Voyager 1 and 2 detect new kind of solar electron burst

Dec. 3 (UPI) — Data collected by the Voyager spacecraft, Voyager 1 and 2, has revealed a new type of solar electron burst — the satellites’ instruments detected speeding cosmic ray electrons accelerated by shock waves produced by solar eruptions.

The phenomenon was described Thursday in the Astrophysical Journal by a team of physicists led by the University of Iowa.

The Voyager spacecraft were launched in 1977. In 2012, Voyager 1 left the heliosphere and entered interstellar space. Its younger sibling, Voyager 2, escaped the solar system in 2018.

The two probes are now 14 billion miles from the sun, farther than any human-built objects.

While traveling through interstellar space, the two craft observed electrons accelerating along magnetic field lines, some moving 670 times faster than the shock waves that initially triggered their acceleration.

The cosmic burst events were followed by plasma wave oscillations, detected by the same instruments several days after the electrons zipped past the spacecraft.

The shockwaves that accelerated the electron bursts detected by Voyager 1 and 2 were produced by coronal mass ejections from the sun. These solar explosions propel hot gas and energy at speeds one million miles per hour.

It took more than a year for the shockwaves emanating from the sun to reach the two Voyager spacecraft.

“What we see here specifically is a certain mechanism whereby when the shock wave first contacts the interstellar magnetic field lines passing through the spacecraft, it reflects and accelerates some of the cosmic ray electrons,” Don Gurnett, the study’s corresponding author, said in a news release.

“We have identified through the cosmic ray instruments these are electrons that were reflected and accelerated by interstellar shocks propagating outward from energetic solar events at the sun. That is a new mechanism,” said Gurnett, a professor of physics and astronomy at Iowa.

Previously, physicists have been forced to study only cosmic ray bursts moving the opposite direction — those propelled toward Earth by explosions on distant variable stars.

Researchers suggest the detections made by Voyager 1 and 2 could help scientists better understand the physics underlying the propulsion of shock waves and cosmic radiation.

Scientists suspect electrons are first reflected off a localized magnetic field strengthened by the bow of the shockwave, and subsequently accelerated by the motion of the shockwave itself.

The reflected and accelerated electrons zip along interstellar magnetic field lines, getting faster as they separate from the shockwave.

This theoretical sequence of events has previously been described in the scientific literature, but — for obvious reasons — has never before detected in interstellar space.

“The idea that shock waves accelerate particles is not new,” Gurnett said. “It all has to do with how it works, the mechanism – and the fact we detected it in a new realm, the interstellar medium, which is much different than in the solar wind where similar processes have been observed.

“No one has seen it with an interstellar shock wave, in a whole new pristine medium,” Gurnett said.

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Researchers measure electron emission to improve understanding of laser-based metal 3-D printing

Researchers measure electron emission to improve understanding of laser-based metal 3D printing
Researchers measured the emission of electrons from the surface of stainless steel under laser powder bed fusion (LPBF) conditions, demonstrating the potential for using thermionic emission signals to detect phenomena that can produce defects in parts and improve understanding of the LPBF process. The top image shows a multi-physics simulation of laser-induced melting of stainless steel, showing the electron emission signal primarily produced at the front of the surface depression. The bottom image depicts cross-sections of laser tracks produced in stainless steel. Monitoring of the thermionic emission can detect transition between conduction (left) and keyhole (right) mode welding regimes. Credit: Aiden Martin/LLNL

Lawrence Livermore National Laboratory (LLNL) researchers have taken a promising step in improving the reliability of laser-based metal 3-D printing techniques by measuring the emission of electrons from the surface of stainless steel during laser processing.


Researchers collected thermionic emission signals from 316L stainless steel under laser powder bed fusion (LPBF) conditions using a custom, testbed system and a current preamplifier that measured the flow of electrons between the metal surface and the chamber. Then they used the generated thermionic emission to identify dynamics caused by laser-metal interactions. The journal Communications Materials published the work online on Nov. 27.

The team said the results illustrate the potential for thermionic emission sensing to detect laser-driven phenomena that can cause defects in parts, optimize build parameters and improve knowledge of the LPBF process while complementing existing diagnostic capabilities. Researchers said the ability to capture thermal emission of electrons will help advance basic understanding of the laser-material interaction dynamics involved in the LPBF process and support the broader technology maturation community in building confidence in parts created using the technique.

“Producing defect-free parts is a major hurdle for widespread commercial adoption of metal additive manufacturing (AM),” said principal investigator Aiden Martin. “LLNL researchers have been addressing this problem by developing processes and diagnostic tools for improving the reliability of metal AM. This new methodology complements these existing diagnostic tools to increase our understanding of the 3-D printing process. Our next steps are to expand this technology into a sensor operating on a full-scale LPBF system to increase confidence in the quality of built parts.”

Researchers said while significant research has been done to understand and measure how parts are printed with LPBF through optical imaging, X-ray radiographs or measuring thermal or acoustic signal emissions, thermionic emission has been overlooked. But by observing and analyzing the electrons emitted during laser processing, Lab researchers demonstrated they could tie increases in thermionic emission to surface temperature and laser scanning conditions that cause pore formation and part defects.

Through experimental data and simulation, researchers reported the thermionic emission signal increased exponentially, and melt pool depth increased linearly, with local energy density, demonstrating the “critical dependence” of the metal’s surface temperature on thermionic emissions and the utility of using thermionic signals as a way to optimize laser focus in LPBF.

