March 31, 2009

U.S. Laser Experiment Becomes Operational

The U.S. construction of the National Ignition Facility (NIF) is complete and researchers are preparing to start the first experiments aimed at recreating conditions at the heart of our Sun, BBC News reported.

Scientists hope the experiments will demonstrate the feasibility of nuclear fusion, a process that could offer abundant clean energy.

They will begin by focusing 192 giant laser beams on a tiny pellet of hydrogen fuel, in hopes they can show that more energy can be extracted from the process than is required to initiate it.

If NIF is successful, it would be a "seismic event," according to Professor Mike Dunne, who leads a European venture that is also pursuing nuclear fusion with lasers.

He told BBC News it would mark the transition for laser fusion from 'physics' to 'engineering reality'.

Scientists at the California-based NIF have spent 12 years building the largest experimental science facility in the U.S. containing the world's most powerful laser.

Dr. Ed Moses, director of the facility called it a "major milestone."

"We are well on our way to achieving what we set out to do - controlled, sustained nuclear fusion and energy gain for the first time ever in a laboratory setting," he added.

The first experiments will begin in June 2009 and researchers expect the first significant results between 2010 and 2012.

Moses said they still have an incredible amount to do and learn.

Experts say fusion has the potential to supply almost limitless clean energy, yet the challenge of creating a practical fusion reactor has eluded scientists for decades.

But science now believes it is getting closer to reaching that goal.

Dunne said they were now very close to the culmination of 50 years of effort, adding there are currently several experimental facilities around the world aimed at demonstrating the building blocks of nuclear fusion.

The process involves the fusing together of two heavier forms of hydrogen, known as deuterium and tritium, to form helium. Deuterium is commonly found in seawater, whilst tritium can be prepared from lithium, a relatively common element found in soil.

A small amount of mass is lost and a colossal amount of energy is released when these isotopes are combined at high temperatures.

A process known as inertially confined fusion, where extreme temperatures are achieved using ultra powerful lasers, will be the primary focus at NIF.

Moses said that when all NIF lasers are fired at full energy, they would deliver 1.8 megajoules of ultraviolet energy to the target. The beams are intended to deliver more than 60 times the energy of any previous laser system.

Experts say the pulse lasts only few nanoseconds (billionths of a second) but it will impart 500 trillion watts of power, which is more than the peak electrical generating power of the entire U.S.

A ball-bearing-sized pellet of fuel will be the focus of this intense energy, ablating the surface and compressing the remaining material inwards.

Moses explained that the process would create temperatures of 100 million degrees and pressures billions of times greater than Earth's atmospheric pressure.

"It will force the hydrogen nuclei to fuse and release many times more energy than the laser energy required to spark the reaction," he said.

If the "energy gain" stage is successful, NIF will release 10 to 100 times more energy than the amount pumped into the lasers to kick-start the reaction.

While NIF is only in the beginning experimental stages, scientists are already planning its successor, a European project known as Hiper (High Power Laser Energy Research).

Dunne, the director of Hiper, said the technology of NIF allows the laser to fire every few hours.

"This is right for the demonstration of the physics 'proof of principle', but does not meet the requirement of a laser fusion power plant, which needs to operate a few times per second," he said.

By demonstrating it can ignite a steady stream of fuel pellets, Hiper hopes to lay the foundations of this continuous fusion cycle.

Dunne said it could result in a fundamentally different laser technology, a new approach to fuel pellet production, and a suite for robotic handling capability.

Engineers plan to begin construction on the Hiper facility by the end of the next decade, bringing the world one step closer to a commercial fusion reactor.

A separate large-scale fusion experiment called the International Thermonuclear Experimental Reactor (Iter) is currently being built in Cadarache, France.

Iter will try to initiate fusion using the magnetic confinement method, in which a super-heated volume of gas is constrained by magnetic fields in a doughnut-shaped vessel known as a tokamak.

Dunne said much of the technology development is common to both approaches, adding that the two-track approach is essential given the scale of the problem, and the predicted impact on society.


Image Caption: A NIF hohlraum. The hohlraum cylinder, which contains the NIF fusion fuel capsule, is just a few millimeters wide, about the size of a pencil eraser, with beam entrance holes at either end.  The fuel capsule is the size of a small pea. (NIF)


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