תחומי התמחות

קניין רוחני


Scientific and Unscientific Thoughts about life and nuclear fusion

When Amir Friedman asked me to write this commemorative piece in honor of his late mother, Rivka Friedman, I wondered how could I tie in science with such heavy and emotional matters as life and death. Not that science is not a “loaded” subject in itself, but it seemed to me that telling the story of my research (pre) occupations, trying to explain lay persons what thermonuclear fusion is and what is it good for, would be almost indecent in this context.

By: Prof. Michael Finkenthal

WA philosophical approach would have helped, but it was made clear to me that I should write about my scientific work and not about philosophy. Science still has a certain prestige in our world in despite of many disappointments; the positive is still perceived by the large public as prevailing over the negative effects generated by some aspects of modern science.

In Newton's time, a poet concluded that Nature “stood all subdued to him (that is, Newton) and open laid/Her every latent glory to his view”. Surprisingly enough, there was a time when poets were the most enthusiast supporters of science and scientists; moreover, to be a good poet one had to be first a good scientist (and philosopher). Dryden (born in 1671), wrote that “a man should be learned in several sciences and should have a reasonable philosophical and in some measure a mathematical head, to be a complete and an excellent poet”.  These words give me comfort and strength as I try to write about science while thinking of such things as the meaning of our lives or the moral quality of our deeds.

My research in physics is in the area of processes and phenomena occurring in hot plasmas. No, this is not the plasma of the doctors (“the colorless fluid part of blood, in which the corpuscles are suspended”, as defined by the Oxford dictionary) but rather a “kind of gas containing positively and negatively charged particles in approximately equal numbers” (again, the same dictionary's definition).

How are such “positive” and “negative” particles born and why would they want to stay together? We all know from the boring physics lessons of our forgotten high school years, that atoms are “neutral”, that is the electrical charge of their nucleus is equal to that of the electrons moving around it. Much like the solar system: the planets move around the Sun, except that they are not electrically charged.

This model is good enough to understand the basic thing. If however, a huge asteroid would hit a smaller planet in the solar system, it could remove it from its orbit, which would be a total catastrophe for us, on Earth!.

In a similar way, if an electron is removed from its orbit around the nucleus, an “ion” is born: it will have a net positive charge, and very different properties from its originator, the atom.

That is because the newly created entity, the “ion”, will always be sensitive to electric and magnetic fields and to fellow ions. Moreover, it will irresistibly attract electrons. Such a mixture of positive ions and negative electrons is called a “plasma.

Why not “recombine” the electrons with the ions to go back to their former status of a gas of neutral atoms? Because the relatively high temperature at which the plasma exists imparts a lot of energy to these particles: they become too restless and lose the quiet, peaceful behavior which would make the match possible.

Higher the temperature, more violent the movement of the particles becomes; hot plasmas are the site of energetic encounters between particles. As a result of such violent encounters, two nuclei can fuse together. We call this process “nuclear fusion”.

Do you remember the Einstein stamp printed in Israel in 1955 (I believe it was printed the year Einstein died)? We see on this stamp the famous formula, energy equals mass multiplied with the square of the velocity of light. It is a mysterious formula to the lay person, but everybody can understand its meaning: mass can be “transformed” into energy.

Now, it turns out that when we add up the masses of two particles, such as those of the two nuclei which fused, the mass obtained after the fusion process is slightly less that the addition of the two initial masses.

Here comes in another law our physics teachers used to drive us crazy about, the “law of conservation of mass”: mass can be transformed but cannot be lost in a physical process. If the product of the fusion reaction is less “heavy” than the sum of the two initial components, the “missing” mass must becomes energy! And indeed, that is what happens: nuclear fusion reactions create a lot of energy.

This is what happens in the core of the Sun (and while a tiny part of this energy makes some of our summer days unpleasant it made at the same time possible life on earth!) and in the stars. That is what happens also in the so called “hydrogen bomb”. But what if one would try to harness this energy, to control it? If we will be clever enough to do it, we could have an amazing energy source.

