飞秒强激光驱动团簇库仑爆炸产生聚变中子的实验研究
文献类型：学位论文
| 作者 | 周子理 |
| 学位类别 | 硕士 |
| 答辩日期 | 2010 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 刘建胜 |
| 关键词 | 飞秒强激光，气体团簇，库仑爆炸，氘-氘核聚变反应，等离子体通道，中子产额优化 |
| 其他题名 | Nuclear Fusion Induced by Coulomb Explosion of Clusters Subjected to Intense Femtosecond Laser Field |
| 中文摘要 | 团簇作为一种介于原子、分子和固体之间的一种特殊的物质形态，在与飞秒强激光相互作用中具有独特的优势。近十几年来，飞秒强激光与团簇相互作用的研究广泛开展，并在实验上取得了许多重大发现，包括高能X射线、keV量级电子、MeV量级离子和聚变中子的产生。其中台式飞秒强激光与含氘团簇相互作用驱动氘-氘核聚变反应为台式化高亮度中子源的实现提供了一种重要途径。本文围绕激光与团簇相互作用中激光的传输效应与中子产额优化等方面展开了相关的实验研究，并取得了以下几个方面的进展： 1，提出了一种能够快速准确地提取等离子体通道中电子密度分布的计算方法。该方法在结合了非对称Abel变换技术后，可获得精度较高的等离子体通道中相位信息和电子密度的分布情况。这为激光与团簇喷流相互作用的实验研究提供了有效的分析手段。 2，详细研究并比较了飞秒强激光脉冲在氘代甲烷和氘团簇喷流中的传输行为，发现电离散焦和团簇喷流中对入射激光的能量吸收在氘代甲烷团簇与氘团簇喷流中存在很大的区别。对等离子体通道径向电子密度分布的分析表明，氘代甲烷分子与氘分子中不同的电离价态是传输效应在这两种团簇喷流中不同的一个主要原因。我们还对飞秒激光脉冲在氘代甲烷与氘团簇喷流中的非线性传输进行了数值模拟，模拟结果与实验现象符合得很好。 3，通过控制飞秒强激光在氘代甲烷团簇喷流中的传输对聚变中子产额进行了优化。同时，对氘离子动能和氘代甲烷团簇喷流中等离子体通道的电子密度进行了相关性测量。我们发现，通过改变激光在氘代甲烷团簇喷流中的聚焦深度，激光电离散焦效应能够和激光本身的紧聚焦达到平衡，形成一圆柱状的相对较细的等离子体通道。与此同时，氘离子能量和中子产额获得了最大。模拟结果表明，在某一聚焦深度，电离散焦和激光紧聚焦之间能够形成平衡，激光能量能够最有效地沉积到氘代甲烷团簇喷流中，并同时获得优化的中子产额。 4，利用飞秒强激光与乙烷团簇的相互作用，分析了在激光与喷气之间的延时改变时乙烷团簇库仑爆炸产生的质子能谱，并且通过对能谱的拟合分析了乙烷团簇的形成随延时的变化过程。实验结果表明，在延时为3.3ms，气体背压为30bar的条件下, 乙烷团簇可获得约6.2nm的尺寸(半径)。我们利用PW级激光系统的单发大能量激光脉冲(6J，55fs，9×1018 W cm-2) 与最佳延时处(3.3ms)的乙烷团簇相互作用，获得了最高能量为98.8keV，平均能量为13.08keV的质子能量。值得注意的是，我们在实验中获得的半径为6.2nm的乙烷团簇是在较低背压30bar下制备的，若使用足够高强度的激光脉冲与高背压下更大尺寸的氘代乙烷团簇(C2D6)N相互作用，可望获得更高动能的氘离子和更高的中子产额。 |
| 英文摘要 | As an intermediate state between molecules and bulk solids, clusters subjected to intense laser fields have many fundamental applications including the generation of intense x-ray, keV electrons, MeV ions and fusion neutrons. Among these interesting applications, the production of 2.45 MeV fusion neutrons has attracted significant attentions since it paves a way to establish a table-top pulsed fast neutrons source. In this thesis, experimental and theoretical studies have been carried out on the propagation of femtosecond laser pulses in cluster jets as well as its influence on the neutrons yields optimization. The research progresses in this thesis are shown as follows: 1. A calculation method has been proposed to extract the electron density distribution in plasma channels. In cooporating with the non-axisymmetric-Abel -inversion technique, this method can calculate the phase information and electron density profiles of the plasma channels precisely and rapidly. It provides an effective analytical means for the studies of laser-cluster interaction. 2. Propagation of intense femtosecond laser pulses in supersonic (CD4)N and (D2)N cluster jets at different backing pressures has been studied. It has been found that propagation effects including ionization-induced defocusing and laser attenuation of incident pulses are very different in the (CD4)N and (D2)N cluster jets. Different ionization states of CD4 and D2 molecules have been observed by analyzing the transverse electron density profiles of the plasma channels, and should be considered as a major reason for the differences in the propagation effects. Numerical simulations for the nonlinear propagation of femtosecond laser pulses in (CD4)N and (D2)N cluster jets have been performed. The simulation results show a good reproduction of the experiments. 3. Fusion neutron yields from Coulomb explosion of (CD4)N clusters under the irradiation of an intense femtosecond laser pulse is optimized by controlling the propagation of the laser pulse in a cluster jet. A correlated study of fusion neutron yields, kinetic energies of the deuterons, together with the plasma channels diagnosed by a pump-probe interferometer, is performed. It has been found that by controlling the focal position related to the cluster jet, the plasma defocusing effect can balance with the tight focusing of the laser pulse induced by an off-axis parabolic mirror, and results in a cylindrical-shaped and relatively narrow plasma channel crossing the gas jet. The most energetic deuterons and the maximum yields of fusion neutron are produced at the same time. Numerical simulations indicate that the plasma defocusing can be balanced with the the tight focusing of the laser pulse, at the same time the laser energy can be most efficiently deposited into the cluster jets, and the optimized neutron yields are obtained as a result. 4. An experiment of intense femtosecond laser pulses interacting with (C2H6)N clusters has been performed. By controlling the time delay between the laser pulse and opening of the nozzle, we have analyzed the kinetic energy spectrum of protons generated from Coulomb explosion of (C2H6)N clusters, and investigated on the process of clusters formation. It has been found that at the optimized time delay (3.3 ms), (C2H6)N clusters under the backing pressure of 30 bar can obtain a radius of about 6.2 nm. At the same optimized time delay, energetic protons with the maximum kinetic energy of 98.8keV and average kinetic energy of 13.08 keV are obtained with a 6J, 55fs single shot driving laser pulse at an intensity of 9×1018 W cm-2. This work provides a possible way to seek for higher neutron yields, which can be realized by employing the laser with intensity higher enough to interact with larger-sized (C2D6)N clusters which can be prepared at a backing pressure higher than 30 bar. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/16686]  |
| 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 | 周子理. 飞秒强激光驱动团簇库仑爆炸产生聚变中子的实验研究[D]. 中国科学院上海光学精密机械研究所. 2010. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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