The thermal energy of fusion plasma particles, measured in electron-volts — fusion requires ion temperatures of 10–20 keV (100–200 million degrees), hotter than the core of the Sun.
Plasma temperature quantifies the average kinetic energy of plasma particles. Fusion physicists measure temperature in electron-volts (eV) rather than degrees: 1 eV = 11,604 K. Fusion-relevant ion temperatures are 10–20 keV, corresponding to 100–200 million degrees Celsius — roughly 10 times hotter than the centre of the Sun.[1]
In a fusion plasma, ions and electrons can have different temperatures. For optimal D–T fusion, high ion temperature (Ti) is what matters, since ions are the particles that fuse. Electrons tend to radiate energy away (bremsstrahlung), so high electron temperature (Te) increases radiation losses. Heating methods that preferentially heat ions (NBI, ICRH minority heating) are therefore advantageous.[2]
KSTAR achieved sustained temperatures above 100 million degrees (8.6 keV) for 30 seconds in 2024. JT-60U achieved ion temperatures above 45 keV (520 million degrees) transiently. The current world record for sustained ion temperature is held by EAST and KSTAR.[3]