* Astronomy

Physicist Rusi Taleyarkhan of Purdue University in West Lafayette, Indiana, published the first evidence of 'sonofusion' in 2002; he has been dogged by sceptics ever since.

The underlying physics behind the idea is valid, according to Ken Suslick. An expert in sonoluminescence at the University of Illinois in Urbana-Champaign, Suslick tried and failed to replicate Taleyarkhan's first results. If the bubbles' collapse is sufficiently intense, it should indeed be able to crush atoms together.

Taleyarkhan's first experiments were conducted while he was based at Oak Ridge National Laboratory in Tennessee. His idea was to use liquid acetone in which hydrogen atoms had been replaced by their heavier brethren, deuterium. When deuterium nuclei fuse together, they emit a characteristic burst of neutrons. But critics pointed out that Taleyarkhan was using an external source of neutrons to 'seed' the bubbles, and that these were swamping his measurements of neutrons produced by the fusion reaction itself.

"This time round there are no external neutrons. In this experiment we use three independent neutron detectors and a gamma-ray detector" - Rusi Taleyarkhan.

Instead, his team loaded a mixture of deuterated acetone and benzene with a uranium salt. As the uranium undergoes radioactive decay it releases alpha particles, which can also seed bubble formation.
The results from the four instruments prove that fusion is happening inside his experiment, asserts Taleyarkhan.
Although uranium can release neutrons during fission reactions, Taleyarkhan rules them out because the neutrons he finds bear the energetic hallmark of having come from the fusion of two deuterium nuclei.
Taleyarkhan's test reactor still puts out a lot less energy than it takes in, making it impractical for generating power.

The results of the new experiment are to be published in Physical Review Letters in a few weeks' time.

There is one big problem, however: the experiment doesn't always work, and the group is not sure why. Seth Putterman, a physicist at the University of California, Los Angeles, who has also tried to verify some of Taleyarkhan's experiments, notes that the paper does not reveal how many failed runs were required before the team saw a trace of fusion neutrons.
Putterman notes that the team did not continuously monitor background neutron levels. Although the neutron count doubles at some points in the experiments, Putterman says that neutrons produced in random showers of cosmic rays, rather than fusion events, could be responsible. But Taleyarkhan points out that the neutron count was smaller in detectors further from the reaction chamber.

To prove that the neutrons are coming from fusion as bubbles burst, Putterman and Suslick suggest that the team closely monitor exactly when the neutrons appear. The current experiment simply counts up the number of neutrons detected over minutes, so correlations with bubble bursts cannot be seen.
Another obvious way to confirm that fusion is happening would be to look for tritium, a heavier isotope of hydrogen produced by fusion reactions. Tritium leaves a telltale signature of high-energy electrons when it decays and Taleyarkhan claimed to see this in similar previous experiments. But in the current tests, tritium's signature is overwhelmed by beta-decay from the uranium, making it impossible to spot.

-- Edited by Blobrana at 05:51, 2006-01-12

Russian scientists have managed to use lasers to create a billion-degree nuclear fireball. The resulting fusion reaction is far cleaner than the kind currently being investigated to generate nuclear power.

Sadly, the team's efforts are no good for power generation at the moment as the laser takes so much energy to run. But achieving this kind of laser-driven fusion in the lab will give scientists a better way to investigate the phenomenon, which could one day be used to create cleaner energy.

Currently, the main contender for generating fusion power uses strong magnetic fields to confine a fiery plasma of atomic nuclei: fusion experts hope that the International Thermonuclear Experimental Reactor (ITER), to be built in Cadarache, France, will fuse deuterium and tritium nuclei together in this way to create energy.

But this reaction also produces copious amounts of neutrons. When these neutrons hit the reactor walls they generate radioactive isotopes that will eventually have to be disposed of. And although this radioactive waste is cleaner than the by-products created by fission, the reaction used by today's nuclear power plants, it isn't perfect.


So some physicists have suggested using a different fusion process instead, which forces protons and boron nuclei together in a reaction that generates virtually no neutrons.

Although this sounds safer, kick-starting proton-boron fusion requires temperatures of a billion degrees, more than ten times the heat needed by the deuterium-tritium reaction.
"Deuterium-tritium fusion is the reaction of choice simply because it's easier to achieve" - Gennady Shvets, a physicist at the University of Texas at Austin.

