Tokamak Reactor Sets New Stable Plasma Record

Nuclear fusion — the process that powers the sun — is often called the ultimate clean energy goal. Experimental tokamak facilities have logged records for confining plasma at 100 million degrees Celsius for increasingly stable durations.

Why it has to be that hot

Atomic nuclei are positively charged and repel one another. For deuterium and tritium to get close enough to fuse, that electrostatic repulsion has to be overcome, and the only practical way is to give both enormous kinetic energy — which means temperatures of hundreds of millions of degrees.

At those temperatures matter exists as plasma, and no physical container can touch it. Because plasma is made of charged particles, it can be held by a magnetic field — and that is how a tokamak works.

Superconducting magnets that change the equation

The latest achievement was made possible by superconducting magnets made of REBCO, which can generate magnetic fields far stronger than earlier-generation materials and operate at temperatures that are easier to maintain.

The significance lies in the maths of confinement: plasma confinement quality scales roughly with the fourth power of magnetic field strength. Doubling the field strength lets a far more compact reactor reach the same conditions — and reactor size is the main driver of construction cost.

Reading the "net-positive energy" claim

The term needs to be read carefully, because it is used for two very different things. What is commonly reported is the ratio of the energy produced by the reaction to the energy fed into the plasma.

The commercially decisive figure is the ratio against the energy fed into the entire facility — including magnets, cooling systems and heating — plus the efficiency of converting heat into electricity. The gap between the two definitions is still wide, and that is where the remaining engineering work lies.

The work that remains

The next challenge is materials, not plasma physics. Reactor walls have to withstand bombardment by high-energy neutrons for years without losing structural integrity. Tritium is also not available in nature in sufficient quantities and must be bred inside the reactor itself — a process that has never been demonstrated at full scale.

The transition from experimental physics to commercial power plants is now the target of global energy consortia. The progress is real, and the timeline is still measured in decades.