Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 1910.01707

Many-body collision contributions to electron momentum damping rates in a plasma influenced by electron strong coupling

Puchang Jiang·John Guthrie·Jacob L. Roberts
View original source ↗Read source document ↗Export metadata ↓

Abstract

Experimental studies of electron-ion collision rates in an ultracold neutral plasma (UNP) can be conducted through measuring the rate of electron plasma oscillation damping. For sufficiently cold and dense conditions where strong coupling influences are important, the measured damping rate was faster by 37\% than theoretical expectations [W. Chen, C. Witte, and J. Roberts, Phys. Rev. E \textbf{96}, 013203 (2017)]. We have conducted a series of numerical simulations to isolate the primary source of this difference. By analyzing the distribution of electron velocity changes due to collisions in a molecular dynamics simulation, examining the trajectory of electrons with high deflection angle in such simulations, and examining the oscillation damping rate while varying the ratio of two-body to three-body electron-ion collision rates, we have found that the difference is consistent with the effect due to many-body collisions leading to bound electrons. This has implications for other electron-ion collision related transport properties in addition to electron oscillation damping.

Explore related subjects

physics.plasm-ph

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Puchang Jiang, John Guthrie, Jacob L. Roberts. 2019-10-03. Many-body collision contributions to electron momentum damping rates in a plasma influenced by electron strong coupling. https://doi.org/10.1063/1.5129383

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Runaway electron interactions with whistler waves in tokamak plasmas: energy-dependent transport scaling

Resonant interactions between high energy runaway electrons (REs) and whistler waves are a promising mechanism for RE mitigation in tokamak plasmas. While prior studies have largely relied on quasi-linear diffusion models in simplified geometries, we present a first-principles-informed framework that models RE-whistler interactions in a 3D tokamak equilibrium. This is achieved by coupling AORSA, which computes whistler eigenmodes for a given tokamak plasma equilibrium, and KORC, a kinetic orbit code that tracks full orbit RE trajectories in prescribed wave fields. Our results demonstrate that REs undergo scattering to large pitch angles and exhibit anomalous diffusion in both pitch-angle and kinetic energy space. Crucially, we observe a transition between diffusive, sub-diffusive, and super-diffusive transport regimes as a function of initial RE energy - an effect not captured by existing quasi-linear models. This anomalous transport behavior represents a significant advancement in understanding RE dynamics in the presence of wave - particle interactions. By identifying the conditions under which anomalous diffusion arises, this work lays the theoretical foundation for designing targeted, wave-based mitigation strategies in future tokamak experiments.

physics.plasm-ph↗
arXiv2026

Geodesic Acoustic Modes in pair plasmas confined in tokamak magnetic fields

This paper is devoted to the derivation of the dispersion relation of the Geodesic Acoustic Mode in pair plasmas, i.e. assuming that ions and electrons have the same mass. Geodesic Acoustic Modes are plasma perturbations playing a crucial role in turbulence regulation, and therefore in the determination of the plasma confinement in tokamaks. Experiments with pair plasmas, like electron-positron plasmas, have been proposed with different kinds of confinements, and aim to study fundamental processes in plasma physics and understanding the formation of the early universe.

physics.plasm-ph↗
arXiv2026

Horizon-Aware Early Event Prediction for Tokamak Disruption Alarms

Reliable disruption prediction is essential for the safe operation of future tokamaks. Existing full-distribution survival methods model the complete residual time-to-disruption distribution, whereas operational decisions primarily depend on disruption risk within a finite prediction horizon. This mismatch motivates introducing Early Event Prediction (EEP) objectives into survival-based disruption prediction. We take Deep Survival Machines (DSM) as the full-distribution baseline and propose applying two established EEP methods to tokamak disruption prediction: Temporal Label Smoothing (TLS), which directly predicts disruption probability within a finite horizon, and survTLS, which additionally models the event-time distribution within that horizon. Using a common causal encoder, we compare these methods on DIII-D, Alcator C-Mod, and EAST. We distinguish threshold-free deadline ranking from validation-selected fixed-policy alarm performance and evaluate prediction horizons and encoder architectures. TLS achieves the best mean alarm performance on DIII-D and EAST, whereas all methods perform poorly on Alcator C-Mod. survTLS does not consistently outperform DSM, suggesting that directly learning horizon-level event probability is more effective than modeling detailed within-horizon event-time distributions in the present setting. Finally, the selected prediction horizons and encoder-ablation results vary across devices, reflecting differences in disruption characteristics.

physics.plasm-ph↗