Ablation excited by current pulses is a very critical physical process in pulse plasma thrusters(PPT).Its effects on wall-plasma interaction directly determine the PPT performances.In order to reveal the process of th...Ablation excited by current pulses is a very critical physical process in pulse plasma thrusters(PPT).Its effects on wall-plasma interaction directly determine the PPT performances.In order to reveal the process of the ablated wall interaction with the discharge plasma in PPT,ablation models formulated by three different boundary conditions at the wall-plasma interface are studied.These are the two widely used high-speed evaporation models(Model-L and Model-M),and the recently developed Keida-Zaghloul model(Model-K)of the Knudsen layer that takes into account the internal degrees of freedom on the energy flux conservation.First,fundamental mechanisms of the three ablation models are clarified by comparative analysis in order to gain a comprehensive understanding of the wall-plasma interaction.Then,the applicability of different ablation models with the numerical solutions of LES-6 PPT is investigated in detail using magnetohydrodynamic(MHD)modeling.Results show that Model-L and Model-M are actually special cases of Model-K when a simplified jump conditions limited by high velocity at the vapor/plasma interface is used;A ratio of ablation rate in Model-L to that in Model-M is about 0.8at the same wall surface temperature,while it rises to 1 at different surface temperature determined by Model-L and Model-M in PPT.Even though Model-K solution requires significant computational time,it shows more accurate ablation feature for the wall-plasma interaction and possesses better computing precision of impulse bit during post-pulse which is useful for future studies of the late time ablation.展开更多
目的探讨工作气压对管内等离子体放电光学现象以及Si/O-DLC(Si and O Incorporated DLC,Si/O-DLC)薄膜结构与性能的影响,为获得管内高质量、均匀的Si/O-DLC薄膜制备工艺技术提供指导。方法利用空心阴极等离子体增强化学气相沉积(Hollow ...目的探讨工作气压对管内等离子体放电光学现象以及Si/O-DLC(Si and O Incorporated DLC,Si/O-DLC)薄膜结构与性能的影响,为获得管内高质量、均匀的Si/O-DLC薄膜制备工艺技术提供指导。方法利用空心阴极等离子体增强化学气相沉积(Hollow Cathode Plasma Enhanced Chemical Vapor Deposition,HC-PECVD)技术,通过改变工作气压在管内沉积Si/O-DLC薄膜。利用高速摄像机记录并对比不同工作气压下管内等离子体放电光学现象。通过SPM、XPS和Raman光谱仪表征不同工作气压下薄膜的三维立体表面形貌和微观结构,并利用SEM、纳米压痕仪以及划痕测试系统,对比研究管内Si/O-DLC薄膜的硬度、弹性模量、膜基结合力以及沿管轴向的薄膜厚度分布。结果随着工作气压的上升,管径向中心处亮斑面积和光强先增大增强后趋于缩小暗淡。在不同工作气压下,均能够在管内获得表面光滑的Si/O-DLC薄膜,粗糙度为3~10 nm。随着工作气压的上升,管内Si/O-DLC薄膜的平均厚度从1.42μm增大到2.06μm,且沿管轴向的薄膜厚度分布均匀度从24%显著提高到65%;不同工作气压下管内Si/O-DLC薄膜沿管轴向平均硬度呈先增大后减小的趋势,总体平均硬度可达(14±1)GPa。管内Si/O-DLC薄膜在工作气压上升到25 mTorr时获得较高的平均膜基结合力。结论改变工作气压能够显著影响管内壁Si/O-DLC薄膜的结构与性能,当工作气压为25 m Torr时,在管内获得均匀性最优、结合力较高的Si/O-DLC薄膜。展开更多
基金Project supported by Ph.D.Programs Foundation of Ministry of Education of China(20121101120004)Basic Research Foundation of Beijing Institute of Technology(20120142015)
文摘Ablation excited by current pulses is a very critical physical process in pulse plasma thrusters(PPT).Its effects on wall-plasma interaction directly determine the PPT performances.In order to reveal the process of the ablated wall interaction with the discharge plasma in PPT,ablation models formulated by three different boundary conditions at the wall-plasma interface are studied.These are the two widely used high-speed evaporation models(Model-L and Model-M),and the recently developed Keida-Zaghloul model(Model-K)of the Knudsen layer that takes into account the internal degrees of freedom on the energy flux conservation.First,fundamental mechanisms of the three ablation models are clarified by comparative analysis in order to gain a comprehensive understanding of the wall-plasma interaction.Then,the applicability of different ablation models with the numerical solutions of LES-6 PPT is investigated in detail using magnetohydrodynamic(MHD)modeling.Results show that Model-L and Model-M are actually special cases of Model-K when a simplified jump conditions limited by high velocity at the vapor/plasma interface is used;A ratio of ablation rate in Model-L to that in Model-M is about 0.8at the same wall surface temperature,while it rises to 1 at different surface temperature determined by Model-L and Model-M in PPT.Even though Model-K solution requires significant computational time,it shows more accurate ablation feature for the wall-plasma interaction and possesses better computing precision of impulse bit during post-pulse which is useful for future studies of the late time ablation.
文摘目的探讨工作气压对管内等离子体放电光学现象以及Si/O-DLC(Si and O Incorporated DLC,Si/O-DLC)薄膜结构与性能的影响,为获得管内高质量、均匀的Si/O-DLC薄膜制备工艺技术提供指导。方法利用空心阴极等离子体增强化学气相沉积(Hollow Cathode Plasma Enhanced Chemical Vapor Deposition,HC-PECVD)技术,通过改变工作气压在管内沉积Si/O-DLC薄膜。利用高速摄像机记录并对比不同工作气压下管内等离子体放电光学现象。通过SPM、XPS和Raman光谱仪表征不同工作气压下薄膜的三维立体表面形貌和微观结构,并利用SEM、纳米压痕仪以及划痕测试系统,对比研究管内Si/O-DLC薄膜的硬度、弹性模量、膜基结合力以及沿管轴向的薄膜厚度分布。结果随着工作气压的上升,管径向中心处亮斑面积和光强先增大增强后趋于缩小暗淡。在不同工作气压下,均能够在管内获得表面光滑的Si/O-DLC薄膜,粗糙度为3~10 nm。随着工作气压的上升,管内Si/O-DLC薄膜的平均厚度从1.42μm增大到2.06μm,且沿管轴向的薄膜厚度分布均匀度从24%显著提高到65%;不同工作气压下管内Si/O-DLC薄膜沿管轴向平均硬度呈先增大后减小的趋势,总体平均硬度可达(14±1)GPa。管内Si/O-DLC薄膜在工作气压上升到25 mTorr时获得较高的平均膜基结合力。结论改变工作气压能够显著影响管内壁Si/O-DLC薄膜的结构与性能,当工作气压为25 m Torr时,在管内获得均匀性最优、结合力较高的Si/O-DLC薄膜。
