Researchers at the National Ignition Facility want to do nothing less than create a star on earth. The nuclear fusion facility in Livermore, California has been under construction since 1997, but now engineers are finally ready to fire up the facility's 192 lasers, and to generate the nuclear reaction present only inside the cores of stars and exploding thermonuclear weapons. At NIF, that reaction will take place inside this tiny gold cylinder, which is the size of a pencil eraser.
NIF has three purposes: To further our basic understanding of stars, to determine how the United States' aging nuclear weapons are holding up without engaging in underground testing, and to explore the enormous potential of nuclear fusion power plants. Its first fusion experiments are expected in May, and in 2010 scientists hope to create something unprecedented: a self-sustained nuclear fusion reaction in a safe, controlled setting.
In NIF's two laser bays, 192 laser beams pick up the power they need. The beams travel a long path of about 1,000 feet, beginning in a control room where scientists create a weak laser pulse. As the beams move through a series of amplifiers, their energy increases exponentially: From beginning to end, the beams' total energy grows from one-billionth of a joule to four million joules, increasing by a factor of more than a quadrillion.
The laser beams complete the journey to the target chamber in less than 25 billionths of a second.
This crucial laser glass amplifies the laser light to the very high energies required for fusion experiments. NIF uses about 3,070 large plates of special phosphate glass doped with neodymium atoms.
A split second before the initial weak laser pulse comes along, more than 7,500 lamps energize the neodymium atoms in the glass by flashing an intense white light on them. The energized atoms then emit photons as the weak laser pulse passes through the glass slabs, allowing the laser beam to pick up trillions of extra photons.
Scientists had to master a new method of growing synthetic crystals to outfit NIF. This 800-pound monster was grown in just two months; the conventional process takes nearly two years.
The crystals are used in NIF's amplifier section, where the polarization of plates of crystal can be switched between two settings. In one setting, the plates bounce the laser light back and forth through the amplifier, letting it pick up energy with each pass. In the other setting, the laser beams slide through and continue on their way towards the target chamber.
Inside NIF's target chamber, the 192 laser beams finally converge on a central point. The chamber is a sphere 32 feet in diameter, with portholes for monitoring and recording the fusion experiments.
The target must be positioned inside the chamber with incredible accuracy, because the laser beams must all hit within 50 microns of the same precise point--less than the thickness of a piece of paper. The lasers blast the target with up to 500 trillion watts of power for 20 billionths of a second.
The laser beams focus on the tiny gold cylinder, which contains a target the size of a BB. The target itself is a tiny hollow shell filled with the heavy hydrogen isotopes deuterium and tritium. When the lasers hit the target they'll generate a bath of X-rays, researchers say, that will rapidly heat the outside of the target. Its outer surface will explode while its inner core implodes, giving it 100 times the density of lead. The temperature inside the core will reach more than 100 million degrees Celsius and the pressure will be 100 billion times that of the Earth's atmosphere.
Then, researchers believe that the deuterium and tritium nuclei will fuse together to form a helium nucleus, releasing a burst of energy.
The goal in all this is to create the elusive "burn," a self-sustaining nuclear fusion reaction that produces more energy than is used by the laser beams.
Many researchers harbor dreams of fusion power plants fueling the 21st century. Such plants would not produce climate-changing gases, and they would create far less radioactive waste than current nuclear fission power plants; what's more, the fusion waste would be dangerous for only 50 to 100 years.
If NIF is successful, it could point the way towards a future with nearly limitless energy.
