New approach to overcome key hurdle for next-generation superconductors

ScienceDaily (Oct. 27, 2011) — Researchers from North Carolina State University have developed a new computational approach to improve the utility of superconductive materials for specific design applications -- and have used the approach to solve a key research obstacle for the next-generation superconductor material yttrium barium copper oxide (YBCO).

A superconductor is a material that can carry electricity without any loss -- none of the energy is dissipated as heat, for example. Superconductive materials are currently used in medical MRI technology, and are expected to play a prominent role in emerging power technologies, such as energy storage or high-efficiency wind turbines.

One problem facing systems engineers who want to design technologies that use superconductive materials is that they are required to design products based on the properties of existing materials. But NC State researchers are proposing an approach that would allow product designers to interact directly with the industry that creates superconductive materials -- such as wires -- to create superconductors that more precisely match the needs of the finished product.

"We are introducing the idea that wire manufacturers work with systems engineers earlier in the process, utilizing computer models to create better materials more quickly," says Dr. Justin Schwartz, lead author of a paper on the process and Kobe Steel Distinguished Professor and head of NC State's Department of Materials Science and Engineering. "This approach moves us closer to the ideal of having materials engineering become part of the product design process."

To demonstrate the utility of the process, researchers tackled a problem facing next-generation YBCO superconductors. YBCO conductors are promising because they are very strong and have a high superconducting current density -- meaning they can handle a large amount of electricity. But there are obstacles to their widespread use.

One of these key obstacles is how to handle "quench." Quench is when a superconductor suddenly loses its superconductivity. Superconductors are used to store large amounts of electricity in a magnetic field -- but a quench unleashes all of that stored energy. If the energy isn't managed properly, it will destroy the system -- which can be extremely expensive. "Basically, the better a material is as a superconductor, the more electricity it can handle, so it has a higher energy density, and that makes quench protection more important, because the material may release more energy when quenched," Schwartz says.

To address the problem, researchers explored seven different variables to determine how best to design YBCO conductors in order to optimize performance and minimize quench risk. For example, does increasing the thickness of the YBCO increase or decrease quench risk? As it turns out, it actually decreases quench risk. A number of other variables come into play as well, but the new approach was effective in helping researchers identify meaningful ways of addressing quench risk.

"The insight we've gained into YBCO quench behavior, and our new process for designing better materials, will likely accelerate the use of YBCO in areas ranging from new power applications to medical technologies -- or even the next iteration of particle accelerators," Schwartz says.

"This process is of particular interest given the White House's Materials Genome Initiative," Schwartz says. "The focus of that initiative is to expedite the process that translates new discoveries in materials science into commercial products -- and I think our process is an important step in that direction."

The paper was co-authored by Dr. Wan Kan Chan, a research associate at NC State. The paper is available online from IEEE Transactions on Applied Superconductivity. The research was funded by the Air Force Research Laboratory.

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Journal Reference:

Wan Kan Chan, Justin Schwartz. Three-Dimensional Micrometer-Scale Modeling of Quenching in High-Aspect-Ratio YBa2Cu3O7-d Coated Conductor Tapes -- Part II: Influence of Geometric and Material Properties and Implications for Conductor Engineering and Magnet Design. IEEE Transactions on Applied Superconductivity, 2011; DOI: 10.1109/TASC.2011.2169670

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Handling nanoscale particles: 'Next-generation' optical tweezers trap tightly without overheating

ScienceDaily (Sep. 27, 2011) — Engineers at Harvard have created a device that may make it easier to isolate and study tiny particles such as viruses.

Their plasmonic nanotweezers, revealed this month in Nature Communications, use light from a laser to trap nanoscale particles. The new device creates strong forces more efficiently than traditional optical tweezers and eliminates a problem that caused earlier setups to overheat.

"We can get beyond the limitations of conventional optical tweezers, exerting a larger force on a nanoparticle for the same laser power," says principal investigator Ken Crozier, Associate Professor of Electrical Engineering at the Harvard School of Engineering and Applied Sciences (SEAS).

"Until now, overheating has been a major problem with tweezers based on surface plasmons. What we've shown is that you can get beyond that limitation by building a plasmonic nanotweezer with an integrated heat sink."

