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Category: nuclear energy

How Neutrino Oscillations Affect Supernovae

Numerical models of core-collapse supernovae have matured greatly over the past few decades. With impressive accuracy, they now couple relativistic gravity, magnetohydrodynamics, nuclear physics, and neutrino transport. Neutrinos, copiously produced in the collapsed core, are the main driver of most of these supernovae. Neutrino oscillations are probably the most crucial ingredient that is still missing from the majority of models, even though their presence and possible importance have long been suggested. The reason for this gap in modeling is twofold: Many relevant physical parameters are poorly known, and the most important oscillation processes are very difficult to simulate. Now Ryuichiro Akaho at Waseda University in Japan and colleagues have made a key step toward a self-consistent model and revealed some complexities that arise when incorporating neutrino oscillations [1].

Stars are supported against their own gravity primarily by gas pressure, which is maintained by exothermic nuclear reactions. In high-mass stars, nuclear burning starts with the fusion of hydrogen into helium and continues through progressively heavier elements until the core is dominated by iron-group nuclei, at which point fusion no longer releases energy. Pressure support then no longer suffices to stabilize the core, and it collapses to a protoneutron star, a hot compact object with about 1.5 solar masses concentrated in a radius of a few tens of kilometers. During the collapse, a shock wave forms at this object’s surface and stalls after propagating outward for only about 100 km (Fig. 1). Neutrinos generated in and around the protoneutron star can heat the surrounding gas, increasing its energy.

“Can We Survive Technology?” by John von Neumann

This is an essay written by John von Neumann in 1955, which I think is fairly described as being about global catastrophic risks from emerging technologies. It discusses a bunch of specific technologies that seemed like a big deal in 1955 — which is interesting in itself as a list of predictions; nuclear power! increased automation! weather control? — but explicitly tries to draw a general lesson.

Von Neumann is regarded as one of the greatest scientists of the 20th century, and was involved in the Manhattan project in addition to inventing zillions of other things.

I’m posting here because a) I think the essay is worth reading in its own right, and b) I find it interesting to see what the past’s intellectuals thought of issues related transformative technology, and how their perspective differs/is similar to ours. Notably, I disagree with several of the conclusions (e.g. von Neumann seems to think differential technological development is doomed).

Void-Filled Material Stops Intense Electron Beam

An intense electron beam is stopped more efficiently by a highly porous material than by a less porous material, suggesting new strategies for controlling beams.

New experiments show that porous materials consisting mostly of empty space can absorb the energy carried by an ultraintense electron beam more effectively than porous media with higher mass densities. The finding contradicts the prevailing notion that denser and thicker obstacles always provide more stopping power and suggests that the microstructure of a material fundamentally changes its electron-stopping ability. Simulations by the experimental team revealed the physical mechanisms behind this “anomalous-stopping” effect, which the researchers believe provides a new way to control the propagation of electron beams in extreme environments [1].

The study focuses on relativistic electron beams (REBs), which travel at close to the speed of light. REBs that carry currents in the mega-ampere regime can deliver petawatts (1015 watts) of power to a small target in a pulse lasting for a few picoseconds. This high intensity makes them ideal for creating and probing extreme states of matter that exist in stars, planetary cores, or nuclear events. The short bursts of intense energy provided by REBs are also used in inertial-confinement fusion—a scheme in which high-power lasers heat a fuel pellet and trigger nuclear fusion.

NASA Powers Down Voyager 1 Instrument As It Fights To Survive Deep Space

Voyager 1 is losing power, and NASA just shut down a decades-old instrument to keep it going. The sacrifice could help the spacecraft continue exploring interstellar space a little longer.

On April 17, engineers at NASA’s Jet Propulsion Laboratory (JPL) in Southern California transmitted commands to switch off an instrument on Voyager 1 known as the Low-energy Charged Particles experiment, or LECP. The spacecraft, which runs on nuclear power, is steadily losing energy, and shutting down this instrument is the most effective way to extend the mission of the first human-made object to reach interstellar space.

A 49-Year-Old Instrument Falls Silent

Understanding how lasers can rapidly magnetize fusion plasmas

The mechanism that can cause a rapidly expanding plasma—the superhot state of matter harnessed in fusion energy systems—to spontaneously generate its own magnetic fields was identified through a new set of simulations. This improves our understanding of naturally occurring plasmas in our universe and advances the development of fusion systems based on an approach called direct-drive inertial fusion.

In a direct-drive inertial fusion system, powerful lasers compress a small, fuel-filled capsule, heating it until fusion reactions occur. Unexpected magnetic fields can change how heat moves through the plasma in ways that existing simulation tools can miss. Accurate simulations are critical to designing fusion systems that will behave as expected and deliver net energy on a long-term basis.

