When Japan, in late 2023, announced a new national fusion energy program coordinating several government agencies, its strength was clearly going to be in building “infrastructure” for international fusion R&D, such as test beds, machine prototypes, diagnostics, superconduction capacity, etc. Japan already operates one of the larger fusion test devices in the world, the Large Helical Device (LHD) operated by the National Institute for Fusion Science at Toki, which is the world’s second-largest superconducting stellarator, after the Wendelstein 7-X at the Max Planck Institute for Plasma Physics in Greifswald, Germany.
Phys.org reported on Jan. 26 that a research group is testing on the LHD, a new system of control of plasma temperature and density called “digital twin.” This system aims at a major problem in fusion experiments—assessing from the inadequate measuring devices and equipment, precisely what happens to the plasma during the experiment. The digital-twin technique is complex to explain, and is mathematical rather than physical; but it is intended, essentially, to perform extremely high-speed simulations along with the plasma experiment, looking for and building up points where the two agree, to create a simulation which actually shows what the plasma is doing.