Stellarators are machines designed to produce energy by fusing light atomic nuclei, a process called fusion. Fusion happens in a plasma, which is a very hot gas made of charged particles. To keep the plasma hot - tens of millions of degrees Celsius - stellarators use magnetic confinement. This means strong magnetic fields trap the plasma inside a donut-shaped vacuum chamber, preventing it from touching the walls and cooling down.
The Wendelstein 7-X (W7-X), located in Greifswald, Germany, and operated by the Max Planck Institute for Plasma Physics with support from the European fusion group EUROfusion, is the largest and most advanced stellarator in the world. It aims to show that stellarators can work as well in practice as they do in theory, making them a possible design for future fusion power plants.
Record-breaking achievements
In its latest experiments, ending on May 22, W7-X achieved a world record for a key measurement called the triple product during long plasma durations. The triple product measures three things: the plasma’s particle density, its temperature, and the energy confinement time.
A high triple product is crucial for a fusion power plant to produce more energy than it consumes. W7-X sustained this record value for 43 seconds, outperforming other fusion devices, like tokamaks, for longer plasma durations. Tokamaks are similar to stellarators but have a simpler design and have been studied more. While tokamaks still hold records for short plasma bursts, W7-X’s success with longer durations is a big step forward.
A major factor in this success was a new pellet injector, developed by the Oak Ridge National Laboratory in the United States. This device shoots tiny frozen hydrogen pellets into the plasma to keep it fueled. During the record experiment, 90 pellets were injected over 43 seconds while microwaves heated the plasma to over 20 million degrees Celsius. Precise control of the pellets and heating was essential. This method could allow future fusion reactors to maintain plasma for minutes. Other achievements included increasing energy turnover to 1.8 gigajoules and reaching a plasma pressure of 3%, both important for future power plant designs.
