by Julien Geffray
May 21, 2007
Activity and news related to nuclear fusion are picking up again, thanks to the Z-machine—at least in the United States. For France’s Z-machine, “Sphinx,” it’s a different story; the DGA has effectively put everything on hold, as you’ll see by reading this article published in Les Échos on May 16, 2007:
Les Échos, May 16, 2007
Nuclear expertise
France’s Z-machine shuns nuclear energy
The little “Sphinx”
Deep in the Quercy region, at the Gramat Research Center (CEG), the DGA has been operating a small French Z-machine (2.5 million amps) called “Sphinx” for several years now. Like its American counterpart, it is mainly used to test the resistance of nuclear warheads. Unlike it, however, there will be no civilian experiments conducted with it. A few years ago, researchers at Gramat tried to persuade their military superiors to diversify their research, but to no avail. When questioned by Les Échos, the very “reserved” CEG today claims it has no energy-related projects whatsoever. This lack of investment worries specialists in plasma physics. “France’s expertise in this field of high-power electrical engineering is at risk,” warns one of them.
In the UK, an equivalent machine, the Imperial College’s Magpie (1.4 million amps), is actively working on magnetic pinch technology, largely funded by the US. Though not powerful enough to achieve full nuclear fusion like the Z-machine, it is used by Americans to supplement their own research on pinch effects. The Russians too seem poised to invest in this area.
Note: “Pinch” is the French translation of “pinch,” meaning “to squeeze.” Thus, the Z-machine belongs to the class of plasma devices known as “Z-pinch” machines, where plasma is compressed along the OZ symmetry axis. All Z-pinch machines are also MHD machines; thirty years ago, France was a leader in this field, but it was completely and deliberately abandoned in the mid-1970s. Part of the reason for this inaction is sheer incomprehension and incompetence among officials. Military MHD, for instance, simply doesn’t exist in France, while it is actively pursued in the US, Russia, and elsewhere. It can be summed up in one sentence:
While other countries are accelerating ahead, the French are hitting the brakes.
One more note: Alain Juppé was appointed “Minister of the Environment.” As such, numerous representatives from environmental organizations were recently invited to meetings. But this cannot be separated from proactive efforts toward developing new energy sources—and here, there is a total absence of any such effort. No motivation, no information, no expertise. But let’s return to our main topic.
In the US, news about next-generation “LTD generators” is exciting; progress is happening faster than expected. On April 24, 2007, Sandia Laboratories issued a press release titled:
Ultra-short pulses bring Z-machine closer to high-yield fusion reactor (archive from March 23, 2010) (Ultra-short pulses bring the Z-machine a step closer to becoming a high-efficiency fusion generator)
The article, translated in full below, describes a generator called LTD (Linear Transformer Driver), which could enable controlled nuclear fusion within the Z-machine. The LTD would make the machine more compact and simpler, rendering obsolete the massive water-and-oil insulation tank and the “water lines” needed to modulate pulses over time. Most importantly, it would allow repeated discharges at a frequency of 0.1 Hz—whereas currently the Z-machine can only fire once per day!
LTD generators aren’t really a surprise; France’s Sphinx Z-machine already uses them. What’s new is the impressive performance achieved by the Russians with their latest LTDZ model:
Russian 100 GW LTDZ generator: 1 million amps and 100 kV. Diameter: 3 meters – Depth: 22 centimeters
Let’s briefly explain how the LTD works: it consists of “bricks,” each about the size of a shoebox, containing two capacitors and a switch. Arranged in parallel and forming a circular array, 40 such bricks create a single toroidal “cavity.”
Cross-section diagram of an LTDZ “brick”: 1: two GA 31165 capacitors (100 kV, 40 nF); 2: HCEI multi-gap switch; 3: output nozzle; 4: magnetic core; 5: insulator; 6: vacuum or oil cavity; 7: charge cavity; 8: caprolactone rods
This Russian version, currently the most advanced, is being tested at the High Current Electronics Institute (HCEI, archive from August 9, 2007) in Tomsk, Siberia; Sandia Labs has just acquired four units. Notice the growing US-Russia cooperation on Z-pinch fusion... This Russian LTD, the most powerful in the world (100 gigawatts), can deliver 1 million amps at 100,000 volts in a pulse lasting naturally 100 nanoseconds (meaning no compression is required). Moreover, it’s designed to fire every 10 seconds! This exact cadence is what’s needed for a future magnetic-confinement nuclear fusion power plant, functioning essentially as a “two-stage fusion” process (compression, then expansion).
The concept seems reliable. An earlier version of this LTD, identical but half as powerful (20 bricks generating 0.5 million amps at 100,000 volts), has already been validated by Sandia after over 11,000 discharges. In Tomsk, one switch fired more than 37,000 times at intervals of 12 seconds.
