Tokamak - SpeedyLook encyclopedia

Principle

The nuclear Fusion makes it possible from two Atome S very light (for example the Deutérium and the Tritium) to create heavier atoms. This transformation produces a mass defect which appears in the form of energy ( E = mc ² where E is the energy produced in joules, m mass disappeared in kg, and C the Célérité of the light in the vacuum, in m.s- ¹). This excess of energy could be transformed into excess of heat, which by Convection could be converted into electricity by means of a Turbine with vapor coupled to a Alternateur.

Requirements

Melting point

To produce a nuclear fusion reaction, should be heated the matter with very high Température S (several tens of million degrees). Under these conditions, the electron S are detached completely from their core - it is said that the atom ionizes. The matter enters a new state then: the state of plasma.

In order to obtain such temperatures, several methods were tested:

the use of the Joule effect produces by the displacement of the electrons (but this phenomenon is not any more very effective beyond of a temperature of 10 million degrees);
injection of particles accelerated in a particle accelerator appendix;
the heating obtained by powerful lasers (Effect Compton);
the use of electromagnetic waves at the frequencies characteristic of the medium plasmic (the principle of heating could be compared with that of the Microwawe oven).

In the engines with fusion of the future, the temperature necessary could be obtained by a combination of these methods.

Containment of plasma

The stake consists in controlling plasma in the middle of tokamak in a volume limited and sufficiently far away from the equipment. As plasma consists of charged particles, one can confine their trajectory of displacement inside a Tore by means of magnetic fields. For that one must create a toroidal field with which one associates a component of field which is perpendicular for him (poloidal field). In the devices of the Tokamak type, the poloidal field is created by a current fort induced within plasma.

This device is distinguished from the Stellarator S, which adopt the same configuration of room with fusion of toric form, but in which no current circulates in plasma.

Energy assessment

It is noted that it is necessary to provide an initial energy to guarantee the conditions of maintenance of the reaction (temperature and containment). In theory, more one injects of fuel, more produced thermal energy is important.

If the produced temperature were equal to that required by the reaction, it would not be necessary any more to heat fuel by average outsides, one would then have reached the threshold of ignition of the reaction.

Thus for such a generator, if the report/ratio of the energy produced compared to provided energy in an external way arrived at balance (as much energy produced than of energy necessary to the maintenance of the reaction), one would speak about breakeven . This generator would be then autonomous on an energy level. Beyond this threshold, any surplus of fuel would produce a surplus of energy for the benefit of the owner.

Advantages

If such a technology managed to be developed, its advantages would be varied:

a great quantity of fusible “fuel” available: the selected fusible matter consists of Deutérium and Tritium. One finds deuterium (or heavy water when this isotope is combined with oxygen) in a natural state (1 deuterium atom for 6 000 atoms of Hydrogène in water is 30 water mg/l). Moreover, if one managed to reintroduce the Tritium produces by the reaction of fusion of the engine, the engine car-would thus produce part of its fuel.
a production of radioactive elements with short life : the fuel is slightly radioactive (Tritium) and its production remains confined in the enclosure of the engine. To the end-of-life of the engine, the radioactive elements to recycle for the majority are said “to short life”.
a weak risk of Nuclear accident major : being given the conditions bare essential for fusion, any anomaly in the state of the reaction would cause the dead halt of the reactions in progress. There would be thus no risk of racing of the reaction.

Difficulties

This technology still remains at the stage of research:

the Physique of plasmas is not yet well controlled, it is in particular very difficult to model the behavior of a plasma in a magnetic containment.
the choices and the use of materials are not yet defined because the imposed constraints are numerous (temperature, resistance to the magnetic fields, stability with radiations, important lifespan…). And one knows for the moment no material able to resist these conditions a long time.
the Tritium poses the problem of its diffusion raised in the various materials (escapes). That complicates of as much the choice of these materials and the decontamination of tritium.
to achieve the goal of a profitable self-sustained fusion, it would be necessary to confine a great quantity of plasma. The profitability of plasmas obtained binds to the size of the installations. For example, the duration of containment of useful plasma (fusible) varies with the square of the large ray of treated plasma. Thus the costs of construction and maintenance of such devices will be very important.

Prototypes

There exist currently several prototypes of tokamak:

International Experimental Thermonuclear Reactor (ITER), which is in the course of construction with Cadarache
KSTAR (Korean Superconducting Tokamak Advanced Research with Daejeon
Joint european torus (JET), based with Culham with the the United Kingdom;
Torus Supra, based with Cadarache in France;
JT-60 or JAERI - Japan Atomic Energy Research Institute - Tokamak 60, in Japan (Naka)
Asdex and its Asdex-Upgrade improvement, conceived in Germany in the Years 1980
Doublet and its improvement DIII-D, conceived in the United States in the years 1980

First prototypes:

Tokamak T3, designed in Soviet Union in the Years 1960
TFR (Tokamak of Fontenay-Aux-Roses), designed in France in the Years 1970
PLT, designed in the United States in the Years 1970
T 10, designed in Soviet Union in the years 1970
TFTR, designed in the United States in the Years 1980, now closed

There exist many other experiments, each one with its specificities:

MAST and Compass D in England
Beaver in Czechoslovakia
FTU in Italy
Tokamak in Variable Configuration, or TCV, based with the federal Polytechnic school of Swiss Lausanne in
Alcator CMod in the United States
TdeV in Canada

Other tracks of product engineering of energy starting from fusion are studied:

the cold Fusion with the engine CFR v2.1 of Jean-Louis Naudin
the Fusion by inertial confinement with the Laser megajoule

External bonds

ECA - magnetic fusion
ECA - the physics of fusion
a Physical named passion - controlled thermonuclear fusion
Lives the energy of fusion - Tokamak (fusion)
nuclear France - dangers of the Tritium
Wise bets - dangers of fusion
Tokamak with Variable Configuration

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