Month: May 2015

By Raphael Rosen, Princeton Plasma Physics Laboratory

Scientists from General Atomics and the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have discovered a phenomenon that helps them to improve fusion plasmas, a finding that may quicken the development of fusion energy. Together with a team of researchers from across the United States, the scientists found that when they injected tiny grains of lithium into a plasma undergoing a particular kind of turbulence then, under the right conditions, the temperature and pressure rose dramatically. High heat and pressure are crucial to fusion, a process in which atomic nuclei – or ions – smash together and release energy — making even a brief rise in pressure of great importance for the development of fusion energy.

“These findings might be a step towards creating our ultimate goal of steady-state fusion, which would last not just for milliseconds, but indefinitely,” said Tom Osborne, a physicist at General Atomics and lead author of the paper. This work was supported by the DOE Office of Science.

The scientists used a device developed at PPPL to inject grains of lithium measuring some 45 millionths of a meter in diameter into a plasma in the DIII-D National Fusion Facility – or tokamak – that General Atomics operates for DOE in San Diego. When the lithium was injected while the plasma was relatively calm, the plasma remained basically unaltered. Yet as reported this month in a paper in Nuclear Fusion, when the plasma was undergoing a kind of turbulence known as a “bursty chirping mode,” the injection of lithium doubled the pressure at the outer edge of the plasma. In addition, the length of time that the plasma remained at high pressure rose by more than a factor of 10.

Experiments have sustained this enhanced state for up to one-third of a second. A key scientific objective will be to extend this enhanced performance for the full duration of a plasma discharge.

Physicists have long known that adding lithium to a fusion plasma increases its performance. The new findings surprised researchers, however, since the small amount of lithium raised the plasma’s temperature and pressure more than had been expected.

These results “could represent the birth of a new tool for influencing or perhaps controlling tokamak edge physics,” said Dennis Mansfield, a physicist at PPPL and a coauthor of the paper who helped develop the injection device called a “lithium dropper.” Also working on the experiments were researchers from Lawrence Livermore National Laboratory, Oak Ridge National Laboratory, the University of Wisconsin-Madison and the University of California-San Diego.

Conditions at the edge of the plasma have a profound effect on the superhot core of the plasma where fusion reactions take place. Increasing pressure at the edge region raises the pressure of the plasma as a whole. And the greater the plasma pressure, the more suitable conditions are for fusion reactions. “Making small changes at the plasma’s edge lets us increase the pressure further within the plasma,” said Rajesh Maingi, manager of edge physics and plasma-facing components at PPPL and a coauthor of the paper.

Further experiments will test whether the lithium’s interaction with the bursty chirping modes — so-called because the turbulence occurs in pulses and involves sudden changes in pitch — caused the unexpectedly strong overall effect.

PPPL, on Princeton University’s Forrestal Campus in Plainsboro, N.J., is devoted to creating new knowledge about the physics of plasmas — ultra-hot, charged gases — and to developing practical solutions for the creation of fusion energy. Results of PPPL research have ranged from a portable nuclear materials detector for anti-terrorist use to universally employed computer codes for analyzing and predicting the outcome of fusion experiments. The Laboratory is managed by the University for the U.S. Department of Energy’s Office of Science, which is the largest single supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

Read the abstract

T.H. Osborne, G.L. Jackson, Z. Yan, R. Maingi, D.K. Mansfield, B.A. Grierson, C.B. Chrobak, A.G. McLean, S.L. Allen, D.J. Battaglia, A.R. Briesemeister, M.E. Fenstermacher, G.R. McKee, P.B. Snyder and The DIII-D Team. “Enhanced H-mode pedestals with lithium injection in DIII-D.” Nuclear Fusion. Published May 8, 2015. DOI:10.1088/0029-5515/55/6/063018

New research published in Nature Communications led by Meiyun Lin of NOAA’s Geophysical Fluid Dynamics Laboratory and NOAA’s cooperative institute at Princeton University, reveals a strong connection between high ozone days in the western U.S. during late spring and La Niña, an ocean-atmosphere phenomena that affects global weather patterns.

