Editing Tokamak (section)

=== Steps toward declassification ===
[[File:Kurchatov at Harwell on 26 April 1956.jpg|thumb|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 (nuclear reactor)|DIDO reactor]].]]

In 1955, with the linear approaches still subject to instability, the first toroidal device was built in the USSR. TMP was a classic pinch machine, similar to models in the UK and US of the same era. The vacuum chamber was made of ceramic, and the spectra of the discharges showed silica, meaning the plasma was not perfectly confined by magnetic field and hitting the walls of the chamber.{{sfn|Shafranov|2001|p=840}} Two smaller machines followed, using copper shells.<ref name=tokomag>{{cite web |url=https://www.iter.org/newsline/55/1194 |title=Which was the first 'tokamak' – or was it 'tokomag'? |first=Robert |last=Arnoux |date=27 October 2008 |website=ITER }}</ref> The conductive shells were intended to help stabilize the plasma, but were not completely successful in any of the machines that tried it.{{sfn|Bromberg|1982|p=70}}

With progress apparently stalled, in 1955, Kurchatov called an All Union conference of Soviet researchers with the ultimate aim of opening up fusion research within the USSR.{{sfn|Shafranov|2001|p=240}} In April 1956, Kurchatov travelled to the UK as part of a widely publicized visit by [[Nikita Khrushchev]] and [[Nikolai Bulganin]]. He offered to give a talk at Atomic Energy Research Establishment, at the former [[RAF Harwell]], where he shocked the hosts by presenting a detailed historical overview of the Soviet fusion efforts.{{sfn|Shafranov|2001|p=841}} He took time to note, in particular, the neutrons seen in early machines and warned that neutrons did not mean fusion.<ref>{{cite speech |title=The possibility of producing thermonuclear reactions in a gaseous discharge |url=https://www.iter.org/doc/www/content/com/Lists/Mag%20Stories/Attachments/64/kurchatov_1956.pdf |date=26 April 1956 |first=Igor |last=Kurchatov |location=UKAEA Harwell}}</ref>

Unknown to Kurchatov, the British [[ZETA (fusion reactor)|ZETA]] stabilized pinch machine was being built at the far end of the former runway. ZETA was, by far, the largest and most powerful fusion machine to date. Supported by experiments on earlier designs that had been modified to include stabilization, ZETA intended to produce low levels of fusion reactions. This was apparently a great success, and in January 1958, they announced the fusion had been achieved in ZETA based on the release of neutrons and measurements of the plasma temperature.{{sfn|McCracken|Stott|2012|p=5}}

[[Vitaly Shafranov]] and Stanislav Braginskii examined the news reports and attempted to figure out how it worked. One possibility they considered was the use of weak "frozen in" fields, but rejected this, believing the fields would not last long enough. They then concluded ZETA was essentially identical to the devices they had been studying, with strong external fields.{{sfn|Shafranov|2001|p=841}}