Bubbling, frothing and sloshing: Long-hypothesized plasma instabilities finally observed

Whether between galaxies or within doughnut-shaped fusion devices known as tokamaks, the electrically charged fourth state of matter known as plasma regularly encounters powerful magnetic fields, changing shape and sloshing in space. Now, a new measurement technique using protons, subatomic particles that form the nuclei of atoms, has captured details of this sloshing for the first time, potentially providing insight into the formation of enormous plasma jets that stretch between the stars.

Scientists at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL) created detailed pictures of a magnetic field bending outward because of the pressure created by expanding plasma. As the plasma pushed on the magnetic field, bubbling and frothing known as magneto-Rayleigh Taylor instabilities arose at the boundaries, creating structures resembling columns and mushrooms.

Then, as the plasma's energy diminished, the magnetic field lines snapped back into their original positions. As a result, the plasma was compressed into a straight structure resembling the jets of plasma that can stream from ultra-dense dead stars known as black holes and extend for distances many times the size of a galaxy. The results suggest that those jets, whose causes remain a mystery, could be formed by the same compressing magnetic fields observed in this research.

"When we did the experiment and analyzed the data, we discovered we had something big," said Sophia Malko, a PPPL staff research physicist and lead scientist on the paper. "Observing magneto-Rayleigh Taylor instabilities arising from the interaction of plasma and magnetic fields had long been thought to occur but had never been directly observed until now. This observation helps confirm that this instability occurs when expanding plasma meets magnetic fields. We didn't know that our diagnostics would have that kind of precision. Our whole team is thrilled!"

"These experiments show that magnetic fields are very important for the formation of plasma jets," said Will Fox, a PPPL research physicist and principal investigator of the research reported in Physical Review Research. "Now that we might have insight into what generates these jets, we could, in theory, study giant astrophysical jets and learn something about black holes."

PPPL has world-renowned expertise in developing and building diagnostics, sensors that measure properties like density and temperature in plasma in a range of conditions. This achievement is one of several in recent years that illustrates how the Lab is advancing measurement innovation in plasma physics.

Using a new technique to produce unprecedented detail

The team improved a measurement technique known as proton radiography by creating a new variation for this experiment that would allow for extremely precise measurements. To create the plasma, the team shone a powerful laser at a small disk of plastic. To produce protons, they shone 20 lasers at a capsule containing fuel made of varieties of hydrogen and helium atoms. As the fuel heated up, fusion reactions occurred and produced a burst of both protons and intense light known as X-rays.

The team also installed a sheet of mesh with tiny holes near the capsule. As the protons flowed through the mesh, the outpouring was separated into small, separate beams that were bent because of the surrounding magnetic fields. By comparing the distorted mesh image to an undistorted image produced by X-rays, the team could understand how the magnetic fields were pushed around by the expanding plasma, leading to whirl-like instabilities at the edges.

"Our experiment was unique because we could directly see the magnetic field changing over time," Fox said. "We could directly observe how the field gets pushed out and responds to the plasma in a type of tug of war."

Diversifying a research portfolio

The findings exemplify how PPPL is expanding its focus to include research focused on high energy density (HED) plasma. Such plasmas, like the one created in this experiment's fuel capsule, are hotter and denser than those used in fusion experiments. "HED plasma is an exciting area of growth for plasma physics," Fox said. "This work is part of PPPL's efforts to advance this field. The results show how the Laboratory can create advanced diagnostics to give us new insights into this type of plasma, which can be used in laser fusion devices, as well as in techniques that use HED plasma to create radiation for microelectronics manufacturing."

"PPPL has an enormous amount of knowledge and experience in magnetized plasmas that can contribute to the field of laser-produced HED plasmas and help make significant contributions," Fox said.

"HED science is complex, fascinating and key to understanding a wide range of phenomena," said Laura Berzak Hopkins, PPPL's associate laboratory director for strategy and partnerships and deputy chief research officer. "It's incredibly challenging to both generate these conditions in a controlled manner and develop advanced diagnostics for precision measurements. These exciting results demonstrate the impact of integrating PPPL's breadth of technical expertise with innovative approaches."

More experiments and better simulations

The researchers plan to work on future experiments that will help improve models of expanding plasma. "Scientists have assumed that in these situations, density and magnetism vary directly, but it turns out that that's not true," Malko said.

"Now that we have measured these instabilities very accurately, we have the information we need to improve our models and potentially simulate and understand astrophysical jets to a higher degree than before," Malko said. "It's interesting that humans can make something in a laboratory that usually exists in space."

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Agricultural impact of flooding

I can barely hear Esther Ngumbi over the roar of greenhouse fans as she shows me around her rooftop laboratory in Morrill Hall. The benches are full of tomato plants, and the tomatoes don't look good. Half of the plants are submerged in bins of water. Their leaves are yellow and withering. Some of the dying tomatoes have flowered. I see one or two baby tomatoes on a couple of spindly plants.

This isn't the only torture inflicted on the tomatoes. Someone has tied little baggies to their stems. Inside the bags, fat green caterpillars are chowing down on the tomato leaves.

Entomology professor Ngumbi has questions -- lots of them -- and this is how she's set out to answer some of them. She is purposely flooding the tomatoes to see how they might respond to flooded conditions in farmers' fields -- a scenario that is becoming more common as a result of climate change.

