Generation scenarios of anodic structures and experimental realization of turbulence in unmagnetized plasma

In the present work,we report development of a DC glow discharge plasma(GDP)set-up to study controlled evolution of anodic structures having distinctive geometry,size and layers,generated in front of a positively biased electrode,submerged in unmagnetized plasma.For such an anodic structure,we have also investigated the condition under which the turbulence is triggered.Characteristic of these structures,generated in front of a positively biased electrode,depends on multiple parameters such as the ratio of anode to cathode size,electrode separation,gas pressure,biasing configuration such as anode bias,cathode bias and grounding schemes.We attempted to classify different anodic structures observed experimentally,as anode glow,fireball,anode spot,double layer and multiple double layers(MDLs)based on its physical characteristics.Among these structures the present investigation is focused on MDLs.The number of layers,observed in MDLs varied from as high as six to as low as zero,by controlling the operating discharge parameters,externally.Diagnostics were carried out using Langmuir probe.The analysis of floating potential fluctuations corresponds to a multiple anodic structure showed emergence of turbulence,at its critical stage,satisfying condition for self-organized criticality(SOC).This was identified with three slopes observed in the power spectrum,resembling the sand-pile model.Though,the GDP is completely different from that of the magnetically confined plasma,the nature of turbulence observed with SOC,is very similar to that observed in the scrape of layer of fusion devices.Therefore,the present investigation could provide new approach to study turbulence of similar nature,under an experimental condition that is free from the complexities of complicated field geometries used in confinement devices.

纳秒、皮秒和飞秒激光脉冲对材料表面的改性(英文)

对基体材料镉镍铁合金600和多层TiAlN/TiN涂层的激光表面改性在基础研究和实际应用中有着很好的前景。本文观察了由超短脉冲(fs和ns)和短脉冲(ns)激光器引起的镉镍铁合金600和TiAlN/TiN镀层的表面变化。结果显示,3种激光都能使靶面发生形态改变,超短脉冲的破坏轮廓更为清晰。与ps激光脉冲相比,fs激光脉冲能产生更严重的破坏。与产生半球体形状的ps激光束相反,fs激光脉冲产生的破坏斑是圆锥形的。另外,ns脉冲辐照时热效应占支配地位,且所有的辐照都伴随着等离子体。