Fusion Energy: JET Sets New Output Record

The quest for unlimited, clean power took a significant leap forward as the Joint European Torus (JET) laboratory smashed its own world record for fusion energy output. In its final run of experiments before retirement, the UK-based facility produced 69 megajoules of energy. This achievement marks a pivotal moment for nuclear physics and offers concrete hope that fusion can eventually transition from an experimental science to a viable power source for the electrical grid.

The Historic 69 Megajoule Burst

Located at the Culham Centre for Fusion Energy in Oxfordshire, the JET reactor has served as the world’s largest and most powerful tokamak for over 40 years. In late 2023, during its final campaign of deuterium-tritium experiments, the machine generated a sustained high fusion power for five seconds.

While five seconds might sound brief, in the context of nuclear fusion, it is a massive duration to hold plasma stable. The reaction produced 69 megajoules of heat energy. To put this energy density into perspective, generating that same amount of heat using fossil fuels would require burning approximately 2 kilograms of coal. JET achieved it with just 0.2 milligrams of fuel.

This new benchmark surpasses the previous record set by the same facility in 2021, which produced 59 megajoules. The ability to repeat and improve upon these results demonstrates reliability, a critical factor if fusion is ever to be used commercially. The scientists at the UK Atomic Energy Authority (UKAEA) and the European consortium EUROfusion view this as definitive proof that magnetic fusion can be scaled up.

Inside the Tokamak: How It Works

Fusion is the same process that powers the sun. It involves forcing light atomic nuclei to combine to form heavier ones, releasing massive amounts of energy in the process. However, replicating this on Earth is incredibly difficult because it requires temperatures far hotter than the core of the sun to overcome the natural repulsion between atomic nuclei.

JET uses a donut-shaped machine called a tokamak. Inside this vacuum vessel, strong magnetic fields confine the plasma (a hot, charged gas). Here are the specific conditions required for this record-breaking run:

Temperature: The plasma reached temperatures of 150 million degrees Celsius, which is ten times hotter than the center of the sun.
Fuel Mix: The reactor used a mix of deuterium and tritium. These are isotopes of hydrogen. Deuterium is abundant in seawater, while tritium can be produced from lithium. This specific “D-T” mix is widely considered the most viable fuel for future commercial power plants.
Magnetic Confinement: Massive magnets prevented the superheated plasma from touching the walls of the reactor, which would instantly cool the reaction and potentially damage the equipment.

One of the key successes of this final experiment was the interaction between the plasma and the reactor walls. JET was upgraded several years ago to replace its carbon wall tiles with tungsten and beryllium. These materials are more resistant to retaining fuel, which is a necessary safety feature for future plants. The success of the 69-megajoule run confirms that these materials can withstand the intense neutron bombardment of a fusion reaction.

Paving the Way for ITER

The primary purpose of JET was not to generate electricity for the grid but to act as a testbed for its successor, ITER (International Thermonuclear Experimental Reactor). Currently under construction in southern France, ITER is a massive international collaboration designed to be much larger and more powerful than JET.

The data gathered from JET’s final experiments is directly applicable to ITER. Because JET is the only machine currently capable of running the deuterium-tritium fuel mix, these results effectively de-risk the ITER project.

Scaling Up: ITER will contain ten times the plasma volume of JET.
The Q Factor: While JET produced a record amount of energy, it did not achieve “net energy” (where output exceeds the total energy put in to heat the plasma). JET required roughly three units of energy to produce one unit of output. ITER is designed to flip this ratio, aiming to produce ten times the energy it consumes (Q=10).
Operational Procedures: The team at Culham developed specific operational scenarios to stabilize the plasma. These “recipes” for running the reactor will be transferred directly to the team in France.

The Difference Between Fusion and Fission

It is important to distinguish this breakthrough from current nuclear power, which relies on fission. Fission splits heavy atoms like uranium, creating radioactive waste that remains hazardous for thousands of years. It also carries the risk of runaway chain reactions.

Fusion offers distinct advantages that make records like the one at JET so promising:

Safety: A fusion reaction is inherently difficult to sustain. If any disturbance occurs, the plasma cools and the reaction simply stops. There is no risk of a meltdown.
Waste: Fusion does not produce high-level, long-lived radioactive waste. The reactor components may become radioactive over time, but the materials can typically be recycled or disposed of within 100 years.
Fuel Supply: The fuel sources are virtually inexhaustible. Deuterium is found in water, and lithium (for tritium breeding) is a common metal.

What Comes Next for Fusion?

Following this historic achievement, JET is moving into a decommissioning phase. This process will last until around 2040 and will provide valuable data on how to dismantle and repurpose radioactive fusion facilities safely.

Meanwhile, the focus shifts to the next generation of machines. Apart from ITER, the UK is proceeding with its own program called STEP (Spherical Tokamak for Energy Production). The goal of STEP is to build a prototype plant capable of delivering net electricity to the grid by 2040.

Private industry is also accelerating. Companies like Commonwealth Fusion Systems in the United States and Tokamak Energy in the UK are utilizing high-temperature superconducting magnets to build smaller, more efficient reactors. The success at JET validates the underlying physics these commercial ventures rely on.

While commercial fusion power is likely still two decades away, the 69-megajoule record proves that the science is sound. The challenge is no longer about whether fusion is possible, but rather an engineering race to make it efficient and economical.

Frequently Asked Questions

Did the JET reactor produce net energy? No. In this specific experiment, the reactor produced 69 megajoules of fusion energy, but it required significantly more energy to heat the plasma and power the magnets. The goal of JET was to study plasma stability, not to generate net electricity. That is the goal of the next reactor, ITER.

Why is the 5-second duration significant? In fusion physics, instabilities usually occur in milliseconds. Holding the plasma stable for 5 full seconds indicates that scientists have mastered the control mechanisms needed for continuous operation. The time was limited only by the heating coils at the facility, not by the stability of the plasma itself.

What is the difference between Deuterium and Tritium? They are both forms of hydrogen. Hydrogen usually has one proton and no neutrons. Deuterium has one proton and one neutron. Tritium has one proton and two neutrons. When they fuse, they release more energy at lower temperatures than any other element pair, making them ideal for power generation.

When will fusion power turn on the lights in my home? Current roadmaps suggest that prototype fusion power plants could put electricity onto the grid in the 2030s or 2040s. Widespread commercial adoption would likely follow in the second half of the century.