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‘Negative mass’ created at Washington State University

Experimental images of an expanding spin-orbit superfluid Bose-Einstein condensate at different expansion times (credit: M. A. Khamehchi et al./Physical Review Letters)

Washington State University (WSU) physicists have created a fluid with “negative mass,” which means that if you push it, it accelerates toward you instead of away, in apparent violation of Newton’s laws.

The phenomenon can be used to explore some of the more challenging concepts of the cosmos, said Michael Forbes, PhD, a WSU assistant professor of physics and astronomy and an affiliate assistant professor at the University of Washington. The research appeared Monday (April 17, 2017)  in the journal Physical Review Letters.

How to create negative mass

The researchers created the conditions for negative mass by cooling about 10,000 rubidium atoms to just above absolute zero, creating a Bose-Einstein condensate (in which individual atoms move as one object). In this state, particles move extremely slowly and, following the principles of quantum mechanics, behave like waves. They also synchronize and move in unison as a “superfluid” that flows without losing energy.

The lasers trapped the atoms as if they were in a bowl measuring less than a hundred micrometers across. At this point, the rubidium superfluid has regular mass. Breaking the bowl will allow the rubidium to rush out, expanding as the rubidium in the center pushes outward.

To create negative mass, the researchers applied a second set of lasers that kicked the atoms back and forth and changed the way they spin. Now when the rubidium rushes out fast enough, if behaves as if it has negative mass.

The technique used by the WSU researchers avoids some of the underlying defects encountered in previous attempts to create negative mass. It could hold clues to the behavior occurring in the heart of ultracold neutron stars, which also act as superfluids, and cosmological phenomena like black holes and dark energy, said Forbes.

The work was supported in part by a WSU New Faculty Seed Grant and the National Science Foundation.

Abstract of Negative-Mass Hydrodynamics in a Spin-Orbit–Coupled Bose-Einstein Condensate

A negative effective mass can be realized in quantum systems by engineering the dispersion relation. A powerful method is provided by spin-orbit coupling, which is currently at the center of intense research efforts. Here we measure an expanding spin-orbit coupled Bose-Einstein condensate whose dispersion features a region of negative effective mass. We observe a range of dynamical phenomena, including the breaking of parity and of Galilean covariance, dynamical instabilities, and self-trapping. The experimental findings are reproduced by a single-band Gross-Pitaevskii simulation, demonstrating that the emerging features—shock waves, soliton trains, self-trapping, etc.—originate from a modified dispersion. Our work also sheds new light on related phenomena in optical lattices, where the underlying periodic structure often complicates their interpretation.

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Astronomers detect atmosphere around Earth-like planet

Artist’s impression of atmosphere around super-Earth planet GJ 1132b (credit: MPIA)

Astronomers have detected an atmosphere around an Earth-like planet beyond our solar system for the first time: the super-Earth planet GJ 1132b in the Southern constellation Vela, at a distance of 39 light-years from Earth.

The team, led by Keele University’s John Southworth, PhD, used the 2.2 m ESO/MPG telescope in Chile to take images of the planet’s host star GJ 1132. The astronomers made the detection by measuring the slight decrease in brightness, finding that its atmosphere absorbed some of the starlight while transiting (passing in front of) the host star. Previous detections of exoplanet atmospheres all involved gas giants reminiscent of a high-temperature Jupiter.

Possible “water world”

“With this research, we have taken the first tentative step into studying the atmospheres of smaller, Earth-like, planets,” said Southworth. “We simulated a range of possible atmospheres for this planet, finding that those rich in water and/or methane would explain the observations of GJ 1132b. The planet is significantly hotter and a bit larger than Earth, so one possibility is that it is a ‘water world’ with an atmosphere of hot steam.”

Very low-mass stars are extremely common (much more so than Sun-like stars), and are known to host lots of small planets. But they also show a lot of magnetic activity, causing high levels of X-rays and ultraviolet light to be produced, which might completely evaporate the planets’ atmospheres. The properties of GJ 1132b show that an atmosphere can endure for a billion years without being destroyed, the astronomers say.

Given the huge number of very low-mass stars and planets, this could mean the conditions suitable for life are common in the Universe, the astronomers suggest.

The discovery, reported March 31 in Astronomical Journal, makes GJ 1132b one of the highest-priority targets for further study by current top facilities, such as the Hubble Space Telescope and ESO’s Very Large Telescope, as well as the James Webb Space Telescope, slated for launch in 2018.

The team also included astronomers at Luigi Mancini Max Planck Institute for Astronomy (MPIA), University of Rome, University of Cambridge, and Stockholm University.

