Physic Labs

Frontier physics

Nuclear fusion

Explore the conditions for thermonuclear fusion: ions in hot plasma must overcome the Coulomb barrier via the Maxwell–Boltzmann tail. Observe the roles of temperature and density and check the trend f(v)∝v2e−mv2/2kBTf(v) \propto v^2 e^{-mv^2/2k_BT}.

Advanced

Equipment

  • Virtual plasma chamber with thermally moving ions
  • Maxwell–Boltzmann distribution plot with Coulomb-barrier region
  • Sliders for relative temperature and density

Procedure

  1. Observe ion collisions

    In figure 1 "Ions in hot plasma", watch the ions move and collide; most encounters are stopped by Coulomb repulsion. Read the current temperature and density in the readout. Only ions in the high-energy tail of the distribution (aided by quantum tunnelling) can fuse.

  2. Raise the temperature

    Drag "Relative temperature" up and watch the Maxwell–Boltzmann curve in figure 2 widen, its high-energy tail thickening: f(v)∝v2e−mv2/2kBTf(v) \propto v^2 e^{-mv^2/2k_BT}. The count of ions fast enough to cross the barrier grows steeply even for a modest temperature rise — which is why stars and fusion reactors need T∼107 ⁣− ⁣108T \sim 10^7\!-\!10^8 K.

  3. Vary density and compare

    With T high, raise "Relative density": more ions means more encounters per second — the reaction rate scales as n2n^2. Compare two settings (high T, low n) and (moderate T, high n): both may yield similar event counts, hinting at the Lawson criterion n T τEn\,T\,\tau_E that a burning plasma must exceed.

Simulation

Experiment history

In the 1920s Arthur Eddington proposed that stars draw energy from fusing hydrogen into helium, even though core temperatures computed classically seemed too low. In 1928 George Gamow (and independently Gurney–Condon) used quantum tunnelling to explain how nuclei can cross the Coulomb barrier below its peak. In 1938–39 Hans Bethe worked out the CNO cycle and the proton–proton chain powering stars — work honoured by the 1967 Nobel Prize. From the 1950s humanity pursued controlled fusion: Soviet tokamaks, stellarators, and laser inertial confinement; in 2022 the US NIF facility first recorded a target releasing more fusion energy than the laser energy delivered.

Related physicists

Marie CurieNiels BohrHans Albrecht Bethe

Related library topics

Nuclear fusion