Dry wall: Fusion reactor chamber’s first wall that employs no liquid or gaseous protection.

Fast ignition: ICF technique whereby the driver gradually compresses the fuel capsule, followed by a high-intensity, ultrashort-pulse laser that strikes the fuel to trigger ignition.

First wall: First surface of the fusion reactor chamber encountered by radiation and/or debris emitted from the target implosion. These walls may vary in composition and execution such as dry, wetted, or liquid jet.

Gain: Ratio of the fusion energy released by the target to the driver energy applied to the target in a single explosion.

Heavy-ion fusion: ICF technique whereby ions of heavy elements are accelerated and directed onto a target.

High average power: Attribute of a driver that, if repeatable, would make it suitable for an IFE-based power plant.

High-energy-density science: Study of the creation, behavior, and interaction of matter with extremely high energy densities.

High repetition rate: Maintaining a high rate for engaging the driver or igniting the target, making it suitable for an IFE-based power plant (e.g., 10 Hz).

Hohlraum: Hollow container in which an ICF target may be placed, whose walls are used to reradiate incident energy to drive the fuel capsule’s implosion.

Hydrodynamic instability: Concept in which fluids of differing physical qualities interact, causing perturbations such as turbulence. Examples include Rayleigh-Taylor and Richtmyer-Meshkov instabilities.

Ignition (broad definition): Condition in a plasma when self-heating from nuclear fusion reactions is at a rate sufficient to maintain the plasma’s temperature and fusion reactions without having to apply any external energy.

Ignition (IFE): State when fusion gain exceeds unity—that is, when the fusion energy released in a single explosion exceeds the energy applied to the target.

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