Inertial confinement fusion – Page 2

Of Cold Fusion and the Timidity of ARPA-E

ARPA-E, or the Advanced Research Projects Agency – Energy, is supposed to be DOE’s version of DARPA. According to its website, its mission,

…is to fund projects that will develop transformational technologies that reduce America’s dependence on foreign energy imports; reduce U.S. energy related emissions (including greenhouse gasses); improve energy efficiency across all sectors of the U.S. economy and ensure that the U.S. maintains its leadership in developing and deploying advanced energy technologies.

So far, it has not come up with anything quite as “transformational” as the Internet or stealth technology. There is good reason for this. Its source selection people are decidedly weak in the knees. Consider the sort of stuff it’s funded in the latest round of contract awards. The people at DARPA would probably call it “workman like.” H. L. Mencken, the great Sage of Baltimore, would more likely have called it “pure fla fla.” For example, there are “transformational” systems to twiddle with natural gas storage that the industry, not exactly short of cash at the moment, would have been better left to develop on its own, such as,

Liquid-Piston Isothermal Home Natural Gas Compressor

Chilled Natural Gas At-Home Refueling

and,

Superplastic-Formed Gas Storage Tanks

There is the “transformational” university research that is eye-glazingly mundane, and best reserved as filler for the pages of obscure academic journals, such as,

Cell-level Power Management of Large Battery Packs

Health Management System for Reconfigurable Battery Packs

and,

Optimal Operation and Management of Batteries Based on Real Time Predictive Modeling and Adaptive Battery Management Techniques.

There is some “groundbreaking” stuff under the rubric of “build a better magnet, and the world will beat a pathway to your door.”

Manganese-Based Permanent Magnet with 40 MGOe at 200°C

Rare‐Earth‐Free Permanent Magnets for Electrical Vehicle Motors and Wind Turbine Generators: Hexagonal Symmetry Based Materials Systems Mn‐Bi and M‐type Hexaferrite

and,

Discovery and Design of Novel Permanent Magnets using Non-strategic Elements having Secure Supply Chains

…and so on. Far be it for me to claim that any of this research is useless. It is, however, also what the people at DARPA would call “incremental,” rather than transformational. Of course, truly transformational ideas don’t grow on trees, and DARPA also funds its share of “workmanlike” projects, but at least the source selection people there occasionally go out on a limb. In the work funded by ARPA-E, on the other hand, I can find nothing that might induce the bureaucrats on Secretary Chu’s staff to swallow their gum.

If the agency is really serious about fulfilling its mission, it might consider some of the innovative ideas out there for harnessing fusion energy. All of them can be described as “high risk, high payoff,” but isn’t that the kind of work ARPA-E is supposed to be funding? According to a recent article on the Science Magazine website, the White House has proposed cutting domestic fusion research by 16%to help pay for the U.S. contribution to the international fusion experiment, ITER, under construction in Cadarache, France. As I’ve pointed out elsewhere, ITER is second only to the International Space Station as the greatest white elephant of all time, and is similarly vacuuming up funds that might otherwise have supported worthwhile research in several other countries. All the more reason to give a leg up to fusion, a technology that has bedeviled scientists for decades, but that could potentially supply mankind’s energy needs for millennia to come. Ideas being floated at the moment include advanced fusor concepts such as the Bussard polywell, magneto-inertial fusion, focus fusion, etc. None of them look particularly promising to me, but if any of them pan out, the potential payoff is huge. I’ve always been of the opinion that, if we ever do harness fusion energy, it will be by way of some such clever idea rather than by building anything like the current “conventional” inertial or magnetic fusion reactor designs.

When it comes to conventional nuclear energy, we are currently in the process of being left in the dust by countries like India and China. Don’t expect any help from industry here. They are in the business to make a profit. There’s certainly nothing intrinsically wrong with that, but at the moment, profits are best maximized by building light water reactors that consume the world’s limited supply of fissile uranium 235 without breeding more fuel to replace it, and spawn long-lived and highly radioactive transuranic actinides in the process that it will be necessary to find a way to safely store for thousands of years into the future. This may be good for profits, but it’s definitely bad for future generations. Alternative designs exist that would breed as much new fuel as they consume, be intrinsically safe against meltdown, would destroy the actinides along with some of the worst radioactive fission products, and would leave waste that could be potentially less radioactive than the original ore in a matter of a few hundred years. DOE’s Office of Nuclear Energy already funds some research in these areas. Unfortunately, in keeping with the time-honored traditions of government research funding, they like to play it safe, funneling awards to “noted experts” who tend to keep plodding down well-established paths even when they are clearly leading to dead ends. ITER and the International Space Station are costly examples of where that kind of thinking leads. If it were really doing its job, an agency like ARPA-E might really help to shake things up a little.

Finally, we come to that scariest of boogeymen of “noted experts” the world over; cold fusion, or, as some of its advocates more reticently call it, Low Energy Nuclear Reactions (LENR). Following the initial spate of excitement on the heels of the announcement by Pons and Fleischmann of excess heat in their experiments with palladium cells, the scientific establishment agreed that such ideas were to be denounced as heretical. Anathemas and interdicts rained down on their remaining proponents. Now, I must admit that I don’t have much faith in LENR myself. I happened to attend the Cold Fusion Workshop in Sante Fe, NM which was held in 1989, not long after the Pons/Fleischmann bombshell, and saw and heard some memorably whacky posters and talks. I’ve talked to several cold fusion advocates since then, and some appeared perfectly sober, but an unsettlingly large proportion of others seemed to be treading close to the lunatic fringe. Just as fusion energy is always “30 years in the future,” cold fusion proponents have been claiming that their opponents will be “eating crow in six months” ever since 1989. Some very interesting results have been reported. Unfortunately, they haven’t been reproducible.

