Particle accelerator region revealed inside a solar flare

Solar flares are among the most violent explosions in our solar system, but despite their immense energy -- equivalent to a hundred billion atomic bombs detonating at once -- physicists still haven't been able to answer exactly how these sudden eruptions on the Sun are able to launch particles to Earth, nearly 93 million miles away, in under an hour.

Now, in a study published June 8 in Nature, researchers at New Jersey Institute of Technology (NJIT) have pinpointed the precise location where solar flare charged particles are accelerated to near-light speed.

The new findings, made possible through observations of an X-class solar flare in 2017 by NJIT's Expanded Owens Valley Solar Array (EOVSA) radio telescope, have revealed a highly efficient particle accelerator located at the tip of the brightest point of the eruption in the Sun's outer atmosphere, called the flare's "cusp region," where the explosion's ambient plasma is converted to high-energy electrons.

Researchers say the discovery of the region, measured at almost twice the volume of Earth, could open new doors for investigating fundamental processes of particle acceleration ubiquitous in the universe.

"The findings in this study help explain the long-standing mystery of how solar flares can produce so much energy in mere seconds," said Gregory Fleishman, corresponding author of the paper and distinguished research professor of physics at NJIT's Center for Solar-Terrestrial Research. "The flare unleashes its power in a much vaster region of the Sun than expected by the classic model of solar flares. Although others have postulated this must happen, this is the first time the specific size, shape, and location of this key region has been identified, and the efficiency of the energy conversion to particle acceleration inside the flare has been measured."

The discovery follows separate studies from 2020 published in Science and Nature Astronomy, where EOVSA's detailed snapshots of the flare and changes in the Sun's magnetic field -- taken at hundreds of radio frequencies at once -- initially gave the NJIT team a lead on the location.

"Our recent studies suggested the flare cusp could be the location where such high-energy electrons are produced, but we weren't certain," explained Bin Chen, NJIT associate professor and a co-author of the paper. "We had originally uncovered a magnetic bottle-like structure at the site that contained an overwhelmingly large number of electrons compared to anywhere else in the flare, but now with the new measurements of this study, we can more confidently say this is the flare's particle accelerator.''

Using the unique microwave imaging capabilities of EOVSA, the team was able to measure the energy spectrum of electrons at hundreds of locations of an X-class solar flare triggered by a reconfiguration of magnetic field lines along the Sun's surface on September 10, 2017.

"EOVSA's spectral imaging gave us a comprehensive map of the flare's thermal plasma as it evolved second-by-second. But to our surprise, what we found was a mysterious hole in the thermal plasma map that began developing at the flare's cusp," said Gelu Nita, NJIT research professor and co-author of the paper. "More than that, as thermal particles in the region disappeared, the hole was then densely filled with non-thermal, high-energy particles."

The team's analysis brought to light an incredibly efficient energy conversion process within the solar flare's particle accelerator, where intense energy from the Sun's magnetic fields is rapidly released and transferred to kinetic energy inside the region.

"We wondered how efficient this energy conversion process would be … how many particles in this area would be accelerated beyond the explosion's thermal energy?" added Sijie Yu, study co-author and NJIT assistant research professor. "Using extreme ultraviolet data of the Sun, we confirmed that virtually no particles remained inside the region at thermal energies below a few million Kelvin, consistent with the EOVSA measurement that the particles had all been accelerated to non-thermal energies greater than 20 keV, or nearly 100 million Kelvin."

The team now says these latest findings could help scientists study fundamental questions in particle physics not possible on Earth, as well as offer fresh insights into how such high-energy particles from the Sun may impact Earth during future space weather events.

"An important aspect of this study is that it directs the attention of theorists to the precise location where most of the energy release and particle acceleration occurs, and provides quantitative measurements to guide numerical models," says Dale Gary, NJIT distinguished professor and director of EOVSA. "However, to extend our measurements to much broader flare regions and weaker but more frequent flare events, we are developing a next-generation, solar-dedicated radio array called the Frequency Agile Solar Radiotelescope, which will be at least 10 times larger and orders of magnitude more powerful."