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Neural networks promise sharpest-ever telescope images

From left to right: an example of an original galaxy image; the same image deliberately degraded; the image after recovery by the neural network; and for comparison, deconvolution. This figure visually illustrates the neural-networks’s ability to recover features that conventional deconvolutions cannot. (credit: K. Schawinski / C. Zhang / ETH Zurich)

Swiss researchers are using neural networks to achieve the sharpest-ever images in optical astronomy. The work appears in an open-access paper in Monthly Notices of the Royal Astronomical Society.

The aperture (diameter) of any telescope is fundamentally limited by its lens or mirror. The bigger the mirror or lens, the more light it gathers, allowing astronomers to detect fainter objects, and to observe them more clearly. Other factors affecting image quality are noise and atmospheric distortion.

The Swiss study uses “generative adversarial network” (GAN) machine-learning technology (see this KurzweilAI article) to go beyond this limit by using two neural networks that compete with each other to create a series of more realistic images. The researchers first train the neural network to “see” what galaxies look like (using blurred and sharp images of the same galaxy), and then ask it to automatically fix the blurred images of a galaxy, converting them to sharp ones.

Schematic illustration of the neural-network training process. The input is a set of original images. From these, the researchers automatically generate degraded images, and train a GAN. In the testing phase, only the generator will be used to recover images. (credit: K. Schawinski / C. Zhang / ETH Zurich)

The trained neural networks were able to recognize and reconstruct features that the telescope could not resolve, such as star-forming regions and dust lanes in galaxies. The scientists checked the reconstructed images against the original high-resolution images to test its performance, finding it better able to recover features than anything used to date.

“We can start by going back to sky surveys made with telescopes over many years, see more detail than ever before, and, for example, learn more about the structure of galaxies,” said lead author Prof. Kevin Schawinski of ETH Zurich in Switzerland. “There is no reason why we can’t then apply this technique to the deepest images from Hubble, and the coming James Webb Space Telescope, to learn more about the earliest structures in the Universe.”

ETH Zurich is hosting this work on the space.ml cross-disciplinary astrophysics/computer-science initiative, where the code is available to the general public.

Abstract of Generative adversarial networks recover features in astrophysical images of galaxies beyond the deconvolution limit

Observations of astrophysical objects such as galaxies are limited by various sources of random and systematic noise from the sky background, the optical system of the telescope and the detector used to record the data. Conventional deconvolution techniques are limited in their ability to recover features in imaging data by the Shannon–Nyquist sampling theorem. Here, we train a generative adversarial network (GAN) on a sample of 4550 images of nearby galaxies at 0.01 < z < 0.02 from the Sloan Digital Sky Survey and conduct 10× cross-validation to evaluate the results. We present a method using a GAN trained on galaxy images that can recover features from artificially degraded images with worse seeing and higher noise than the original with a performance that far exceeds simple deconvolution. The ability to better recover detailed features such as galaxy morphology from low signal to noise and low angular resolution imaging data significantly increases our ability to study existing data sets of astrophysical objects as well as future observations with observatories such as the Large Synoptic Sky Telescope (LSST) and the Hubble and James Webb space telescopes.

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Compact new microscope chemically identifies micrometer-sized particles

Multiple types of micrometer-sized particles are simultaneously illuminated by a far-infrared laser and a green laser beam. Absorption of the infrared laser energy by the particles increases their temperatures, causing them to expand and slightly altering their visible-light optical properties. These changes are unique to the material composition of each particle and can be measured by examining the modulation of scattered green light from each particle. (credit: Ryan Sullenberger, MIT Lincoln Laboratory)

MIT researchers have developed a radical design for a low-cost, miniaturized microscope that can chemically identify individual micrometer-sized particles. It could one day be used in airports or other high-security venues as a highly sensitive and low-cost way to rapidly screen people for microscopic amounts of potentially dangerous materials. It could also be used for scientific analysis of very small samples or for measuring the optical properties of materials.

Optical setup for PMMS measurement scheme. A tunable far-IR laser (QCL) or pump projects laser light (shown in this illustration as red, but actually invisible far-IR, or thermal energy) and a 532 nm laser (probe) projects green light onto the same location on a sample, which consists of microspheres deposited onto a ZnSe substrate in this experiment. A visible-light camera fitted with a 16× microscopic lens images the particles directly. The white LED is used to help locate the particles. (credit: R. M. Sullenberger et al./ Optics Letters)

In an open-access paper in the journal Optics Letters, from The Optical Society (OSA), the researchers demonstrated their new “photothermal modulation of Mie scattering” (PMMS) microscope by measuring infrared spectra of individual 3-micrometer spheres made of silica or acrylic. The new technique uses a simple optical setup consisting of compact components that will allow the instrument to be miniaturized into a portable device about the size of a shoebox.

