Ultra-dense Deuterium May Be Nuclear Fuel Of The Future

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ScienceDaily (May 12, 2009) — A material that is a hundred thousand times heavier than water and more dense than the core of the Sun is being produced at the University of Gothenburg. The scientists working with this material are aiming for an energy process that is both more sustainable and less damaging to the environment than the nuclear power used today.

Imagine a material so heavy that a cube with sides of length 10 cm weights 130 tonnes, a material whose density is significantly greater than the material in the core of the Sun. Such a material is being produced and studied by scientists in Atmospheric Science at the Department of Chemistry, the University of Gothenburg.
Towards commercial use
So far, only microscopic amounts of the new material have been produced. New measurements that have been published in two scientific journals, however, have shown that the distance between atoms in the material is much smaller than in normal matter. Leif Holmlid, Professor in the Department of Chemistry, believes that this is an important step on the road to commercial use of the material.
The material is produced from heavy hydrogen, also known as deuterium, and is therefore known as “ultra-dense deuterium”. It is believed that ultra-dense deuterium plays a role in the formation of stars, and that it is probably present in giant planets such as Jupiter.
An efficient fuel
So what can this super-heavy material be used for?
“One important justification for our research is that ultra-dense deuterium may be a very efficient fuel in laser driven nuclear fusion. It is possible to achieve nuclear fusion between deuterium nuclei using high-power lasers, releasing vast amounts of energy”, says Leif Holmlid.
The laser technology has long been tested on frozen deuterium, known as “deuterium ice”, but results have been poor. It has proved to be very difficult to compress the deuterium ice sufficiently for it to attain the high temperature required to ignite the fusion.
Energy source of the future
Ultra-dense deuterium is a million times more dense than frozen deuterium, making it relatively easy to create a nuclear fusion reaction using high-power pulses of laser light.
“If we can produce large quantities of ultra-dense deuterium, the fusion process may become the energy source of the future. And it may become available much earlier than we have thought possible”, says Leif Holmlid.
“Further, we believe that we can design the deuterium fusion such that it produces only helium and hydrogen as its products, both of which are completely non-hazardous. It will not be necessary to deal with the highly radioactive tritium that is planned for use in other types of future fusion reactors, and this means that laser-driven nuclear fusion as we envisage it will be both more sustainable and less damaging to the environment than other methods that are being developed.”
Deuterium – brief facts
Deuterium is an isotope of hydrogen that is found in large quantities in water, more than one atom per ten thousand hydrogen atoms has a deuterium nucleus. The isotope is denoted “2H” or “D”, and is normally known as “heavy hydrogen”. Deuterium is used in a number of conventional nuclear reactors in the form of heavy water (D2O), and it will probably also be used as fuel in fusion reactors in the future.
Adapted from materials provided by University of Gothenburg.

How Electrons 'Gain Weight' In Metal Compounds Near Absolute Zero

Source:

http://www.sciencedaily.com/releases/2007/11/071101144954.htm

ScienceDaily (Nov. 5, 2007) — Rutgers University physicists have performed computer simulations that show how electrons become one thousand times more massive in certain metal compounds when cooled to temperatures near absolute zero -- the point where all motion ceases. The models may provide new clues as to how superconductivity works and how new superconducting materials could be fabricated.