For all that, LENR keeps hanging around. It continues to find advocates among those who, for one reason or another, aren’t worried about their careers, or lack respect for authority, or are just downright contrarians. The Science of Low Energy Nuclear Reactions by Edmund Storms is a useful source for the history of and evidence for LENR. Websites run by the cold fusion faithful may be found here and here. Recently, stories have begun cropping up again in “respectable” mags, such as Forbes and Wired. Limited government funding has been forthcoming from NASA Langley and, at least until recently, from the Navy at its Space and Naval Warfare Systems Command (SPAWAR). Predictably, such funding is routinely attacked as support for scientific quackery. The proper response to that from the source selection folks at ARPA-E should be, “So what?” After all,

ARPA-E was created to be a catalyst for innovation. ARPA-E’s objective is to tap into the risk-taking American ethos and to identify and support the pioneers of the future. With the best research and development infrastructure in the world, a thriving innovation ecosystem in business and entrepreneurship, and a generation of youth that is willing to engage with fearless intensity, the U.S. has all the ingredients necessary for future success. The goal of ARPA-E is to harness these ingredients and make a full-court press to address the U.S.’s technological gaps and leapfrog over current energy approaches.

The best way to “harness these ingredients and make a full-court press” is not by funding of the next round of incremental improvements in rare earth magnets. Throwing a few dollars to the LENR people, on the other hand, will certainly be “high risk,” but it just might pan out. I hope the people at ARPA-E can work up the minimal level of courage it takes to do so. If the Paris fashions can face down ridicule, so can they. If they lack the nerve, then DOE would probably do better to terminate its bad imitation of DARPA and feed the money back to its existing offices. They can continue funding mediocrity just as well as ARPA-E.

pons and fleischmann — Pons & Fleischmann

The NIF Misses its Ignition Milestone

We have passed the end of the fiscal year, and the National Ignition Facility, or NIF, at Lawrence Livermore National Laboratory (LLNL) failed to achieve its goal of ignition (more fusion energy out than laser energy in). As I noted in earlier post about the NIF more than three years ago, this doesn’t surprise me. Ignition using the current indirect drive approach (most of the jargon and buzzwords are explained in the Wiki article on the NIF) requires conversion of the laser energy into an almost perfectly symmetric bath of x-rays. These must implode the target, preserving its spherical shape in the process in spite of a very high convergence ratio (initial radius divided by final radius), and launching a train of four shocks in the process, which must all converge in a tiny volume at the center of the target, heating it to fusion conditions. That will release energetic alpha particles (helium nuclei) which must then dump their energy in the surrounding, cold fuel material, causing a “burn wave” to propagate out from the center, consuming the remaining fuel. It would have been a spectacular achievement if LLNL had pulled it off. Unfortunately, they didn’t, for reasons that are explained in an excellent article that recently appeared in the journal Science. (Unfortunately, it’s behind a subscriber wall, and I haven’t found anything as good on the web at the moment. You can get the gist from this article at Huffpo.) The potential political implications of the failure were addressed in a recent article in the New York Times.

All of which begs the question, “What now?” My opinion, in short, is that the facility should remain operational, at full capacity (not on half shifts, which, for various reasons, would reduce the experimental value of the facility by significantly more than half).

I certainly don’t base that opinion on the potential of inertial confinement fusion (ICF), the technology implemented on the NIF, for supplying our future energy needs. While many scientists would disagree with me, I feel it has virtually none. Although they may well be scientifically feasible, ICF reactors would be engineering nightmares, and far too expensive to compete with alternative energy sources. It would be necessary to fabricate many thousands of delicate, precisely built targets every day and fill them with highly radioactive tritium. Tritium is not a naturally occurring isotope of hydrogen, and its half-life (the time it takes for half of a given quantity to undergo radioactive decay) is just over 12 years, so it can’t be stored indefinitely. It would be necessary to breed and extract the stuff from the reactor on the fly without releasing any into the environment (hydrogen is notoriously slippery stuff, that can easily leak right through several types of metal barriers), load it into the targets, and then cool them to cryogenic temperatures. There is not a reactor design study out there that doesn’t claim that this can be done cheaply enough to make ICF fusion energy cost-competitive. They are all poppycock. The usual procedure in such studies is to pick the cost number you need, and then apply “science” to make it seem plausible.

However, despite all the LLNL hype, the NIF was never funded as an energy project, but as an experimental tool to help maintain the safety and reliability of our nuclear stockpile in the absence of nuclear testing. The idea that it will be useless for that purpose, whether it achieves ignition or not, is nonsense. The facility has met and in some cases exceeded its design goals in terms of energy and precision. Few if any other facilities in the world, whether existing or planned, will be able to rival its ability to explore equations of state, opacities, and other weapons-relevant physics information about materials at conditions approaching those that exist in nuclear detonations. As long as the ban on nuclear testing remains in effect, the NIF will give us a significant advantage over other nuclear states. It seems to me that maintaining the ban is a good thing.