Since these cavities are modular, Sandia plans to stack them like doughnuts on metal rods, then multiply such arrays. There would thus be 70 cylindrical modules arranged radially, each containing 70 coaxially stacked LTD units. This setup is incredibly efficient:
- Within each module, 70 internal LTD units are wired in series to add their voltages. Each module would thus output 1 million amps and 7 million volts.
- All 70 modules would then be connected in parallel, adding their currents together, resulting in a machine delivering 70 million amps at 7 million volts.
Sandia’s “IFE driver” project: 104-meter diameter. 70 million amps, 7 million volts, 490 terawatts theoretically. 70 modules, each with 70 LTD units, totaling 392,000 capacitors.
Accounting for inevitable losses—especially along the Magnetically Insulated Transmission Lines—Sandia estimates it can still achieve 60 million amps at 6 million volts. That translates to 360 terawatts of power directed at the target.
This test rig would lie flat on the ground, arranged as shown in the diagram. Russian scientists at the Kurchatov Institute have also suggested stacking these modules vertically. Spherical symmetry is even conceivable. As one scientist working on this says: it’s a bit like playing with Meccano...
May 22, 2007, from J.P. Petit:
Ultra-high-voltage hyper-generators? Complicated? Not at all...
To better understand Julien Geffray’s text, here are some simple diagrams with arrows:
Diagram of the LTD setup
It’s... purely Russian, really. A simple idea. Yet the progress is considerable. As stated in Sandia’s text (which echoes what I’ve said for ages: my first mention of “two-stage fusion” using MHD compressors appears in Science et Vie in 1975), this is the path toward pulsed fusion via compression. The “explosion engine” versus the steam engine of the third millennium: ITER.
If we look back at the January 1979 issue of Pour la Science, we find the original Z-machine, built at Sandia by Yonas. Its power was already impressive, but focusing it remained a challenge. In 1976, when I met Gérald at Sandia, he told me: “We manage to concentrate energy in a volume the size of a pigeon egg, but we can’t do any better.” The key breakthrough came with the “birdcage”—the famous “wire liner” that enabled unprecedented focusing. They packed 240 stainless steel wires into a cylinder 8 cm in diameter, creating a plasma filament just 1.5 mm thick. And voilà, temperature skyrocketed, bingo! Everything else is standard high-power electrotechnology, well-known since long ago. Add to that the legendary Russian knack for slashing costs. They quickly grasped the potential of the 2005 experiment producing three and a half billion degrees. They know full well this isn’t a limit: it’s 35 times hotter than temperatures reached at JET in Culham—ITER’s costly successor. It’s seven times hotter than a hydrogen bomb’s core, 175 times hotter than the Sun’s interior.
Some people say/write: “We must emphasize that fusion conditions haven’t yet been achieved with these Z-pinches (unlike Tokamaks...). First, we must demonstrate that fusion reactions are possible via this method...”
Demonstrate how? Where? With what funds? Which researchers?...
It’ll happen, but not in France.
At this rate—that is, at breakneck speed, except in France where everyone’s fast asleep, as usual—the pulsed route will yield fusion reactions before a single shovelful of earth is moved for that monumental project. Recall that the decision to pursue it was personally made by a well-known French scientist: Professor Jacques Chirac. Will Sarkozy dare halt this “regional-scale social plan” before it gets underway? Given recent advances, this deserves serious consideration.
Chirac’s two seven-year terms were truly pure politics: how to sway public opinion, get re-elected, manipulate various groups. Want a prediction? Chirac will rebrand himself as a staunch defender of the planet and environment. He’ll play the role of Capitol goose now that he’s no longer President. Remember when Hulot regularly visited him, arriving at the Élysée on his scooter? Jacquot delivered grand speeches... outside France. He’ll find some perch somewhere to preach eco-morality.
Wanna bet?
My readers ask: “Why not contact Juppé? Or new Research Minister Valérie Pécresse?”
I meet anyone I want, tomorrow. But for a year we chased politicians from all parties, to no avail. We thought elections would improve our chances. Wrong. Outreach to Hulot (even Hubert Reeves, his scientific advisor) went nowhere. Many didn’t... literally grasp anything, nor did their technical teams. Bayrou stared wide-eyed. Ségolène Royal’s campaign staff advised us to read her blog. Etc...
Anyway, since early 2007 we’ve had one trump card: a letter from a top Russian official heading fusion research at the Kurchatov Institute, a man loaded with scientific honors and titles, member of the Academy of Sciences. He wrote it; it’s at our disposal. It advocates development of Z-pinches. But as I’ve said, we have no... recipient! We can’t post such a document on a public blog. If someone from Valérie Pécresse’s circle steps forward (or she herself, who knows?), the Russian will sign and send it.
