The Intermediate-Current Stability Experiment (ICSE, pronounced "ice") was a fusion power device designed in the United Kingdom in the late 1950s. It was to have been built at the newly opened AEA Culham center for fusion research, but was cancelled in the summer of 1960 when the ever-rising budget led to further investigations of the theoretical basis of the machine that suggested it did not have a high chance of being successful. ICSE was a response to the failure of the earlier ZETA design. ZETA produced neutrons in 1957 which were interpreted as a sign of successful fusion reactions. Further research demonstrated they were not, that the neutrons were the result of instabilities in the plasma, something that had been seen before on earlier devices and should have been more seriously considered here. The claims of fusion had to be retracted in a humiliating May 1958 release, which cast a pall over the entire fusion field. That research, along with general studies of plasma stability in toroidal designs, suggested that the system would be stable if everything occurred much more rapidly and had a particular magnetic layout. Instead of pulses that lasted about 1,500 microseconds in ZETA, pulses in ICSE would last only 25 microseconds. It was believed this would cause the current induced in the plasma to flow only into the outer layer of the plasma, creating a magnetic field which would be much more stable than one that flowed through the entire body of the plasma. Construction of the buildings for ICSE had just begun when a number of theoretical arguments were raised that suggested there was no real reason to believe it would be more successful than ZETA. Combined with an ever-increasing price tag, the project was soon in trouble. When William Penny heard one more particularly worrying theoretical problem with the concept, he cancelled development in August 1960, and Culham moved on to other experiments.
History
Early fusion program in the UK UK researchers were among the first to seriously consider the topic of controlled fusion, dating to the immediate post-war era. With the worldwide news reporting following the announcement of Argentina's fusion project, the UK atomic labs were able to quickly set up a fusion program. Over the next two years, early work quickly focussed their efforts on a concept today known as z-pinch, in which a large transformer is used to induce an electrical current in a plasma of a suitable fusion fuel - which at the time was pure deuterium. Two teams were formed, one at the Atomic Energy Research Establishment (AERE) at Harwell, and a second at the Atomic Weapons Establishment (AWRE) in Aldermaston. By the mid-1950s, this program had advanced to the point of discovering a number of serious problems related to the stability of the plasma when a current was running through it. This led to some consternation, but was almost immediately resolved by new work by teams in the US, and especially the work of Marshall Rosenbluth. This led to a second round of machines at both sites using the so-called "stabilized pinch", which showed a great improvement in performance. With some confidence that the stabilized pinch design solved the earlier problems, the researchers at Harwell pressed for funding to construct a much larger machine. This emerged as ZETA, by far the largest and most powerful fusion machine in the world at that time. They became so confident of its success that early planning for an even more powerful machine, ZETA II, began as early as 1957. Shortly after ZETA was first turned on, test runs using deuterium began to generate neutrons. Over the next months, the team was increasingly convinced they had succeeded in creating fusion, even though there were a number of reasons to believe this was not the case. In January 1958, the results were announced to the world - fusion was no longer just for bombs and although much more development was needed, a fusion-powered future appeared inevitable. Over the next few months, it became clear that there was a serious problem with the results. Temperature measurements that suggested the plasma was very hot were inaccurate and the plasma was nowhere near what was required of fusion. More in-depth testing revealed yet another class of current-driven instabilities that were causing the neutrons.
ZETA II Before the issues with ZETA were known, even before construction had completed, plans for ZETA II were advancing. It was, essentially, a version of ZETA with much more powerful magnets and pinch currents. There was the belief that this machine might approach break-even conditions, and thus be a model for future commercialization. This led to extensive discussions about where such a device would be built, and who might build it. Harwell was running out of room for machines, and if the new design was going to be much larger it would be difficult to find the space. Moreover, the number of people working on it would make management of the site difficult. If the system was going to be a commercial prototype, then it seemed it should be built at AEA Winfrith, a larger site were a number of experimental fission reactors were being built, and if it was going to be turned over to industry, then perhaps Metropolitan-Vickers should pay a larger share of the costs. These decisions ran into a firestorm of protest inside Harwell. Some felt that they were nowhere near a production concept, regardless of any projected performance on ZETA, and it was too early to push development to industry. Others noted that the Winfrith site was remote to the point that none of the physicists who worked on the theory side would want to move there, nor would the ones that stayed back be easily available to those that did move. While there was agreement that Harwell would be too small, there was very little support for a move as far as Winfrith to solve that. Further confusion ensued when John Cockcroft announced he was retiring from the executive role in the AEA's Research Group, leading to many of the people important to the ZETA effort moving chairs within the establishment. After much confusion, during which the problems with ZETA became clear, the ultimate decision was to move any future machines from Harwell to a new location today known as the Culham Centre for Fusion Energy. This was only a short distance from Harwell, making the travel issues minor, as well as being near Oxford University which provided ample manpower and theory support.
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