"In nature, there are many stressors on plants during flooding," Ngumbi says. "Once the tomatoes get flooded, they're already weak, so most likely they will be attracting insects, which like to eat weaker plants. We're investigating how the plants deal with the combined stress of flooding and herbivory."

This explains the caterpillars. They are the larval form of Manduca sexta, the tobacco hornworm. They are feasting on one of the two heirloom tomato varieties Ngumbi is using in the experiment: Cherokee purple and striped German.

Half of the tomato plants in the greenhouse are not flooded, allowing the team to compare the stressed plants with those grown in more common conditions. But there are more investigations going on here.

"Also, within this experiment, we're looking at the microbes," Ngumbi says. "We want to understand how the microbial community changes in flooded conditions."

One of Ngumbi's key focuses is how soil microbes influence plant health and productivity. She's fascinated by mycorrhizal fungi, which form intimate associations with plant roots, offering essential elements like nitrogen to the plants in exchange for glucose supplied by the roots.

The tomato plants are all growing in soil from an Illinois farm, but half were also inoculated with mulch from a local farmer who has developed his own recipe for nurturing mycorrhizal fungi in the soil. Ngumbi wants to see if this inoculation makes any difference to the plants' ability to defend themselves from the fat caterpillars.

To measure plant defenses, Ngumbi's team collects samples of gases emitted by the plants and screens them for volatile organic compounds, the chemicals plants use to ward off bugs that would eat them.

Two years later, Ngumbi publishes the results of these and other laboratory experiments. She found that the two tomato varieties differed in gene expression and in the volatile compounds they emitted -- before any intervention. And when flooded, both varieties of tomatoes had very different chemical emission profiles than when grown in normal conditions. Herbivory influenced the production of these volatile compounds, but not as much as flooding did.

Today, the experiments continue, and Ngumbi's interest in the effects of flooding has only intensified. In a new review published in the journal Trends in Plant Research, she spells out the many changes that occur when plants are inundated with water for days or weeks at a time.

"Flooding is different from other climate-related stressors because it deprives plants of oxygen, an essential and indispensable element and substrate for plant growth and development," Ngumbi writes. Flooding disrupts plant metabolism and energy generation. It interferes with photosynthesis. Flooding kills beneficial bacteria and promotes pathogenic microbes in the soil. It also can compromise plants' ability to defend themselves from disease and harmful insects like the tobacco hornworm.

Ngumbi also warns that increased flooding can undermine decades of research aimed at making plants more resilient to climate change. Flooding may thwart efforts to build soil quality and microbial health to make crops more resilient to stressors such as heat and drought. Flooding also may eliminate gains derived from genetic engineering or plant breeding.

With flooding intensity and frequency predicted to increase by roughly 7% for every 1° C increase in global average temperatures, Ngumbi writes, scientists must consider the impacts of floods to "protect the monumental gains made in building climate-resilient crops."

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Drug may stop migraines before headache starts

When taken at the first signs of a migraine, before headache pain begins, a drug called ubrogepant may be effective in helping people with migraine go about their daily lives with little or no symptoms, according to a new study published in the August 28, 2024, online issue of Neurology®, the medical journal of the American Academy of Neurology. The study focused on people with migraine who could tell when an attack was about to happen, due to early symptoms such as sensitivity to light and sound, fatigue, neck pain or stiffness, or dizziness.

Ubrogepant is a calcitonin gene-related peptide receptor antagonist, or CGRP inhibitor. CGRP is a protein that plays a key role in the migraine process.

"Migraine is one of the most prevalent diseases worldwide, yet so many people who suffer from this condition do not receive treatment or report that they are not satisfied with their treatment," said study author Richard B. Lipton, MD, of Albert Einstein College of Medicine in Bronx, New York, and Fellow of the American Academy of Neurology. "Improving care at the first signs of migraine, even before headache pain begins, can be a key to improved outcomes. Our findings are encouraging, suggesting that ubrogepant may help people with migraine function normally and go about their day."

The study involved 518 participants who had migraine for at least one year and two to eight migraine attacks per month in the three months before the study. All of the participants regularly experienced signs that a migraine would be starting within the next few hours. Participants were asked to treat two attacks during a two-month period.

Researchers divided participants into two groups. The first group received a placebo for their first set of pre-headache symptoms of migraine, followed by taking 100 milligrams (mg) of ubrogepant for their second instance of symptoms. The second group took ubrogepant for the first instance and placebo for the second instance.

Participants evaluated limitations on their activity in their diary using a scale ranging from zero to five, with 0 meaning "not at all limited -- I could do everything"; 1, "a little limited"; 2, "somewhat limited"; 3, "very limited"; or 4, "extremely limited."

Twenty-four hours after taking the drug or a placebo, 65% of people who took ubrogepant reported themselves as "not at all limited -- I could do everything," or "a little limited," compared to 48% of those who took the placebo.

Researchers found that as early as two hours post-medication, people who took the drug were 73% more likely to report that they had "no disability, able to function normally," than those who took the placebo.

"Based on our findings, treatment with ubrogepant may allow people with migraine who experience early warning signs before a migraine occurs to quickly treat migraine attacks in their earliest stages and go about their daily lives with little discomfort and disruption," said Lipton. "This could lead to an improved quality of life for those living with migraine."

Lipton noted that participants showed that based on their headache warning symptoms, they could reliably predict impending migraine headaches. These findings apply only to those with reliable warning symptoms.

A limitation of the study was that participants recorded their symptoms and medication use in electronic diaries, so it is possible some people may not have recorded all information accurately.

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