Tag Archives: magnetic field

Crab pulsar beams most energetic gamma rays ever detected from a pulsar

The Crab Nebula is a supernova remnant contain...

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Astrophysicists have detected pulsed gamma-ray emission from the Crab pulsar at energies far beyond what current theoretical models of pulsars can explain. With energies exceeding 100 billion electron-volts (100 GeV), the surprising gamma-ray pulses were detected by the VERITAS telescope array at the Whipple Observatory in Arizona and reported by an international team of scientists in a paper in the October 7 issue of Science. Corresponding author Nepomuk Otte, a postdoctoral researcher at the University of California, Santa Cruz, said that some researchers had told him he was crazy to even look for pulsar emission in this energy realm.

“It turns out that being persistent and stubborn helps,” Otte said. “These results put new constraints on the mechanism for how the gamma-ray emission is generated.”

Otte, Andrew McCann of McGill University in Montreal, and Martin Schroedter of the Smithsonian Astrophysical Observatory performed most of the analytic work for the study, which involved nearly 100 scientists in the VERITAS collaboration. VERITAS spokesperson Rene Ong, professor of physics and astronomy at UCLA, credited Otte as the leading advocate for using the powerful gamma-ray observatory to study the Crab pulsar.

“To me it’s a real triumph of the experimental approach, not going along with the flow and making assumptions, but just observing to see what there is. And lo and behold, we see something different than what everybody expected,” Ong said.

The Crab pulsar is a rapidly spinning neutron star, the collapsed core of a massive star that exploded in a spectacular supernova in the year 1054, leaving behind the brilliant Crab Nebula, with the pulsar at its heart. It is one of the most intensively studied objects in the sky. Rotating about 30 times a second, the pulsar has an intense, co-rotating magnetic field from which it emits beams of radiation. The beams sweep around like a lighthouse beacon because they are not aligned with the star’s rotation axis. So although the beams are steady, they are detected on Earth as rapid pulses of radiation.

Scientists have long agreed on a general picture of what causes pulsar emission. Electromagnetic forces created by the star’s rapidly rotating magnetic field accelerate charged particles to near the speed of light, producing radiation over a broad spectrum. But the details remain a mystery.

“After many years of observations and results from the Crab, we thought we had an understanding of how it worked, and the models predicted an exponential decay of the emission spectrum above around 10 GeV. So it came as a real surprise when we found pulsed gamma-ray emission at energies above 100 GeV,” said coauthor David Williams, adjunct professor of physics at UC Santa Cruz and a member of the VERITAS collaboration.

Prior to these new results, a phenomenon known as curvature radiation was the leading explanation for the Crab’s pulsed gamma-ray emission. Curvature radiation is produced when a high-energy charged particle moves along a curved magnetic field. But according to Otte, this mechanism cannot account for gamma rays with energies above 100 GeV.

“The conventional wisdom was that the dominant mechanism is curvature radiation. But the VERITAS results have shown that there must be a different mechanism at work,” Otte said. “Curvature radiation can explain the lower-energy emission, but we really don’t know what causes the very high-energy emission.”

One possible scenario may be a process known as inverse Compton scattering, which involves energy transfer from charged particles to photons. “That seems to be a more likely scenario now, but we still don’t know the details of how this works,” Otte said. It is also not clear whether one mechanism dominates at all gamma-ray energies, or if curvature radiation dominates at lower energies and something like inverse Compton scattering dominates at higher energies.

According to Ong, researchers will need to characterize the very high-energy gamma-ray emission in much greater detail in order to gain more insight into the mechanisms behind it. “We need to take more measurements and get the exact shape of the spectrum at these very high energies,” he said.

The VERITAS observations open up a new avenue for testing Einstein’s theory of special relativity, which says that the speed of light is a universal constant. One of the predictions of a quantum theory of gravity, which emerges from efforts to reconcile quantum mechanics and general relativity, is that the speed of light actually may have a small dependence on the energy of the photon. This would be a violation of “Lorentz invariance,” which is at the core of special relativity, but it might be detectable in the VERITAS data, Otte said. Photons with a range of energies are emitted by the pulsar at the same time. If photons with different energies travel at different speeds, the effect would manifest itself as a slight shift in the position of the pulses at different energies.

