The Fusion Questby T. Kenneth Fowler
A few minutes before midnight on December 9, 1993, a group of scientists at the Princeton University Plasma Physics Laboratory produced the first definitive demonstration of controlled fusion energy. Within the confines of a doughnut-shaped device known as TFTR, a plasma consisting of equal parts tritium and deuterium was superheated by atomic beams--producing a
A few minutes before midnight on December 9, 1993, a group of scientists at the Princeton University Plasma Physics Laboratory produced the first definitive demonstration of controlled fusion energy. Within the confines of a doughnut-shaped device known as TFTR, a plasma consisting of equal parts tritium and deuterium was superheated by atomic beams--producing a second-long burst of energy that peaked at three million watts. For a brief instant, the power of the Sun had been captured on Earth.
In The Fusion Quest, T. Kenneth Fowler offers a vivid and colorful insider's account of the decades-long search for fusion power--a potentially abundant and environmentally "clean" energy source that could sustain industrial society in the twenty-first century and beyond. Scientists have known for more than sixty years that nuclear fusion powers the sun and stars. But would it work on Earth? To help answer this question, Fowler explains the physical principles on which fusion is based, describes the experiments that have led to the present state of the art, and shows how all these considerations would affect the design of possible fusion-based nuclear power plants.
Fowler describes magnets nearly as cold as outer space surrounding miniature "stars" hotter than the sun; lasers that for the merest split-second produce a blinding flash more powerful than every light bulb in America turned on at once. And he recounts the exciting discoveries of classical physics from Newton to Einstein, from Faraday to Lorentz, that provide the foundation of fusion science today. Ultimately, The Fusion Quest offers an informative and timely look at fusion's potential to provide an environmentallyacceptable new energy source in a future more vulnerable to energy shortages and pollution than many of us realize.
- Johns Hopkins University Press
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1: The Allure of Fusion
According to Greek mythology, fusion energy, the fire of the Sun, is a gift hard won. When the Titan god Prometheus stole the Sun's fire to give helpless humans the power of survival, Zeus was so angered that he chained Prometheus to a mountain, where a vulture tore away at his liver for a thousand years. Today, irresistibly drawn to the challenge of bringing fusion energy down to Earth from the stars, scientists tempt Zeus still. Recently, after forty years of strenuous effort, fusion power was finally demonstrated in the laboratory, first in the Joint European Torus in 1991, and then definitively at Princeton University, in a series of experiments that began in December 1993. This book traces the scientific journey that led up to this exciting achievement, and examines what lies ahead and the impact that fusion could have on the survival and well-being of industrial society in the future. It is not an accident that, in Greek, the name Prometheus means "forethought."
Predating even Prometheus and the Sun, fusion is as old as the universe. Just a few minutes after the Big Bang, when time began, the unbelievably hot universe had expanded and cooled sufficiently to allow hydrogen nuclei to form deuterium, and deuterium to fuse into helium. Though most of the deuterium was consumed in this early, cataclysmic burst of fusion reactions, a trace survived. It is this trace of deuterium, together with small amounts created in later astronomical events such as supernovas, that is the main motivation for fusion energy research today. This deuterium, itself a form of hydrogen, is a small constituent of all water, about one part in five thousand. Yet, given the vast amount of water available, even this trace amount of deuterium represents an almost limitless supply of energy on Earth.
The first speculations about how to tap this vast store of energy were made a few years after Albert Einstein's brilliant deduction, in 1905, that mass can produce energy, according to his famous formula E = [mc.sup.2]. Since the days of the ancient Greeks, philosophers and scientists have sought the nature of things in tiny building blocks, called atoms, of which all material objects are composed. These atoms were thought to be indestructible. Then, in 1911 Lord Rutherford postulated the nuclear atom, consisting of a heavy nucleus with a positive electric charge, surrounded by a cloud of negatively charged electrons. Electrons had been discovered earlier, by J. J. Thomson, in 1897. The ultralight electrons, jumping from one atom to another, would turn out to explain all of chemistry, the roaring energy of steam engines, automobiles, and blast furnaces, and all that constitutes the industrial age as we have known it. But the tiny, heavy nucleus of atoms held a secret store of energy far greater than anything ever imagined before.
The first publication tying Rutherford's atom and Einstein's theory to an explanation of the stars appeared at the start of the Great Depression, in 1929. On the basis of the known masses of atoms, the paper's authors, R. d'E. Atkinson and F. G. Houtermans, predicted that the fusing together of the nuclei of very light atoms (such as hydrogen) would produce new atoms that would weigh less than the total weight of the original constituents. According to Einstein's formula, this loss of mass should produce an enormous amount of energy, enough to account for the light from stars.
