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题名	飞秒强激光与薄膜靶相互作用加速带电粒子的研究
作者	王凤超
学位类别	博士
答辩日期	2009
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	飞秒激光脉冲 有质动力 复合靶 靶后鞘层加速
其他题名	Charged Particle Acceleration in Interaction of Femtosecond Intense Laser Pulse with Thin Foil Target
中文摘要	随着激光技术的飞速发展，人们已能获得聚焦强度超过1022W/cm2、单脉冲宽度小于10fs的相对论激光脉冲，这种激光脉冲与物质的相互作用与许多应用有关，像粒子加速、激光驱动的X射线源、快点火惯性约束核聚变方案等。特别是用飞秒强激光加速带电粒子，这种新型加速器与传统加速器相比有着巨大的优势，因此近年来受到人们的广泛关注。强激光与等离子体相互作用加速电子和质子，已经得到了广泛的理论和实验的研究，目前电子加速的主要机制有激光有质动力加速和激光尾波场加速。离子的主要加速机制有激波加速、光压加速以及靶后鞘层加速机制等。本论文主要对激光有质动力真空中加速电子及靶后壳层加速质子做了深入的研究。 本论文的主要工作可概括如下： 1、对激光有质动力加速电子进行了理论分析，并详细的讨论了线偏振光和圆偏振光两种情况下电子加速的情况。由于处于激光上升沿的电子会被激光的有质动力加速，相反如果电子处在激光的下降沿，则激光的有质动力会使电子减速，因此当电子处于激光脉冲峰值位置时得到最大能量，与之对应加速距离就是最佳的加速距离。最佳加速距离与激光的强度和脉宽成正比 。理论分析表明，线偏振激光能够更有效的加速电子，并且电子在线偏振激光下加速的最佳距离是圆偏振激光的一半，但是另一方面，由于线偏振激光的有质动力表达式有振荡项的存在，因此用线偏振激光加速很难得到单能的电子束。而用圆偏振激光则更容易得到单能的电子束。 2、根据上述1中的理论基础，利用VORPAL模拟程序分析研究了强激光与薄膜靶相互作用，提出了一种获得单能电子束的方案，当激光足够强时，薄膜靶中的电子在强大的激光有质动力作用下克服电场力的作用，被全部推出，进而在真空中加速。另外为了将高能电子束从激光场中分离出来，我们在最佳位置处放了块挡板，这样激光就会被挡板完全反射，而电子则会穿过挡板，从而将电子从激光场中分离出来。在理论分析中，我们也相应的考虑了反射光对加速电子的影响。从一维模拟的结果来看，尽管电子束通过挡板是有少部分的能量损失，但是我们依然能够得到高能量的单能的电子束。这充分说明了我们的方案是一种获得高质量的单能电子束的有效途径。 3、利用两维VORPAL模拟程序研究了P偏振飞秒强激光与复合靶相互作用，利用靶后壳层加速机制加速得到高质量的单能质子束。我们所选用的复合靶与简单的双层靶的区别在于，我们在原来简单的双层靶前面加了个薄片（两维）或者细丝（三维），当激光与薄片（细丝）相互作用时，在表面有质动力（SPF）作用下，薄片（细丝）中的电子被激光电场力拉出，并且沿着薄片的表面被激光向前加速。这样具有定向速度的电子是很容易穿过双层靶进而在靶后形成强大的电场，附着在重离子层后面的质子在这个静电场的作用下将被加速。由于在我们的这个方案中，电子有定向的速度，因此当电子到达靶后时不容易散开，从而更有效的加速质子，模拟结果表明，激光与复合靶相互作用时，我们得到的质子束不但能量是简单双层靶的三倍多，而且能散度还下降到原来的一半。通过对靶和激光进行优化，质子束的能量将会有所提高，而能散度也可以进一步降低。这样根据现有的实验数据（60MeV），用我们的方案，我们可以得到大于180MeV的质子束，而这种质子束在医疗上可用于癌症治疗，具有很高的应用价值。
英文摘要	The rapid development of the laser technology has made available ultraintense (1022W/cm2) ultrashort (10fs) laser pulses. The interaction of such pulses with matter is related to many applications, such as particle acceleration, ultra-short and coherent X-ray radiation source, and fast ignitor inertial confinement fusion schemes etc. especially for the femtosecond intense laser acceleration of charged particle. It has attracted much attention due to the new accelerator has huge advantage compare with the conventional accelerator. Electron and proton acceleration in interaction of intense laser pulse with the plasmas has been studied widely by experiments and theoretics. The main mechanism of the electron acceleration is laser ponderomotive force acceleration and laser weak wave acceleration. And for ion acceleration, several schemes, including shock acceleration, light-pressure acceleration, target-normal sheath acceleration (TNSA) and so on, have been proposed. In this paper, laser ponderomotive force acceleration of electron in vacuum and the target-normal sheath acceleration of proton are focused and some results are given as follows: 1 Electrons accelerated by a propagating laser pulse of linear or circular polarization in vacuum have been investigated by analytical modeling. It is known that a plane wave cannot be used for electron acceleration, since when the wave overtakes the electron the ponderomotive force drives the electron forward in the ascending front but backward in the descending part of the laser pulse. There is an optimal acceleration length for electrons to gain maximum energywhere electrons meet the peak of the laser pulse. The optimum acceleration length depends strongly on the intensity and duration ( ) of the laser pulse。From analytical results, we know that the linearly polarized laser pulse is more effective to accelerate electron than circularly polarized one, and the optimal acceleration length of linearly polarized laser is only half of the circularly one. But it is difficult to obtain a monoenergetic electron bunch with a linearly polarized laser pulse due to the electron energy oscillation. And it is easy to do that with a circularly laser pulse. 2 Base on the theory of above mentioned in 1, we propose a scheme to obtain monoenergetic electron bunch in the interaction of ultrashot intense laser pulse with a thin foil. When the intensity of laser pulse is high enough, all the electrons of the thin foil will be pushed out from the foil, and accelerated in the vacuum by the laser pulse. In order to extract the energetic electrons from the laser field, we put a stopping target at the optimal position. The laser pulse can be reflected by the stopping target and the electron can easily pass through it with almost no energy loss. From the one-dimensional simulation results of VORPAL, we know that although there is a little energy loss when electrons pass through the stopping target. We can still obtain a high quality monoenergetic electron bunch. This demonstrates that our acceleration and extraction scheme is valid. 3 Generation of high-energy proton bunch in the interaction of a high-power laser pulse with a complex target consisting of a front horizontal slice (two-dimension) or wire (three-dimension) adjoining a conventional heavy ion and proton double-layer slab is investigated using two-dimensional particle-in-cell simulation code VORPAL. The laser pulse is incident onto the front edge of the slice. Most of the slice electrons are then pulled out from the slice and accelerated forward along the slice surface by the surface ponderomotive force acceleration (SPFA). These electrons are not only energetic, but also highly collimated, so that they can easily propagate through the adjoining double-layer to form a stronger, longer-living, and more localized sheath field behind the target. Protons can be effectively accelerated in this field. The simulation results show that not only the peak energy of proton bunch is about three times of the simple double-layer one, but also the energy spread is only a half of the simple double-layer one. Base on the present experiment data (60MeV). The peak energy of 180MeV’s proton bunch can be obtain using our scheme, is just at the energy level required for proton-therapy.
语种	中文
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/15272]
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	王凤超. 飞秒强激光与薄膜靶相互作用加速带电粒子的研究[D]. 中国科学院上海光学精密机械研究所. 2009.

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