Germany's Wendelstein 7-X (W7-X) stellarator, located at the Max Planck Institute for Plasma Physics (IPP) in Greifswald, has commenced its second major operational phase (OP2). This new campaign follows a multi-year shutdown for significant hardware upgrades, most notably the installation of a water-cooled divertor system. The primary objective of this phase is to demonstrate the device's capability to sustain high-performance plasmas for extended durations, a critical step in validating the steady-state potential of the stellarator concept. The initial experiments in this new run aim to progressively increase plasma energy and duration, building on the successes of the previous operational phase which concluded in 2018. Source: IEEE Spectrum

The centerpiece of the upgrade is the new divertor, composed of 120 water-cooled modules designed to handle heat fluxes up to 10 MW per square meter. This system is essential for managing the intense heat exhausted from the plasma edge during long-pulse operations. Without active cooling, plasma durations were limited to approximately 100 seconds. The upgrade also included enhancements to the plasma heating systems, which can now deliver a total of 18 MW of power into the plasma. These combined improvements are engineered to enable W7-X to confine a plasma with a total energy content exceeding 1 gigajoule for the first time, a key performance metric for the program. Source: IEEE Spectrum

The centerpiece of the upgrade is the new divertor, composed of 120 water-cooled modules designed to handle heat fluxes up to 10 MW per square meter.

Prior to the shutdown, W7-X had already achieved significant results, including a record ion temperature of 40 million kelvins and a confinement time of 200 milliseconds, resulting in a fusion triple product of 6 x 10^26 kelvin-seconds per cubic meter. While impressive for a stellarator, these achievements were in short-pulse scenarios. The new campaign's focus shifts from peak transient performance to sustained, steady-state operation. Researchers will test the stability and confinement properties of the optimized magnetic field configuration over timescales relevant to a future power plant, a distinct operational challenge compared to the pulsed nature of most tokamak experiments. Source: IEEE Spectrum

The operational plan for the coming months involves a cautious, phased approach. Initial plasma shots will be short, allowing physicists and engineers to commission the new hardware and integrated control systems. As confidence in the system's performance grows, the duration and heating power will be incrementally increased. The ultimate goal of OP2 is to achieve 30-minute discharges, which would demonstrate a level of plasma control and heat management unprecedented in a stellarator device. This would provide critical data for the design of next-generation stellarators and bolster the concept's viability as an alternative to tokamaks for commercial fusion energy. The results will be closely watched by the global fusion science community. Source: IEEE Spectrum