Optical tweezers have been an essential tool in biophysics for several decades, often used for studying cellular components such as molecular motors. Researchers can trap and manipulate the proteins that whip a flagellum, for example, and measure the force of its swimming motion.

But optical tweezers have drawbacks and limits, so researchers like Crozier are perfecting what might be called the "next-generation" model: plasmonic nanotweezers.

To create conventional optical tweezers, which were invented at Bell Labs in the 1980s, scientists shine a laser through a microscope lens, which focuses it into a very tight spot. The light, which is made up of electromagnetic waves, creates a gradient force at that focused spot that can attract a tiny particle and hold it within the beam for a short period of time -- until random motion, radiation pressure, or other forces knock it out.

The trouble with these optical tweezers is that a lens cannot focus the beam any smaller than half the wavelength of the light. If the targeted particle is much smaller than the focal spot, the trapping will be imprecise.

At the same time, the focal size limit places an upper limit on the gradient force that can be generated. A stronger force is necessary for trapping nanoscale particles, relative to larger, microscopic particles, so conventional optical tweezers must use a very high-powered laser to trap the tiniest targets.

To overcome these problems, researchers in applied physics discovered a few years ago that they could enhance the trapping field by focusing the laser onto an array of nanoscale gold disks. The light excites the electrons at the surface of the metal, creating rapid waves of electromagnetic charge called plasma oscillations, resulting in "hot spots" of enhanced fields around the edges of the disk.

In other researchers' designs, the tiny gold disks were arrayed on a sheet of glass, and the whole setup was submerged in water with the target particles. In tests with those devices, one problem was that the brightest hotspots were at the base of the pillars, partially inside the glass, where the particles could never be trapped. A bigger problem, as Crozier's team discovered, was that unless they kept the laser power very low, the water boiled.

The Harvard team has solved both problems by replacing the glass with a piece of silicon coated in copper and then gold, with raised gold pillars. These materials are much more thermally conductive than glass, so they act as a heat sink.

"The gold, copper, and silicon under the pillars act just like the heat sink attached to the chip in your PC, drawing the heat away," says lead author Kai Wang (Ph.D. '11), who completed the work at SEAS and is now a postdoctoral fellow at the Howard Hughes Medical Institute.

The new device reduces the water heating by about 100-fold and produces hotspots at the top edges of the pillars, where Crozier's team was able to trap polystyrene balls as small as 110 nanometers.

In an unusual twist, the team discovered that they were able to rotate the trapped particles around the pillars by rotating the linear polarizer on the optical table where they conducted the experiments. Going further, they replaced the linear polarizer with a circular one and found that the particle automatically and continuously traveled around the pillar.

As the electromagnetic field circled the pillar, it created an optical force that pushed the particle. Interestingly, despite the fact that the electromagnetic field traveled at about 1014 rotations per second, the balance between the optical force and the fluid drag resulted in a particle velocity of about 5 rotations per second, effectively a terminal velocity.

"This phenomenon seems to be entirely novel," says Crozier. "People have trapped particles before, but they've never done anything like that."

As tools for trapping and manipulating nanoparticles become more advanced, the potential applications in biophysics are extensive. One remaining challenge, however, is the researchers' ability to detect and quantify the motion of such tiny particles.

"It's going to be harder and harder to precisely track the center of the particle when we do these manipulations," says Crozier. "Progress in the realm of sensing tools will need to keep up."

Crozier and Wang's co-authors were Ethan Schonbrun, a former research associate, and Paul Steinvurzel, a former postdoctoral researcher, both from Crozier's lab at SEAS. The work was supported by the National Science Foundation, the Defense Advanced Research Projects Agency, and the U.S. Department of Energy.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Harvard University, via EurekAlert!, a service of AAAS.

Journal Reference:

Kai Wang, Ethan Schonbrun, Paul Steinvurzel, Kenneth B. Crozier. Trapping and rotating nanoparticles using a plasmonic nano-tweezer with an integrated heat sink. Nature Communications, 2011; 2: 469 DOI: 10.1038/ncomms1480

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Handling nanoscale particles: 'Next-generation' optical tweezers trap tightly without overheating

ScienceDaily (Sep. 27, 2011) — Engineers at Harvard have created a device that may make it easier to isolate and study tiny particles such as viruses.

