Nuclear Fusion: Future or Fallacy?
With the energy crisis nearing, if not already upon us, there emerges a need for energy sources that give more than they take. Many debate about the means of energy production, with arguments favoring wind energy, solar energy, and energy through hydropower. They each also have their drawbacks, with particular criticism being made of Nuclear fission power by Green Parties in various countries. The main reason cited is that the nuclear waste produced has lethal effects for the environment and is a solution to the energy crisis with a lot of strings attached to it.
While there continue to be many sides to the debate, this blog is not focused on the the benefits and drawbacks of nuclear fission. This blog discusses a relatively lesser talked about (for obvious reasons) source of clean energy: Nuclear Fusion. I will present to you the bare bones that there is to know about Nuclear Fusion. What it is, method of energy production, viability, related technology, and the pros and cons. It is then unto you to reflect and to evaluate this method of energy production.
Nuclear Fusion refers to the controlled process where the nuclei of two atoms are smashed together such that they fuse, liberating energy in the process. The reason energy is released can be explained by the concept of binding energy.
We must first recall one of the most famous equations in the world of Physics. Einstein’s relation between mass and energy. E=mc^2. The relation says the mass and energy of a particle are proportional to each other, and indicates that the mass of a particle can be converted to energy and vice versa.
When two or more particles bind together, the overall energy of the system decreases due to finding a stable configuration, and hence the mass of the system decreases. When a nucleus is assembled, with all its nucleons (constituent particles), the sum of the nucleus is less than the sum of the individual masses of the nucleons. This mass difference results in an energy difference, which is called the binding energy. Consequentially, the binding energy is the amount of energy put into a nucleus to separate all of its nucleons into their individual selves.
Energy can not just disappear, it has to go somewhere. Hence, during the creating of a nucleus, the binding energy of the nucleus is liberated. This makes the creation a nucleus a theoretically viable process for energy production.
Granted, one does not make a nucleus out of thin air, we need the components to make a new nucleus. One way to do it is by using other nuclei. This method is called nuclear fusion. The nuclei of two atoms are brought together, and fused to make a new nucleus with a larger number of nucleons in it. The process releases a lot of energy.
The above image gives us the binding energy for each nucleon in a given element. The mass number refers to the total number of protons+ neutrons in the nucleus. We notice at this point, that the graph assumes a particular shape. One with a peak, a maximum binding energy. This occurs for the element Iron, which has 56 nucleons. Now that we know what nuclear fusion is, the question becomes, which two atoms do we fuse to liberate energy?
The curve serves as an indicator. To have energy be liberated, the binding energy of the atoms before fusion must be less than the binding energy of the atom after fusion. Hence, to produce energy via nuclear fusion, one must fuse atoms of a smaller mass number than 56, hence creating an atom with a higher mass number, thus higher binding energy.
Keep in mind that the atoms to be fused need to have a mass number less than 56, so everything to the left of iron fuses, but nothing to the right of iron will produce fusion energy. This is because the binding energy decreases after iron.
Fantastic, this is a method that can produce more energy for a given amount of mass being fused than even nuclear fission (splitting heavy nuclei to the right of Iron to smaller nuclei). Then, why is it not the most used form of energy production? The answer boils down to the net energy liberated.
The nucleus repels itself, due to the presence of protons in it. Hence, to get two nuclei to stick together, one must first overcome this repulsive electrostatic force, and push them all the way close until, at the point of the separation, the attractive ‘strong nuclear force’ is higher than the repulsive electrostatic force. The issue is that poshing repelling nuclei towards each other takes energy, and to achieve the outlined scenario, the fusing energy is larger than the energy liberated, hence resulting in the net energy loss. Even if there is no net energy loss but gain, the gain is so small, that it is of no use for mainstream energy production.
One of the main research interests in viable methods for fusion is the TOKAMAK project. It explores the idea of magnetic fusion. To get nuclei to fuse, massive pressure must be put on them. Also, the nuclei can be smashed at very high velocities so that they fuse. This is the principle of magnetic fusion. It is conducted via the means of a high temperature plasma. Plasma is a state of matter where the atoms can exist as separate electrons and nuclei at high temperatures. The higher the temperature, the faster the nuclei in the plasma move, hence more successful high speed reactions result in higher amount of fusion.
The TOKAMAK is a donut shaped “cage”, that uses magnetic fields to confine extremely high temperature plasma where nuclear fusion can take place. The advantage a magnetic field offers is that no solid material can contain the plasma at such high temperatures, but a magnetic field can confine the plasma. Hence, the high temperatures can be confined in a magnetic field and then shielded with vacuum, hence creating an insulation. So far, magnetic fusion is one of the most successful methods of nuclear fusion known to man, with other methods not yielding as well. Research continues to be done in the field, with the focus now on the idea of minimizing energy losses, how to achieve even higher temperatures, and extracting the produced energy.
Therefore, Nuclear Fusion remains a hot (hah!) bed for research, and the viability as a real source of energy is a question of when, not if. The advantages nuclear fusion offers is more than any other method of energy production. Some of them include no carbon footprint, abundancy of fuel, and very low level of radioactive waste. With the very small amount of drawbacks, this makes it one of the best energy sources we have available.