1) Introduction: the goals

The origin of the word "plasma" is attributed to two English physicists, Tonks and Langmuir, to designate an ionised gas (they were studying gas discharges during the 1920s). Since then, interest for this discipline has grown considerably as the multiple uses of plasmas were discovered, both in fundamental research (astrophysics) and in industry (surface coating, welding, flat screens and so on). Plasma physics thus developed, integrating all the breakthroughs in modern physics. It is a complex science, with its roots in many concepts used to describe solids, liquids or gases, yet calling on practically all the fields in physics (electrodynamics, statistical mechanics, quantum mechanics, collision theory, molecular and atomic physics, nuclear physics, kinetic theory, transport equations, thermodynamics, wave propagation, radiation, spectroscopy and so on), all of this generally resulting in coupled non-linear equations, difficult to work out even with today’s numerical techniques. 

In addition to many technological challenges (components capable of withstanding intense heat, superconducting magnets, remote handling and so on), thermonuclear fusion poses huge theoretical difficulties, and has given birth to a particularly active branch of plasma physics.

 The goal of controlled thermonuclear fusion research is to produce energy by efficiently confining a sufficiently hot and dense plasma. Start then by learning about Lawson’s criterion, fixing the conditions in which energy may be produced from a fusion plasma. The questions which come up may thus be summarised in the following way:

	How may the plasma particles be confined effectively? This is the main problem of magnetic confinement and of heat and particles transport.
	How may the temperatures required for the future reactor be attained? This is the main problem of plasma heating, which also enables current generation in the machine.
	How may the components of the plasma vacuum chamber, and therefore the plasma from impurities emitted by the surrounding walls, be protected? This is the main problem of plasma wall interaction and particles and heat extraction, with the original solution from Tore Supra: the ergodic divertor concept.

Finally, it is impossible to answer all these questions without possessing well-adapted measurement devices to analyse what happens in the heart of the tokamak. These are the diagnostics.

Tore Supra, the only large machine in the world capable of obtaining long pulses thanks to its supra-conducting magnets, offers physicists the unique opportunity of handling these problems with a view to steady-state operation, indispensable to the future reactor. This is the speciality of Tore Supra: long pulses.