In laboratory experiments, researchers found that high-powered lasers can vaporize a solid target in an instant, turning it into plasma that rapidly expands. Experiments have repeatedly detected very strong magnetic structures emerging from this expanding plasma, but the precise origin of these fields has long been a matter of debate.

DAMPE satellite reveals cosmic rays share spectral break near 15 teravolts

A century after their discovery, cosmic rays—particles of extreme energy originating from the far reaches of the universe—remain a mystery to scientists. The DAMPE (Dark Matter Particle Explorer) space telescope is tackling this phenomenon, particularly investigating the role that dark matter may play in their formation. This international mission, which includes the University of Geneva (UNIGE), has made a major breakthrough by highlighting a universal feature of these particles. The results are published in the journal Nature.

Cosmic rays are the most energetic particles observed in the universe, far surpassing the energies of particles produced by man-made accelerators on Earth. Their exact origin is still under study, and it is believed that they originate from extreme astrophysical phenomena, such as supernovae, black hole jets, or pulsars.

The DAMPE space telescope, launched in December 2015, aims to provide answers regarding the origin and nature of these cosmic rays. This space mission, with the astrophysics group from the Department of Nuclear and Particle Physics (DPNC) at the University of Geneva (UNIGE) being one of its main contributors, has made a crucial breakthrough. Through the analysis of high-precision measurements collected by the telescope, scientists have identified a universal feature in the energy spectra of primary cosmic ray nuclei, ranging from protons to iron.

Laser-plasma accelerators can preserve polarization of Helium-3 ions

Particle accelerators such as those at the European Organization for Nuclear Research (CERN) in Geneva are typically highly complex large-scale devices. In these ring-shaped facilities, which are often several kilometers in length, magnets and radio-frequency cavities are used to accelerate elementary particles. An alternative approach is now emerging: compact laser–plasma accelerators that can be built and operated at a fraction of the cost. These accelerators can achieve acceleration gradients up to around 1,000 times higher than those of conventional accelerators. Researchers at HHU contributed significantly to this development.

A research team led by Prof. Dr. Markus Büscher, a professor of physics at HHU and group leader at the Peter Grünberg Institute in Jülich, presented the current state of research in a review article in Reports on Progress in Physics. In a separate study published in High Power Laser Science and Engineering, they report on one specific aspect of laser–plasma acceleration, namely whether the polarization—that is to say, the collective spin alignment—of accelerated particles is preserved in laser–plasma accelerators.

Why is this relevant? “Spin alignment is crucial to a range of fundamental scientific questions as it influences the interaction between particles,” explains Professor Büscher. “In controlled nuclear fusion, the reaction probability—and thus ultimately the energy produced in the reactor—increases significantly when the spins of the fusing nuclei, the ‘fusion fuel’ so to speak, are aligned in parallel.”

A New Way to View Shockwaves Could Boost Fusion Research

At the heart of our sun, fusion is unfolding. As hydrogen atoms merge to form helium, they emit energy, producing the heat and light that reach us here on Earth. Inspired by our nearby star, researchers want to create fusion closer to home. If they can crack the engineering challenges underlying the process, they would create an abundant new source of power to eclipse all others.

One of those challenges is understanding what happens at the smallest scales during fusion reactions so that researchers can better control the process. In one of the two main kinds of fusion, inertial confinement fusion (ICF), researchers bombard a fuel-filled capsule with lasers to create shockwaves and heat and compress the target, kicking off fusion. That means lots of complex interactions that scientists haven’t been able to get a good look at — until now.

A team of researchers used a new approach at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) to watch how a shockwave moved through water in extreme detail, making a never-before-seen movie of how the material compressed and how the electric and magnetic fields evolved. They were intrigued to discover that water provided a good analog for what happens when a laser strikes an ICF target. Scientists captured the process using both X-rays and an electron beam, a unique dual view known as “multi-messenger” imaging.

DuctGPT demonstrates how AI can accelerate discovery of next-generation fusion materials

Scientists at Ames National Laboratory developed a new artificial intelligence (AI) tool that accelerates discovery of materials needed for next-generation fusion energy systems. The tool, DuctGPT, combines advanced AI with physics-based modeling to help researchers predict materials with the appropriate properties to function in the extreme conditions inside of fusion reactors.

This research is discussed in “DuctGPT: A Generative Transformer for Forward Screening of Ductile Refractory Multi-Principal Element Alloys,” published in Acta Materialia.

The challenge is to rapidly explore a wide range of potential alloy compositions that can maintain high-temperature strength, while retaining the ductility necessary for manufacturing the materials.

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