W7-X, in operation since 2015 in Greifswald, Germany, Germany, is the largest, most advanced stellarator ever constructed and was designed to demonstrate steady-state reactor-relevant operation. The confining magnetic field is provided by a set of 50 computer-designed non-planar superconducting coils and does not require a plasma current.
The tokamak is the most common fusion research device. The confining magnetic field is generated by currents flowing in the toroidal field coils and, superimposed on this, a smaller field due to a transformer-induced current flowing in the plasma itself. At fusion temperatures, the plasma conducts current as freely as copper.
Since 1983, JET has been the largest operating tokamak in the world - the human figure on the lower left of the image above gives a sense of the scale of the device! It holds many world records for the best fusion parameters achieved, including that for the most fusion power created in a plasma.
These two photos show an inner view of the ASDEX Upgrade tokamak at the Max-Planck-Institut für Plasmaphysik in Garching, Germany. The Plasma Data Analysis Group at UCC has a long-standing collaboration with this institute involving work on the ASDEX and ASDEX Upgrade tokamaks and the W7-AS and W7-X stellarators. The left-hand photo shows an engineer inspecting the inner wall of ASDEX Upgrade during a maintenance phase, the other shows the experiment during an actual plasma discharge, captured on CCD camera.