DIII-D is a tokamak that has been operated since the late 1980s by General Atomics (GA) in San Diego, California, for the United States Department of Energy.

The mission of the DIII-D Research Program is to establish the scientific basis for the optimization of the tokamak approach to fusion energy production.

DIII-D is one of two large magnetic fusion experiments in the U.S. (the other being NSTX-U at Princeton Plasma Physics Laboratory) supported by the U.S. Department of Energy Office of Science.

ITER is designed to demonstrate a self-sustained burning plasma that will produce 10 times as much energy from fusion reactions as it requires for heating.

The plasma is heated to temperatures ten times hotter than that of the sun by a combination of high-power neutral beams and microwaves.