Recognizing this link offers an opportunity to forecast ozone several months in advance, which could improve public education to reduce health effects. It would also help western U.S. air quality managers prepare to track these events, which can have implications for attaining the national ozone standard.

Exposure to ozone is harmful to human health, can cause breathing difficulty, coughing, scratchy and sore throats, and asthma attacks, and can damage sensitive plants.

“Ozone in the stratosphere, located 6 to 30 miles (10 to 48 kilometers) above the ground, typically stays in the stratosphere,” said Lin, an associate research scholar in the Program in Atmospheric and Oceanic Sciences at Princeton University. “But not on some days in late spring following a strong La Niña winter. That’s when the polar jet stream meanders southward over the western U.S. and facilitates intrusions of stratospheric ozone to ground level where people live.”

Over the last two decades, there have been three La Niña events – 1998-1999, 2007-2008 and 2010-2011. After these events, scientists saw spikes in ground level ozone for periods of two to three days at a time during late spring in high altitude locations of the U.S. West.

While high ozone typically occurs on muggy summer days when pollution from cars and power plants fuels the formation of regional ozone pollution, high-altitude regions of the U.S. West sometimes have a different source of high ozone levels in late spring. On these days, strong gusts of cold dry air associated with downward transport of ozone from the stratosphere pose a risk to these communities.

Lin and her colleagues found that these deep intrusions of stratospheric ozone could add 20 to 40 parts per billion of ozone to the ground-level ozone concentration, which can provide over half the ozone needed to exceed the standard set by the U.S. Environmental Protection Agency. The EPA has proposed tightening that standard currently set at 75 parts per billion for an eight-hour average to between 65 and 70 parts per billion.

Under the Clean Air Act, these deep stratospheric ozone intrusions can be classified as “exceptional events” that are not counted towards EPA attainment determinations. As our national ozone standard becomes more stringent, the relative importance of these stratospheric intrusions grows, leaving less room for human-caused emissions to contribute to ozone pollution prior to exceeding the level set by the U.S. EPA.

“Regardless of whether these events count towards non-attainment, people are living in these regions and the possibility of predicting a high-ozone season might allow for public education to minimize adverse health effects,” said Arlene Fiore, an atmospheric scientist at Columbia University and a co-author of the research.

Predicting where and when stratospheric ozone intrusions may occur would also provide time to deploy air sensors to obtain evidence as to how much of ground-level ozone can be attributed to these naturally occurring intrusions and how much is due to human-caused emissions.

The study involved collaboration across two NOAA laboratories, NOAA’s cooperative institutes at Princeton and the University of Colorado Boulder, and scientists at partner institutions in the U.S., Canada and Austria. It was also supported in part by the NASA Air Quality Applied Sciences Team whose mission is to apply earth science data to help address air quality management needs.

“This study brings together observations and chemistry-climate modeling to help understand the processes that contribute to springtime high-ozone events in the western U.S.,” said Andrew Langford, an atmospheric scientist at NOAA’s Earth System Research Laboratory in Boulder, Colorado, whose teams measure ozone concentrations using lidar and balloon-borne sensors.

“You’ve heard about good ozone, the kind found high in the stratosphere that protects the earth from harmful ultraviolet radiation,” said Langford. “And you’ve heard about bad ozone at ground level. This study looks at the factors that cause good ozone to go bad.”

Lin, Fiore and Langford conducted the research with Larry Horowitz of NOAA’s Geophysical Fluid Dynamics Laboratory; Samuel Oltmans of the Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder, who works in NOAA’s Earth System Research Laboratory; David Tarasick of Environment Canada; and Harald Rieder of the University of Graz in Austria.

Read the article in Nature Communications.

Citation:

Meiyun Lin, Arlene M. Fiore, Larry W. Horowitz, Andrew O. Langford, Samuel J. Oltmans, David Tarasick & Harald E. Rieder. Climate variability modulates western US ozone air quality in spring via deep stratospheric intrusions. Nature Communications 6, No 7105 doi:10.1038/ncomms8105

Courtesy of National Oceanic and Atmospheric Administration (NOAA) Communications & External Affairs