Inertial Confinement Fusion

While magnetic confinement seeks to extend the time that ions spend close to each other in order to facilitate fusion, the inertial confinement strategy seeks to fuse nuclei so fast that they don't have time to move apart. The two approaches to inertial confinement have been laser fusion and ion-beam fusion.

Directed onto a tiny deuterium-tritium pellet, the enormous energy influx evaporates the outer layer of the pellet, producing energetic collisions which drive part of the pellet inward. The inner core is increased a thousandfold in density and its temperature is driven upward to the ignition point for fusion. Accomplishing this in a time interval of 10^-11 to 10^-9 seconds does not allow the ions to move appreciably because of their own inertia; hence the name inertial confinement.

Laser Fusion

Laser fusion attempts to force nuclear fusion in tiny pellets or microballoons of a deuterium-tritium mixture by zapping them with such a high energy density that they will fuse before they have time to move away from each other. This is an example of inertial confinement.

Two experimental laser fusion devices have been developed at Lawrence Livermore Laboratory, called Shiva and Nova. They deliver high power bursts of lase light from multiple lasers onto a small deuterium-tritium target. These lasers are neodymium glass lasers which are capable of extremely high power pulses.

Shiva Laser System

At Lawrence Livermore Laboratories, a collection of 20 neodynium lasers are focused to a precise position in a target chamber. The multi-laser device, called Shiva after the multi-armed Hindu god, seeks to initiate laser fusion in small microballoons of a deuterium-tritium gas mixture. One of the 0.1 mm pellets is supposed to contain the energy equivalent of a barrel of oil.

The Shiva system is the first generation machine at Livermore, put into operation in 1978. A second, more powerful machine called Nova has been built which offers the possibility of reaching the fusion breakeven point.

Nova Laser System

Nova is the name given to the second generation laser fusion device at Lawrence Livermore Laboratories. It employs lasers ten times more powerful than the Shiva laser fusion device and will attempt to reach the breakeven point for fusion. Nova makes use of ten lasers which are focused on a 1 mm diameter target area, dumping 100,000 joules of energy into the target in a nanosecond.

As of 1994, Nova has reached the Lawson criterion, but at a temperature too low for fusion ignition.

Particle Beam Fusion

If a high energy beam of electrons or other particles can be directed onto a tiny pellet or microballoon of deuterium-tritium mixture, it could cause it to explode like a miniature hydrogen bomb, fusing the deuterium and tritium nuclei in a time frame too short for them to move apart.