A tokamak confines superheated plasma with magnetic fields strong enough that particles spiral along field lines instead of hitting the wall. Net fusion output follows the Lawson criterion:
n · T · τE ≥ ~3×10²¹ keV·s/m³ (ignition threshold)
τE ∝ B² · a² / P_heat (confinement time)
β = plasma pressure / magnetic pressure (stability limit)
Stronger magnetic field tightens the confining spiral and raises confinement time τE; more heating power raises plasma temperature but also tends to reduce τE per unit power (a real tradeoff in tokamak physics). If plasma pressure (β) rises too high relative to the magnetic field, instabilities grow until the plasma disrupts — dumping its energy into the vessel wall in milliseconds, exactly what the "trigger disruption" button demonstrates.
- Magnetic field — tightens plasma confinement (smaller helical drift radius) and raises the disruption safety margin.
- Plasma density — more fuel ions available for fusion reactions, but also raises β and disruption risk at low field.
- Auxiliary heating — raises plasma temperature toward the ~100-150 million K needed for D-T fusion.
- Trigger disruption — forces an instability event so you can see confinement collapse and particles hit the vessel wall.
This is the working principle behind ITER and other tokamak fusion projects racing to reach net energy gain (Q>1) as a future carbon-free power source.