The LTD-boosted Z-machine
by Julien Geffray
May 21, 2007
Activity and news are resuming around nuclear fusion thanks to the Z-machine— at least in the United States. For France’s Z-machine, Sphinx, it’s a different story, as the DGA has firmly locked down all access, as you’ll see by reading this article published in the journal Les Echos on May 16, 2007:
Les Echos, May 16, 2007
Nuclear Competence
France’s Z-machine boycotts energy
Small "Sphinx."
Deep in Quercy, at the Gramat Research Center (CEG), the DGA has operated for several years a small French Z-machine (2.5 million amperes), named "Sphinx." Like its larger American sister machine, it is primarily used to test the resilience of nuclear warheads.
Unlike its American counterpart, however, it will never undergo civilian experiments. A few years ago, the researchers at Gramat had indeed petitioned their military superiors to diversify their studies—but without success. When questioned by "Les Echos," the very "fierce" CEG today insists it has no energy-related projects. This lack of investment worries specialists in magnetic compression.
"French expertise in this field of high-power electrical engineering is under threat," one of them asserts.
In the United Kingdom, a comparable machine—the Imperial College’s Magpie (1.4 million amperes)—is actively working on magnetic compression, partly funded by American sources. Though not powerful enough to reach the nuclear objectives of the Z-machine, it is used by Americans to complement their research on compression itself. The Russians are also reportedly preparing to invest in this research area.
Note: "Striction" is the French translation of "pinch," meaning "to pinch." Thus, the Z-machine belongs to the class of so-called "Z-pinch" plasma machines, where plasma is "pinched" along the OZ symmetry axis of the system. All Z-pinch machines are also MHD machines— a discipline in which France was once at the forefront, but which was completely and deliberately abandoned in the mid-1970s. This lack of official response also stems from a large measure of misunderstanding and outright incompetence. For instance, military MHD remains entirely absent in France, while in the United States, Russia, and other countries it is actively advancing. One could summarize this situation with a single sentence:
While other nations are pressing the accelerator to the floor, the French are standing on the brakes.
Another observation: Alain Juppé has been appointed "Minister of the Environment." In this capacity, numerous representatives of environmental protection associations have recently been invited. But this is inseparable from proactive energy policy favoring new energy sources. And there, there is a complete absence—of motivation, of information, and even of expertise. Let us return to the subject of the article.
In the United States, the news about the latest-generation LTD generators is fascinating, with progress even faster than expected. On April 24, 2007, Sandia Laboratories released a press release titled:
Rapid-fire pulse brings Sandia Z method closer to goal of high-yield fusion reactor
(Ultra-fast pulses bring the Z-machine closer to a high-yield fusion reactor)
The article, fully translated below on this page, describes a generator called LTD (for Linear Transformer Driver), which could be translated as "linear transformer driver." This device should enable truly usable controlled nuclear fusion within the Z-machine. The LTD would make the machine more compact and less complex by rendering obsolete the massive water-and-oil insulating tank and the "water lines" previously required to shape the pulse over time.
Most importantly, it will allow repeated shots at a frequency of 0.1 hertz—where the current Z-machine can manage only one shot per day!
LTD generators are not truly surprising, since France’s Sphinx Z-machine has been equipped with them for a long time. The novelty here lies in the performance achieved by the Russians with their latest LTDZ model:
Russian LTDZ Generator: 100 GW, 1 million amperes, 100 kV
Diameter: 3 meters – Depth: 22 centimeters
Let us briefly explain the LTD generator: it consists of modular "bricks," each about the size of a shoebox, containing two capacitors and a switch. When interconnected in parallel and arranged in a circle—our focus here—40 of these "bricks" form a single toroidal "cavity."
Cross-sectional diagram of a constitutive "brick" of the LTDZ
1: Two GA 31165 capacitors (100 kV, 40 nF),
2: Multi-gap HCEI switch,
3: Output nozzle,
4: Magnetic core,
5: Insulator,
6: Vacuum or oil cavity,
7: Charging cavity,
8: Caprolactone rods
This Russian version, currently the most advanced, is being tested at the High Current Electronics Institute (HCEI) in Tomsk, Siberia, where Sandia Laboratories has just acquired four units. Note the growing American-Russian collaboration on z-pinch fusion... This Russian LTD, the most powerful in the world (100 gigawatts), is capable of delivering 1 million amperes at 100,000 volts in a pulse lasting 100 nanoseconds natively (thus without needing to compress the pulse duration). Furthermore, it is designed to fire every 10 seconds! This is precisely the firing rate defined for a future operational magnetic compression fusion power plant, which would function literally like a "two-stroke fusion" engine (compression, expansion).
The concept appears reliable. The previous version of this LTD—identical but twice less powerful (20 bricks generating 0.5 million amperes at 100,000 volts)—has already been validated by Sandia Laboratories following a cycle of over 11,000 shots. At Tomsk, one switch has fired more than 37,000 times every 12 seconds.
Since these cavities are modular, Sandia plans to stack them like doughnuts on a rod, then multiply these rods. There would thus be 70 radially arranged cylindrical modules, each containing 70 coaxially stacked LTDs. The efficiency of this configuration is undeniable:
In each module, about twenty meters long, the 70 internal LTDs are connected in series to add their voltages. Each module would therefore produce at output a current of 1 million amperes and a voltage of 7 million volts.
The 70 modules would then be connected in parallel to add their currents, resulting in a final machine delivering 70 million amperes at 7 million volts.
Sandia’s "IFE driver" project: 104 meters in diameter.
70 million amperes, 7 million volts, 490 terawatts theoretical.
70 modules of 70 LTDs each, totaling 392,000 capacitors.
Accounting for inevitable losses—especially along the MITL (Magnetically Insulated Transmission Line)—Sandia estimates 60 million amperes at 6 million volts as usable. This would represent a power of 360 terawatts before injection onto the target.
This test bench would be laid flat, as shown in the diagram. The Kurchatov Institute scientists in Russia have suggested stacking these modules vertically as well. One could even imagine a spherical symmetry. As one scientist working on the topic put it: it’s a bit like playing Meccano...