Disclaimer: This paper partially fulfills a writing requirement for first year (freshman) engineering students at the University of Pittsburgh Swanson School of Engineering. This paper is a student paper, not a professional paper. This paper is based on publicly available information and may not provide complete analyses of all relevant data. If this paper is used for any purpose other than this author’s partial fulfillment of a writing requirement for first year (freshman) engineering students at the University of Pittsburgh Swanson School of Engineering, users are doing so at their own risk.
Nuclear fusion is a process where atoms are smashed into each other and combine to form a different element and excess energy. That energy can be captured and used to power anything, just like the energy-producing methods we use today.
The biggest fusion reactors that exist right now are stars. Stars function in the same way as the reactors that are possible to build on Earth. Intense pressures and temperatures cause hydrogen atoms to collide with each other and fuse. While we can’t simulate the pressures of the sun on the Earth, we can make up for it by using hotter temperatures than stars do .
Fusion is very similar to nuclear fission: the energy harnessed in nuclear reactors and released in most nuclear explosions. The benefits to using fusion instead of fission is that fission requires a rare and highly dangerous material (radioactive uranium) to generate the power and it leaves radioactive waste as a product that has to be carefully disposed of. Fusion eliminates both of those problems because the fuel is hydrogen, which is easily extracted from water, and the product is helium and neutrons, both of which are significantly less dangerous than nuclear waste.
The way that it works is hydrogen gas is heated to temperatures on the order of billions of degrees Celsius for fractions of a second, which turns the gas into a plasma and initiates the fusion reaction. The energy released by the atoms as they collide is used to keep the reaction running. All of the energy that is not used to maintain the reaction is harnessed and converted into the electricity that we use .
If a fusion reactor is successfully constructed and it functions perfectly, a large city such as San Francisco could be powered for a year with just a couple hundred gallons of water. Even a single drop of water could support a single person's power needs for a year .
There are currently a few designs for the reactors. One of those designs, the ARC (affordable, robust, compact) reactor relies on extremely powerful magnets to hold the plasma hydrogen in place. The energy that is possible to be extracted from a fusion reactor is strongly related to the strength of the magnetic field .
Another design uses two metal rods to generate a powerful magnetic field that initiates the fusion reaction. The magnetic field is generated by a mega-ampere-scale capacitor discharging rapid bursts of current .
In the most interesting design, super powerful lasers are used instead of magnets to generate the magnetic field required . It is the laser-style reactor ideas that are actively being tested .
Nuclear fusion is the energy of the future, but how far into the future will we have to go before it becomes possible? That depends on how much funding is put into the development of this technology. Scientists have been working on this concept since the 1960’s and, at the time, they believed that they would have a working fusion reactor by 1980. Since then, the estimated date has been pushed back over and over again . All we know for sure about the timeline is that, whenever we do develop this technology, it will be worth it. But before harnessing fusion will be possible, we will need to make a few advancements in technology.
This is where engineers are going to come into play. One of the main advances that will need to be made is in materials. During fusion, neutrons are released and their energy is captured. At the same time, the neutron joins the atoms of the material that it collides with. In order for this system to work, a material will have to be created that can extract heat effectively while surviving the neutron-induced structural weakening for extended periods of time .
Another problem that needs to be addressed is impurities in the plasma. Even single atoms of reactor material (or other elements besides the fuel) can cause a dramatic decrease in operating temperature . A drop in temperature could cause the reaction to stop or to not even start in the first place. In addition to these major fields, advances will need to be made in the superconducting magnet field and the advanced vacuum systems field .
If fusion energy becomes a real technology that can be used in different implementations, then the world will have access to an almost unlimited electricity supply. The biggest use for fusion will be a standard electricity generator. A few reactors could supply the entire world with all the energy that they need, and we wouldn’t run out for millions or billions of years. There is enough water in the oceans to be converted into an extremely large amount of hydrogen fuel for the reactors and the waste will be minimal .
Another main use of fusion would be propulsion. Fusion could be harnessed to generate thrust for spacecraft. The fuel would last a lot longer than current fuels do due to the fact that nuclear reactions don’t consume fuel anywhere near as fast as combustion reactions. Nuclear fusion could very well be the solution to long distance space travel .
While using fusion as propulsion will occur further in the future than reactors will, Boeing has actually already patented a design for a fusion engine. It works in a similar fashion to the laser powered reactors. A pellet of fuel is blasted by lasers, which initiates the fusion reaction, and the energy expands outwards. The structure that this occurs in is a bowl-shaped nozzle. When the energy collides with the walls of the bowl, it exerts pressure that, in addition to the force from the exhaust exiting the bowl, generates thrust . This method could accelerate a spacecraft to a substantial fraction of the speed of light .
Another design for a fusion powered engine is the Heat Transfer Reactor Experiment-3, a concept developed by General Electric. The device works by using a fusion reactor to generate heat instead of electricity. That heat is then used to power two turbojet engines . Turbojet engines use the combustion of jet fuel to heat up air as it passes through the engine. In the fusion model, there is no need for jet fuel because the reactor heats up the air. Besides that, the engines work the same as any other turbojets. The benefit to this system is fuel consumption. Nuclear fuel lasts a lot longer than combustion fuel.
Most professionals seem to agree that fusion is possible and necessary, but that it won’t be available for a long time. Dennis Whyte, director of MIT’s Plasma Science and Fusion Center, says “How can we afford not to be doing this? Fusion is hard. But it’s worthwhile”. John Holdren, physicist and former director of the U.S. Office of Science and Technology, says “I think that we should be spending in the range of three to four times as much on energy research and development overall as we've been spending.” He also mentioned that fusion is the only form of propulsion that will get us to other stars.
I believe that fusion is necessary. I am a firm believer that, if the human race is to survive forever, we will have to resort to space travel in the semi-near future. Fusion is the most realistic method of propulsion at this point in time due to its low rate of fuel consumption and its potential for accelerating spaceships to extraordinary speeds.
I also believe that humans will require a lot of electricity to develop a ship capable of interstellar travel and fusion will be the most efficient method. Fusion reactors will support our electricity needs without depleting the Earth’s resources. In terms of feasibility. I agree that a lot of advances in technology will be required, but based on how fast technology is advancing in modern times, I’d say it will be available in my lifetime.
Thank you to Promise Chapman, Josh Connelly, and Frank Card for keeping me on task and entertained while I worked.