Fusion Reactors: How Tokamaks Try to Bottle a Star

01 The Fusion Reaction

The leading power-plant reaction combines deuterium and tritium, two hydrogen isotopes, to produce helium and a high-energy neutron. The mass difference becomes energy under Einstein's relation E=mc².

Deuterium is abundant in seawater. Tritium is scarce and radioactive, so a practical reactor must breed it from lithium blankets while also extracting heat and protecting materials.

02 Why the Plasma Must Be Extreme

Fusion requires temperature, density, and confinement time to overlap. A tokamak plasma reaches roughly 100 million degrees Celsius, hotter than the Sun's core because laboratory plasma is far less dense.

At those temperatures no solid container can touch the fuel. Magnetic fields guide charged particles around a torus, while control systems fight turbulence, instabilities, and disruptions.

03 The Tokamak Geometry

A tokamak uses toroidal and poloidal magnetic fields. The combined field winds around the doughnut-shaped chamber, reducing particle losses and keeping the plasma away from the wall.

The design is conceptually simple but operationally difficult. Plasma shape, current, pressure, edge behavior, and wall conditions must be controlled together.

04 ITER and the Gain Question

ITER is an international experimental tokamak under construction in southern France. Its goal is to demonstrate a burning plasma and a fusion gain target of roughly Q=10: ten units of fusion power for one unit of external plasma heating.

ITER will not sell electricity. It is a physics and engineering bridge to demonstration reactors, designed to test magnets, tritium handling, remote maintenance, and heat exhaust at large scale.

05 The Materials Problem

The fusion reaction's neutron stream damages structural materials and activates components. The divertor, which handles extreme heat and impurity control, is one of the most demanding parts of the machine.

A power plant must survive this environment while remaining maintainable. Remote robotics, replaceable modules, neutron-resistant materials, and a workable breeding blanket are all essential.

06 What Counts as Success

Fusion is not automatically clean, cheap, or limitless. A reactor must produce net electricity after magnets, pumps, cryogenics, heating, maintenance, and fuel-cycle systems consume their share.

The near-term success criterion is disciplined engineering: demonstrate the integrated conditions, measure the losses, and expose the problems early enough that a commercial design can solve them.