The new microscope’s use of visible wavelengths for imaging gives it a spatial resolution of around 1 micrometer, compared to the roughly 10-micrometer resolution of traditional infrared spectroscopy methods. This increased resolution allows the new technique to distinguish and identify individual particles that are extremely small and close together.*

“If there are two very different particles in the field of view, we’re able to identify each of them,” said Stolyarov. “This would never be possible with a conventional infrared technique because the image would be indistinguishable.”

“The most important advantage of our new technique is its highly sensitive, yet remarkably simple design,” said Ryan Sullenberger, associate staff at MIT Lincoln Labs and first author of the paper. “It provides new opportunities for nondestructive chemical analysis while paving the way towards ultra-sensitive and more compact instrumentation.”

Probing spectral fingerprints

A typical far-IR spectrometer (credit: NYU)

Infrared spectroscopy is typically used to identify unknown materials because almost every material can be identified by its unique far-infrared absorption spectrum, or fingerprint. The new method detects this fingerprint without using actual far-infrared detectors, which add significant bulk to traditional instruments. That limits their use as portable devices — also because of their requirement for cooling.

The new technique works by illuminating particles with both an far-infrared laser and a green laser. The far-infrared laser deposits energy into the particles, causing them to heat up and expand. The green laser light is then scattered by these heated particles. A visible-wavelength camera is used to monitor this scattering, tracking physical changes of the individual particles through the microscope’s lens.

The instrument can be used to identify the material composition of individual particles by tuning the far-infrared laser to different wavelengths and collecting the visible scattered light at each wavelength. The slight heating of the particles doesn’t impart any permanent changes to the material, making the technique ideal for non-destructive analysis.

The ability to excite particles with infrared light and then look at their scattering with visible wavelengths — a process called photothermal modulation of Mie scattering — has been used since the 1980s. This new work uses more advanced optical components to create and detect the Mie scattering and is the first to use an imaging configuration to detect multiple species of particles.

“We’re actually imaging the area that we’re interrogating,” said Alexander Stolyarov, technical staff and a co-author of the paper. “This means we can simultaneously probe multiple particles on the surface at the same time.”

Compact, tunable infrared laser

The development of compact, tunable quantum-cascade infrared lasers was a key enabling technology for the new technique. The researchers combined a quantum-cascade laser with a very stable visible laser source and a commercially available scientific-grade camera.

“We are hoping to see an improvement in high-power wavelength-tunable quantum cascade lasers,” said Sullenberger. “A more powerful infrared laser enables us to interrogate larger areas in the same amount of time, allowing more particles to be probed simultaneously.”

The researchers plan to test their microscope on additional materials, including particles that are not spherical in shape. They also want to test their setup in more realistic environments that might contain interfering particles.

The work was supported by the U.S. Assistant Secretary of Defense for Research and Engineering under an Air Force contract.

* “By using a visible probe beam and camera for registering the particle absorption, we are able to spectroscopically identify individual particles that are spaced closer than the IR diffraction limit, which represents a significant improvement over conventional IR spectroscopic imaging techniques,” the authors note.

Abstract of Spatially-resolved individual particle spectroscopy using photothermal modulation of Mie scattering

We report a photothermal modulation of Mie scattering (PMMS) method that enables concurrent spatial and spectral discrimination of individual micron-sized particles. This approach provides a direct measurement of the “fingerprint” infrared absorption spectrum with the spatial resolution of visible light. Trace quantities (tens of picograms) of material were deposited onto an infrared-transparent substrate and simultaneously illuminated by a wavelength-tunable intensity-modulated quantum cascade pump laser and a continuous-wave 532 nm probe laser. Absorption of the pump laser by the particles results in direct modulation of the scatter field of the probe laser. The probe light scattered from the interrogated region is imaged onto a visible camera, enabling simultaneous probing of spatially-separated individual particles. By tuning the wavelength of the pump laser, the IR absorption spectrum is obtained. Using this approach, we measured the infrared absorption spectra of individual 3 μm PMMA and silica spheres. Experimental PMMS signal amplitudes agree with modeling using an extended version of the Mie scattering theory for particles on substrates, enabling the prediction of the PMMS signal magnitude based on the material and substrate properties.

