Thermonuclear fusion is a powerful process that powers the stars. The nuclei of lighter atoms fuse into heavier ones, releasing large amounts of energy. Since the mid-20th century, scientists have been trying to master this process as an energy source on Earth. Deuterium-tritium fusion was chosen, with an ignition temperature of about 150 million kelvin. Many approaches to confining hot plasma have been tried. Two major ways are magnetic confinement (tokamaks and stellarators) and inertial confinement (laser-driven fusion). Fusion has been achieved many times, but ignition was first reached in 2022 by laser fusion at NIF. ITER, the biggest tokamak being built, is expected to start research operation in 2034.