What Causes Cosmic Rays? Plasma From Lasers Helps Study Particle Acceleration

It has long been observed that sub-atomic particles like electrons and atomic nuclei accelerate to very high speeds in space. The cause of this acceleration has not been defined yet but scientists believe plasma might hold the answer.

Plasma, the hot fourth form of matter, is a state where electrons have separated from atomic nuclei. The magnetic field lines in the plasma break and then snap back into place, which releases enormous amounts of energy. A team of researchers set out to study the effect of this released energy on particles in space.

Researchers from United States’ Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) recently used lasers that generate plasma to create conditions which mimic astrophysical behavior. They found these lasers can provide insight into bursts of subatomic particles that occur in deep space.

Such findings could help scientists understand cosmic rays, solar flares and solar eruptions, according to their paper published in the journal Physics of Plasmas. The solar activity releases a stream of particles called a solar storm. These storms can disrupt cell phone service and knock out power lines on Earth.

The team of researchers, led by Will Fox, physicist at the PPPL, used a laboratory technique to mimic the plasma found in space to successfully study the effect it has on particles in a controlled environment.

“We want to reproduce the process in miniature to conduct these tests,” he said in a press release on PPPL website.

The team, using a simulation program called Plasma Simulation Code (PSC), monitored the movement and position of plasma particles in a virtual environment. When simulated magnetic and electric fields encountered the plasma, the team observed that snapped plasmas bubble outward and crash into each other, triggering reconnection in the magnetic field lines. The simulations, conducted on the Titan supercomputer at the Oak Ridge Leadership Computing Facility, showed two kinds of processes transfer energy from the reconnection event to particles.

One of the processes, known as Fermi acceleration, occurred when the particles gained energy because of the repeated back and forth movement between the outer edges of two converging plasma bubbles. Also, another effect called the X-line acceleration was observed. Here, the energy transfers to particles as they interact with the electric fields that arise during reconnection causing the acceleration.

Fox and the team plan on doing a slew of experiments to study the effect of plasma in particle acceleration in space. They plan on utilizing the features the OMEGA laser facility at the University of Rochester’s Laboratory for Laser Energetics and the National Ignition Facility at the DOE’s Lawrence Livermore National Laboratory provide.

“We’re trying to see if we can get particle acceleration and observe the energized particles experimentally,” Fox said in the release.

The Laboratory is managed by the University for the U.S. Department of Energy’s Office of Science. They look to decipher the basic problems in the physical sciences in the U.S. and also the most pressing challenges of our time.