Recent experimental results from Russia’s LTDZ generators will be presented at the 2007 International Pulsed Power Conference (archive from February 3, 2015) and Symposium on Fusion Engineering (archive from September 20, 2007) in Albuquerque, New Mexico, June 17–21. Interested readers can already consult a popular science report by Sandia Labs from September 2006 (archive from October 8, 2012), which introduces the LTD concept coupled with the Saturn machine. Though Saturn is less powerful, its contents apply directly to the Z-machine. Also read the Russian scientific paper on these latest-generation generators, presented at the last international congress: 100 GW Fast LTD Stage.
Below is the French translation of the article published on Sandia Labs’ official website on April 24, 2007:
Link to original article: http://www.sandia.gov/news/resources/releases/2007/rapid-fire-pulse.html (archive from March 23, 2010)
April 24, 2007
Ultra-short pulses bring Z-machine closer to high-yield fusion generator
Revolutionary circuit capable of thousands of flawless discharges
In Siberia, not Area 51: Sandia researcher Bill Fowler tests circuits of an LTD generator able to produce extremely powerful electrical pulses rapidly and repeatedly. (Photo by Randy Montoya) Download 300dpi JPEG “fowler.jpg” – 2.2 MB (archive from May 12, 2009)
ALBUQUERQUE, N.M.—An electrical circuit capable of delivering sufficient power to finally achieve controlled nuclear fusion at high efficiency—and crucially, capable of doing so every 10 seconds—has undergone intensive preliminary testing and computer simulation at Sandia Labs, home of the Z-machine.
Currently, when activated, the Z-machine is the world’s biggest producer of X-rays; it has already generated fusion neutrons. But repeated rapid-fire discharges are essential for future power plants aiming to extract electricity from abundant, cheap seawater. Until now, this was deemed impossible.
Sandia is a laboratory of the National Nuclear Security Administration.
How does it work?
An engine firing only one cylinder and then waiting hours before repeating wouldn’t get a car very far.
Similarly, a machine meant to provide humanity with unlimited electricity from plentiful, inexpensive seawater cannot simply fire once and then idle for the rest of the day. It must generate fusion reactions every 10 seconds, maintaining this rhythm through millions of cycles between maintenance periods—basically an internal-combustion engine for nuclear fusion. At least, this is the “inertial confinement fusion” approach advocated at Sandia Labs and elsewhere.
Sandia scientists Dillon McDaniel (second from left) and Steve Glover inspect a 500 kA LTD unit in Siberia alongside Alexandar Kim (HCEI, Tomsk, Russia). The person on the left is Sandia interpreter Roman Kahn. This LTD has been tested at Sandia for two and a half years. Download 300dpi JPEG “LTD-check-out.jpg” – 2.1 MB (archive from May 12, 2009)
Because this method could only achieve fusion intermittently, it was overshadowed by “magnetic confinement fusion”—which uses magnetic fields to maintain continuous fusion reactions, from which energy is extracted.
Yet this emerging electrical circuit could tip the balance between both approaches. Already regarded as “revolutionary” even by typically conservative researchers, it might close the apparent gap between the two techniques.
The generator can fire every 10.2 seconds, producing brief, powerful bursts of electricity.
“This is the most significant advance in fusion energy research in decades,” declares Keith Matzen, director of Sandia’s Pulsed Power Center.
This new system, called Linear Transformer Driver (LTD), was developed by researchers at Russia’s High Current Electronics Institute in Tomsk, in collaboration with American scientists from Sandia.
Rick Stulen, vice president of Sandia’s Foundation for Science, Technology and Research, states: “This novel technology represents not only remarkable technical progress, but also demonstrates Sandia scientists and engineers’ strong commitment to the global scientific community.”
The royal road to nuclear fusion
The circuit—a switch tightly linked to two capacitors—is roughly the size of a shoebox and nicknamed a “brick.” When 20 such bricks are grouped together and electrically linked in parallel inside a circular container resembling a giant LifeSaver candy, the resulting cavity can transmit 500,000 amps at 100 kilovolts.
Such a cavity was tested in Sandia’s Zone 4, where it fired flawlessly over 11,000 times.
Boris Kovalchuk (HCEI, gray suit) shows blueprints of a new LTD device to Sandia researcher Dillion McDaniel, with Alexandar Kim present (person on right unidentified). Download 300dpi JPEG “LTD-system.jpg” – 1.6 MB (archive from May 12, 2009)
Because these cavities are modular, they can be stacked like doughnuts on metal rods called “tubes.” Arranged appropriately, they could deliver 60 million amps at 6 million volts—enough (theoretically) to achieve high-efficiency nuclear fusion with all parameters needed for a real power plant.
