Scientific Raison d’Etre for JET

Prof. François Waelbroeck former Director IPP-Jülich Ex member of JET Supervisory Board and JET Scientific Council Prof. F.Waelbroeck “Scientific Raison d’Etre for JET” 25th JET Anniversary 20 May 2004 25th JET Anniversary, Culham 20th May 2004 Fusion Research end of 1950’s • Larger devices built, assuming :

It sufficed to have a good idea to build a sufficiently large device. It would do the job for you

• Detailed measurements within the devices seemed superfluous. We could calculate the behaviour.

• However, dissappointing results from first devices

Prof. F.Waelbroeck “Scientific Raison d’Etre for JET” 25th JET Anniversary 20 May 2004 Configurations under study in the early years of fusion research (1950-1965) • Toroidal pinches, e.g.: Zeta (Culham), Perhapsatron S-3/S-4/S-5 (Los Alamos),… Confinement properties and reactor prospects disappointing

Perhapsatron device Los Alamos

Prof. F.Waelbroeck “Scientific Raison d’Etre for JET” 25th JET Anniversary 20 May 2004 Configurations under study in the early years of fusion research (1950-1965)

• , e.g.: Initial results very disappointing C- (Spitzer, Princeton, USA - later converted into the ST ), Sirius (USSR), Initial Wendelsteins (IPP- Garching),….

The Model B-3 stellarator Princeton University

Prof. F.Waelbroeck “Scientific Raison d’Etre for JET” 25th JET Anniversary 20 May 2004 Configurations under study in the early years of fusion research (1950-1965) • Mirror machines, e.g.: USSR : Ioffe, OGRA France : DECA I, II, III (later withdrawn) and MMII (CEA) USA (Livermore): Table Top and Toy Top, MFTF-B (abandoned) …… The OGRA Device Kurchatov Institute, Moscow

Prof. F.Waelbroeck “Scientific Raison d’Etre for JET” 25th JET Anniversary 20 May 2004 Fusion Research end of 1950’s • Larger devices built, assuming :

It sufficed to have a good idea to build a sufficiently large device. It would do the job for you

• Detailed measurements within the devices seemed superfluous. We could calculate the behaviour.

• However, dissappointing results from first devices

• Small devices were used to examine confinement in different configurations and to develop diagnostic and heating methods Prof. F.Waelbroeck “Scientific Raison d’Etre for JET” 25th JET Anniversary 20 May 2004 Diagnostics on JET An illustration of the large progress made in diagnostics

Prof. F.Waelbroeck “Scientific Raison d’Etre for JET” 25th JET Anniversary 20 May 2004 Fundamental difficulties in early years of fusion research (1950-1965)

• Several instabilities discovered reducing confinement

• Most toroidal machines followed the so-called Bohm scaling for the confinement time :

τ ∝ BR2/T

Very low confinement times predicted by this formula (for JET this would predict 10-40µs …)

• Need for better machine configurations

Prof. F.Waelbroeck “Scientific Raison d’Etre for JET” 25th JET Anniversary 20 May 2004 The tokamak shows much better confinement than all other configurations

• T-3 : first device with temperatures in the keV range

Tokamak T-3 Kurchatov Institute, Moscow

Prof. F.Waelbroeck “Scientific Raison d’Etre for JET” 25th JET Anniversary 20 May 2004 The tokamak shows much better confinement than all other configurations

• T-3 : first device with temperatures in the keV range

• Confinement time more than 30 times higher than predicted by Bohm scaling

• 1969 : General redirection towards the tokamak (‘Tokamakitis’)

• Would the tokamak be a possible reactor ?

Prof. F.Waelbroeck “Scientific Raison d’Etre for JET” 25th JET Anniversary 20 May 2004 Tokamak : A possible fusion reactor ? Better understanding needed :

– We had been blind at the start of the fusion programme – Diagnostic development on smaller devices – Fast techniques developed : streak cameras, digital techniques – Data acquisition, feedback and heating techniques had become available – It appeared then that a large device could and had to be build to make further progress : JET

Prof. F.Waelbroeck “Scientific Raison d’Etre for JET” 25th JET Anniversary 20 May 2004 Why a large tokamak like JET ? Make the largest reasonable step towards a possible reactor – Determine best materials/conditioning for the first wall – Investigate further additional heating and fuelling methods (i.e. in more reactor relevant conditions) Radio frequency heating (ICRH, ECRH, LH) Neutral beam heating at high voltages Pellet fuelling – Above all : which processes govern the energy balance of the tokamak ? How will the confinement time and temperature extrapolate ? – If possible, study of the D-T reaction

Prof. F.Waelbroeck “Scientific Raison d’Etre for JET” 25th JET Anniversary 20 May 2004 Lawson diagram : mid 1970s

Parameter domain foreseen for JET

Prof. F.Waelbroeck “Scientific Raison d’Etre for JET” 25th JET Anniversary 20 May 2004 Who would build this device ? Paul-Henri Rebut • I knew him as a young and dynamic engineer • He had built several smaller devices, planned Superstator, and built TFR • In parallel, incorporated all positive results in private studies for an upgrade to a large tokamak -- in his so-called ‘Chambre Noire’ in TFR lab • I considered him as the natural candidate to lead the JET design team ! • I have never regretted having recommended him to Prof.Palumbo for this position

Prof. F.Waelbroeck “Scientific Raison d’Etre for JET” 25th JET Anniversary 20 May 2004 Prof. F.Waelbroeck “Scientific Raison d’Etre for JET” 25th JET Anniversary 20 May 2004