Now a team of Russian scientists have topped the billion-degree mark in a system that does not need huge magnets to confine the reaction.
"We have achieved a neutronless proton-boron reaction for the first time using a laser" - Vadim Belyaev, physicist from the Central Research Institute of Machine Building, Koralev, Russia.

The team blasted polythene pellets containing boron atoms with laser pulses that last for just over a trillionth of a second (10^-12 seconds). This creates an intensely hot plasma where protons from the polythene merge into boron atoms, which then fall apart to release a stream of helium nuclei, also known as alpha particles.

Lumbering alpha particles tend to stay within the reaction mixture rather than escaping to make surrounding equipment radioactive. Crucially, the team detected no neutrons coming from the reaction at all.


The success opens the door to "an ecologically pure technology of nuclear energy production", says Belyaev, whose team reports its research in the journal Physical Review E.

An added advantage to the system is that the charged alpha particles could be directly tapped as a source of electric current. A power plant based on ITER would simply use the heat from fusion to turn electrical turbines, much as coal-fired power stations do today.

And laser-driven fusion might be easier to sustain than the reaction inside magnetic bottles used by projects such as ITER. In theory, once the reaction is going, all one would have to do is keep dropping fuel pellets into the beam. In contrast, ITER will use giant magnets to keep a turbulent, burning ball of plasma confined. "Unfortunately (confinement) is the least understood process in fusion" - Gennady Shvets.

Other labs, including the National Ignition Facility at Lawrence Livermore National Laboratory in California, similarly use lasers to investigate fusion, but of the dirtier deuterium-tritium type. Belyaev now hopes to see a wider international project to investigate the proton-boron reaction.

source

Hum,
how about a bit of DIY?

"Sonofusion" generates nuclear reactions by creating tiny bubbles that implode with tremendous force.
The original researchers produced tritium; and there is only one way to produce tritium – through nuclear processes
The findings were reported in a paper that appeared in the journal Physical Review E, published by the American Physical Society.

The discovery was first reported in March 2002 in the journal Science.
Since then the researchers have acquired additional funding from the U.S. Defence Advanced Research Projects Agency, purchased more precise instruments and equipment to collect more accurate data, and successfully reproduced and improved upon the original experiment.
A fair amount of very substantial new work was conducted and also, this time top scientists and physicists from around the world and experts in neutron science came to the lab to review the procedures and findings before the manuscript was submitted to a journal.

The device is a clear glass canister about the height of two coffee mugs stacked on top of one another. Inside the canister is a liquid called deuterated acetone (C3D6O). The acetone contains a form of hydrogen called deuterium, or heavy hydrogen, which contains one proton and one neutron in its nucleus.
Normal hydrogen contains only one proton in its nucleus.
The researchers expose the clear canister of liquid to pulses of neutrons every five milliseconds, or thousandths of a second, causing tiny cavities to form.
At the same time, the liquid is bombarded with a specific frequency of ultrasound, which causes the cavities to form into bubbles that are about 60 nanometres – or billionths of a meter – in diameter.
The bubbles then expand to a much larger size, about 6,000 microns, or millionths of a metre – large enough to be seen with the unaided eye.
The process is analogous to stretching a slingshot from Earth to the nearest star, our sun, thereby building up a huge amount of energy when released.
Within nanoseconds these large bubbles contract with tremendous force, returning to roughly their original size, and release flashes of light in a well-known phenomenon known as sonoluminescence..

Because the bubbles grow to such a relatively large size before they implode, their contraction causes extreme temperatures and pressures comparable to those found in the interiors of stars. Researches estimate that temperatures inside the imploding bubbles reach 10 million degrees Celsius and pressures comparable to 1,000 million earth atmospheres at sea level.

At that point, deuterium atoms fuse together, the same way hydrogen atoms fuse in stars, releasing neutrons and energy in the process.
The process also releases a type of radiation called gamma rays and a radioactive material called tritium, all of which have been recorded and measured by the team. In future versions of the experiment, the tritium produced might then be used as a fuel to drive energy-producing reactions in which it fuses with deuterium.
Whereas conventional nuclear fission reactors produce waste products that take thousands of years to decay, the waste products from fusion plants are short-lived, decaying to non-dangerous levels in a decade or two.

