Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 1911.06424

Interaction of Biased Electrodes and Plasmas: Sheaths, Double Layers and Fireballs

Scott D. Baalrud·Brett Scheiner·Benjamin Yee·Matthew M. Hopkins·Edward Barnat
View original source ↗Read source document ↗Export metadata ↓

Abstract

Biased electrodes are common components of plasma sources and diagnostics. The plasma-electrode interaction is mediated by an intervening sheath structure that influences properties of the electrons and ions contacting the electrode surface, as well as how the electrode influences properties of the bulk plasma. A rich variety of sheath structures have been observed, including ion sheaths, electron sheaths, double sheaths, double layers, anode glow, and fireballs. These represent complex self-organized responses of the plasma that depend not only on the local influence of the electrode, but also on the global properties of the plasma and the other boundaries that it is in contact with. This review summarizes recent advances in understanding the conditions under which each type of sheath forms, what the basic stability criteria and steady-state properties of each are, and the ways in which each can influence plasma-boundary interactions and bulk plasma properties. These results may be of interest to a number of application areas where biased electrodes are used, including diagnostics, plasma modification of materials, plasma sources, electric propulsion, and the interaction of plasmas with objects in space.

Explore related subjects

physics.plasm-ph

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Scott D. Baalrud, Brett Scheiner, Benjamin Yee, Matthew M. Hopkins, Edward Barnat. 2019-11-15. Interaction of Biased Electrodes and Plasmas: Sheaths, Double Layers and Fireballs. https://doi.org/10.1088/1361-6595%2Fab8177

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↗