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Source: University of California – Santa Cruz

Cloaking magnetic fields — the first antimagnet

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Spanish researchers have designed what they believe to be a new type of magnetic cloak, which shields objects from external magnetic fields, while at the same time preventing any magnetic internal fields from leaking outside, making the cloak undetectable. The development of such a device, described as an ‘antimagnet’, could offer many beneficial applications, such as protecting a ship’s hull from mines designed to detonate when a magnetic field is detected, or allowing patients with pacemakers or cochlear implants to use medical equipment.

In their study, published Sept. 23, in the Institute of Physics and German Physical Society’s New Journal of Physics, researchers have proved that such a cloak could be built using practical and available materials and technologies, and used to develop an array of applications.

Take, for example, a patient with a pacemaker undergoing an MRI scan. If an MRI‘s large magnetic field interacts with the pacemaker, it can cause serious damage to both the device and the patient. The metal in the pacemaker could also interact with and distort the MRI‘s large magnetic field, affecting the machine’s detection capabilities.

The researchers, from Universitat Autònoma de Barcelona, are aware that the technology could also be used by criminals to dodge security systems, for example in airports and shops, but they are confident that the new research could benefit society in a positive way, while the risks could be minimized by informing security officials about potential devices, enabling them to anticipate and neutralize problems.

Lead author, Professor Alvar Sanchez, said, “The ideas of this device and their potential applications are far-reaching; however it is conceivable that they could be used for reducing the magnetic signature of forbidden objects, with the consequent threat to security. For these reasons, this research could be taken into account by security officials in order to design safer detection systems and protocols.”

The antimagnet has been designed to consist of several layers. The inner layer would consist of a superconducting material that would function to stop a magnetic field from leaking outside of the cloak, which would be very useful to cloak certain metals.

A downside to using this material, however, is that it would distort an external magnetic field placed over the cloak, making it detectable, so the device would need to be combined with several outer layers of metamaterials, which have varying levels of magnetic field permeability, to correct this distortion and leave the magnetic field undisturbed.

The researchers demonstrated the feasibility of the cloak using computer simulations of a ten-layered cylindrical device cloaking a single small magnet.

Impressively, the researchers also showed that the cloak could take on other shapes and function when the cylinder was not fully enclosed, meaning that applications for pacemakers and cochlear implants are even more feasible, given that they require wires to connect to other parts of the body.

“We indeed believe, and hope, that some laboratories could start constructing an antimagnet soon. Of the two components, superconductors are readily available, for example in cylindrical shape, and the key point would be to make the magnetic layers with the desired properties. This may take a bit of work but in principle the ingredients are there,” continued Professor Sanchez.

An Institute of Physics spokesperson said, “The research group have put forward a novel and, most importantly, conceivable plan for a magnetic cloak. The obvious next step will be to translate design into fabrication so some of the wide-ranging applications can be realised.”

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Source: Institute of Physics

Big machines: 2 radiation generators mark major milestones in helping protect the US

Two remarkable pulsed-power machines used to test the nation’s defenses against atomic weapons have surpassed milestones at Sandia National Laboratories: 4,000 firings, called ‘shots,’ on the Saturn accelerator and 9,000 shots on the HERMES III accelerator. Saturn — originally projected to last 5 to 10 years — began operating in 1987. Its major function has been to produce X-rays to test the effectiveness of countermeasures used to protect electronics and other materials against X-ray radiation from nuclear weapons. The machine, used broadly as a physics research testbed , provides data that can be used either directly or as input for computer simulations. The machine can fire twice a day. All these characteristics make it a spry source for data.

HERMES (High-Energy Radiation Megavolt Electron Source) III, which can fire six to eight times daily, is used primarily to demonstrate the effect of gamma ray radiation — another component of a nuclear weapon burst — on electronics and larger military hardware. First fired in 1988, it is still the world’s most powerful gamma ray generator.

“The continued operation of these facilities is a testament to the ingenuity and dedication of personnel and management,” said Sandia manager Ray Thomas.

Saturn is a predecessor to Sandia’s more awesome Z machine, but still fills a significant niche. Though it operates at roughly one-third the power of Z, Saturn can accelerate electrons at voltages and amperages that allow materials to be tested for so-called hard X-ray effects; the Z facility is not configured to produce X-rays in this critical range of frequencies.

Twenty-one years ago, in what proved to be one of Saturn‘s most high-profile endeavors, it hosted its first wire-array tests, which pulsed millions of amperes in nanoseconds through a number of wires each thinner than a human hair. The success of these tests led to installation of wire-array hardware on the larger Z machine, with gains in X-ray output that astonished the world and led to Z’s consideration as a potentially reliable way to create electricity essentially from seawater, the world’s largest natural resource.

