Magnetic fields are detected throughout the universe and play a major role in astrophysical dynamics. Various fundamental phenomena, including coronal mass ejections, solar flares, gamma-ray bursts and pulsar winds, are dominated by variations in magnetic fields. Although the mechanisms involved in the origin of magnetic fields in space are still uncertain, one widely accepted plausible scenario is the turbulent dynamo, which amplifies weak magnetic fields. Recent numerical studies and experiments with colliding plasma streams produced by long-pulse laser have demonstrated the ability of seed field amplification. The coupling of strong magnetic fields and high-powered lasers supports cutting-edge research in laboratory astrophysics and laser charged particle accelerations. With moderate laser intensities and a relatively long pulse length, mega-gauss (MG) magnetic fields in the plasmas at the edges of the focal spots were obtained. Numerical and theoretical studies predict a magnetic field strength of 100 MG, while peak experimental results are around 10 MG.
Recently, scientists from Osaka University investigated the mechanism of magnetic field growth from a weak seed field in a so-called “microtube implosion” scenario and demonstrated an amplification of three orders of magnitude magnetic fields of order MG to GG via kinetic simulations. The intensity of the magnetic field obtained is even stronger than that of the electromagnetic fields of pumping. Such high magnetic fields are comparable to astrophysical bodies like neutron stars and black holes. Also, depending on the strength of the seed magnetic field and the target structure, the polarity of the resulting magnetic field flips instantaneously.
The magnetic field amplification process can be separated into the following three steps. The first is laser implosion, in which hot electrons and imploded ions gain energy from pumping pulses. The second is electron trapping, in which the angular momentum of electrons is converted to induce a magnetic field. When the number of electrons injected and trapped increases, the induced magnetic field is amplified. The third step is the dissipation of the induced magnetic field, in which the energy of the magnetic field is transferred to the angular momentum of the internal ions. The strength of the magnetic field decreases as the ions expand. Although the growth and amplification of the magnetic field is mainly dominated by the dynamics of electrons, the lifetime of the magnetic field is determined by the movement of ions from collapse to explosion. The size of the field is of the order of ten microns, and its lifetime lasts hundreds of femtoseconds.
The study conducted by Yan-Jun Gu and Masakatsu Murakami confirmed that current laser technology can realize GG-order magnetic fields based on this concept. The presented concept and theoretical scaling laws for generating GG-order magnetic fields will be beneficial for pioneering basic research in various fields including materials science, quantum electrodynamics (QED), and astrophysics, as well as other advanced practical applications.
Towards the realization of megatesla magnetic fields in the laboratory
Yan-Jun Gu et al, Magnetic Field Amplification Driven by Gyroscopic Motion of Charged Particles, Scientific reports (2021). DOI: 10.1038/s41598-021-02944-2
Provided by Osaka University
Quote: Instant turn-over of magnetism by gyro motion of relativistic electrons (2022, January 26) retrieved January 29, 2022 from https://phys.org/news/2022-01-instant-turn-over-magnetism-gyro-motion . html
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