Even in 1929, the possibility of using this new kind of energy on Earth did not escape notice. In a monograph on fusion that he edited in 1981, the physicist Edward Teller relates the story that, when a young Russian, George Gamow, reported on the paper by Atkinson and Houtermans at a meeting, a leading member of the Communist party offered the entire electrical output of the city of Leningrad for one hour each night if Gamow would undertake to produce fusion energy in the laboratory. According to Teller, "Gamow, a physicist of unusual taste and common sense, did not accept the offer." In America, Eastman Jacobs and Arthur Kantrowitz of the Langley Memorial Aeronautical Laboratory did make an aborted attempt to produce fusion in the laboratory in 1939, but the project was soon canceled by the laboratory director.
While nuclear fusion reactions such as those speculated about by Atkinson and Houtermans were soon discovered, and Hans Bethe went on to produce the quantitative theory of fusion energy in stars that would earn him a Nobel Prize, fusion soon took a back seat to the discovery, in 1939, of the nuclear fission reaction, which led to the development of the atomic bomb during World War II and the fission-based nuclear reactors of today. To date, both fusion and fission are seen as a source of nuclear energy to produce heat, which in turn produces steam to drive electric generators. However, the nuclear energy itself is produced in very different ways in fusion and fission reactions.
As its name implies, nuclear fission is the splitting in half of a heavy nucleus, such as that of uranium-235 (so named because it has 235 times the mass of a hydrogen nucleus). The two halves, called "fission fragments," form lighter elements that are usually radioactive. This is the nuclear waste from today's nuclear reactors, which must be safely protected from accidents during reactor operation and eventually disposed of in deep underground vaults away from public exposure. By contrast, as we have seen, nuclear fusion is the combining of two very light atomic nuclei, usually forms of hydrogen, to form a heavier element. Though fusion is not totally devoid of radioactivity, its main by-product is usually helium, the harmless gas used to fill balloons. The other main difference between fusion and fission is that fission can be made to occur relatively easily, by assembling a sufficient mass of uranium or plutonium in one place, whereas fusion only occurs at the enormous temperatures found at the center of stars, or in a nuclear bomb blast. Thus, while both fission and fusion have been used in nuclear weapons, a fission bomb is needed to detonate a fusion bomb. It is these differences that lead us to believe that fusion power, if it could be developed, would give fusion advantages in terms of environmental acceptance. But it is because creating fusion is such a demanding task that fusion is still in the research stage, while fission-based nuclear reactors already provide about 20 percent of the electricity generated in the United States and 70 percent of the electricity generated in France.
The first public evidence that anyone was thinking about fusion reactors appeared in the newspapers in March 1951, when I was a sophomore engineering student at Vanderbilt University. President Juan Peron of Argentina had claimed that a German scientist in his employ had produced fusion in the laboratory. While I do not remember seeing this in the Nashville newspapers, and the New York Times immediately claimed that such a thing would violate the laws of physics, an astute astrophysicist named Lyman Spitzer, tantalized by the claim, set about devising his own solution to the problem. Soon thereafter, with the approval of the U.S. Atomic Energy Commission, Spitzer established what would become the Princeton Plasma Physics Laboratory.
All of this was still unknown to me when I took my first job in 1957, fresh out of graduate school, in the still-secret fusion research program at the Oak Ridge National Laboratory. It is amazing now to think back to how little--and yet how much--we knew at that time. The seeds were there, many of them in a book Spitzer had published in 1956, which I devoured in every spare moment. Yet for every answer, ten new questions appeared. So that you can begin to share this experience, please join me now as we delve back in time to the discoveries that lay the groundwork for fusion science.
Let us start from the Rutherford atom, with its heavy nuclear core surrounded by electrons circulating around the nucleus, somewhat as planets circulate around the Sun. Picturing atoms in this concrete way is metaphorical, but useful. Looking more deeply, we find that the nucleus itself is a cluster of even smaller particles: protons, each with one positive charge (exactly equal to the negative charge of an electron); and neutrons, electrically neutral particles postulated by Rutherford but first discovered in the laboratory by James Chadwick in 1932.
