Weimin Zhou

Effects of Cr addition on glass-forming ability and mechanical properties of Cu–Zr–Al bulk metallic glass

Effects of a small amount addition of Cr on glass-forming ability (GFA) and mechanical properties of Cu–Zr–Al bulk metallic glass were investigated. The GFA of (Cu46Zr46Al8)100−xCrx (xxa0=xa00, 0.25, 0.5, 0.75, and 1 at%) alloys tends to decrease with the increasing Cr content. A good correlation between the GFA and the temperature interval of supercooled liquid region ΔTx or parameter γ exists in these alloys. Addition of an appropriate amount of Cr can significantly improve the plasticity of the alloys. The bulk metallic glass with xxa0=xa00.5 exhibits promising mechanical properties with high fracture strength of 1870xa0MPa and obvious plastic strain of 2.23%.

Microstructure and mechanical property of Zr65Al7.5Ni10Cu12.5Ag5 bulk metallic glass subjected to rolling

The as-cast and the pre-annealed Zr65Al7.5Ni10Cu12.5Ag5 bulk metallic glasses were rolled at room temperature to different deformation degrees, and the microstructure and microhardness were examined. It is revealed that no phase transformation occurs in the as-cast/rolled specimen except for localized shear bands, indicating that the material has a good structural stability against plastic deformation. When the glass is pre-annealed in the supercooled liquid region for a short time, however, the stability deteriorates significantly. In this case, rolling deformation results in nanocrystallization in the specimen. The pre-annealed glass has less free volume than the as-cast glass, but it does not exhibit a quicker increase in free volume content during the rolling, suggesting that free volume is prone to annihilate at the crystal/glass interfaces. With nanocrystallization occurred, the microhardness of the pre-annealed specimen decreases at a slower rate than that of the as-cast one during rolling deformation.

New scheme for enhancement of maximum proton energy with a cone-hole target irradiated by a short intense laser pulse

Improvement of proton energy from short intense laser interaction with a new proposal of a cone-hole target is investigated via two-dimensional particle-in-cell simulations. The configuration of the target is a cone structure with a hole of changeable diameter through the center of the tip, with proton layers contaminated both on the target rear surface and at the rear part of the hole. In the interacting process, the cone-hole geometry enables the focus of the laser pulse by the cone structure and the consequent penetration of the intensified laser through the tip along the hole instead of reflection, which can increase the energy coupling from laser field to plasmas. The heated electrons, following the target normal sheath acceleration scheme, induce a much stronger electrostatic field in the longitudinal direction at the rear surface of the target than that in the traditional foil case. The simulation results indicate that the accelerated proton beam from the cone-hole target has a cutoff energy about ...

Micro-spot gamma-ray generation based on laser wakefield acceleration

The radiography of gamma-ray is one of the most important non-destructive testing in many fields. However, the spot size is always in millimeter scale for the generation of gamma-ray by conventional way. As the development of laser wakefield acceleration, the electron beam with small divergence and spot size can be generated easily in the experiment by tens of terawatt ultra-short laser pulse. Based on this electron beam, gamma-ray with micro spot size is generated and the properties are measured and tested in detail experimentally. The experiment demonstrates that the spot size of this gamma-ray is always smaller than 200u2009μm, no matter the conversion target thickness, and can be as small as about 40u2009μm when the conversion target thickness of 0.2u2009mm is used. The spatial resolution of this gamma-ray is much better than 2.5 LP/mm, the fitting temperature (which is relative to the average energy of gamma-ray) is between 5u2009MeV and 8u2009MeV, and the maximum yield per shot of the gamma-ray can be up to 9.1u2009×u2009109 photons (energy higher than 1u2009MeV). High-resolution radiography shows that the areal density of the gamma-ray radiography can be up to 51.3u2009g/cm2 (stainless steel thickness equivalent is about 6.5u2009cm). Such micro-spot gamma-ray can play an important role in the high-resolution radiography of high areal density objects.The radiography of gamma-ray is one of the most important non-destructive testing in many fields. However, the spot size is always in millimeter scale for the generation of gamma-ray by conventional way. As the development of laser wakefield acceleration, the electron beam with small divergence and spot size can be generated easily in the experiment by tens of terawatt ultra-short laser pulse. Based on this electron beam, gamma-ray with micro spot size is generated and the properties are measured and tested in detail experimentally. The experiment demonstrates that the spot size of this gamma-ray is always smaller than 200u2009μm, no matter the conversion target thickness, and can be as small as about 40u2009μm when the conversion target thickness of 0.2u2009mm is used. The spatial resolution of this gamma-ray is much better than 2.5 LP/mm, the fitting temperature (which is relative to the average energy of gamma-ray) is between 5u2009MeV and 8u2009MeV, and the maximum yield per shot of the gamma-ray can be up to 9.1u2009×u2009109 p...