Their plasmonic nanotweezers, revealed this month in Nature Communications, use light from a laser to trap nanoscale particles. The new device creates strong forces more efficiently than traditional optical tweezers and eliminates a problem that caused earlier setups to overheat.

"We can get beyond the limitations of conventional optical tweezers, exerting a larger force on a nanoparticle for the same laser power," says principal investigator Ken Crozier, Associate Professor of Electrical Engineering at the Harvard School of Engineering and Applied Sciences (SEAS).

"Until now, overheating has been a major problem with tweezers based on surface plasmons. What we've shown is that you can get beyond that limitation by building a plasmonic nanotweezer with an integrated heat sink."

Optical tweezers have been an essential tool in biophysics for several decades, often used for studying cellular components such as molecular motors. Researchers can trap and manipulate the proteins that whip a flagellum, for example, and measure the force of its swimming motion.

But optical tweezers have drawbacks and limits, so researchers like Crozier are perfecting what might be called the "next-generation" model: plasmonic nanotweezers.

To create conventional optical tweezers, which were invented at Bell Labs in the 1980s, scientists shine a laser through a microscope lens, which focuses it into a very tight spot. The light, which is made up of electromagnetic waves, creates a gradient force at that focused spot that can attract a tiny particle and hold it within the beam for a short period of time -- until random motion, radiation pressure, or other forces knock it out.

The trouble with these optical tweezers is that a lens cannot focus the beam any smaller than half the wavelength of the light. If the targeted particle is much smaller than the focal spot, the trapping will be imprecise.

At the same time, the focal size limit places an upper limit on the gradient force that can be generated. A stronger force is necessary for trapping nanoscale particles, relative to larger, microscopic particles, so conventional optical tweezers must use a very high-powered laser to trap the tiniest targets.

To overcome these problems, researchers in applied physics discovered a few years ago that they could enhance the trapping field by focusing the laser onto an array of nanoscale gold disks. The light excites the electrons at the surface of the metal, creating rapid waves of electromagnetic charge called plasma oscillations, resulting in "hot spots" of enhanced fields around the edges of the disk.

In other researchers' designs, the tiny gold disks were arrayed on a sheet of glass, and the whole setup was submerged in water with the target particles. In tests with those devices, one problem was that the brightest hotspots were at the base of the pillars, partially inside the glass, where the particles could never be trapped. A bigger problem, as Crozier's team discovered, was that unless they kept the laser power very low, the water boiled.

The Harvard team has solved both problems by replacing the glass with a piece of silicon coated in copper and then gold, with raised gold pillars. These materials are much more thermally conductive than glass, so they act as a heat sink.

"The gold, copper, and silicon under the pillars act just like the heat sink attached to the chip in your PC, drawing the heat away," says lead author Kai Wang (Ph.D. '11), who completed the work at SEAS and is now a postdoctoral fellow at the Howard Hughes Medical Institute.

The new device reduces the water heating by about 100-fold and produces hotspots at the top edges of the pillars, where Crozier's team was able to trap polystyrene balls as small as 110 nanometers.

In an unusual twist, the team discovered that they were able to rotate the trapped particles around the pillars by rotating the linear polarizer on the optical table where they conducted the experiments. Going further, they replaced the linear polarizer with a circular one and found that the particle automatically and continuously traveled around the pillar.

As the electromagnetic field circled the pillar, it created an optical force that pushed the particle. Interestingly, despite the fact that the electromagnetic field traveled at about 1014 rotations per second, the balance between the optical force and the fluid drag resulted in a particle velocity of about 5 rotations per second, effectively a terminal velocity.

"This phenomenon seems to be entirely novel," says Crozier. "People have trapped particles before, but they've never done anything like that."

As tools for trapping and manipulating nanoparticles become more advanced, the potential applications in biophysics are extensive. One remaining challenge, however, is the researchers' ability to detect and quantify the motion of such tiny particles.

"It's going to be harder and harder to precisely track the center of the particle when we do these manipulations," says Crozier. "Progress in the realm of sensing tools will need to keep up."

Crozier and Wang's co-authors were Ethan Schonbrun, a former research associate, and Paul Steinvurzel, a former postdoctoral researcher, both from Crozier's lab at SEAS. The work was supported by the National Science Foundation, the Defense Advanced Research Projects Agency, and the U.S. Department of Energy.