The various chemical elements are then built up in the following way: First there is the nucleus of an ordinary hydrogen atom, consisting of a single proton and no neutrons. One proton with one electron circulating around it is a hydrogen atom. Adding one neutron to the hydrogen nucleus produces a deuterium nucleus. Because it still has only one positive charge, deuterium behaves chemically like hydrogen, and it is called an "isotope" of hydrogen. It is for this reason that deuterium is found thoroughly mixed with ordinary hydrogen in water; chemically, one isotope of hydrogen is as likely as another to join with oxygen to form water. Combining two neutrons with a proton gives yet another isotope of hydrogen, called tritium. To obtain heavier elements, we simply add more protons and neutrons, either one at a time, or by combining, or fusing, lighter elements.
As we shall see, the fusion process most likely to be used in the first fusion reactor is the combining of deuterium and tritium nuclei to make the common form of helium, helium-4. It works like this:
(p) (p) (p)(p) (n) + (n)(n) = (n)(n) + (n) deuterium tritium helium neutron
Here p stands for proton and n stands for neutron. Deuterium and tritium nuclei contain one proton apiece, and combine to form helium, which has two protons. The helium nucleus also contains two neutrons, one from the deuterium and one from the tritium; one neutron is left over, since tritium has two neutrons. We will call this the DT reaction.
This little sketch is the only nuclear physics we will need to know. I have used it many times to explain what fusion is all about to lay persons and students alike. This sketch can tell us about both the promise and the problems of fusion research. It simply says that fusing deuterium and tritium, which are forms of hydrogen, produces helium and a neutron.
The first point to be made from this sketch of the DT reaction is this: Though we have accounted for all the protons and neutrons making up the various nuclei, if we were to carefully weigh the deuterium and the tritium together (or more realistically, a large batch of deuterium and tritium in equal proportions), and then were to weigh the helium and the neutron, we would find that a tiny fraction of the original mass had been lost when the deuterium and tritium nuclei were fused to create the helium and the neutron; one helium nucleus plus one neutron weighs less than one deuterium nucleus plus one tritium nucleus. Of course, as we have seen, it is this loss of mass that accounts for the large energy release in the fusion process, according to Einstein. This energy shows up as the fast motion of the helium nucleus and the neutron, each moving at speeds exceeding 10 million ([10.sup.7]) meters per second. (A meter is about 3.28 feet.) This corresponds to millions of times more energy than is produced by a typical chemical reaction such as the burning of gasoline; hence the enormous energy available in even the trace amounts of deuterium in water--just the tiny amount of deuterium in one gallon of water would produce as much energy as three hundred gallons of gasoline.
The second point is that the product of the DT reaction, helium, is neither radioactive nor chemically harmful. So the "ashes" from fusion are benign. Again, contrast this with the nuclear fission of a heavy nucleus such as uranium, which, when it splits, invariably produces smaller nuclei that are radioactive and therefore must be carefully disposed of as nuclear waste. Note, however, that DT fusion reactions do produce free neutrons moving at high speed. These fast neutrons create radioactivity when they bombard the materials--especially metals--of which the fusion reactor is constructed. Thus, while the fusion process does not produce nuclear waste directly, the fusion reactor itself does become radioactive, and its components must be disposed of safely when the reactor is finally shut down after the usual thirty-to fifty-year life of any electric power plant. In principle, this problem can be minimized by deliberately choosing construction materials that either produce less radioactivity or produce radioactivity that dies away more rapidly, so that the disposal deep underground that is required for fission waste is not needed. Choosing construction materials wisely is a vital part of fusion research. We shall return to this important point in discussing the environmental characteristics of fusion energy in chapter 15.
The last point to be made in this discussion of the DT fusion reaction concerns the positive charges of the deuterium and tritium nuclei that we would like to fuse together. Ordinarily, atomic nuclei, protected by their clouds of electrons, never come close enough to fuse, so fusion could never happen between ordinary atoms. Even if we strip away the electrons (not too difficult a task), the nuclei would strongly repel each other because of their positive electric charge. The reason is that the forces that bind nuclei together, though very strong, act only at extremely tiny subatomic distances, whereas the positive electric charges of the two nuclei would begin repelling each other at much larger distances. This suggests that the only way to bring about fusion is to create circumstances in which the deuterium and tritium nuclei are moving toward each other at sufficient speeds to overcome their mutual repulsion and allow a close collision, so that nuclear forces can take over. Since motion (or, more precisely, random motion) is heat, fusion is only likely if the deuterium-tritium gas mixture is very hot--at a temperature of many millions of degrees. The recent "cold fusion" attempt to sidestep the need for high temperatures claimed a different mechanism for getting nuclei together, but so far this idea, and almost all other such ideas, have proved to be vain hopes. A genuine exception is "muon catalysis," involving the use of subatomic particles called "muons," artificially created by particle accelerators, to enhance the fusion rate, but this has not yet seemed sufficiently feasible to attract much attention. Thus all serious fusion research today assumes that we must do it Nature's way, by creating on Earth the extremely high temperatures that caused fusion to turn deuterium into helium at the beginning of time.
