Researchers at the Max Planck Institute for Plasma Physics (IPP) in Greifswald, Germany, have reported a significant operational milestone for the Wendelstein 7-X (W7-X) stellarator. The device sustained a plasma discharge for 480 seconds, achieving a total injected-to-extracted energy of 1.3 gigajoules. This result, detailed in a recent EUROfusion press release, surpasses the device's previous record from 2018 and represents a critical step in demonstrating the steady-state capabilities of the optimized stellarator concept. The experiment was conducted with an upgraded water-cooled divertor system, which was instrumental in handling the high heat flux over the extended pulse duration, a key challenge for long-pulse fusion devices. Source: EUROfusion

The 1.3 GJ discharge was achieved with 10 MW of electron cyclotron resonance heating (ECRH), maintaining an average central electron temperature of approximately 4 keV and a line-averaged density of 4.5 x 10^19 m^-3. According to the IPP team, the upgraded divertor, featuring carbon-fiber-reinforced carbon (CFC) tiles, performed within thermal limits, successfully extracting heat loads that averaged 5 MW/m^2 with peaks approaching 10 MW/m^2. This performance is a direct validation of the island divertor concept, a magnetic topology unique to advanced stellarators designed to spread the plasma exhaust over a larger surface area compared to the more localized strike points in a tokamak. Source: EUROfusion

[Source: EUROfusion](https://www.euro-fusion.org/news/wendelstein-7-x-achieves-gigajoule-milestone/)

This achievement builds on a multi-year upgrade campaign (OP2) focused on equipping W-7X for high-power, long-pulse operation. The primary goal of the device is not to achieve a net energy gain, or Q_plasma, but to demonstrate that a HELIAS (Helical-Axis Advanced Stellarator) configuration can confine a reactor-relevant plasma with low neoclassical transport and good stability in steady-state conditions. The sustained high performance over eight minutes provides strong evidence that the intricate, 3D-shaped magnetic fields are performing as predicted by complex numerical modeling, effectively minimizing the bootstrap current that can drive instabilities in other toroidal confinement concepts. Source: EUROfusion

The successful long-pulse operation provides critical data for the design of next-generation stellarator power plants. While tokamaks like ITER represent the most developed path toward a fusion reactor, stellarators offer the potential advantage of inherent steady-state operation without the need for complex and power-intensive current drive systems. The W-7X results directly inform the European DEMO design strategy, which includes a stellarator power plant concept as a potential long-term alternative or successor to a tokamak-based reactor. The data on plasma-wall interactions, impurity transport, and heat exhaust management over these extended time scales are invaluable for validating materials and engineering solutions for future devices. Source: EUROfusion

Next experimental campaigns on Wendelstein 7-X will focus on further increasing plasma density and temperature toward reactor-relevant parameters within these long-pulse scenarios. The IPP team plans to test the divertor system at its full design specification of 18 GJ of total energy over a 30-minute discharge. Achieving this ultimate goal would firmly establish the stellarator as a viable concept for a steady-state fusion power plant. These future experiments will also continue to benchmark sophisticated plasma simulation codes, enhancing the predictive capability required for designing a commercially viable stellarator. Source: EUROfusion