In those early tests, the wires of course disintegrated like overstressed fuses from the great flood of electricity. But the powerful magnetic field always associated with a powerful electric current grabbed the floating ions created from the shorted-out wires and pulled them together at great speeds. When the ions ran out of room to travel, they stopped suddenly, confronting each other along a relatively vertical axis that was the hub of the magnetic field. Their sudden braking led them to release X-ray energy, similar to the release of heat from a car’s tires when the driver jams on the brakes. The scientific process, called a z-pinch by geometrical reference, caused an extraordinary increase of X-ray energy output over previous methods. Such intense X-rays can be used to compress a BB-sized hydrogen capsule, fusing its contents to release enormous energies that eventually could be used to drive an electrical power plant on very little fuel.

Unlike Saturn and Z, whose modules are each arranged in a circular pattern that resembles a wagon wheel, with electrical transmission lines like spokes leading to the target at the axle, HERMES uses 20 inductively isolated modules coupled to a linear transmission line that resembles a short subway train in size, shape and amount of metal. The output voltage from each module is added in series, the reason for the very high voltage achieved. Saturn‘s outdoor test facility is large enough to accommodate military tanks.

Continued improvements on both machines have enhanced their capabilities to map portions of the X-ray spectra previously unattainable, and to reach radiation dose rates never before achieved by an accelerator.

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Source: DOE/Sandia National Laboratories

Scientists observe smallest atomic displacements ever

LONDON, ENGLAND - DECEMBER 09:  Chancellor of ...

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This photo shows the experimental set-up at ESRF beamline ID20, with the cryostat of a large superconducting magnet in the upper part. The experiment took place in the gray disk-shaped chamber between the two blue split-coils of the magnet. The polarized X-ray beam is led to the experiment in the long steel tube from the right. The detector arm to the left can rotate about the cryostat and may be tilted up and down. It detects scattered X-rays, and in the circular chamber at its end is an analyzer crystal to determine also the polarization state of the scattered X-ray beam.
This photo shows the sample holder, made of copper, which was used in the experiment. The small gray crystal of TbMnO3 that was studied, is in the center, between two electrodes to apply an electric field.
The European Synchrotron Radiation Facility is located in Grenoble, France. The experiments were performed using beams of X-rays provided by one of the world's most brilliant light sources.

An international team of scientists has developed a novel X-ray technique for imaging atomic displacements in materials with unprecedented accuracy. They have applied their technique to determine how a recently discovered class of exotic materials — multiferroics — can be simultaneously both magnetically and electrically ordered. Multiferroics are also candidate materials for new classes of electronic devices. The discovery, a major breakthrough in understanding multiferroics, is published in Science dated 2 September 2011.

The authors comprise scientists from the European Synchrotron Radiation Facility (ESRF) in Grenoble (France), the University of Oxford and the University College London (both UK). Helen Walker from the ESRF is the main author of the publication.

Everybody is familiar with the idea that magnets are polarized with a north and a south pole, which is understood to arise from the alignment of magnet moments carried by atoms in magnetic materials. Certain other materials, known as ferroelectrics, exhibit a similar effect for electrical polarisation. The exotic “multiferroic” materials combine both magnetic and ferroelectric polarizations, and can exhibit a strong coupling between the two phenomena.

This leads to the strange effect that a magnetic field can electrically polarise the material, and an electric field magnetise it. A class of strong multiferroics was discovered ten years ago and has since led to a new, rapidly growing field of research, also motivated by the promise of their exotic properties for new electronic devices. One example is a new type of electronic memory, in which an electric field writes data into the memory and a magnetic detector is used to read it. This process is faster, and uses less energy than today’s hard disk drives.

However, the origin of the electric polarisation in multiferroics remained mostly elusive to date. The team’s work unambiguously shows that the polarization in the multiferroic studied proceeds from the relative displacement of charges of different signs, rather than the transfer of charge from one atom to another.

As the displacement involves a high number of electrons, even small distances can lead to significant polarisation. The actual distance of the displacement still came as a surprise: about 20 femtometres, or about 1/100,000th of the distance between the atoms in the material. Measuring such small displacements was actually believed to be impossible.

