Early machines Pinch devices were among the earliest efforts in fusion power. Research began in the UK in the immediate post-war era, but a lack of interest led to little development until the 1950s. The announcement of the
Huemul Project in early 1951 led to fusion efforts around the world, notably in the UK and in the US (see
Perhapsatron, a z-pinch machine at
LANL). Small experiments were built at labs as various practical issues were addressed, but all of these machines demonstrated unexpected instabilities of the plasma that would cause it to hit the walls of the container vessel. The problem became known as the "
kink instability".
Stabilized pinch By 1953 the "stabilized pinch" seemed to solve the problems encountered on earlier devices. Stabilized pinch machines added external magnets that created a toroidal magnetic field inside the chamber. When the device was fired, this field added to the one created by the current in the plasma. The result was that the formerly straight magnetic field was twisted into a helix, which the particles followed as they traveled around the tube driven by the current. A particle near the outside of the tube that wanted to kink outward would travel along these lines until it returned to the inside of the tube, where its outward-directed motion would bring it back into the centre of the plasma. Researchers in the UK started construction of
ZETA in 1954. ZETA was by far the largest fusion device of its era. At the time, almost all fusion research was classified, so progress on ZETA was generally unknown outside the labs working on it. However US researchers visited ZETA and realized that they were about to be outpaced. Teams on both sides of the Atlantic rushed to be the first to complete stabilized pinch machines. ZETA won the race, and by the summer of 1957 it was producing bursts of
neutrons on every run. Despite the researchers' reservations, their results were released with great fanfare as the first successful step on the path to commercial fusion energy. However, further study soon demonstrated that the measurements were misleading, and none of the machines were near fusion levels. Interest in pinch devices faded, although ZETA and its cousin
Sceptre served for many years as experimental devices.
Fusion-based propulsion A concept of Z-pinch fusion propulsion system was developed through collaboration between
NASA and private companies. The energy released by the Z-pinch effect would accelerate lithium propellant to a high speed, resulting in a
specific impulse value of 19400 s and
thrust of 38 kN. A magnetic nozzle would be required to convert the released energy into a useful impulse. This propulsion method could potentially reduce interplanetary travel times. For example, a mission to Mars would take about 35 days one-way with a total burn time of 20 days and a burned propellant mass of 350 tonnes. In 2018, a sheared-flow stabilized Z-pinch demonstrated neutron generation. It was built by a fusion company,
Zap Energy, Inc., a
spin-off from the
University of Washington, and funded by strategic and financial investors and grants from the Advanced Research Projects Agency – Energy (
ARPA-E). Flow stabilized plasma remained stable 5,000 times longer than a static plasma. A mix of 20% deuterium and 80% hydrogen by pressure, produced neutron emissions lasting approximately 5 μs with pinch currents of approximately 200 kA during an approximately 16 μs period of plasma quiescence. Average neutron yield was estimated to be (1.25±0.45)×105 neutrons/pulse. Plasma temperatures of 1–2 keV (12–24 million °C) and densities of approximately 1017 cm−3 with 0.3 cm pinch radii were measured.
Companies , at least two companies are pursuing magneto-inertial z-pinch fusion reactors, both fueled by
deuterium–
tritium reactions, and in the United States: Magneto Inertial Fusion Technology Inc. (MIFTI), founded in 2008, as a
spin-off of the
University of California, Irvine, and now a division of
US Nuclear Corp, and
Zap Energy, founded in 2017, as a
spin-off of the
University of Washington. ==Experiments==