World's most powerful nuclear fusion experiment sets a new record

Wendelstein 7-X in Greifswald, Germany, the largest stellarator, has set a new high bar for sustained fusion performance. Researchers held a high quality plasma steady for 43 seconds using frozen hydrogen, pushing a key performance yardstick to a new fusion record.

The team fed the plasma with about 90 pellets of frozen hydrogen, each roughly 0.04 inch across, while high power microwaves heated the fuel to more than 20 million degrees Celsius with peaks near 30 million.

The result shows progress toward the kind of steady operation future reactors will need to make electricity.

Fusion and the triple product

“The new record is a tremendous achievement by the international team. It impressively demonstrates the potential of Wendelstein 7-X,” said Thomas Klinger, head of operations at Wendelstein 7-X.

Klinger is also head of stellarator dynamics and transport at the Max Planck Institute for Plasma Physics (IPP) in Greifswald.

Fusion researchers track progress with the triple product, which multiplies plasma density, temperature, and energy confinement time.

A widely cited threshold for power producing reactors is often called the Lawson criterion, and it tells you when a plasma could produce more power than it consumes.

Hitting that line at relevant conditions is the long term goal for magnetic confinement experiments.

Each factor in the triple product must be high at the same time, not one after another. That is why long pulses matter, because they test how well heating, fueling, and walls hold up together under stress.

Frozen hydrogen and hot plasma

Long lasting plasmas need steady refueling, and that is where Oak Ridge National Laboratory (ORNL), and their new pellet system came in.

Engineers built a continuously operating injector that forms a strand of solid hydrogen and slices off tiny cylinders that shoot into the plasma in a carefully timed rhythm.

Operators used variable pre programmed rates to match the incoming fuel to the heating pattern. That control kept the density in a sweet range without smothering the heat that the plasma needed to stay active.

The pellets did more than feed the plasma. They also helped tame impurities and stabilized the edge conditions that otherwise sap energy and shorten pulses.

Pellet fueling is a bridge to reactor operation. Future machines will need continuous or near continuous fueling to balance outburn and to keep the core from starving during steady operation.

Measuring heat, density, and time

Good records are only as solid as the measurements behind them. Princeton Plasma Physics Laboratory supplied an X-ray imaging crystal spectrometer that reads ion temperatures across the plasma cross section.

The electron density was tracked with a precision interferometer developed at IPP, and the energy confinement time followed from the detailed diagnostics suite. These inputs give the triple product value its credibility.

Diagnostics have to agree and stay calibrated over long runs. Teams adjust for viewing angles, background light, and small drifts that creep in during minutes of operation.

Steady path for stellarators

Stellarators twist the magnetic cage in three dimensions, and they aim for continuous operation without pulsed currents in the plasma.

That design avoids disruptions that have challenged tokamak machines and reduces the need for complex current drive systems.

The price of that stability has been complexity in coil shapes and manufacturing.

Wendelstein 7-X was built to show that optimized magnetic geometry can still confine heat well and limit losses that once plagued this approach.

This latest run strengthens that case. It points to a route where heat exhaust, fueling, and plasma control can be planned for steady operation rather than bursts.

Two more milestones to note

The same campaign increased the total energy turnover to 1.8 gigajoules over six minutes, up from 1.3 gigajoules in early 2023.

The plasma also reached about 3 percent pressure relative to the magnetic pressure, a step toward the 4 to 5 percent that a future plant will likely require.

That pressure ratio is often called beta, and it matters because higher pressure at a fixed magnetic field means more power for the same size device.

Raising beta without triggering instabilities is a central theme in fusion design work.

Heating relied on electron cyclotron resonance (ECR), a microwave method that directly energizes electrons in the plasma.

Careful coordination between heating and fueling kept conditions near the planned targets.

The device did not just run hot, it ran calmly. That behavior matters because power plants will need stable discharges that can track control inputs for long stretches.

Plasma, hydrogen, and the future

The W7 X program now turns to longer heaters, added pellet control modes, and improved wall conditioning.

The goal is to hold high performance for many minutes while protecting components and keeping impurities low.

Engineers will push toward higher beta at larger density while keeping the confinement time strong. That balance is essential for any path that leads to a power producing reactor based on magnetic confinement.

Teams also plan to refine how pellets are timed with the heating cycles. Better timing can stretch pulses without adding extra power or stress to the hardware.

Researchers will keep comparing results with the global database on long pulse operation. Shared methods help everyone learn faster and reduce dead ends in the next round of tests.

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