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Researchers produce tabletop fusion. [Copy link] 中文

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Post time 2005-4-28 05:57:31 |Display all floors
Researchers Say They Achieved Nuclear Fusion in Tabletop Experiment
By THE ASSOCIATED PRESS

Published: April 27, 2005


Filed at 2:48 p.m. ET

LOS ANGELES (AP) -- A tabletop experiment created nuclear fusion -- long seen as a possible clean energy solution -- under lab conditions, scientists reported.

But the amount of energy produced was too little to be seen as a breakthrough in solving the world's energy needs

For years, scientists have sought to harness controllable nuclear fusion, the same power that lights the sun and stars. This latest experiment relied on a tiny crystal to generate a strong electric field. While falling short as a way to produce energy, the method could have potential uses in the oil-drilling industry and homeland security, said Seth Putterman, one of the physicists who did the experiment at the University of California, Los Angeles.

The experiment's results appear in Thursday's issue of the journal Nature.

Previous claims of tabletop fusion have been met with skepticism and even derision by physicists. In 1989, Dr. B. Stanley Pons of the University of Utah and Martin Fleischmann of Southampton University in England shocked the world when they announced that they had achieved so-called cold fusion at room temperature. Their work was discredited after repeated attempts to reproduce it failed.

Fusion experts noted that the UCLA experiment was credible because, unlike the 1989 work, it didn't violate basic principles of physics.

''This doesn't have any controversy in it because they're using a tried and true method,'' said David Ruzic, professor of nuclear and plasma engineering at the University of Illinois at Urbana-Champaign. ''There's no mystery in terms of the physics.''

Fusion power has been touted as the ultimate energy source and a cleaner alternative to fossil fuels like coal and oil. Fossil fuels are expected to run short in about 50 years.

In fusion, light atoms are joined in a high-temperature process that frees large amounts of energy.

It is considered environment-friendly because it produces virtually no air pollution and does not pose the safety and long-term radioactive waste concerns associated with modern nuclear power plants, where heavy uranium atoms are split to create energy in a process known as fission.

In the UCLA experiment, scientists placed a tiny crystal that can generate a strong electric field into a vacuum chamber filled with deuterium gas, a form of hydrogen capable of fusion. Then the researchers activated the crystal by heating it.

The resulting electric field created a beam of charged deuterium atoms that struck a nearby target, which was embedded with yet more deuterium. When some of the deuterium atoms in the beam collided with their counterparts in the target, they fused.

The reaction gave off an isotope of helium along with subatomic particles known as neutrons, a characteristic of fusion. The experiment did not, however, produce more energy than the amount put in -- an achievement that would be a huge breakthrough.

UCLA's Putterman said future experiments will focus on refining the technique for potential commercial uses, including designing portable neutron generators that could be used for oil well drilling or scanning luggage and cargo at airports.

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Post time 2005-5-3 01:15:00 |Display all floors

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Nature 434, 1057 (28 April 2005) | doi: 10.1038/4341057a

Physicists look to crystal device for future of fusion

Mark Peplow, London

Desktop apparatus yields stream of neutrons.

Seth Putterman is usually on the side of the sceptics when it comes to tabletop fusion. But now he has created a device that may convince researchers to change their minds about the 'f-word'.

Tabletop fusion has been a touchy subject since Stanley Pons and Martin Fleischmann said in 1989 that they had achieved 'cold fusion' at room temperature. Putterman helped to discredit this claim, as well as more recent reports of 'bubble fusion'.

Now Putterman, a physicist at the University of California, Los Angeles, has turned a tiny crystal into a particle accelerator. When its electric field is focused by a tungsten needle, it fires deuterium ions into a target so fast that the colliding nuclei fuse to create a stream of neutrons.

Putterman is not claiming to have created a source of virtually unlimited energy, because the reaction isn't self-sustaining. But until now, achieving any kind of fusion in the lab has required bulky accelerators with large electricity supplies. Replacing that with a small crystal is revolutionary. "The amazing thing is that the crystal can be used as an accelerator without plugging it in to a power station," says Putterman.

Putterman got the idea when he delivered a lecture on sonoluminescence and energy focusing at the Georgia Institute of Technology, Atlanta. Physicist Ahmet Erbil suggested that Putterman should instead consider ferroelectricity.

"Here's someone telling me in front of 100 people that I'm working on the wrong thing," recalls Putterman. But the comment got him started on his fusion reactor. The result is published in this week's Nature (see page 1115).

Will he be able to avoid the controversy that has dogged other fusion claims? "My first reaction when I saw the paper was 'oh no, not another tabletop fusion paper'," says Mike Saltmarsh, an acclaimed neutron hunter who was called in to resolve the dispute over bubble fusion. "But they've built a neat little accelerator. I'm pretty sure no one has been able to generate neutrons in this way before."

Putterman himself isn't worried. "If people think this is a crackpot paper that's just fine," he says. "We're right. Any scientist who says this is too wonderful to believe is welcome to reproduce the experiments."

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Post time 2005-5-3 01:25:31 |Display all floors

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Observation of nuclear fusion driven by a pyroelectric crystal

B. Naranjo1, J.K. Gimzewski2,3 and S. Putterman1,3

Abstract

While progress in fusion research continues with magnetic and inertial confinement, alternative approaches—such as Coulomb explosions of deuterium clusters and ultrafast laser−plasma interactions—also provide insight into basic processes and technological applications. However, attempts to produce fusion in a room temperature solid-state setting, including 'cold' fusion and 'bubble' fusion, have met with deep scepticism. Here we report that gently heating a pyroelectric crystal in a deuterated atmosphere can generate fusion under desktop conditions. The electrostatic field of the crystal is used to generate and accelerate a deuteron beam (> 100 keV and >4 nA), which, upon striking a deuterated target, produces a neutron flux over 400 times the background level. The presence of neutrons from the reaction D + D  3He (820 keV) + n (2.45 MeV) within the target is confirmed by pulse shape analysis and proton recoil spectroscopy. As further evidence for this fusion reaction, we use a novel time-of-flight technique to demonstrate the delayed coincidence between the outgoing -particle and the neutron. Although the reported fusion is not useful in the power-producing sense, we anticipate that the system will find application as a simple palm-sized neutron generator.

Because its spontaneous polarization is a function of temperature, heating or cooling a pyroelectric crystal in vacuum causes bound charge to accumulate on faces normal to the polarization. A modest change in temperature can lead to a surprisingly large electrostatic field. For example, heating a lithium tantalate crystal from 240 K to 265 K decreases its spontaneous polarization by 0.0037 C m-2. In the absence of spurious discharges, introducing this magnitude of surface charge density into the particular geometry of our experiment  gives a potential of 100 kV. Attempts to harness this potential have focused on electron acceleration and the accompanying bremsstrahlung radiation, but using the crystal to produce and accelerate ions has been studied much less. Seeking to drive the D−D fusion reaction, we set out to develop a method of reliably producing an ion beam of sufficient energy (> 80 keV) and current (> 1 nA). We demonstrate such a method using a tungsten tip to generate the high field (> 25 V nm-1) necessary for gas phase field ionization of deuterium...

Read the rest of the article here :

http://www.nature.com/nature/journal/v434/n7037/full/nature03575.html




http://www.nature.com/nature/journal/v434/n7037/index.html

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