All Quiet on the Fusion Front: Notes on ITER and the National Ignition Facility

It’s quiet out there – too quiet.  The National Ignition Facility, or NIF, at Lawrence Livermore National Laboratory, a giant, 192 beam laser facility, has been up and running for well over a year now.  In spite of that, there is a remarkable lack of the type of glowing journal articles with scores of authors one would expect to see if the facility had achieved any notable progress towards its goal of setting off fusion ignition in a tiny target with a mix of fuel in the form of tritium and deuterium, two heavy isotopes of hydrogen.  Perhaps they will turn things around, but at the moment it doesn’t look good.

The NIF was built primarily to study various aspects of nuclear weapons science, but it is potentially also of great significance to the energy future of mankind.  Fusion is the source of the sun’s energy.  Just as energy is released when big atoms, such as uranium, are split, it is also released when the central core, or nuclei, of light atoms are “fused” together.  This “fusion” happens when the nuclei are moved close enough together for the attraction of the “strong force,” a very powerful force but one with a range limited to the very short distances characteristic of atomic nuclei, to overwhelm the “Coulomb” repulsion, or electric force that tends to prevent two like charges, such as positively charged atomic nuclei, from approaching each other.  When that happens with deuterium, whose nucleus contains a neutron and a proton, and tritium, whose nucleus contains two neutrons and a proton, the result is a helium nucleus, containing two neutrons and two protons, and a free neutron that carries off a very large quantity of energy.

The problem is that overcoming the Coulomb force is no easy matter.  It can only be done if you pump in a lot of energy to “light” the fusion fire.  On the sun, this is accomplished by the massive force of gravity.  Here on earth the necessary energy can be supplied by a fission explosion, the source of energy that “lights” thermonuclear bombs.  Mother Nature decided, no doubt very wisely, to make it very difficult to accomplish the same thing in a controlled manner on a laboratory scale.  Otherwise we probably would have committed suicide with pure fusion weapons by now.  At the moment, two major approaches are being pursued to reach this goal.  One is inertial confinement fusion, or ICF, as used on the NIF.  In inertial confinement fusion, the necessary energy is supplied in such a short period of time by massive lasers or other “drivers” that the fuel is held in place by its own inertia long enough for significant fusion to occur.  In the other approach, magnetic fusion, the fusion fuel is confined by powerful magnetic fields as it is heated to fusion temperatures.  This is the approach being pursued with ITER, the International Thermonuclear Experimental Reactor, currently under construction in France.

Based on computer models and the results of experiments on much smaller facilities, such as NOVA at Livermore, and OMEGA at the University of Rochester, it was expected that fusion could be accomplished with the nominal 1.8 megajoules of energy available from the 192 NIF laser beams.  It was to happen like this – carefully shaped laser pulses would implode the fusion fuel to extremely high densities.  Such implosions have already been demonstrated many times in the laboratory.  The problem is that, to achieve the necessary densities, one must compress the fuel while it is in a relatively “cold” state (it is much more difficult to “squeeze” something that is “hot” in that way).  Unfortunately, fusion doesn’t happen in cold material.  Once the necessary high densities have been achieved, it is somehow necessary to heat at least a small portion of the material to the extreme temperatures necessary for fusion to occur.  If that can be done, a “burn wave” will move out from this “hot spot,” igniting the rest of the cold fuel material.   Of course, this begs the question of how one is to produce the “hot spot” to begin with.

On the NIF, the trick was to be accomplished by setting off a series of converging shocks in the fuel material during the implosion process.  Once the material had reached the necessary high density, these shocks would converge at a point in the center of the imploded target, creating a spot hot enough to set off the burn wave referred to above.  It would be a neat trick if it could be done.  Unfortunately, it was never demonstrated on a laboratory scale before the NIF was built.  Obviously, the “trick” is turning out to be harder than the scientists at Livermore expected.  There could be many reasons for this.  If the implosion isn’t almost perfectly symmetric, the hot and cold fuel materials will mix, quenching the fusion reaction.  If the timing of the shocks isn’t just right, or the velocity of the implosion is too slow, the resulting number of fusion reactions will not be enough to achieve ignition.  All kinds of complicated physical processes, such as the generation of huge magnetic and electric fields, so-called laser-plasma instabilities, and anomalies in the absorption of laser light, can happen that are extremely difficult to include in computer models.

