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The process that powers a star - cheaply

Some scientists hope to control hydrogen fusion - the process that powers a star - using huge magnetic chambers costing hundreds of millions to billions of dollars. Others are building a multibillion-dollar laser array to ignite the stellar fire.

Glen Wurden says he thinks he can do it 10 to 100 times more cheaply by crushing the nuclear fuel in an aluminum canister the size of a large tomato-juice can.

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It's a third route to controlled fusion - science's long-range hope for generating electric power on earth. It's inherently less expensive than anything pursued so far. Fusion scientists have speculated about it for decades. Now, Dr. Wurden and his colleagues at the Los Alamos National Laboratory in New Mexico are ready to give it a try. They are beneficiaries of what a draft report of a National Research Council review calls "significant progress" in understanding how to control fusion with magnetic fields. They benefit from weapons-oriented research on igniting fusion with lasers.

And they benefit from unrelated defense research on materials - what Wurden calls "technology to move metal fast." All this has come together to make it practical to build a research device in which an aluminum "can" - 10 centimeters wide, 30 centimeters long, with walls only one millimeter thick - crushes together in 10 millionths of a second. That's long enough to get a fusion reaction going and see where this line of research may lead.

Fusion is a nuclear process that literally needs astronomical temperatures. Atomic nuclei, including hydrogen, have a positive electric charge. Bring two hydrogen or deuterium (doubly heavy hydrogen) nuclei together and their charges repel each other. They have to slam together fast to overcome that repulsion and fuse - forming helium nuclei and releasing energy. Since speed is equivalent to temperature for such particles, that means temperatures in the 100 million degree range. At that temperature, the hydrogen nuclei are moving so fast it's hard to keep a bunch of them together long enough for any of them to fuse. Stars do it with the intense pressure at their cores. Some research devices do it by confining the electrically charged nuclei with strong - and expensive - magnetic fields.

Laser fusion works by compression. Powerful laser beams are precisely focused on a BB-size pellet containing hydrogen. They heat the outer part of the target pellet. The vaporized material reacts back on the target, compressing it until fusion occurs. The nearly $4 billion National Ignition Facility under construction at Lawrence Livermore National Laboratory in California is designed to ignite stellar fire in this way.

The Los Alamos experiments work on a far smaller scale. What physicists call a magnetized target - a small charge of deuterium with a magnetic field inside - enters the aluminum canister. A pulse of electric current sent through the walls of the container cause it to collapse. This crushes the deuterium to high enough temperature and pressure to allow fusion. The magnetic field in the deuterium insulates it from the imploding container wall long enough so that the purity of the deuterium charge needed to sustain fusion is not spoiled by reactions with the wall material.

The result, says Wurden, is that "you get this literally astronomical" condition in a small device. Over the past three years, Wurden's group has shown it can produce the magnetized deuterium target and get it into the canister - a tricky feat. Working with the US Air Force Research Laboratory in Albuquerque, N.M., it has shown it can crush the "can" as needed. Now, the team is ready to put it all together and begin studying this third route to fusion power.

Wurden says that, if they continue to be successful, they may be able to build "fusion experiments and testing facilities ... that cost in the tens of million-dollar range, rather than in the billion-dollar range."

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(c) Copyright 2000. The Christian Science Publishing Society


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