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Laser Fusion - Does this technology represent a clean tomorrow? Image Credits: sxc.hu
Recently, there has been a lot of discussion regarding the development of an 'invisibility time cloak' using laser pulses to manipulate light. This technology represents the potential for laser technology although one other major development, laser fusion is something that could benefit all mankind in the not to distant future.
Fusion is the reaction in which two atoms of hydrogen combine to form a helium atom. During this process, hydrogen is converted into energy, potentially giving this fusion technique the potential to serve as an inexhaustible energy source.
Laser fusion, also known as 'inertial confinement fusion', is a method of initiating nuclear fusion reactions through heating, and compressing, fuel targets in the form of pellets containing deuterium and tritium.
It is one of the most-promising approaches to achieving controlled thermonuclear fusion. Think of laser fusion as being similar to that of the internal combustion engine approach to release nuclear fusion energy.
Laser fusion attempts to achieve nuclear fusion in small pellets of deuterium-tritium mixture at high energy density.
Although high energy laser fusion experiments began in early 1970s, Shiva and Nova developed at Lawrence Livermore Laboratory are the first experimental laser fusion devices that started operation in 1978. They employ neodymium glass laser capable of producing extremely high power pulses.
During laser fusion, small pellets of deuterium-tritium (DT) isotopes are introduced into a blast chamber where the pellets are compressed to high densities using an intense laser.
This technique employs a single laser beam that is divided into a number of beams which are amplified and passed into the chamber.
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Laser Inertial Fusion Energy (LIFE) - A modular fusion chamber design to reduce costs and speed maintenance. Image Credits: lasers.llnl.gov
The combination of high density and heat due to compression, induces the thermonuclear explosion ignition.
The kinetic energy produced by the reaction products such as charged particles, x-rays and neutrons is stored as heat in a blanket that serves as a source in a steam thermal cycle to generate power.
The compression of the DT pellet can be carried out using two approaches: direct and indirect-drive laser fusions.
In direct-drive laser fusion, a number of intense laser beams are symmetrically radiated on a hollow plastic pellet containing a mixture of tritium and deuterium gas.
The intense laser energy implodes the pellet shell thereby compressing the gas. If the densities of the compressed gas reach the order of 1000 times that of liquid DT, extraordinary nuclear energy gain is achieved in addition to sufficient heating of the gas.
In the indirect-drive method, the pellet is centered inside an enclosure, and x-rays are produced when intense laser beams enters the enclosure and strikes the walls.
The resulting cloud of x-rays symmetrically implode the pellet shell to generate the necessary compression and heating.
Laser fusion ensures the use of high-quality raw materials, product reliability and functionality in a fully controlled environment.
In the direct laser fusion approach, no debris is left to recycle, and the materials do not cause activation problem.
Unlike nuclear fission plants, laser fusion does not produce large amounts of high-level nuclear waste which requires long-term disposal.
No active intervention, cooling, reprocessing and external power is required at the time the shutdown of a laser fusion power plant. The plant allows for periodic replacement of materials under high-risk environments without requiring changes to the rest of the plant.
It provides an essentially carbon-free energy source with a practically unlimited supply of fuel.
High-powered lasers are the key to this technique, as achieving fusion in this way needs an enormous amount of energy to be delivered as a pulse.
However, one major problem with the most advanced lasers today is that they are relatively inefficient at converting electrical energy into beam energy. In addition, not all of the laser energy ends up being delivered to the fusion target.
Some of the laser light end up being scattered or reflected away.
Laser fusion greatly benefits from its ability to use modular advancements in component technologies and enhanced fusion performance. Therefore, future designs can readily be implemented as long as they maintain the same interface characteristics to the rest of the plant.
Sources and Further Reading