It also seems to me that it would behoove us to maintain a robust nuclear stockpile. Nuclear disarmament sounds nice on paper. In reality it would invite nuclear attack. The fact that nuclear weapons have not been used since 1945 is a tremendous stroke of luck. However, it has also seduced us into assuming they will never be used again. They will. The question is not if, but when. We could continue to be very lucky. We could also suffer a nuclear attack tomorrow, whether by miscalculation, or the actions of terrorists or rogue states. If we continue to have a stockpile, it must be maintained. Highly trained scientists must be available to maintain it. Unfortunately, babysitting a pile of nuclear bombs while they gather dust is not an attractive career path. Access to facilities like the NIF is a powerful incentive to those who would not otherwise consider such a career.

One of the reasons this is true is the “dual use” capability of the NIF. It can be used to study many aspects of high energy density physics that may not be relevant to nuclear weapons, but are of great interest to scientists in academia and elsewhere who are interested in fusion energy, the basic science of matter at extreme conditions, astrophysics, etc. Some of the available time on the facility will be reserved for these outside users.

As for the elusive goal of ignition itself, we know that it is scientifically feasible, just as we know that its magnetic fusion equivalent is scientifically feasible. The only question remaining is how big the lasers have to be to reach it. It may eventually turn out that the ones available on the NIF are not big enough. However, the idea that because we didn’t get ignition in the first attempts somehow proves that ignition is impossible and out of the question is ridiculous. It has not even been “proven” that the current indirect drive approach won’t work. If it doesn’t, there are several alternatives. The NIF is capable of being reconfigured for direct drive, in which the lasers are aimed directly at the fusion target. For various reasons, the beams are currently being frequency-tripled from the original “red” light of the glass lasers to “blue.” Much more energy, up to around four megajoules instead of the current 1.8, would be available if the beams were only frequency-doubled to “green”. It may be that the advantage of the extra energy will outweigh the physics-related disadvantages of green light. An interesting dark horse candidate is the “fast ignitor” scenario, in which the target would be imploded as before, but a separate beam or beams would then be used to heat a small spot on the outer surface to ignition conditions. An alpha particle “burn wave” would then propagate out, igniting the rest of the fuel, just as originally envisioned for the central hot spot approach.

Some of the comments following the Internet posts about NIF’s failure to reach ignition are amusing. For example, following an article on the Physics Today website we learn to our dismay:

With all due respect to the NIF and its team of well-meaning and enthusiastic researchers here, I am sorry to state hereby that sustainable nuclear fusion is predestined to fail, whether it be in the NIC, the Tokamak or anywhere else in solar space, for fundamentally two simple reasons paramount for fusion: ((1) vibrational synchronism (high-amplitude resonance) of reacting particles; and (2) the overall isotropy of their ambient field.

Obviously the commenter hadn’t heard that the scientific feasibility of both inertial and magnetic fusion has already been established. He reminds me of a learned doctor who predicted that Zadig, the hero of Voltaire’s novel of that name, must inevitably die of an injury. When Zadig promptly recovered, he wrote a thick tome insisting that Zadig must inevitably have died. Voltaire informs us that Zadig did not read the book. In an article on the IEEE Spectrum website, suggestively entitled National Ignition Facility: Mother of All Boondoggles?, another commenter chimes in:

How about we spend the billions on real research that actually has a chance of producing something useful? There are a gazillion ideas out there for research that has a much higher probability of producing useful results. Must be nice to work for LLNL where your ideas don’t need vetting.

In fact, the NIF was “vetted” by a full scale Federal Advisory Committee. Known as the Inertial Confinement Fusion Advisory Committee, or ICFAC, its members included Conrad Longmire, Marshall Rosenbluth, and several other experts in plasma physics and technology of world renown who had nothing whatsoever to gain by serving as shills for LLNL. It heard extensive testimony on plans to build the NIF, both pro and con, in the mid-90’s. Prominent among those who opposed the project was Steve Bodner, head of the ICF Program at the Naval Research Laboratory (NRL) at the time. Steve cited a number of excellent reasons for delaying major new starts like the NIF until some of the outstanding physics issues could be better understood. The Committee certainly didn’t ignore what he and other critics had to say. However, only one of the 15 or so members dissented from the final decision to recommend proceeding with the NIF. I suspect that LLNL’s possession of the biggest, baddest ICF computer code at the time had something to do with it. No one is better at bamboozling himself and others than a computational physicist with a big code. The one dissenter, BTW, was Tim Coffey, Director of NRL at the time, who was convinced that Bodner was right.

There are, of course, the predictable comments by those in the habit of imagining themselves geniuses after the fact, such as,

I am convinced. Garbage research.

and,

Don’t these people feel ashamed telling so many lies?

after the IEEE Spectrum article, and,

It’s amazing to think that you can spout lies to the government to receive $6 billion for a machine that doesn’t come close to performing to spec and there are no consequences for your actions.

Following a post on the NIF at the LLNL – The True Story blog. Fortunately, most of the comments I’ve seen recently have been at a rather more thoughtful level. In any event, I hope Congress doesn’t decide to cut and run on the NIF. Pulling the plug at this point would be penny-wise and pound-foolish.

