New research could open up another viable pathway to fusion energy, the process that powers the stars and creates their heat and light emissions.
Scientists have detected neutrons created by thermonuclear reactions in a device theorized since the 1930s.
New research led by scientists from the Lawrence Livermore National Laboratory (LLNL), may solve a decades-old problem and show that so-called Sheared Flow Stabilized Z-pinch devices (a method of manipulating plasma a vital element of nuclear fusion) could be cured of the instabilities that disrupt fusion reactions.
The team used advanced computer modeling techniques and diagnostic measurement devices to show a sheared-flow stabilized Z-pinch device was creating neutrons as a side effect of thermonuclear reactions like those that power the stars—rather than from undesired instabilities in plasmas.
This could show these devices have the ability to generate the high-temperature conditions required to create plasma and initiate fusion within it, providing a new viable pathway to fusion power, if of course researchers can now get more energy out of them than it takes to kick start reactions.
LLNL physicist Drew Higginson is one of the co-authors of a paper Plasma Physics that discusses the team's work. He said in an LLNL press release: "This is direct proof that thermonuclear fusion produces these neutrons and not ions driven by beam instabilities.
"It's not proven they're going to get energy gain, but it is a promising result that suggests they are on a favorable path."
Bringing the Stars Down to Earth
In stars such as our Sun the conditions needed to push together atoms of hydrogen and trigger nuclear fusion that transforms them into helium, thus releasing the difference in mass as energy, are generated by the stellar body's intense gravitational influence.
Because this gravitational effect can't be replicated here on Earth, devices that attempt to replicate the fusion process must generate plasmas at temperatures many times that found even at the center of the Sun.
This superheated plasma must be contained in these "artificial suns" or tokamaks using incredibly powerful magnetic fields.
Z pinch machines accomplish fusion using a powerful magnetic field to confine and "pinch" the plasma, creating the conditions needed for fusion. Sheared-flow stabilized Z-pinch devices, rather than using powerful and stabilizing magnetic fields to provide this pinch, use pulsed electrical currents to create a magnetic field in a column of plasma that reduces instabilities.
Higginson said: "The problem with instabilities is that they don't create a viable path to energy production, whereas thermonuclear fusion does. It's always been tricky to diagnose this difference, especially in a Z-pinch."
As part of the University of Washington's Fusion Z-Pinch Experiment (FuZE) project, the team measured neutron emissions that were created during the fusion process.
They found that as the radius of FuZE cylinder was narrowed to increase compression, it created dips in the plasma that generated much stronger magnetic fields. This caused the plasma to pinch inwards more in certain spots than in others.
These instabilities created beams of faster ions which in turn produced neutrons that could be confused with desired neutrons created by thermonuclear processes. Placing detectors outside of the device allowed the team to measure neutrons just microseconds after they emerged from the Z-pinch chamber at different angles and at a variety of points.
The team found emitted neutron energies were equal at different points around this device, something which is indicative of thermonuclear fusion reactions.
The experiments will now continue with more detailed measurements taken by 16 detectors and conducted by a privately funded Seattle startup named Zap Energy
Higginson concluded: "We want to be involved because we don't know what surprises might arise.
"It could turn out that as you go to higher current, all of a sudden you start driving instabilities again. We want to be able to prove as the current goes up that it is possible to maintain a high quality and stable pinch."
