PPPL researchers combine quantum mechanics and Einstein’s theory of special relativity to clear up puzzles in plasma physics (Phys. Rev. A)

Sketch of a pulsar, center, in binary star system (Photo credit: NASA Goddard Space Flight Center)

Sketch of a pulsar, center, in binary star system (Photo credit: NASA Goddard Space Flight Center)

By John Greenwald, Princeton Plasma Physics Laboratory Communications

Among the intriguing issues in plasma physics are those surrounding X-ray pulsars — collapsed stars that orbit around a cosmic companion and beam light at regular intervals, like lighthouses in the sky.  Physicists want to know the strength of the magnetic field and density of the plasma that surrounds these pulsars, which can be millions of times greater than the density of plasma in stars like the sun.

Researchers at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have developed a theory of plasma waves that can infer these properties in greater detail than in standard approaches. The new research analyzes the plasma surrounding the pulsar by coupling Einstein’s theory of relativity with quantum mechanics, which describes the motion of subatomic particles such as the atomic nuclei — or ions — and electrons in plasma. Supporting this work is the DOE Office of Science.

Quantum field theory

Graduate student Yuan Shi Graduate student Yuan Shi (Photo by Elle Starkman/PPPL Office of Communications)

Graduate student Yuan Shi (Photo by Elle Starkman/PPPL Office of Communications)

The key insight comes from quantum field theory, which describes charged particles that are relativistic, meaning that they travel at near the speed of light. “Quantum theory can describe certain details of the propagation of waves in plasma,” said Yuan Shi, a graduate student at Princeton University in the Department of Astrophysics’ Princeton Program in Plasma Physics, and lead author of a paper published July 29 in the journal Physical Review A.  Understanding the interactions behind the propagation can then reveal the composition of the plasma.

Shi developed the paper with assistance from co-authors Nathaniel Fisch, director of the Princeton Program in Plasma Physics and professor and associate chair of astrophysical sciences at Princeton University, and Hong Qin, a physicist at PPPL and executive dean of the School of Nuclear Science and Technology at the University of Science and Technology of China.  “When I worked out the mathematics they showed me how to apply it,” said Shi. 

In pulsars, relativistic particles in the magnetosphere, which is the magnetized atmosphere surrounding the pulsar, absorb light waves, and this absorption displays peaks. “The question is, what do these peaks mean?” asks Shi. Analysis of the peaks with equations from special relativity and quantum field theory, he found, can determine the density and field strength of the magnetosphere.

Combining physics techniques

The process combines the techniques of high-energy physics, condensed matter physics, and plasma physics.  In high-energy physics, researchers use quantum field theory to describe the interaction of a handful of particles. In condensed matter physics, people use quantum mechanics to describe the states of a large collection of particles. Plasma physics uses model equations to explain the collective movement of millions of particles. The new method utilizes aspects of all three techniques to analyze the plasma waves in pulsars.

The same technique can be used to infer the density of the plasma and strength of the magnetic field created by inertial confinement fusion experiments. Such experiments use lasers to ablate — or vaporize —a target that contains plasma fuel. The ablation then causes an implosion that compresses the fuel into plasma and produces fusion reactions.

Standard formulas give inconsistent answers

Researchers want to know the precise density, temperature and field strength of the plasma that this process creates. Standard mathematical formulas give inconsistent answers when lasers of different color are used to measure the plasma parameters. This is because the extreme density of the plasma gives rise to quantum effects, while the high energy density of the magnetic field gives rise to relativistic effects, says Shi. So formulations that draw upon both fields are needed to reconcile the results.

For Shi, the new technique shows the benefits of combining physics disciplines that don’t often interact. Says he: “Putting fields together gives tremendous power to explain things that we couldn’t understand before.”

Read the abstract

Yuan Shi, Nathaniel J. Fisch, and Hong Qin. Effective-action approach to wave propagation in scalar QED plasmas. Phys. Rev. A 94, 012124 – Published 29 July 2016.

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 Princeton 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, visit science.energy.gov.

PPPL scientists challenge conventional understanding and improve predictions of the bootstrap current at the edge of fusion plasmas (Physics of Plasmas)

Simulation shows trapped electrons at left and passing electrons at right that are carried in the bootstrap current of a tokamak. Credit: Kwan Liu-Ma, University of California, Davis.

