Sun in a Bottle - Charles Seife [43]
Despite Spitzer’s bold plans, Teller’s Livermore got the largest share of funding, about half of the Project Sherwood money. Princeton came in second, and Los Alamos, with its pinch program, was a distant third. Yet it was Los Alamos that first claimed victory.
By the beginning of 1955—just before Bhabha’s speech at the UN conference brought worldwide attention to the promise of fusion energy—the Los Alamos researchers saw indications that their plasma was hot enough to fuse deuterium. Every time they initiated a strong, fast pinch in their latest machine, the scientists saw a burst of tens of thousands of neutrons. This was very encouraging, because neutrons are the best indicator of a fusion reaction.
Everyone in the fusion community was hoping to achieve two main kinds of thermonuclear fusion in a reactor. The easier kind used a mixed fuel: deuterium and tritium. When a deuterium (a proton and a neutron) and a tritium (a proton and two neutrons) strike each other hard enough, they fuse, creating helium-4 (two protons and two neutrons). The remaining neutron flies off with a great deal of energy. So in a successful deuterium-tritium reaction, the products will be helium-4 and neutrons. Deuterium-deuterium reactions are a little more complicated; there are two ways this kind of fusion reaction tends to happen. As the two deuterium nuclei collide and stick, either a proton flies off (leaving behind a tritium nucleus) or a neutron flies off (leaving behind a helium-3 nucleus). These two branches of the reaction are roughly equally probable. Thus, if a reactor succeeds in fusing deuterium fuel, then the products will be helium-3, tritium, protons, and neutrons. Neutrons are produced by both deuterium-tritium and deuterium-deuterium fusion reactions. A burst of fusion—no matter whether the fuel is pure deuterium or deuterium mixed with tritium—will be accompanied by a corresponding burst of energetic neutrons.37
FUSION REACTIONS: (a) Two deuteriums collide and produce either a tritium and a proton or a helium-3 and a neutron. (b) A deuterium strikes a tritium and produces a helium-4 and a neutron.
Despite the problem with the kink instabilities, Los Alamos scientists were optimistic. If they could make the pinch strong enough and fast enough, they thought, they could get fusion going before the kink instability destroyed the pinch. In fact, Tuck’s calculations showed that such a machine could achieve breakeven—the fusion reaction in the machine would produce energy equal to what was needed to get the reaction going in the first place. (A fusion reactor that absorbs more energy than it produces is of no use to anyone.) And, Tuck argued, a larger machine could produce explosions equivalent to several tons of TNT per pinch. These explosions could be turned into usable energy, just as an internal combustion engine makes little fuel-air explosions turn a crank. Tuck built successively bigger pinch machines that could pinch the plasma harder and faster, and eagerly awaited neutrons produced by thermonuclear fusion.
When, early in 1955, the Los Alamos researchers turned on their newest, biggest pinch machine, Columbus I, they saw a burst of neutrons every time they pinched the plasma hard enough. Pinch. Neutrons. Pinch. Neutrons. No pinch, no neutrons. It seemed like a great success. From the number of neutrons they were seeing, the pinch scientists concluded they had attained fusion; the plasma inside the Columbus machine must have been heated to millions of degrees Celsius. But not everybody was convinced. Researchers at Livermore were skeptical that the pinch machine could reach the temperatures advertised. Thus, the plasma couldn’t possibly be hot enough to ignite a fusion reaction. So where were the neutrons coming from?
The Los Alamos physicists started making