Fusion
Currently there is much discussion about the energy security of not just the United States but the world. This includes not just our access to energy but also its impact on the environment. The use of fossil fuel-based energy has changed over the last 20 years, but in many ways, it has also remained the same. Though coal use has decreased natural gas use has increased and oil usages still remains the largest use of energy. Renewables are growing but their overall impact on the energy market remains low. Ultimately to replace fossil fuels with reliable base load power that we can access all the time, nuclear technology will have to grow. This includes not only fission in the short to medium term but also nuclear fusion in the medium to long term!
Nuclear Fusion is one of the most fundamental energy processes in the universe. In fact, all matter on earth can be traced back to being formed through this process either in the heart of a star or in a supernova. At its most fundamental level, fusion takes two light ions (for example isotopes of hydrogen, deuterium and tritium), forces them together i.e. fusing of fusion, and the resulting daughter ions that are created are usually heavier and carry the released energy. For example, the Sun has a series of fusion reactions called the proton-proton (p-p) chain (note: a proton is just a hydrogen ion):
Where: H is hydrogen, D is deuterium, ν is a neutrino, e+ is a positron, γ gamma photon, 4He is helium and 3He is the helium-3 isotope.
Here on Earth, we don’t not have the advantage the sun has when it comes to confining and forcing these ions to fuse, namely gravity. Thus, we need to find a different trick to do fusion. This is to use magnetic fields to confine the plasma and heat it up through various means and the fuel rather than being hydrogen is two isotopes of hydrogen, deuterium (D) and tritium (T):
There are two by-products made from the reaction, helium and a neutron. 20% of the energy is carried by the helium ion (or alpha, α, particle since it’s a helium ion with a +2 charge on it, He+2) and the other 80% is carried by the neutron. Ultimately the α-particle goes back into the plasma to keep heating it while the neutron can be captured to produce the electric it that is needed.
Ultimately despite what fusion offers in terms of putting reliable, clean and affordable electricity on the grid the technological challenges that are faced are probably the greatest that humanity have ever faced, greater than even putting a man on the moon!
Why Lithium
Why does the Sun work? We know how it works; gravity compresses mass at the core driving the temperatures and densities up and getting nuclear fusion reaction to occur. Buy why does it keep doing that? It’s a question that is not often asked and one that at the very heart tells us how we need to run our fusion devices. As always mother nature has beaten us to the punch!
When the Sun ejects plasma from its surface during a transient event, like a solar flare, the material always travels away from the sun. It never comes back. The Sun has no wall, and so never has any “cold” material coming back into it to cool it down. This is not the case in a fusion device where ions heat the wall and come back as cold atoms. The plasma edge then has use energy to re-ionize and reheat these “recycled” atoms and so this background gas becomes an energy sink. The effect is that the edge temperature drops. The core plasma sees this and moves energy to prop the edge up, however, as long as there is recycled gas then energy will always be lost. The effect is the core plasma loses energy and so cools down and there is a temperature gradient from the core to the edge. These temperature gradients drive many of the worst plasma instabilities.
So how do you build a device that has no wall, but still has a wall? Lithium solves this! By reacting and interacting with the ions. It grabs onto them and does not let go. Thus, there is no recycled cold gas coming back to bleed energy away. The effect is that the plasma, with more stored energy, increases in temperature and with no temperature gradient, the profile flattens out. Thus, the instabilities quieten down and disappear. With lithium you get more bang for your buck since fusion is directly a function of temperature. So now instead of just the core of your reactor doing fusion, you are doing it all the way to the edge. More volume means more power without increasing the device size. In fact, you could start to make the device smaller!
