Scientists at the Max Planck Institute for Plasma Physics (IPP) have successfully generated a heat-insulating transport barrier in a tokamak plasma without applying external torque. The experiment, conducted on the ASDEX Upgrade device in Garching, Germany, as part of the EUROfusion consortium, demonstrated that a sufficiently steep temperature gradient can induce plasma turbulence that drives the necessary plasma rotation spontaneously. This self-generated rotation creates an internal transport barrier (ITB), a region of reduced turbulence that dramatically improves heat confinement. This finding addresses a significant operational challenge for future power plants, as creating these barriers via external neutral beam injection is energetically costly and may not be scalable to reactor-sized devices. Source: EUROfusion

The formation of transport barriers is critical for achieving the high core temperatures required for fusion. Traditionally, these barriers are induced by spinning the plasma at high speeds, which requires substantial power input from external systems. The IPP team's work, led by Dr. Andreas Angioni, shows that under specific conditions, the plasma can generate its own rotation. The new method produces a barrier described as "almost as good" as those created with external momentum injection, but with a significantly lower power requirement. This self-organization phenomenon is a crucial validation of theoretical models predicting that turbulence can drive macroscopic flows, improving the overall energy balance of a tokamak system. Source: EUROfusion

The formation of transport barriers is critical for achieving the high core temperatures required for fusion.

This result has direct implications for the design and operation of next-generation fusion devices like ITER and the demonstration power plant, DEMO. The energy cost of driving plasma rotation with external beams has been considered a potential "Achilles' heel" for the economic viability of tokamak-based power plants. By demonstrating a path to forming effective transport barriers with minimal external power, this research lowers a key uncertainty in reactor design. The ability to achieve high-confinement modes (H-modes) more efficiently makes the net energy gain targets for future facilities, such as the 2,000 MW thermal output planned for DEMO, more attainable. This work contributes to a more robust physics basis for reactor-scale plasma control and sustainment. Source: EUROfusion

The next step is to verify if this self-generated barrier mechanism scales to larger machines and different operating conditions. The EUROfusion team plans to replicate these experiments on other tokamaks, including the Joint European Torus (JET) in the UK, which is the largest currently operating tokamak. Success in these larger devices would build confidence that the same principle can be applied to the even larger ITER project. Validating this phenomenon across multiple devices is essential to confirm its universality and incorporate it into the operational scenarios planned for future fusion power plants, ultimately improving their projected Q_engineering values. Source: EUROfusion