A method of compressing plasma using an electric current that runs down the axis of the device (e.g., a cylinder filled with gas) while the magnetic field is azimuthal. It uses the pinch effect, where the plasma column is compressed by the Lorentz force. The first device to use the Z-pinch was the Perhapsatron, built in 1953 at LANL. Because of minor inhomogeneities in the compressed gas, the resulting plasma column was prone to instabilities (called kink instability and sausage instability) — areas of higher density were compressed more, resulting in regions of even higher density. Because of the instabilities, the discharge could not be sustained long enough and fusion was not achieved. The theta pinch concept, which avoided the current flowing through the plasma, was supposed to eliminate the problems. The theta pinch was named after the direction in which the current flowed in the plasma, and devices previously referred to as “pinch” were retroactively renamed “Z-pinch” to distinguish them.