Throughout this book, we are concerned mainly with quantum mechanics as applied to the electrons surrounding the nucleus and the associated electronic “chemical” (rather than nuclear) properties of the elements. But in this chapter we discuss several large-scale fusion power approaches that involve the nucleus of the atom. Here we deal with quantum-based nuclear processes and quantum-based technologies that are employed to enable the fusion process. And, along with presenting the laser as a tool for fusion, I also mention several laser-based military applications.

Nuclear processes such as fission and fusion are understood through a quantum mechanics that considers what happens inside of the nuclei of atoms. In these processes we deal with isotopes. Atoms having the same atomic number (that is, the same number of protons in their nuclei) but having different numbers of neutrons in their nuclei are different isotopes. Most elements can be found in several different isotopic forms.

FISSION AND FISSION REACTORS

It is the fission (splitting) of some isotopes of the heavier elements (such as the isotope of uranium, U235, Z = 92 with the atomic weight of 235 protons and neutrons) into atoms of lighter elements that produces what has generally been called atomic energy.

Isotopes that undergo a spontaneous fission are called “radioactive.” It is the carefully controlled stimulation of this radioactive release of energy that is at work in our present-day nuclear power plants.

(The uncontrolled “chain-reaction” of the fission of one isotope to release neutrons that trigger the fission of more isotopes produces the enormous energy of the “atomic bomb.”) Exaggerated fear of such a runaway situation in fission reactors [such as occurred at Chernobyl and Fukushima] has unfortunately curtailed the use of this present lowest-cost, carbon-emissions-free, present mode [see * below] for generating electrical power.

Those were very unfortunate accidents, but modern reactors today may be considered to be safe. And work is underway to develop inherently even safer and smaller and less-expensive fission reactors. For example, Terrestrial Energy in Mississauga, Ontario, Canada, is designing a reactor that uses molten salt, rather than water, as a coolant, essentially making the reactor meltdown-proof.¹)

*In a paper to be quoted later in this chapter,² Lev Grossman shows the results of a study giving the energy produced per dollar to build and maintain the power plant: fusion (projected for the future) at 27 wins over (present-day) gas at 5, coal at 11, and fission at 16.

FUSION TO LIGHT CITIES, THE “HOLY GRAIL” OF ENERGY SOURCES

As noted above, fusion is the same process that releases the energy that heats our sun and other stars. Because its fuel is or is derived from isotopes of hydrogen that are found in vast quantities (compared to what will be needed) in either freshwater or seawater, there is an essentially limitless supply of fuel. Enormous as the energy may be in an atomic bomb, it is small compared to the fusion energy that is released in a hydrogen bomb. But since the fusion reaction tends to stop in a fusion reactor if there are any problems, and there are no radioactive “spent” nuclear fuels to store or dispose of, nuclear fusion is an inherently safe, carbon-emissions-free, source of energy for our planet. These factors, plus its ratio of power delivered to relative cost (as noted above), make nuclear fusion the “holy grail” of energy sources.

In fusion, the nuclei of atoms of lighter elements fuse together to make heavier elements, and they give off a tremendous amount of energy in the process. Tritium is an isotope of hydrogen, Z = 1, having the same single proton and single electron as hydrogen, that is, behaving “chemically” the same and occasioning no new place in the periodic table, but having two neutrons in its nucleus in addition to the one proton. And so, since a neutron is about as heavy as a proton, the tritium isotope is three times as heavy as hydrogen. Deuterium, known as “heavy hydrogen,” has one neutron in addition to the proton in its nucleus, and so it is twice as heavy as hydrogen.

A very large amount of energy is released as each tritium nucleus combines by fusion with a deuterium nucleus to form a nucleus of helium, giving off a highly energetic extra neutron in the process. Tritium can be produced in sufficient quantity for a fuel as these neutrons combine with the nuclei of lithium in a surrounding “blanket” that captures the energy and prevents the neutrons from irradiating and destroying its surroundings. So the reaction of the neutrons with the blanket generates the reactor's own tritium fuel. As noted above, deuterium is present in essentially limitless quantity in seawater, so getting enough deuterium is not a problem.

And the process is safe. In the tokomak, a loss in the magnetic confinement of the fusion plasma abruptly shuts off the fusion process, which needs the confinement to be sustained. And because for laser fusion tritium and deuterium fuel is provided in tiny pellet-sized doses, only a limited amount of fuel is available for each laser pulse. If anything goes wrong, the pellets aren't supplied or the energy delivered by the lasers is insufficient to ignite the reaction.

Fusion in a Gigantic Superconducting Torus, the Tokomak

The leading approach for fusion power, the tokomak, relies on the quantum phenomenon of superconductivity for effective operation. A plasma of hydrogen isotopes is heated and contained in the magnetic field of a “tokomak” (so named by the Russians who first explored this toroidal [doughnut-shaped] field arrangement for magnetic confinement fusion). The magnetic field, which holds the hot plasma as if it were in a magnetic bottle, is provided by as few as six D-shaped superconducting coils that are stacked together with the straight parts of the D back to back so that the toroidal (doughnut-shaped) magnetic field rings the entire stack through the open center of the Ds. (Superconductors are described in Chapters 19, and 24.) Over sixteen megawatts of fusion power has already been generated using this arrangement, close to the power required to ignite the plasma. Ignition occurs when more energy is produced by the fusion reaction than is put into it to get the fusion process started. Were the windings of the tokomak not superconducting, economically producing the toroidal magnetic field of the tokomak would be a much harder and possibly impossible project. Take a look at the enormous power consumption and vast flow of cooling water already required for the very much smaller copper alloy Bitter magnet described in Chapter 21!)

