

physics.optics↗

arXiv2025

Nonlinear edge localized mode with impurity seeding in CFETR hybrid scenario

A critical challenge for operating fusion burning plasma in high confinement mode lies in mitigating damage caused by edge localized modes (ELMs). While impurity seeding has been experimentally validated as a reliable and effective ELM mitigation technique, its underlying physics remains insufficiently understood and requires further clarification. Through nonlinear magnetohydrodynamic (MHD) simulations, this work reproduces key features of natural ELM crash and reveals its trigger mechanism. Impurity seeding significantly affects nonlinear ELM dynamics by inducing local and global modifications to the pedestal pressure profile, driving high-n ballooning mode instabilities that govern ELM crash. Two critical control parameters -- impurity density level and poloidal seeding location -- are systematically investigated, which play key roles in the ELM crash onset timing and the resulting energy loss magnitude.

physics.plasm-ph↗

arXiv2025

Serving Large Language Models on Huawei CloudMatrix384

The rapid evolution of large language models (LLMs), driven by growing parameter scales, adoption of mixture-of-experts (MoE) architectures, and expanding context lengths, imposes unprecedented demands on AI infrastructure. Traditional AI clusters face limitations in compute intensity, memory bandwidth, inter-chip communication, and latency, compounded by variable workloads and strict service-level objectives. Addressing these issues requires fundamentally redesigned hardware-software integration. This paper introduces Huawei CloudMatrix, a next-generation AI datacenter architecture, realized in the production-grade CloudMatrix384 supernode. It integrates 384 Ascend 910 NPUs and 192 Kunpeng CPUs interconnected via an ultra-high-bandwidth Unified Bus (UB) network, enabling direct all-to-all communication and dynamic pooling of resources. These features optimize performance for communication-intensive operations, such as large-scale MoE expert parallelism and distributed key-value cache access. To fully leverage CloudMatrix384, we propose CloudMatrix-Infer, an advanced LLM serving solution incorporating three core innovations: a peer-to-peer serving architecture that independently scales prefill, decode, and caching; a large-scale expert parallelism strategy supporting EP320 via efficient UB-based token dispatch; and hardware-aware optimizations including specialized operators, microbatch-based pipelining, and INT8 quantization. Evaluation with the DeepSeek-R1 model shows CloudMatrix-Infer achieves state-of-the-art efficiency: prefill throughput of 6,688 tokens/s per NPU and decode throughput of 1,943 tokens/s per NPU (<50 ms TPOT). It effectively balances throughput and latency, sustaining 538 tokens/s per NPU even under stringent 15 ms latency constraints, while INT8 quantization maintains model accuracy across benchmarks.

cs.DC↗

arXiv2025

Single-shot 3D characterization the spatiotemporal optical vortex via a spatiotemporal wavefront sensor (STWFS)

The advent of spatiotemporal wave packets (STWPs), represented by spatiotemporal optical vortices (STOVs), has paved the way for the exploration in optics and photonics. To date, despite considerable efforts, a comprehensive and efficient practical means to characterizing wave packets with such complex structures is still lacking. In this study, we introduced a new method designed to achieve high-precision and high-throughput spatiotemporal wave packet measurements using a user-friendly set up. This method is based on a quadriwave lateral shearing interferometric wavefront sensor that utilizes wavelength division multiplexing, termed the "spatiotemporal wavefront sensor (STWFS)." Using this method, we have fabricated a compact prototype with 295 * 295 spatial pixels * 36 wavelength channels of 0.5 nm spectral resolution in a single frame. This STWFS enabled, for the first time, single-shot self-referenced spatiotemporal three-dimensional (3D) optical field characterizations of STOV pulses with transverse orbital angular momenta L of 1 and 2, and obtained the dynamic visualization of the focused propagation of STOV pulses. Furthermore, the STWFS provides a 1.87 nm (0.95%) root mean square (RMS) absolute accuracy for spatiotemporal phase reconstruction. This achievement represents the highest performance compared with other three-dimensional spatiotemporal metrology methods. As a spatiotemporal optical field characterization method, the STWFS offers ultrafast 3D diagnostics, contributing to spatiotemporal photonics and broader applications across different fields, such as light-matter interactions and optical communications.

