In all of the known universe, nuclear fusion is the most common type of reaction
(physical, chemical, or nuclear). Nuclear fusion is a nuclear reaction in which lighter elements combine nuclei to form heavier elements, and release energy . Considering that this is how stars burn, without fusion, there would be no sun, no earth, no massive sources of energy, and no life. Understanding this topic is important for us, because if we can recreate it and harness its power, fusion could replace all other forms of energy.
This document is educational in nature, and assumes that the the audience has basic understanding of physical and chemical principles. Most importantly these include the concepts of energy, electromagnetic forces, atomic structure, conservation of momentum, and atomic mass. I will provide a background for the nuclear fusion process, and define any terms or concepts that relate to it.
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In order for this reaction to occur and remain sustained, three conditions must be

The substance must be under high pressure and temperature.

The nuclei must overcome the repulsive electromagnetic barrier.

The reaction must be confined.
The electromagnetic barrier is the repelling forces of positively charged nuclei that get stronger as the nuclei become closer until the much stronger nuclear forces take over . When the nuclear forces become stronger than the electromagnetic forces, fusion occurs. This is illustrated in red in Figure 1.
Figure 1: The
Electromagnetic
Barrier

All elements have a binding energy , or energy associated with holding the nucleus of the atom together . When two light elements fuse, the energy released is equal to the difference in binding energies between the final product and the reactants.
Figure 2 shows the different binding energies of the elements.
Figure 2: Nuclear Binding Energy
The trend of binding energies as elements get heavier helps us to distinguish fusion from fission. Fission is when a heavier element’s nucleus splits into lighter elements and releases energy . Similar to fusion, the difference in binding energies between the products and reactants in a fission reaction is the energy released during the reaction. Since iron (atomic symbol Fe) has the highest binding energy of all the elements, only elements lighter than iron that fuse will yield a net positive energy. On the opposite side, to yield net positive energy for fission , the elements that split must be heavier than iron.

Another important factor that we learn from the binding energies of elements is that there is a much greater difference in binding energies among the lightest elements
(hydrogen, helium, lithium, etc.) than among any of the other elements. This is why the fusion of hydrogen into helium yields the greatest release of energy in a nuclear reaction.
Since there is such a high energy release in a nuclear fusion reaction, in order for the reaction to reach ignition ( the point at which a nuclear fusion reaction begins to sustain itself, yielding more energy output than input ), the reaction must somehow be confined. Otherwise the “fuel” would expand or escape and the reaction would end.
There are three major types of confinement for a fusion reaction:

Gravitation Confinement: the gravity of a star such as our sun prevents the fuel from expanding

Magnetic Confinement: strong magnetic fields in a structure called a solenoid
(cylinder) or a tokomak (doughnut shaped) prevent the plasma fuel from escaping

Inertial Confinement: high powered lasers fire upon a sphere of fuel from all sides to both initialize and confine the reaction
The National Ignition Facility (NIF) is the world’s largest research facility attempting to create nuclear fusion by inertial confinement . The target fuel for the process is a small sphere (see Figure 3) filled with two types of hydrogen (see the appendix for more information on this hydrogen mixture). In order for the reaction to work, the lasers that strike the target must all have the same intensity and they must all
Figure 3: Target Fuel Microcapsule hit it at the same time, from all sides. Accuracy is absolutely crucial. NIF uses 192 lasers to achieve this [Rincon]. There are many steps for the total process at NIF, including an amplification system that produces the world’s most powerful laser, but I will focus on the physical steps that occur during the inertial confinement process.

