Sunday, March 15, 2009

World's highest-energy laser to create mini-stars

To produce the temperatures and pressures needed for fusion, the facility will aim all of its 192 laser beams simultaneously on a hydrogen target. This all happens inside this 10-metre-diameter chamber, which weighs 130 tonnes. The sphere is made up of 18 aluminium sections that are each 10 centimetres thick.

The square openings are for the lasers, and the round openings are used to accommodate nearly 100 pieces of diagnostic equipment.

This is a view of the target chamber from the inside. The laser beams enter through ports in the chamber to deliver almost 500 trillion watts of power to the tip of the positioner (right), which will hold the target for each experiment. When all of its beams are fully operational, NIF will focus nearly 2 million joules of ultraviolet laser energy at that tiny target, delivering 60 times more energy than any previous laser system.

All 192 lasers that enter the National Ignition Facility chamber will be trained on this pencil-eraser-sized cylinder. This capsule will hold the pea-sized target, which for fusion experiments will be a pellet of frozen hydrogen. Laser beams will enter through openings at each end to compress and heat the hydrogen in the hopes of creating a self-sustaining fusion reaction.

As laser beams hit the interior of the gold-plated capsule, they will create intense X-rays that can squeeze the pea-sized pellet of hydrogen down to a speck about the width of a human hair and heat it to some 3 million °C. The burst of laser light will last just billions of a second, but physicists hope the intense pulse will force hydrogen atoms to combine to form helium, releasing enough energy to fuse all other neighbouring hydrogen atoms until the fuel is spent.

Before reaching the chamber, laser light must be converted from infrared light to ultraviolet light, which is more effective at heating the target.

This conversion is accomplished with plates sliced from large potassium dihydrogen phosphate (KDP) crystals.

This crystal, which weighed about 360 kilograms, started out from a seed crystal and grew to its pictured size inside a 2-metre-tall vat of solution over a period of two months. Each crystal is sliced into plates measuring 40 cm2. More than 600 of these plates are needed for the National Ignition Facility. (Image: Lawrence Livermore National Security, LLC/Lawrence Livermore National Laboratory/Department of Energy)

Tuesday, March 10, 2009

World's largest laser gears up for ignition experiments

( -- Construction of the National Ignition Facility (NIF), the world's largest and highest-energy laser system, was essentially completed on Feb. 26, when technicians at Lawrence Livermore National Laboratory (LLNL), where the laser is located, fired the first full system shot to the center of the NIF target chamber.

The test was the first time all 192 laser beams converged simultaneously in the 10-meter-diameter chamber. NIF has met all of its project completion criteria except for official certification of project completion by the U.S. Department of Energy, due by March 31.

An average of 420 joules of ultraviolet laser energy, known as 3-omega, was achieved for each beamline, for a total energy of more than 80 kilojoules (a joule is the energy needed to lift a small apple one meter against the Earth's gravity).

The energy level will be increased during the next several months, and when all NIF lasers are fired at full energy, they will deliver 1.8 megajoules of ultraviolet energy to a BB-sized target in a 20-nanosecond shaped laser pulse, generating 500 trillion watts of peak power -- more than the peak electrical generating power of the entire United States. This is considered more than enough energy to fuse the hydrogen isotopes of deuterium and tritium in the target into helium nuclei (alpha particles) and yield considerably more energy in the process than was required to initiate the reaction.

The last of NIF's 6,206 various optical-mechanical and controls system modules, called "line replaceable units" or LRUs, was installed on Jan. 26. The first LRU, a flashlamp, was installed on Sept. 26, 2001.

Workers have aligned and tuned NIF's final optical assemblies, which focus and convert the frequency of the project's 192 laser beams as they enter the target chamber and converge on the tiny target. Experimental systems and diagnostics are also being installed. Software for the integrated computer control system, which handles shot automation, has been completed.