Studies of plasma production at hypervelocity microparticle impact
Studies of plasma production at hypervelocity microparticle impact
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超高速微粒撞击等离子体产生的研究
DOI：
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发表时间：
1973
期刊：
影响因子：
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通讯作者：
N. Adams
中科院分区：
文献类型：
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作者：
David R. Smith;N. Adams
研究了超高速微粒撞击金属靶时产生的等离子体。超高速微米级铁粒子的实验室来源首先描述了它利用2 MV的货车德格拉夫发电机，其次是用于确定粒子的质量和速度的技术的讨论。在铁射弹撞击板条钼靶时，产生电荷，通过适当地偏置网格电极从撞击区域提取电荷，并且随后使用常规宽带电子放大器或电子倍增器检测电荷。从统计学上表明，在撞击过程中产生了相同数量的电子和正离子--表明等离子体的产生--并且释放的总电荷（Q）可以根据粒子的质量（m）和速度（v）通过简单的幂律关系Qαmαvβ经验地描述，在研究的整个速度范围内（005至10 km s-1），β = 32 ± 01，对于v>1 km s-1，α = 085，对于v<1 km s-1，α = 133。它还表明，从等离子体中提取的电荷达到最大的几微秒后的影响，随后以几微秒的时间常数呈指数衰减。使用简单的飞行时间质谱仪对撞击过程中产生的正离子进行了粗略的质量分析，结果表明，在所研究的速度范围内，光谱中的主导离子是抛射体的特征，而不是目标材料的特征。根据光谱中金属离子的相对丰度，以及铁射弹中已知的相对金属原子浓度，等离子体的温度（根据萨哈平衡考虑）估计为数千开尔文。在详细的讨论中，试图考虑如何在现有的超高速碰撞的理论模型的弹丸的动能耗散-最终产生等离子体。结果表明，这种非常复杂的相互作用的最令人满意的模型似乎是一个在其中的冲击波传播到弹丸和目标材料的相对重要性被认为是。最后，讨论的影响产生的等离子体的属性和时间行为，以评估扩散和重组过程的相对重要性，从而协助解释在这项研究中获得的实验结果。
This paper is concerned with an investigation of the plasma generated during the impact of hypervelocity microparticles with a metal target. A laboratory source of hypervelocity micron-sized iron particles is first described which utilizes a 2 MV Van de Graaff generator, followed by a discussion of the techniques used to determine the mass and velocity of the particles. On impact of the iron projectiles on a slatted molybdenum target, charge is generated, extracted from the region of impact by suitably biasing a gridded electrode, and subsequently detected using a conventional wideband electronic amplifier or an electron multiplier. It is shown statistically that during impact equal numbers of electrons and positive ions are produced - indicating plasma generation - and that the total charge released (Q) may be described empirically in terms of the mass (m) and velocity (v) of the particle by a simple power law relationship of the kind Qαmαvβ, with β = 32 ± 01 over the complete velocity range investigated (005 to 10 km s−1) and with α = 085 for v>1 km s−1 and 133 for v<1 km s−1. It is also shown that the charge extracted from the plasma reaches a maximum a few microseconds after impact and subsequently decays exponentially with a time constant of several micro-seconds. A crude mass analysis of the positive ions generated during the impact using a simple time-of-flight mass spectrometer has indicated that, over the velocity range investigated, the dominant ions in the spectrum are characteristic of the projectile and not the target material. From considerations of the relative abundance of the metal ions in the spectra, together with the known relative metal atom concentrations in the iron projectiles, the temperatures of the plasmas have been estimated (from Saha equilibrium considerations) to be of the order of several thousands of degrees Kelvin. In a detailed discussion, attempts are made to consider how the kinetic energy of the projectile is dissipated - eventually producing plasma - in terms of available theoretical models of hypervelocity impact. It is shown that the most satisfactory model of this very complex interaction appears to be one in which the relative importance of shock-wave propagation into the projectile and target materials is considered. Finally, a discussion of the properties and the temporal behaviour of the impact-produced plasma is presented in order to assess the relative importance of diffusion and recombination processes, thus to assist in the interpretation of the experimental results obtained in this study.