Future

Fusion technology

Magnetic containment

This approach makes magnetic field usage to control hot plasma in the reaction tunnel. Because of inherent plasma feature that it is ionized gas with separated positive and negative charges it can be capture in reaction chamber by magnetic field. Electrons and nuclei follows the field in closed loop. It prevents hot plasma from getting to the reactor's walls and get cooled as this will cause reaction slow down. Moreover such 100 MēC plasma's contact with the burn chamber wall will probably burn every blankets at current material development. Studies have indicated that the most effective shape of tunnel loop for plasma is toroid. Magnetic fields with two components: toroidal and poloidal (perpendicular to toloidal) form spiral lines that plasma follows along and is trapped and well controlled.

There are three types of constructions based on magnetic containment system. The most popular and probably the most advanced are tokamaks. Name derived from Russian definition that in translation reads as follow: "torus shaped magnetic chamber". The tokamak uses circle of plasma as the secondary transformer winding. The primary winding is a central solenoid. Current changes in the solenoid induce a plasma current. Although it stabilizes the plasma, transformer is not able to continuous current generation what causes that to achieve long-lasting reaction and steady plasma state other means are needed. The tokamak has also two additional coils, mentioned above: toroidals and poloidal. They generate very strong magnetic field about 5 tesla. It is value 100 000 times larger than earth's magnetic field [62]. These fields stop plasma to act on the burning chamber wall and capture it. The current in the plasma serves also to heat the gas because it has a resistance. But this ohmic heating is limited to temperature about 10 MēC because of plasma density. Further heating is solved with external devices like radio frequency antenna or Hydrogen Ion Source. The tokamak technology is the most developed among fusion reactor and further R&D are undertaken on prototypes around the world.

Second type are stellarators. They are not using transformer principle to induce current in the plasma. There is no need to induce it. Spiral magnetic field lines are formed only by serial external coils of a complex shape. This special shape was a serious problem in the past when computer modelling did not exist. This is a reason why its development is less advanced than tokamaks. Today, undoubted advantages were noticed. Without current in the plasma, stellarators have large potential for steady state operation. However, despite of computer designing possibilities stellarators are still difficult to design and build, because of high level of complexity.

Third type of magnetic containment fusion reactor is reversed field pinch - RFP. It is similar to tokamak with difference in current strength and toroidal field's direction. There is RFP device, operating in Italy, but it serves only for studies physical problems.

Ref. [60],[61],[62],[63]

  • Copyrights 2011 © Michal Wierzbowski