Aneutronic Fusion 2: Creating An Artificial Star

To feed, house and educate our growing population humanity must develop a better way to produce energy. In last week’s lesson on the Astrophysics of Fusion we learned that the strong nuclear force holds nuclei together but is very short range. Since all nuclei in regular matter have a positive charge from their protons… and the electromagnetic force is long range… like charges repel and the nuclei are pushed apart. The core of a star has enough pressure and heat to overcome this repulsion and the strong nuclear force takes over. This is how stars produce energy… through the fusion of lighter elements into heavier ones. These reactions produce a LOT of energy. Stars can do this because their incredible mass creates extremely high pressure and temperature in their core. We can’t reproduce this method of fusion energy here on Earth. We can’t accumulate that much mass… and it would be hard to fit it into our cars and spaceships. We need a better way. Fusion energy has been the dream of humanity since we figured out that our sun was not a giant ball of gasoline around the turn of the 20th century. We described how protons fuse to diprotons with on of the protons sometimes decaying into a neutron creating deuterium. The deuterium will fuse with another proton making helium 3 which combines with another helium 3 to produce helium 4 and eject two protons. This is the only method of fusion readily available to the sun and all stars early in their lives… because they are made mostly of protons with a little helium 4. Nuclear scientists learned early on that if they wanted to produce fusion, they would have to do it another way. But understand that fusion is not that hard to accomplish in the laboratory. In many ways fusion was easier than fission. The first particle accelerators were really charged energy particle beams. Strip electrons from an atom, put a large negative charge behind them and watch them speed away. Put a large positive charge behind your target and have everything in a vacuum and you have an effective particle gun. These early guns became the first vacuum tubes and were used in televisions and computer displays for almost half a century. Now let’s do the same thing with protons…as Professor Ernest Walton did in April 1932 at the Cavendish Laboratory in Cambridge University. We should all know this man’s name since he was the first to accomplish artificial fission. He used this device to slam protons into lithium atoms producing fission and causing helium 4, also known as alpha particles, to be produced. Think about this…he artificially turned one element into another. Something alchemists had been trying to do for millennia and thought by many scientists at that time to be impossible. But that was not enough of an accomplishment for this lab. In the 1920s theoretical scientists like Einstein, Aston, Eddington, and others had elucidated the process behind the nuclear fusion that powers the stars. Professor Mark Oliphant later decided to fire deuterium or heavy hydrogen at a target and at each other. This resulted in the formation of tritium and helium three, both of which he discovered. This was the first example of artificial fusion being accomplished. If fusion was relatively easy way back in the 1930s then why are we still struggling with it today? The terribly difficult thing about fusion is not how to do it… but how to make it efficient…to get out more energy than you have to put in. Why is that so hard?... I held a little back in our last discussion. If fusion worked by just slamming particles together hard enough to overcome the electromagnetic repulsion between the positively charged nuclei the temperature at the core of stars would have to be 40 million kelvin. But that is not what we observe.

Credit:
NASA
Max Planck Institute for Plasma Physics
ITER
General Fusion
General Atomics
Seeker
First Light Fusion
https://spectrum.ieee.org/energy/nuclear/5-big-ideas-for-making-fusion-power-a-reality
https://www.quantamagazine.org/physicists-finally-nail-the-protons-size-and-hope-dies-20190911/

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