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Nuclear Fusion Energy

February 13, 2023

In the early 1990s, several of my colleagues were doing research on a laser sensing system for the International Thermonuclear Experimental Reactor (ITER), a large tokamak magnetic confinement nuclear fusion reactor. ITER is an international collaboration intended to become the largest of more than a hundred fusion reactors built since the 1950s, and at 22 billion dollars it's the most expensive science experiment of all time, exceeding even the cost of the Large Hadrian Collider. I mention this as an illustration that serious attempts at nuclear fusion energy have been ongoing for many decades.

Deuterium-tritium fusion

What could be easier? Fuse deuterium (2H) nuclei and tritium (3H) nuclei to create helium (4He) and a lot of energy.

The essential problem is the large activation energy of nuclear reaction. Deuterium and tritium will only fuse at temperatures of about 100 million degrees Celsius.

Our Sun and other stars, which are giant fusion reactors, produce these temperatures by gravitational forces.

(Modified Wikimedia Commons image. Click for larger image.)

Hans Bethe's 1939 theory of stellar energy production established the basic mechanism for fusion energy production in stars. Theory is one thing, but confirmation is another. That's the reason why Bethe's Nobel Prize in Physics wasn't awarded until 28 years later, in 1967. Frederick Reines (1918-1998) was awarded the Nobel Prize in Physics in 1995 for his 1956 experiment with Clyde Cowan (1919-1974) that confirmed the existence of neutrinos. That's a gap of 39 years that denied Cowan a share in the prize since the Nobel Prize is never awarded posthumously.

Before the basic structure of the atomic nucleus was elucidated in the 1930s, leading to Bethe's theory, scientists wrestled with the problem of solar energy production. According to Maslow's law of the instrument, If the only thing you have is a hammer, everything looks like a nail; so, 19th century scientists used the physical principles known at their time for an explanation. Their speculations are discussed in a paper by the ever-enlightening Helge Kragh (b. 1944).[1]

One such theory was the idea that the Sun's energy was a consequence of an infall of asteroids. This theory was supported by the idea that the heat developed by an asteroid would be about 10,000 times greater per unit mass than the very energetic chemical reaction of oxygen and hydrogen to form water.[1] A problem with this concept is that it would require an annual infall of about 100 Earth masses, something that would shorten the sidereal year by about half a second. This was not observed, and such a dense cloud of asteroids would affect the orbits of Mercury and comets.

A similar mechanical theory proposed by the discoverer of the electron, J.J. Thomson (1856-1940), and others, supposed that a gravitational contraction of the Sun was the source of its heat. This model predicted a long Solar lifetime of 100-500 million years. but still too short to account for the geological history of the Earth.[1] There was also the strange idea that the Sun's radiant energy might return to it after a long cosmic journey in a non-Euclidean universe.[1]

In 1903, Marie Curie (1867-1934) and her rassistant, Albert Laborde, reported that radium disintegration generated about 100 calories per gram per hour, which is about 200,000 times greater than for coal combustion.[1] Ernest Rutherford (1871-1937) calculated that just 2.5 ppm of radium in the Sun would account for its energy emission.[1] Helium is a product of radium disintegration, and there's a lot of helium in the Sun. However, the half-life of radium isotopes is too short, and radium was never detected in the Sun.

The big fusion energy news at end of 2022 was from Lawrence Livermore National Laboratory's National Ignition Facility (NIF), which announced on December 14, 2022, that scientific energy breakeven was achieved for the first time in a nuclear fusion experiment on December 5, 2022.[2-5] Breakeven means that the experiment produced more energy from fusion than the energy needed to create it.[2] In this case, the energy used was from a tremendously large array of 192 lasers focused on a small specimen of deuterium and tritium.[2-3]

National Ignition Facility hohlraum

The frozen specimen of deuterium and tritium is contained within a cavity called a hohlraum, a German word for a "hollow space."