This much was known in the early 1950s when, flush with the success of having developed the hydrogen bomb, physicists in America, England, and the Soviet Union first began to contemplate how to put fusion to practical use, not as an explosive but as an abundant and--as they thought--environmentally clean source of energy, for the benefit of all humanity. They knew that the idea was an old one. As we have seen, Atkinson and Houtermans had first postulated nuclear fusion as the source of energy in the stars in 1929, a few years before fusion reactions were actually discovered in the laboratory. Researchers in the 1950s knew also that they could not simply copy the hydrogen bomb, in which the high temperatures needed to trigger fusion are obtained by first exploding a smaller fission bomb made of uranium or plutonium. Nor, they thought then, could they simply imitate the fusion that had occurred naturally during the "Big Bang" explosion that created the universe. As it turned out, some fifteen years later scientists would, with the aid of lasers, successfully create in a microscopic pellet of deuterium and tritium conditions very similar to those of the Big Bang. We will return to this "inertial confinement" approach to fusion in chapters 11, 12, and 13. But in the early 1950s, the scientists' thoughts turned instead to the stars.
About a million years after fusion ceased in the early universe, the hydrogen and helium that then constituted all matter had, through the continuing expansion of the universe, cooled to the point that great clouds of these gases began to collect as stars. Because of their great mass, these stars--initially very cold and diffuse balls of gas--began to be compressed under the force of their own gravitational attraction. Any gas cools as it expands and heats as it is compressed. And as the stars were compressed, their centers became hotter, eventually reaching temperatures of millions of degrees, at which point fusion began all over again.
The main fuel for fusion in the stars--which even today is their primary source of heat and light--is the abundant ordinary hydrogen left over from the Creation. (The other main constituent of stars is the primordial helium produced by fusion, accounting for about a quarter of the mass.) The fusion of ordinary hydrogen in stars is a very improbable process, only possible because gravity prevents the escape of the hydrogen so that it eventually undergoes fusion reactions no matter how long it takes. The reaction rate is enhanced by the fact that the density of the compressed stars is high, often much greater than that of water, or any of the other materials familiar to us on Earth. By imagining water heated to a temperature of millions of degrees, one can appreciate the extreme outward pressure in the center of stars, pressure that only stars' enormous gravitational forces could withstand.
In contrast with the exploding early universe, our Sun, or any other star, can be thought of as a steadily burning fusion "furnace" in which the fusion reactions themselves continuously heat the fuel to the extraordinary temperatures required to maintain the fusion process, much as an ordinary fire continually heats and consumes more fuel. Indeed, we often refer to fusion as "burning," and to the fusion reaction, because heat is required, as a "thermonuclear" reaction. The stellar fusion furnace burns more or less steadily because it is held together by its own gravitational attraction, which just balances the tremendous outward pressure of the hot fuel at its core. To imitate a star on Earth, we would strive to create a steadily burning fusion furnace, but one of practical size.
Our first decision would be the choice of fuel, for just as some chemicals burn more easily than others, some types of nuclei fuse more easily than others (and heavy ones do not fuse at all). Scientists in the 1950s soon focused on the DT reaction discussed above. They chose this reaction because the temperature at which fusion proceeds rapidly enough to be useful is lower for this reaction--about 100 million degrees Celsius (180 million degrees Fahrenheit)--than for any other that we might consider. For this same reason, a mixture of deuterium and tritium remains the fuel of choice for the first generation of fusion reactors, although other choices, such as pure deuterium fuel, are still being considered. The use of tritium as fuel does add a complication. Tritium is radioactive, decaying to helium-3 in a dozen years or so, and therefore it is not available in nature. However, enough artificially produced tritium is available for experiments, and the tritium fuel to sustain a fusion electric power industry could readily be produced inside the fusion reactors themselves by bombarding lithium, which is abundant in nature, with the extra neutrons produced in the DT reaction. This added complexity in using DT fuel, and the safety issues posed by the fact that tritium is radioactive, will be discussed in chapters 10 and 15.
