This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Understanding instabilities and turbulence in plasmas is one of the key challenges across a wide range of plasma research fields, including nuclear fusion, astrophysics and laser-plasma physics. In plasmas, slight disturbances can grow due to instabilities, and energy is transferred between structures of various sizes due to turbulence.
These phenomena give rise to structures ranging from very small to large, which significantly influence the overall motion and energy flow of the plasma. Since structures generated by instabilities and turbulence vary with even slight differences in conditions, it is not easy to reproduce the same state in every experiment. Therefore, there is a need for "spatially multiscale single-shot measurements" that can simultaneously capture structures of a wide range of sizes in a single measurement.
In particular, in high-energy-density plasmas, instabilities grow in an extremely short time, so high temporal and spatial resolution is also required to capture their initial stages. By combining the newly developed "beamstop-free X-ray small-angle scattering method" with an X-ray free-electron laser and a microscale rod assembly target, an international research group, led by Assistant Professor Masato Ota of the National Institute for Fusion Science (then a graduate student at the Graduate School of Science, Osaka University), Associate Professor Yoichi Sakawa of the Institute of Laser Engineering, Osaka University, succeeded in measuring the structural collapse and rarefaction processes of high-energy-density plasma across a wide range of spatial scales—from 10 nm to 500 nm—with sub-picosecond temporal resolution. The findings are published in the journal Communications Physics.
This is the first time in the world that structures across such a wide range of spatial scales have been measured simultaneously using a single X-ray pulse and a single camera. In conventional small-angle X-ray scattering, the central portion of the beam is shielded by a beam stop to protect the camera from the intense X-ray beam, and the small-angle diffraction patterns appearing around it are measured. However, with this method, it is fundamentally impossible to obtain signals from the ultra-small-angle region hidden by the beamstop.
In the newly developed beamstop-free X-ray small-angle scattering method, a light-attenuation filter system—composed of stacked metal foils optimized for thickness, size and shape—was employed to expand the intensity range measurable by a single X-ray camera to more than 100 times that of conventional methods. This allows the intense X-ray beam at the center to be attenuated to the camera's measurable range, enabling the simultaneous acquisition of a wide range of diffraction signals—including those from the ultra-small-angle region—from the target, thereby revealing microstructures that could not previously be measured. The experiments were conducted using a high-brightness, short-pulse X-ray beam generated by the SACLA (SPring-8 Angstrom Compact free electron LAser) X-ray free-electron laser in Harima, Hyogo Prefecture, and a high-intensity femtosecond pulsed laser installed at the same facility.
Discover the latest in science, tech, and space with over 100,000 subscribers who rely on Phys.org for daily insights. d research that matter—daily or weekly. The researchers used a high-intensity laser to instantaneously transform a silicon microscale rod assembly target—consisting of submicrometer-scale cylinders arranged in a regular pattern—from a solid to a plasma state, and observed the process of structural collapse and rarefaction as changes in the X-ray small-angle scattering signal on picosecond time scales and nanometer spatial scales. The X-ray beam directed at the rod assembly is diffracted by the individual rods, and the diffracted waves interfere, forming characteristic periodic peak signals on a distant detector.
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