The game isn’t up yet, though.  There are some very bright folks at Livermore, and they may yet pull a rabbit out of the hat.  Even if the current “mainline” approach using central hot spot ignition doesn’t work, it may be possible to create a hot spot on the outer surface of the imploded target using a technique known as fast ignition.  Currently, “indirect drive” is being used on the NIF.  In other words, the laser beams are shot into a cylindrical can, or “hohlraum,” where their energy is converted to x-rays.  These x-rays then “indirectly” illuminate the target.  The NIF can also accommodate a “direct drive” approach, in which the laser beams are aimed directly at the target.  Perhaps it will work better.  One hopes so.  Some of the best old knights of science have been riding towards that El Dorado for a long time.  It would be great to see them finally reach it.  Alas, to judge by the deafening silence coming out of Livermore, it seems they are still a long way off.

And what of ITER?  Let me put it this way.  Along with the International Space Station, the project is one of the two greatest scientific white elephants ever concocted by the mind of man.  The NIF is justified because it cost only a fraction of ITER, and it was never conceived as an energy project.  It was always intended as an above ground experimental facility that would enable us to maintain our nuclear arsenal in the absence of testing.  As such, it is part of an experimental capability unequalled in the rest of the world, and one which will give us a very significant advantage over any potential enemy as long the ban on testing continues.  ITER, on the other hand, can only be justified as an energy project.  The problem with that is that, while it may work scientifically, it will be an engineering nightmare.  As a result, it is virtually inconceivable that magnetic fusion reactors similar to ITER will ever produce energy economically any time in the next few hundred years.

A big part of the problem is that such reactors will require a tritium economy.  Each of them will burn on the order of 50 kilograms of tritium per year.  Tritium is highly radioactive, with a half-life of 12.3 years, is as difficult to contain as any other form of hydrogen, and does not occur naturally.  In other words, failing some outside source, each reactor will have to produce as much tritium as it consumes.  Each fusion reaction produces a single neutron, and neutrons can interact with an isotope of lithium to produce tritium.  However, some of the neutrons will inevitably be lost, so it will be necessary to multiply their number.  This trick can be accomplished with the element beryllium.  In other words, in order to build a workable reactor, it will be necessary to have a layer of some extremely durable material containing the plasma, thick enough to resist radiation embrittlement and corrosion for some reasonable period of time, followed by a layer of highly toxic beryllium thick enough to generate enough neutrons, followed by a layer of highly reactive lithium thick enough to produce enough tritium to keep the reaction going.  But wait, there’s more!  It will then be necessary to somehow quickly extract the lithium and return it to the reaction chamber without losing any of it.  Tritium?  Lithium?  Beryllium?  Forget about it!  I’m sure there are any number of reactor design studies that all “prove” that all of the above can be done economically.  I’m also sure none of them are worth the paper they are printed on.  We have other options that don’t suffer from the drawbacks of a tritium economy and are far more likely to produce the energy we need at a fraction of the cost.

Meanwhile, ITER crawls ahead, sucking enormous amounts of research money from a host of more worthy projects.  A classic welfare project for smart guys in white coats, there are no plans to even fuel it with tritium before the year 2028!  I’m sure that at this point many European scientists are asking a simple question; Can’t we please stop this thing?

Fusion is immensely promising as a potential future source of energy.  However, we should not be seduced by that promise into throwing good money after bad, funding a white elephant that has virtually no chance of ever fulfilling that promise.  I suspect that one of these days we will “finesse” Mother Nature, and devise a clever way to overcome the Coulomb barrier without gigantic superconducting magnets or massive arrays of lasers.  Scientists around the world are currently working on many novel and speculative approaches to fusion.  Few of them are likely to succeed, but it just takes one.  We would be much better off funding some of the more promising of these approaches with a fraction of the money currently being wasted on ITER, and devoting the rest to developing other technologies that have at least a fighting chance of eventually producing energy economically.

Meanwhile, I’m keeping my fingers crossed for the NIF crew at Livermore.  It ain’t over until the fat lady sings, and she’s still a long way off.

Author: Helian

I am Doug Drake, and I live in Maryland, not far from Washington, DC. I am a graduate of West Point, and I hold a Ph.D. in nuclear engineering from the University of Wisconsin. My blog reflects my enduring fascination with human nature and human morality.

2 thoughts on “All Quiet on the Fusion Front: Notes on ITER and the National Ignition Facility”

  1. “tritium economy.  Each of them will burn on the order of 50 kilograms of tritium per year”

    That’s fantastic news if we can base the entire US “tritium economy” on a measly 50 kg’s of the isotope. I thought you were going to say 50 kilo tons or something substantial. If the USA cannot come up with 50kg of tritium why don’t we just fold and disband.

  2. Actually, you have it backwards on the money front. Fusion isn’t sucking money away from more worthy research projects. Fusion research is being used as a plausibly deniable slush fund to funnel research funding to more worthy research projects that would never get the funding because they are not as sexy as fusion.
    That’s why they have been “twenty years away from controlled nuclear fusion” for over seventy years.

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