NEW PARTICLE ACCELERATORS COULD EXPAND USE TO SCIENCE AND INDUSTRY

FROM:  NATIONAL SCIENCE FOUNDATION
Smaller and cheaper particle accelerators?

Scientists developing technology that could expand use for medicine, national security, materials science, industry and high energy physics research
Traditionally, particle accelerators have relied on electric fields generated by radio waves to drive electrons and other particles close to the speed of light. But in radio-frequency machines there is an upper limit on the electric field before the walls of the accelerator "break down," causing it to not perform properly, and leading to equipment damage.

In recent years, however, scientists experimenting with so-called "plasma wakefields" have found that accelerating electrons on waves of plasma, or ionized gas, is not only more efficient, but also allows for the use of an electric field a thousand or more times higher than those of a conventional accelerator.

And most importantly, the technique, where electrons gain energy by "surfing" on a wave of electrons within the ionized gas, raises the potential for a new generation of smaller and less expensive particle accelerators.

"The big picture application is a future high energy physics collider," says Warren Mori, a professor of physics, astronomy and electrical engineering at University of California, Los Angeles (UCLA), who has been working on this project. "Typically, these cost tens of billions of dollars to build. The motivation is to try to develop a technology that would reduce the size and the cost of the next collider."

The National Science Foundation (NSF)-funded scientist and his collaborators believe the next generation of smaller and cheaper accelerators could enhance their value, expanding their use in medicine, national security, materials science, industry and high-energy physics research.

"Accelerators are also used for sources of radiation. When a high energy particle wiggles up and down, it generates X-rays, so you could also use smaller accelerators to make smaller radiation sources to probe a container to see whether there is nuclear material inside, or to probe biological samples," Mori says. "Short bursts of X-rays are currently being used to watch chemical bonds form and to study the inner structure of proteins, and viruses."

Just as important, albeit on a more abstract level, "the goal of the future of high-energy physics is to understand the fundamental particles of matter," he says. "To have the field continue, we need these expensive, large, and complex tools for discovery."

NSF has supported basic research in a series of grants in recent years totaling $4 million, including computational resources. The Department of Energy (DOE) has provided the bulk of the funding for experimental facilities and experiments, and has contributed to theory and simulations support.

"Mori's work is the perfect example of an innovative approach to advancing the science and technology frontiers that can come about when the deep understanding of fundamental laws of nature, of the collective behavior of charged particles that we call a plasma, is combined with state-of-the-art numerical modeling algorithms and simulation tools," says Vyacheslav (Slava) Lukin, program director in NSF's physics division.

Using DOE's SLAC National Accelerator Laboratory, the scientists from SLAC and UCLA increased clusters of electrons to energies 400 to 500 times higher than what they could reach traveling the same distance in a conventional accelerator. Equally important, the energy transfer was much more efficient than that of earlier experiments, a first to show this combination of energy and efficiency using "plasma wakefields."

In the experiments, the scientists sent pairs of electron bunches containing 5 billion to 6 billion electrons each into a laser-generated column of plasma inside an oven of hot lithium gas. The first bunch in each pair was the "drive" bunch; it blasted all the free electrons away from the lithium atoms, leaving the positively charged lithium nuclei behind, a configuration known as the "blowout regime." The blasted electrons then fell back in behind the second bunch of electrons, known as the "trailing" bunch to form a "plasma wake" that thrust the trailer electrons to higher energy.

While earlier experiments had demonstrated high-field acceleration in plasma wakes, the SLAC/UCLA team was the first to demonstrate simultaneously high efficiency and high accelerating fields using a drive and trailer bunch combination in the strong "blowout" regime. Furthermore, the accelerated electrons ended up with a relatively small energy spread.

"Because it's a plasma, there is no breakdown field limit," Mori says. "The medium itself is fully ionized, so you don't have to worry about breakdown. Therefore, the electric field in a plasma device can be pushed to a thousand or more times higher amplitude than that in a conventional accelerator."

Chandrashekhar Joshi, UCLA professor of electrical engineering, led the team that developed the plasma source used in the experiment. Joshi, the director of the Neptune Facility for Advanced Accelerator Research at UCLA is the UCLA principal investigator for this research and is a long-time collaborator with the SLAC group. The team also is made up of SLAC accelerator physicists, including Mike Litos and Mark Hogan; Mori leads the group that developed the computer simulations used in the experiments. Their findings appeared last fall in the journal Nature.

"The near term goal of this research is to produce compact accelerators for use in universities and industry, while a longer term goal remains developing a high energy collider operating at the energy frontier of particle physics," Mori says.

-- Marlene Cimons, National Science Foundation
Investigators
Warren Mori
Frank Tsung
Viktor Decyk
Russel Caflisch
Michail Tzoufras
Philip Pritchett
Related Institutions/Organizations
University of California-Los Angeles

COMPARE AND CONTRAST AURORA SIGHTINGS

FROM:  NATIONAL SCIENCE FOUNDATION
Springtime night lights: Finding the aurora
Aurorasaurus project allows aurora-viewers around the world to compare sightings

Dance of the spirits, it's known by the Cree, one of North America's largest groups of Native Americans.

The phenomenon, called the aurora borealis in the Northern Hemisphere and aurora australis in the Southern Hemisphere, is indeed a dance of particles and magnetism between the sun and the Earth.

