keV is the kiloelectronvolt, the working temperature unit of plasma physics, where 1 keV corresponds to roughly 11.6 million degrees Celsius.
The unit is borrowed from particle physics. An electronvolt is the energy an electron gains crossing one volt of electric potential; a kiloelectronvolt is a thousand of them. Plasma physicists quote a 📝plasma's temperature as the characteristic thermal energy of its particles, which turns an unwieldy figure in kelvins into a small, workable number: 1 eV corresponds to about 11,605 kelvin, so 1 keV is about 11.6 million kelvin — indistinguishable from Celsius at that scale.
The same unit also measures particle and photon energies — an X-ray's energy is quoted in keV — so context decides whether a given keV is a temperature or an energy; in 📝fusion writing it is almost always a temperature. The numbers worth carrying: the sun's core sits near 1.3 keV, about 15 million degrees Celsius, while a magnetically confined fusion plasma must reach 10 to 20 keV — on the order of 150 million degrees, roughly ten times hotter than the center of the sun — because a reactor cannot rely on the sun's enormous density and gravitational patience.