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Researchers hunt for one-pole magnets by combining cosmic rays and particle accelerators

Some of the world's most powerful particle accelerators have helped researchers draw new leading limits on the existence of long theorized magnetic monopoles from the collisions of energetic cosmic rays bombarding the Earth's atmosphere, reports a new study published in Physical Review Letters.

Magnets are intimately familiar to everyone, with wide-ranging applications within daily life, from TVs and computers to kids toys. However, breaking any magnet, such as a navigation compass needle consisting of north and south poles in half, will result in just two smaller two-pole magnets. This mystery has eluded researchers for decades since 1931, when physicist Paul Dirac theorized the existence of one-pole "magnetic monopoles'' -- particles comparable to electrons but with a magnetic charge.

To explore whether magnetic monopoles exist, an international team of researchers, including the University of Tokyo's Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) Fellow Volodymyr Takhistov, studied available data from a variety of terrestrial experiments and have carried out the most sensitive searches to date for monopoles over a broad range of possible masses. The researchers focused on an unusual source of monopoles -- atmospheric collisions of cosmic rays that have been occurring for eons.

The interdisciplinary research required bringing together expertise from several distinct corners of science -- including accelerator physics, neutrino interactions and cosmic rays.

Cosmic ray collisions with the atmosphere have already played a central role in advancing science, especially the exploration of ghostly neutrinos. This lead to Kavli IPMU Senior Fellow Takaaki Kajita's 2015 Nobel Prize in Physics for the discovery by the Super-Kamiokande experiment that neutrinos oscillate in flight, implying that they have mass.

Partially inspired by the results of Super-Kamiokande, the team set to work on monopoles. Particularly intriguing were light monopoles with masses around the electroweak scale, which can be readily accessible to conventional particle accelerators.

By carrying out simulations of cosmic ray collisions, analogously to particle collisions at the LHC at CERN, the researchers obtained a persistent beam of light monopoles raining down upon different terrestrial experiments.

This unique source of monopoles is especially interesting, as it is independent of any pre-existing monopoles such as those potentially left over as relics from the early Universe, and covers a broad range of energies.

By re-analyzing data from a wide range of previous experimental monopole searches, the researchers identified novel limits on monopoles across a wide range of masses, including those beyond the reach of conventional collider monopole searches.

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The future of particle accelerators is here

When the Electron Ion Collider received the go-ahead in January 2020, it became the only new major accelerator in the works anywhere in the world.

"All the stars aligned," said Elke-Caroline Aschenauer, Brookhaven National Laboratory Staff Scientist and a leader in developing the EIC plans. "We have the technology to build this unique particle accelerator and detector to do the measurements that, together with the underlying theory, can for the first time provide answers to longstanding fundamental questions in nuclear physics."

The EIC isn't the only Brookhaven project poised to reshape nuclear and particle physics. Forthcoming data from the Relativistic Heavy Ion Collider could finally detect the elusive chiral magnetic effect. Meanwhile, planned accelerators could run on sustainable energy, a drastic departure from today's machines.

At a press conference during the 2021 APS April Meeting, researchers will discuss how cutting-edge accelerators could collide with both energy consumption and our assumptions about the nature of matter.

A powerful new facility for nuclear physics

"The scientific advances of the EIC will help us all to understand where we come from and how the visible matter around us is composed from its elementary building blocks," said Aschenauer.

The accelerator and detector will serve as a kind of camera, taking 3D images and movies of electrons colliding with polarized protons and ions. Like a CT scanner for atoms, the EIC will let scientists see how force-carrying gluon particles hold together quarks, the internal components of protons and neutrons. It will also offer insights into the spin of fundamental particles.

Aschenauer will give status updates from the first year of the EIC project -- a collaboration between BNL and Thomas Jefferson National Accelerator Facility -- and an overview of its experimental equipment.

Hunting for the chiral magnetic effect

The EIC will build on the Relativistic Heavy Ion Collider, which will soon produce major results of its own.

In summer 2021, data analysis will likely conclude on an experiment searching for decisive proof of the chiral magnetic effect. This proposed effect helps explain many fundamental features of the Standard Model and could unlock why our universe contains overwhelmingly more matter than antimatter, crucial to human existence.

Jinfeng Liao, a theoretical nuclear physicist at Indiana University Bloomington, will share key predictions about what the experiment might uncover.