Simulation shows trapped electrons at left and passing electrons at right that are carried in the bootstrap current of a tokamak. Credit: Kwan Liu-Ma, University of California, Davis.

By John Greenwald, PPPL Office of Communications

Researchers at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have challenged understanding of a key element in fusion plasmas. At issue has been an accurate prediction of the size of the “bootstrap current” — a self-generating electric current — and an understanding of what carries the current at the edge of plasmas in doughnut-shaped facilities called tokamaks. This bootstrap-generated current combines with the current in the core of the plasma to produce a magnetic field to hold the hot gas together during experiments, and can produce stability at the edge of the plasma.

The recent work, published in the April issue of the journal Physics of Plasmas, focuses on the region at the edge in which the temperature and density drop off sharply. In this steep gradient region — or pedestal — the bootstrap current is large, enhancing the confining magnetic field but also triggering instability in some conditions.

The bootstrap current appears in a plasma when the pressure is raised. It was first discovered at the University of Wisconsin by Stewart Prager, now director of PPPL, and Michael Zarnstorff, now deputy director for research at PPPL. Prager was Zarnstorff’s thesis advisor at the time.

Physics understanding and accurate prediction of the size of the current at the edge of the plasma is essential for predicting its effect on instabilities that can diminish the performance of fusion reactors. Such understanding will be vital for ITER, the international tokamak under construction in France to demonstrate the feasibility of fusion power. This work was supported by the DOE Office of Science (FES).

The new paper, by physicists Robert Hager and C.S. Chang, leader of the Scientific Discovery through Advanced Computing project’s Center for Edge Physics Simulation headquartered at PPPL, discovered that the bootstrap current in the tokamak edge is mostly carried by the “magnetically trapped” electrons that cannot travel as freely as the “passing” electrons in plasma. The trapped particles bounce between two points in the tokamak while the passing particles swirl all the way around it.

The discovery challenges conventional understanding and provides an explanation of how the bootstrap current can be so large at the tokamak edge, where the passing electron population is small. Previously, physicists thought that only the passing electrons carry the bootstrap current. “Correct modeling of the current enables accurate prediction of the instabilities,” said Hager, the lead author of the paper.

The researchers performed the study by running an advanced global code called “XGCa” on the Mira supercomputer at the Argonne Leadership Computing Facility, a DOE Office of Science User Facility located at the Department’s Argonne National Laboratory. Researchers turned to the new global code, which models the entire plasma volume, because simpler local computer codes can become inadequate and inaccurate in the pedestal region.

Numerous XGCa simulations led Hager and Chang to construct a new formula that greatly improves the accuracy of bootstrap current predictions. The new formula was found to fit well with all the XGCa cases studied and could easily be implemented into modeling or analysis codes.

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 and article.

The paper, “Gyrokinetic neoclassical study of the bootstrap current in the tokamak edge pedestal with fully non-linear Coulomb collisions,” by Robert Hager and C.S. Chang, was published in the April, 2016, Physics of Plasmas, doi: 10.1063/1.4945615.

Support for this work was provided through the Scientific Discovery through Advanced Computing (SciDAC) program funded by the U.S. Department of Energy Office of Advanced Scientific Computing Research and the Office of Fusion Energy Sciences.

Compressing turbulence to improve inertial confinement fusion experiments (PRL)

Compression of a turbulent plasma. Credit: Seth Davidovits

Compression of a turbulent plasma. Credit: Seth Davidovits

By John Greenwald, Princeton Plasma Physics Laboratory

Physicists have long regarded plasma turbulence as unruly behavior that can limit the performance of fusion experiments. But new findings by researchers associated with the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) and the Department of Astrophysical Sciences at Princeton University indicate that turbulent swirls of plasma could benefit one of the two major branches of such research.   The editors of Physical Review Letters highlighted these findings — a distinction given to one of every six papers per issue — when they published the results last week on March 11.

Lead author Seth Davidovits, a Princeton University graduate student, and Professor of Astrophysical Sciences Nathaniel Fisch, his thesis adviser and Associate Director for Academic Affairs at PPPL, produced the findings. They modeled the compression of fluid turbulence, showing effects that suggested a surprising positive impact of turbulence on inertial confinement fusion (ICF) experiments.