Our second decision would concern what kind of force we might apply to hold the hot DT fuel together, as gravity holds stars together. The high temperatures involved preclude simply putting the DT gas in a box. We certainly could not do so if the hot gas were as dense as the interior of stars, for the box would explode. That problem could be overcome by evacuating all the air from the box and introducing only a tiny amount of DT gas, in order to reduce the pressure. But the gas, being in contact with the walls of the box, would quickly cool off and fusion would cease. Still thinking of the stars, the early fusion scientists began to think of ways to suspend the burning gas inside the box, touching nothing, as a star is suspended in space. Realizing that the hot gas would conduct electricity, they began to think of magnetic fields.
Because we will encounter magnetic fields over and over in the next few chapters, let us pause a moment to recall what magnetism is all about. Magnetism was known to the ancients in the form of lodestone, and nearly every child today has played with horseshoe magnets, or the magnets that hold reminder notes on the refrigerator door. The idea of a "field" surrounding a magnet was invented by Michael Faraday and others, in the early nineteenth century, to describe the force between a magnet and a piece of iron (or another magnet). This force is felt long before the objects touch--hence the idea of a field, or aura, around the magnet.
We also speak of electric fields around electric charges. Thus, there is an electric field surrounding every electron and an electric field surrounding the positively charged nucleus of every atom. It is the electric field of the nucleus, reaching out to the electrons, that holds the atom together.
One of the greatest discoveries in all of physics, probably of even greater practical consequence than Isaac Newton's laws of motion, was the discovery that electricity and magnetism are one and the same. From this discovery came the electric generator, the electric motor, the theory of light, the laser, radio, television, microwaves, and the theory of relativity, with its new idea of the equivalence of mass and energy; and from the equivalence of mass and energy came nuclear power and fusion. We will return to this later, when we are better prepared and when we need it. But by way of preview, I would like to share two points that sum it up.
First, there is a fascinating historical linkage between the explanation of magnetism and our quest for fusion today. This linkage started with Michael Faraday's discovery in 1831 of magnetic induction, which launched the age of electricity. The mission of fusion research is the replacement of the polluting fossil fuels that now power Faraday's dynamos by cleaner fusion energy. Yet, as a purely scientific discovery, it was Faraday's law of induction that led to James Clerk Maxwell's theory of electricity, magnetism, and light; then to Hendrik Lorentz's law of motion of charged particles; and on to Einstein's equivalence of mass and energy. These form the foundation of all branches of fusion science today.
Second, as we shall see, the magnetic force itself is truly strange, a challenge for inventors to visualize. Though trained as an engineer and theoretical physicist, I always wanted to be an inventor, and I finally got my chance, in a modest way, through fusion.
All of the pioneers of fusion research, in the early 1950s, were scientist-inventors, working from limited knowledge and keen intuition about magnetic fields. As our first introduction to their accomplishments, let us look at the early work at Los Alamos, spearheaded by the late James Tuck, an English physicist who spent World War II at Los Alamos and later created the Los Alamos fusion program in 1951, at about the same time that Lyman Spitzer began the work at Princeton. The U.S. Atomic Energy Commission gave the secret project the code name Sherwood, which some said was inspired by "Friar Tuck."
The Los Alamos group focused their work on the "pinch" effect, discovered by Willard Bennett in 1934. The first and simplest magnetic pinch experiments evolved from the study of ionized gases, which also gave us fluorescent lights. As we have seen, the atoms of which a gas is composed are usually electrically neutral, with as many negatively charged electrons as there are positive electric charges on the nucleus. However, many circumstances occur in which collisions among the atoms knock off electrons, leaving free electrons, and atoms with a net positive charge, called "ions." (A bare hydrogen or deuterium nucleus, having lost its only electron, is an ion with one unit of positive charge.) For example, in the fluorescent light the electric current creates ions when the streaming electrons carrying the current collide with atoms in the tube. The early universe also was ionized. It was born this way, the temperature being so high that electrons and nuclei could not stick together to form neutral atoms, any atom so formed being quickly reionized by colliding with another nucleus or electron. We call such a fully ionized gas a "plasma." The hot interior of a star is a plasma.