physics.optics↗

arXiv2025

Increasing the density limit with ECRH-assisted Ohmic start-up on EAST

High plasma density operation is crucial for a tokamak to achieve energy breakeven and a burning plasma. However, there is often an empirical upper limit of electron density in tokamak operation, namely the Greenwald density limit $n_G$, above which tokamaks generally disrupt. Achieving high-density operations above the density limit has been a long-standing challenge in magnetic confinement fusion research. Here, we report experimental results on EAST tokamak achieving the line-averaged electron density in the range of 1.3 $n_G$ to 1.65 $n_G$,while the usual range in EAST is (0.8-1.0)$n_G$. This is performed with ECRH-assisted Ohmic start-up and a sufficiently high initial neutral density. This is motivated by and consistent with predictions of a recent plasma-wall self-organization (PWSO) theory, that increasing ECRH power or pre-filled gas pressure leads to lower plasma temperatures around divertor target and higher density limits. In addition, the experiments are shown to operate in the density-free regime predicted by the PWSO model. These results suggest a promising scheme for substantially increasing the density limit in tokamaks, a critical advancement toward achieving the burning plasma.

physics.plasm-ph↗

arXiv2025

Enhanced dynamo drive for the sawtooth relaxation process due to non-uniform resistivity distribution in a reversed field pinch

In this work, we use the three-dimensional resistive MHD code NIMROD to investigate the impact of resistivity inhomogeneity on the sawtooth process of an reversed field pinch (RFP) plasma. The simulation employs a non-uniform resistivity profile similar to experiments, which monotonically increases from the core to the edge as the temperature decreases. The resistivity inhomogeneity introduces an additional electric field in the plasma, which accelerates the inward diffusion of magnetic flux and changing the self sustained reversal state, hence significantly enhances the dynamo effect and the sawtooth process in the RFP plasma.

physics.plasm-ph↗

arXiv2025

Power dependence of density limit due to plasma-wall interaction in a burning plasma

The density limit is one of the major obstacles to achieving the desired fusion performance in tokamaks. However, the underlying physics mechanism for its recently observed power dependence in experiments has not been well understood or predicted in theory. In this work, the power dependent scalings of density limit are obtained based on the plasma-wall self-organization model [D.F. Escande 2022 NF], which are able to match the power dependence of density limits in multiple tokamak devices. The key factors influencing the power dependence are found to be the plasma-wall sputtering and the particle confinement time. The effects of non-sputtered impurities and fusion products are further evaluated. This PWSO-density limit model is then extended to the burning plasma regime and used to predict the conditions for entering burning plasma.

physics.plasm-ph↗

arXiv2024

Numerical solutions of resistive finite-pressure magnetohydrodynamic equilibria for non-axisymmetric toroidal plasmas

A hybrid spectral/finite-element code is developed to numerically solve the resistive finite-pressure magnetohydrodynamic equilibria without the necessity of postulating nested magnetic flux surfaces in the non-axisymmetric toroidal systems. The adopted approach integrates a hyperbolic parallel damping equation for pressure updating, along with a dynamic resistive relaxation for magnetic field. To address the nonaxisymmetry in toroidal geometry, a pseudo flux mapping is employed to relate the axisymmetric computational domain to the physical domain. On the computational mesh, an isoparametric C1-continuous triangular element is utilized to discretize the poloidal plane, which is complemented with a Fourier decomposition in the toroidal direction. The versatility of the code is demonstrated through its application to several different non-axisymmetric toroidal systems, including the inherently three-dimensional equilibria in stellarators, the helical-core equilibrium states in tokamak plasmas, and the quasi-single-helicity states in a reversed-field pinch.