“I think that everyone involved was surprised, if not staggered, by the result that we can now image the position of atoms with such accuracy. The work is testament to the fantastic facilities available in Grenoble to the UK science community,” says Prof. Des McMorrow, Deputy Director of the London Centre for Nanotechnology, leader of the UCL part of the project.

Walker and her colleagues developed a smart new experimental technique exploiting the interference between two competing processes: charge and magnetic scattering of a powerful, polarized X-ray beam. They studied a single crystal of TbMnO3 which shows a strong multiferroic coupling at temperatures below 30K, and were able to measure the displacements of specific atoms within it with an accuracy approaching one femtometre (10-15m). The atoms themselves are spaced apart 100,000 times this distance.

The new interference scattering technique has set a world record for accuracy in absolute measurements of atomic displacements. (It is also the first measurement of magnetostriction in antiferromagnets.) Most significantly the identification of the origin of ferroelectricty in a multiferroic material is a major step forward in the design of multiferroics for practical applications.

“By revealing the driving mechanism behind multiferroics, which offer so many potential applications, it underlines how experiments designed to understand the fundamental physics of materials can have an impact on the wider world,” concludes Dr. Helen Walker who led the work at the ESRF.

Source: European Synchrotron Radiation Facility

NIST achieves record-low error rate for quantum information processing with one qubit

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Micrograph of NIST ion trap with red dot indicating where a beryllium ion hovers above the chip. The horizontal and vertical lines separate gold electrodes, which are tuned to hold the ion and generate microwave pulses to manipulate it. The chip was used in experiments demonstrating record-low error rates in quantum information processing with a single quantum bit.

Thanks to advances in experimental design, physicists at the National Institute of Standards and Technology (NIST) have achieved a record-low probability of error in quantum information processing with a single quantum bit (qubit) — the first published error rate small enough to meet theoretical requirements for building viable quantum computers. A quantum computer could potentially solve certain problems that are intractable using today’s technology, even supercomputers. The NIST experiment with a single beryllium ion qubit, described in a forthcoming paper, is a milestone for simple quantum logic operations. However, a working quantum computer also will require two-qubit logic operations with comparably low error rates.

“One error per 10,000 logic operations is a commonly agreed upon target for a low enough error rate to use error correction protocols in a quantum computer,” explains Kenton Brown, who led the project as a NIST postdoctoral researcher. “It is generally accepted that if error rates are above that, you will introduce more errors in your correction operations than you are able to correct. We’ve been able to show that we have good enough control over our single-qubit operations that our probability of error is 1 per 50,000 logic operations.”

The NIST experiment was performed on 1,000 unique sequences of logic operations randomly selected by computer software. Sequences of 10 different lengths, ranging from one to 987 operations, were repeated 100 times each. The measured results were compared to perfect theoretical outcomes. The maximum length of the sequences was limited by the hardware used to control the experiment.

The record low error rate was made possible by two major changes in the group’s experimental setup. First, scientists manipulated the ion using microwaves instead of the usual laser beams. A microwave antenna was incorporated into the ion trap, with the ion held close by, hovering 40 micrometers above the trap surface. The use of microwaves reduced errors caused by instability in laser beam pointing and power, as well as spontaneous ion emissions. Second, the ion trap was placed inside a copper vacuum chamber and cooled to 4.2 K with a helium bath to reduce errors caused by magnetic field fluctuations in the lab.

Brown now works at the Georgia Institute of Technology. Co-author Christian Ospelkaus contributed to the research while at NIST and is now at research institutions in Germany. The research was supported in part by the Intelligence Advanced Research Projects Activity, the National Security Agency, the Defense Advanced Research Projects Agency and the Office of Naval Research.

Source: National Institute of Standards and Technology (NIST)

Los Alamos achieves world-record pulsed magnetic field

Researchers at the National High Magnetic Field Laboratory’s Pulsed Field Facility at Los Alamos National Laboratory have set a new world record for the strongest magnetic field produced by a nondestructive magnet. The scientists achieved a field of 92.5 tesla on Thursday, August 18, taking back a record that had been held by a team of German scientists and then, the following day, surpassed their achievement with a whopping 97.4-tesla field. For perspective, Earth’s magnetic field is 0.0004 tesla, while a junk-yard magnet is 1 tesla and a medical MRI scan has a magnetic field of 3 tesla.

