generalfusion

Magnetic fusion is the first of two primary areas of fusion research. It involves using magnetic fields to hold relatively low-density deuterium-tritium plasma contained for sufficient time such that enough the nuclei collide and fuse to produce energy.

Tokamak operating principle

Magnetic fusion works on the principle that plasmas are electrically charged, making it possible to shape, compress and confine them using magnetic fields. In essence, magnetic fusion machines inject hot plasma of deuterium and tritium into a toroidal (doughnut-shaped) cavity. The cavity is surrounded by electro-magnets that create a strong, closed twisted magnetic field within the toroid. Since the plasma is electrically charged, it spirals along the field lines as it circulates around the toroid, but only diffuses across the field lines slowly. This arrangement is called a “tokamak” and was invented in the 1950s by Soviet physicists.

During confinement, the plasma nuclei have the opportunity to collide and fuse. However, the fusion rate is low since the plasma density is also low, even when using superconducting magnets to produce the strongest magnetic field possible. The plasma and energy must be confined for many seconds to achieve break-even, but even so, many complex mechanisms cause some particles and energy to leak out of the trap. In essence, the energy escapes from the plasma faster than the fusion reaction can replace it.

Bigger machines have a greater chance of breaking even than smaller ones since the surface area (through which energy is lost) increases more slowly than the volume (where fusion energy is created). This has pushed researchers to build bigger and bigger tokamak machines.

Existing tokamak machines

Sixteen tokamak machines are currently operating worldwide; the oldest in Russia (since 1975) and the newest in China (since 2006). Six machines have been decommissioned and three new machines are under construction or are planned in South Korea, India and France. Key tokamak projects include:

• Experimental Advanced Superconducting Tokamak (EAST), China [en.wikipedia.org/wiki/EAST]

• Joint European Torus (JET), United Kingdom [www.jet.efda.org/]
JET is the biggest tokamak currently in use and achieved the world record for fusion energy in 1997 by producing approximately 70% of the power needed to operate the machine. JET is not expected to break even.

• ITER, consortium of USA, Russia, Japan, China, India, South Korea, and the European Union. [www.iter.org/]
The ITER project was started in 1988. Construction is now underway in France. It is expected to produce net energy in 2021 with full deuterium-tritium power reactions by 2025. However, it will not capture the energy produced to generate electricity, nor will it include long-term tritium breeding.

• Beyond ITER, an even larger postulated machine, called DEMO, would produce 500 MW of net electrical power by 2035.

• Future power plants, called Proto, could produce 1,000 MW to 1,350 MW of electrical power sometime after 2065.