Stimulating this work were experiments conducted by Professor Yitzhak Maron at the Weizmann Institute of Science in Israel. Those experiments, on a Z-pinch inertial confinement machine, showed turbulence that contained a surprising amount of energy, which caught Fisch’s attention during a recent sabbatical at Weizmann.

In a Z-pinch and other inertial confinement (ICF) machines, plasma is compressed to create fusion energy. The method contrasts with the research done at PPPL and other laboratories, which controls plasma with magnetic fields and heats it to fusion temperatures in doughnut-shaped devices called tokamaks. The largest Z-pinch device in the United States is at the DOE’s Sandia National Laboratory. Other inertial confinement approaches are pursued at, among other places, the DOE’s Lawrence Livermore National Laboratory.

Present ICF approaches use compression to steadily heat the plasma. Methods range from squeezing plasma with magnetic fields at Sandia to firing lasers at capsules filled with plasma at Livermore’s National Ignition Facility. The presence of turbulence in the plasma is widely thought to increase the difficulty of achieving fusion.

But there could be advantages to turbulence if handled properly, the authors point out, since energy contained in turbulence does not radiate away. This compares with hotter plasmas in which heat radiates away quickly, making fusion harder to achieve. By storing the energy of the compression in turbulence rather than temperature, the authors suppress the energy lost to radiation during the compression.

The turbulent energy also does not immediately lead to fusion, which requires high temperature. This means a mechanism is needed to change the turbulence into the temperature required for fusion once the plasma has been compressed.

Davidovits used a software code called Dedalus to show that turbulent energy is increased during the compression, but then suddenly transformed into heat. As external forces in his simulation compress the turbulence to increase the energy stored within it, they also gradually raise the temperature and viscosity of the plasma. The viscosity, which describes how “thick” or resistant to flow a fluid is, acts to slow the turbulence and convert its energy to temperature. The viscosity started small so that the turbulence was initially unhindered. The rapid compression then kept the viscosity growing until it suddenly catalyzed the transfer of energy from the turbulence to the temperature.

In an experiment, this process would create the conditions for nuclear fusion in a plasma composed of the hydrogen isotopes deuterium and tritium. “This suggests a fundamentally different design for compression-based fusion experiments,” Davidovits said, “and a new paradigm for the inertial technique of producing fusion energy.”

He warns, however, that the simulation includes caveats that could diminish the findings. For example, the model doesn’t consider any possible interaction between the plasma and the containing capsule, and highly energetic turbulence might mix parts of the capsule into the plasma and contaminate the fusion fuel.

Nonetheless, the authors call the rapid transfer of turbulent energy into temperature during ICF experiments a “tantalizing” prospect that could benefit such research. And they note that their findings could lead to new understanding of the evolution of the relationship between the pressure, volume and temperature of a gas that is substantially turbulent. Determining this will be quite challenging, they say, “but the understanding will be important not only for the new fusion approach, but also for many situations involving the behavior of low viscosity compressible fluids and gases.”

This research was initiated through a grant by the Defense Threat Reduction Agency, a unit of the U.S. Department of Defense, and has been supported also by the DOE’s National Nuclear Security Administration through a consortium with Cornell University. Recently, the National Science Foundation and the Israel Binational Science Foundation combined funding opportunities to ensure further experiments at Weizmann on this topic and continued collaboration with the Princeton researchers.

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 or paper here.

S. Davidovits, N. Fisch, Sudden Viscous Dissipation of Compressing Turbulence. Phys. Rev. Lett. 116, 105004 – Published 11 March 2016.

This work was supported by DOE through Contracts No. DE-AC02-09CH1-1466 and NNSA 67350-9960 (Prime No. DOE DE-NA0001836), by DTRA HDTRA1-11-1-0037, and by NSF Contract No. PHY-1506122.

 

PPPL physicists simulate innovative method for starting up tokamaks without using a solenoid (Nuclear Fusion)

Francesca Poli

PPPL Scientist Francesca Poli. Photo Credit: Elle Starkman / PPPL Office of Communications. PPPL, located on Princeton University’s Forrestal Campus and managed by the University, is devoted to developing practical solutions for the creation of sustainable energy from fusion and to creating new knowledge about the physics of ultra-hot, charged gases known as plasmas.

