Japanese Physicists Propose Method to Generate Megatesla Magnetic Fields

Physicists at the University of Osaka in Japan have proposed a groundbreaking method to generate exceptionally strong magnetic fields, potentially reaching megatesla levels. This innovative approach involves directing ultra-short, intense laser pulses into a specially designed hollow tube that features sawtooth-like inner blades. The technique, an enhancement of the established “microtube implosion” method, aims to replicate phenomena observed in high-energy-density processes such as laser fusion and astrophysical events.

The research team, led by Masakatsu Murakami, has built on previous findings that showed ultra-intense femtosecond (10^-15 seconds) lasers can produce magnetic fields of several kilotesla. Their latest work introduces a suite of advanced laser technologies combined with intricate microstructures, pushing the limits of magnetic field generation into the megatesla regime.

Revolutionizing Magnetic Field Generation

The microtube implosion technique uses femtosecond laser pulses with intensities ranging from 10^20 to 10^22 W/cm². By targeting a hollow cylindrical structure with an inner radius of 1 to 10 millimeters, the process creates a plasma of high-energy electrons. These electrons, reaching mega-electronvolt (MeV) energies, generate a sheath field along the inner wall of the tube, leading to the implosion of the cylinder. At this critical moment, a “seed” magnetic field directs the ions and electrons in opposing azimuthal directions, resulting in a significant axial magnetic field.

Despite its effectiveness, the traditional microtube implosion technique necessitates a kilotesla-scale seed field, complicating the apparatus and making it bulkier. The new method proposed by Murakami and his colleagues eliminates this requirement by utilizing a micron-sized cylinder with a periodically slanted inner surface. This design creates sawtooth-shaped blades that induce geometrical asymmetry within the cylinder, causing the imploding plasma to swirl asymmetrically and generate circulating currents at the center.

Implications for Research and Applications

Using “particle-in-cell” simulations with the fully relativistic EPOCH code on Osaka’s SQUID supercomputer, the researchers demonstrated that these vortex structures lead to the self-consistent generation of a powerful axial magnetic field, reaching magnitudes in the gigagauss range (1 gigagauss = 100,000 T). The simulations revealed a positive feedback mechanism where the initial loop current amplifies the central magnetic field, further constraining the motion of charged particles and reinforcing the loop current.

“This approach offers a powerful new way to create and study extreme magnetic fields in a compact format,” said Murakami. He highlighted its potential to bridge experimental laboratory plasmas with astrophysical phenomena, paving the way for controlled studies of strongly magnetized plasmas, relativistic particle dynamics, and magnetic confinement strategies pertinent to both fusion energy and astrophysics.

The researchers have published their findings in the journal Physics of Plasmas and are planning experimental validations using petawatt-class lasers. Murakami indicated that the team aims to explore how these intense magnetic fields could be used to steer particles or compress plasmas, opening new avenues for research in high-energy physics.

This development marks an exciting advance in the field of plasma physics, with implications that could extend far beyond the laboratory, potentially enriching our understanding of the universe’s most extreme environments.