质子束驱动的尾波场加速带正电粒子研究
文献类型：学位论文
| 作者 | 易龙卿 |
| 学位类别 | 博士 |
| 答辩日期 | 2014 |
| 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 | 质子束驱动 等离子体尾波场 正电子加速 |
| 其他题名 | Proton driven wakefields acceleration of positively charged particles |
| 中文摘要 | 1979年，Tajima和Dawson提出了激光尾场加速电子的概念。基于等离子体中的电荷分离，激发的尾波场可以提供高于传统加速器上千倍的加速梯度。这一理论引起了人们广泛的兴趣并得到了深入的研究，并促生了“高能量密度物理”这门学科。近年来，基于突飞猛进的激光技术，“高能量密度物理”发展迅猛。然而对比“高能（粒子）物理”领域，即使是目前最好的等离子体加速结果也与传统加速器中的粒子能量相去甚远。这是因为虽然激光的能量密度极高，但目前其能够携带的总能量毕竟有限。 另一方面，利用高能粒子束替代激光作为驱动源的方案也逐渐引起人们的重视。尤其是当采用传统加速器中的高能质子束来驱动等离子体尾波场的时候，被加速粒子能够获得高达TeV（10^12 eV）量级的单级能量增益。这使得“高能量密度物理”与“高能物理”这两门学科之间有望架起一座桥梁，从而能够推动彼此的发展。 本论文基于质子束驱动的等离子体尾波场加速的概念，开创性地提出了利用质子束驱动非线性等离子体空泡加速带正电荷的粒子。并进行了逐步深入的研究，旨在探索将等离子体加速的方案应用在高能物理的研究领域的新途径。这对于未来新型的小型化粒子对撞机的建造乃至粒子物理学的发展都具有积极的作用。主要做了以下几个方向的工作： 1. 自从“空泡”的概念被首次提出以来，就被广泛地用于电子加速。而在带正电荷粒子的加速方面进展较慢，因为空泡中横向的排斥作用使其难以稳定地被加速。而通过研究质子束驱动的等离子体尾波场，我们发现大量背景等离子体电子会在质子束电荷力的吸引下随着质子束一同运动。这些电子集中在空泡的最前端形成一个高密度区域。它们产生的洛伦兹力能够在附近的小范围内抵消“空泡”中（对带正电粒子的）的横向排斥力。这对质子加速有重要的意义。我们通过2维PIC模拟证实这种“自约束效应”能够使进入“空泡”前端加速相位的一部分驱动质子稳定地被加速一段较长的距离，获得较为明显的能量增益。这一方案使目前传统加速器中得到的高能质子束有望能够在等离子体中进一步加速，从而达到更高的能量。 2. 针对“空泡”中质子的稳定传输问题，我们提出了一种新的方案。在等离子体中引入一条直径与驱动质子束横向尺寸相当的真空通道。当质子束在通道中传输的时候，它的电荷力将会导致通道壁上的电荷分离，将一部分电子拉进“空泡”。同时，另一束质子跟随在驱动束的后。通过通道壁附近的电荷分离场的作用下，第二束质子能够在横向上被稳定的约束。采用通道的方案之后，非线性尾波场中适合质子的加速区域显著增大，从而解决了前一个工作中遗留下来的失相过快的问题，大大提高了质子束能够被加速到的能量。在2维模拟中我们成功使质子束在1 km的加速距离内获得了1.3 TeV的能量增益。并且通过调节初始的质子能量分布，我们最终获得了一束能散约为2%的准单能质子束。 3. 目前，加速器中产生的轻子（电子与正电子）的能量通常在100 GeV以下。在传统加速器中，受限于较低的加速梯度，TeV量级或者更高能的轻子，特别是正电子很难获得。而基于我们提出的等离子体通道加速的方案，正电子有望通过等离子体加速器中高达GV/m的加速梯度进行稳定的加速。通道壁上的电荷分离场能够对正电子进行横向约束。同时，进一步的分析表明在驱动质子束的传播中轴附近能够形成一个弱聚焦的区域，在这一区域中的正电子在加速过程中能够保持发射度恒定，同时辐射损失也能够被降低到极低的范围。并且在加速的最终阶段，加速场的分布能够抑制正电子束的能散，从而使单能性显著提高。 |
| 英文摘要 | In 1979, Tajima and Dawson proposed the concept of laser wakefield acceleration. The excited plasma wakefield behind the laser pulse is thousands of times larger than the acceleration gradient in the conventional accelerators. Due to this advantage, it has been widely researched and a lot of progress have been made since then, which prompted the study of "high energy density physics". However, although it developed very fast in the past a few years, even the highest energy achieved in the plasma acceleration is much less than that achieved in "particle physics" (i.e. conventional accelerators). This is because the total energy in a laser pulse is limited, though the energy density is extremely large On the other hand, high energetic particle beams have also been proposed to be alternate drivers. Espectially, it has been suggested that the powerful proton beams available from conventional accelerators can accelerate witness particles to TeV energies in a single acceleration stage. This concept may build a bridge between the topics of "high energy density physics" and "particle physics", prompting development in both fields. This thesis has the following parts, all of which are based on the theory of plasma wakefield acceleration.driven by energetic proton beams. The main idea is to find a way to apply plamsa accelerators in the research of particle physics, which may guarantee future TeV-range linear colliders based on plasma accelerators and give hints on the research of particle physics 1. Plasma wakefield excited by a short TeV-scale proton beam is investigated in the highly nonlinear regime. Analysis of the “bubble” field illustrates that the co-propagating electrons within the proton bunch can be compensat the transverse expelling force of the wakefield in the very head of “bubble”, leading to a collimation effect that stabilizes the beam propagation. The protons in the driven beam tail which fall into the accelerating phase of the bubble can be well-confined and accelerated forward for a long distance. Two-dimensional simulations show that after a 1-TeV proton bunch propagating through plasma for a distance, several percentages of the protons achieve a remarkable energy gain. This scheme presents a potential that proton beams from conventional accelerators may gain considerable additional energy through plasmas wakefields 2. We propose a new scheme for accelerating positively charged particles in a plasma-wakefield accelerator. If the proton drive beam propagates in a hollow plasma channel, and the beam radius is of order of the channel width, the space charge force of the driver causes charge separation at the channel wall, which helps to focus the positively charged witness bunch propagating along the beam axis. In the channel, the acceleration buckets for positively charged particles are much larger than in the blowout regime of the uniform plasma. Two-dimensional simulations suggest that, for proton drivers likely available in future, positively charged particles can be stably accelerated by 1.3 TeV over 1 km with the energy spread of about 2%. 3. Leptons, such as electrons and positrons, usually gain energies merely less than 100 GeV at present. Multi-TeV lepton accelerators are still absent due to the relatively low acceleration gradient of conventional methods, which may induce unbearable cost. Plasmas have shown extraordinary potential in accelerating electrons and ions, providing orders of magnitude higher acceleration fields of GV/m. In such context, a plasma-based high-energy lepton accelerator is proposed, in which a weakly focusing plasma structure is formed near the beam axis. The structure preserves the emittance of the accelerated beam and produces low radiation losses. Moreover, the structure allows for a considerable decrease of the witness energy spread at the driver depletion stage |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15888]  |
| 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 | 易龙卿. 质子束驱动的尾波场加速带正电粒子研究[D]. 中国科学院上海光学精密机械研究所. 2014. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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