NIF-0506-11956_14: LB2 from crane (west view) — One of the two NIF laser bays

The NIF: Lots of Power and Energy, but No Ignition

According to a recent press release from Lawrence Livermore National Laboratory (LLNL) in California, the 192-beam National Ignition Facility (NIF) fired a 500 terawatt shot on July 5. The world record power followed a world record energy shot of 1.89 Megajoules on July 3. As news, this doesn’t rise above the “meh” category. A shot at the NIF’s design energy of 1.8 Megajoules was already recorded back in March. It’s quite true that, as NIF Director Ed Moses puts it, “NIF is becoming everything scientists planned when it was conceived over two decades ago.” The NIF is a remarkable achievement in its own right, capable of achieving energies 50 times greater than any other laboratory facility, with pulses shaped and timed to pinpoint precision. The NIF team in general and Ed Moses in particular deserve great credit, and the nation’s gratitude, for that achievement after turning things around following a very shaky start.

The problem is that, while the facility works as well, and even better than planned, the goal it was built to achieve continues to elude us. As its name implies, the news everyone is actually waiting for is the announcement that ignition (defined as fusion energy out greater than laser energy in) has been achieved. As noted in the article, Moses said back in March that “We have all the capability to make it happen in fiscal year 2012.” At this point, he probably wishes his tone had been a mite less optimistic. To reach their goal in the two months remaining, the NIF team will need to pull a rabbit out of their collective hat. A slim chance remains. Apparently the NIF’s 192 laser beams were aimed at a real ignition target with a depleted uranium capsule and deuterium-tritium fuel on July 5, and not a surrogate. The data from that shot may prove to be a great deal more interesting than the 500 terawatt power announcement.

Meanwhile, the Russians are apparently forging ahead with plans for their own superlaser, to be capable of a whopping 2.8 Megajoules, and the Chinese are planning another about half that size, to be operational at about the same time (around 2020). That, in itself, speaks volumes about the real significance of ignition. It may be huge for the fusion energy community, but not that great as far as the weaponeers who actually fund these projects are concerned. Many weapons designers at LLNL and Los Alamos were notably unenthusiastic about ignition when NIF was still in the planning stages. What attracted them more was the extreme conditions, approaching those in an exploding nuke, that could be achieved by the lasers without ignition. They thought, not without reason, that it would be much easier to collect useful information from such experiments than from chaotic ignition plasmas. Apparently the Russian bomb designers agree. They announced their laser project back in February even though LLNL’s difficulties in achieving ignition were well known at the time.

The same can be said of some of the academic types in the NIF “user community.” It’s noteworthy that two of them, Rick Petrasso of MIT and Ray Jeanloz of UC Berkeley, whose enthusiastic comments about the 500 terawatt shot where quoted in the latest press release, are both key players in the field of high energy density physics. Ignition isn’t a sine qua non for them either. They will be able to harvest scores of papers from the NIF whether it achieves ignition or not.

The greatest liability of not achieving early ignition may be the evaporation of political support for the NIF. The natives are already becoming restless. As noted in the Livermore Independent,

In early May, sounding as if it were discussing an engineering project rather than advanced research, the House Appropriations Committee worried that NIF’s “considerable costs will not have been warranted” if it does not achieve ignition by September 30, the end of the federal fiscal year.

and,

Later that month, in a tone that seemed to demand that research breakthroughs take place according to schedule, the House Armed Services Committee recommended that NIF’s ignition research budget for next year be cut by $30 million from the requested $84 million budget unless NIF achieves ignition by September 30.

Funding cuts at this point, after we have come so far, and are so close to the goal, would be short-sighted indeed. One must hope that a Congress capable of squandering billions on white elephants like the International Space Station will not become penny-wise and pound-foolish about funding a project that really matters.

Nuclear Fusion Update

As I mentioned in a previous post about fusion progress, signs of life have finally been appearing in scientific journals from the team working to achieve fusion ignition at the National Ignition Facility, or NIF, located at Lawrence Livermore National Laboratory (LLNL) in California. At the moment they are “under the gun,” because the National Ignition Campaign (NIC) is scheduled to end with the end of the current fiscal year on September 30. At that point, presumably, work at the facility will be devoted mainly to investigations of nuclear weapon effects and physics, which do not necessarily require fusion ignition. Based on a paper that recently appeared in Physical Review Letters, chances of reaching the ignition goal before that happens are growing dimmer.

The problem has to do with a seeming contradiction in the physical requirements for fusion to occur in the inertial confinement approach pursued at LLNL. In the first place, it is necessary for the NIF’s 192 powerful laser beams to compress, or implode, a target containing fusion fuel in the form of two heavy isotopes of hydrogen to extremely high densities. It is much easier to compress materials that are cold than those that are hot. Therefore, it is essential to keep the fuel material as cold as possible during the implosion process. In the business, this is referred to as keeping the implosion on a “low adiabat.” However, for fusion ignition to occur, the nuclei of the fuel atoms must come extremely close to each other. Unfortunately, they’re not inclined to do that, because they’re all positively charged, and like charges repel. How to overcome the repulsion? By making the fuel material extremely hot, causing the nuclei to bang into each other at high speed. The whole trick of inertial confinement fusion, then, is to keep the fuel material very cold, and then, in a tiny fraction of a second, while its inertia holds it in place (hence the name, “inertial” confinement fusion), raise it, or at least a small bit of it, to the extreme temperatures necessary for the fusion process to begin.

