Germany's Wendelstein 7-X (W7-X) stellarator has set a new device record for the fusion triple product, a key performance metric combining plasma density, temperature, and energy confinement time. In a recent experimental campaign, the device achieved a value of 6 x 10^20 m⁻³·s·keV, a significant advancement for the stellarator concept. The result was obtained in a high-density deuterium plasma scenario sustained for over five seconds with 10 MW of electron cyclotron resonance heating (ECRH). This milestone, announced by the Max Planck Institute for Plasma Physics, underscores the progress in optimizing the complex, 3D-shaped magnetic fields unique to the stellarator design, which aims to provide stable, continuous plasma confinement without the large, disruption-prone plasma currents required in tokamaks. Source: EUROfusion
The record-setting discharge achieved a central ion temperature (Ti) of approximately 3.5 keV and an average plasma density (n) of 2 x 10^20 particles per cubic meter. The crucial parameter, energy confinement time (τE), was maintained at just under one second. These parameters were measured using a suite of diagnostics, including Thomson scattering for temperature and density profiles. The sustained duration of the high-performance phase is particularly notable, as it demonstrates the effectiveness of the actively cooled divertor in handling heat exhaust and managing plasma-wall interactions. This result moves the stellarator concept closer to the conditions required for a net-energy-gain fusion power plant, validating the computational models used to design W7-X's intricate magnetic coil system. Source: EUROfusion
The record-setting discharge achieved a central ion temperature (Ti) of approximately 3.5 keV and an average plasma density (n) of 2 x 10^20 particles per cubic meter.
This achievement surpasses the previous W7-X record set in 2018 and places its performance in a competitive context with leading tokamak experiments, although still below the values achieved in machines like JET or JT-60SA operating with different parameters. The primary scientific goal of W7-X is not to achieve ignition but to demonstrate that a quasi-isodynamic optimized stellarator can confine a high-temperature plasma as effectively as a conventional tokamak, but in steady state. The triple product, also known as the Lawson criterion, is a direct indicator of this confinement quality. This result provides critical data for designing next-generation stellarators and strengthens the case for this alternative magnetic confinement fusion approach. Source: EUROfusion
The successful experiment is the culmination of the OP2.1 campaign, which began after significant upgrades to the device's water-cooling systems and plasma-facing components. These enhancements were designed to enable higher heating power and longer pulse durations, targeting half-hour discharges at lower densities. While this record was set in a shorter, high-power pulse, the operational experience gained is directly applicable to the long-term goal of demonstrating steady-state operation. Researchers at the Max Planck Institute will now focus on analyzing the vast dataset from this discharge to further refine plasma control techniques and prepare for future experiments aimed at pushing both performance and duration. The results are currently being prepared for submission to a peer-reviewed journal. Source: EUROfusion