However, energy produced through nuclear reactions, is suspicious. We all know about the “Tchernobil” and the “Three Mile Island” accidents, we all live with the danger of nuclear arms proliferation hidden behind “peaceful” nuclear power programs. Except that this is a different kind of nuclear reaction; this is a reaction of “fission”, not of “fusion”. What's the difference?

In this case, unlike in the one explained above in connection with plasma physics, heavy nuclei (such as those of uranium for instance), are split. Again, when we “weigh” the reaction products, we find that some mass is missing. As in the case of the fusion reactions, some of the mass has been transformed into energy.

The problem though with this fission reaction is that it produces dangerous by products which can be used to produced atomic bombs. The waste is also very dangerous because its radioactivity is very long lived (thousands of years). The disposal of such waste materials is a very long term risk.

This is not the case with the fusion reactions: in this case, light nuclei - such as for instance those of Hydrogen - fuse together and the Helium nuclei produced are not ecologically dangerous and cannot be used as weapon materials. Not less important is the fact that the “fuel” of these reactions is “Hydrogen” which can be extracted from … sea water! Amazing, isn't it? But if things are so good, why didn't we do it already?

I am often asked the above question when I try to explain nuclear fusion to people outside this domain.  The easiest way out is to say that intuition would tell that it is much more difficult to bring something together that to break something apart. This image might be helpful but of course, it is an oversimplification and it doesn't explain in fact, anything.

Let us go back to the beginning of my exposition. I said above that once we heat up a “plasma”, some of its constituents will reach such temperatures that nuclei will start to fuse. How high a temperature would be therefore, needed? If the interior of the Sun is a good indication, fusion temperatures should be of the order of hundreds of millions of degrees Celsius! How can we possibly create on Earth such temperatures and how can we contain material under such conditions?!

In simple terms, these are big challenges in the “Controlled Thermonuclear Research”. We need to create conditions in the laboratory, on Earth, which would simulate those existing inside the stars. And as one may imagine, this is not an easy matter. Now the metaphor I used above makes probably more sense.

As surprising though as it may be, even the physicist miscalculated the difficulties involved in nuclear fusion. They looked at the history of the nuclear fission and assumed that things will happen on the same time scales.

The fission of nuclei was first demonstrated in the laboratory in 1934 (in Germany, by Otto Hahn and Lise Meitner), the first controlled “chain reaction” was performed during the WWII years (by Enrico Fermi in Chicago); the bombs followed about ten years later; another ten years roughly and nuclear power reactors were working on submarines.

Therefore a ten-years cycle was assumed for the development of nuclear fusion technology, from feasibility experiments to application. The success of the hydrogen bomb programs in USA and Russia convinced scientists and politicians alike, that they are very close to fusion reactors which will produce endless amounts of energy at no risk. 

Everybody wanted to have the monopoly of this cheap and practically endless source of energy, therefore everybody kept secret the work on this subject. Until 1959, when people realized that it will not be easy at all to achieve nuclear fusion. The experiments are very complicated, the equipment is costly, some technologies needed to handle heat and materials to be exposed to such levels of heat were (and are) not yet available.

It would probably be a better idea, concluded scientists and politicians alike, to open up the research for international cooperation. And since, that is exactly what happens: for more than thirty years scientists from the entire world work together on a multitude of nuclear fusion scattered all over the globe.

As a result, at these very days a decision is expected concerning the future site of the International Test Reactor (ITER), which will be the first prototype of a fusion reactor to be built in common by USA, Russia, Europe and Japan.

But we are not there yet; to understand what such a project means, we have to go back to the basics for another brief moment. Charged particles have this strange property: they 'feel' the presence of electric and magnetic fields: moreover, when in a magnetic field, a charged particle, ion or electron, will follow the field lines. If you want to trap them therefore, what you have to do - in principle - is to have them confined within a magnetic field.

Imagine a donut shaped magnetic structure; plasma particles will circle round-and-round the donut, trapped inside it. This is the principle of operation of a device called a “tokamak” (this an acronym of several words in Russian; they invented this particular confining concept). The Americans had a different confining scheme, the “stellarator” (named so for obvious reasons; we try to simulate a star, don't we?).

