South Korea’s KSTAR sustains 100 million°C plasma for 102 seconds

South Korea’s KSTAR did something fusion people actually care about: it held a 100 million°C plasma together for 102 seconds, not just long enough to flash a headline, but long enough to show the machine is getting better at the hard part, keeping a tokamak stable while it is being cooked from the inside.

That temperature is hotter than the Sun’s core, but the real significance was duration in high-confinement mode, or H-mode, the operating state tokamaks need for long-pulse, reactor-relevant plasma. During the same 2023 to 2024 campaign, KSTAR also sustained 100 million°C plasma for 48 seconds, beating its own 30-second record from 2021. The 102-second run was achieved between December 2023 and February 2024 at the Korea Institute of Fusion Energy’s KSTAR device in Daejeon, South Korea.

The breakthrough was tied to a new tungsten divertor installed in December 2023. KFE credited the tungsten hardware with helping the machine survive the longer discharge, and the temperature data backs up that claim: the divertor’s thermocouple readings varied by less than 15°C during the 102-second pulse. That kind of thermal steadiness matters because the divertor is where the exhaust heat and particle load land first, and carbon was never going to be the long-pulse answer. KSTAR also kept key plasma-shape variables within a maximum error of 2 cm, which is the kind of control margin that separates a clean physics run from a messy one.

The discharge ran at 400 kA plasma current, 1.95 T toroidal magnetic field, 3.9 MW of neutral-beam heating, and 1.1 MW of electron-cyclotron heating. Core electron temperature stayed above 6.0 keV, core ion temperature was around 2.5 keV, and core electron density sat near 3.0 × 10^19 m^-3. Those numbers show a disciplined confinement experiment, not a power plant. They do not yet solve the central fusion problem: making the plasma produce more energy than the machine consumes, continuously, while surviving neutron damage, heat exhaust, and component wear.

That is why this result matters as a reality check, not a victory lap. KSTAR was built with domestic technology to serve as a testbed for ITER-relevant long-pulse scenarios, and its leadership says the next target is 300 seconds at 100 million°C by 2026. KFE is also pushing toward all-tungsten inner-wall components and AI-based real-time feedback control. For ITER in Cadarache, France, and for any future fusion demonstration reactor, the lesson is simple: the field is still learning how to hold the fire, not yet how to sell the electricity.