The proposed technique for creating the necessary hot spot was always somewhat speculative, and more than one fusion expert at the national laboratories were dubious that it would succeed. It consisted of creating a train of four shocks during the implosion process, which were to overtake one another all at the same time precisely at the moment of maximum compression, thereby creating the necessary hot spot. Four shocks are needed because of well-known theoretical limits on the increase in temperature that can be achieved with a single shock. Which brings us back to the paper in Physical Review Letters.

The paper, entitled Precision Shock Tuning on the National Ignition Facility, describes the status of efforts to get the four shocks to jump through the hoops described above. One cannot help but be impressed by the elegant diagnostic tools used to observe and measure the shocks. They are capable of peering through materials under the extreme conditions in the NIF target chamber, focusing on the tiny, imploded target core, and measuring the progress of a train of shocks over a period that only lasts for a few billionths of a second! These diagnostics, developed with the help of another team of brilliant scientists at the OMEGA laser facility at the University of Rochester’s Laboratory for Laser Energetics, are a triumph of human ingenuity. They reveal that the NIF is close to achieving the ignition goal, but not quite close enough. As noted in the paper, “The experiments also clearly reveal an issue with the 4th shock velocity, which is observed to be 20% slower than predictions from numerical simulation.”

It will be a neat trick indeed if the NIF team can overcome this problem before the end of the National Ignition Campaign. In the event that they don’t, one must hope that the current administration is not so short-sighted as to conclude that the facility is a failure, and severely reduce its funding. There is too much at stake. I have always been dubious about the possibility that either the inertial or magnetic approach to fusion will become a viable source of energy any time in the foreseeable future. However, I may be wrong, and even if I’m not, achieving inertial fusion ignition in the laboratory may well point the way to as yet undiscovered paths to the fusion energy goal. Ignition in the laboratory will also give us a significant advantage over other nuclear weapons states in maintaining our arsenal without nuclear testing.

Based on the progress reported to date, there is no basis for the conclusion that ignition is unachievable on the NIF. Even if the central hot spot approach currently being pursued proves too difficult, there are alternatives, such as polar direct drive and fast ignition. However, pursuing these alternatives will take time and resources. They will become a great deal more difficult to realize if funding for NIF operations is severely cut. It will also be important to maintain the ancillary capability provided by the OMEGA laser. OMEGA is much less powerful but also a good deal more flexible and nimble than the gigantic NIF, and has already proved its value in testing and developing diagnostics, investigating novel experimental approaches to fusion, developing advanced target technology, etc.

We have built world-class facilities. Let us persevere in the quest for fusion. We cannot afford to let this chance slip.

Fusion Update: Signs of Life from the National Ignition Facility

The National Ignition Facility, or NIF, is a huge, 192 beam laser system, located at Lawrence Livermore National Laboratory in California. It was designed, as the name implies, to achieve thermonuclear ignition in the laboratory. “Ignition” is generally accepted to mean getting a greater energy output from fusion than the laser input energy. Unlike magnetic confinement fusion, the approach currently being pursued at the International Thermonuclear Experimental Reactor, or ITER, now under construction in France, the goal of the NIF is to achieve ignition via inertial confinement fusion, or ICF, in which the fuel material is compressed and heated to the extreme conditions at which fusion occurs so quickly that it is held in place by its own inertia.

The NIF has been operational for over a year now, and a two year campaign is underway with the goal of achieving ignition by the end of this fiscal year. Recently, there has been a somewhat ominous silence from the facility, manifesting itself as a lack of publications in the major journals favored by fusion scientists. That doesn’t usually happen when there is anything interesting to report. Finally, however, some papers have turned up in the journal Physics of Plasmas, containing reports of significant progress.

To grasp the importance of the papers, it is necessary to understand what is supposed to occur within the NIF target chamber for fusion to occur. Of course, just as in magnetic fusion, the goal is to bring a mixture of deuterium and tritium, two heavy isotopes of hydrogen, to the extreme conditions at which fusion takes place. In the ICF approach, this hydrogen “fuel” is contained in a tiny, BB-sized target. However, the lasers are not aimed directly at the fuel “capsule.” Instead, the capsule is suspended in the middle of a tiny cylinder made of a heavy metal like gold or uranium. The lasers are fired through holes on each end of the cylinder, striking the interior walls, where their energy is converted to x-rays. It is these x-rays that must actually bring the target to fusion conditions.

It was recognized many years ago that one couldn’t achieve fusion ignition by simply heating up the target. That would require a laser driver orders of magnitude bigger than the NIF. Instead, it is first necessary to compress, or implode, the fuel material to extremely high density. Obviously, it is harder to “squeeze” hot material than cold material to the necessary high densities, so the fuel must be kept as “cold” as possible during the implosion process. However, cold fuel won’t ignite, begging the question of how to heat it up once the necessary high densities have been achieved.

