Researchers created tiny solar flares using twelve powerful lasers to understand the principles underlying an actual astronomical event known as magnetic reconnection.
The universe is anything but “the immense expanse of space,” however familiar the phrase may be. Although it may seem like there are few celestial bodies, the universe is teeming with different materials, including charged particles, gases, and cosmic rays.
Magnetic reconnection, as the name implies, occurs when two antiparallel magnetic fields, i.e. magnetic fields moving in opposite directions, collide, split apart and realign. Even though it sounds simple, the process is anything but smooth.
Taichi Morita, assistant professor at Kyushu University’s Faculty of Engineering and first author of the study, said: “This phenomenon can be seen all over the universe. At home, you can see them in solar flares or in the Earth’s magnetosphere. When a solar flare builds up and a solar flare appears to “squeeze,” that’s magnetic reconnection. Auroras are formed from charged particles ejected by the magnetic reconnection in the Earth’s magnetic field.”
Nevertheless, many mechanisms underlying the phenomenon, despite its frequent occurrence, remain a mystery. Studies are being conducted, such as in NASA’s Magnetospheric Multiscale Mission, where satellites flown into Earth’s magnetosphere are used to study magnetic reconnections in real time. The rate of reconnection and how the energy of the magnetic field is transformed and distributed across the plasma particles is still unknown.
An alternative to launching satellites into orbit is to create magnetic reconnections with laser-induced plasma arcs. However, the plasma created is too small and unstable to accurately analyze the phenomenon without appropriate laser power.
said Morita, “One facility that has the necessary power is Osaka University’s Institute for Laser Engineering and their Gekko XII laser. It’s a huge 12-beam, high-powered laser that can generate plasma stable enough to study. Studying astrophysical phenomena using high energy lasers is called ‘laser astrophysics experiments’. It has been an evolving methodology in recent years.”
During experiments, scientists used powerful lasers to generate two plasma fields with antiparallel magnetic fields. They then targeted a low-energy laser at the center of the plasma, where the magnetic fields would meet and where, in theory, magnetic reconnection would occur.
said Morita, “We are essentially mimicking the dynamics and conditions of a solar flare. However, by analyzing how the light from that energy-efficient laser is scattered, we can measure all kinds of parameters, from plasma temperature, velocity, ion valence, current and plasma flow rate.”
One of their most important discoveries was the observation of electric currents appearing and disappearing where the magnetic fields collide, indicating magnetic reconnection. They also received information about the acceleration and heating of the plasma.
The group plans to continue its research in the hope that these “laser astrophysics experiments” will be used more often as a complementary or alternative method to study astrophysical events.
- T. Morita, T. Kojima, S. Matsuo, S. Matsukiyo, et al. Detection of current-sheet and bipolar ion current in a self-generated antiparallel magnetic field of laser-produced plasmas for magnetic reconnection studies. Physical Review E, DOI: 10.1103/PhysRevE.106.055207