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How to 3D-print your own baby universe

Cosmic microwave background radiation — 2D view (credit: NASA)

Researchers have created a 3D-printed cosmic microwave background (CMB) — a map of the oldest light in the universe — and have provided the files for download.

The cosmic microwave background (CMB) is the “glow” that the universe had in the microwave range. It maps the oldest light in the universe and tells astronomers more about the early universe and the formation of structures within it, such as galaxies. It was imprinted when the universe was only 380,000 years old — when the universe first became transparent, instead of an opaque fog of plasma and radiation.

The Planck satellite is making increasingly more detailed maps of the CMB, which are increasingly difficult to view and explore. To address this issue, Dave Clements, PhD, from the Department of Physics at Imperial College London and team have created plans for 3D printing the CMB. The work is published (open access) in the European Journal of Physics.

3D-printed CMB model. The bumps (not to scale) and associated colors represent both higher temperatures and higher densities of matter (credit: D. L. Clements et al./European Journal of Physics)

The 3D-printed model represents differences in the temperature as bumps and dips on a spherical surface and also as colors (from blue for coldest to red as warmest, corresponding to colors in the flat view). These temperature differences relate to different densities of matter, which correspond to the formation of structures in the universe, including stars, galaxies, galaxy clusters, and superclusters.

The CMB can be printed from a range of 3D printers, and two file types have been created by the team: one for simple single-color structures and one that includes the temperature differences represented as colors as well as bumps and dips. The files are free to download.

Dave Clements’ latest book, Infrared Astronomy — Seeing the Heat: from William Herschel to the Herschel Space Observatory, is available now.

Abstract of Cosmic sculpture: a new way to visualise the cosmic microwave background

3D printing presents an attractive alternative to visual representation of physical datasets such as astronomical images that can be used for research, outreach or teaching purposes, and is especially relevant to people with a visual disability. We here report the use of 3D printing technology to produce a representation of the all-sky cosmic microwave background (CMB) intensity anisotropy maps produced by the Planck mission. The success of this work in representing key features of the CMB is discussed as is the potential of this approach for representing other astrophysical data sets. 3D printing such datasets represents a highly complementary approach to the usual 2D projections used in teaching and outreach work, and can also form the basis of undergraduate projects. The CAD files used to produce the models discussed in this paper are made available.

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Zapping deep tumors with microwave-heated photosensitizer nanoparticle

A schematic illustration of microwave-induced photodynamic therapy for cancer treatment (credit: UTA)

Physicists at The University of Texas at Arlington have invented a new photosensitizer  nanoparticle called copper-cysteamine (Cu-Cy) that when heated by microwave energy can precisely zap cancer cells deep in the body .

Photodynamic therapy kills cancer cells when a photosensitizer* nanoparticle introduced into tumor tissue is stimulated by (typically) near-infrared light, generating toxic reactive oxygen species (ROS), such as singlet oxygen, by photoexcitation. However, near-IR light cannot penetrate deeper than 10 mm in tissue while retaining enough energy to activate ROS.**

The new “microwave-induced photodynamic therapy (MIPDT)” method can “propagate through all types of tissues and target deeply situated tumors, without harming surrounding tissue,” according to Wei Chen, UTA professor of physics and lead author of the study, published in the October 2016 issue of The Journal of Biomedical Nanotechnology.***

TEM images of Cu-Cy particles (left) and particles after uptake by osteosarcoma cells (right) (Mengyu Yao et al./J. Biomed. Nanotechnol.)

The new nanoparticle demonstrates “very low toxicity, is easy to make and inexpensive, and also emits intense luminescence, which means it can also be used as an imaging agent,” said Chen.

*  A photosensitizer is a molecule that can be activated by light to a high-energy state. It may then collide with oxygen and transfer its extra energy to oxygen, forming toxic singlet oxygen.

** In previous research, the researchers found that the Cu-Cy nanoparticle could be activated by X-rays to produce singlet oxygen and slow the growth of tumors. X-ray radiation, however, poses significant risks to patients and can harm healthy tissue. Other photodynamic therapy activation methods that have been explored, with limited results, include upconversion nanoparticles that can be excited at NIR and emit light in the UV-visible range, scintillation or afterglow nanoparticles, and Cerenkov light (generated in nuclear reactors).

*** Scientists from the The Guangdong Key Laboratory of Orthopaedic Technology and Implant Materials, Department of Orthopedics, Guangzhou General Hospital of Guangzhou Military Command, Guangzhou, China; and the Physics Department at Beihang University in Beijing, China, were also involved in the research. The U.S. Army Medical Research Acquisition Activity, the National Science Foundation, the Department of Homeland Security’s joint Academic Research Initiative program, the National Basic Research Program of China, the National Natural Science Foundation of China, and the five-year plan of the Chinese Military.