The sun continuously produces a solar wind of charged particles, or plasma. As that "breath" reaches Earth, it causes our planet's magnetic field to shapeshift from round to teardrop--with a long tail on the side farthest from the sun.

The teardrop-stretched field ultimately reconfigures into two parts, one controlled by Earth's magnetic field, the other by the solar wind.

The instability excites the solar-charged particles. They follow spiral paths along lines connecting Earth's north and south magnetic poles to its atmosphere.

"What happens next," says scientist Elizabeth MacDonald of the New Mexico Consortium in Los Alamos, "is one of nature's most spectacular sights: the aurora."

The light of the aurora is emitted when the charged particles collide with gases in Earth's upper atmosphere.

Glimpsing an aurora

How often the aurora is visible in an area, MacDonald says, depends upon a host of factors, including the intensity of the solar wind; the season--the aurora may be strongest around the spring and fall equinoxes; whether the sun is near the peak of its 11-year cycle; and how far someone is from what scientists call the auroral oval, the lights' ring-shaped display.

Knowing where and when an aurora is happening has been difficult to find out--until now. A new project called Aurorasaurus allows citizens around the world to track auroras and report on their progress.

Visitors to the Aurorasaurus website can see where an aurora is happening in real-time, let other Aurorasaurus visitors know of an aurora's existence, and receive "early warnings" when an aurora is likely to happen in their Earth-neighborhood.

Aurora-power

"Auroras are beautiful displays that have fascinated humans through the ages," says Therese Moretto Jorgensen, program director in the National Science Foundation's (NSF) Directorate for Geosciences, which, along with NSF's Directorate for Education and Human Resources and Directorate for Computer & Information Science & Engineering, funds Aurorasaurus through NSF's INSPIRE program.

INSPIRE supports projects whose scientific advances lie outside the scope of a single program or discipline, lines of research that promise transformational advances, and prospective discoveries at the interfaces of scientific boundaries.

"Auroras are of major interest," says Moretto Jorgensen, "because of their effects on Earth. There's a close relationship between auroras and the magnetic variations that pose a threat to the power grid.

"A better understanding of when and where auroras happen will help us develop models that can forecast these potentially hazardous events."

Amassing new data

Scientists hope that by amassing data from thousands of aurora-viewers, they'll learn more about the solar storms that can disrupt or destroy Earth's communications networks and affect the planet's navigation, pipeline, electrical and transportation systems.

During one solar storm in 1989, transformers in New Jersey melted and wiped out power all the way to Quebec, leaving millions of people in the dark.

The largest such solar storm in history, the Carrington Event, zapped Earth in 1859. It was so large it lit up the skies with auroras from the poles to the tropics. Electrical currents from the storm caused fires in telegraph systems and knocked out communications.

St. Patrick's Day magic in the skies

Could it happen again? Yes, if St. Patrick's Day this year is any guide.

On March 17, 2015, researchers and the public were treated to once-a-decade views. As people waited for glimpses of leprechauns, they saw something even more magical, viewers say.

Earth experienced the biggest solar storm to date of this 11-year sun cycle, sparking auroras around the world.

The St. Patrick's Day auroras, many of which were indeed green, were a fortuitous combination of events. Two days earlier, there was an explosion on the sun. The explosion, called a coronal mass ejection (CME), unleashed a blast of gas bubbles that created a strong disturbance as it collided with Earth's magnetic field.

The CME's magnetic field was directed southward, opposite to the Earth's magnetic field, and the solar wind whipped by very fast, says MacDonald.

"The storm's conditions led to a perfect environment for aurora-hunting," she says. On a scale of G1 (minor) to G5 (extreme), the storm reached a G4, or "severe" level.

The storm's Kp index, a global solar storm index, registered in the 6-8 range (9 is the highest).

Rare aurora-viewing--all the way to the southern U.S.

The strong solar wind blew for more than 24 hours, creating auroras visible as far south as the central and southern United States--a very rare occurrence.

The solar storm's peak hit during the daytime over most of the United States and Europe, but the storm persisted into the night and offered Americans and Europeans a brilliant nighttime light show.

Aurorasaurus reports came in from unusual regions: the south of England, Germany and Poland. In the United States, people spotted auroras in states such as Pennsylvania, Virginia and Colorado.

Data peak from Aurorasaurus users

Aurorasaurus participants logged more than 160 sightings during the St. Patrick's Day solar storm.

From midnight on March 17th through mid-day on March 18th, the number of registered users increased by 50 percent. Registering allows Aurorasaurus to communicate information in return, sending location-based sighting alerts.

"We combine reports to provide real-time alerts when auroras might be visible nearby," says MacDonald. "During this storm alone, we issued 361 such notifications.

"We're using Aurorasaurus data to improve auroral oval models, and to develop a better notification system using both satellite-based data and citizen science data."

Adds Moretto Jorgensen, "Auroras on a global scale are very difficult to capture using traditional scientific methods. Human observers linked through Aurorasaurus are a unique network for documenting them."

Whether on St. Patrick's Day or any other Earth-day, the aurora carries a message: take time to look up at one of the planet's most breathtaking sights.

Then look down, to be sure you can send photos of the event from your cell phone. Spirits dancing across the skies may have played havoc with its transmissions.

-- Cheryl Dybas, NSF
Investigators
Andrea Tapia
Michelle Hall
Elizabeth MacDonald