"The signatures, as predicted by our theoretical study, show clear promise of unambiguously establishing the existence of chiral magnetic effect in the isobar collision experiment," said Liao.

Liao and colleagues created a custom fluid-dynamics-based computational tool to simulate experimental collisions and any changes the chiral magnetic effect would cause.

They show that the new experiment has a better chance of detecting the effect than previous attempts, long plagued by weak signals and strong background contamination. The predictions were published in Physical Review Letters.

Probing profound subatomic questions requires a lot of power.

"Large particle accelerators use a shockingly large amount of energy," said Georg Hoffstaetter, a professor at Cornell University.

He will share results from the Cornell-BNL Test Accelerator, or CBETA, the world's first to accelerate a beam multiple times while powering itself by reusing beam energy. It further reduces electricity demands with superconducting and magnetic equipment.

The Energy Recovery Linacs technology that enables the test accelerator could lead to smaller particle accelerators with higher beam currents and reduced energy consumption.

"People may benefit from the industrial applications of Energy Recovery Linacs by using better computer chips, by being cured in radiation therapy centers that guide beams with permanent magnets, or by inhaling accelerator-produced medical isotopes," said Hoffstaetter.

Building on the success of the test accelerator, its principal investigator and Brookhaven Senior Physicist Dejan Trbojevic will present designs for a new green energy collider. Particles speed along racetrack beam lines, formed from high-quality permanent magnets which require no use of electrical power.

"The 'green accelerator' shows a completely new way of accelerating particles with very tight control of their motion and with an extremely high energy range. It has never been done before," said Trbojevic.

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Giant particle accelerator in the sky

 The Earth's magnetic field is trapping high energy particles. When the first satellites were launched into space, scientists led by James Van Allen unexpectedly discovered the high energy particle radiation regions, which were later named after its discoverer Van Allen Radiation Belts. Visualized, these look like two donut-shaped regions encompassing our planet.

Now, a new study led by researchers from GFZ German Research Centre for Geosciences shows that electrons in the radiation belts can be accelerated to very high speeds locally. The study shows that magnetosphere works as a very efficient particle accelerator speeding up electrons to so-called ultra-relativistic energies. The study conducted by Hayley Allison, a postdoctoral scholar at GFZ Potsdam, and Yuri Shprits from GFZ and Professor at the University of Potsdam, is published in Nature Communications.

To better understand the origin of the Van Allen Belts, in 2012 NASA launched the Van Allen Probes twin spacecraft to traverse this most harsh environment and conduct detailed measurements in this hazardous region. The measurements included a full range of particles moving at different speeds and in different directions and plasma waves. Plasma waves are similar to the waves that we see on the water surface, but are in fact invisible to the naked eye. They can be compared to ripples in the electric and magnetic field.

Recent observations revealed that the energy of electrons in the belts can go up to so called ultra-relativistic energies. These electrons with temperatures above 100 Billion degrees Fahrenheit, move so fast that their energy of motion is much higher than their energy of rest given by Einstein's famous E=mc2 formula. They are so fast that the time flow significantly slows down for these particles.

Scientists were surprised to find these ultra-relativistic electrons and assumed that such high energies can be only reached by a combination of two processes: the inward transport of particles from the outer regions of the magnetosphere, which accelerates them; and a local acceleration of particles by plasma waves.

However, the new study shows that electrons reach such incredible energies locally, in the heart of the belts, by taking all this energy from plasma waves. This process turns out to be extremely efficient. The unexpected discovery of how acceleration of particles to ultra-relativistic energies operates in the near-Earth space, may help scientists understand the fundamental processes of acceleration on the Sun, near outer planets, and even in the distant corners of the universe where space probes cannot reach.

From Science Daily

A new machine learning method streamlines particle accelerator operations

Each year, researchers from around the world visit the Department of Energy's SLAC National Accelerator Laboratory to conduct hundreds of experiments in chemistry, materials science, biology and energy research at the Linac Coherent Light Source (LCLS) X-ray laser. LCLS creates ultrabright X-rays from high-energy beams of electrons produced in a giant linear particle accelerator.

