Fusion Reactor Cross-Section Simulator (2D)

Plasma Conditions

Plasma temperature 15 keV

Magnetic field strength 65%

Confinement building — plasma heating.

Lawson Criterion

Confinement time τ

0.0 s

Density n

1.0×10²⁰ m⁻³

Triple product nTτ

% of ignition

D-T Reaction

Fusion power density

0 MW/m³

Fusion events

How it works

This is a poloidal cross-section of a tokamak: the ring you see is a slice through the donut-shaped vacuum vessel. Coils around the vessel generate a toroidal magnetic field; combined with a current driven through the plasma itself, the field lines twist into helices that trap charged deuterium and tritium ions away from the walls (magnetic confinement).

Fusion only happens if the ions are hot and dense enough for long enough — the Lawson criterion. It is usually expressed as a triple product n·T·τ (density × temperature × energy confinement time), which must exceed roughly 3×10²¹ keV·s/m³ for deuterium-tritium ignition. Raise the temperature slider and the field slider (which lengthens confinement time τ) to push the triple product toward that threshold — the bar and percentage track how close you are.

The fusion reaction rate depends steeply on temperature: D + T → ⁴He + n releases 17.6 MeV per reaction, and the reaction rate coefficient ⟨σv⟩ grows roughly as T² in the 10-20 keV range used here. Fusion power density is estimated as (n/2)²⟨σv⟩×17.6 MeV, assuming a 50:50 D-T mix at a fixed density of 10²⁰ particles per cubic metre, typical of a real tokamak core.

Low temperature or weak field: ions drift and collide with the wall before fusing.
High temperature + strong field: triple product approaches ignition, fusion flashes appear more often.

Magnetic field line Deuterium / tritium ion Fusion event