Nuclear Fusion: Tokamaks, Inertial Confinement & Commercial Prospects

1. Fusion Physics Fundamentals

Fusion: light nuclei combine to form heavier nuclei, releasing energy (E = Δmc²). Primary reaction: D + T → ⁴He (3.5 MeV) + n (14.1 MeV). Conditions: Lawson criterion for ignition: nτ_E T > 3×10²¹ keV·s/m³. Triple product: density × confinement time × temperature. Plasma temperature: 100–200 million °C (10–20 keV) — 10× hotter than the Sun's core. Coulomb barrier: ~10 keV for D-T, overcome by quantum tunneling. Cross-section σ(E) peaks at ~100 keV. D-D reaction: lower cross-section but avoids tritium breeding. Advanced fuels: p-¹¹B (aneutronic, but requires 10× higher temperature). Plasma state: fully ionized gas, described by magnetohydrodynamics (MHD) and kinetic theory.

2. Magnetic Confinement: Tokamaks

Tokamak: toroidal vacuum vessel with combined toroidal and poloidal magnetic fields creating helical field lines that confine plasma. Key parameters: major radius R, minor radius a, aspect ratio A = R/a, safety factor q, plasma beta β = p/(B²/2μ₀). Plasma heating: ohmic (limited by resistivity drop at high T), neutral beam injection (NBI, 80–1000 keV), ion/electron cyclotron resonance heating (ICRH/ECRH), lower hybrid current drive (LHCD). MHD instabilities: kink modes, tearing modes (magnetic islands), edge-localized modes (ELMs). Disruptions: sudden loss of confinement — major engineering challenge. H-mode: high-confinement regime with edge transport barrier, 2× improvement in τ_E. JET achieved 69 MJ of fusion energy (2024 record), Q = 0.33 (P_fusion/P_heating).

3. ITER & Beyond

ITER (International Thermonuclear Experimental Reactor): under construction in Cadarache, France. 35 nations, ~$22B+ budget. Goals: Q = 10 (500 MW fusion from 50 MW heating), 400s burn. Superconducting magnets: Nb₃Sn (13 T toroidal field coils), NbTi (poloidal). Plasma volume: 840 m³, major radius 6.2 m. First plasma target: 2025→2035 (delayed). DEMO: planned successor, first electricity-generating fusion plant, ~2050. EU-DEMO: 2–4 GW thermal, superconducting. Chinese CFETR: plans for DEMO-class device by 2035. K-DEMO (Korea): compact tokamak aiming for electricity by 2040s. STEP (UK Spherical Tokamak for Energy Production): compact high-beta design.

4. Inertial Confinement & Alternative Concepts

Inertial Confinement Fusion (ICF): compress fuel pellet to extreme density using lasers or particle beams. NIF (National Ignition Facility): 192 laser beams, 2.05 MJ UV energy, achieved ignition (December 2022) — 3.15 MJ fusion output from 2.05 MJ laser input (scientific breakeven). Target physics: ablator (CH/HDC) → radiation-driven implosion → 100 g/cm³ DT density, 50 million atmospheres. Stellarator: twisted 3D magnets, inherently steady-state (no disruptions). Wendelstein 7-X: world's largest stellarator, 30-min plasma operations achieved. Spherical tokamak: low aspect ratio (A < 2), higher β, more compact — NSTX-U, MAST-U. Field-reversed configuration (FRC): TAE Technologies. Magnetized target fusion: General Fusion (compression). Z-pinch: Zap Energy (sheared-flow stabilized).

5. Commercial Fusion Ventures

Private fusion companies have raised >$7 billion: Commonwealth Fusion Systems (MIT spinoff, SPARC tokamak with HTS magnets, 20 T on coil, targeting Q > 2 by 2025→2027), TAE Technologies ($1.2B raised, FRC, p-¹¹B fuel goal), Helion Energy ($577M, FRC, direct energy conversion, targeting 2028 grid connection, 50 MW PPA with Microsoft), General Fusion (magnetized target, demo plant in UK), Zap Energy (Z-pinch, $300M+), Type One Energy (stellarator), Tokamak Energy (spherical tokamak, HTS magnets). High-temperature superconducting (HTS) magnets: REBCO tape enables >20 T fields in compact devices — game-changer for fusion economics. Key challenges: tritium breeding blanket, neutron-resistant materials (reduced activation ferritic-martensitic steels, SiC/SiC composites), remote maintenance of activated structures.

Try it live

Everything above runs in your browser — open Tokamak Fusion Reactor Simulator and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.