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The X-point target radiator is created by adding an additional X-point at the bottom of the TCV vessel. The image on the left shows spectral imaging data of a conventional divertor, with emission extending all the way to the floor. On the right is the X-point target divertor, illustrating the radiative second X-point. Credit: SPC\/EPFL.<\/p>\n
Nuclear fusion reactors are highly powerful technologies that can generate energy by fusing (i.e., joining) two light atomic nuclei to form a heavier nucleus. These fusion reactions release large amounts of energy, which can then be converted into electrical power without emitting greenhouse gases.<\/p>\n
One of the most reliable and promising fusion reactor designs is the so-called tokamak. Tokamaks are devices that use a doughnut-shaped magnetic field to confine and heat plasma (i.e., superhot, electrically charged gas) for the time necessary for fusion reactions to take place.<\/p>\n
Despite their potential for the generation of large amounts of clean energy, future reactor tokamaks may face huge challenges in managing the intense heat produced by fusion reactions<\/a>. Specifically, some of the confined plasma can interact with the walls of the reactors, damaging them and adversely impacting both their durability and performance.<\/p>\n Researchers at the TCV tokamak experiment at \u00c9cole Polytechnique F\u00e9d\u00e9rale de Lausanne (EPFL) recently discovered a new form of plasma radiation that could prevent tokamaks from overheating, allowing them to shed excess heat and thus potentially boosting their performance over time.<\/p>\n The new solution they proposed, which they dubbed X-point target radiator (XPTR), was introduced in a paper<\/a> published in Physical Review Letters.<\/p>\n “Reducing divertor heat loads is a key challenge for future fusion power plants,” Kenneth Lee, first author of the paper, told Phys.org.<\/p>\n “One promising approach, the X-point radiator, dissipates plasma energy near the X-point, but scalability is uncertain due to its proximity to the core. We investigate experimentally the effect of adding a secondary X-point along the divertor channel to broaden operational range and maintain core plasma confinement\u2014a concept known as the X-point target divertor.”<\/p>\n In tokamaks, an X-point is a location where magnetic field lines<\/a> run purely toroidally, which is central in shaping the plasma and guiding heat away from the core via a narrow magnetic funnel known as a “divertor.” X-point radiators are plasma operating conditions which convert a large fraction of the plasma heat into uniform radiation in proximity to the X-point.<\/p>\n In their paper, Lee and his colleagues perform experiments on introducing another X-point along the divertor, which is located outside of the zone in which the plasma is confined. Adding this secondary X-point could further support the removal of excess heat, thus preventing damage to the tokamak and enhancing its durability.<\/p>\n “We leverage TCV tokamak’s unique magnetic shaping flexibility to introduce a secondary X-point, and we discovered localized radiation (the ‘XPTR’) far from the plasma core, which preserves core performance while significantly reducing divertor heat loads,” explained Lee.<\/p>\n “We found that the X-point target radiator is highly stable and can be sustained over a wide range of operational conditions, potentially offering a much more reliable method for handling power exhaust in a fusion power plant.”<\/p>\n In initial tests, the approach introduced by the researchers was found to perform remarkably well, removing excess heat from magnetically confined plasma<\/a> more effectively than conventional setups.<\/p>\n This newly explored X-point target configuration is set to be implemented in next-generation tokamak devices that are being developed by Commonwealth Fusion Systems in collaboration with Massachusetts Institute of Technology (MIT).<\/p>\n “We are now conducting new high-power experiments to explore the parameter range of the X-point target radiator, complemented by state-of-the-art numerical simulations<\/a> to better understand its underlying physical mechanisms,” added Lee.<\/p>\n “The next-generation tokamak<\/a>, SPARC, plans to incorporate the X-point target divertor into its baseline design, making our findings timely and crucial.”<\/p>\n