Ignition of turbulent plasma via the shear flow reactivity enhancement effect
ORAL · Invited
Abstract
Turbulence increases the reactivity of fusion plasma, allowing ignition at lower temperature. This “shear flow reactivity enhancement” [1] occurs because in plasma, as opposed to other fluids, particles’ collisional mean free paths increase rapidly with their velocity. In sheared or turbulent flow, fast particles from one region can travel long distances and sample regions of large relative flow, ending up even faster relative to the local fluid. Such a velocity boost greatly increases the number of tail particles available to participate in energy-sensitive processes, such as fusion. Furthermore, because the mean free paths of thermal ions and tail ions are widely separated, the effect can appear even in highly collisional plasmas; in fact, because thermal ions determine viscosity, their short mean free paths at low temperature help to support strong flow gradients, allowing a large reactivity enhancement.
Remarkably, under some conditions, driving small-scale turbulent motion increases fusion reactivity more efficiently than simply heating the fuel [2]. A central paradigm in inertial confinement fusion (ICF) – that imploding kinetic energy should thermalize to maximize fusion reactivity – must therefore be revised. If micron-scale turbulence is driven inside an ICF hot spot, ignition can be accomplished with less confined energy [3]. Colder fuel allows for a smaller hot spot, reducing the heating required in fast ignition [1]. These results suggest a new paradigm for ICF in which targets are designed to generate turbulence on optimized scales during compression, increasing fusion yield or enabling ignition at lower driver energy.
[1] "Enhancement to fusion reactivity in sheared flows." H. Fetsch and N. J. Fisch, arXiv 10.48550/arXiv.2410.03590 (2024)
[2] "Analytical models for the enhancement of fusion reactivity by turbulence." H. Fetsch and N. J. Fisch, arXiv 10.48550/arXiv.2506.13711 (2025)
[3] "An ignition criterion for inertial fusion boosted by microturbulence." H. Fetsch and N. J. Fisch, arXiv 10.48550/arXiv.2507.18917 (2025)
Remarkably, under some conditions, driving small-scale turbulent motion increases fusion reactivity more efficiently than simply heating the fuel [2]. A central paradigm in inertial confinement fusion (ICF) – that imploding kinetic energy should thermalize to maximize fusion reactivity – must therefore be revised. If micron-scale turbulence is driven inside an ICF hot spot, ignition can be accomplished with less confined energy [3]. Colder fuel allows for a smaller hot spot, reducing the heating required in fast ignition [1]. These results suggest a new paradigm for ICF in which targets are designed to generate turbulence on optimized scales during compression, increasing fusion yield or enabling ignition at lower driver energy.
[1] "Enhancement to fusion reactivity in sheared flows." H. Fetsch and N. J. Fisch, arXiv 10.48550/arXiv.2410.03590 (2024)
[2] "Analytical models for the enhancement of fusion reactivity by turbulence." H. Fetsch and N. J. Fisch, arXiv 10.48550/arXiv.2506.13711 (2025)
[3] "An ignition criterion for inertial fusion boosted by microturbulence." H. Fetsch and N. J. Fisch, arXiv 10.48550/arXiv.2507.18917 (2025)
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Publication: "Enhancement to fusion reactivity in sheared flows." H. Fetsch and N. J. Fisch, arXiv 10.48550/arXiv.2410.03590 (2024) <br>"Analytical models for the enhancement of fusion reactivity by turbulence." H. Fetsch and N. J. Fisch, arXiv 10.48550/arXiv.2506.13711 (2025) <br>"An ignition criterion for inertial fusion boosted by microturbulence." H. Fetsch and N. J. Fisch, arXiv 10.48550/arXiv.2507.18917 (2025)
Presenters
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Henry Fetsch
Princeton University
Authors
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Henry Fetsch
Princeton University