JET's first plasma

Contribution by P-H Rebut, former director of JET:

"JET came to life with the first plasma on June 25th 1983 after five years of frantic construction. It was a great day even if a plasma of only a few kA was achieved. At this time all the elements of the machine were not yet tested including the plasma positioning which was not active; nevertheless JET was in operation.

The decision to finance and construct JET was taken on the first of June 1978 after three years of conception and detailed design and two years of pain and despair, hoping for the project to be approved. At the time of the site decision the team was reduced to 35 but JET had already inspired the modification of DIII into DIIID at San Diego.

During the construction, maintaining the planning and the cost was a struggle: we had said in 1975 that the construction would require five years: the 25th of June we got the first plasma in line with the planning and the cost foreseen.

A few months later we achieved a one MA plasma for more than 2 seconds and won our bet with TFTR. Later on, in 1984, the solemn JET inauguration by the Queen and the President F. Mitterand had taken place.

This first plasma opened the way to a long story of successes and performances. I would like only to mention here the first experiment with tritium where 2 MW of fusion power were produced to be increased later on to 16 MW. I still think that JET could double its fusion power but this is the responsibility of the present team.

JET is the physics model for ITER and, without the results achieved, ITER would not have been possible. I want to praise the European team who constructed the project, a team who was so dedicated and who felt so strongly that this project belonged to them. This team was composed of physicists and personnel coming mainly from the European fusion laboratories.

All of us owe a great thanks to those who fought and allowed JET construction to be decided in 1978. I would like also to remember Hans-Otto Wüster, the first JET Director.

The decision was only possible thanks to the confidence and the will of Donato Palumbo, the fusion Director at the European commission who supported the Joint European Torus."

Excerpts from the JET Annual Report 1983 about JET's startup

"The JET machine was completed and commissioned in its basic performance configuration in June 1983. The experimental programme began on 25 June, with a plasma current of 19,000 amps at the first attempt to obtain plasma. Within the remaining six months of the year, currents of up to 3 million amps within overall pulse lengths exceeding 10 seconds were achieved and this performance remains a world record. The plasma parameters achieved in 1983 did not compare favourably with the more established smaller tokamaks - and would not have been expected to. JET's plasma temperature was around 5 million degrees."

"As mentioned earlier, the first experimental campaign began on 25 June, with a plasma current of 19,000 amps at the first attempt (see figure). Later in the campaign, which ended with the August shutdown, a current of 600 kA was obtained with a loop voltage of 14 volts. From the high loop voltage, it was clear that the plasma resistivity was high and the temperature correspondingly low, at around 50 electron volts. Spectroscopic measurements showed that the discharge was dominated by radiation from the light impurities, carbon and oxygen. In this first campaign, the vertical position control had not been commissioned. As a result, the plasma was vertically unstable and moved to the bottom of the vacuum vessel, terminating the pulse when contact was established."

"At the start of the second campaign in October, the bakeout temperature for the torus and ports was raised to 270C. It was immediately apparent that the discharge was much cleaner. (...) By the end of October, 1.4MA was obtained with 4 volts around the torus."

"In November, a more sophisticated feedback system was implemented to give tight control of the horizontal and vertical positions of the plasma. (...) By the end of November, 1.9 MA was reached with 1.3 volts around the torus. The discharge showed all the attributes of a true tokamak discharge, i.e. low loop voltage and sawtooth oscillations at the plasma centre."

"In December, plasma currents in the range 2 to 3 MA were obtained. The pulse length was typically 10 seconds with a flat top of some 4 seconds. Central electron temperatures measured by the newly commissioned electron cyclotron emission diagnostic were in the region of 1.5 to 2 keV. The loop voltage was down to around 1 volt, and the safety factor q at peak current was in the range 2.4 to 5.0. Towards the end of the second campaign, control was established over the density behaviour by adjusting the gas feed rate and density flat tops of 4 seconds were obtained. Average plasma density was approximately 2.5x10¹⁹ per cubic metre, plasma radius 1.1 metres, and elongation 1.2. The highest global energy confinement time was estimated at three-tenths of a second."

"These results were much in line with expectation. (...) Up to the end of 1983, only about half the full volume of the torus had been used for the discharge.(...)"

"The importance of the Project both as a scientific experiment and as an exercise in European co-operation was fittingly underscored by the official opening ceremony performed by Her Majesty Queen Elizabeth II on 9 April 1984, at which the European Communities were represented by M. François Mitterand, President of the French Republic and M. Gaston Thorn, President of the Commission. Each of the member countries was also represented. It was an elegant occasion."