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Dynamic characteristics of multi-charged ions emitted from nanosecond laser produced molybdenum plasmas
Journal of Analytical Atomic Spectrometry ( IF 3.1 ) Pub Date : 2020-02-18 , DOI: 10.1039/c9ja00411d Ding Wu 1, 2, 3, 4, 5 , Xianglei Mao 5, 6, 7 , George C.-Y. Chan 5, 6, 7 , Richard E. Russo 5, 6, 7 , Vassilia Zorba 5, 6, 7, 8, 9 , Hongbin Ding 1, 2, 3, 4
Journal of Analytical Atomic Spectrometry ( IF 3.1 ) Pub Date : 2020-02-18 , DOI: 10.1039/c9ja00411d Ding Wu 1, 2, 3, 4, 5 , Xianglei Mao 5, 6, 7 , George C.-Y. Chan 5, 6, 7 , Richard E. Russo 5, 6, 7 , Vassilia Zorba 5, 6, 7, 8, 9 , Hongbin Ding 1, 2, 3, 4
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Diagnostics of plasma–wall interaction processes provide important information on nuclear fusion devices. Elucidation of the charge state distribution and temporal evolution of multi-charged ions is essential to improve laser ablation-based diagnostics of the plasma–wall interaction processes. Molybdenum is a material of interest in fusion and has been used as the plasma-facing material of the first wall in the EAST tokamak. In this work, the dynamic characteristics of multi-charged ions emitted from a molybdenum plasma produced by a Q-switched Nd:YAG nanosecond laser (wavelength 1064 nm, pulse width 7 ns) were studied using time of flight mass spectroscopy under a pressure of 6 × 10−4 Pa. The charge state distribution and temporal evolution of the multi-charged ions at various laser power densities from 0.85 GW cm−2 to 7.9 GW cm−2 were systematically investigated. This power density range is commensurate with that used in LIBS and LIAS diagnostics of the plasma–wall interaction process in EAST tokamaks. The ion charge state was found to increase with laser power density and the observed maximum charge state was up to seven at the highest laser power density used in these experiments. The higher charged ions had greater velocities indicating that separation took place between the different charged ions during the plasma expansion process. The origin of multi-charged ions is attributed to step-wise ionization due to plasma shielding from strong laser absorption in the plasma and the reduction of the ablation rate with the increase in laser power density. The velocities between these multi-charged ions were related to the acceleration of the transient plasma sheath during the laser interaction with the target and plasma.
中文翻译：
纳秒激光产生的钼等离子体发射的多电荷离子的动态特性
等离子体-壁相互作用过程的诊断为核聚变设备提供了重要信息。阐明电荷状态分布和多电荷离子的时间演化对于改善基于激光烧蚀的等离子体-壁相互作用过程的诊断至关重要。钼是熔融过程中关注的一种材料，已被用作EAST托卡马克第一壁的等离子材料。在这项工作中，使用飞行时间质谱法在压力为0的条件下研究了Q开关Nd：YAG纳秒激光（波长1064 nm，脉冲宽度7 ns）产生的钼等离子体发射的多电荷离子的动态特性。 6×10 -4Pa。在0.85 GW cm -2至7.9 GW cm -2的各种激光功率密度下，多电荷离子的电荷状态分布和时间演化被系统地调查。该功率密度范围与EAST托卡马克中等离子体-壁相互作用过程的LIBS和LIAS诊断中使用的功率密度范围相当。发现离子电荷状态随激光功率密度的增加而增加，在这些实验中使用的最高激光功率密度下，观察到的最大电荷状态高达7。较高电荷的离子具有较高的速度，表明在等离子体膨胀过程中不同电荷离子之间发生了分离。多电荷离子的起源归因于逐步离子化，这是由于等离子体屏蔽了等离子体中强烈的激光吸收，并且随着激光功率密度的增加，烧蚀速率降低。
更新日期：2020-02-18
中文翻译：
纳秒激光产生的钼等离子体发射的多电荷离子的动态特性
等离子体-壁相互作用过程的诊断为核聚变设备提供了重要信息。阐明电荷状态分布和多电荷离子的时间演化对于改善基于激光烧蚀的等离子体-壁相互作用过程的诊断至关重要。钼是熔融过程中关注的一种材料，已被用作EAST托卡马克第一壁的等离子材料。在这项工作中，使用飞行时间质谱法在压力为0的条件下研究了Q开关Nd：YAG纳秒激光（波长1064 nm，脉冲宽度7 ns）产生的钼等离子体发射的多电荷离子的动态特性。 6×10 -4Pa。在0.85 GW cm -2至7.9 GW cm -2的各种激光功率密度下，多电荷离子的电荷状态分布和时间演化被系统地调查。该功率密度范围与EAST托卡马克中等离子体-壁相互作用过程的LIBS和LIAS诊断中使用的功率密度范围相当。发现离子电荷状态随激光功率密度的增加而增加，在这些实验中使用的最高激光功率密度下，观察到的最大电荷状态高达7。较高电荷的离子具有较高的速度，表明在等离子体膨胀过程中不同电荷离子之间发生了分离。多电荷离子的起源归因于逐步离子化，这是由于等离子体屏蔽了等离子体中强烈的激光吸收，并且随着激光功率密度的增加，烧蚀速率降低。
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