Model B-640

Model B-640 was the Model B-64 reassembled in a race-track geometry (represented in the 0) for an experimental campaign in 1956. In this new geometry, the rotational transform was zero and a strong ohmic heating was used. Even though it was not realized at that moment, that characteristic made the device a tokamak and not a stellarator. For this reason the B-640 is considered the first tokamak in the United States.