It turns out that the answer is shocks. When the laser generated x-rays hit the target surface, they do so with such force that it begins to implode faster than the speed of sound. Everyone knows that when a plane breaks the sound barrier, it, too, generates a shock, which can be heard as a sonic boom. The same thing happens in ICF fusion targets. When such a shock converges at the center of the target, the result is a small “hot spot” in the center of the fuel. If the temperature in the hot spot were high enough, fusion would occur. Each fusion reaction would release a high energy helium nucleus, or alpha particle, and a neutron. The alpha particles would be slammed to a stop in the surrounding cold fuel material, heating it, in turn, to fusion conditions. This would result in a fusion “burn wave” that would propagate out through the rest of the fuel, completing the fusion process.

The problem is that one shock isn’t enough to create such a “hot spot.” Four of them are required, all precisely timed by the carefully tailored NIF laser pulse to converge at the center of the target at exactly the same time. This is where real finesse is needed in laser fusion. The implosion must be extremely symmetric, or the shocks will not converge properly. The timing must be exact, and the laser pulse must deliver just the right amount of energy.

One problem in the work to date has been an inability to achieve high enough implosion velocities for the above scenario to work as planned. One of the Physics of Plasmas papers reports that, by increasing the laser energy and replacing some of the gold originally used in the wall of the cylinder, or “hohlraum,” in which the fuel capsule is mounted with depleted uranium, velocities of 99% of those required for ignition have been achieved. In view of the recent announcement that a shot on the NIF had exceeded its design energy of 1.8 megajoules, it appears the required velocity is within reach. Another of the Physics of Plasmas papers dealt with the degree to which implosion asymmetries were causing harmful mixing of the surrounding cold fuel material into the imploded core of the target. It, too, provided grounds for optimism.

In the end, I suspect the success or failure of the NIF will depend on whether the complex sequence of four shocks can really be made to work as advertised. That will depend on the accuracy of the physics algorithms in the computer codes that have been used to model the experiments. Time and again, earlier and less sophisticated codes have been wrong because they didn’t accurately account for all the relevant physics. There is no guarantee that critical phenomena have not been left out of the current versions as well. We may soon find out, if the critical series of experiments planned to achieve ignition before the end of the fiscal year are carried out as planned.

One can but hope they will succeed, if only because some of our finest scientists have dedicated their careers to the quest to achieve the elusive goal of controlled fusion. Even if they do, fusion based on the NIF approach is unlikely to become a viable source of energy, at least in the foreseeable future. Laser fusion may prove scientifically feasible, but getting useful energy out of it will be an engineering nightmare, dangerous because of the need to rely on highly volatile and radioactive tritium, and much too expensive to compete with potential alternatives. I know many of the faithful in the scientific community will beg to differ with me, but, trust me, laser fusion energy aint’ gonna happen.

On the other hand, if ignition is achieved, the NIF will be invaluable to the country, not as a source of energy, but for the reason it was funded in the first place – to insure that our nation has an unmatched suite of experimental facilities to study the physics of nuclear weapons in a era free of nuclear testing. As long as we have unique access to facilities like the NIF, which can approach the extreme physical conditions within exploding nukes, we will have a significant leg up on the competition as long as the test ban remains in place. For that, if for no other reason, we should keep our fingers crossed that the NIF team can finally clear the last technical hurdles and reach the goal they have been working towards for so long.

hohlraum ignition — Fusion ignition process,courtesy of Lawrence Livermore National Laboratory

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.

The NIF: No News is Bad News

For those who don’t follow fusion technology, the National Ignition Facility, or NIF, is a giant, 192 beam laser facility located at Lawrence Livermore National Laboratory. As its name would imply, it is designed to achieve fusion ignition, which has been variously defined, but basically means that you get more energy out from the fusion process than it was necessary to pump into the system to set off the fusion reactions. There are two “classic” approaches to achieving controlled fusion in the laboratory. One is magnetic fusion, in which light atoms stripped of their electrons, or ions, typically heavy isotopes of hydrogen, are confined in powerful magnetic fields as they are heated to the temperatures necessary for fusion to occur. The other is inertial confinement fusion, or ICF, in which massive amounts of energy are dumped into a small target, causing it to reach fusion conditions so rapidly that significant fusion can occur in the very short time that the target material is held in place by its own inertia. The NIF is a facility of the latter type.

There are, in turn, two basic approaches to ICF. In one, referred to as direct drive, the target material is directly illuminated by the laser beams. In the other, indirect drive, the target is placed inside a small container, or “hohlraum,” with entrance holes for the laser beams. These are aimed at the inside walls of the hohlraum, where they are absorbed, producing x-rays which then compress and ignite the target. The NIF currently uses the latter approach.

The NIF was completed and became operational in 2009. Since that time, the amount of news coming out of the facility about the progress of experiments has been disturbingly slight. That is not a good thing. If everything were working as planned, a full schedule of ignition experiments would be underway as I write this. Instead, the facility is idle. The results of the first experimental campaign, announced in January, sounded positive. The NIF had operated at a large fraction of its design energy output of 1.8 Megajoules. Surrogate targets had been successfully compressed to very high densities in symmetric implosions, as required for fusion. However, on reading the tea leaves, things did not seem quite so rosy. Very high levels of laser plasma interaction (LPI) had been observed. In such complex scattering interactions, laser light can be scattered out of the hohlraum, or in other undesired directions, and hot electrons can be generated, wreaking havoc with the implosion process by preheating the target. We were assured that ways had been found to control the excess LPI, and even turn it to advantage in controlling the symmetry of the implosion. However, such “tuning” with LPI had not been foreseen at the time the facility was designed, and little detail was provided on how the necessary delicate, time-dependent shaping of the laser pulses would be achieved under such conditions.