While the vapor in ordinary fluorescent light tubes is only partially ionized, turning up the voltage and current makes the gas hotter, which is to say, its atoms move about more rapidly, until finally collisions among the atoms produce a fully ionized gas, or plasma, similar to the interior of stars (but much less dense). This is the kind of fusion experiment that was first performed, with ordinary hydrogen (not DT fuel), just to see how hot the gas would get. The researchers were also very much interested in the magnetic field created by the currents in the tube.
The voltage applied to a fluorescent light tube, or to the heftier but similar devices used in the early fusion experiments, applies to the negative electrons and positive ions a force that causes them to move in opposite directions along the length of the tube. The electrons, being lightweight, move fastest. The motion of these electrically charged electrons constitutes an electric current flowing along the tube, just as electrons moving in a copper wire constitute an electric current in the wire.
Now, an electric current creates a magnetic field, and magnetic fields exert forces on electric currents. This is the principle of the electric motor. In the pinch experiment, the electric currents flowing in the plasma cause forces that constrict, or "pinch," the plasma, much as gravitational forces constrict or compress stars. However, magnetic forces are much stronger than gravitational forces; hence the hope that strong magnetic fields could be the basis for a practical fusion reactor. Another important difference, not so favorable, is the fact that, whereas gravitational forces act symmetrically, so that stars are spheres, the magnetic force is two-dimensional, acting only in the two directions perpendicular to the direction of the current, so that a magnetically "pinched" plasma is a cylinder.
It is the two-dimensional nature of the magnetic force that makes this force so strange and taxes the intuition of inventors. The question of how to use a two-dimensional force to confine a three-dimensional plasma suggested a variety of arrangements of external magnets to surround the plasma in a satisfactory way. At Princeton, Spitzer's original idea looked like a pretzel, or a figure eight. Appealing to the stars, Spitzer called his device a "stellarator." At the Livermore branch of the University of California's Radiation Laboratory (now the Lawrence Livermore National Laboratory), Richard F. Post tried to block the ends of a linear device with strong magnets that he called "magnetic mirrors." Bending the straight pinch into a circle yielded yet another shape, which, with a note of whimsy, the Los Alamos team called the "Perhapstron," thinking that perhaps it would work, or perhaps it wouldn't.
Though all these inventions had progeny that are still with us, it soon became clear that they tended to have in common two problems that would demand systematic theory and understanding if magnetic confinement fusion was to succeed. These two major problems, soon evident in the early experiments, have dominated magnetic fusion research ever since. First, whereas in stars the plasma pressure and the gravitational forces confining the plasma are in stable balance, a magnetically confined plasma column is often very unstable, the least disturbance causing an initially straight column to kink and bend sufficiently to come into contact with the tube walls. Second, it was generally found that heat energy flowed away rapidly, cooling the plasma.
Fusion researchers struggled in secret for a few years, but in 1958, at the second Atoms for Peace Conference in Geneva, fusion scientists from around the world were allowed to share the results of their research and lay the foundation for one of the most closely collaborative scientific endeavors ever undertaken. This spirit of collaboration evolved none too soon, as the reality of the two major problems--stability and energy confinement--began to turn early optimism into sobering concern.
The first theoretical progress, beginning in the late 1950s, was the development of a principle to determine whether a given magnetic field arrangement would confine a plasma stably. As we have seen, by the time of the Geneva conference the scientists had produced a variety of inventions. But now, with the new "energy principle," at last one could actually calculate which of these schemes would perform stably.
The second major problem, energy confinement, has proved more stubborn anti remains at the cutting edge of magnetic fusion research even today. Much progress has been made. A convenient way of measuring this progress is the so-called Lawson number, which indicates how close we are to demonstrating energy confinement sufficient for a practical fusion reactor. The goal--the value of the Lawson number at which energy confinement is adequate for a reactor--is called the Lawson criterion, after J. D. Lawson, who first published it in 1956.
Meet the Author
T. Kenneth Fowler is Professor of the Graduate School at the University of California at Berkeley. Before joining the Berkeley faculty in 1988, he spent thirty years in fusion energy research at the Oak Ridge National Laboratory, at General Atomics, and finally at the Lawrence Livermore National Laboratory, where he served as associate director and head of magnetic fusion research from 1970 to 1987. He was elected to the National Academy of Sciences in 1987.
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I was looking for more information concerning the Princeton fusion research project. I am very interested in the future of our power resources. Fusion seems to me to be a really good option. Reading this book gave me a lot of insight to the extreme chalanges involved with magnetic confinement of plasmas. The book explaines in detail some of the obstacles we are trying to overcome in order for this technology to become a reality. Also discussed are other technologies that are very promissing.