The principle of compressing a plasma by an electric current so that the electric field is in the azimuthal direction of the device (e.g., a cylinder filled with gas) while the magnetic field runs down the axis. The theta pinch device consists of a flat copper conductor wrapped around a tube containing gas. A sharp increase in current in the conductor induces an axial magnetic field which heats and compresses the plasma. Because the compression is induced by electromagnetic fields acting at the edges of the plasma, the electric current that was the source of the strong instabilities in the Z-pinch does not flow through the plasma centre. The first device to successfully achieve thermonuclear fusion of deuterium atoms using the theta pinch was Scyla I, built in 1958 at Los Alamos.