By Raphael Rosen, PPPL Office of Communications

Scientists at the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) have produced self-consistent computer simulations that capture the evolution of an electric current inside fusion plasma without using a central electromagnet, or solenoid.

The computer simulations of the process, known as non-inductive current ramp-up, were performed using TRANSP, the gold-standard code developed at PPPL. The results were published in October 2015 in the journal Nuclear Fusion. The research was supported by the DOE Office of Science.

In traditional donut-shaped tokamaks, a large solenoid runs down the center of the reactor. By varying the electrical current in the solenoid scientists induce a current in the plasma. This current starts up the plasma and creates a second magnetic field that completes the forces that hold the hot, charged gas together.

But spherical tokamaks, a compact variety of fusion reactor that produces high plasma pressure with relatively low magnetic fields, have little room for solenoids. Spherical tokamaks look like cored apples and have a smaller central hole for the solenoid than conventional tokamaks do. Physicists, therefore, have been trying to find alternative methods for producing the current that starts the plasma and completes the magnetic field in spherical tokamaks.

One such method is known as coaxial helicity injection (CHI). During CHI, researchers switch on an electric coil that runs beneath the tokamak. Above this coil is a gap that opens into the tokamak’s vacuum vessel and circles the tokamak’s floor. The switched-on electrical current produces a magnetic field that connects metal plates on either side of the gap.

Researchers next puff gas through the gap and discharge a spark across the two plates. This process causes magnetic reconnection — the process by which the magnetic fields snap apart and reconnect. This reconnection creates a magnetic bubble that fills the tokamak and produces the vital electric current that starts up the plasma and completes the magnetic field.

This current must be nurtured and fed. According to lead author Francesca Poli, the new computer simulations show that the current can best be sustained by injecting high-harmonic radio-frequency waves (HHFWs) and neutral beams into the plasma.

HHFW’s are radio-frequency waves that can heat both electrons and ions. The neutral beams, which consist of streams of hydrogen atoms, become charged when they enter the plasma and interact with the ions. The combination of the HHFWs and neutral beams increases the current from 300 kiloamps to 1 mega amp.

But neither HHFWs nor neutral beams can be used at the start of the process, when the plasma is relatively cool and not very dense. Poli found that HHFWs would be more effective if the plasma were first heated by electron cyclotron waves, which transfer energy to the electrons that circle the magnetic field lines.

“With no electron cyclotron waves you would have to pump in four megawatts of HHFW power to create 400 kiloamps of current,” she said. “With these waves you can get the same amount of current by pumping in only one megawatt of power.

“All of this is important because it’s hard to control the plasma at the start-up,” she added. “So the faster you can control the plasma, the better.”

PPPL is managed by Princeton University for the U.S. Department of Energy’s Office of Science.

Read the abstract.

F.M. Poli, R.G. Andre, N. Bertelli, S.P. Gerhardt, D. Mueller and G. Taylor. “Simulations towards the achievement of non-inductive current ramp-up and sustainment in the National Spherical Torus Experiment Upgrade.” Nuclear Fusion. Published October 30, 2015. DOI: 10.1088/0029-5515/55/12/123011

Using powerful computers, physicists uncover mechanism that stabilizes plasma (Physical Review Letters)

Virtual plasma

A cross-section of the virtual plasma showing where the magnetic field lines intersect the plane. The central section has field lines that rotate exactly once. Image Credit: Stephen Jardin, PPPL.

By Raphael Rosen, Princeton Plasma Physics Laboratory Communications

A team of physicists led by Stephen Jardin of the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) has discovered a mechanism that prevents the electrical current flowing through fusion plasma from repeatedly peaking and crashing. This behavior is known as a “sawtooth cycle” and can cause instabilities within the plasma’s core. The results have been published online in Physical Review Letters. The research was supported by the DOE Office of Science.

The team, which included scientists from General Atomics and the Max Planck Institute for Plasma Physics, performed calculations on the Edison computer at the National Energy Research Scientific Computing Center, a division of the Lawrence Berkeley National Laboratory. Using M3D-C1, a program they developed that creates three-dimensional simulations of fusion plasmas, the team found that under certain conditions a helix-shaped whirlpool of plasma forms around the center of the tokamak. The swirling plasma acts like a dynamo — a moving fluid that creates electric and magnetic fields. Together these fields prevent the current flowing through plasma from peaking and crashing.