Experiments at LCLS run around the clock, in two 12-hour shifts per day. At the start of each shift, operators must tweak the accelerator's performance to prepare the X-ray beam for the next experiment. Sometimes, additional tweaking is needed during a shift as well. In the past, operators have spent hundreds of hours each year on this task, called accelerator tuning.

Now, SLAC researchers have developed a new tool, using machine learning, that may make part of the tuning process five times faster compared to previous methods. They described the method in Physical Review Letters on March 25.

Tuning the beam

Producing LCLS's powerful X-ray beam starts with the preparation of a high-quality electron beam. Some of the electrons' energy then gets converted into X-ray light inside special magnets. The properties of the electron beam, which needs to be dense and tightly focused, are a critical factor in how good the X-ray beam will be.

"Even a small difference in the density of the electron beam can have a huge difference in the amount of X-rays you get out at the end," says Daniel Ratner, head of SLAC's machine learning initiative and a member of the team that developed the new technique.

The accelerator uses a series of 24 special magnets, called quadrupole magnets, to focus the electron beam similarly to how glass lenses focus light. Traditionally, human operators carefully turned knobs to adjust individual magnets between shifts to make sure the accelerator was producing the X-ray beam needed for a particular experiment. This process took up a lot of the operators' time -- time they could spend on other important tasks that improve the beam for experiments.

A few years ago, LCLS operators adopted a computer algorithm that automated and sped up this magnet tuning. However, it came with its own disadvantages. It aimed at improving the X-ray beam by making random adjustments to the magnets' strengths. But unlike human operators, this algorithm had no prior knowledge of the accelerator's structure and couldn't make educated guesses in its tuning that might have ultimately led to even better results.

This is why SLAC researchers decided to develop a new algorithm that combines machine learning -- "smart" computer programs that learn how to get better over time -- with knowledge about the physics of the accelerator.

"The machine learning approach is trying to tie this all together to give operators better tools so that they can focus on other important problems," says Joseph Duris, a SLAC scientist who led the new study.

A better beam, faster

The new approach uses a technique called a Gaussian process, which predicts the effect a particular accelerator adjustment has on the quality of the X-ray beam. It also generates uncertainties for its predictions. The algorithm then decides which adjustments to try for the biggest improvements.

For example, it may decide to try a dramatic adjustment whose outcome is very uncertain but could lead to a big payoff. That means this new, adventurous algorithm has a better chance than the previous algorithm of making the tweaks needed to create the best possible X-ray beam.

The SLAC researchers also used data from previous LCLS operations to teach the algorithm which magnet strengths have typically led to brighter X-rays, giving the algorithm a way of making educated guesses about the adjustments it should try. This equips the algorithm with knowledge and expertise that human operators naturally have, and that the previous algorithm lacked.

"We can rely on that physics knowledge, that institutional knowledge, in order to improve the predictions," Duris says.

Insights into the magnets' relationships to each other also improved the technique. The quadrupole magnets work in pairs, and to increase their focusing power, the strength of one magnet in a pair must be increased while the other's is decreased.

With the new process, tuning the quadrupole magnets has become about three to five times faster, the researchers estimate. It also tends to produce higher-intensity beams than the previously used algorithm.

"Our ability to increase our tuning efficiency is really, really critical to being able to deliver a beam faster and with better quality to people who are coming from all over the world to run experiments," says Jane Shtalenkova, an accelerator operator at SLAC who worked with Duris, Ratner and others to develop the new tool.

Beyond LCLS

The same method can be extended to tune other electron or X-ray beam properties that scientists may want to optimize for their experiments. For example, researchers could apply the technique to maximize the signal they get out of their sample after it's hit by LCLS's X-ray beam.

This flexibility also makes the new algorithm useful for other facilities.

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Researchers build a particle accelerator that fits on a chip

On a hillside above Stanford University, the SLAC National Accelerator Laboratory operates a scientific instrument nearly 2 miles long. In this giant accelerator, a stream of electrons flows through a vacuum pipe, as bursts of microwave radiation nudge the particles ever-faster forward until their velocity approaches the speed of light, creating a powerful beam that scientists from around the world use to probe the atomic and molecular structures of inorganic and biological materials.

Now, for the first time, scientists at Stanford and SLAC have created a silicon chip that can accelerate electrons -- albeit at a fraction of the velocity of that massive instrument -- using an infrared laser to deliver, in less than a hair's width, the sort of energy boost that takes microwaves many feet.