Towards high-energy, high-resolution computed tomography via a laser driven micro-spot gamma-ray source

Computed Tomography (CT) is a powerful method for non-destructive testing (NDT) and metrology awakes with expanding application fields. To improve the spatial resolution of high energy CT, a micro-spot gamma-ray source based on bremsstrahlung from a laser wakefield accelerator was developed. A high energy CT using the source was performed, which shows that the resolution of reconstruction can reach 100u2009μm at 10% contrast. Our proof-of-principle demonstration indicates that laser driven micro-spot gamma-ray sources provide a prospective way to increase the spatial resolution and toward to high energy micro CT. Due to the advantage in spatial resolution, laser based high energy CT represents a large potential for many NDT applications.

An angular-resolved multi-channel Thomson parabola spectrometer for laser-driven ion measurement

A multi-channel Thomson parabola spectrometer was designed and employed to diagnose ion beams driven by intense laser pulses. Angular-resolved energy spectra for different ion species can be measured in a single shot. It contains parallel dipole magnets and wedged electrodes to fit ion dispersion of different charge-to-mass ratios. The diameter and separation of the entrance pinhole channels were designed properly to provide sufficient resolution and avoid overlapping of dispersed ion beams. To obtain a precise energy spectral resolving, three-dimensional distributions of the electric and magnetic fields were simulated. Experimental measurement of energy-dependent angular distributions of target normal sheath accelerated protons and deuterons was demonstrated. This novel compact design provides a comprehensive characterization for ion beams.

DOSIMETRIC EVALUATION OF LASER-DRIVEN X-RAY AND NEUTRON SOURCES UTILIZING XG-III PS LASER WITH PEAK POWER OF 300 TERAWATT

Current short-pulse high-intensity lasers can accelerate electrons and proton/ions to energies of giga-electron volts. For certain advanced applications, laser-accelerated electrons and protons are optimised for high-energy X-ray and neutron generation at the XG-III picosecond (ps) laser beamline. These energetic X-ray and neutron beams can significantly affect radiation safety at the facility; therefore, proper evaluation of the radiological hazards induced by laser-driven X-ray and neutron sources is required. This study presents a dosimetric evaluation of laser-driven X-ray and neutron sources at the XG-III ps laser beamline. The source terms of the laser-accelerated electrons and protons are characterised utilising the particle-in-cell method and an analytical model, respectively. The Monte Carlo code FLUKA is used to calculate prompt and residual dose yields due to all radiation field components and the number of residual activated nuclei. Our results can provide a reference for radiation hazard analysis at short-pulse high-intensity laser facilities worldwide.

Enhanced focusing of relativistic lasers by plasma lens with exponentially increasing density profiles

The self-focusing of ultraintense laser in plasma lenses with exponentially increasing density profiles is studied. And the robustness of this design is proved by theoretical estimates and 3D particle-in-cell simulations. Attributed to the density compensation for the increase of laser intensity during self-focusing, a modulated exponential density plasma lens can efficiently focus the laser to higher peak intensity and smaller spot than that by using optimized uniform plasma lens. In near critical density plasmas, laser focusing experiences two stages with different dominant mechanisms: self-focusing at earlier time and magnetic constraint in the plasma channel. And more enhanced effects are achieved by exponential density plasma in both stages. The focal position and the optimal density scalelength for this kind of plasma lens are also estimated through theoretical derivation. Our findings indicate the possibility for the preplasma to experimentally serve as a novel plasma lens to obtain relativistic la...

Optimization of direct drive irradiation uniformity of cylindrical target

The irradiation uniformity of a cylindrical target directly driven by laser beams has been considered, which is relevant for fast ignition electron-transport experiments. The laser intensity distribution on the cylindrical target surface is analyzed and optimized by applying the polar direct drive technique and adjusting the laser beam parameters. Moreover, the rotation of laser spot around its propagation axis is taken into consideration. A case study based on the SG-III prototype laser configuration is presented to demonstrate the optimization approach. The irradiation uniformity is reduced from 10% to 1.6% for perfectly balanced beams, and the effects of uncertainties in beam errors (power imbalance and pointing error) are also studied. Furthermore, differences in laser absorption with different incident angles are taken into account and the results show that highly uniform energy deposition can be achieved.

Generation of high-power few-cycle lasers via Brillouin-based plasma amplification

Strong coupling stimulated Brillouin backscattering (sc-SBS) in plasma is potentially an efficient method of amplifying laser pulses to reach exawatt powers. Here, we report on a new regime of brillouin-based plasma amplification, producing an amplified pulse with a duration of 5 fs and unfocused intensity of 6u2009×u20091017u2009W/cm2. The results are obtained from 2D particle-in-cell simulations, using two circularly polarized pump and seed pulse with Gaussian transverse profile, both at an intensity of 2.74u2009×u20091016u2009W/cm2, counter-propagating in a 0.3nc plasma. The significant compression of amplified seed is achieved as a result of sc-SBS amplification as well as additional compression by the interplay between self-phase modulation and negative group delay dispersion. We show that the amplified seed retains high beam qualities since the filamentation can be prevented due to the fast compression. This scheme may pave the way for few-cycle laser pulses to reach exawatt or even zetawatt regime.