Part 5 of 5 Parts (Please read Parts 1, 2, 3 and 4 first)
Z-pinch
     There are other approaches to inertial confinement besides laser implosion. One of these is known as the Z-pinch. Instead of using complex and powerful external magnets to compress and confine plasma, a Z-pinch reactor uses electromagnetic fields that are generated within the plasma itself. Since the 1950s, Z-pinch has been considered somewhat of a dark horse in fusion research because it has promised but not delivered a much simpler configuration than tokamaks or stellarators. However, like those other inertial confinement fusion reactor types, Z-pinch is prone to serious instabilities in the plasma which escapes from the magnetic field lines and forms problematic bulges.
     The name “Z-pinch” refers to the direction of the current in the fusion reactor on a three-dimensional graph. There are many different devices that employ such a directed current. They are used for many applications. The original version of an experimental Z-pinch fusion reactor used a donut-shaped reaction vessel with the current running down the inside of the donut. Now Z-pinch fusion reactors are usually cylinders.
     The Z-pinch makes use of a principle called the Lorentz force which causes current carrying wired to pull together. In the case of the Z-pinch, there is a plasma instead of a set of physical wires. The current causes the particles to attract each other. The magnetic field induced into the plasma must be varying. The current in these devices is provided by a big bank of capacitors and triggered by a spark gap called a Marx generator.
     Z-pinch fusion reactors were some of the earliest attempts to produce nuclear fusion. Research began just after World War II. But development did not really take off until the 1950s. All of these early reactors had problems with instability in the plasma referred to as the “kink instability.” By 1953, the Z-pinch reactors had managed to solve the problem of instabilities. External magnets were added to the design which converted the current path into a helix that stabilized the plasma.
     In 1954, researchers in the U.K. began the construction of the Zero Energy Thermonuclear Assembly (ZETA). This project stimulated an explosion of Z-pinch research projects. By 1957, Z-pinch reactors were generating neutrons. However, further studies showed that the neutron readings were misleading and none of the devices were anywhere near producing fusion reactions. Interest waned and researchers turned to other approaches to fusion. Z-pinch machines such as ZETA continued to serve as experimental devices for many years.
     In 2019, researchers at the University of Washington managed to find a way to smooth out the plasma bulges by modifying the fluid dynamics of the plasma. In a twenty-inch X-pinch column, the U of W team was able to maintain flowing plasma five thousand times longer than previous static plasma designs. They observed energetic neutrons that they say is a sign of nuclear fusion. Like the HB11 laser approach, Z-pinch reactors are pulsed devices, and the challenge is to convert them to continuous operation. Matthew Hole is a nuclear fusion expert and research fellow at Australian National University. He said, “The Z-pinch is an intrinsically pulsed, they implode a set of wires. It’s not going to be intrinsically steady state.”