The ability to create pulses of extremely high magnetic fields nondestructively (high-power magnets routinely rip themselves to pieces due to the large forces involved) provides researchers with an unprecedented tool for studying fundamental properties of materials, from metals and superconductors to semiconductors and insulators. The interaction of high magnetic fields with electrons within these materials provides valuable clues for scientists about the properties of materials. With the recent record-breaking achievement, the Pulsed Field Facility at LANL, a national user facility, will routinely provide scientists with magnetic pulses of 95 tesla, enticing the worldwide user community to Los Alamos for a chance to use this one-of-a-kind capability.

The record puts the Los Alamos team within reach of delivering a magnet capable of achieving 100 tesla, a goal long sought by researchers from around the world, including scientists working at competing magnet labs in Germany, China, France, and Japan.

Such a powerful nondestructive magnet could have a profound impact on a wide range of scientific investigations, from how to design and control material functionality to research into the microscopic behavior of phase transitions. This type of magnet allows researchers to carefully tune material parameters while perfectly reproducing the non-invasive magnetic field. Such high magnetic fields confine electrons to nanometer scale orbits, thereby helping to reveal the fundamental quantum nature of a material.

Thursday’s experiment was met with as much excitement as trepidation by the group of condensed matter scientists, high-field magnet technicians, technologists, and pulsed-magnet engineers who gathered to witness the NHMFL-PFF retake the world record. Crammed into the tight confines of the Magnet Lab’s control room, they gathered, lab notebooks or caffeine of choice in hand. Their conversation reflected a giddy sense of anticipation tempered with nervousness.

With Mike Gordon commanding the controls that draw power off of a massive 1.4-gigawatt generator system and directs it to the magnet, all eyes and ears were keyed to video monitors showing the massive 100 tesla Multishot Magnet and the capacitor bank located in the now eerily empty Large Magnet Hall next door. The building had been emptied as a standard safety protocol.

Scientists heard a low warping hum, followed by a spine-tingling metallic screech signaling that the magnet was spiking with a precisely distributed electric current of more than 100 megajoules of energy. As the sound dissipated and the monitors confirmed that the magnet performed perfectly, attention turned to data acquired during the shot through two in-situ measurements — proof positive that the magnet had achieved 92.5 tesla, thus yanking back from a team of German scientists a record that Los Alamos had previously held for five years.

The next day’s even higher 97.4-tesla achievement was met with high-fives and congratulatory pats on the back. Later, researchers Charles Mielke, Neil Harrison, Susan Seestrom, and Albert Migliori certified with their signatures the data that would be sent to the Guiness Book of World Records.

The NHMFL is sponsored primarily by the National Science Foundation, Division of Materials Research, with additional support from the State of Florida and the DOE. These recent successes were enabled by long-term support from the U.S. Department of Energy‘s Office of Basic Energy Sciences, and the National Science Foundation‘s 100 Tesla Multi-Shot magnet program.

Source: DOE/Los Alamos National Laboratory

Better ‘photon loops’ may be key to computer and physics advances

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Artist's rendering of the proposed <b>JQI</b> fault-tolerant photon delay device for a future photon-based microchip. The devices ordinarily have a single row of resonators; using multiple rows like this provides alternative pathways for the photons to travel around any physical defects.

Surprisingly, transmitting information-rich photons thousands of miles through fiber-optic cable is far easier than reliably sending them just a few nanometers through a computer circuit. However, it may soon be possible to steer these particles of light accurately through microchips because of research performed at the Joint Quantum Institute of the National Institute of Standards and Technology (NIST) and the University of Maryland, together with Harvard University. The scientists behind the effort say the work not only may lead to more efficient information processors on our desktops, but also could offer a way to explore a particularly strange effect of the quantum world known as the quantum Hall effect in which electrons can interfere with themselves as they travel in a magnetic field. The corresponding physics is rich enough that its investigation has already resulted in three Nobel Prizes, but many intriguing theoretical predictions about it have yet to be observed.

The advent of optical fibers a few decades ago made it possible for dozens of independent phone conversations to travel long distances along a single glass cable by, essentially, assigning each conversation to a different color-each narrow strand of glass carrying dramatic amounts of information with little interference.

Ironically, while it is easy to send photons far across a town or across the ocean, scientists have a harder time directing them to precise locations across short distances-say, a few hundred nanometers-and this makes it difficult to employ photons as information carriers inside computer chips.

