The concept of controlled nuclear fusion has been of increasing interest over the last few decades. However, the physical limitations that ultimately make controlled fusion physically impossible are simple and unavoidable.

It is impossible to harness nuclear fusion because it is humanly impossible to create continuous fusion. Humanity has already been able to harness the power of fusion for nearly 70 years, with the testing of the first hydrogen bomb in 1954. A fusion reactor is, in essence, a repeatedly detonable hydrogen bomb used to create energy. The fundamental problem with fusion energy is that nuclear fusion is an instantaneous and violent release of energy. Unlike nuclear fission, which can be slowed by simply diluting the fissile material, or the number of neutrons via control rods, fusion cannot be slowed. Attempting to use fusion as an energy source is analogous to replacing gasoline with nitroglycerin in internal combustion engines. At best, we may be able to achieve a one-shot device that self-destructs in a single energy-producing cycle.

Currently, leading programs have achieved fusion on tiny scales by using extremely powerful lasers to induce the implosion of a capsule filled with deuterium-tritium fuel. This method is conceptually analogous to the decades-old technology found in two-stage thermonuclear weapons, where a fission primary explosive implodes a fusion secondary charge. This advancement, where fusion ignition was achieved for a few tenths of a nanosecond, has been reported in a paper with over 1,000 listed authors in the Physical Review Letters.

Nuclear fusion is the highest energy output process observed by man. The enormous release of energy results from the conversion of mass to energy during the fusion of light atoms such as hydrogen isotopes. Approximately two-thirds of the energy released during nuclear fusion is in the form of high-energy gamma rays. These gamma rays have extreme penetrating power, and due to their uncharged nature, cannot be contained by a magnetic field. Furthermore, neutrons are also an inevitable product of nuclear fusion. Like gamma rays, neutrons are uncharged and require many meters of dense shielding material to attenuate the ionizing power of the emitted particles.

Neutron emission is particularly harmful as the ejected particles have very high kinetic energy and are around ten times more damaging to human tissue than gamma rays. Additionally, when materials are bombarded with neutrons, they can potentially become radioactive. Shielding material exposed to either of these emissions will rapidly deteriorate due to the ability of gamma rays and neutrons to destroy chemical bonds.

Assuming that the ionizing radiation produced during nuclear fusion can be controlled, the infernal conditions required to initiate fusion, and produced upon successful fusion, simply cannot be contained by any fathomable means. Although it is claimed that the plasma can be contained using extremely powerful magnetic fields, it is impossible to control the electromagnetic waves produced in the 100 million kelvin reactor core. The electromagnetic radiation produced ranges the full optical spectrum, with most of the photons being released in the x-ray and gamma wavelengths. The high-intensity emission of energetic photons will heat the surrounding containment to a plasma, thus destroying the reactor.

The feasibility of a fusion reactor relies on the assumption that the sun can be scaled down to produce fusion energy. Stars are simply not scalable objects as the mechanism by which they produce fusion relies on mass and gravity. Stars are born when huge clouds of hydrogen and other matter condense so that the gravitational force squeezes hydrogen atoms together, resulting in nuclear fusion. Gravity is the driving force that keeps stars lit, despite the explosive emission of energy following every fusion event; it ensures that the star does not lose mass through explosions. Gravity is the only viable containment system for continuous fusion. For this reason, it is impossible to achieve continuous fusion without a star. All other man-made fusions on smaller scales can only occur once and end in containment failure.

As appealing as it may seem, and as much as we desire to utilize fusion energy, it is impossible to achieve as long as our understanding of physics is not improved. This glamorous and fancy technology is little more than the latest tech fad and is ultimately doomed to fail due to insurmountable physical limitations that can be understood by a high school student.