The “tokamak” was a better confining device than the “stellarator” and it is also a simpler concept. By the early seventies it was adopted by almost the entire fusion community as the mainstream fusion reactor concept.

There are alternatives to it (the so called “alternative concepts”): what one tries to optimize in all these devices is the plasma temperature (as high as possible), the confinement time (as long as possible) and the plasma density (as many colliding particles as possible).

When all these parameters will reach simultaneously a given value, we will have a break-even situation. That is, from the thermonuclear reactions realized within the hot plasma confined by the magnetic field, we shall get as much energy as we put in. The proof-of-feasibility of this stage has been achieved already a few years ago at the Princeton Plasma Physics Laboratory in US and in Europe, at the Joint European Torus experiment in England.

The next stage to be attained will be that of the “ignition”: the fusion reaction will produce during this stage net energy to be transformed into electricity. This is still ahead of us. How far ahead? It depends: at one of the American Physical Society meetings a few years ago, a distinguished Indian physicist complained in a keynote speech about the selfishness of the Western world: “it will take some fifty billion dollars to get to a fusion reactor, that is about ten dollars every human being alive on earth (at that time). Most of the world is poor, the West though could do it, but it doesn't care because it has access to large sources of cheap energy”.

This is partly true. We humans are not too wise a species: as long as we can spend and/or plunder mother nature, we will do it. When we feel endangered, we are smart and try to get out of the trap. Sometime we succeed, but it is hard to tell how well we will do in very complex situations when we not only lose control but  the alternatives we shall face, will be many and it will be impossible to predict which one will materialize.

During the years of the oil-crisis of the late seventies, America was scarred and as a result decided to try to achieve the goal of fusion energy by the year 2000! The Mc Cormick amendment passed by the Congress in 1980, predicted that by that date USA would have spent about twenty billion dollars in this area of research (on the average, a billion dollars a year).

Since then, many things happened and the American fusion budget settled down for years at annual budget levels of the order of two three hundred million dollars. It seems still a lot of money, but keep in mind that a small experimental “tokamak” device costs about fifty million dollars and the ITER project mentioned above, is estimated at between three and six billion dollars!

By now the reader has asked probably himself where do we, that is Israel, stand on all these and has - in view of the things said in the last paragraph - reached the conclusion that all this is above our head.

In a way this  right. However, we (a bunch of scientists with the support of a few politicians and technocrats) tried to bring our country into the orbit of the world fusion research effort. The person who helped a lot was Yuval Neeman; he encouraged me and a few enthusiasts at the Hebrew University and at the Atomic Energy Commission to try to set up a fusion experiment in Israel.

During the first half of the nineties, I worked hard to promote a project I named SARIT (acronym standing for Small Aspect Ratio Israeli “Tokamak”). I thought that the time was ripe for such an adventure: Russia just opened up for scientific collaborations unthinkable before, we could purchase very inexpensive equipment there and in addition, use the expertise of many new immigrants from Russia as well as know-how of Russian scientists.

Together with a friend and colleague from AEC we visited the Ioffe and Kurchatov Institutes in St. Petersburg and Moscow, established the appropriate contacts, set up working teams in the relevant area of research and invited prominent scientists from the newly opened up country, to Israel. I envisaged the project as a national collaboration effort based in Jerusalem, at the Hebrew University. It was supposed to be funded by several governmental organizations and ministries and the work would have been done by small groups belonging to several universities and research institutions in the country.

But the logistics seemed too complicated to the bureaucrats; on the other hand, some colleagues were afraid that such a big effort will drain the resources of other research groups. There were institutional interests at work too. The end result was that tired of fighting the windmills at home, I left for a sabbatical and continued my collaboration with the Princeton group (and I am still doing it to this day).

At present, there are individuals involved in fusion research and quite a bit of expertise floating around in Israel, in this domain. I am sure that a day will come when we will join formally the fusion effort.

When I started my involvement with this field of research I came to it from a very special angle. Neither myself, nor the people I was working with (my teachers at first, my students latter), intended to do fusion research proper. We worked in a field which was in a way a supporting area, that of “spectroscopic diagnostics” of hot plasmas.

