时间：2026年5月18日（周一）10:00

地点：紫金港校区海纳苑8幢322教室

报告题目：The Smoothness Paradox in Plasma Waves: Coarse-Grained Resonance and the Breakdown of Landau Damping

报告人：谢华生博士

摘要： 

The classic theory of Landau damping requires the velocity distribution function (VDF) to be analytically continued into the complex plane, implicitly requiring analyticity, which imposes constraints far more severe than infinite smoothness. Yet physical plasmas---encountered in discrete simulations, noisy spacecraft measurements, or truncated fusion distributions---are inherently non-analytic. This discrepancy poses a foundational ``smoothness paradox'': why does Landau damping robustly persist in systems where the mathematical prerequisite of analyticity is profoundly violated? Here we resolve this paradox by demonstrating that wave-particle interaction is governed by a time-dependent resonance width $\Delta v_\mathrm{res}\sim 1/kt$. Using a dispersion-free Lagrangian time-domain solver, we show that this finite width kinematically coarse-grains microscopic VDF defects at early times, acting as a natural low-pass filter that validates smooth analytical proxies---explaining the observed robustness. However, as $t\to\infty$ the resonance width narrows, inevitably forcing the wave to resolve exact topological non-smoothness. This late-time resolution triggers three distinct breakdowns: VDF truncation arrests the resonant phase transition to yield undamped discrete Van Kampen modes; observational noise induces transient algebraic spikes via linear phase-space aliasing; and step-like gradients drive anomalously violent reactive instability growth. We establish the breakdown timescale $t_b\sim 1/k\delta v$, where $\delta v$ is the characteristic scale of the non-smooth defect, providing a quantitative criterion that redefines the validity boundaries of analytic continuation in kinetic theory.

报告人简介：

Huasheng XIE, born in November 1987 in Hengyang, China. Earned a BS degree from Zhejiang University (2010) and a PhD (2015). Completed a postdoctoral fellowship at Peking University (Oct 2015 – Nov 2017). Currently Founder of VeloAlpha (since May 2026) and Chief Scientist of Fusion Theory and Simulation at ENN (since Nov 2017). Specializes in fundamental and fusion plasma theory and simulation. Developed widely used open-source codes, including the plasma wave series GPDF, PDRF/PDRK/BO, and BORAY. Author of 80+ SCI papers in plasma physics. Also authored two monographs: Introduction to Computational Plasma Physics (Science Press, 2018, in Chinese) and Introduction to Fusion Ignition Principles (USTC Press, 2023, in Chinese).

代表性成果：

1. H. S. Xie, Y. Xiao and Z. Lin, New Paradigm for Turbulent Transport Across a Steep Gradient in Toroidal Plasmas, Physical Review Letters, 2017, 118, 095001.

2. H.S. Xie, BO: A unified tool for plasma waves and instabilities analysis, Computer Physics Communications, 2019, 244, 343–371.

3. H.S. Xie, Efficient framework for solving plasma waves with arbitrary distributions, Phys. Plasmas 32, 060702 (2025).

4. 谢华生，计算等离子体物理导论，科学出版社，北京，2018. 

5. 谢华生，聚变点火原理概述，中国科学技术大学出版社，合肥，2023.

欢迎各位老师和同学参加！