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Man-made star to unlock cosmic secrets
05-23-2009, 07:31 PM,
Man-made star to unlock cosmic secrets
Man-made star to unlock cosmic secrets

[Image: _45762511_supernova_cgi_416_spl.jpg]
NIF can recreate the conditions inside an exploding star

When the world's most powerful laser facility flicks the switch on its first full-scale experiments later this month, a tiny star will be born on Earth.

The National Ignition Facility (NIF) in California aims to demonstrate the feasibility of nuclear fusion, the reaction at the heart of the Sun and a potentially abundant, clean energy source for the planet.

But whilst many eyes at the facility will be locked on the goal of satisfying humanity's energy demands, many scientists hope to answer other fundamental questions for mankind.

"In recreating the process of fusion it was always understood that we could pursue three areas of interest and value," explained Dr Erik Storm of the Lawrence Livermore National Laboratory (LLNL), the home of NIF.

First and foremost, NIF has been built for national security purposes, to study the conditions that exist in nuclear explosions and the way that nuclear weapons perform.

"That gives you an ability to maintain a credible nuclear deterrent in the absence of underground nuclear testing," said Dr Storm.

"Then, we can study the physics of fusion - can you make a fusion power plant here on our planet? And we can do basic physics and planetary science."

Right on time

It is this last area that has got the attention of scientists around the world, who hope to use the machine to study distant phenomena, such as the formation of planets or the violent explosions of supernovae, from the comfort of the lab.

"To understand where we find ourselves in the Universe and what we find ourselves made of, one really needs to understand exploding stars," explained Professor Paul Drake of the University of Michigan.

He is just one of a number of researchers waiting in the wings at NIF who hope to test their theories using the giant facility.

"At NIF you can schedule a supernova explosion for Thursday at nine in the morning instead of waiting for one to happen by accident in the Universe," said Dr Storm.

"And you can change experiments each time. So you can do a supernova explosion again, and again and again."

Other facilities, such as the Omega laser at the University of Rochester in New York, are already used for this kind of test.

But NIF's 192 lasers will deliver more energy than any facility has ever done, giving scientists an unprecedented glimpse into what are usually distant cosmic processes.

During fusion experiments, the beams briefly focus 500 trillions watts of power - more than the peak electrical generating power of the entire United States - on to a ball-bearing-sized pellet of hydrogen fuel.

See how the laser works

The intense energy creates temperatures of 100 million degrees and pressures billions of times greater than Earth's atmospheric pressure, forcing the hydrogen nuclei to fuse and a colossal amount of energy to be released.

In the astrophysical experiments, however, the fuel pellet would be substituted for a half-sphere of layered elements, designed to mimic the core of a star.

"You choose the material and the structures between them to be relevant to what happens when the star explodes," explained Professor Drake.

"The laser would strike the centre - the analogue of the core of the star- launching a tremendously strong shock wave that would blow the material apart."

The whole experiment may take just billionths of a second, meaning the explosion has to be monitored in incredible detail by a suite of sensors.

"The challenge is to do experiments that reproduce the conditions that occur and then scale the results to the astrophysical environment."

This should allow the researchers to probe the insides of stars and supernovae in unprecedented detail and understand more about how these astronomical objects came into being.

Diamond showers

But it is not just astrophysicists who are excited about getting their hands on NIF. Planetary scientists also want to get hold of the machine to test their theories about how planets and solar systems formed.

"The architecture of the Solar System was very likely controlled to some extent by the existence of planets like Jupiter," said Professor David Stevenson of the California Institute of Technology.

The gravity of the giant planet controlled the position of vast clouds of dust and debris in our cosmic neighbourhood and therefore what building blocks were available to form the other planets, including Earth.

And since 300 gas giants that have a similar mass or are bigger than Jupiter have recently been found orbiting other distant stars, understanding how and when these giants form could also help shed light on the evolution of other planetary systems.

To do this, scientists have turned to NIF to try to understand more about the extreme temperatures and pressures at the heart of the planets and their effects on matter.

Previous generations of experimental facilities were able to create pressures up to a million times that found at sea level on Earth; NIF's lasers will be able to produce pressures up to billions of atmospheres.

"These are conditions that exist inside these super giant planets," Professor Ray Jeanloz, of the University of California, Berkeley, told BBC News.

At these crushing pressures, he said, the conventional understanding of chemistry and the behaviour of materials is turned on its head.

"The periodic table that we learn about when we first start chemistry is fundamentally altered at pressures of a million atmospheres," he said.

"By a billion atmospheres, we expect even more dramatic changes."

For example, at millions of atmospheres, the bonds between atoms begin to break down. At billions of pressures, the atoms themselves begin to be crushed.

"This regime has never been explored before," Professor Jeanloz told BBC News.

Scientists hope to probe what happens to abundant elements such as hydrogen and helium, as well as life-critical materials such as carbon and water.

"It's only been in the last year that the theoretical community has really pursued these calculations. We're just beginning to get a more detailed sense [of what might come out of NIF]."

However, even lower pressure experiments hint that the results may range from the exotic to the bizarre.

For example, tests have shown that hydrogen - the most abundant element in the Universe - becomes a metallic fluid at pressures similar to those found inside the Earth.

Whilst at higher pressures, such as those found on Jupiter, stranger things begin to happen.

"Hydrocarbons would actually decompose to a mixture of hydrogen and a carbon," explained Professor Jeanloz. "The end result being that diamonds would actually be hailing out of the atmosphere.

"That's the kind of process you would never have guessed unless you had studied the materials themselves."

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