Sceptre (stabilized controlled pinch thermonuclear reactor experiment) was a series of early fusion power devices based on the Z-pinch concept of plasma confinement, built in the UK starting in 1956. They were the ultimate versions of a series of devices tracing their history to the original pinch machines, built at Imperial College London by Cousins and Ware in 1947. When the UK's fusion work was classified in 1950, Ware's team was moved to the Associated Electrical Industries (AEI) labs at the Atomic Weapons Establishment (AWE, Aldermaston). The team worked on small linear tubes like the ones that were known to be used in the Soviet Union, but these demonstrated problems and work on these ended. They then turned their attention to the problems associated with using metal tubes with high voltages, in support of the efforts at Harwell. As part of this AEI built a 64-segment metal tube that could be connected together in various ways to conduct experiments. Following this, they were eventually allowed to make several smaller toroidal devices, similar to those at Harwell, as purely experimental devices. When Harwell's ZETA machine emitted seeming fusion neutrons, AEI quickly built a smaller machine out of parts of the earlier metal-liner testbed, producing Sceptre III. Sceptre III also emitted neutrons, seeming to confirm the ZETA results. It was later found that the neutrons were spurious, and UK work on Z-pinch ended in the early 1960s.
History
Background
Fusion research in the UK started on a shoestring budget at Imperial College in 1946. When George Paget Thomson failed to gain funding from John Cockcroft's Atomic Energy Research Establishment (AERE), he turned over the project to two students, Stanley (Stan) W. Cousins and Alan Alfred Ware (1924-2010). They started working on the concept in January 1947, using a glass tube and old radar parts. Their small experimental device was able to generate brief flashes of light, but the nature of the light remained a mystery as they could not come up with a method of measuring its temperature. Little interest was shown in the work, although it was noticed by Jim Tuck, who was interested in all things related to fusion. He met fellow fusion-fascinated Peter Thonemann, and the two developed a similar small machine of their own at Oxford University's Clarendon Laboratory. Tuck left for the University of Chicago before the device was built. After moving to Los Alamos, Tuck introduced the pinch concept there, and eventually built the Perhapsatron along the same lines. In early 1950 Klaus Fuchs' admitted to turning UK and US atomic secrets over to the USSR. As fusion devices would generate copious amounts of neutrons, which could be used to enrich nuclear fuel for atomic bombs, the UK immediately classified all their fusion work. The research was considered important enough to continue, but it was difficult to maintain secrecy in a university setting. The decision was made to move both teams to secure locations. Imperial team under Ware was set up at the new Associated Electrical Industries (AEI) labs at Aldermaston in November while the Oxford team under Thonemann were moved to UKAEA Harwell.
By 1951 there were numerous pinch devices in operation; Cousins and Ware had built several follow-on machines, Tuck built his Perhapsatron, and another team at Los Alamos built a linear machine known as Columbus. It was later learned that Fuchs had passed information about the early UK work to the Soviets, and they had started a pinch program as well. By 1952 it was clear to everyone that something was wrong in the machines. As current was applied, the plasma would first pinch down as expected, but would then develop a series of "kinks", evolving into a sinusoidal shape. When the outer portions hit the walls of the container, a small amount of the material would spall off into the plasma, cooling it and ruining the reaction. This so-called "kink instability" appeared to be a fundamental problem.
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