The researchers found two specific conditions under which the plasma behaves like a dynamo. First, the magnetic lines that circle the plasma must rotate exactly once, both the long way and the short way around the doughnut-shaped configuration, so an electron or ion following a magnetic field line would end up exactly where it began. Second, the pressure in the center of the plasma must be significantly greater than at the edge, creating a gradient between the two sections. This gradient combines with the rotating magnetic field lines to create spinning rolls of plasma that swirl around the tokamak and gives rise to the dynamo that maintains equilibrium and produces stability.

This dynamo behavior arises only under certain conditions. Both the electrical current running through the plasma and the pressure that the plasma’s electrons and ions exert on their neighbors must be in a range that is “not too large and not too small,” said Jardin. In addition, the speed at which the conditions for the fusion reaction are established must be “not too fast and not too slow.”

Jardin stressed that once a range of conditions like pressure and current are set, the dynamo phenomenon occurs all by itself. “We don’t have to do anything else from the outside,” he noted. “It’s something like when you drain your bathtub and a whirlpool forms over the drain by itself. But because a plasma is more complicated than water, the whirlpool that forms in the tokamak needs to also generate the voltage to sustain itself.”

During the simulations the scientists were able to virtually add new diagnostics, or probes, to the computer code. “These diagnostics were able to measure the helical velocity fields, electric potential, and magnetic fields to clarify how the dynamo forms and persists,” said Jardin. The persistence produces the “voltage in the center of the discharge that keeps the plasma current from peaking.”

Physicists have indirectly observed what they believe to be the dynamo behavior on the DIII-D National Fusion Facility that General Atomics operates for the Department of Energy in San Diego and on the ASDEX Upgrade in Garching, Germany. They hope to learn to create these conditions on demand, especially in ITER, the huge multinational fusion machine being constructed in France to demonstrate the practicality of fusion power. “Now that we understand it better, we think that computer simulations will show us under what conditions this will occur in ITER,” said Jardin. “That will be the focus of our research in the near future.”

Learning how to create these conditions will be particularly important for ITER, which will produce helium nuclei that could amplify the sawtooth disruptions. If large enough, these disruptions could cause other instabilities that could halt the fusion process. Preventing the cycle from starting would therefore be highly beneficial for the ITER experiment.

Read the abstract.

S.C. Jardin, N. Ferraro, and I. Krebs. “Self-Organized Stationary States of Tokamaks.” Physical Review Letters. Published November 17, 2015. DOI: http://dx.doi.org/10.1103/PhysRevLett.115.215001

This article is courtesy of the Princeton Plasma Physics Laboratory.

X marks the spot: Researchers confirm novel method for controlling plasma rotation to improve fusion performance (Physical Review Letters)

Representative plasma geometries, with the X-point location circled in red. (Reprinted from T. Stoltzfus-Dueck et al., Phys. Rev. Lett. 114, 245001, 2015. Copyright 2015 by the American Physical Society.)

Representative plasma geometries, with the X-point location circled in red. (Reprinted from T. Stoltzfus-Dueck et al., Phys. Rev. Lett. 114, 245001, 2015. Copyright 2015 by the American Physical Society.)

By Raphael Rosen, Princeton Plasma Physics Laboratory

Rotation is key to the performance of salad spinners, toy tops, and centrifuges, but recent research suggests a way to harness rotation for the future of mankind’s energy supply. In papers published in Physics of Plasmas in May and Physical Review Letters this month, Timothy Stoltzfus-Dueck, a physicist at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL), demonstrated a novel method that scientists can use to manipulate the intrinsic – or self-generated – rotation of hot, charged plasma gas within fusion facilities called tokamaks. This work was supported by the DOE Office of Science.

Such a method could prove important for future facilities like ITER, the huge international tokamak under construction in France that will demonstrate the feasibility of fusion as a source of energy for generating electricity. ITER’s massive size will make it difficult for the facility to provide sufficient rotation through external means.

