From the historical point of view, the year 2008 seems more than symbolic to start the construction of ITER. The whole fusion community celebrated 50 years of the first open fusion conference (the 2nd International Conference on the Peaceful Uses of Atomic Energy in Geneva, 1958). It is also 40 years ago that the IAEA Novosibirsk conference marked a turning point of fusion research with the reported success of tokamaks, see e.g.

Indeed, many tokamaks have been built since then all around the world to culminate in the present ITER design. In this article we would like to recall the first ten years of tokamak studies during which the team of the Kurchatov Institute in Moscow fostered tokamak R&D from the first device T-1 to the success of its bigger, more advanced version T-3.

In the evening talk of the IAEA Fusion Energy Conference in Geneva (see other article in this issue) this year, given by the current director of fusion research at the Kurchatov Institute Prof. V.P. Smirnov, the year 1958 was mentioned as the year when the tokamak programme started. “I would definitely agree that 1958 is the year of birth of tokamaks, because T-1 started operation then” says Prof V.S. Strelkov from the Kurchatov Institute, who personally participated in the tokamak T-1 work. “One can even find this facility mentioned in the proceedings of the 1958 Geneva conference as ‘Experimental arrangement 5’, however without mentioning any results, because the facility was only about to start operation.”

T-1 was the first toroidal facility with a steel vacuum vessel that satisfied the Kruskal-Shafranov stability condition. The condition requires that the safety factor q is bigger than one, i.e. the pitch angle of the magnetic field helicity needs to be very low – in practice it means that the toroidal field must be strong, which distinguishes tokamaks from the then popular toroidal pinches like ZETA in Harwell. The tokamak T-1 major and minor radius were 62.5 cm and 24 cm, respectively, with the main toroidal field approximately one tesla. Interestingly, the word ‘tokamak’ – a Russian abbreviation of Toroidal Chamber with Magnetic Coils – was coined probably the same year by I. N. Golovin, head of a neigbouring laboratory.

Fusion research was launched in the U.S.S.R in the 1950s under the expert supervision of I. V. Kurchatov. In the LIPAN Institute in Moscow (nowadays the Kurchatov Institute) the fusion sector was headed by the young and charismatic L. A. Artsimovich. Like in the other institutes, also in LIPAN priority was originally given to pinch experiments. Future tokamaks were developed in a rather small laboratory under the enthusiastic leadership of N. A. Yavlinskij. Quite naturally, a few other facilities preceded T-1 in order to validate the basic ideas of toroidal magnetic confinement set in the work of I. E. Tamm and A. D. Sakharov, who introduced the field helicity in plasma in order to close the particle drift trajectories. Among these facilities, the machine TMP with ceramic vessel and strong toroidal field is often mentioned as the direct predecessor of tokamaks. When N. A. Yavlinskij tragically dies in an airplane accident in 1962, the results of tokamaks are already so prominent that L. A. Artsimovich himself assumes leadership of the laboratory, including the brand new T-3 machine which later allows for the tokamak breakthrough.

Past and present: the first tokamak T1 (top) and tokamak Golem (bottom) based on TM-1 from the early 60s

Still, it is the tokamak T-1 that can be considered the first experiment proving the Kruskal-Shafranov stability condition. Results also indicated that the main power losses were due to the radiation of impurities and not anomalous diffusion. As the level of impurities was high, the next step T-2 (of the same size, commissioned in 1959) had for the first time a system for vacuum vessel baking. The system heated the vessel in between experiments in order to release residual impurity gases attached to the vessel surface. This procedure – standard in all tokamaks today – clearly led to less impurities and increased temperatures in T-2 plasmas. In the early 1960s, two smaller tokamaks TM-1 and TM-2 were built, both with major radius 40 cm, to provide more detailed insight into specific problems of experimental research. TM-1 is probably the oldest tokamak still in service, as its main components form the basis of the Golem facility at the Technical University in Prague, currently under construction to become a new plasma hands-on experiment for students.

In the following machine T-3 (commissioned in 1962), the major radius was increased to one meter in order to allow for full ionisation of major impurities in ohmically heated plasmas. The choice was right, full ionisation minimised radiation losses and T-3 achieved macroscopically stable plasmas with the then record temperatures of 1 keV (10 million degrees). This result was confirmed by the Thomson scattering system imported and operated by a team of British scientists in 1969. This led to a real worldwide “tokamania”.

What determined the success of the Kurchatov team? And did it surprise its members? “For sure I would not say that it came as a surprise. Our determi- nation was based on the results of our experiments. We could see that unlike in pinches, our discharges were stable. We worked, analysed results and progressed without really paying attention to the claims that the Bohm diffusion, predicting extremely high losses of heat of plasmas, may be universal,” pointed out Prof. V. S. Strelkov from the Kurchatov institute.

Scientific team of tokamak T-1: G.G. Dolgov-Saveljev, V.S. Muchovatov, V.S. Strelkov, M.H. Shepelev and N.A. Yavlinskij.

Jan Mlynár and Milan Ripa