Pellet-Size Scaling of Quasi-Steady-State Plasma Performance in Wendelstein 7-X
Abstract
A continuous cryogenic-pellet injector has been used to realize long-pulse high-performance plasmas in Wendelstein 7-X (W7-X). A hydrogen ice pellet deposits particles directly in the confined region. If the particles are deposited sufficiently far inside the plasma, they produce a density gradient that suppresses ion-temperature-gradient turbulence and improves plasma confinement. However, after multiple pellets have been injected and the plasma density and temperature have increased, the plasma performance begins to saturate. In this work, we analyze multiple pellet-injection experiments conducted in 2024 and 2025, during which the injected pellet sizes varied unintentionally. This analysis reveals a positive correlation between pellet size and the quasi-steady-state stored energy of W7-X plasmas. Although this pellet-size dependence can be understood qualitatively from pellet-ablation physics, the measured deposition position differs quantitatively from the neutral-gas-shielding (NGS) model prediction. This discrepancy suggests significant inward transport of the pellet cloud. The trend identified here suggests that injection of even larger pellets could further improve plasma performance.
Related
- Atmospheric-Pressure Microwave Plasma Deposition of Highly Fluorine-Doped Silica Claddings for High-Performance Optical Fibers
- Theory of steady states for Lindblad equations beyond time-independence: Classification, uniqueness and symmetry
- Cramer-Rao Inequality Generalizes the Equilibrium Energy Fluctuation-Response Relation to Nonequilibrium Steady States
- Steady-state spin order and superradiance beyond the single-mode Dicke limit
- Intrinsic evolution pathway connecting two quasi-steady dissipative soliton states in a pulsating Yb-doped fiber laser
BibTeX
@misc{fujii2026pelletsize,
title = {{Pellet-Size Scaling of Quasi-Steady-State Plasma Performance in Wendelstein 7-X}},
author = {Keisuke Fujii and Edgardo Villalobos Granados and Maryam Huck and Jürgen Baldzuhn and Naoki Tamura and Steven Meitner and Larry Baylor and Golo Fuchert and Kai Jakob Brunner and Jens Knauer and Ekkehard Pasch and Jannik Wagner and Bart Lomanowski and W7-X Team},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.17751},
eprint = {2609.17751},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.17751},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Pellet-Size Scaling of Quasi-Steady-State Plasma Performance in Wendelstein 7-X
AU - Keisuke Fujii
AU - Edgardo Villalobos Granados
AU - Maryam Huck
AU - Jürgen Baldzuhn
AU - Naoki Tamura
AU - Steven Meitner
AU - Larry Baylor
AU - Golo Fuchert
AU - Kai Jakob Brunner
AU - Jens Knauer
AU - Ekkehard Pasch
AU - Jannik Wagner
AU - Bart Lomanowski
AU - W7-X Team
PY - 2026
DA - 2026/09/15
PB - arXiv
DO - 10.48550/arxiv.2609.17751
UR - https://arxiv.org/abs/2609.17751
AB - A continuous cryogenic-pellet injector has been used to realize long-pulse high-performance plasmas in Wendelstein 7-X (W7-X). A hydrogen ice pellet deposits particles directly in the confined region. If the particles are deposited sufficiently far inside the plasma, they produce a density gradient that suppresses ion-temperature-gradient turbulence and improves plasma confinement. However, after multiple pellets have been injected and the plasma density and temperature have increased, the plasma performance begins to saturate. In this work, we analyze multiple pellet-injection experiments conducted in 2024 and 2025, during which the injected pellet sizes varied unintentionally. This analysis reveals a positive correlation between pellet size and the quasi-steady-state stored energy of W7-X plasmas. Although this pellet-size dependence can be understood qualitatively from pellet-ablation physics, the measured deposition position differs quantitatively from the neutral-gas-shielding (NGS) model prediction. This discrepancy suggests significant inward transport of the pellet cloud. The trend identified here suggests that injection of even larger pellets could further improve plasma performance.
ER -