physics.plasm-ph↗

arXiv2024

Impurity radiation seeding of neoclassical tearing mode growth

The physics of neoclassical tearing mode (NTM) is of great concern to the tokamak plasma stability and performance, especially in the burning plasma regime. Whereas a great deal about the different seeding mechanisms have been understood, and in many situations the seed event can be clearly identified, the potential seeding process of NTM due to the resistive tearing instability driven by the impurity radiation cooling still needs more studies. Recent NIMROD simulations have demonstrated that the local impurity radiation cooling can drive the seed island growth and trigger the subsequent onset of neoclassical tearing mode instability. The seed island is mainly driven by the local helical perturbation of the diamagnetic current induced by the perturbed pressure gradient as a result of the impurity radiative cooling on the rational surface. A heuristic closure for the neoclassical viscosity is adopted, and the seed island is further driven by the perturbed bootstrap current induced from the neoclassical electron viscous stress in the extended Ohm's law. The growth rate of the NTM in simulations is found proportional to the electron neoclassical viscosity, and a theoretical neoclassical driving term is adopted to account for the nonlinear neoclassical island growth in the simulations.

physics.plasm-ph↗

arXiv2024

Generation of 10 kT Axial Magnetic Fields Using Multiple Conventional Laser Beams: A Sensitivity Study for kJ PW-Class Laser Facilities

Strong multi-kilotesla magnetic fields have various applications in high-energy density science and laboratory astrophysics, but they are not readily available. In our previous work [Y. Shi et al., Phys. Rev. Lett. 130, 155101 (2023)], we developed a novel approach for generating such fields using multiple conventional laser beams with a twist in the pointing direction. This method is particularly well-suited for multi-kilojoule petawatt-class laser systems like SG-II UP, which are designed with multiple linearly polarized beamlets. Utilizing three-dimensional kinetic particle-in-cell simulations, we examine critical factors for a proof-of-principle experiment, such as laser polarization, relative pulse delay, phase offset, pointing stability, and target configuration, and their impact on magnetic field generation. Our general conclusion is that the approach is very robust and can be realized under a wide range of laser parameters and plasma conditions. We also provide an in-depth analysis of the axial magnetic field configuration, azimuthal electron current, and electron and ion orbital angular momentum densities. Supported by a simple model, our analysis shows that the axial magnetic field decays due to the expansion of hot electrons.

physics.plasm-ph↗

arXiv2024

Formation of quasi-single helicity state from a paramagnetic pinch in KTX regime

The formation of quasi-single helicity (QSH) state from a paramagnetic pinch in the KTX-RFP regime has been observed in recent NIMROD simulations. The quasi-single helicity state has a dominant helical component of the magnetic field that is known to improve the RFP confinement. For the initial paramagnetic pinch, linear calculations indicate that the tearing mode growth rate decreases with the plasma $β$. The initial QSH state arises from the dominant linear instability of the initial force-free paramagnetic pinch. The plasma's self-organization towards the second QSH state after the relaxation of the initial QSH state is found to depend on $β$. Specifically, when $β<4\%$, the plasma relaxes to an MH state; when $4\% \leq β\leq 8\%$, the plasma first transitions from a double axis (DAx) to a single helical axis (SHAx) state, and eventually return to the DAx state. The existence of such an optimal $β$ regime that is beneficial to the formation and maintenance of the QSH state, suggests an experimental scheme for the QSH formation based on $β$ tuning and control.

physics.plasm-ph↗

arXiv2024

Invariant regimes of Spencer scaling law for magnetic compression of rotating FRC plasma

