Thursday, June 2, 2011

Nuclear Fusion: the elusive genie

The recent announcement by two Italian researchers of a new method of attaining energy from nuclear fusion has brought back hopes of an easy and inexpensive way of generating energy. It is almost if the nuclear genie that Walt Disney had created in the 1950s is back with new promises of energy "too cheap to meter." But what exactly do we expect from fusion? Why do we think it could solve our problems? Perhaps, these possibilities have been much overrated.

Maybe it is because of the brightness of the sun. Maybe it is because of the awesome power of the "hydrogen bomb." Or, maybe, it is the abundance of hydrogen in the oceans that makes us think of it as an inexhaustible fuel supply.  Whatever the case, the concept of "nuclear fusion" has a nearly magic ring to it. Touted as the ultimate solution to all of our problems, the dream of nuclear fusion is nicely summarized in the slogan coined in the 1950s: "energy too cheap to meter".

And, yet, dreams have a way of shattering when confronted with the hard reality. Fusing two hydrogen nuclei together, the way used by the Sun to produce energy, turns out to be extremely difficult to do on earth; even though we try to do it along an easier route that uses the isotopes of hydrogen called "deuterium" and "tritium."

There are good reasons for this task to be so difficult. Two atomic nuclei face a formidable electrostatic barrier that repels each other as they get closer. We tried just about everything possible to overcome that barrier. With the "tokamak" machine, atoms collide inside a plasma that reaches extremely high temperatures. In inertial confinement fusion, pellets of frozen deuterium-tritium mixtures are bombarded with laser beams and electron beams. Exotic particles called muons have been generated expressly to lower the repulsion barrier that keeps nuclei separated. And then, there is piezo-fusion, sono-fusion, bubble-fusion, the "fusor" machine, the fusion of boron with hydrogen in the so called "plasma-focus" technology, the "H-bomb" and, finally, the large number of claims of "cold fusion" (or "LENR" - low energy nuclear reactions).

Many of these devices work; in the sense that they generate observable fusion events that appear as emissions of gamma rays or neutrons. The problem is that we could never manage to attain a flux of fusion events large enough to repay the energy needed to start it. There have been many claims of "anomalous heat" in LENR, but no clear demonstration that fusion reactions were involved.

The only case where fusion is said to produce energy is the "hydrogen bomb" or "H-bomb." But even this device turns out to be overrated in terms of fusion power. There simply doesn't exist a "hydrogen bomb" intended as deriving its explosive power directly from fusion. All existing nuclear bombs are based on the fission of uranium or plutonium, although most are "two-stage" weapons in the sense that they use the fusion of deuterium and tritium as a way to create a neutron flux that increases the fission yield.

So, there is no evidence that we ever came close to obtain useful energy out of nuclear fusion. There remains the example of the Sun. It is up there, so bright; why can't we obtain something similar, here? But, maybe, even the power of the sun has been somewhat overrated. Here are some considerations on this point by the Italian nuclear physicist Luigi Sertorio. He has 50 years of experience in the field and in a recent interview he compared the search for fusion to the search for perpetual motion. To check his numbers, you may go to this link.

Luigi Sertorio on Nuclear Fusion. (translated from Italian)

It is obvious that, as a scientific theme, nuclear fusion on earth is an interesting phenomenon, be it inertial fusion by laser or magnetic confinement fusion. That, then, it can be made to work, is another story. When they say, "fusion is the energy of the sun; man wants to replicate on earth what happens on the sun", it is a hoax; it is due to ignorance. Those who say this should not pass the entrance exam for college. Stars produce a power of one tenth of a thousandth of a watt (10E-4) per kg. Do you realize what this means? A car engine produces something like hundreds of watt per kg. There is a ratio of one million in favor of a car or a scooter in comparison to the sun. So, when we want to make a terrestrial fusion machine that produces power, we are very far away from the way stars work. 

Stars are fusion energy machines that work at extremely low specific power. What happens inside stars is the minimum that exists in nature. And the funny thing is that stars work for billions of years. What we want to do on earth in terms of nuclear fusion is completely different. It is supposed to be one million, ten million times more efficient in terms of energy per kg. Nature said that when she wants to do nuclear fusion she does it in stars. She taught us how it can be done. Man says: "thanks a lot, mother nature, I want to do something completely different." And mother nature says, "All right, big head, now let's see what you can do!" I hope I shall live long enough to see the Lawrence Livermore lab in California shutting down. It has been gobbling up money for 30 or 40 years, maybe half a century, and it makes "boom, boom", these big booms, but no fusion comes out of it.

To finish this story, physics should go on - it must go on. Any idea can be pursued, until the physics community says "enough. It doesn't work, it makes no sense, let's look for another way." Science has always been going on in this way. Some people look for perpetual motion because they haven't understood that there exist some thermodynamic principles that exclude perpetual motion. I can tell you that it happened to me to be the referee for papers proposed to editors, or to journals such as the “Nuovo Cimento.” Someone in his solitude had found the perpetual motion machine. All right, as a physicists who knows of thermodynamics it is my duty to tell to this gentleman "go read papers which are based on physical principles and stop looking for perpetual motion". But it is not stuff that should be forbidden. If someone wants to look at this subject - and he doesn't bother us too much - let him look for perpetual motion. If someone wants to look for inertial fusion; look for it - fine. But don't use up too much money and don't ruin the California budget because you want to look for inertial fusion. But it should not be condemned. Already Cardinal Bellarmino and the Church have condemned research. It is research that, at some point, must say to itself. "Stop, this direction is not the good one. Let's look for another one."

So, what is that we are seeking for, exactly? What miracle do we expect to receive from fusion power? It looks like we are looking for some magical lamp buried in the sand, out of which a magic genie will come out and save us from ourselves. We started looking in the 1950s and it seems that we haven't grown up, yet.


Ugo Bardi is a member of the Club of Rome, faculty member of the University of Florence, and the author of "Extracted" (Chelsea Green 2014), "The Seneca Effect" (Springer 2017), and Before the Collapse (Springer 2019)