Abstract of A New Modality for Cancer Treatment—Nanoparticle Mediated Microwave Induced Photodynamic Therapy

Photodynamic therapy (PDT) has attracted ever-growing attention as a promising modality for cancer treatment. However, due to poor tissue penetration by light, photodynamic therapy has rarely been used for deeply situated tumors. This problem can be solved if photosensitizers are activated by microwaves (MW) that are able to penetrate deeply into tissues. Here, for the first time, we report microwave-induced photodynamic therapy and exploit copper cysteamine nanoparticles as a new type of photosensitizer that can be activated by microwaves to produce singlet oxygen for cancer treatment. Both in vitro and in vivo studies on a rat osteosarcoma cell line (UMR 106-01) have shown significant cell destruction using copper cysteamine (Cu-Cy) under microwave activation. The heating effects and the release of copper ions from Cu-Cy upon MW stimulation are the main mechanisms for the generation of reactive oxygen species that are lethal bullets for cancer destruction. The copper cysteamine nanoparticle-based microwave-induced photodynamic therapy opens a new door for treating cancer and other diseases.

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Nobel Prize in Chemistry 2016 awarded to three pioneers of molecular machines

The Nobel Prize in Chemistry 2016 was awarded today to Jean-Pierre Sauvage, PhD, Sir J. Fraser Stoddart,PhD, and Bernard L. Feringa, PhD, for their design and production of molecular machines. They have developed molecules with controllable movements, which can perform a task when energy is added.

Jean-Pierre Sauvage used a copper ion to interlock molecules using a mechanical bond. (credit: The Royal Swedish Academy of Sciences)

The first step towards a molecular machine was taken by Jean-Pierre Sauvage in 1983, when he succeeded in linking two ring-shaped molecules together to form a chain, called a catenane. Normally, molecules are joined by strong covalent bonds in which the atoms share electrons, but in the chain they were instead linked by a freer mechanical bond. For a machine to be able to perform a task it must consist of parts that can move relative to each other. The two interlocked rings fulfilled exactly this requirement.

Fraser Stoddart created a rotaxane cyclophane ring that could act as a molecular shuttle, moving along an axle in a controlled manner. (credit: The Royal Swedish Academy of Sciences)

The second step was taken by Fraser Stoddart in 1991, when he developed a rotaxane. He threaded a rotaxane cyclophane molecular ring onto a thin molecular axle and demonstrated that the ring was able to move along the axle — the start of applying topological entanglement in the development of molecular machinery.

(Left) Fraser Stoddart’s (left) rotaxane-based “molecular elevator” and (right) “artificial muscle,” using extension and contraction in a daisy-chain rotaxane structure (credit: The Royal Swedish Academy of Sciences)

Among his other developments based on rotaxanes are a molecular lift, a molecular muscle and a molecule-based computer chip.

Ben Feringa’s molecular motor (the first) was mechanically constructed to spin in a particular direction. His research group has optimized the motor so that it now spins at 12 million revolutions per second. (credit: The Royal Swedish Academy of Sciences)

Bernard Feringa was the first person to develop a molecular motor; in 1999 he got a molecular rotor blade to spin continually in the same direction.

Ben Feringa’s four-wheel drive nanocar, with a molecular chassis and four motors that functioned as wheels (credit: The Royal Swedish Academy of Sciences)

Using molecular motors, he has also rotated a glass cylinder that is 10,000 times bigger than the motor and also designed a nanocar.

2016′s Nobel Laureates in Chemistry have taken molecular systems out of equilibrium’s stalemate and into energy-filled states in which their movements can be controlled. In terms of development, the molecular motor is at the same stage as the electric motor was in the 1830s, when scientists displayed various spinning cranks and wheels, unaware that they would lead to electric trains, washing machines, fans and food processors. Molecular machines will most likely be used in the development of things such as new materials, sensors and energy storage systems.

