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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…
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…
Years from now—maybe in a decade, maybe sooner—if all goes according to plan, the most complex machine ever built will be switched on in an Alpine forest in the South of France. The machine, called the International Thermonuclear Experimental Reactor, or iter, will stand a hundred feet tall, and it will weigh…
It is a feature of the way the world is made that two protons together have less mass than two protons separately. This is a startling but indisputable fact. Weigh two protons separately, then weigh them together: the numbers don't match. The numbers differ by about 1 percent. This curious difference is not to be…
Moving back to the sub-light-speed world: We are not through with Einstein yet. His famous relation between mass and energy, E=mc 2 , which is a consequence of special relativity, presents a further challenge to space travel at impulse speeds. As I have described it in chapter 1, a rocket is a device that propels…