“Electron emission in metal additive manufacturing has generally been overlooked by the community, and we were

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Voyager spacecraft detect new type of solar electron burst

Voyager spacecraft detect new type of solar electron burst
The Voyager spacecraft continue to make discoveries even as they travel through interstellar space. In a new study, University of Iowa physicists report on the Voyagers’ detection of cosmic ray electrons associated with eruptions from the sun–more than 14 billion miles away. Credit: NASA/JPL

More than 40 years since they launched, the Voyager spacecraft are still making discoveries.


In a new study, a team of physicists led by the University of Iowa report the first detection of bursts of cosmic ray electrons accelerated by shock waves originating from major eruptions on the sun. The detection, made by instruments onboard both the Voyager 1 and Voyager 2 spacecraft, occurred as the Voyagers continue their journey outward through interstellar space, thus making them the first craft to record this unique physics in the realm between stars.

These newly detected electron bursts are like an advanced guard accelerated along magnetic field lines in the interstellar medium; the electrons travel at nearly the speed of light, some 670 times faster than the shock waves that initially propelled them. The bursts were followed by plasma wave oscillations caused by lower-energy electrons arriving at the Voyagers’ instruments days later—and finally, in some cases, the shock wave itself as long as a month after that.

The shock waves emanated from coronal mass ejections, expulsions of hot gas and energy that move outward from the sun at about one million miles per hour. Even at those speeds, it takes more than a year for the shock waves to reach the Voyager spacecraft, which have traveled further from the sun (more than 14 billion miles and counting) than any human-made object.

“What we see here specifically is a certain mechanism whereby when the shock wave first contacts the interstellar magnetic field lines passing through the spacecraft, it reflects and accelerates some of the cosmic ray electrons,” says Don Gurnett, professor emeritus in physics and astronomy at Iowa and the study’s corresponding author. “We have identified through the cosmic ray instruments these are electrons that were reflected and accelerated by interstellar shocks propagating outward from energetic solar events at the sun. That is a new mechanism.”

The discovery could help physicists better understand the dynamics underpinning shock waves and cosmic radiation that come from flare stars (which can vary in brightness briefly due to violent activity on their surface) and exploding stars. The physics of such phenomena would be important to consider when sending astronauts on extended lunar or Martian excursions, for instance, during which they would be exposed to concentrations of cosmic rays far exceeding what we experience on Earth.

The physicists believe these electrons in the interstellar medium are reflected off of a strengthened magnetic field at the edge of the shock wave and subsequently accelerated by the motion of the shock wave. The reflected electrons then spiral along interstellar magnetic field lines, gaining speed as the distance between them and the shock increases.

In a 2014 paper in the journal Astrophysical Letters, physicists J.R. Jokipii and Jozsef

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DeepMind open-sources the FermiNet, a neural network that simulates electron behaviors

In September, Alphabet’s DeepMind published a paper in the journal Physical Review Research detailing Fermionic Neural Network (FermiNet), a new neural network architecture that’s well-suited to modeling the quantum state of large collections of electrons. The FermiNet, which DeepMind claims is one of the first demonstrations of AI for computing atomic energy, is now available in open source on GitHub — and ostensibly remains one of the most accurate methods to date.

In quantum systems, particles like electrons don’t have exact locations. Their positions are instead described by a probability cloud. Representing the state of a quantum system is challenging, because probabilities have to be assigned to possible configurations of electron positions. These are encoded in the wavefunction, which assigns a positive or negative number to every configuration of electrons; the wavefunction squared gives the probability of finding the system in that configuration.

The space of possible configurations is enormous — represented as a grid with 100 points along each dimension, the number of electron configurations for the silicon atom would be larger than the number of atoms in the universe. Researchers at DeepMind believed that AI could help in this regard. They surmised that, given neural networks have historically fit high-dimensional functions in artificial intelligence problems, they could be used to represent quantum wavefunctions as well.

FermiNet

Above: Simulated electrons sampled from the FermiNet move around a bicyclobutane molecule.

By way of refresher, neural networks contain neurons (mathematical functions) arranged in layers that transmit signals from input data and slowly adjust the synaptic strength — i.e., weights — of each connection. That’s how they extract features and learn to make predictions.

Because electrons are a type of particle known as fermions, which include the building blocks of most matter (e.g., protons, neutrons, quarks, and neutrinos), their wavefunction has to be antisymmetric. (If you swap the position of two electrons, the wavefunction gets multiplied by -1, meaning that if two electrons are on top of each other, the wavefunction and the probability of that configuration will be zero.) This led the DeepMind researchers to develop a new type of neural network that was antisymmetric with respect to its inputs — the FermiNet — and that has a separate stream of information for each electron. In practice, the FermiNet averages together information from across streams and passes this information to each stream at the next layer. This way, the streams have the right symmetry properties to create an antisymmetric function.

FermiNet

Above: The FermiNet’s architecture.

The FermiNet picks a random selection of electron configurations, evaluates the energy locally at each arrangement of electrons, and adds up the contributions from each arrangement. Since the wavefunction squared gives the probability of observing an arrangement of particles in any location, the FermiNet can generate samples from the wavefunction directly. The inputs used to train the neural network are generated by the neural network itself, in effect.

“We think the FermiNet is the start of great things to come for the fusion of deep learning and computational

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