The Sun in a Bottle - Part I

The Sun in a bottle: Nuclear Fusion Reactors

Hi everyone! In this article, divided into two parts, I am going to talk about fusion reactors! You’ve probably heard of them, maybe in a sci-fi movie or in documentary. Fusion reactors are devices supposed to harness energy from nuclear fusion reactions. They will produce energy so clean that we could stop using fossil fuels, resolving our biggest problem: global warming.

In this first part, we are going to talk about the basics of nuclear physics: nuclear reactions!

To better understand nuclear reactions, first we need to know who the protagonist of this processes is: atoms.

Reality 101

Atoms are the fundamental unit of matter. Everything in the Universe is made of atoms, including of course, us. Although they are not the smallest possible forms of matter (subatomic particles do exist), an atom is the smallest particle of an element that retains the element’s properties. Atoms consist of a nucleus made up of protons, positively charged particles, and neutrons, neutrally charged particles.

The nucleus is orbited by electrons, negatively charged particles. Electrons do not follow a specific orbit around the nucleus, their behaviour is described by a function, called atomic orbital. This function is used to calculate the probability of finding an electron in a specific region around the atom’s nucleus.

Most of the mass of an atom is given by the masses of protons and neutrons in the nucleus. Electron mass is negligible. Usually, an atom has the same number of protons and electrons, that gives them a neutral charge. 

The number of protons (which is equal to the number of electrons) is represented by the atomic number, indicated by the letter Z, and used in the periodic table.

The number of neutrons, instead, is represented by the neutronic number, indicated by the letter N.

If the number of electrons is different from the number of protons, then the atom is electrically charged, and it is called an ion.

Splitting and merging: fission and fusion

Atomic nuclei can interact with each other in processes called nuclear reactions. In these processes, atomic nuclei collide with each other, or with an external subatomic particle, to produce new nuclides with a different atomic number. There are two types of nuclear reactions: fission and fusion. In a fission reaction, a heavier nucleus splits into lighter nuclei, with a different atomic number.

This process releases a lot of energy, in the form of heat. In fact, fission reaction is used to produce electricity, by heating up water to create steam, which turns a turbine connected to an alternator. 

The fission reaction that takes place in a nuclear reactor is a self-sustaining one, and it is initiated by bombarding nuclei with neutrons, to split them.

In a fusion reaction, lighter nuclei combine to create a heavier nucleus, releasing 3-4 times the energy of a fission reaction in the process.

For nuclei to combine, they need to be extremely close, and a lot of energy is needed to beat the repulsion between them. So, how can fusion happen?

The fourth state of matter: Plasma

Matter has four states in which it can exist: solid, liquid gas and plasma. Plasma is ionized gas, in which temperature is so high that electrons have been stripped from atoms, creating electrically charged  atoms, or ions.

Plasma is exactly what a fusion reactor needs to initiate a fusion reaction, because it provides the environment in which light elements can fuse, releasing energy. In a plasma, electrons and nuclei move around freely, and, since nuclei are all positively charged, they repel each other.

As I said before, for nuclei to combine, they need to overcome the repulsion between them. To do this, they need to go very fast.

Since we are talking about gases, the kinetic energy of the particles, as stated by the kinetic theory of gases, is related to the temperature of the gas. The higher the temperature, the higher the “speed”.

So, plasma is really hot! We are talking about millions of degrees Celsius!

Stars are also made of plasma, and the fusion reaction is the same process that powers them and enables them to emit light!

This means that fusion reactors will produce energy in the same wat as stars do! It’s like having the Sun in a bottle!

In the next part, I am going to talk about the two fundamental types of fusion reactors: magnetic confinement and inertial confinement reactors!

Today's blogger

Hello, world! I'm Edoardo Cignitti, a passionate enthusiast of computer science, physics, and aviation. I have an insatiable curiosity about the world and love understanding why things happen, which is why I'm particularly drawn to physics, with a keen interest in nuclear and quantum physics. I also have a soft spot for sci-fi films and enjoy playing board games. I'm excited to share my interests with you here on Let's Blog!