Nuclear Fusion 129 - Pros And Cons Of Four Types Of Nuclear Fusion Reactors - Part 5 of 5 Parts


University of Washington Z-pinch experiment

Part 5 of 5 Parts (Please read Parts 1, 2, 3 and 4 first)
     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."

Geiger Readings for Apr 09, 2021

Latitude 47.704656 Longitude -122.318745

Ambient office = 72 nanosieverts per hour

Ambient outside = 88 nanosieverts per hour

Soil exposed to rain water = 90 nanosieverts per hour

Blueberry from Central Market = 100 nanosieverts per hour

Tap water = 115 nanosieverts per hour

Filter water = 98 nanosieverts per hour

Nuclear Fusion 128 - Pros And Cons Of Four Types Of Nuclear Fusion Reactors - Part 4 of 5 Parts

inertial confinement.jpg

Diagram of inertial confinement

Part 4 of 5 Parts (Please read Parts 1, 2 and 3 first)
Inertial Confinement
     While the tokamaks and stellarators make great use of powerful magnets, they are not the only experimental fusion reactors. Inertial confinement fusion reactors utilize precisely targeted lasers or ion beams to rapidly heat up a solid pellet of fuel usually made up of deuterium and tritium. These fuel pellets are about the size of a pinhead and they contain about ten milligrams of fuel.
      The basic concept of inertial confinement is that the sudden and intense heat applied to the fuel pellet would cause tremendous compressive forces that would trigger a chain reaction through the layers of material in which nuclear fusion can take place and release huge amounts of energy.
      The first mention of inertial confinement was at an international conference called Atoms for Peace in Geneva, Switzerland in 1957. In the late 1950s, John Nuckolls at the Lawrence Livermore National Laboratory (LLNL) ran a number of computer simulations of the implosion of a pellet of fuel. His results indicated that inertial confinement could be much more efficient than heating a plasma enough to allow fusion. In 1967, a Soviet researcher named Gurgen Askaryan published an article suggesting the use of lasers to heat a pellet of fuel for fusion. Friedwardt Winterberg, a German Physicist proposed in 1968 the use of electron and ion beams to vaporize a pellet of fuel.
      Serious research into the design and construction of an inertial confinement fusion reactor began in the 1970s with the arrival of lasers that were sufficiently powerful. The LLNL began work on its Janus reactor design in 1974. Following a great deal of work on the use of lasers to trigger fusion, the LLNL started the construction of the National Ignition Facility (NIF) in 1997. The NIF was completed in 2009. In 2018, the NIF announced reaching a record production of fifty-four kilojoules of fusion energy output. The most recent development for inertial confinement is what is called “fast ignition”. In fast ignition, lasers first subject the fuel pellet to compression and then an extremely short and powerful laser pulse heats the pellet.
     While deuterium/tritium has been the fuel of choice for inertial confinement, HB11 Energy is working on a new approach involving hydrogen and boron-11 for the fuel pellet. Using the fast ignition process, the hydrogen-boron fusion creates charged particles which can be used to generate an electrical current. This current can be fed into the nation electrical grid. The company is very excited by its novel approach and says that experiments returned much great reaction rates that were predicted by computer simulations. They believe they can construct a working nuclear fusion power reactor much sooner than and of the other approaches.
      Matthew Hole is a nuclear fusion expert and research fellow at Australian National University. He said, “It is interesting science. But I wouldn't say there is credible evidence to suggest you could turn that into a power plant on a timescale faster than ITER or toroidal magnetic confinement. In my mind, there are even more challenges. If I fire a bunch of lasers at a target and the whole thing is over in a nanosecond, that is a pulsed experiment. To repeat it, I put the target back in place and I put the wires back in place, because I blew the whole thing up, it is gone. The question is how do you translate something that is intrinsically pulsed into something that is intrinsically steady state? In the case of these experiments, you'd need to go from one pellet a week, to 10 pellets a second."
Please read Part 5 next