Figure 4: Inertial Confinement Fusion Process
The fusion process is broken down into four steps starting when the lasers strike the fuel target. The blue arrows in Figure 4 represent radiation energy from the lasers.
1. Lasers strike the target and heat the outer shell to a plasma
2. Outer shell explodes off. Conservation of momentum forces the fuel inside to implode
3. Fuel continues to compress to a super dense state until fusion occurs
4. Ignition occurs and the fuel burns itself out
The project at NIF has not yet achieved ignition, but in late September of 2013,
NIF became the world’s first fusion experiment facility to gain more energy from the fusion reaction than put in to initialize burning the fuel [Rincon].
In nuclear fusion, lighter elements combine nuclei to form heavier elements and release energy. This is the process that lights our sun and all stars. In order for sustained fusion to occur, the nuclei of the lighter atoms must come close enough overcome the repulsive electromagnetic forces until the stronger nuclear forces take over. The substance must also be confined to achieve ignition. At the National Ignition
Facility, researchers use the inertial confinement process.
The energy released during a fusion reaction is equal to the difference in binding energies of the products and reactants. Since the difference in binding energies between helium and hydrogen is so much more than any other elements, it is the most viable option to recreate a bountiful energy source. Also, because hydrogen is abundant on earth and fusion yields many times the energy than even fission, if we could harness the power of fusion, it could fuel the world.

The Hydrogen Mixture: An isotope of an element is a type of that element with a specific number of neutrons.
For example, deuterium and tritium are two different isotopes of hydrogen. Deuterium has one neutron and tritium has two neutrons (see
Figure A1). On Earth, deuterium is very abundant, so naturally a deuterium- deuterium
(D-D) fusion reaction seems the most viable option. However, as we can see in Figure
A2, the thermal energy to create a D-D reaction is much higher than that of a deuteriumtritium (D-T) reaction. Also, while less abundant on Earth, tritium can be manufactured from water using a process called electrolysis. For these reasons, scientists choose to use a mixture of deuterium and tritium for the fusion reaction (Figure A1).
Figure A1: Nuclear Fusion Reaction Figure A2: Fusion Energies and
Temperatures
The Use of a Hohlraum: A hohlraum (see Figure A3) is a hollowed out cylinder used to create a more uniform radiating effect on the target fuel.
At NIF, instead of firing the lasers directly at the fuel capsule, the lasers are fired into the hohlraum. The walls on the interior of the hohlraum reflect the radiation energy, which creates a high powered X-ray bath for the fuel (Figure 4A). This cuts down on risks associated with imperfect laser intensities or geometry when firing on the capsule.
Figure A3: A Hohlraum Figure A4: Use of Hohlraum

Works Cited
Rincon, Paul, ed. "BBC News - Nuclear fusion milestone passed at US lab." BBC . BBC
News, 07 Oct 2013. Web. 18 Oct 2013. <http://www.bbc.co.uk/news/scienceenvironment-24429621>.
Images
Esham, Benjamin. Figure 4: Inertial Confinement Fusion Process . 2007. Graphic.
WikipediaWeb. 18 Oct 2013.
<http://en.wikipedia.org/wiki/File:Inertial_confinement_fusion.svg>.
Figure 3: Target Fuel Microcapsule . 1999. Photograph. Wikipedia, Livermore. Web. 18
Oct 2013. <http://en.wikipedia.org/wiki/File:Fusion_microcapsule.jpg>.
Figure A1: Nuclear Fusion Reaction . 2010. Graphic. Universe TodayWeb. 18 Oct 2013.
<http://d1jqu7g1y74ds1.cloudfront.net/wp-content/uploads/2010/01/fusion.jpg>.
Figure A3: A Hohlraum . 2006. Photograph. WikipediaWeb. 21 Oct 2013.
<http://en.wikipedia.org/wiki/File:Nif_hohlraum.jpg>.
Lawson, Barrie. Figure 2: Nuclear Binding Energy . 2005. Chart. Electropaedia, Chester.
Web. 16 Oct 2013. <http://www.mpoweruk.com/nuclear_theory.htm>.
Michaluk, Nate. Figure 1: The Electromagnetic Barrier . 2012. Chart. n.p. Web. 16 Oct
2013.
Michaluk, Nate. Figure A2: Fusion Energies and Temperatures . 2012. Chart. n.p. Web.
21 Oct 2013.
Seaver, Linda. Figure A4: The Use of a Hohlraum . 2010. Graphic. Lawrence Livermore
National Laboratory, Livermore. Web. 21 Oct 2013.
<https://www.llnl.gov/news/newsreleases/2010/NR-10-01-06.html>.