研究人员使用高能激光研究磁重联

NASA 概念图像实验室关于“穿越太阳系的磁重联”的屏幕截图。 当平行磁场（在这种情况下出现在太阳耀斑中）发生碰撞、断裂和重新排列时，就会发生磁重联。 这个过程会产生高能爆炸，将粒子弹射到太空中。 图片来源：NASA 概念图像实验室

科学家使用强大的激光制造微型太阳耀斑来研究磁重联过程。

科学家们使用十二束高能激光束来模拟小型太阳耀斑，以研究磁重联这一基本天文现象的潜在机制。

与普遍的看法相反，宇宙并不是空的。 尽管有“浩瀚太空”之说，但宇宙中充满了带电粒子、气体和宇宙射​​线等各种物质。 虽然天体可能看起来很少见，但宇宙却充满了活力。

一种这样的粒子和能量通过空间的驱动是一种称为磁重联的现象。 顾名思义，当两个平行磁场（如两个沿相反方向传播的磁场）碰撞、断裂和重新对齐时，就会发生磁重联。 看似无害，实则远非平静。

这种现象在宇宙中随处可见。 在家里，您可以在太阳耀斑或地球磁层中看到它们。 森田太一副教授 九州大学 工程科学学院和该研究的第一作者。 “事实上，北极光的形成是带电粒子从地球磁场中的磁重联中喷射出来的结果。”

然而，尽管它们很常见，但这些现象背后的许多机制仍然是个谜。 正在进行研究，例如在[{” attribute=””>NASA’s Magnetospheric Multiscale Mission, where magnetic reconnections are studied in real-time by satellites sent into Earth’s magnetosphere. However, things such as the speed of reconnection or how energy from the magnetic field is converted and distributed to the particles in the plasma remain unexplained.

An alternative to sending satellites into space is to use lasers and artificially generate plasma arcs that produce magnetic reconnections. However, without suitable laser strength, the generated plasma is too small and unstable to study the phenomena accurately.

“One facility that has the required power is Osaka University’s Institute for Laser Engineering and their Gekko XII laser. It’s a massive 12-beam, high-powered laser that can generate plasma stable enough for us to study,” explains Morita. “Studying astrophysical phenomena using high-energy lasers is called ‘laser astrophysics experiments,’ and it has been a developing methodology in recent years.”

In their experiments, reported in Physical Review E, the high-power lasers were used to generate two plasma fields with anti-parallel magnetic fields. The team then focused a low-energy laser into the center of the plasma where the magnetic fields would meet and where magnetic reconnection would theoretically occur.

“We are essentially recreating the dynamics and conditions of a solar flare. Nonetheless, by analyzing how the light from that low-energy laser scatters, we can measure all sorts of parameters from plasma temperature, velocity, ion valence, current, and plasma flow velocity,” continues Morita.

One of their key findings was recording the appearance and disappearance of electrical currents where the magnetic fields met, indicating magnetic reconnection. Additionally, they were able to collect data on the acceleration and heating of the plasma.

The team plans on continuing their analysis and hopes that these types of ‘laser astrophysics experiments’ will be more readily used as an alternative or complementary way to investigate astrophysical phenomena.

“This method can be used to study all sorts of things like astrophysical shockwaves, cosmic-ray acceleration, and magnetic turbulence. Many of these phenomena can damage and disrupt electrical devices and the human body,” concludes Morita. “So, if we ever want to be a spacefaring race, we must work to understand these common cosmic events.”

Reference: “Detection of current-sheet and bipolar ion flows in a self-generated antiparallel magnetic field of laser-produced plasmas for magnetic reconnection research” by T. Morita, T. Kojima, S. Matsuo, S. Matsukiyo, S. Isayama, R. Yamazaki, S. J. Tanaka, K. Aihara, Y. Sato, J. Shiota, Y. Pan, K. Tomita, T. Takezaki, Y. Kuramitsu, K. Sakai, S. Egashira, H. Ishihara, O. Kuramoto, Y. Matsumoto, K. Maeda and Y. Sakawa, 10 November 2022, Physical Review E.
DOI: 10.1103/PhysRevE.106.055207

The study was funded by the Japan Society for the Promotion of Science.