“We run into problems when trying to use photons in microcircuits because of slight defects in the materials chips are made from,” says Jacob Taylor, a theoretical physicist at NIST and JQI. “Defects crop up a lot, and they deflect photons in ways that mess up the signal.”

These defects are particularly problematic when they occur in photon delay devices, which slow the photons down to store them briefly until the chip needs the information they contain. Delay devices are usually constructed from a single row of tiny resonators, so a defect among them can ruin the information in the photon stream. But the research team perceived that using multiple rows of resonators would build alternate pathways into the delay devices, allowing the photons to find their way around defects easily.

As delay devices are a vital part of computer circuits, the alternate-pathway technique may help overcome obstacles blocking the development of photon-based chips, which are still a dream of computer manufacturers. While that application would be exciting, lead author Mohammad Hafezi says the prospect of investigating the quantum Hall effect with the same technology also has great scientific appeal.

“The photons in these devices exhibit the same type of interference as electrons subjected to the quantum Hall effect,” says Hafezi, a research associate at JQI. “We hope these devices will allow us to sidestep some of the problems with observing the physics directly, instead allowing us to explore them by analogy.”

Source: National Institute of Standards and Technology (NIST)

Predicting space climate change

The recent decline in the open magnetic flux of the Sun heralds the end of the Grand Solar Maximum (GSM) that has persisted throughout the space age, during which the largest-fluence Solar Energetic Particle (SEP) events have been rare and Galactic Cosmic Ray (GCR) fluxes have been relatively low. In the absence of a predictive model of the solar dynamo, we here make analogue forecasts by studying past variations of solar activity in order to evaluate how long-term change in space climate may influence the hazardous energetic particle environment of the Earth in the future. We predict the probable future variations in GCR flux, near-Earth interplanetary magnetic field (IMF), sunspot number, and the probability of large SEP events, all deduced from cosmogenic isotope abundance changes following 24 GSMs in a 9300-year record. http://dx.doi.org/10.1029/2011GL048489

Juno space probe prepares for a suicide mission to Jupiter


Nasa’s Juno mission to Jupiter, and the mythological roots of its name. Video: Nasa Link to this video

A spacecraft destined to become the fastest manmade object in history is set for launch on Friday on a mission that will end in a high-speed crash into the largest planet in the solar system.

Nasa’s $1bn Juno satellite is bound for Jupiter on a mission to peer through the clouds of the Jovian atmosphere and deep into the planet’s interior.

The 3.5-tonne probe is due to blast off on an Atlas V rocket from Cape Canaveral in Florida at 4.34pm BST (11.34am local time) on a 2,800 million kilometre voyage that will take it far out into the solar system before looping back around the Earth in a slingshot manoeuvre that will hurl the spacecraft towards its target.

Before Juno arrives at its destination, rocket motors will fire up and set the satellite spinning like a three-bladed propeller so that each of its scientific instruments can get a regular and clear view of the planet.

The five-year journey will bring Juno in over the north pole of Jupiter to begin the first of 33 orbits at speeds of up to 160,000kph. To minimise damage from Jupiter’s intense radiation fields, the spacecraft will follow a highly elliptical orbit that goes far out into space before returning low over the north and south poles.

The spinning satellite will photograph Jupiter’s spectacular aurora and map its intense magnetic and gravitational fields for a year in a bid to understand the planet’s formation and the inner workings that make it one of the most extraordinary bodies in the solar system.

“Juno will help us understand how the solar system formed, and how all the planets formed, from the solar nebula some 4.5bn years ago,” said Jack Connerney, deputy principal investigator on the Juno mission at Nasa’s Goddard Space Flight Centre in Maryland.

“After the formation of the sun, the vast majority of mass left over in the solar system resides in Jupiter. The planet is so massive that none of the material that was originally there could escape its gravity, so Jupiter is effectively a sample of the primitive solar nebula that all the planets formed from.”

A major question Juno will seek to answer is the nature of the dynamo that generates Jupiter’s powerful magnetic field, which is 20,000 times stronger than that of the Earth. On our home planet, the magnetic field is produced by a spinning core of molten iron.

“Jupiter’s magnetic field may be generated by the layer of liquid metallic hydrogen in the planet’s interior, but another school of thought says it may be generated from a layer of molecular hydrogen above that. With a good map of the magnetic field, we should be able to tell which it is,” Connerney told the Guardian.

Other instruments aboard Juno will compile detailed maps of Jupiter’s gravitational field to reveal how heavier elements are distributed throughout the planet, and confirm whether or not it has a sold rocky core.

