Non-polluting fusion, another possible path?
The Focus experiment
The results obtained so far do not have the same level of reliability as those of the Sandia Z-machine, but we found it interesting to mention these experiments to show the very wide range that MHD allows in increasing the density and temperature of a plasma. In this regard, the Focus experiment is very original. It remains to be seen, in this case, whether the high temperatures measured using the X-ray flux actually correspond to the plasma temperature or to the impact effect on the anode. E. Lerner, who certainly does not have the means of the powerful New Mexico laboratory, is convinced that this indicates that a temperature of more than one billion degrees (100 keV) would have been achieved. We will leave him the responsibility for this conclusion.
Working principle
June 1st, 2006
FOCUS is an experiment that many people have been talking about since the beginning of the 2000s. You can find information in the Wikipedia encyclopedia at:
http://en.wikipedia.org/wiki/Plasma_focus
Fusion, for everyone, immediately evokes two unique paths.
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Fusion in Tokamaks, corresponding to the expensive ITER experiment, which will be installed in Cadarache, north of Aix-en-Provence
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Fusion by lasers, as in this other "cathedral for engineers" called the Megajoule project, located in Barp, near Bordeaux.
Fusion also exclusively refers to the fusion of deuterium and tritium, which occurs at the lowest temperature. Deuterium is the first isotope of hydrogen, whose nucleus consists of one proton and one neutron. The nucleus of tritium contains one proton and two neutrons.
Their fusion, occurring when the temperature reaches one hundred million degrees (at a rapid rate), produces a helium nucleus and a fast neutron with an energy of 14 MeV (14 million electron volts). At the core of the Sun, the temperature of the "boiler" is only 15 to 20 million degrees, and fusion occurs at a much slower rate (otherwise the Sun would explode).
The molecules of heavy hydrogen resemble those of light hydrogen almost identically. They have the same chemical properties:
On the left, a D-D molecule and on the right, a T-T molecule. The bond is ensured by electrons, here represented by bees. The "nucleons" are represented by little devils. Protons, electrically charged, are in purple, and neutrons, electrically neutral, are in red.
From 3000°C, hydrogen "is completely ionized", the electrons leave the nuclei and hydrogen (light or heavy) becomes plasma, a mixture of an "electron gas" and electrically charged nuclei. But around 100-150 million degrees, these nuclei tend to react:
Here is the diagram of the fusion of heavy hydrogen:
The reader can become familiar with all these concepts related to nuclear energy by consulting my free downloadable comic strip
Energétiquement Vôtre
available on the site
http://www.savoir-sans-frontieres.com
at the address:
http://www.savoir-sans-frontieres.com/JPP/telechargeables/Francais/energetiquement_votre.htm
It is the emission of this 14 MeV fusion neutron that causes problems because these particles cause
induced radioactivity
in all the structures constituting the reactor. These neutrons integrate into the materials of the reactor structures, creating a number of unstable substances that become radioactive immediately and will become waste. This neutron flux also alters the reactor structures, can ultimately compromise the solidity of its components and affect the proper functioning of the solenoids ensuring plasma confinement.
The drawing above evokes the regeneration of tritium. In practice, fusion neutrons do not only recreate tritium. They also create many radioactive isotopes, through the effect of artificial radioactivity (in contrast to "natural radioactivity" linked to radioactive isotopes existing in nature, which were initially created in supernova explosions, then integrated into the mass of the Earth at the time of its formation). A lithium envelope behaves like a "fertile material" which is supposed to continuously recreate tritium, which is radioactive (half-life: 12 years) and does not exist in nature.
The average person generally does not know that fusion is like "nuclear chemistry", where you start from a "fusion mixture", a "reaction", and obtain "reaction products". Deuterium-tritium fusion is just one of the possible reactions. But it is the one that occurs at the lowest temperature.
Non-polluting fusion reactions, free of radioactivity and radioactive waste!
We have seen, in a dossier dedicated to the Z-machine, that a temperature of two billion degrees was achieved in 2005 at the Sandia laboratories in New Mexico. Let us note in passing that the purpose of the experiment was not to achieve such high temperatures, but to create a simple X-ray source at several million degrees. However, unexpectedly, this plasma compressor provided... two billion degrees, in a perfectly undeniable way. This result
outlier
immediately caused unease among the teams who have been managing these expensive projects for decades:
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Fusion by laser (in France: Megajoule)
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Fusion in tokamak machines (in France: ITER)
But we will see that this Z-machine could not be the only one capable of producing such hot plasmas (while the ITER device, operating continuously, cannot increase its temperature). By analogy, one could say that there is as much difference between this new range of high-temperature fusion machines and the tokamak as between explosion engines and steam engines.
Thus, by comparison, ITER is the steam engine of modern times.
To better understand these types of machines, it is necessary to become familiar with the electromagnetic forces at work in electrical conductors, then in discharges.
Take a "flexible" solenoid, a simple loop in which we pass a current. This coil will generate a field that will act on the wire carrying the electric current through the Lorentz force I x B.
Expansion of a coil due to its own magnetic field
This is typically the experiment you may have seen at high school or at the Palais de la Découverte.
If the current is strong enough, this can cause the electrical conductor to rupture. In my laboratory in the 1960s, we created magnetic fields of 2 teslas (20,000 Gauss) using currents of 50,000 amperes, delivered by a capacitor battery. The windings were made of copper foil. If they were not securely clamped (held by a glass fiber envelope glued with araldite), these solenoids would immediately explode, scattering the lab with debris.
Now take an electric discharge. You have all seen the experiment consisting of making an electric discharge between two metal rods. This "rises" and eventually breaks.
We find the diagram of the coil from earlier, with the difference...