After a long pause, another series of “integrated” experiments was announced in October. Even less information was released on this occasion. We were informed that symmetric implosions had been achieved, and that, “From both a system integration and from a physics point of view, this experiment was outstanding,” Since then, nothing.

It’s hard to imagine that the outlook is really as rosy as the above statement would imply. The NIF was designed for a much higher shot rate. If it sat idle through much of 2010, there must be a reason. It could be that damage to the laser optics has been unexpectedly high. This would not be surprising. Delicate crystals are used at the end of the chain of laser optics to triple the frequency of the laser light, and, given that the output energy of the facility is more than an order of magnitude larger than that of its next largest competitor, damage may have occurred in unexpected ways, as it did on Nova, the NIF’s predecessor at Livermore. LPI may, in fact, be more serious, more difficult to control, and more damaging than the optimistic accounts in January implied. Unexpected physics may be occurring in the absorption of laser light at the hohlraum walls. Whatever the problem, Livermore would be well advised to be forthcoming about it in its press releases. After all, the NIF will achieve ignition or not, regardless of how well the PR is managed.

All this seems very discouraging for the scientists who have devoted their careers to the quest for fusion energy, not to mention the stewards of the nation’s nuclear weapons stockpile, whose needs the NIF was actually built to address. In the end, these apparent startup problems may be overcome, and ignition achieved after all. However, I rather doubt it, unless perhaps Livermore comes up with an alternative to its indirect drive approach.

ITER on the Move, or White Elephants have Long Lives

The International Thermonuclear Experimental Reactor, or ITER, is a prototype magnetic confinement fusion reactor currently being built at Cadarache in the south of France. According to a message by the new director of the ITER organization posted at facility’s Newsline,

The Baseline describes ITER all the way from the beginning of construction, through commissioning, and on to Deuterium-Tritium operation. The main milestones will be the achievement of First Plasma in November 2019 and the start of Deuterium-Tritium operation by March 2027 ultimately taking ITER to 500 MW of fusion power.

He adds that “The world is watching us closely.” If so, it appears we’re going to be watching closely for a very long time. Evidently the plasma physics guys are nursing this thing like an all day sucker. It sounds like the scheduled building time is already running neck and neck with the Great Pyramid, and will soon be giving some of the Gothic cathedrals of the Middle Ages a run for their money.

With any luck, some bright physicist(s) will finesse Mother Nature out of her fusion secrets using some known (see, for example, here and here) or yet to be discovered alternative to the “traditional” brute force magnetic and inertial confinement fusion approaches well before they ever get around to feeding tritium to this white elephant. Failing that, maybe the upcoming experiments on the National Ignition Facility (NIF) will be a lot more successful than I expect. Either way, some excuse to pull the plug on ITER is sorely needed. If nothing else, it will encourage some very bright scientists to do something useful with their talents for a change. All complex cost analyses done using the most up to date methods to the contrary, ITER will never be able to compete with the available alternative energy sources in terms of cost any time in the next few centuries.

“On Deception Watch” – The “Conspiracy” to Kill Fusion

In wandering here and there on the Internet I ran across mention of a new novel by David H. Spielberg entitled “On Deception Watch.” According to the Amazon blurb about it,

This is an epic drama about unlimited energy, the realignment of international power in a truly new world order unlike anything envisioned before, and deadly conflict between political and military centers of power. Controlled fusion energy ignites a firestorm of competing interests from within the top levels of government to the “oil patch” to the United Nations and ultimately to the world. How is it that a visionary physicist/entrepreneur was able to achieve the technological breakthrough of the century?

The author himself adds some detail to the picture;

I wrote a novel, “On Deception Watch,” that was triggered by my visit to KMS Fusion,” a real company that in 1975 really accomplished laser fusion ignition of a deuterium/tritium target and was then harassed to death by the federal government and its assets essentially looted by the feds. My novel is about the premise of a company that does what KMS Fusion did and then what. Check out KMS Fusion, Keeve Siegel, the president of the company, and my novel. One exploration in it is about what replaces the United Nations. The story takes place about 25 years in the future.

W-e-e-e-l-l-l. It wasn’t quite like that, and I doubt the author believes it himself. According to Xlibris, he has a Ph.D. in physics and, if so, I’m sure he doesn’t really believe KMS accomplished ignition back in 1975. Still, the above account isn’t going to mislead anyone whose tastes don’t already run to yarns about the Da Vinci Code, the Celestine Prophecy, and the Maya calendar, because the original papers about what happened then are still available, and many of the people who did the experiments are still around. We’ll cut Spielberg some slack and call it “poetic license,” forgivable from an author who’s just published his first novel. Regardless, the story of KMS is certainly fascinating even without such embellishments.

