螺线管传输并聚焦高能质子束的数值模拟研究
文献类型：学位论文
| 作者 | 张忠亚 |
| 文献子类 | 硕士 |
| 导师 | 沈百飞 |
| 关键词 | 强场激光物理 high field laser physics 螺线管 solenoid PIC数值模拟 PIC numerical simulation 质子束 proton beam 离子光学 ion optics 像差 aberration |
| 其他题名 | Particle-In-Cell Simulation of High Energy Proton Beam Transported and Focused by a Solenoid |
| 英文摘要 | 高品质高能质子束在众多领域都有着重要的应用前景，为了得到高能量低能散度的质子束，各国研究者进行了多方面的深入研究。一方面，研究者们对超强超短激光与等离子体相互作用的过程开展了广泛的理论和实验研究，提出了诸如靶背法向鞘层加速（TNSA）、光压整体加速（RPA）、无碰撞静电激波加速（CSA）等加速机制，并尝试优化靶材的结构和参数特性，提高了质子的最大能量，提升了质子束品质。但由于目前激光技术及理论模型对加速效果的限制，激光离子加速能达到的最高能量相比传统加速器仍有很大差距，单能性也较差。比如质子癌症治疗所需的质子能量普遍在250 MeV以上，能散度要求1%以内，现有条件还难以满足。另一方面，为了能在现有加速机制和激光条件下，尽可能地获得单能性好、发散角小，品质高的质子束，国内外的研究者在束流传输方面，也进行了诸多的模拟和实验研究，其中常见的方式是利用永磁体磁四极子和通脉冲电流的螺线管等磁透镜装置。随着激光技术的不断发展，新一代10PW激光装置的建成，实验室中可以实现的激光聚焦强度将达到1022-1023W/cm2量级，激光离子加速产生的质子束，其最大能量也会得到进一步提高。本文正是基于以上研究背景，采取Particle-In-Cell数值模拟方法，重点研究了通脉冲电流的螺线管，对具有一定能散度和空间发散角的高能质子的传输和聚焦特性，并分析了空间电荷效应的影响，同时对电磁透镜的各类主要像差进行分析与模拟论证。这三方面的具体内容如下： 1. 束流光学研究的是带电粒子在电磁场中的运动，与几何光学有一定相似性，自1926年起，布许（H.busch）等人陆续证明了利用旋转对称静磁场可以对带电粒子进行聚焦和成像，类似光学透镜对于光线的作用。基于此，本文采用3D Particle-In-Cell（PIC）数值模拟方法，研究了高品质高能质子束经由通脉冲电流螺线管传输并聚焦于远端的情况。模拟结果表明，初始时刻中心能量为250 MeV，能散度为10 %，空间发散角小于15 mrad的质子束，通过长度760 mm，中心磁感应强度为10.87 T的通电螺线管，可以被聚焦于距离质子源约2.5 m的远端，质子数目的损失小于3%。利用通电螺线管来传输和调控高能质子束流的方案是可行的，该方案可用于优化质子束流品质。 2. 强流电子光学中，电子束导流系数较大，需要将空间电荷效应考虑在内。空间电荷效应的存在，使得束流传输中的单粒子假设不再成立，场方程也由拉普拉斯方程变为泊松方程，其直接的后果就是空间电荷将引起所在电位的下降，使电子束趋于发散。强流情况下的空间电荷效应，将对质子束的聚焦特性造成影响，带来空间电荷像差。本文针对质子束不同的中心能量和不同离子数密度，比如中心能量70MeV，数目109个，进行了具体的模拟研究，探究空间电荷效应带来的影响大小。 3. 理想情况下，旁轴电子轨迹在轴对称静磁场中满足理想成像条件，当理想成像所需的假设不被满足时，就会引入像差。按照像差的成因主要分为几何像差（主要是球差和像散）、色差（质子束存在一定能量散度）、空间电荷像差、衍射像差几类，本文主要探究前两类，而忽略其它像差。具体方法是设定单一变量进行模拟，对比模拟结果，验证不同因素对聚焦效果的影响大小。; High-quality high-energy proton beams have important application prospects in many fields. In order to obtain high-energy and low-energy divergence proton beams, researchers in various countries have conducted in-depth research in various fields. On the one hand, researchers have conducted extensive theoretical and experimental studies on ulter-strong ultra-short laser plasma interaction, and proposed methods such as target normal sheath acceleration (TNSA), Radiation pressure acceleration (RPA), and collisionless electrostatic shock acceleration mechanism (CSA) and so on, and attempts are made to optimize the structure and parameter characteristics of the target, increase the maximum energy of the proton, and improve the quality of the proton beam. However, due to the limitations of laser technology and theoretical models on the acceleration mechanism, the maximum energy that can be achieved by laser ion acceleration still has a considerable gap compared to conventional accelerators, and the beam quality is also poor. For example, the proton energy required for proton therapy is generally above 250 MeV, the energy divergence is required within 1%, while the existing conditions are still difficult to meet. On the other hand, in order to obtain the best quasimonoenergetic proton beam,with small divergence angle and high beam quality under the existing acceleration mechanism and laser conditions, researchers at home and abroad have conducted many simulation and experimental studies on beam transmission, among which the common ones are magnetic lens devices such as permanent magnet magnetic quadrupoles and pulse power solenoids. With the continuous development of laser technology and the completion of the new generation 10PW laser device, the laser focusing intensity that can be achieved in the laboratory will reach the order of 1022-1023W/cm2, The maximum energy of the proton beam generated by the laser