ZETA (fusion reactor)

Based on the pinch plasma confinement technique, and built at the Atomic Energy Research Establishment in the United Kingdom, ZETA was larger and more powerful than any fusion machine in the world at that time.

Front-page articles in newspapers around the world announced it as a breakthrough towards unlimited energy, a scientific advance for Britain greater than the recently launched Sputnik had been for the Soviet Union.

George Gamow's 1928 exploration of quantum tunnelling demonstrated that nuclear reactions could take place at lower energies than classical theory predicted.

[26] With the formation of the Atomic Energy Research Establishment (AERE) at Harwell, Oxfordshire, in 1945, Thomson repeatedly petitioned the director, John Cockcroft, for funds to develop an experimental machine.

[30] When this presentation also failed to gain funding, Thomson passed along his concepts to two graduate students at Imperial, Stanley (Stan) W. Cousins and Alan Alfred Ware (1924-2010[31]).

[26] Thomson continued to pressure the government to allow him to build a full-scale device, using his considerable political currency to argue for the creation of a dedicated experimental station at the Associated Electrical Industries (AEI) lab that had recently been constructed at Aldermaston.

[33] Tuck was joined by Australian Peter Thonemann, who had worked on fusion theory, and the two arranged funding through Clarendon to build a small device like the one at Imperial.

Starting with linear tubes and mercury gas, he found that the current tended to expand outward through the plasma until it touched the walls of the container (see skin effect).

Because these projects were secret, based on the little information available the press concluded they were versions of the same conceptual device, and that the British were far ahead in the race to produce a working machine.

[48] In 1956, while planning a well publicised state visit by Nikita Khrushchev and Nikolai Bulganin to the UK, the Harwell researchers received an offer from Soviet scientist Igor Kurchatov to give a talk.

[59] Kurchatov's speech revealed the Soviet efforts to produce fast pinch devices similar to the American designs, and their problems with instabilities in the plasmas.

These runs demonstrated that ZETA was not suffering from the same stability problems that earlier pinch machines had seen and their plasmas were lasting for milliseconds, up from microseconds, a full three orders of magnitude improvement.

[70] Things came to a head on 12 December when a former member of parliament, Anthony Nutting, wrote a New York Herald Tribune article claiming: Some people have suggested darkly to me that the real reason for this American reluctance to have this momentous news released is politics.

[72] The affair eventually led to the UKAEA making a public announcement that the U.S. was not holding back the ZETA results,[73] but this infuriated the local press, which continued to claim the U.S. was delaying to allow them to catch up.

The U.S. team, including Stirling Colgate, Lyman Spitzer, Jim Tuck and Arthur Edward Ruark, all visited ZETA and concluded there was a "major probability" the neutrons were from fusion.

If the temperature was increasing at the relatively slow rate his calculations suggested, fusion would not be taking place early in the reaction, and could not be adding energy that might make up the difference.

The Observer wrote that "Admiral Strauss' tactics have soured what should be an exciting announcement of scientific progress so that it has become a sordid episode of prestige politics.

[75] He began by introducing the fusion programme and the ZETA machine, and then noted: In all experiments on toroidal discharges neutrons have been observed in about the numbers to be expected if thermonuclear reactions were proceeding.

It is well known, however, from previous experiments carried out in Russian and other laboratories that instabilities in the current channel can give rise to strong electric fields which accelerated deuterons and can produce neutrons.

[76] Failing to do so meant they could not eliminate the possibility that the neutrons were being released due to electrical effects in the plasma, the sorts of reactions that Kurchatov had pointed out earlier.

[85][87][88] They also noted that the energy of the neutrons was extremely close to that of a D-D fusion reaction, which suggested that the source was D particles colliding with a solid in the reactor.

[90] This is the same physical process that had been creating neutrons in earlier designs, the problem Cockcroft had mentioned during the press releases, but their underlying cause was more difficult to see and in ZETA they were much more powerful.

"[91] Le Monde raised the issue to a front-page headline in June, noting "Contrary to what was announced six months ago at Harwell – British experts confirm that thermonuclear energy has not been 'domesticated'".

[92] The event cast a chill over the entire field; it was not only the British who looked foolish, every other country involved in fusion research had been quick to jump on the bandwagon.

The entire affair was a major strain on Basil Schonland, who took over the Research division when Cockcroft left in October 1959 to become the Master of the newly formed Churchill College, Cambridge.

[97] While this was taking place, the original ZETA II proposal had been growing ever-larger, eventually specifying currents as powerful as the Joint European Torus that was built years later.

[83][100] ICSE was designed to take advantage of further stabilising effects noticed in M-theory, which suggested that very fast pinches would cause the current to flow only in the outer layer of the plasma, which should be much more stable.

[110] In 1968 a meeting of fusion researchers took place in Novosibirsk, where, to everyone's astonishment, the Soviet hosts introduced their work on their tokamak designs which had performance numbers that no other experiment was even close to matching.

[113][114] The Soviets were equally concerned about this, and even though it was the height of the Cold War, Artsimovich invited UKAEA to bring their laser system to the Kurchatov Institute and independently measure the performance.

A ZETA-type machine could reach this q, but would require enormously powerful external magnets to match the equally large fields being generated by the current.

The ZETA device at Harwell, United Kingdom. The toroidal confinement tube is roughly centred. The larger device on the right encircling the tube is the magnet used to induce the pinch current.
A modern induction lamp is a low-temperature version of a toroidal plasma tube. At these temperatures the plasma can hit the tube walls without harm; further confinement is not needed.
This lightning rod was crushed when a large current passed through it. Studying this phenomenon led to the discovery of the pinch effect .
A photograph of the kink instability in an early experiment at Aldermaston. The dark rectangle on the right is the induction magnet.
To test the basic concept of stabilised pinch, additional magnets were added to the earlier Mark 2 Torus, seen here as the wires wound around the vacuum chamber.
Elizabeth II , guided by UKAEA Research Director John Cockcroft , visits the ZETA fusion reactor while it is under construction. The main induction magnet dominates the left side of the image, the toroidal vacuum chamber has not yet been installed.
Khrushchev (roughly centred, bald), Kurchatov (to the right, bearded), and Bulganin (to the right, white-haired) visited Harwell on 26 April 1956. Cockcroft stands across from them (in glasses), while a presenter points to mockups of various materials being tested in the newly opened DIDO reactor .
A "shot" using deuterium is being prepared at the operator's station. Peter Thonemann is in the foreground. The reactor can be seen through the window.
ZETA as seen from above in late 1957
Close-up of the ZETA reactor while undergoing maintenance. The main toroidal vacuum chamber is in the lower left, wound around by the current cables of the stabilising magnets. The larger device on the right is the main induction magnet, which created the pinch current in the plasma.
A team of reporters asks Cockcroft (centre) questions about ZETA. It was during this interview that Cockcroft offered his assessment that he was 90% sure the neutrons seen from the device were caused by fusion.
Bas Pease (centre) and Bob Carruthers (right) are interviewed by the BBC in front of the ZETA reactor.
The ZETA release was front-page news around the world.
Mike Forrest operates a hand-built laser that is part of a Thomson scattering system used to measure temperatures in ZETA. This became a major diagnostic technique in the fusion field, used to this day.