Rotation is essential to the performance of all tokamaks. Rotation can stabilize instabilities in plasma, and sheared rotation – the difference in velocities between two bands of rotating plasma – can suppress plasma turbulence, making it possible to maintain the gas’s high temperature with less power and reduced operating costs.

Today’s tokamaks produce rotation mainly by heating the plasma with neutral beams, which cause it to spin. In intrinsic rotation, however, rotating particles that leak from the edge of the plasma accelerate the plasma in the opposite direction, just as the expulsion of propellant drives a rocket forward.

Stoltzfus-Dueck and his team influenced intrinsic rotation by moving the so-called X-point – the dividing point between magnetically confined plasma and plasma that has leaked from confinement – on the Tokamak à Configuration Variable (TCV) in Lausanne, Switzerland. The experiments marked the first time that researchers had moved the X-point horizontally to study plasma rotation. The results confirmed calculations that Stoltzfus-Dueck had published in a 2012 paper showing that moving the X-point would cause the confined plasma to either halt its intrinsic rotation or begin rotating in the opposite direction. “The edge rotation behaved just as the theory predicted,” said Stoltzfus-Dueck.

A surprise also lay in store: Moving the X-point not only altered the edge rotation, but modified rotation within the superhot core of the plasma where fusion reactions occur. The results indicate that scientists can use the X-point as a “control knob” to adjust the inner workings of fusion plasmas, much like changing the settings on iTunes or a stereo lets one explore the behavior of music. This discovery gives fusion researchers a tool to access different intrinsic rotation profiles and learn more about intrinsic rotation itself and its effect on confinement.

The overall findings provided a “perfect example of a success story for theory-experiment collaboration,” said Olivier Sauter, senior scientist at École Polytechnique Fédérale de Lausanne and co-author of the paper.

Along with the practical applications of his research, Stoltzfus-Dueck enjoys the purely intellectual aspect of his work. “It’s just interesting,” he said. “Why do plasmas rotate in the way they do? It’s a puzzle.”

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.

Stoltzfus-Dueck, A. N. Karpushov, O. Sauter, B. P. Duval, B. Labit, H. Reimerdes, W. A. J. Vijvers, the TCV Team, and Y. Camenen. “X-Point-Position-Dependent Intrinsic Toroidal Rotation in the Edge of the TCV Tokamak.” Physical Review Letters 114, 245001 – Published 17 June 2015.

Researchers correlate incidences of rheumatoid arthritis and giant cell arteritis with solar cycles (BMJ Open)

Solar storm

Coronal mass ejection hurling plasma from the sun. (Image credit: NASA)

By John Greenwald, Princeton Plasma Physics Laboratory

What began as a chat between husband and wife has evolved into an intriguing scientific discovery. The results, published in May in BMJ (formerly British Medical Journal) Open, show a “highly significant” correlation between periodic solar storms and incidences of rheumatoid arthritis (RA) and giant cell arteritis (GCA), two potentially debilitating autoimmune diseases. The findings by a rare collaboration of physicists and medical researchers suggest a relationship between the solar outbursts and the incidence of these diseases that could lead to preventive measures if a causal link can be established.

RA and GCA are autoimmune conditions in which the body mistakenly attacks its own organs and tissues. RA inflames and swells joints and can cause crippling damage if left untreated. In GCA, the autoimmune disease results in inflammation of the wall of arteries, leading to headaches, jaw pain, vision problems and even blindness in severe cases.

Inspiring this study were conversations between Simon Wing, a Johns Hopkins University physicist and first author of the paper, and his wife, Lisa Rider, deputy unit chief of the Environmental Autoimmunity Group at the National Institute of Environmental Health Sciences in the National Institutes of Health, and a coauthor. Rider spotted data from the Mayo Clinic in Rochester, Minnesota, showing that cases of RA and GCA followed close to 10-year cycles. “That got me curious,” Wing recalled. “Only a few things in nature have a periodicity of about 10-11 years and the solar cycle is one of them.”

Wing teamed with physicist Jay Johnson of the U.S. Department of Energy’s Princeton Plasma Physics Laboratory, a long-time collaborator, to investigate further. When the physicists tracked the incidence of RA and GCA cases compiled by Mayo Clinic researchers, the results suggested “more than a coincidental connection,” said Eric Matteson, chair of the division of rheumatology at the Mayo Clinic, and a coauthor. This work drew upon previous space physics research supported by the DOE Office of Science.