In a paper posted to Science Express, a Web site of research reports slated for upcoming print editions of Science, the researchers describe how electrons interact with other particles in these compounds to morph into what physicists call a fluid of "heavy quasiparticles" or a "heavy fermion fluid." While this effect has been previously observed in some materials, the Rutgers work employs new materials to provide a level of detail that has eluded scientists so far.
"In this paper, we essentially track the fate of electrons as we lower the temperature," said Gabi Kotliar, Board of Governors Professor of Physics in the School of Arts and Sciences. "Experimental physicists may have seen different aspects of this behavior, or they may have seen behaviors they did not understand. Our calculations reconcile what they've seen."
The Rutgers researchers based their models on experiments using a new metallic crystalline compound made of the elements cerium, indium and iridium. This and similar compounds that substitute cobalt and rhodium for iridium are excellent test beds for observing heavy electron behavior.
Earlier investigations used high-temperature superconducting materials called cuprates, which failed to give physicists a clear view of electron behavior because of disorders in the crystalline structure caused by doping. The new cerium-based compounds are simpler to study because they are free of dopants.
"The new compounds are for us what fruit flies are for genetics researchers," said Kristjan Haule, assistant professor of physics and astronomy. "Fruit flies are easy to breed and have a simple gene makeup that's easy to change. Likewise, these compounds are easy to make, structurally straightforward and adjustable, giving us a clearer view into the many properties of matter that arise at low temperatures. For example, we can use a magnetic field to kill superconductivity and examine the state of matter from which superconductivity arose."
These compounds are examples of strongly correlated materials, or materials with strongly interacting electrons, that can't be described by theories that treat electrons as largely independent entities. The terms "heavy quasiparticles" refers to how electrons interact with each other and, as a result of those interactions, form a new type of particle called a "quasiparticle."
In explaining how this effect appears at low temperatures and vanishes at higher ones, Haule noted that electrons in f-orbitals are tightly bound to cerium atoms at room temperature. But as the temperature drops, the electrons exhibit coherent behavior, or delocalization from their atoms. At 50 degrees above absolute zero, or 50 degrees Kelvin, the researchers clearly observe quasiparticles as electrons interact with each other and other electrons in the metal known as conduction electrons.
The work done by Haule and his colleagues is in a branch of physics known as condensed matter physics, which deals with the physical properties of solid and liquid matter. Their models of heavy quasiparticles draw from Haule's earlier work merging two theories of atomic modeling, known as local density approximation and dynamical mean field theory, or LDA+DMFT.
Collaborating with Haule and Kotliar was Ji-Hoon Shim, a postdoctoral fellow. The National Science Foundation's Division of Materials Research and the Rutgers Center for Materials Theory supported their research. Shim received postdoctoral research funding from the Korean Research Foundation.
Adapted from materials provided by Rutgers University.

Fausto Intilla

www.oloscience.com

Laser Joining Of Solar Cells

Source:

http://www.sciencedaily.com/releases/2007/10/071007203636.htm

Science Daily — A single solar cell produces a relatively low output – it’s a case of strength in numbers. Tiny strips of metal are used to link cells together. If the laser soldering temperature is too high, the solder joint may fracture. A new system provides automatic temperature regulation.

Teamwork is what matters – even in the case of solar cells: To obtain sufficient power to operate a pocket calculator, parking ticket dispenser or photovoltaic module, sunlight has to be captured simultaneously by an array of cells. They are connected in series using tiny strips of metal known as stringers. Each stringer has to be positioned in precisely the right spot, then its solder coating is melted using a hot electrode.
When the solder sets, it forms a stable bond with the metallic coating on the silicon. The amount of heat induced in the stringer and the silicon depends on the contact between the soldering electrode and the stringer. Applying too much energy causes thermal stress which in the worst case could destroy the solder joint, leaving a break in the electrical circuit that makes the solar module unfit for use.
Researchers at the Fraunhofer Institute for Laser Technology ILT in Aachen have developed a non-contact soldering system in which the temperature is constantly monitored. If the temperature deviates beyond set limits, the system automatically adjusts it to an acceptable value. “Instead of an electrode, we use a laser beam for the soldering operation,” says ILT department head Dr. Arnold Gillner.
“To melt the solder, we pass a laser beam over the solder-coated stringer. An infrared heat camera derives the temperature of the silicon and of the metal strip from real-time measurements of their emitted radiant heat. If the temperature is too high or too low, a feedback control circuit automatically adapts the laser output within milliseconds.” The system is already in use for industrial surface engineering applications. Solar applications could be on the market in a year or so.
The researchers’ next project is to develop a faster, more reliable method of connecting solar cells by means of laser welding. “Whereas soldering only involves melting the solder, in laser welding the stringer itself is melted,” explains Gillner. This means applying more heat than for soldering, but only for a very short time. “Since the laser is only in contact with the materials for a brief instant, only a small amount of energy is transferred to the materials despite the higher temperature – resulting in even fewer heat-induced defects,” he adds.
What complicates the matter is the fact that the stringer has a diameter of about 200 micrometers, whereas the metallic coating on the silicon required to conduct electricity has a thickness of a mere 10 micrometers. The laser beam has to be modulated in such a way that the stringer will melt while leaving the coating on the silicon intact.
Note: This story has been adapted from material provided by Fraunhofer-Gesellschaft.

Fausto Intilla

www.oloscience.com