Clarifications
June 20, 2006.
Last update: July 14, 2006 (below)
June 21, 2006: Post on Agoravox, June 19 edition. Title:
"2 billion degrees. Humanity discovers absolute fire and everyone couldn't care less." 128 reactions
After briefly browsing the Agoravox forum, I realized that while some readers seemed to grasp the significance of the breakthrough achieved in May 2005 at Sandia on the Z-Machine, others still had a rather confused understanding of the whole matter—probably because I hadn't explained myself clearly enough. I will therefore address here the questions that emerged from the forum or the erroneous remarks. In no particular order, from memory:
Reader's comment:
These two billion degrees aren't particularly exceptional. We achieve much higher temperatures in particle colliders.
Response:
That's completely different. Indeed, we can accelerate particles and make them collide at high relative velocity (V). Since these particles have mass (m), one can "deduce an equivalent temperature." A reader mentioned that in colliders, we can cause collisions involving up to 200 nuclei. Can we consider this population as "a gas"? That's debatable. But in any case, it remains extremely rarefied compared to a plasma—especially a dense plasma like the one created in the Z-machine.
In general, one cannot extrapolate conclusions from "high-energy physics," which deals with hyper-rarefied environments, to apply to the hyper-dense plasmas of "inertial fusion."
I notice that some readers still don't properly understand the concept of "inertial confinement." Atoms are packed tightly together for a certain period. If the conditions are such that the mean free path for reaction (here, fusion) is small compared to the confinement time, then the reaction (fusion) occurs.
A hydrogen bomb operates via inertial confinement. Lithium deuteride is compressed and remains "confined" for a sufficient duration for fusion reactions to take place. In bombs, this lasts tens of nanoseconds.
Reader's comment:
Achieving two billion degrees is impressive, but you still need to maintain that temperature! I remind you that this is the main challenge in tokamaks and machines like ITER, which still have many years ahead of them.
Response:
In "inertial fusion," confinement is precisely due to inertia and lasts only a very brief time. But it is sufficient for fusion reactions to occur. A hydrogen bomb is an inertial confinement system where lithium hydride is abruptly compressed by radiation pressure from an atomic bomb explosion (in the form of X-rays). Simpler still: an atomic bomb works via inertial confinement. A hollow plutonium sphere is rapidly compressed using explosives. Everything happens in tens of nanoseconds—and it works with "only" 500 million degrees. If we placed a lithium hydride needle on the axis of the Z-machine's "wire array," with two billion degrees, I believe fusion would be instantaneous. I suspect the Americans rushed to perform the experiment, but didn't publicize it widely, given the defense implications. This might explain the U.S. Congress's decision to replace the 6,000 American warheads with "newer bombs."
Conversely, in the Sun's core, where temperatures reach only 20 million degrees, fusion proceeds slowly.
The famous "Lawson criterion" simply states that fusion reactions have time to occur during the period when the temperature is reached. It's a matter of "collision cross-sections." In a tokamak like ITER, fusion is obviously slow (otherwise the machine would explode like a bomb).
The internal combustion engine is a good analogy for an inertial confinement reaction. Combustion is extremely rapid and occurs during the brief temperature spike (at the end of compression in a diesel engine). Thus, the comparison of ITER to a steam engine isn't as silly as it may seem. In a steam engine, heat is supplied continuously, in a boiler. In an "explosion engine," heat is supplied in pulses, during very short periods.
Reader's comment:
I don't see how one could turn a Z-machine into an electricity generator. You'd have to reassemble everything each time, right?
Response:
The first cannons weren't loaded from the muzzle. You had to insert powder, wadding, and the projectile—very slow. In a machine gun or rapid-fire cannon, it's much faster, because in the meantime, the cartridge was invented. Imagine "cartridges" made of disk-shaped electrodes, wire liners ("birdcage"), and a lithium hydride target (soft metal) placed along the axis. Imagine reloading these cartridges into the machine at a rapid pace.
This idea comes from a non-scientific reader!
Reader's comment:
I don't see how one could turn a Z-machine into a bomb. It's too heavy and bulky.
Response:
Re-read my articles. The Z-machine delivers 20 million amperes in a fraction of a microsecond (0.1 µs). But the Russian disk generator delivers 35 million amperes in a similar fraction of a microsecond and is an explosive device weighing around a hundred kilograms. On my website, readers can find "Meccano-like" components to build a pure fusion lithium hydride bomb by chaining together magneto-pyrotechnic systems (Russian-style). If fusion was indeed achieved at Sandia (and I am convinced it was), then teams at Los Alamos and Livermore (see the Los Angeles Times article) have been working around the clock on these systems for the past year.
Reader's comment:
We should wait for other teams to confirm this result—those two billion degrees.
Response:
For now, this pulsed electrical generator—since the Sandia machine is primarily that—delivers 20 million amperes in 0.1 µs. It is the only machine capable of doing so. The French military research center at Gramat (Lot, France) delivers 2.5 million amperes, also in sub-microsecond regime. The British Magpie generator delivers 1.4 million amperes. The Russians may not yet have an equivalent to the Z-machine, but they won't be far behind.
Until now, people didn't feel the need to aim for higher amperage levels, because these machines were designed primarily as X-ray sources, with final compression temperatures of a few million degrees (2 million degrees at Sandia a few years ago, around 1999, I believe).
That said, a machine like Sandia's Z-Machine costs 100 million dollars—the hundredth of ITER (10 billion dollars, and likely more in the long run). Logically, this should be implemented immediately. Bavay, in his thesis (see my website), recommended 60 million amperes in 100 nanoseconds. The French already have the expertise to build such a device in less than a year. Believe me, "other teams are forming," but very probably...