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and Google +1:

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Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Harvard University, via EurekAlert!, a service of AAAS.

Journal Reference:

Kai Wang, Ethan Schonbrun, Paul Steinvurzel, Kenneth B. Crozier. Trapping and rotating nanoparticles using a plasmonic nano-tweezer with an integrated heat sink. Nature Communications, 2011; 2: 469 DOI: 10.1038/ncomms1480

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

First X-ray lasing of SACLA: Next-generation facility up and running with powerful new X-ray laser

ScienceDaily (June 13, 2011) — RIKEN and the Japan Synchrotron Radiation Research Institute (JASRI) have successfully produced a first beam of X-ray laser light with a wavelength of 1.2 Angstroms. This light was created using SACLA, a cutting-edge X-ray Free Electron Laser (XFEL) facility unveiled by RIKEN in February 2011 in Harima, Japan. SACLA (SPring-8 Angstrom Compact free electron LAser) opens a window into the structure of atoms and molecules at a level of detail never seen before.

The use of ultra high-intensity X-ray free electron laser light to explore the miniature structure of matter, until recently inconceivable, is today transforming how we visualize the atomic world. By providing much shorter wavelengths and higher intensities than other lasers, XFEL enables researchers to directly observe and manipulate objects on an unrivalled scale, opening new research opportunities in fields ranging from medicine and drug discovery to nanotechnology.

One of only two facilities in the world to offer this novel light source, SACLA has the capacity to deliver radiation one billion times brighter and with pulses one thousand times shorter than other existing X-ray sources. In late March, the facility marked its first milestone with beam acceleration to 8GeV and spontaneous X-rays of 0.8 Angstroms.

Only three months later, SACLA has marked a second milestone. On June 7, SACLA successfully increased the density of the electron beam by several hundred times and guided it with a precision of several micrometers to produce a bright X-ray laser with a wavelength of only 1.2 Angstroms (a photo energy of 10 keV). This matches the record of 1.2 Angstroms set at the only other operational XFEL facility in the world, the Linac Coherent Light Source (LCLS) in the United States.

With experiments soon to commence and user operations at the facility to begin by the end of fiscal 2011, this new record offers a taste of things to come with SACLA's powerful beam, the world's most advanced X-ray free electron laser.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by RIKEN.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

First X-ray lasing of SACLA: Next-generation facility up and running with powerful new X-ray laser

ScienceDaily (June 13, 2011) — RIKEN and the Japan Synchrotron Radiation Research Institute (JASRI) have successfully produced a first beam of X-ray laser light with a wavelength of 1.2 Angstroms. This light was created using SACLA, a cutting-edge X-ray Free Electron Laser (XFEL) facility unveiled by RIKEN in February 2011 in Harima, Japan. SACLA (SPring-8 Angstrom Compact free electron LAser) opens a window into the structure of atoms and molecules at a level of detail never seen before.

The use of ultra high-intensity X-ray free electron laser light to explore the miniature structure of matter, until recently inconceivable, is today transforming how we visualize the atomic world. By providing much shorter wavelengths and higher intensities than other lasers, XFEL enables researchers to directly observe and manipulate objects on an unrivalled scale, opening new research opportunities in fields ranging from medicine and drug discovery to nanotechnology.

One of only two facilities in the world to offer this novel light source, SACLA has the capacity to deliver radiation one billion times brighter and with pulses one thousand times shorter than other existing X-ray sources. In late March, the facility marked its first milestone with beam acceleration to 8GeV and spontaneous X-rays of 0.8 Angstroms.

Only three months later, SACLA has marked a second milestone. On June 7, SACLA successfully increased the density of the electron beam by several hundred times and guided it with a precision of several micrometers to produce a bright X-ray laser with a wavelength of only 1.2 Angstroms (a photo energy of 10 keV). This matches the record of 1.2 Angstroms set at the only other operational XFEL facility in the world, the Linac Coherent Light Source (LCLS) in the United States.

With experiments soon to commence and user operations at the facility to begin by the end of fiscal 2011, this new record offers a taste of things to come with SACLA's powerful beam, the world's most advanced X-ray free electron laser.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by RIKEN.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here