Jean-Pierre Sauvage, born 1944 in Paris, France. Ph.D. 1971 from the University of Strasbourg, France. Professor Emeritus at the University of Strasbourg and Director of Research Emeritus at the National Center for Scientific Research (CNRS), France.
https://isis.unistra.fr/laboratory-of-inorganic-chemistry-jean-pierre-sauvage

Sir J. Fraser Stoddart, born 1942 in Edinburgh, UK. Ph.D. 1966 from Edinburgh University, UK. Board of Trustees Professor of Chemistry at Northwestern University, Evanston, IL, USA.
http://stoddart.northwestern.edu

Bernard L. Feringa, born 1951 in Barger-Compascuum, the Netherlands. Ph.D.1978 from the University of Groningen, the Netherlands. Professor in Organic Chemistry at the University of Groningen, the Netherlands.
www.benferinga.com

 

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‘Star in a jar’ could lead to limitless fusion energy

A test cell for the National Spherical Torus Experiment Upgrade with tokamak in the center. (credit: Elle Starkman/PPPL Office of Communications)

Physicists at the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL)* are building a “star in a jar” — a miniature version of the how our Sun creates energy through fusion. It could provide humankind with near limitless energy, ending dependence on fossil fuels for generating electricity — without contributing greenhouse gases that warm the Earth, and with no long-term radioactive waste.

But that requires a “jar” that can contain superhot plasma — and is low-cost enough to be built around the world. A model for such a “jar,” or fusion device, already exists in experimental form: the tokamak, or fusion reactor. Invented in the 1950s by Soviet physicists, it’s a device that uses a powerful magnetic field to confine plasma (superhot charged gas) in the shape of a torus.

Diagram of magnetic confinement in a tokamak; interactive version: http://www.ccfe.ac.uk/tokamak.aspx (credit: EUROfusion)

There are many experimental tokamaks currently in operation, but they all face physics challenges, the PPPL physicists explain. “For example, they must control the turbulence that arises when superhot plasma particles are subjected to powerful electromagnetic fields. They must also carefully control how the plasma particles interact with the surrounding walls to avoid possible disruptions that can halt fusion reactions if the plasma becomes too dense or impure.”

Spherical tokamak: a new, compact “jar”

Spherical torus/tokamak design for a fusion nuclear science facility showing magnets and other systems and structures (credit: J.E. Menard et al./Nucl. Fusion)

So researchers at PPPL and in and Culham, England  are looking at ways of solving these challenges for the next generation of fusion devices, based on compact spherical tokamaks. They suggest that these could provide the design for possible next steps in fusion energy: a Fusion Nuclear Science Facility (FNSF) that would develop reactor components and also produce electricity as a pilot plant for a commercial fusion power station.

The detailed proposal for such a “jar” is described in a paper published in August 2016 in the journal Nuclear Fusion. “We are opening up new options for future plants,” said lead author Jonathan Menard, program director for the recently completed National Spherical Torus Experiment-Upgrade (NSTX-U) at PPPL. The $94-million upgrade of the NSTX, financed by the U.S. Department of Energy’s Office of Science, began operating last year.

Spherical tokamaks are compact devices shaped like cored apples, compared with the bulkier doughnut-like shape of conventional tokamaks. The increased power of the upgraded PPPL machine and the soon-to-be completed MAST Upgrade device “will push the physics frontier, expand our knowledge of high temperature plasmas, and, if successful, lay the scientific foundation for fusion development paths based on more compact designs,” said PPPL Director Stewart Prager.

Next steps in fusion energy

ITER design (credit: ITER Organization)

The spherical design produces high-pressure plasmas  — the superhot charged gas (also known as the “fourth state of matter”) that fuels fusion reactions, using relatively low, inexpensive magnetic fields. This unique capability points the way to a possible next generation of fusion experiments to complement ITER, the international tokamak that 35 nations including the U.S. are building in France to demonstrate the feasibility of fusion power. ITER will be the largest in the world when completed within the next decade.

But ITER is a doughnut-shaped tokamak. “The main reason we research spherical tokamaks is to find a way to produce fusion at much less cost than conventional tokamaks require,” said Ian Chapman, the newly appointed chief executive of the United Kingdom Atomic Energy Authority and leader of the UK’s magnetic confinement fusion research programme at the Culham Science Centre.

The 43-page Nuclear Fusion paper describes how the spherical design can provide the next steps in fusion energy. A key issue is the size of the hole in the center of the tokamak, which holds and shapes the plasma. In spherical tokamaks, this hole can be half the size of the hole in conventional tokamaks, and that enables control of the plasma with relatively low magnetic fields.

The smaller hole could also be compatible with a blanket system for the FNSF that would breed tritium, a rare isotope of hydrogen. Tritium will fuse with deuterium, another isotope of hydrogen, to produce fusion reactions in next-step tokamaks.

Superconducting magnets for pilot plants

For pilot FNSF plants, the authors call for superconducting magnets to replace the primary copper magnets in the FNSF. Superconducting magnets can be operated far more efficiently than copper magnets, but require thicker shielding. However, recent advances in high-temperature superconductors could lead to much thinner superconducting magnets that would require less space and reduce considerably the size and cost of the machine.