“This is revolutionary progress,” says Craig Olson, senior scientist and head of Sandia’s “Inertial Fusion Energy” program.
The current-generation model, currently tested in Tomsk, delivers 1 million amps at the same voltage and speed. Five units have been built; four acquired by Sandia, one by the University of Michigan. Each costs $160,000. According to Sandia scientist Mike Mazarakis, who supervised Siberian tests, they function perfectly as planned.
“This is an incredible achievement,” says Sandia Vice President Gerry Yonas, a leading expert on the Z-machine and Sandia’s Advanced Concepts Group.
Advantages of the new technology
Fortunately for Sandia accountants—but unfortunately for fans of those iconic photos showing electric arcs and sparks taken by Sandia photographer Randy Montoya—this new switch renders obsolete the massive water-and-oil insulation tank integral to the current Z-machine design. It was above the liquid surface that those characteristic arcs formed; a phenomenon admired artistically but loathed by engineers due to wasted energy. Also obsolete is the elaborate array of power switches needed to compress initial microsecond-long pulses down to nanoseconds.
The LTD generator produces its pulse directly within the 100-nanosecond range. This works thanks to its design, which drastically reduces inductance—normally a major obstacle to rapid current transmission.
Dillon McDaniel examines insulators separating capacitor layers in 250, 500, and 1000 kilo-amp LTD units. Download 300dpi JPEG “insulators.jpg” – 1.4 MB (archive from May 12, 2009)
It achieves this partly by eliminating huge plates and lengthy cables present in the current Z-machine, all of which generate magnetic fields. In the new system, each brick has almost no wires. Two thermos-sized capacitors are tightly linked to a switch the size of a Tupperware container. This leaves little opportunity for slowing magnetic fields to appear.
Moreover, wiring bricks in parallel adds their currents together, while simultaneously lowering inductance to levels far lower than previously attainable.
Multiple such sub-assemblies are then wired in series to add their voltages.
The result is an extremely powerful machine capable of rapid successive discharges, requiring merely a thin layer of oil surrounding its loops and switches.
This LTD technology is 50% more efficient than existing Z-machine ignition devices, measured by ratio of usable energy to input energy. Presently, the Z-machine achieves 15% efficiency on its load (already quite good compared to competing fusion methods).
There is a cost to this efficiency, though.
Historically, funding for the Z-machine has served military purposes tied to national defense: experiments aim to produce data for supercomputer simulations helping maintain U.S. nuclear deterrence strength, effectiveness, and safety. Even without rapid-fire capability, an LTD-based powerhouse would simulate nuclear weapon conditions far better; thus data gathered from lab explosions could be applied with greater certainty in refined computer simulations. The US has refrained from testing actual nuclear warheads for 15 years.
With repeated firing capability, this machine could become the basis for the first operational nuclear fusion power plant within two decades. Such progress will eventually require budget allocations from the Energy Department’s “Energy” branch.
To establish itself as a viable solution, this new concept would need $35 million over five to seven years to build a test rig with 100 cavities. If successful, future Z-machine generations would be constructed using LTD generators.
So far, funding has come from two congressional initiatives under the Energy Department’s National Nuclear Security Administration, Sandia’s own internal research funds, and Sandia’s Inertial Fusion Energy program.
“It’s like building a Meccano toy,” says Matzen. “We believe 60 million amps will yield decent fusion efficiency. Though simulations suggest this is achievable, we won’t know for sure until we actually build it.”
The device was designed by high-voltage pulsed power chief Alexandar Kim at Tomsk; the switch by Boris Kovalchuk; acceleration from microseconds to 100 nanoseconds supervised by Sandia’s Dillon McDaniel, aided by colleagues Rick Spielman and Ken Struve; testing overseen by Sandia’s Mike Mazarakis at both Sandia and Tomsk; the Z-IFE fusion energy program initiated and managed by Craig Olson.
Latest findings on LTD development will be presented at the upcoming International Pulsed Power Conference and Symposium on Fusion Engineering in Albuquerque, June 2007.
Sandia filed a patent application for a high-power pulsed accelerator invented by William Stygar, using an LTD system as primary current generator instead of conventional Marx generators.
Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin subsidiary, on behalf of the National Nuclear Security Administration under the Department of Energy. Sandia plays a major role in national security R&D, energy, environmental technologies, and economic competitiveness.
Sandia News & Media Contact: Neal Singer, nsinger@sandia.gov, (505) 845-7078
To conclude these two articles, which J.P. Petit asked me to write for his site, I should note that although he was among the first to draw public attention, as well as that of scientists and... science journalists, to these issues—providing often very detailed explanations and analyses (such as Malcom Haines’ paper)—none of them acknowledged his efforts or linked to his site. This isn’t new; sadly, it’s unlikely to change.
May 21, 2007Julien Geffray
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