Energy Deposition of Heavy Ions in Matter

The energy loss of heavy ions in matter is completely different from the case of laser beams. Whereas laser radiation produces a plasma on the surface of the target and heats the volume mostly by shock waves, heavy ions penetrate deep into the target with an almost-constant energy loss in the beginning and a very high energy loss at the end of the range, the so called Bragg peak. This special behavior offers excellent possibilities for the examination of critical points of different materials, the measurement of benchmarks for equations of state, production and detection of X-rays and XUV radiation, investigations in physics of overdense plasma, and many more topics. In particular, heavy ion beams are considered to be a very efficient driver for an inertial confinement fusion power plant. Thus, research on the elementary processes of the energy deposition of heavy ions in matter with respect to inertial fusion energy is of primary interest.     

氢化锂薄膜的应用研究

阐述了氢化锂薄膜在惯性约束聚变中的应用背景,介绍了多层膜间隔层和惯性约束聚变中靶丸燃料的研究现状及存在的问题,展望了利用脉冲激光沉积技术制备氢化锂薄膜用作多层膜间隔层和靶丸燃料的发展方向。     

Particle acceleration and coherent radiation by subcycle laser pulses

Electron acceleration by subcycle laser pulses is studied. It is shown in the particle simulations that the irradiation of an intense subcycle pulse on a thin plasma layer gives rise to a pickup of all plasma electrons on the spot and accelerate them to lead to a formation of the high-energy bunched electrons. The condition of generating coherent synchrotron radiation from the bunched electrons is estimated to apply to a bright X-ray source.     

An industrial approach of laser polishing with different laser sources

Surface finishing of dies and molds is one of the most interesting applications of laser polishing process. Because of the variety of materials used in die and mold manufacturing, as well as the different surface topographies, in each case, it is necessary to use appropriate process parameters. The presented work focuses on the study of laser polishing process on three commonly used materials in the manufacture of dies and molds, such as tool steels AISI D2 and AISI P20, ductile cast iron GGG70L and LaserForm ST‐100, a specific material developed for plastic injection mold making. Experimental studies were carried out determining the influence of the energy density on the roughness reduction rate. A key point that has a direct impact on the resulting surface roughness is the initial surface finishing of the material before laser polishing. In order to determine the degree of influence, experimental studies were conducted on two steels, AISI H13 and AISI P20, which are typically used in mold making industry. The experimental tests showed that a random distribution of peaks and valleys allows more homogenous material melting and gives as result a smoother surface after laser polishing.     

The three-prong method: a novel assessment of residual stress in laser powder bed fusion

ABSTRACT

Residual stress is a major problem for most metal-based laser powder bed fusion (L-PBF) components. Residual stress can be reduced by appropriate build planning and post-process heat treatments; however, it is not always avoidable and can lead to build failures due to distortion and cracking. Accurate measurement of residual stress levels can be difficult due to high equipment set-up costs and long processing times. This paper introduces a simple but novel method of measuring residual stresses via a three-pronged cantilever component, the three-prong method (TPM). The method allows for a quick and easy characterisation of residual stress for a wide range of machine parameters, build strategies and materials. Many different cantilever designs have been used to indicate residual stress within additive manufacturing techniques. All of which share the same shortcoming that they indicate stress in one direction. If the principal component of stress is not aligned with the beam geometry, it will underestimate peak stress values. A novel three-prong design is proposed which covers two dimensions by utilising three adjoined cantilever beams, a configuration which echoes that of hole-drilling where three measurements are used to calculate the stress field around a drilled hole. Each arm of the component resembles a curved bridge-like structure; one end of each bridge is cut away from the base plate leaving the centre intact. Deformation of the beams is then measured using a co-ordinate measurement machine. Stress profiles are then estimated using finite element analysis by meshing the deflected structure and forcing it back to its original shape. In this paper, the new TPM is used to compare the residual stress levels of components built in Ti–6Al–4V with different hatch patterns, powers and exposure times.