Laboratory evidence of Weibel magnetogenesis driven by temperature gradient using three-dimensional synchronous proton radiography.

The origin of the cosmic magnetic field remains an unsolved mystery, relying not only on specific dynamo processes but also on the seed field to be amplified. Recently, the diffuse radio emission and Faraday rotation observations reveal that there has been a microgauss-level magnetic field in intracluster medium in the early universe, which places strong constraints on the strength of the initial field and implies the underlying kinetic effects; the commonly believed Biermann battery can only provide extremely weak seed of 10-21 G. Here, we present evidence for the spontaneous Weibel-type magnetogenesis in laser-produced weakly collisional plasma with the three-dimensional synchronous proton radiography, where the distribution anisotropy directly arises from the temperature gradient, even without the commonly considered interpenetrating plasmas or shear flows. This field can achieve sufficient strength and is sensitive to Coulomb collision. Our results demonstrate the importance of kinetics in magnetogenesis in weakly collisional astrophysical scenarios.

Reduction of Backward Scatterings at the Low-Coherence Kunwu Laser Facility.

We report the first experimental observation on the reduction of backward scatterings by an instantaneous broadband laser with 0.6% bandwidth in conditions of interest for inertial confinement fusion at the low-coherence Kunwu laser facility. The backscatter of stimulated Brillouin scattering (SBS) was robustly reduced by half at intensities of 1-5×10^{14} W/cm^{2} with the 0.53-µm broadband laser in comparison with the monochromatic laser. As SBS dominates energy loss of laser-plasma interactions, the reduction of that demonstrates the enhancement of laser-target coupling by the use of broadband laser. The mitigation of filamentation leads to the reduction of stimulated Raman backscattering at low intensities. In addition, the three-halves harmonic emission was reduced with the broadband laser as well.

Double-spherically bent crystal scheme of stigmatic x ray monochromatic backlit imaging.

We propose an aberration-free monochromatic x ray backlit imaging scheme using a combination of convex and concave spherically bent crystals. This configuration works with a wide range of Bragg angles, satisfying the conditions for stigmatic imaging at a particular wavelength. However, the assembly accuracy of the crystals must meet the Bragg relation criteria for spatial resolution to increase the detection efficiency. Here, we develop a collimator prism with a cross reference line engraved on a plane mirror to adjust a matched pair of Bragg angles as well as the intervals between the two crystals and the object to be coupled with the detector. We explore the realization of monochromatic backlighting imaging with a concave Si-533 crystal and a convex α-Quartz-2023 crystal, obtaining a spatial resolution of approximately 7 µm and a field of view of at least 200 µm. To the best of our knowledge, this is the best spatial resolution of monochromatic images of a double-spherically bent crystal to date. Our experimental results are presented to demonstrate the feasibility of this imaging scheme with x rays.

Demonstration of laser-produced neutron diagnostic by radiative capture gamma-rays.

We report a new scenario of the time-of-flight technique in which fast neutrons and delayed gamma-ray signals were both recorded in a millisecond time window in harsh environments induced by high-intensity lasers. The delayed gamma signals, arriving far later than the original fast neutron and often being ignored previously, were identified to be the results of radiative captures of thermalized neutrons. The linear correlation between the gamma photon number and the fast neutron yield shows that these delayed gamma events can be employed for neutron diagnosis. This method can reduce the detecting efficiency dropping problem caused by prompt high-flux gamma radiation and provides a new way for neutron diagnosing in high-intensity laser-target interaction experiments.

Design and calibration of hot-electron spectrometer array for angle-resolved measurement.

A hot-electron spectrometer array with two-dimensional distribution has been designed with a wide-angle range and high-energy resolution to measure the spatially resolved electron spectra for high-power-laser plasma interaction experiments. It consisted of 19 identical electron spectrometers set in three directions with an interval of 10°. Each electron spectrometer was designed with a uniform magnetic field to detect electrons in the range from 20 to 500 keV. The spectrometers were calibrated using electrons from an accelerator. In an experiment, the spatially resolved electron energy spectra, which approximately had a Maxwell distribution, were obtained from an aluminum foil target irradiated by a 0.53-µm laser pulse.