7.1.1 Tokamak

The tokamak, acronym for the Russian phrase toroidál'naja kámera s magnitnymi katúškami meaning toroidal chamber with magnetic coils, was designed in 1951 by Soviet physicists Andrei Sakharov and Igor Tamm [8]. It is a doughnut-shaped device in which the combination of two sets of magnetic coils, known as toroidal and poloidal field coils, creates a field in both vertical and horizontal directions. The magnetic fields hold and shape the charged particles of the plasma by forcing them to follow the magnetic field lines. They essentially create a "cage," a magnetic bottle, inside which the plasma is confined. A strong electric current is induced in the plasma using a central solenoid, and this induced current also contributes to the poloidal field.

#### 7.1.2 Stellarators

Unlike tokamaks, stellarators [9, 10] do not require a toroidal current to be induced in the plasma. Instead, the plasma is confined and heated by means of helical magnetic field lines. They are produced by a series of coils which may themselves be helical in shape. As a result, plasma stability is increased compared with tokamaks. Since heating the plasma can be more easily controlled and monitored with stellarators, they have an intrinsic potential for steady-state, continuous operation. The disadvantage is that, due to their more complex shape, stellarators are much more complicated than tokamaks to design and build.

### 7.2 Inertial confinement

After the invention of laser in 1960 at Hughes Research Laboratory in California, researchers sought to heat the fusion fuels with a laser so suddenly that the plasma would not have time to escape before it was burned in the fusion reaction. It would be trapped by its own inertia, hence the name "inertial confinement," because it relies on the inertia of the implosion to bring nuclei close together. This approach to confinement was developed at Lawrence Livermore National Laboratory in California [11].

Within the context of inertial confinement, laser beams with an intensity of the order of 10<sup>14</sup> <sup>10</sup>15W=cm2 are fired on a solid pellet filled with a low-density mixture of deuterium and tritium. The energy of the laser vaporizes the pellet

instantly producing a surrounding plasma environment for a short period of time. During the process, the density and temperature of the fuel attains a high enough value to ignite the fusion reaction.

These methods produce temperatures of 100 million degrees Celsius in present-day

Experiments with d-t fuel began in the early 1990s in the Tokamak Fusion Test Reactor in Princeton (USA) [14] and the Joint European Torus (JET) in Culham (UK) [15]. The world's first controlled release of fusion power using a 50–50 mix of tritium and deuterium with a fusion output of 16 MW from an input of 24 MW heating (Q-factor is 0.67) was achieved in 1991 by JET. The Q-factor is used to represent the ratio of the power produced in the fusion reaction to the power required to produce the fusion. It should not be confused with the Q-value of a reaction, which is the amount of energy released by that reaction. Obviously, Q-factor of 1 is breakeven. To achieve commercially viable fusion energy, the

The 35-nation International Thermonuclear Experimental Reactor (ITER, "The Way" in Latin) project currently under construction in Cadarache, France, is the

1. To operate at 500 MW (for at least 400 s continuously) with less than 50 MW

2. Demonstrate the integrated operation of technologies for a fusion power plant and test technologies for heating, control, diagnostics, cryogenics, and

3. Achieve a deuterium-tritium plasma in which the reaction is sustained through internal heating and stays confined within the plasma efficiently

4.Test tritium breeding because the world supply of tritium (used with

deuterium to fuel the fusion reaction) is not sufficient to cover the needs of

Launched in 2006, the project has been beset with technical delays, labyrinthine decision-making, and cost estimates that have soared. The reactor is now expected

According to ITER Newsletter [16], "When completed, the plasma circulating in the core of the reactor will be 150 million degrees Celsius, or about 10 times hotter than the Sun. The massive superconducting magnets surrounding the core will be cooled to 270 degrees, as cold as the depths of space. So many of the technologies

There is a considerable amount of research into many other fusion projects at various stages of development, but ITER is the largest, with 10 times more plasma capacity than any other reactor. Although China is a participating country in the ITER project, the Chinese are nevertheless building a tokamak reactor by themselves. Known as the Experimental Advanced Superconducting Tokamak (EAST), they managed to heat hydrogen gas to a temperature of about 50 million degrees

5. Demonstrate the safety characteristics of a fusion device, particularly the control of the plasma and fusion reactions with negligible consequences to the

world's largest tokamak fusion reactor [16]. The goals of ITER are:

of input power for a tenfold energy gain (Q-factor is 10).

enough for the reaction to be sustained for a long duration.

fusion devices.

9.1 Research programs

Nuclear Fusion: Holy Grail of Energy

DOI: http://dx.doi.org/10.5772/intechopen.82335

Q-factor must be much greater than one.

remote maintenance.

future power plants.

to be completed and become operational by 2030.

involved are really at the cutting edge."

environment.

Celsius [17].

13

The capability of present lasers does not allow the inertial confinement technique to obtain break-even conditions, simply because the efficiency for converting electrical energy into radiation is very low, about 1–10%. Consequently, alternative approaches are being explored to achieve the ignition temperature. One such approach involves using beams of charged particles instead of lasers.
