Glossary

The vocabulary of inertial confinement, defined the way the family's repositories use it.

Inertial confinement

Compressing and heating a fuel capsule faster than its own inertia lets it disassemble; there is no confining field.

Direct and indirect drive

Laser light on the capsule itself; or laser light heating a hohlraum whose X-rays drive the capsule.

Fast ignition, shock ignition

Staged schemes that separate compression from ignition: a short-pulse igniter after compression; a late strong shock.

Hot spot

The small central region that must ignite: \(\rho R \ge 0.3\) g/cm² and \(T_i \ge 5\) keV in the laser review's floors.

Areal density \(\rho R\)

Density times radius, in g/cm²; what stops the alpha particles in a hot spot, and what an ion range is measured in.

Coupled fraction \(f_k\), shell kinetic energy \(E_k\)

The share of the imploding shell's kinetic energy that ends up in the hot spot; \(f_kE_k = 2\pi P_{hs}R_{hs}^3\).

Adiabat \(\alpha\)

Shell pressure over the Fermi-degenerate pressure, \(P/(2.2\rho^{5/3})\); low adiabat means compressible fuel.

In-flight aspect ratio (IFAR)

Ablation-front radius over shell thickness at the evaluation point the review fixes, two thirds of the initial inner radius.

Convergence ratio \(C_r\)

Initial inner radius over stagnation inner radius, defined with alpha deposition switched off.

Hydrodynamic efficiency

Shell kinetic energy over absorbed (not incident) laser energy.

Burnup fraction, yield, gain

The share of the fuel inventory consumed; the energy released; yield over incident or driver energy.

Ablator

The outer layer that is driven off to push the fuel inward; 1.85 g/cm³ in the beam capsule.

Converter

A body a beam heats so that its radiation drives the capsule; the conversion efficiency \(\eta_c\) and the coupling efficiency \(\eta_e\) chain driver to capsule.

Focal spot, fluence

The elliptical footprint \(\pi ab\) of one beam and the energy per unit area on it; effective radius \(\sqrt{ab}\).

Range

The matter an ion traverses before stopping, in g/cm²; the exponent between two range–energy pairs is reported, never a fitted law.

Flying plate

A projectile presenting a face; its areal density \(m/A\) and the energy per face area \(mv^2/2A\) are what the impact core carries.

Plane versus convergent compression

A slab compressed along one axis keeps its areal density; a sphere compressed by a radial factor \(C_r\) multiplies its density by \(C_r^3\) and its areal density by \(C_r^2\).

Truncation versus rounding

Two of the family's sources print values cut rather than rounded; the tests assert the truncation and that the rounding is a different number.

Anchor, implied, reconstructed, not reproduced

A printed value the core returns; a value the source's other numbers require of a fifth; a value neither source prints, recovered by a round trip; a printed value the relations do not return, recorded and never absorbed into a tolerance.

Evidence maturity

One of six states per capability; all three cores are at computational_prototype, and none of the states means machine-ready, safety-certified or reactor-ready.