The exploration of this more favored of the different types of fusion approaches is of such great scale and cost that it is being pursued in a joint effort by the more developed nations of the world. Construction of the next large experimental device, called ITER (International Thermonuclear Experimental Reactor), is already well underway in the south of France and is scheduled to begin operation in 2020 at an expected total cost of $20 billion. The construction of a demonstration reactor has been proposed to begin in 2024. The full-scale commercial tokomak reactor might stand fifty feet high, with an overall torus diameter of fifty feet. An update on the ITER project has been provided in the American Physical Society magazine, Physics Today.³

Various projects have been underway worldwide to explore alternative magnetic confinement fusion approaches. For example, it was announced in January 2016 that an alternative, stellarator, geometry of magnetic-confinement system, Wendelstein 7-X, has just been started up after eighteen years of construction. It has completed the first step, producing a plasma.⁴ (The “Stellarator,” a name coined to reflect the intent to create the conditions within a star, is like a torus, but the field windings are of such geometry as to cause the plasma to twist like a single braid in a multistrand hoop.)

Recent Designs for Nuclear Fusion at a Smaller Scale

Some other approaches to fusion that are being explored are described in an article in Time magazine of November 2015.⁵ Lev Grossman reports on an innovative fusion development in a $500 million startup company called Tri Alpha Energy in Orange County, California. Grossman sets the context by explaining that this is one of a number of small commercial operations tackling the fusion problem, including efforts that he outlines as being pursued at General Fusion outside of Vancouver and Helion Energy in Redmond, Washington.

The challenge for fusion is getting the plasma hot enough and keeping it hot long enough. The Tri Alpha Energy reactor approach is described as having two canons “firing smoke rings, except that the smoke rings are hot plasma rings.”6 They are shot at each other at “just under a million kilometers per hour.” The “violence of the collision of the two rings heats the combined plasma to ten million degrees Celsius and combines the rings into a plasma 80 centimeters across, shaped more or less like a football with a hole through it the long way, quietly spinning in place…. The plasma itself generates the field that confines it.” In June the reactor proved able to hold its plasma for (a long) 5 milliseconds, indicating that a stable plasma had been created.

Gigantic Laser-Produced Nuclear Fusion

The laser is a quantum device, but that doesn't mean that it must be small. In a $3 billion experiment toward one long-shot application, 192 huge lasers were assembled to converge a pulse of simultaneous laser beams from many directions onto a pellet about the size of a peppercorn.⁷ The objective was to use the power and coherence of lasers (as described in Chapter 4) to vaporize the pellet so rapidly that the expanding vapors compress and heat the pellet's tritium and deuterium contents to the enormous pressures and temperatures required to “ignite” controlled nuclear fusion.

The laser-fusion concept was first examined in the 1970s at KMS Industries in Ann Arbor, Michigan, and this examination was continued, starting in the 1980s, at the US government's Lawrence Livermore Laboratory (about an hour east of San Francisco). Construction of the laser-fusion National Ignition Facility was begun at LLL in 1997. The device occupies an area as large as three football fields.

In July 2012, this laser system delivered a whopping peak power of 500 trillion watts.8 In September 2013, a laser shot produced fusion within the pellet that delivered more power than was driven into it, but this fusion energy was well short of the energy put into the entire system, as would be required to meet the goal of ignition. For the present time, at least, the machine is being used for other purposes.⁹

PROBABILITIES AND TIME FRAMES FOR FUSION POWER

Even if ignition is achieved, major engineering problems still need to be solved, and the construction and successful operation of a commercial fusion reactor by any approach is viewed as a long shot and probably would not take place before 2050 (though the aim of startup companies with their smaller-scale approaches is to do it much sooner). In any case, many argue that the prospect of safe, unlimited energy supply and the related prospect of a safer world (with less fighting over limited energy resources) makes it worth the development efforts that are underway.

LASERS IN DEFENSE APPLICATIONS

Not only does the generation and coherence of the laser beam as described in Chapter 4 allow it to have great power, it also allows the intensity of the beam to stay intact over long distances, rather than becoming spread out and diffuse, as occurs with ordinary light. This property has made the laser attractive for laser-guided weaponry, and as a potential antimissile weapon, since intensive bursts of laser power could potentially be beamed out at the speed of light over long distances to destroy incoming missiles. The US Department of Defense also uses the laser to examine the processes that would take place during the explosion of nuclear bombs or the nuclear warheads on missiles. This is a parallel use of the huge laser system at LLL that, as described above, was also targeted at developing unlimited fusion power toward a more peaceful world.