The question we asked was: how do you measure any parameter in an “object” heated at temperatures of the order of millions of degrees? You clearly cannot “stick in” any thermometers, any probing devices, as you would do in ordinary matter.

As in astrophysics, where you learn about things by remote sensing, in plasma physics experiments you have to understand the properties of the magnetically confined or free plasmas and measure their parameters, by interpreting the “light” emitted by them. But as visible light can be dispersed into the colors of the spectrum, the same is true of any kind of light, visible or invisible (like the X-rays for instance).

The behavior of the charged particles determines the emission patterns of the plasma; parameters such as temperature or density of particles, influence their light emission patterns. Somewhat as the passing of electricity is affecting the light emitted by a filament (this illustration is not to be taken though, too literally!). The plasma properties are encoded in their spectroscopic emission, we say.

At the Racah Institute of Physics in Jerusalem there was a very long tradition of studying atomic physics and spectroscopy. Giulio Racah was a bright young Italian physicist  and a Zionist; unlike many of his peers before WWII, he decided to emigrate to the Holy Land and help build in Jerusalem a strong Department of Physics. Everybody trained afterwards in the graduate courses of this department was well educated in the area of atomic spectroscopy.

That is why, we could address quite complicated problems posed by the newly started “tokamak” programs in Europe and USA during the seventies.  Gently- slowly, we have become a very well known support group of many fusion research programs in the world. In time, the exposure to this research brought me -and some of my students - to become involved with other research topics related to hot plasmas, such as turbulence, fluctuations, particle transport, etc. And we moved also beyond the realm of the fusion experiments: we extended our interests into laser produced plasma physics, X-ray lasers, astrophysics.

But to be situated at the forefront of these lines of research, one needs indeed extensive material resources. What can we do, with our limited means, if anything at all, in our universities? Some would say that we should renounce “expensive science” and set priorities. Some would think that we should squeeze more our brains and if we are good enough we can still do significant things even in these expensive areas of research, with limited means. This question has brought me back to the gray area of philosophy and sociology of science. However, since I was asked not to get entangled in philosophy,  I do not need to answer the above question here.

I must end however this brief account of my scientific whereabouts recognizing that I cannot say though, a thing about how science relates to our great existential problems. To say that science makes possible for us to continue to practice and/or cope with them, sounds trivial. True, in a peaceful world, with plenty of clean energy, we shall live better and think better. Some sort of “ein kemach ein Tora”, I guess.

The only meaningful, sober thing I can state is that seeing clearly what science is and what it can do, enables us to see also what science cannot provide. Science deals with everything which can be quantified in a meaningful way. Of course, we may try to quantify happiness, but that will not be too useful.

On the other hand there are so many things which touch us deeply, such as human suffering, fear of death, love and hate, which science will never be able to make sense of. They are of the domain of the artist, of the poet, of the philosopher. There is scientific truth we seek in Nature and there is poetic or religious truth which is to be found in the Human Soul and beyond. Some call this beyond God, some Beauty and some will use the word Transcendental.

We as scientists, have the duty to be open to these other truths and sensitive to the interrogation of the poet: “Where is the wisdom we have lost in knowledge. Where is the knowledge we have lost in information?”. We should try to explain the world while remaining conscious that we are only a tiny part of it and of its infinite mystery.

* Prof. Michael Finkenthal (Johns Hopkins University, Baltimore). 

אין באמור לעיל כדי להוות ייעוץ משפטי או חוות דעת, או תחליף ליעוץ משפטי אצל עורך דין.
בכל מקרה ספציפי יש לפנות לקבלת ייעוץ משפטי מעורך הדין העוסק בתחום.


כתבות נוספות בתחום


אין באמור לעיל כדי להוות ייעוץ משפטי או חוות דעת, או תחליף ליעוץ משפטי אצל עורך דין.
בכל מקרה ספציפי יש לפנות לקבלת ייעוץ משפטי מעורך הדין העוסק בתחום.