Writing in the Jan. 3 issue of Science, a team led by electrical engineer Jelena Vuckovic explained how they carved a nanoscale channel out of silicon, sealed it in a vacuum and sent electrons through this cavity while pulses of infrared light -- to which silicon is as transparent as glass is to visible light -- were transmitted by the channel walls to speed the electrons along.

The accelerator-on-a-chip demonstrated in Science is just a prototype, but Vuckovic said its design and fabrication techniques can be scaled up to deliver particle beams accelerated enough to perform cutting-edge experiments in chemistry, materials science and biological discovery that don't require the power of a massive accelerator.

"The largest accelerators are like powerful telescopes. There are only a few in the world and scientists must come to places like SLAC to use them," Vuckovic said. "We want to miniaturize accelerator technology in a way that makes it a more accessible research tool."

Team members liken their approach to the way that computing evolved from the mainframe to the smaller but still useful PC. Accelerator-on-a-chip technology could also lead to new cancer radiation therapies, said physicist Robert Byer, a co-author of the Science paper. Again, it's a matter of size. Today, medical X-ray machines fill a room and deliver a beam of radiation that's tough to focus on tumors, requiring patients to wear lead shields to minimize collateral damage.

"In this paper we begin to show how it might be possible to deliver electron beam radiation directly to a tumor, leaving healthy tissue unaffected," said Byer, who leads the Accelerator on a Chip International Program, or ACHIP, a broader effort of which this current research is a part.

Inverse design

In their paper, Vuckovic and graduate student Neil Sapra, the first author, explain how the team built a chip that fires pulses of infrared light through silicon to hit electrons at just the right moment, and just the right angle, to move them forward just a bit faster than before.

To accomplish this, they turned the design process upside down. In a traditional accelerator, like the one at SLAC, engineers generally draft a basic design, then run simulations to physically arrange the microwave bursts to deliver the greatest possible acceleration. But microwaves measure 4 inches from peak to trough, while infrared light has a wavelength one-tenth the width of a human hair. That difference explains why infrared light can accelerate electrons in such short distances compared to microwaves. But this also means that the chip's physical features must be 100,000 times smaller than the copper structures in a traditional accelerator. This demands a new approach to engineering based on silicon integrated photonics and lithography.

Vuckovic's team solved the problem using inverse design algorithms that her lab has developed. These algorithms allowed the researchers to work backward, by specifying how much light energy they wanted the chip to deliver, and tasking the software with suggesting how to build the right nanoscale structures required to bring the photons into proper contact with the flow of electrons.

"Sometimes, inverse designs can produce solutions that a human engineer might not have thought of," said R. Joel England, a SLAC staff scientist and co-author on the Science paper.

The design algorithm came up with a chip layout that seems almost otherworldly. Imagine nanoscale mesas, separated by a channel, etched out of silicon. Electrons flowing through the channel run a gantlet of silicon wires, poking through the canyon wall at strategic locations. Each time the laser pulses -- which it does 100,000 times a second -- a burst of photons hits a bunch of electrons, accelerating them forward. All of this occurs in less than a hair's width, on the surface of a vacuum-sealed silicon chip, made by team members at Stanford.

The researchers want to accelerate electrons to 94 percent of the speed of light, or 1 million electron volts (1MeV), to create a particle flow powerful enough for research or medical purposes. This prototype chip provides only a single stage of acceleration, and the electron flow would have to pass through around 1,000 of these stages to achieve 1MeV. But that's not as daunting at it may seem, said Vuckovic, because this prototype accelerator-on-a-chip is a fully integrated circuit. That means all of the critical functions needed to create acceleration are built right into the chip, and increasing its capabilities should be reasonably straightforward.

The researchers plan to pack a thousand stages of acceleration into roughly an inch of chip space by the end of 2020 to reach their 1MeV target. Although that would be an important milestone, such a device would still pale in power alongside the capabilities of the SLAC research accelerator, which can generate energy levels 30,000 times greater than 1MeV. But Byer believes that, just as transistors eventually replaced vacuum tubes in electronics, light-based devices will one day challenge the capabilities of microwave-driven accelerators.

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