The findings found increased incidents of RA and GCA to be in periodic concert with the cycle of magnetic activity of the sun. During the solar cycle, dramatic changes that can affect space weather near Earth take place in the sun. At the solar maximum, for example, an increased number of outbursts called coronal mass ejections hurl millions of tons of magnetic and electrically charged plasma gas against the Earth’s magnetosphere, the magnetic field that surrounds the planet. This contact whips up geomagnetic disturbances that can disrupt cell phone service, damage satellites and knock out power grids. More importantly, during the declining phase of the solar maximum high-speed streams develop in the solar wind that is made up of plasma that flows from the sun. These streams continuously buffet Earth’s magnetosphere, producing enhanced geomagnetic activity at high Earth latitudes.

The research, which tracked correlations of the diseases with both geomagnetic activity and extreme ultraviolet (EUV) solar radiation, focused on cases recorded in Olmsted County, Minnesota, the home of the Mayo Clinic, over more than five decades. The physicists compared the data with indices of EUV radiation for the years 1950 through 2007 and indices of geomagnetic activity from 1966 through 2007. Included were all 207 cases of GCA and all 1,179 cases of RA occurring in Olmsted County during the periods and collected in a long-term study led by Sherine Gabriel, then of the Mayo Clinic and now dean of the Rutgers Robert Wood Johnson Medical School.

Correlations proved to be strongest between the diseases and geomagnetic activity. GCA incidence — defined as the number of new cases per capita per year in the county — regularly peaked within one year of the most intense geomagnetic activity, while RA incidence fell to a minimum within one year of the least intense activity. Correlations with the EUV indices were seen to be less robust and showed a significantly longer response time.

The findings were consistent with previous studies of the geographic distribution of RA cases in the United States. Such research found a greater incidence of the disease in sections of the country that are more likely to be affected by geomagnetic activity. For example, the heaviest incidence lay along geographic latitudes on the East Coast that were below those on the West Coast. This asymmetry may reflect the fact that high geomagnetic latitudes — areas most subject to geomagnetic activity — swing lower on the East Coast than on the opposite side of the country. While Washington, D.C., lies just 1 degree farther north than San Francisco geographically, for example, the U.S. capital is 7 degrees farther north in terms of geomagnetic latitude.

Although the authors make no claim to a causal explanation for their findings, they identify five characteristics of the disease occurrence that are not obviously explained by any of the currently leading hypotheses. These include the east-west asymmetries of the RA and GCA outbreaks and the periodicities of the incidences in concert with the solar cycle. Among the possible causal pathways the authors consider are reduced production of the hormone melatonin, an anti-inflammatory mediator with immune-enhancing effects, and increased formation of free radicals in susceptible individuals. A study of 142 electrical power workers found that excretion of melatonin — a proxy used to estimate production of the hormone — was reduced by 21 percent on days with increased geomagnetic activity.

Confirming a causal link between outbreaks of RA and GCA and geomagnetic activity would be an important step towards developing strategies for mitigating the impact of the activity on susceptible individuals. These strategies could include relocating to lower latitudes and developing methods to counteract direct causal agents that may be controlled by geomagnetic activity. For now, say the authors, their findings warrant further investigations covering longer time periods, additional locations and other autoimmune diseases.

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.

This work was funded from NIH grants (NIAMS R01 AR046849, NIA R01 AG034676). This research was supported in part by the Intramural Research Program of the NIH, National Institute of Environmental Health Sciences. This work has also benefited from the works funded by NSF grants (ATM-0802715, AGS-1058456, ATM09002730, AGS1203299), NASA grants (NNX13AE12G, NNH09AM53I, NN09AK63I, NNH11AR07I), and DOE contract (DE-AC02-09CH11466).

Read the abstract

Wing, Simon; Rider, Lisa G.; Johnson, Jay R.; Miller, Frederick W.; Matteson, Eric L.; Crowson, Cynthia S.; Gabriel, Sherine E. “Do solar cycles influence giant cell arteritis and rheumatoid arthritis incidence?” BMJ Open, May 2015