Setting up nuclear fusion with 12 beams, GEKKO XII at the University of Osaka ILE

Fusion fuel of about 1 mm in diameter is placed in a spherical stainless-steel vacuum vessel with a 1-meter radius, and 12 laser beams are irradiated from directions perpendicular to each face of the dodecahedron to compress the fuel uniformly and increase the density to set it up. This is rapidly heated by instantaneously irradiating a separately generated laser beam to cause a highly efficient nuclear fusion ignition reaction. This is the laser fusion system "GEKKO XII" at the Institute of Laser Engineering, the University of Osaka.

Nuclear fusion is the reaction that occurs in the sun. When the fuel components - deuterium and tritium - are fused under high temperature and pressure, they form helium-4 (two protons) and a neutron, and the mass difference before and after the reaction is converted into enormous amounts of energy.

Laser fusion is a method that rapidly increases the density of the fuel in a very short time. It stands alongside magnetic confinement approaches, such as the large international project ITER (International Thermonuclear Experimental Reactor), an experimental reactor currently under construction in France, and the Large Helical Device at the National Institute for Fusion Science in Toki, Gifu, Japan. These systems gradually heat the fuel into a plasma state in which fusion reactions can occur and then confine it using magnetic fields.

According to Director Ryosuke Kodama, who specializes in plasma science at the University of Osaka ILE, laser fusion, which directly irradiates fuel to compress it and initiates central ignition at peak compression, requires laser beams to be distributed uniformly around the fuel. To achieve more uniform irradiation, the institute has progressively increased the number of laser beams, from two in Gekko II (1974) to four in Gekko IV (1977), and eventually to the current Gekko XII system. However, this still does not match the 60-beam system in the United States. Even with 60 beams, irradiation non-uniformities remain, making it difficult to achieve stable fusion reactions.

A turning point came in 2001. Kodama discovered that dividing the process into two stages, fuel compression and ignition, makes it easier to induce fusion reactions. "To use a familiar analogy, it is like a gasoline engine, where air and fuel are compressed and then ignited by a spark plug to create an explosion that moves a piston," he explained. The long-term goal is to build a fusion reactor about the size of a school gymnasium and place it next to a data center.