Laser Fusion Ignition: Inertial Confinement

Laser Drive

Laser energy 1.80 MJ

Beam count (symmetry) 192

Capsule radius 1.10 mm

DT-ice shell thickness 80 µm

Shot Diagnostics

Capsule loaded — ready to fire

Implosion velocity

— km/s

Convergence ratio

—

Hot-spot temp.

— keV

Ignition param. χ

—

How it works

A spherical DT-ice capsule is struck symmetrically by N laser beams. The outer surface ablates explosively; by momentum conservation this drives the remaining shell inward — the same rocket principle as a spacecraft ejecting propellant:

v_imp = √(2 η E_L / M_shell)
CR    = R₀ / R_final           (convergence ratio)
T_hs  ∝ v_imp²                 (stagnation heating)
ρR    = M_shell / (4π R_final²) (compressed areal density)

η is the fraction of laser energy that ends up as shell kinetic energy — it degrades when fewer beams illuminate the capsule, because the resulting drive asymmetry seeds Rayleigh–Taylor growth that shreds the imploding shell before it can converge.

At stagnation the shell's kinetic energy thermalizes into a central hot spot. Ignition needs both a high enough areal density (ρR) to trap the fusion α-particles and a high enough temperature (T_hs) to sustain the reaction — the two combine into an ignition parameter:

χ = (ρR / 0.3 g/cm²) · (T_hs / 10 keV)²
Ignition when χ ≥ 1

This mirrors the real hot-spot ignition criterion used to assess NIF-class implosions (Lindl/Atzeni scaling) — thin shells and tight, symmetric drive push χ up; thick shells, low energy or few beams keep it below threshold and the shot fizzles.

Laser beams DT-ice capsule Hot spot

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