Economically viable fusion energy will be one of the greatest boons in human history, but it remains frustratingly elusive
Kahled Talaat in Tablet: The 21st century may one day be known more than anything else for the period when human beings transitioned from fossil fuels to clean renewable energy. Such a transition, as we know even now, is crucial to sustaining our physical environment and to supporting the growth of human civilization.
Debates have been raging around the role that nuclear fusion might play in this transition. Last February, the JET reactor in the United Kingdom broke the record for the amount of energy produced per pulse; last year, the experimental advanced superconducting tokamak (EAST) in China broke the record for highest plasma temperature achieved in a tokamak. Such developments stir up enormous excitement about a potential epoch-making breakthrough in fusion technology. Media reports and press releases on individual developments in fusion, however, often fail to provide a bird’s eye view of the field, exaggerating progress or selling fusion as a magical, “unlimited” source of energy not bound by the engineering or economic limitations of other forms of energy.
The truth is there are multiple approaches to fusion simultaneously being pursued, and they all have advantages and disadvantages. To get a more accurate idea of where we are in a technological field so crucial to the future of humanity, it helps to review some of the scientific and economic fundamentals at play before making any predictions about the future.
Fusion reactions are thermonuclear reactions, which means they occur at the level of the nucleus—unlike chemical reactions, which occur at the level of electrons—and are triggered by thermal conditions. As readers might recall from elementary school, the nucleus of any atom consists of protons, which are positively charged electrostatically, and neutrons, which are electrically neutral. Although positive protons repel each other, the nucleus is held together by a force known as the “strong nuclear force”—one of the four fundamental forces of nature—which acts in short range. Electrostatic repulsion due to positively charged protons acts in a relatively longer range than the strong nuclear force and extends beyond the nucleus. The nucleus is positively charged electrostatically as a result of the charges of the protons.
When two nuclei collide with each other, they can repel each other or they can fuse together (among other possible interactions). As repulsive electrostatic forces act in the longer range, fusion occurs if the colliding positively charged nuclei are fast enough to overcome the repulsive barriers and penetrate to the range of the attractive strong nuclear force interaction, and if they try enough times until they fuse. The number of fusion reactions within a given time period for particular reactants multiply substantially with increased temperature and increased packing (or density), as the nuclei are faster and more likely to collide when they’re closer together. It is possible, although not a likely outcome at the level of a single interaction, that a slow collision below the barrier energy can result in fusion, as the reactions are quantum mechanical in nature.
Electrical energy production from fusion relies in principle on heat and radiation released from fusion of lighter nuclei, such as hydrogen isotopes: deuterium and tritium. This energy from fusion reactions comes from changes in the combined mass of the products compared to the reactants in accordance with Albert Einstein’s E = mc² equation, and can be predicted from the nuclear binding energy curve. There are different types of fusion reactions in nature, and not just those of hydrogen isotopes. Light or heavy nuclei can fuse or combine given suitable conditions, but not all will release energy. It is possible to tell whether a fusion reaction will release energy or not from the nuclear binding energy curve. Energy-releasing fusion reactions are typically those involving light nuclei, particularly those that are lighter than iron-56. Lighter nuclei are favored because they tend to release more energy per unit mass and are relatively easier to fuse due to weaker repulsion.
Here, “energy-releasing” does not take into consideration the cost of overcoming the electrostatic repulsion of the positively charged protons to initiate the reaction which, despite being a small fraction of the reward (or output), remains difficult to overcome. The reason it is difficult to overcome is because, effectively, only a small fraction of the energy given to reactants in a system actually ends up causing fusion. This is in large part due to scattering collisions that occur more frequently than fusion reactions, especially at lower energies, and thereby hinder simple approaches to fusion, such as accelerator-based fusion. More here.
Honorary contributors to DesPardes: Adil Khan, Ajaz Ahmed, Anwar Abbas, Arif Mirza, Aziz Ahmed, Bawar Tawfik, Dr. Razzak Ladha, Dr. Syed M. Ali, G. R. Baloch, Hasham Saddique, Jamil Usman, Jawed Ahmed, Ishaq Saqi, Khalid Sharif, Majid Ahmed, Masroor Ali, Md. Ahmed, Md. Najibullah, Mustafa Jivanjee, Nusrat Jamshed, Shahbaz Ali, Shahid Hamza, Shahid Nayeem, Shareer Alam, Syed Ali Ammaar Jafrey, Syed Hamza Gilani, Mushtaq Siddiqui, Shaheer Alam, Syed Hasan Javed, Syed M. Ali, Tahir Sohail, Usman Nazir