The scaling laws for the magnetic compression of a toroidally rotating field reversed configuration (FRC) have been investigated in this work. The magnetohydrodynamics (MHD) simulations of the magnetic compression on rotating FRCs employing the NIMROD code [C. R. Sovinec \textit{et al.}, J. Comput. Phys. \textbf{195}, 355 (2004)], are compared with the Spencer's one-dimensional (1D) theory [R. L. Spencer \textit{et al.}, Phys. Fluids \textbf{26}, 1564 (1983)] for a wide range of initial flow speeds and profiles. The toroidal flow can influence the scalings directly through the alteration of the compressional work as also evidenced in the 1D adiabatic model, and indirectly by reshaping the initial equilibrium. However, in comparison to the static initial FRC equilibrium cases, the pressure and the radius scalings remain invariant for the magnetic compression ratio $B_{w2}/B_{w1}$ up to 6 in presence of the initial equilibrium flow, suggesting a broader applicable regime of the Spencer scaling law for FRC magnetic compression. The invariant scaling has been proven a natural consequence of the conservation of angular momentum of both fluid and magnetic field during the dynamic compression process.

physics.plasm-ph↗

arXiv2024

Effects of zero and reversed magnetic shear on resistive wall modes in a limiter tokamak plasma

Advanced tokamak scenarios often feature equilibriums with zero and reversed magnetic shear. To isolate and investigate their impacts on the resistive wall mode (RWM) instability analytically, we construct a series of cylindrical limiter equilibriums with reversed magnetic shear in the core and zero magnetic shear towards plasma edge, as a prototype of the configurations in advanced tokamak scenarios. Uniform plasma pressure is assumed, so that we can focus our analysis on the current-driven RWMs. Based on the reduced ideal MHD equations, analytical solutions for the $n=1$ resistive wall mode are obtained, which indicate that increasing the reversal of magnetic shear in the core region enhances the RWM instability, whereas the widened region of zero shear near edge leads to lower growth rate of RWM, except when the $q$ value with zero magnetic shear approaches rational values. On the other hand, enhanced positive shear at plasma edge is found to be stabilizing on RWM. NIMROD calculation results confirm these analytical findings.

physics.plasm-ph↗

arXiv2024

Roles of non-axisymmetric perturbations in free drift vertical displacement events on EAST

The safe operation of most tokamaks, especially the largen sized ones, rely on the feedback control of the vertical displacement events (VDEs). However, most these feedback control systems are based on the axisymmetric VDE models. In this work, we use NIMROD simulations to study the roles of non-axisymmetric perturbations in free drift vertical displacement events on EAST. The high-$n$ modes in non-axisymmetric VDE grow first, which drive the formation of high-$n$ magnetic island chains. Subsequently, the magnetic island chains grow and overlap with each other, leading to the destruction of the magnetic flux surface, which induces a minor disruption and accelerates the start of the following major disruption. The magnetic island and the stochastic magnetic field allow the toroidally asymmetric poloidal plasma current to jet towards the hoop force direction, forming the finger and filamentary structures. Such a plasma current asymmetry strongly depends on the anisotropy in thermal transport coefficients.

physics.plasm-ph↗

arXiv2023

Limited bisimulations for nondeterministic fuzzy transition systems

The limited version of bisimulation, called limited approximate bisimulation, has recently been introduced to fuzzy transition systems (NFTSs). This article extends limited approximate bisimulation to NFTSs, which are more general structures than FTSs, to introduce a notion of $k$-limited $α$-bisimulation by using an approach of relational lifting, where $k$ is a natural number and $α\in[0,1]$. To give the algorithmic characterization, a fixed point characterization of $k$-limited $α$-bisimilarity is first provided. Then $k$-limited $α$-bisimulation vector with $i$-th element being a $(k-i+1)$-limited $α$-bisimulation is introduced to investigate conditions for two states to be $k$-limited $α$-bisimilar, where $1\leq i\leq k+1$. Using these results, an $O(2k^2|V|^6\cdot\left|\lra\right|^2)$ algorithm is designed for computing the degree of similarity between two states, where $|V|$ is the number of states of the NFTS and $\left|\lra\right|$ is the greatest number of transitions from states. Finally, the relationship between $k$-limited $α$-bisimilar and $α$-bisimulation under $\widetilde{S}$ is showed, and by which, a logical characterization of $k$-limited $α$-bisimilarity is provided.

math.DS↗