Stowed away on the spacecraft will be a plaque dedicated to Galileo Galilei, who discovered moons in orbit around Jupiter in 1610, and three Lego figures – of Galileo, the Roman god Jupiter and his wife, Juno.

The electronics aboard Juno are encased in a titanium vault designed to protect components from high levels of radiation, but even with this shielding, the spacecraft is expected to sustain serious damage after a year in Jupiter’s orbit. Any loss of control of Juno could leave the spacecraft in danger of crashing into Europa, one of Jupiter’s moons, where future missions may look for signs of extraterrestrial life, so Nasa controllers have developed a final act for the mission.

“You hear of Nasa missions that go on and on, but to be sure we don’t contaminate the surface of Europa, we are going to send Juno crashing into Jupiter,” Connerney said. “I think we will communicate with Juno until the last moment.”

The Great Red Spot on Jupiter’s flank is a hurricane twice the size of Earth that has raged for 300 years. The storms that build on the planet produce winds up to 600kph and flashes of lightning 100 times brighter than those on Earth.

The gas giant is 1,300 times larger than Earth and made almost entirely of hydrogen. It carries more than twice the mass of all the other planets in the solar system combined.

The intense gravitational forces inside the planet compress the gas to such an extent it forms a vast subsurface sea of liquid metallic hydrogen that reaches more than 25,000km deep. Around 10% of Jupiter is helium with trace levels of heavier elements. The core may be solid rock.

Spacewatch: Juno to Jupiter

Juno, the next spacecraft in Nasa‘s New Frontiers programme, is now poised for launch atop an Atlas 5 rocket at Cape Canaveral. Its destination is Jupiter and liftoff should occur during the three weeks that begin on Friday, the 5th, with arrival at the giant planet scheduled for the same date in 2016. The five year journey includes a return fly-by visit to the Earth to receive a “gravity assist” boost in October 2013.

The craft is due to enter an elongated orbit about Jupiter, taking 11 days to loop within 4,300 km of Jupiter’s equatorial cloud-tops at its low-point, or perijove, and a high-point, or apojove, some 2.7 million km further out, beyond the orbit of Callisto which is the farthest of Jupiter’s four main moons.

The orbit sweeps over the poles to provide our first clear views of those regions and their spectacular displays of aurorae. It also means that Juno avoids the worst of the Jovian radiation belts, though the craft’s sensitive electronics must still be shielded within a protective titanium vault. Powered by the first solar arrays to be deployed so far from the Sun, Juno’s prime aim it to study Jupiter’s origin and composition.

It should tell us how much water and ammonia exist in the atmosphere, how the latter varies and moves far below the visible clouds, and whether Jupiter has a rocky heart, perhaps even larger than the Earth. And how does its intense magnetic field shape its environment, including the aurorae and those lethal radiation belts?

A hot topic: Radioactive decay is key ingredient behind Earth’s heat, research shows

Nearly half of the Earth‘s heat comes from the radioactive decay of materials inside, according to a large international research collaboration that includes a Kansas State University physicist. Glenn Horton-Smith, associate professor of physics, was part of a team gathering some of the most precise measurements of the Earth‘s radioactivity to date by observing the activity of subatomic particles — particularly uranium, thorium and potassium. Their work appears in the July issue of Nature Geoscience in the article “Partial radiogenic heat model for Earth revealed by geoneutrino measurements.”

“It is a high enough precision measurement that we can make a good estimate of the total amount of heat being produced by these fissions going on in naturally occurring uranium and thorium,” Horton-Smith said.

Itaru Shimizu of Tohoku University in Sendai, Japan, and collaborating physicists, including Horton-Smith, made the measurement using the KamLAND neutrino detector in Japan. KamLAND, short for Kamioka Liquid-Scintillator Antineutrino Detector, is an experiment at the Kamioka Observatory, an underground neutrino observatory in Toyama, Japan. Neutrinos are neutral elementary particles that come from nuclear reactions or radioactive decay. Because of their small size, large detectors are needed to capture and measure them.

Horton-Smith was involved with developing the KamLAND detector from 1998 to 2000 and he helped prepare it to begin taking data in 2002. Several years later, he was involved in an upgrade of the detector to help it detect solar neutrinos. For the most recent project, Horton-Smith’s role was to help keep the detector running and taking measurements from nuclear reactors in Japan.