Included in the paper is a description of a device called a “neutral beam injector” that will start and sustain plasma current without relying on a heating coil in the center of the tokamak. Such a coil is not suitable for continuous long-term operation. The neutral beam injector will pump fast-moving neutral atoms into the plasma and will help optimize the magnetic field that confines and controls the superhot gas.

The researchers believe the upgraded NSTX and MAST facilities will provide crucial data for determining the best path for ultimately generating electricity from fusion. The research is funded by the U.S. Department of Energy.

* PPPL, on Princeton University’s Forrestal Campus in Plainsboro, N.J., is devoted to creating new knowledge about the physics of plasmas and to developing practical solutions for the creation of fusion energy. Results of PPPL research have ranged from a portable nuclear materials detector for anti-terrorist use to universally employed computer codes for analyzing and predicting the outcome of fusion experiments. The Laboratory is managed by the University for the U.S. Department of Energy’s Office of Science, which is the largest single supporter of basic research in the physical sciences in the U.S.

Abstract of Fusion nuclear science facilities and pilot plants based on the spherical tokamak

A fusion nuclear science facility (FNSF) could play an important role in the development of fusion energy by providing the nuclear environment needed to develop fusion materials and components. The spherical torus/tokamak (ST) is a leading candidate for an FNSF due to its potentially high neutron wall loading and modular configuration. A key consideration for the choice of FNSF configuration is the range of achievable missions as a function of device size. Possible missions include: providing high neutron wall loading and fluence, demonstrating tritium self-sufficiency, and demonstrating electrical self-sufficiency. All of these missions must also be compatible with a viable divertor, first-wall, and blanket solution. ST-FNSF configurations have been developed simultaneously incorporating for the first time: (1) a blanket system capable of tritium breeding ratio TBR  ≈  1, (2) a poloidal field coil set supporting high elongation and triangularity for a range of internal inductance and normalized beta values consistent with NSTX/NSTX-U previous/planned operation, (3) a long-legged divertor analogous to the MAST-U divertor which substantially reduces projected peak divertor heat-flux and has all outboard poloidal field coils outside the vacuum chamber and superconducting to reduce power consumption, and (4) a vertical maintenance scheme in which blanket structures and the centerstack can be removed independently. Progress in these ST-FNSF missions versus configuration studies including dependence on plasma major radius

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Mystery radio signal may be from distant star system — or a military transmitter

RATAN-600 radio telescope (credit: nat-geo.ru)

A star system 94 light-years away known as HD 164595 is a possible candidate for intelligent life, based on an announcement by an international team of researchers.

On May 15, 2015, Russian astronomers picked up a radio signal on the RATAN-600 radio telescope in Russia “in the direction of HD164595,” an international group of astronomers stated in a document* now being circulated through contact person Alexander Panov, according to Paul Gilster of Centauri Dreams, who blogged about the data on Saturday, August 27, 2016.

This HD164595 system is known to have one planet, a Neptune-sized world in such a very tight orbit, making it unattractive for life. However, there could be other planets in this system that are still undiscovered, said Seth Shostak, Senior Astronomer at the Seti Institute in a post.

“Raw” record of the signal (purple) together with expected shape of the signal (green) for point-like source in the position of HD 164595. (credit: Bursov et al.)

The observations were not ideal, Shostak notes. They were made with a receiver having a bandwidth of 1 GHz — a billion times wider than the bandwidths traditionally used for SETI, and the strength of the signal was 0.75 Janskys (weak). In addition, the RATAN-600 beam design does not uniquely identify the source direction.

Power required for such a signal would be astronomical, he explains. If broadcast in all directions, the required power is 1020 watts (100 billion billion watts) — hundreds of times more energy than all the sunlight falling on Earth. If aimed at us, assuming an antenna the size of the 1000-foot Arecibo instrument, they would still need to transmit more than a trillion watts.

In addition, the signal was received at 11Ghz (2.7 cm wavelength), in a part of the radio spectrum used by the military, so the signal may be due to terrestrial radio-frequency interference, or to gravitational lensing from a more distant source.

Shostak said the SETI Institute swung the Allen Telescope Array (ATA) in the direction of HD 164595 beginning Sunday evening, August 28. No detections reported yet.

The radio signal and the ensuring follow-up investigations will be discussed at the 67th International Astronautical Congress in Guadalajara, Mexico on September 27th.

