相对论激光驱动的离子加速问题的研究
文献类型：学位论文
| 作者 | 王晓峰 |
| 学位类别 | 博士 |
| 答辩日期 | 2015 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 沈百飞 |
| 关键词 | 相对论激光 离子加速 三倍频 连续加速 |
| 其他题名 | Ion acceleration driven by relativistic intensity laser |
| 中文摘要 | 高能离子束（ MeV， GeV） 在医疗、质子成像、激光聚变等领域具有重要的应用价值而受到广泛关注。要想获得高能离子并避免传统同步加速器的一些缺点（如体积大、价格昂贵），利用超强激光与等离子体相互作用是一种非常有前景的解决方案。 实验上目前已经可以实现聚焦强度达到~1022 W/cm2、脉冲宽度小于 10fs 的超短相对论激光脉冲。 这为研究相对论激光驱动的离子加速带来非常有利的条件。 激光驱动离子加速方案有多种，相比而言，光压加速具有较高的能量转换效率，而且得到的单能离子束能谱窄、 发散角小。理论模拟与实验都取得了积极的进展， 但仍存在一些改进空间。本文主要对三倍频（ 3ω） 激光与固体薄膜靶相互作用过程中的离子加速， 以及双脉冲驱动的离子连续加速方案进行了研究，具体如下： 1. 从激光与等离子体相互作用的物理过程着手利用二维 Particle-in-Cell（ PIC） 拟研究了 3ω 激光驱动的离子加速， 以及 3ω 情况下加速场强度和加速时间等物理量的变化。 在相同激光能量的前提下， 三倍频后加速电场强度有较大提高，在相同的作用距离里内，离子可以得到更多的能量。 相比基频激光的情况， 即使考虑在三倍频过程中的能量损失， 三倍频后仍然可以得到更高的离子峰值能量。 2. 双脉冲驱动的离子连续加速方案选用稠密等离子体与低密度等离子体组成的复合结构靶，先用超短圆偏振超高斯（ SG）光对稠密等离子体中的离子进行预加速，然后利用拉盖尔—高斯（ LG）光在低密度等离子体中产生的特殊空泡结构对其进一步稳定加速。在第一阶段 SG 光驱动的光压加速过程中，在很短时间内离子被加速到相对论速度。在第二阶段，离子在发散之前被 LG 光产生的特殊空泡捕获，受横向场的约束得以较长时间地稳定加速。模拟结果表明，利用强度为 2×1022 W/cm2 SG 光和峰值强度稍低的 LG 光可以得到峰值能量 6.7 GeV 的质子束。 |
| 英文摘要 | Ions on million electron volts (MeV) or giga electron volts (GeV) energy scales are pursued for their valuable applications in medical therapy, proton imaging, laser fusion, and other areas. High-intensity laser is regarded as a prospective solution to accelerate ions to high energy, while avoiding shortcomings encountered in traditional synchronous accelerators, such as large volume, high cost. Nowadays, the ultra-short intense laser with intensity ~1022 W/cm2 and pulse width less than 10 fs is approachable in laboratories, which brings great convenience to study the ion acceleration driven by relativistic intensity laser. Several mechanisms have been proposed for the laser-induced ion acceleration, and light pressure acceleration, also known as radiation pressure acceleration (RPA), is regarded as an efficient way to obtain a monoenergetic ion beam, with high laser-ion conversion efficiency, narrow energy spectrum, and reduced divergence compared with other schemes. Progress in theory and experiments has been reported frequently, however some points still remain unclear. In this thesis, the proton acceleration process in the interaction of frequency tripled (????) laser and foil target, and the sequential acceleration of ions driven by two intense laser pulses, are studied, and the details are as follows: 1. Taking the 3?? laser as an example, the frequency conversion effect on ion acceleration is studied using two-dimensional Particle-in-Cell simulation, and the physical process is considered. The result is compared with that from the 1?? laser. With the same laser pulse energy, the 3?? laser will produce higher acceleration field, which results in stronger acceleration for the same acceleration distance. Much higher ion energy peak value is obtained even when a certain amount of laser energy loss is considered during the frequency conversion process. 2. A novel sequential acceleration scheme is proposed, in which ions in the dense plasma adhered to underdense plasma are first pre-accelerated by the radiation pressure of an ultra-short circularly polarized (CP) super-Gaussian (SG) laser pulse. Subsequently, the ions are trapped in a special bubble driven by an CP Laguerre-Gaussian (LG) laser pulse and stably re-accelerated. The former relativistic CP SG laser pulse irradiates the dense plasma and the ions are accelerated to approach the light speed in a short time. Prior to their dispersion in the transverse direction, ions are trapped in the special bubble driven by the following LG10 pulse. In the latter acceleration process, ions are well confined by the transverse focusing force, which is naturally generated in the special bubble, and experience another stable acceleration process. Simulation results show that protons of 6.7 GeV may be obtained with a 2×1022 W/cm2 SG laser pulse and an LG pulse at a lower peak intensity. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15910]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 王晓峰. 相对论激光驱动的离子加速问题的研究[D]. 中国科学院上海光学精密机械研究所. 2015. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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