Blog Archive

Saturday, March 22, 2014

It is called a tokamak -- old Soviet shorthand for a more precise and geometrical name, toroidalnaya kamera s aksialnym magnitnym polem, or 'toroidal chamber with an axial magnetic field.'

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Today's selection -- from "A Star in a Bottle" by Raffi Khatchadourian. Deep in a forest in Provence, France an international consortium of physicists and engineers are building an International Thermonuclear Experimental Reactor, or ITER. When finished it will stand one hundred feet tall and weigh twenty-three thousand tons and will ionize hydrogen to achieve temperatures of over two hundred million degrees Celcius. The current formal target date for its first experiment is 2020, and its purpose is research to further understand the mysteries of the subatomic world. One byproduct could be new sources of energy:

"No natural phenomenon on Earth will be hotter. Like the sun, the cloud will go nuclear. The zooming hydrogen atoms, in a state of extreme kinetic excitement, will slam into one another, fusing to form a new element -- helium -- and with each atomic coupling explosive energy will be released: intense heat, gamma rays, X rays, a torrential flux of fast-moving neutrons propelled in every direction. There isn't a physical substance that could contain such a thing. Metals, plastics, ceramics, concrete, even pure diamond -- all would be obliterated on contact, and so the machine will hold the superheated cloud in a 'magnetic bottle,' using the largest system of superconducting magnets in the world. Just feet from the reactor's core, the magnets will be cooled to two hundred and sixty-nine degrees below zero, nearly the temperature of deep space. Caught in the grip of their titanic forces, the artificial earthbound sun will be suspended, under tremendous pressure, in the pristine nothingness of ITER's vacuum interior. ...

"ITER's design is based on an idea that Andrei Sakharov and another Russian physicist, Igor Tamm, sketched out in the nineteen-fifties. It is called a tokamak -- old Soviet shorthand for a more precise and geometrical name, toroidalnaya kamera s aksialnym magnitnym polem, or 'toroidal chamber with an axial magnetic field.' Sakharov's rough sketch depicted a doughnut-shaped vacuum chamber, or torus, ringed with electromagnets, and that is how ITER's core will look, too, once it is completed.

"The basic physics of thermonuclear energy is seductively simple. Fission produces energy by atomic fracture, fusion by tiny acts of atomic union. Every atom contains at least one proton, and all protons are positively charged, which means that they repel one another, like identical ends of a magnet. As protons are forced closer together, their electromagnetic opposition grows stronger. If electromagnetism were the only force in nature, the universe might exist only as single-proton hydrogen atoms keeping solitary company. But as protons get very near -- no farther than 0.000000000000001 metres -- another fundamental force, called the strong force, takes over. It is about a hundred times more powerful than electromagnetism, and it binds together everything inside the atomic nucleus.

"Getting protons close enough to cross this barrier and to allow the strong force to bind them requires tremendous energy. Every atom in the universe is moving, and the hotter something is the greater its kinetic agitation. Thermonuclear temperatures -- in the sun's core, fifteen million degrees -- are high enough to cause protons to slam together so forcefully that they are united by the strong force. Hydrogen nuclei slam together and form helium. Helium nuclei slam together and form beryllium. The atoms take on more protons, and become heavier. But, strangely, with each coupling a tiny amount of mass is lost, too. In 1905, Einstein demonstrated, with his most famous equation, E=mc2, that the missing mass is released in the form of energy as the nucleus is bound together. The quantity of energy is awesome -- in some cases, a thousand times what is needed to get atoms to bind in the first place. Without it, stars would not burn, and space would remain forever cold. ...

"At the super-high temperatures necessary for fusion, the hydrogen atoms would be unlike any of the common states of matter -- solids, liquids, or gases -- but would exist as ionized gas, or plasma, which would have unique electrical properties. Ninety-nine per cent of the visible universe is plasma. ... No matter the approach, the physicists reasoned that, as the plasma became denser, hotter, and longer-lasting, the conditions for fusion would eventually be met. But, because the point of the research was to build a commercial reactor, simply fusing atoms would not be enough. The plasma would have to produce at least as much energy as the physicists were pouring into it -- an atomic break even -- and then, beyond that, generate a net gain in energy. The ultimate goal, which the physicists called 'ignition,' is to excite the plasma to a state where it will heat itself like a star, requiring the barest effort to sustain and control."

"A Star in a Bottle"
Author: Raffi Khatchadourian
Publisher: The New Yorker
Date: March 3, 2014
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