强激光与等离子体相互作用加速高品质离子束的理论与粒子模拟研究

The short-duration ions produced in the interaction of intense laser pulses with plasmas have proven to be effective for many potential applications. As a rule, these applications generally require a high-energy ion beam with low energy spread and high collimation. Thus, one of the important tasks on studing the laser-plasma ion acceleration is to improve the quality of the accelerated ion beams. This project is intended to study the generation of the high-quality ion beams in the interation of intense laser pulses with plasmas, including increasing the number and the energy of the accelerated ions, improving the ions collimation, as well as decreasing the energy spread of them. In the project, two hot topics of the laser-plasma ion acceleration will be mainly concerned, one is the radiation pressure acceleration(RPA) of ultrathin solid targets irradiated by an ultraintense laser pulse, the other is the ultrahigh energy ion generation by the sequential radiation pressure and bubble acceleration. The main problems should be investigated in the project are summarized as the following. Firstly,in order to obtain a high-quality heavy-ion beams in the RPA, the instability of the RPA in a mixed foil with multi-ion species or with some complex strutures will be investigated, which would put forward some effective schemes to depress the instability in a mixed foil. Secondly, we will investigate the realization of the RPA under some non-ideal conditions, including using a Gauss pulse and a near-critical density target. Thirdly, the dust effects on the RPA will be studied in the project, such as the influences of the particle size distribution, the species difference, and the charge change of the dust grains. Finally, in the ultrahigh energy ion generation by the sequential radiation pressure and bubble acceleration, we will investigate the scale laws of ion acceleration and develop some schemes of controlling the dephasing and the transverse emittance of the accelerated ion beams in the bubble regime by optimizing plasma density, or adding a dense-plasma wall ,etc.

超强超短激光与等离子体相互作用产生的快离子在很多方面有着潜在的应用，如桌面型加速器、医学治疗以及惯性约束核聚变中的快点火等。如何提高被加速离子的品质，即获得高能量、高流强、准直性好和能散度低的高品质离子束是当前强场加速离子的研究热点和难点之一。 本课题将在前期相关研究工作的基础上，围绕激光与等离子体相互作用加速离子中的两个研究热点--辐射压力加速、辐射压力加速和空泡加速相结合的级联加速，从理论分析和等离子体粒子模拟两方面进一步研究高品质离子束的获得问题。研究的主要问题有：几种离子构成的混合靶或具有某种复杂结构的混合靶中辐射压力加速不稳定性的发展规律和抑制；非理想条件下辐射压力加速的实现；尘埃颗粒对辐射压力加速的影响；抑制离子在空泡前段的失相和横向发散、以及探索空泡加速离子的重要标度律等。

项目围绕强激光与等离子体相互作用加速离子，从理论分析和等离子体粒子模拟两方面为获得高能量、高流强、准直性好和能散度低的高品质离子束探索可行的理论与实验方案。本项目开展的主要研究内容及研究成果有：. 1. 研究了非高斯激光束和非抛物预等离子体通道对激光传输的影响，包括q-Gauss激光束在抛物预等离子体通道中的传播，Gauss激光束在横向密度为幂函数分布的预等离子体通道(power-law channel)中的传播，以及Laguerre-Gauss激光束在纵向密度调制的抛物预等离子体通道(corrugated plasma channel)中的传播。这些激光传输过程的研究为非理想条件下实现离子加速和通过新型通道型结构靶获得高品质的离子束提供了理论依据。. 2. 提出了3种获得高品质离子束的离子加速新方案：一是圆偏振激光辐照“超薄固体层-临界密度层(HD-NCD)”组合靶产生高品质质子束的辐射压力加速新方案；二是在“锥-毛细管”(cone-capillary)型通道导引下圆偏振激光与超薄固体靶相互作用产生高品质质子束的辐射压力加速新方案；三是在锥形通道(tapered channel)导引下线偏振激光辐照超薄固体靶产生高品质碳离子束的重离子加速新方案。这些新方案产生的高品质离子束不仅是基础物理研究的重要手段，也在桌面型加速器、医学治疗、医学同位素产生、质子成像、激光等离子体相互作用的诊断、传统加速器的注入、高能量密度物理以及惯性约束核聚变中的快点火等方面有着重要的潜在应用。. 3. 研究了尘埃颗粒的存在对离子加速所涉及的静电波动及其各种不稳定性的影响。研究结果表明在辐射压力加速中，如果存在尘埃颗粒时，为了抑制各种不稳定的增长而最终获得高品质的离子束，应有效避免长波扰动。