* “The presentation [was] forwarded to me by Claudio Maccone [the chair of the International Academy of Astronautics Permanent SETI Committee], from which I learn that the team behind the detection was led by N.N. Bursov and included L.N. Filippova, V.V. Filippov, L.M. Gindilis, A.D. Panov, E.S. Starikov, J. Wilson, as well as Claudio Maccone,” said Gilster. The detection was made in Zelenchukskaya, in the Karachay–Cherkess Republic of Russia.

UPDATE 8/31/2016 Added “Monitoring of the continuum of SETI candidates with RATAN-600 (SAO RAS official comment)” to references (H/T: GatorALLin)

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A possible habitable planet is only four light-years away, astronomers discover

Artist’s impression shows a view of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. The double star Alpha Centauri AB also appears in the image to the upper-right of the star Proxima. (credit: ESO/M. Kornmesser)

A rocky planet called Proxima b — the closest exoplanet to us — is in the habitable zone of Proxima Centauri, the closest star to our Solar System, a team of astronomers has found after painstaking observation and data analysis.

The new world orbits its cool red-dwarf parent star every 11.2 days and has a temperature suitable for liquid water to exist on its surface. A paper describing this milestone finding was published online today (Aug. 24) in the journal Nature.

The star Proxima Centauri, which is 4.2 light-years from Earth, in the constellation of Centaurus, is too faint to be seen with the naked eye and is close to the much brighter pair of stars known as Alpha Centauri A and B.

A view of the skies over the European Southern Observatory’s La Silla Observatory in Chile (credit: Y. Beletsky (LCO)/ESO/ESA/NASA/M. Zamani)

During the first half of 2016, the HARPS spectrograph on the European Southern Observatory’s 3.6-meter telescope at La Silla regularly observed the star Proxima Centauri, as did other professional and amateur telescopes around the world in a collaboration known as the Pale Red Dot campaign — looking for a tiny back-and-forth wobble in the star caused by the gravitational pull of an orbiting planet. (Other scientists have also been observing Proxima Centauri for years.)

The two bright stars are (left) Alpha Centauri and (right) Beta Centauri. The faint red star in the center of the red circle is Proxima Centauri. (credit: Skatebiker/CC)

So here’s what the Pale Red Dot data — when combined with earlier observations — shows:

  • At regular intervals, the star Proxima Centauri is approaching Earth at about 5 kilometers per hour — normal human walking pace — and at opposite times in those cycles it is receding at the same speed. This regular pattern repeats with a period of 11.2 days.
  • Analysis of the resulting Doppler shifts (and removing brightness-variation artifacts from the star) indicated the presence of a planet with a mass at least 1.3 times that of the Earth, orbiting about 7 million kilometers from Proxima Centauri (about 5 percent of the distance of Earth for our Sun, and coser than the planet Mercury is to our Sun — but Proxima Centauri is cooler than our Sun).
  • Proxima b is tidally locked to its star (one side is always sunny, the other is dark) and has an estimated temperature that would allow for a liquid state on its surface, thus placing it within the “habitable zone” around the star (assuming water is present). Atmosphere: unknown.
  • Proxima may be strongly affected by ultraviolet and x-ray flares from the star — far more intense than the Earth experiences from the Sun. (Extreme sun glasses recommended if you visit.)

Meanwhile a wild project by Stephen Hawking and philanthropist Yuri Milner — who announced in April a $100 million research and engineering program, Breakthrough Starshot, to study the concept of using laser light beams to propel gram-scale “nanocraft” to 20 percent of light speed to travel to Alpha Centauri — (KurzweilAI: Breakthrough Starshot’ aims to reach Alpha Centauri 20 years after launch) has been vindicated — with a minor detour.

Abstract of A terrestrial planet candidate in a temperate orbit around Proxima Centauri

At a distance of 1.295 parsecs, the red dwarf Proxima Centauri (α Centauri C, GL 551, HIP 70890 or simply Proxima) is the Sun’s closest stellar neighbour and one of the best-studied low-mass stars. It has an effective temperature of only around 3,050 kelvin, a luminosity of 0.15 per cent of that of the Sun, a measured radius of 14 per cent of the radius of the Sun and a mass of about 12 per cent of the mass of the Sun. Although Proxima is considered a moderately active star, its rotation period is about 83 days and its quiescent activity levels and X-ray luminosity are comparable to those of the Sun. Here we report observations that reveal the presence of a small planet with a minimum mass of about 1.3 Earth masses orbiting Proxima with a period of approximately 11.2 days at a semi-major-axis distance of around 0.05 astronomical units. Its equilibrium temperature is within the range where water could be liquid on its surface.