The desktop experiment is safe because, although the reactions generate extremely high pressures and temperatures, those extreme conditions exist only in small regions of the liquid in the container – within the collapsing bubbles.
One key to the process is the large difference between the original size of the bubbles and their expanded size. Going from 60 nanometres to 6,000 microns is about 100,000 times larger, compared to the bubbles usually formed in sonoluminescence, which grow only about 10 times larger before they implode.
This means you've got about a trillion times more energy potentially available for compression of the bubbles than you have with conventional sonoluminescence.
When the light flashes are emitted, it's getting extremely hot, and if your liquid has deuterium atoms compared to ordinary hydrogen atoms, the conditions are hot enough to produce nuclear fusion.
The ultrasound switches on and off about 20,000 times a second as neutrons are bombarding the liquid.
Each five-millisecond pulse of neutrons is followed by a five-millisecond gap, during which time the bubbles implode, release light and emits a surge of about 1 million neutrons per second.

In the first experiments carried out, with the less sophisticated equipment, the team was only able to collect data during a small portion of the five-millisecond intervals between neutron pulses. The new equipment enabled the researchers to see what was happening over the entire course of the experiment.
The data clearly show surges in neutrons emitted in precise timing with the light flashes, meaning the neutron emissions are produced by the collapsing bubbles responsible for the flashes of light.

Neutrons are emitted each time the bubble is implodes with sufficient violence.
Fusion of deuterium atoms emits neutrons that fall within a specific energy range of 2.5 mega-electron volts or below, which was the level of energy seen in neutrons produced in the experiment.
The production of tritium also can only be attributed to fusion, and it was never observed in any of the control experiments in which normal acetone was used.
Whereas data from the previous experiment had roughly a one in 100 chance of being attributed to some phenomena other than nuclear fusion, the new, more precise results represent more like a one in a trillion chance of being wrong.

(adapted from source)

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Using concentrated sulphuric acid as the medium subjected to acoustic treatment, a pair of scientists, David J. Flannigan and Dr Kenneth Suslick, have obtained the most intense sonoluminescence yet seen. With this spectral information they confirm that temperatures reach as high as 15,000 K, and thus indicate that the collapsed bubble has a hot plasma core.
Link:

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Impulse Devices, a developer of sonofusion power (acoustic inertial confinement fusion, AICF), announced on Dec 14th 2004, the availability of its research reactor to laboratories, universities, power equipment manufacturers and utilities attempting to produce a new alternative energy.

The IDI reactor is a stainless steel sphere filled with heavy water and, at its centre, a small bubble of deuterium (heavy hydrogen). The IDI research reactor has a diameter of 1 foot and costs $250,000 with custom input-output systems and instrumentation.

http://www.impulsedevices.com/


-- Edited by Blobrana at 19:04, 2005-06-09

(old news)

A very reputable, very careful group of scientists at the University of Los Angeles (Brian Naranjo, Jim Gimzewski, Seth Putterman) has initiated a fusion reaction using a laboratory device that's not much bigger than a breadbox, and works at roughly room temperature. This time, it looks like the real thing.

Before going into their specific experiment, it's probably a good idea to define exactly what nuclear fusion is, and why we're so interested in understanding the process. This also gives me an excuse to talk about how things work deep inside the nuclei of atoms, a topic near and dear to most astronomers (more on that later).

Simply put, nuclear fusion means ramming protons and neutrons together so hard that they stick, and form a single, larger nucleus. When this happens with small nuclei (like hydrogen, which has only one proton or helium, which has two), you get a lot of energy out of the reaction. This specific reaction, fusing two hydrogen nuclei together to get helium, famously powers our sun (good), as well as hydrogen bombs (bad).

Fusion is a tremendous source of energy; the reason we're not using it to meet our everyday energy needs is that it's very hard to get a fusion reaction going. The reason is simple: protons don't want to get close to other protons.

Do you remember learning about electricity in high school? I sure do - I dreaded it whenever that topic came around. I had a series of well-meaning science teachers that thought it would be fun for everyone to hold hands and feel a mild electric shock pass their arms. Every time my fists clenched and jerked and I had nothing consciously do with it, my stomach turned.

In addition, I have long, fine hair, and was often made a victim of the Van de Graf generator - the little metal ball with a rubber belt inside it that creates enough static electricity to make your hair stand on end. Yeesh.

Anyway, hopefully you remember the lesson that two objects having different electrical charges (positive and negative) attract one another, while those with the same charge repel. It's a basic law of electricity, and it definitely holds true when two protons try to get close together. Protons have positive charges, and they repel each other. Somehow, in order for fusion to work, you've got to overcome this repulsive electrical force and get the things to stick together.

