Scientific

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Scientific Raison dEtre for JET
Prof. François Waelbroeck former Director
IPP-Jülich Ex member of JET Supervisory Board
and JET Scientific Council 25th JET Anniversary,
Culham 20th May 2004
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Fusion Research end of 1950s

• 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

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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

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Configurations under study in the early years of
fusion research (1950-1965)

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

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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• France DECA I, II, III (later withdrawn) and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)

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Fusion Research end of 1950s

• 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

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Diagnostics on JET
An illustration of the large progress made in
diagnostics
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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
• ? ? BR2/T
• Very low confinement times predicted by this
  formula
• (for JET this would predict 10-40?s )

• Need for better machine configurations

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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 ?

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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

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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 plasma
  temperature extrapolate ?
• If possible, study of the D-T reaction

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Lawson diagram mid 1970s
Parameter domain foreseen for JET
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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 himto
  Prof.Palumbo for this position

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