Sun in a Bottle - Charles Seife [51]
Sakharov’s intellectual trajectory was an eerie mirror image of Teller’s, always delayed by a few years.42 Teller came up with the imprac- tical Alarm Clock configuration for the hydrogen bomb in 1946; Sakharov hit on his sloika in 1949. In 1946, Teller proposed boosting the yield of a fission bomb by injecting a tiny dollop of fusion fuel (the idea tested in Greenhouse Item). Boosting atom bombs was Sakharov’s “second idea,” which came soon after his first. In 1949, Ulam and Teller solved the problem of igniting a fusion reaction by separating the primary fission device from the secondary fusion one; Sakharov and his colleagues came to the same solution—Sakharov’s “third idea”—in 1953.
Not everything, though, occurred to the Americans first, especially when it came to fusion reactors. In 1950, Sakharov was hard at work trying to figure out how to build a hydrogen bomb—an uncontrolled fusion reaction—when he began to ponder whether the reaction could be controlled. Like his American counterparts, he came up with a scheme using magnetic fields, but his idea was slightly different from the ones that would guide Project Sherwood. Sakharov’s device was neither a Stellarator nor a pinch machine. It was somewhere in between. It was a novel design, one that combined some advantages of a pinch machine with those of a Stellarator. It was just what scientists were looking for.
In a pinch machine, the plasma confines itself. The pinch begins by inducing a current of some sort in the plasma, forcing it to contract and to heat up. The Perhapsatron, ZETA, and Columbus all did this by running a current down the length of the plasma, while Scylla ran an electrical current around the circumference of the tube of plasma. In both cases, though, there is a current inside the plasma; this current induces a magnetic field, which squashes the plasma. Pinch machines were successful at making a plasma very dense and hot, even inducing a bit of fusion, but physicists couldn’t keep those conditions going for very long. The pinch was extremely short-lived. Once the current disappeared, so did the confinement of the plasma. Given the enormous energy it took to set up a pinch, and how little energy was generated by the brief fusion reaction, a pinch machine could not ultimately become a working reactor.
In a Stellarator, on the other hand, the plasma is confined from the outside. The machine uses carefully arranged electromagnets to generate intricate magnetic fields that bottle up the cloud. In theory, these fields would allow a Stellarator to confine the plasma for a relatively long time. Unlike a crush-and-release machine, a Stellarator attempted to maintain its hold on the plasma, keeping a fairly stable cloud. But scientists were having difficulty not only confining the plasma but also heating and compressing the cloud. It was much harder to warm and squash plasmas in a Stellarator than it was in a pinch machine.
The choice was bleak for American scientists in the late 1950s and early 1960s. They could get high temperatures and densities for a short time or lower temperatures and densities for a longer time, but not both. Yet scientists really needed a magnetic bottle that could heat the plasma to tens of millions of degrees, keep it very dense, and hold it for a relatively long time. The heating and density would ensure that the fusion reaction took place, while the confinement would ensure that the plasma reacted long enough to generate a significant amount of energy. Only then could physicists hope to turn such a magnetic bottle into a fusion reactor.
Sakharov’s