ion acceleration will also be further enhanced. This paper is based on this research background and applies the Particle-In-Cell numerical simulation method. It focuses on the transmission and focusing characteristics of high-energy protons with a certain energy divergence and spatial divergence, meanwhile, the influence of the space charge effect was analyzed. At the same time, various main aberrations of the electromagnetic lens were analyzed and simulated. The specific contents of these three aspects are as follows: 1. Beam optics studies the motion of charged particles in electromagnetic fields and has some similarities with geometric optics. Since 1926, H. busch et al. have successively demonstrated that the use of rotationally symmetric static magnetic fields can focus charged particles and imaging, just like the effect of an optical lens on light. Based on this, this paper uses 3D Particle-In-Cell (PIC) numerical simulation method to study high quality high energy proton beam transported and focused by a pulse power solenoid. Simulation results show that proton beam with peak energy of 250 MeV, energy spreads of 10% and a spatial divergence angle less than 15 mrad can be focused on a spot 2.5 m away from the proton source, by using a pulse power solenoid which runs at a magnetic field strength of 10.87 T and has a specific length, manwhile, the number loss of proton beam is less than 3 %. We concluded that optimize proton beam quality is feasible by using a pulse power solenoid to transport and focus the beam, and it is necessary for laser proton acceleration to practical applications such as proton therapy and others which require high beam quality. 2. In high density electron beam optics, the electron beam perveance is large and the space charge effect needs to be considered. The existence of the space charge effect makes the single-particle assumption in the beam transport no longer valid, and the field equation also changes from the Laplace equation to the Poisson equation. The direct consequence of this is that the space charge will cause the falling of the potential, making the electron beam tends to diverge. The space charge effect under high beam density conditions will affect the focusing characteristics of the proton beam and bring about space charge aberration. This paper focuses on the different center energies and different ion number densities of the proton beam, such as the center energy of 70 MeV and the number of 109. A detailed simulation study was conducted to explore the effect of the space charge effect. 3. Ideally, the paraxial electron trajectory satisfies the ideal imaging conditions in an axisymmetric static magnetic field, and aberrations are introduced when the assumptions required for ideal imaging are not satisfied. According to the causes of aberrations, it is mainly divided into geometric aberrations (mainly spherical aberration and astigmatism), chromatic aberrations (proton beams have a certain energy divergence), space charge aberrations, and diffraction aberrations. This article mainly discusses the first two categories and ignore other aberrations. The specific method is to set a single variable then simulate, compare the simulation results and verify the influence of different factors on the focusing effect. |
| 学科主题 | 光学 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/31052]  |
| 专题 | 中国科学院上海光学精密机械研究所 |
| 作者单位 | 中国科学院上海光学精密机械研究所 |
| 推荐引用方式 GB/T 7714 | 张忠亚. 螺线管传输并聚焦高能质子束的数值模拟研究[D]. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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