Europe is widely regarded as the global leader in stellarator research and reactor development, thanks to decades of sustained investment and the operation of world-leading experimental devices such as Germany’s Wendelstein 7-X and Spain’s TJ-II. Within the European Fusion Program, first through EFDA (European Fusion Development Agreement) and later through EUROfusion, fusion laboratories across Europe have built the scientific foundation and the collaborative framework on which optimized stellarator development now rests. Additionally, the success of the HELIAS line of stellarators – exemplified by Wendelstein 7-X, developed at IPP Greifswald with strong European collaboration – has led to increased interest in new devices based on next-generation designs.
CIEMAT’s National Fusion Laboratory has taken part in this European effort over the last decades. This long-standing collaboration allowed its scientists to participate in cutting-edge research at home and in other European experiments, and to develop the expertise and capabilities required to design and build a reactor-relevant stellarator. TJ-II in particular has played an important role in advancing stellarator physics and magnetic confinement research in Europe.
Building on this foundation, scientists at CIEMAT achieved two results that made a reduced-scale reactor study possible. First, they obtained optimized stellarator configurations that reach the confinement quality required for a fusion reactor. Second, they established rigorous principles of geometric and dynamic similarity to determine the parameters of a reduced-scale device capable of accurately predicting the behaviour of a full-size reactor.
Together, these results define the WISER (WInd-tunnel for a StEllarator Reactor) concept: a device much smaller and less costly than a full-scale fusion reactor while still providing highly reliable information about reactor performance. This approach is intended to reduce the financial, scientific, and technological risks associated with the future design and construction of commercial stellarator fusion reactors.
On this basis, Spain has just launched Project WISER. On 30 April 2026, the Spanish Minister of Science, Innovation and Universities, Diana Morant, officially announced the project, an investment of approximately €500 million that is the result of an alliance between CIEMAT, the Centre for Technological Development and Innovation (CDTI) and the company Técnicas Reunidas. Project WISER includes both the construction of the WISER stellarator and the development of enabling technologies required for future fusion reactors. WISER continues a long trajectory at CIEMAT’s National Fusion Laboratory, where it will become the fourth fusion machine developed by the institution after TJ-I, TJ-IU, and TJ-II.
Within this European context, WISER represents a further step in strengthening Europe’s leadership in optimized stellarator research and future reactor development. The project also reinforces collaboration between major European fusion laboratories and aligns with a growing ecosystem of private companies investing in stellarator technologies as a promising pathway toward commercial fusion energy. It is also expected to stimulate the development of high-tech, high added-value industrial capabilities in Europe, particularly in areas such as superconducting technologies, advanced manufacturing, precision engineering, and plasma-related systems. Together, these efforts contribute to an increasingly dynamic international fusion landscape combining public research institutions, industrial partners, and emerging technology developers.
Although the primary focus of WISER is the advancement of stellarator reactor technology, the project will also benefit from its proximity to IFMIF-DONES, the international neutron irradiation facility currently under construction in Granada. The coexistence of both initiatives contributes to a broader Spanish research environment that combines reactor design, plasma physics, and materials testing capabilities necessary for the future deployment of fusion energy.
As international competition in advanced energy technologies continues to intensify, projects such as WISER highlight the importance of sustained scientific cooperation and long-term investment in fusion research. More broadly, the initiative reflects Europe’s continuing effort to maintain a leading role in the development of technologies that could play a central role in the future global energy system.