Here's where an amazing and mysterious force comes in that, although we don't think about it in our day-to-day lives, literally holds our matter together. There are four universal forces of nature, two of which you're probably familiar with: gravity and electromagnetism.

But there are two other forces that really only come in to play inside atomic nuclei: the strong and weak nuclear forces (and yes, the strong force is the stronger of the two, the weak is weaker. Scientists really have a way with names, dont they?) I'm going to focus on the strong force, as that's the one responsible for nuclear fusion.

The strong force is an attractive force between protons and neutrons - it wants to stick them together. If the strong force had its way, the entire universe would be one big super-dense ball of protons and neutrons, one big atomic nucleus, in fact.

Fortunately, the strong force only becomes strong at very small scales: about one millionth billionth of a meter. Yes, that's 0.000000000000001 meters. Any farther away, and the strong force loses its grip. But if you can get protons and neutrons that close together, the strong force becomes stronger than any other force in nature, including electricity.

That's important- all protons have the same charge, so they'd like to fly away from each other. But if you can get them close together, inside the volume of an atomic nucleus, the strong force will bind them together.

The whole trick with fusion is you've got to get protons close enough together for the strong force to overcome their electrical repulsion and merge them together into a nucleus. The sun does this pretty much by brute force. The sun has over 300,000 times the mass of the Earth, which means there's a lot of gravity weighing down on its core.

That pressure gets the sun's internal temperature up to several millions of degrees, which means that particles inside the sun's core are flying around at huge velocities. Everything is moving around so fast that protons sometimes get slammed together before their charges have a chance to repel. The strong force takes hold, and a new atom (helium) is born.

In this process, some of the mass of the protons is converted into energy, powering the sun and producing the light that will eventually reach the Earth as sunlight.

Scientists have gotten fusion to occur in the laboratory before, but for the most part, they've tried to mimic conditions inside the sun by whipping hydrogen gas up to extreme temperatures or slamming atoms together in particle accelerators. Both of those options require huge energies and gigantic equipment, not the sort of stuff easily available to build a generator. Is there any way of getting protons close enough together for fusion to occur that doesnt require the energy output of a large city to make it happen?

The answer, it turns out, is yes.

Instead of using high temperatures and incredible densities to ram protons together, the scientists at UCLA cleverly used the structure of an unusual crystal.

Crystals are fascinating things; the atoms inside are all lined up in a tightly ordered lattice, which creates the beautiful structure we associate with crystals. Sometimes those orderly atoms create neat side-effects, like piezoelectricity, which is the effect of creating an electrical charge in a crystal by compressing it. Stressing the bonds between the atoms of some crystals causes electrons to build up on one side, creating a charge difference over the body of the crystal. Other crystals do this when you heat or cool them; these are called pyroelectric crystals.

The new cold fusion experiment went something like this: scientists inserted a small pyroelectric crystal (lithium tantalite) inside a chamber filled with hydrogen. Warming the crystal by about 100 degrees produced a huge electrical field of about 100,000 volts across the small crystal.

The tip of a metal wire was inserted near the crystal, which concentrated the charge to a single, powerful point. Remember, hydrogen nuclei have a positive charge, so they feel the force of an electric field, and this one packed quite a wallop! The huge electric field sent the nuclei careening away, smacking into other hydrogen nuclei on their way out. Instead of using intense heat or pressure to get nuclei close enough together to fuse, this new experiment used a very powerful electric field to slam atoms together.

Unlike some previous claims of room-temperature fusion, this one makes intuitive sense: its just another way to get atoms close enough together for the strong force to take over and do the rest. Once the reaction got going, the scientists observed not only the production of helium nuclei, but other tell-tale signs of fusion such as free neutrons and high energy radiation.

This experiment has been repeated successfully and other scientists have reviewed the results: it looks like the real thing this time.

For the time being, don't expect fusion to become a readily available energy option. The current cold fusion apparatus still takes much more energy to start up than you get back out, and it may never end up breaking even. In the mean time, the crystal-fusion device might be used as a compact source of neutrons and X-rays, something that could turn out to be useful making small scanning machines. But it really may not be long until we have the first nuclear fusion-powered devices in common use.

So cold fusion is back, perhaps to stay. After many fits and starts, its finally time for everyday fusion to come in out of the cold.

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