In a groundbreaking achievement for fusion research, Germany’s Wendelstein 7-X, the world’s largest stellarator has once again proven its potential to bring humanity closer to limitless clean energy. Researchers successfully maintained a stable, high-quality plasma for 43 seconds, using frozen hydrogen pellets to sustain and control the fusion process.
At the heart of this record-setting experiment, scientists injected around 90 pellets of frozen hydrogen, each about 0.04 inches wide, into the plasma chamber. Meanwhile, powerful microwaves heated the plasma to over 20 million degrees Celsius, occasionally peaking near 30 million. This extreme environment allowed the plasma to remain stable for a record 43 seconds, an important step toward reactors that can operate continuously rather than in short bursts.
Thomas Klinger, head of operations at Wendelstein 7-X and a leading figure at the Max Planck Institute for Plasma Physics (IPP), hailed the milestone, stating: “The new record is a tremendous achievement by the international team. It impressively demonstrates the potential of Wendelstein 7-X.”
Fusion scientists measure progress through the triple product, a performance indicator that multiplies three vital factors — plasma density, temperature, and confinement time. Meeting the Lawson criterion, where a plasma produces more energy than it consumes, remains the ultimate goal. For this, all three parameters must peak simultaneously, making long, stable plasma pulses essential for testing real-world reactor conditions.
A key breakthrough came from Oak Ridge National Laboratory (ORNL), whose innovative pellet injector provided a steady hydrogen feed. The system continuously formed and fired frozen hydrogen cylinders into the plasma, syncing perfectly with heating cycles. This controlled refueling kept plasma density in an optimal range, ensuring it stayed hot enough to maintain fusion reactions without collapsing.
Beyond fueling, the pellets also stabilized impurities and smoothed out edge conditions, which often rob plasmas of energy. This precise control marks an important transition from experimental pulses to sustained operation, the mode that future reactors will require for commercial power generation.
The credibility of these records lies in meticulous diagnostics. Tools from the Princeton Plasma Physics Laboratory and IPP worked in tandem to track ion temperatures, electron density, and energy confinement time , the core metrics of the triple product. Accurate calibration and continuous monitoring ensured reliable data over the long plasma runs.
Unlike tokamaks, which rely on pulsed currents, stellarators twist magnetic fields into complex 3D shapes that naturally confine plasma without needing current-driven stability. This design offers a path to continuous, disruption-free operation, though it comes with engineering challenges in coil design and precision manufacturing.
Wendelstein 7-X’s latest success strengthens confidence in this approach, showing that optimized magnetic geometry can confine heat effectively while maintaining stability.
Alongside the main record, Wendelstein 7-X achieved two other notable milestones: total energy turnover reached 1.8 gigajoules over six minutes, up from 1.3 gigajoules in early 2023. And plasma pressure ratio (beta) hit 3%, moving closer to the 4–5% target expected for commercial reactors.
Raising beta values without triggering instabilities remains one of the toughest challenges in fusion design, one the W7-X team continues to master through refined heating and fueling coordination using electron cyclotron resonance (ECR) technology.
The next phase for the W7-X project includes longer heating durations, enhanced pellet control, and improved wall conditioning. Engineers aim to sustain high performance over several minutes while preserving equipment and reducing impurities.