Nuclear Fusion: Hot Box

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Nuclear Fusion: Hot Box
Nuclear Fusion: Hot Box

Hot Box

Many hope that generating energy by fusing atomic nuclei will make a significant contribution to ensuring future electricity production. However, there are still many stumbling blocks to be cleared before we get there. An American-French research group now claims to have made a decisive contribution to this. A notable result of the most recent Delphi study – which, after all, dates back several years – was that the experts believed then, as now, that it would take at least 50 years for a power plant to supply energy through the fusion of atomic nuclei. The technicians and engineers involved in this task seem to be more or less stationary, or at least moving very slowly.

It's no wonder. After all, taming the fire that gives the sun its power involves a tremendous engineering effort: before two atomic nuclei fuse, they must overcome their electromagnetic repulsion. This requires high pressures and enormous temperatures. Inside our central star, where there is a pressure of over ten thousand trillion pascals, these processes "already" start at a heat of 10 million Kelvin. Because it is difficult to generate similarly high pressures on Earth, the fusion researchers have to heat their fuels – mostly the two hydrogen isotopes deuterium and tritium – to at least 100 million Kelvin.

At these beefy temperatures, the electrons have long since escaped their atomic nuclei. The engineers are therefore faced with the task of capturing such an incredibly hot, electrically charged plasma. This is not so easy, because at these temperatures all known materials would vaporize if they came into direct contact with this wafting fuel. The experimenters keep the wildly buzzing, charged atomic nuclei of the plasma in limbo with the help of strong magnetic fields.

So much for the theory. In practice, obviously, everything is much more complicated. Sudden instabilities in the peripheral areas of the fuel often lead to heavy loads on the vessel walls and thus to their premature aging. But a fusion reactor should provide energy for at least twenty or thirty years before it becomes ailing. Otherwise the energy balance and the electricity generation costs are poor.

Now Todd Evans from the American company General Atomics in San Diego, California has apparently found a solution to punish these outbreaks. Together with colleagues, including representatives of the Euratom-CEA from Cadarache, France, the location of the future international tokomak experimental reactor ITER, he subjected the magnetic field that surrounds the plasma like a tube to small disturbances. And although the magnetic fields then behaved chaotically, Evans and his team were able to suppress the instabilities in this way for more than two and a half seconds. That doesn't sound like much, but it's about 17 times the time it takes for the plasma to generate usable energy.

That these small disturbances calm the squirming mass is a surprise even for the scientists. Finally, the observation is not consistent with the current theories of magneto-hydrodynamics, with which the behavior of the plasma in magnetic fields is usually described. More important to the researchers than an all-explaining theory is that the sun's fire can be tamed in this way. With the completion of this task, they therefore hope that it will soon be possible to obtain energy from the fusion of atomic nuclei - and not only in 50 years.

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