The incident ultraviolet radiation from the lasers is converted into X-rays inside the hohlraum, and this radiation compresses the isotope mixture into a high temperature plasma.[2]

(Portion of a Lawrence Livermore National Laboratory image. Click for larger image.)

The NIF approach is known as inertial confinement fusion in which the lasers create shock waves that compress pinhead-sized spherical specimens of a few milligrams of deuterium and tritium. More likely to be commercialized is Magnetic confinement fusion in which magnetic fields are used to confine a heated plasma reaching fusion initiation temperature. Around 1940, Arthur Kantrowitz (1913-2008) and Eastman Jacobs (1902–1987) were the first to build a magnetic confinement fusion reactor, a torus ringed with electromagnets and a hydrogen plasma heated by electromagnetic radiation.[4] Their experiment did not create fusion, but it was a significant start for this concept.[4]

Laser inertial confinement was conceived at LLNL in the 1960s; and, over the course of the subsequent sixty years there have be continuing improvements in the creation of more powerful lasers, optics, target fabrication, and computer modeling.[2] Today's NIF is now the size of a sports stadium.[2] In August, 2021, an experiment came close to breakeven.[3] Now, with an improved target and alignment of the lasers to create a more spherical implosion, breakeven was achieved.[3] The 192 lasers delivered 2.05 megajoules of energy onto a frozen specimen of deuterium and tritium, and 3.15 MJ of energy were released, giving a gain of (3.15/2.05) = 1.53; that is, about 50% more energy was released from the reaction than the incident laser radiation.[3] However, at a system level, the lasers needed 322 MJ for operation, so the system gain was 0.98%.[3,5] Also, the energy released was "...only enough to boil a few kettles of water."[5]

Reddy Kilowatt

Reddy Kilowatt, a cartoon spokesman for the United States electric power industry, was conceived in 1926, but he reached peak potential (pun intended) in the 1950s.

In 1954, chairman of the United States Atomic Energy Commission, Lewis Strauss (1896-1974), stated that nuclear power would eventually make electricity "too cheap to meter." Perhaps nuclear fusion will finally make that prediction a reality.

(Portion of a Wikimedia Commons image. Click for larger image.)

Stephen Mihm, a professor of history at the University of Georgia, has written an opinion piece about fusion energy in which he reviews its slow progress and the hyperbole surrounding news coverage of the field over its many decades.[4] He reports that a 1959 article in Popular Mechanics entitled, "Fusion Power for the World of Tomorrow," predicted that "It may come sooner than you think!"[4]

Mihm reports on the slow, but steady, progress of magnetic confinement fusion from Lyman Spitzer's stellarator at Princeton University through Andrei Sakharov's and Igor Tamm's Tokamak to today's more advanced magnetic confinement reactors that have nearly reached breakeven.[4] The next version of ITER is under construction in France,[3] and First Light Fusion has proposed an inertial confinement reactor that uses projectiles instead of lasers.[5]


  1. H. Kragh, "The source of solar energy, ca. 1840–1910: From meteoric hypothesis to radioactive speculations," European Journal of Physics, vol. H 41, no. 4 (November 2016), pp. 365-394, doi: https://doi.org/10.1140/epjh/e2016-70045-7. Also at arXiv, doi: https://doi.org/10.48550/arXiv.1609.02834.
  2. National Ignition Facility achieves fusion ignition, Lawrence Livermore National Laboratory Press Release, December 14, 2022.
  3. Jeff Tollefson and Elizabeth Gibney, "Nuclear-fusion lab achieves 'ignition': what does it mean?" Nature vol. 612 (December 13, 2022), pp. 597-598, doi: https://doi.org/10.1038/d41586-022-04440-7.
  4. Stephen Mihm, "Fusion skepticism follows a century of genius, fraud and hype," Bloomberg Opinion (via Pittsburgh Post-Gazette), December 18, 2022.
  5. Sabine Hossenfelder, "Science News Dec 21," Backreaction Blog, December 21, 2022. Related YouTube Video.

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