Sustainable Energy

Fusion Reactions Using Massive Lasers

Researchers at Lawrence Livermore National Lab will try to start self-sustaining fusion reactions using the world’s largest laser system.

  • by Kevin Bullis
  • June 23, 2009
  • Ground Zero: A circular access port affords a glimpse into a 10-meter-diameter target chamber where, in the coming months, powerful lasers will be fired with the goal of setting off small thermonuclear explosions. The laser beams will enter through square ports at the bottom (and through more ports, not pictured, at the top). The circular openings allow access for instruments that will monitor the explosions. Extending into the center of the chamber is a camera used to peer back along the paths taken by the beams, examining mirrors and lenses for damage.
Light show: The enormous lasers start as a 50-micrometer-wide beam generated inside fiber-optic coils and fed by light from a simple diode.
The initial pulse is amplified 10,000 times and split into 48 beams. Each beam is then delivered to its own “preamplifier,” one of which is shown here in a maintenance room. The preamplifiers, which are transported on a system of rails, amplify the lasers 20 billion times. At this stage, each beam travels inside the steel tubes seen above and then is split four ways.
Laser bay two: The laser beams reach peak energy levels after being amplified 15,000 times in two vast rooms, one of which is pictured here.
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An optical switch causes the beams to travel through the same amplifier four times before being released to the target. In place of conventional electrodes, which would be vaporized by the beams, the switch uses a plasma (purple) to convey electrical charge.
To make the 3,072 one-meter-long neodymium-doped glass slabs required by the main amplifiers, researchers had to invent new, faster manufacturing methods.
The business end: Aluminum ducts each deliver four laser beams to the target chamber (blue, at bottom). They are equipped with access panels so the focusing optics can be removed for repair if they are damaged by the powerful lasers.
Before the lasers enter the chamber, they pass through crystal plates, cut from one-meter pyramids like the one here, that convert infrared light into ultraviolet light.
The beams converge on a cylinder equipped with heat sinks (long arms) and heating coils (wrapped around the cylinder) that are engineered to uniformly cool a two-millimeter sphere of hydrogen inside to about 20 K. The laser beams, focused from 40 centimeters to a point thinner than a hair, enter from both ends of the nine-millimeter-long cylinder and collide with its inside walls, generating x-rays that compress and ignite the fuel pellet.

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