Blue Waters pushes magnetic reconnection research

12.06.16 -

by Travis Tate

Opposites often attract, but that attraction can cause an explosion. Magnetizing forces in space are the same: but in space, reconnection is always possible.

Magnetic reconnection is the scientific process in which oppositely aligned magnetic field lines in a plasma break and form new connections. The newly connected magnetic fields are bent and have a tension that can accelerate the plasma like a slingshot.

This process is still not well-understood, but base knowledge is the energy released from the magnetic field accelerates the particles in the plasma during reconnection.

Plasma jets, and more generally, plasma, is an important subject in high-energy-density laboratory astrophysics.

"Plasma is the most abundant form of ordinary (non-dark) matter in the universe, so understanding plasmas is necessary for understanding systems in astrophysics," said Sam Totorica, NCSA Blue Waters Graduate Fellow from Stanford University. "Some experimental facilities with high-power lasers are now able to produce plasmas in the lab that mimic those in astrophysical systems."

Plasma is the fourth state of matter, along with solid, liquid, and gas states, and can be incredibly energy-dense.

"You can think of plasma like this," began Totorica. "If you heat a solid, you get a liquid. If you heat a liquid, you get a gas. If you heat a gas enough that the electrons are freed from the positively-charged nuclei, you get a plasma. Plasmas are made of electrically-charged particles like ions and electrons which interact to each other via long-ranged electromagnetic forces. This makes plasma behavior very complicated and much different from an ordinary gas."

Totorica is part of a research team that studies the massive energy production that comes from magnetic reconnection. Totorica is PhD student being co-advised by Tom Abel and Frederico Fiuza and was also the lead author on a paper, "Nonthermal Electron Energization from Magnetic Reconnection in Laser-Driven Plasmas" published by Physical Review Letters.

As revealed in the title of his paper, Totorica is expanding the ways in which future research will use laser-driven plasma experiments, and Blue Waters is an essential part of Totorica's work.

Specifically, Totorica is using high power lasers to study "inertial confinement fusion," which looks at how high power lasers can create plasmas that are hot and dense enough for nuclear fusion reactions to occur. Understanding how magnetic fields affect the behavior of plasma in those systems can potentially lead to effective energy production in fusion plasmas.

In the lab, Totorica's peers in the study of magnetic reconnection have focused lasers onto solid foils, which are small millimeter-scale plastic foils, producing plasma bubbles that expand and self-generate magnetic fields. The expansion of two nearby plasma bubbles can then drive reconnection between the oppositely aligned magnetic fields.

Basically, Totorica's team was able to show particle acceleration from magnetic reconnection can be studied in lab experiments: "Particle acceleration by reconnection is important in astrophysics, but poorly understood, so a new way to study this in the lab could be very valuable," said Totorica.

Magnetic Reconnection and You

As magnetic reconnection occurs, many different physical phenomena occur, including non-thermal emissions like solar flares or jets spewing from active galactic nuclei, events which are commonly called "space weather."

Magnetic reconnection became a big news story in 2003, when massive solar flares sent x-rays shooting towards earth causing a geomagnetic storm. That storm affected aircraft, satellite systems and communications, and caused a power outage in Sweden.

That very storm came from the coupling and uncoupling of many magnetic fields on the sun.

Harnessing this incredible output of power could one day lead to fusion reactors that could in turn provide clean energy.

Using Blue Waters

Totorica's team did particle-in-cell (PIC) simulations using the OSIRIS code on Blue Waters and measured the experimental signatures of electrons energized by reconnection, including both in two dimensions and three; of course, doing 3-D simulations can account for more detail, but takes much more compute power.

Blue Waters is the fastest supercomputer on an academic campus and is hosted at the National Center for Supercomputing Applications (NCSA) at the University of Illinois at Urbana-Champaign.

"Our simulations must bridge all of multiscale physics, from fluid dynamics to the kinetic microscopic processes. Modeling these can require billions of particles in simulation. Such simulations require large-scale computational resources and Blue Waters was perfect for this kind of simulation."

By doing the simulations on a supercomputer like Blue Waters, Totorica was able to show that these laser-driven plasmas can be used to study particle acceleration induced by reconnection. These results will help guide future experimental studies to shed light on this poorly understood subject.

This work was supported by the U.S. Department of Energy SLAC Contract No. DE-AC02-76SF00515. The authors acknowledge the OSIRIS Consortium, consisting of UCLA and IST (Portugal) for the use of the OSIRIS 3.0 framework and the visXD framework. Totorica was supported by the Blue Waters Graduate Fellowship and the DoD NDSEG Fellowship. This work was also partially supported by the DOE Fusion Energy Science, the SLACLDRD program, and by the NSF Grant No. AC11339893 (PICKSC). Simulations were run on Mira (ALCF supported under Contract No. DE-AC02-06CH1135) through an INCITE award, on Blue Waters (supported by NSF awards OCI-0725070 and ACI-1238993, and by the state of Illinois), and on the Bullet Cluster at SLAC.

National Science Foundation

Blue Waters is supported by the National Science Foundation through awards ACI-0725070 and ACI-1238993.