By gathering measurements of radioactive decay, the KamLAND researchers were able to observe geoneutrinos, or neutrinos from a geological source. They gathered data from 2002 to 2009 and had published their preliminary findings in Nature in 2005.

“That was the first time that observation of excess antineutrinos and a neutrino experiment were attributed to geoneutrinos,” Horton-Smith said.

Previous research has shown that Earth‘s total heat output is about 44 terawatts, or 44 trillion watts. The KamLAND researchers found roughly half of that — 29 terawatts — comes from radioactive decay of uranium, thorium and other materials, meaning that about 50 percent of the earth’s heat comes from geoneutrinos.

The researchers estimate that the other half of the earth’s heat comes from primordial sources left over when the earth formed and from other sources of heat. Earth‘s heat is the cause behind plate movement, magnetic fields, volcanoes and seafloor spreading.

“These results helps geologists understand a model for the earth’s interior,” Horton-Smith said. “Understanding the earth’s heat source and where it is being produced affects models for the earth’s magnetic field, too.”

The research also provides better insight for instances when materials within the earth undergo natural nuclear reactions. Based on their research, the physicists placed a five-terawatt limit on the heat cause by such reactions, meaning that if there is any geological heating from nuclear reactors in the Earth‘s core it is quite small when compared to heat from ordinary radioactive decay.

Source: Kansas State University

The art of magnetic writing

Computer files that allow us to watch videos, store pictures, and edit all kinds of media formats are nothing else but streams of “0″ and “1″ digital data, that is, bits and bytes. Modern computing technology is based on our ability to write, store, and retrieve digital information as efficiently as possible. In a computer hard disk, this is achieved in practice by writing information on a thin magnetic layer, where magnetic domains pointing “up” represent a “1″ and magnetic domains pointing down represent a “0″. The size of these magnetic domains has now reached a few tens of nanometers, allowing us to store a Terabyte of data in the space of just about 4 square centimeters. Miniaturization, however, has created numerous problems that physicists and engineers worldwide struggle to solve at the pace demanded by an ever-growing information technology industry. The process of writing information on tiny magnetic bits one by one, as fast as possible, and with little energy consumption, represents one of the biggest hurdles in this field.

As reported this week in Nature, a team of scientists from the Catalan Institute of Nanotechnology, ICREA, and Universitat Autonoma de Barcelona, Mihai Miron, Kevin Garello, and Pietro Gambardella, in collaboration with Gilles Gaudin and colleagues working at SPINTEC in Grenoble, France, have discovered a new method to write magnetic data that fulfils all of these requirements.

Magnetic writing is currently performed using magnetic fields produced by wires and coils, a methodology suffering severe limitations in scalability and energy efficiency. The new technique eliminates the need for cumbersome magnetic fields and provides extremely simple and reversible writing of memory elements by injecting an electric current parallel to the plane of a magnetic bit. The key to this effect lies in engineering asymmetric interfaces at the top and bottom of the magnetic layer, which induces an electric field across the material, in this case a cobalt film less than one nanometer thick sandwiched between platinum and aluminum oxide.

Due to subtle relativistic effects, electrons traversing the Co layer effectively see the material’s electric field as a magnetic field, which in turn twists their magnetization. Depending on the intensity of the current and the direction of the magnetization, one can induce an effective magnetic field, intrinsic to the material that is strong enough to reverse the magnetization. The research team showed that this method works reliably at room temperature using current pulses that last less than 10 ns in magnetic bits as small as 200 x 200 square nanometers, while further miniaturization and faster switching appear easily within reach. Although there is currently no theory describing this effect, this work has many interesting applications for the magnetic recording industry, and in particular for the realization of magnetic random access memories, so-called MRAMs. By replacing standard RAMs, which need to be refreshed every few milliseconds, non-volatile MRAMs would allow instant power up of a computer and also save a substantial amount of energy.

An additional advantage of the discovery reported here is that current-induced magnetic writing is more efficient in “hard” magnetic layers than in “soft” ones. This is somehow counterintuitive, as soft magnetic materials are by definition the easier to switch using external magnetic fields, but very practical since hard magnets can be miniaturized to nanometer dimensions without losing their magnetic properties. This would allow the information storage density to be increased without compromising the ability to write it. The results of this work have also led to three patent applications dealing with the fabrication of magnetic storage and logic devices.

Source: Institut Català de Nanotecnologia