In fact, there was a guy named Keeve (or “Kip” as he was better known) Siegel, his initials were KMS, and he was a brilliant entrepreneur who, back in the 60’s, became convinced that inertial confinement fusion (ICF) was within reach using the laser technology then available. Gathering a crew of talented scientists, he founded KMS Fusion and built the “Chroma” laser in Ann Arbor, Michigan, and, without government funding, actually succeeded (in 1974, not 1975) in demonstrating fusion from a laser-driven implosion in the laboratory for the first time, beating embarrassed teams at Los Alamos and Livermore National Laboratories to the punch. It was a remarkable achievement, but was still orders of magnitude away from “ignition,” usually defined as equivalent to “scientific breakeven,” which occurs when the energy released from fusion equals the energy carried by the laser beams driving the reaction. Siegel, a very heavy man, died dramatically less than a year later, suffering a stroke while appealing for government funding before the Joint Congressional Committee on nuclear power. According to the Wikipedia article about him linked above,

At this time, KMS Fusion was indisputably the most advanced laser-fusion laboratory in the world. Unfortunately, outright harassment from the AEC only increased after the announcement of these results. According to one source in the faculty of the University of Michigan, the campaign against KMS Fusion culminated with a massive incursion into the KMS Fusion facilities by federal agents, who effectively put an end to its operations by confiscating essential materials on the grounds that, inter alia, all information concerning the production of nuclear energy is classified information which belongs exclusively to the federal government.

As usual, caution is due in taking Wiki at face value, and this account is pure mythology. The AEC was abolished in 1974, so was in no position to “harass” KMS. If the government continued to “harass” KMS after that, it chose an odd way of doing it, because KMS actually succeeded in securing a multi-million dollar government contract to continue its research after Siegel’s death. This was renewed several times, and KMS became a major player in the government ICF program, eventually becoming the lead laboratory for target development and production. The company eventually ran afoul of its sponsors at the Department of Energy in the early 90’s for reasons that had nothing to do with suppressing its research results, and lost its government contract to General Atomics, which continues as the “lead lab” for inertial fusion targets to this day. KMS continued a shadow existence for many years, but that effectively ended its role as a player in ICF.

That said, it’s quite true that there was friction between KMS and the inertial fusion guys at the national laboratories, just as there has always been friction between the national laboratories themselves. The teams at Los Alamos, Livermore, and Sandia all coveted the research dollars that were going to KMS, whose management didn’t endear itself by a bad habit of lobbying for earmarks over and above the funding DOE wanted it to have with the aid of Michigan representatives in Congress. The lab guys all seemed to believe that this money came out of their hide. They argued that the Chroma laser in Ann Arbor was obsolete, and that KMS should end experiments there and concentrate on target fabrication. Well, after KMS’ collapse, Chroma was cannibalized, the lion’s share of its optical innards going to Los Alamos. There, after being rechristened “Trident,” this “obsolete” laser continues in operation to this day!

As for ignition, it turned out that the slogan of “online by ’79” was a tad optimistic. Mother Nature had other ideas. The computer power available when KMS was founded was very limited, and the computer programs that had predicted the possibility of ignition with relatively small lasers like Chroma were limited to looking at the problem in one dimension. It turns out that multi-dimensional effects, such as the Rayleigh-Taylor instability, make ignition much harder to achieve than the first generation of computer codes predicted. It’s probably a good thing, too, because otherwise we may have succeeded in blowing ourselves up by now with pure fusion weapons. In any case, we kept building bigger laser facilities, eventually culminating in the recent completion of the National Ignition Facility at Livermore, a massive, 192 beam system capable of delivering a nominal 1.8 megajoules of blue (frequency-tripled) light. As its name implies, its goal is to achieve ignition, and the critical experiments designed to achieve that goal will take place in the next couple of years. I am not optimistic that they will succeed, but am keeping my fingers crossed that they do.

Meanwhile, I wish Dr. Spielberg every success with his novel. It sounds like a great yarn, and should bring a smile to the faces of ICF old timers.

“Stealth” Fusion Progress

It didn’t take us long to master the destructive force of fusion, but taming it for more constructive applications, such as electricity production, has been harder than anyone imagined back in the day when a popular slogan was “online by ’79.” Right, maybe in 2079 with any luck. We know of two scientifically feasible ways to get more energy out of fusion than it’s necessary to put in to ignite the fuel materials; magnetic fusion, as in ITER, or inertial confinement fusion (ICF) as at the National Ignition Facility (NIF). The problem with both approaches is not the science, but the engineering challenge of building reactors capable of generating electricity anywhere near as cheaply as the alternatives. At the moment, the chances that we will be able to do so any time in the foreseeable future seem remote.

If anyone around today lives to see the dawn of the era of fusion energy, it will probably be because some exceptionally clever researcher has hoodwinked Mother Nature and discovered how to finesse his way past the Coulomb barrier that usually keeps atomic nuclei too far apart to come within the range of the fusion-enabling strong force. Several promising candidates are already in the field, and one of them, Tri-Alpha Energy, has apparently managed to attract $50 million in private research funding. The company hasn’t revealed the nature of its approach, but it is apparently inspired by the work of Prof. Norman Rostoker of UC Irvine. One can get a broad hint from this paper co-authored by Rostoker and Tri-Alpha entitled, “Colliding Beam Fusion Reactors.” Rostoker is an emeritus professor who has been publishing papers since the 50’s, some co-authored with fusion superstars such as Nicholas Krall and Marshall Rosenbluth. Octogenarian physicists don’t often pull off such miracles, but you never know.

If he or someone else ever does manage to pull the fusion rabbit out of the hat, it would potentially put an end to our worries about energy for a very long time. It could also enable pure fusion weapons. Let’s keep our fingers crossed that it doesn’t.