| 题名 | 强场激光产生伽马射线和反质子 |
| 作者 | 李顺 |
| 文献子类 | 博士 |
| 导师 | 沈百飞 |
| 关键词 | 飞秒相对论激光 Relativistic laser pulse 能谱探测 Spectrum measurement 超快伽马射线 Ultrafast gamma-ray beam 反质子 Antiproton Geant4 Geant4 |
| 其他题名 | Generation of Intense Laser-driven Ultrafast Gamma-Ray and Antiproton Beam |
| 英文摘要 | 随着激光技术的快速发展，特别是啁啾脉冲放大技术的提出和实现，目前实验室中已经获得峰值功率到10PW的飞秒相对论激光脉冲，100PW甚至更高功率的激光装置也正在规划。相对论激光脉冲可以加速产生几十MeV到数GeV 的高能电子束。高能电子束可以通过多种机制产生伽马射线：高能电子与高Z原子核相互作用，通过轫致辐射过程产生伽马射线；高能电子束与次级激光脉冲相互作用，通过逆康普顿散射过程产生高能伽马射线；高能电子在尾场中横向静电场作用下通过回旋辐射产生高亮度的伽马射线；强场激光与等离子体相互作用进入辐射主导区时（10PW级激光），电子在激光场中运动时就可产生极强的伽马辐射。由于强场激光脉宽是飞秒量级，其产生的伽马射线源脉宽一般小于皮秒量级。另外，强场激光也可以基于多种机制加速产生质子束，当激光强度大于1022W/cm2时，基于光压或者空泡等加速机制可以产生GeV以上的高能质子束。高能质子束也可以进一步用来产生反质子、π介子或μ子等粒子。 基于以上几点，本论文主要做了以下几个方面的工作： 飞秒相对论激光脉冲驱动产生的超快伽马射线源，其脉宽通常小于皮秒，传统的闪烁体或高纯锗探测器由于时间分辨率限制，无法进行有效探测。为了获得伽马射线的能谱信息，本论文根据伽马射线与物质相互作用的过程，设计加工了适用于超快伽马射线的谱仪：康普顿散射谱仪和能量沉积谱仪。两种谱仪分别通过测量伽马射线散射的次级电子和伽马射线穿过材料后的剩余强度信息反推出伽马射线能谱。伽马光束能谱的精确探测非常有利于激光驱动超快伽马射线源的后续应用。 基于单光子的思想，提出了一种新的多通道超快伽马射线谱仪，其可以实现高分辨率、宽能谱测量。该谱仪主要由闪烁体阵列、光电探测阵列以及信号获取系统构成。超快伽马射线探测实验中，通过调整谱仪的位置和距离，使得每一路通道最多探测一个光子信号，综合多路信号可以获得伽马射线源的能谱信息。目前已搭建4×4阵列的伽马谱仪原型机，并做了标定测试。 利用强场激光物理国家重点实验室飞秒拍瓦激光装置，进行了飞秒激光脉冲驱动的超快伽马射线产生实验和应用研究。飞秒相对论激光脉冲与氩气团簇靶相互作用，产生了电量超过10 nC的相对论高能电子束。高能电子束入射到毫米厚度的铜靶时，通过轫致辐射过程产生高通量超快MeV伽马射线束，其峰值强度超过1023 s-1。伽马射线能谱采用能量沉积法测量，为截止能量超过15MeV的连续能谱分布。能谱测量的实验结果与Geant4模拟近似一致。该高通量高能超快伽马射线源可用于光核反应、无损诊断以及临床应用等方面。另外，利用Geant4模拟程序，将实验中产生的高能电子束入射到厘米厚度的铜靶，模拟了伽马驱动光核反应的中子产生过程，产生了超过106个中子，中子在4π立体角内近乎均匀分布。 基于飞秒超强激光脉冲，利用二维PIC模拟和Geant4模拟来研究超快反质子束的产生过程。首先，基于光压空泡联合加速机制，飞秒超高强度激光脉冲可以产生几十GeV的高通量质子束；然后，该高能质子束入射到高Z靶产生反质子。反质子束的产额和能量几乎随着激光强度线性增加。激光强度为"2.14×" 〖"10" 〗^"23" "W" ?〖"cm" 〗^"2" 时，产生的反质子束脉冲宽度约为5 ps，其通量为"2×" 〖"10" 〗^"20" " " "s" ^"-1" 。与基于直线加速器的传统方法相比，这种基于超强激光脉冲的新方案能够提供紧凑、可调谐的超快反质子源，将在夸克胶子等离子体研究，全光学反氢生成等方面都有潜在的应用价值。同时也模拟了π介子和μ子的产生过程，它们需要的质子能量阈值更低，反应截面也较大，更容易在短期内实验上实现。随着激光功率的提高，激光驱动的粒子源也将更加丰富。; With the rapid development of laser technology, especially implementation of the chirped pulse amplification technology, relativistic laser pulses with a peak power of 10 PW have been obtained in the laboratory, and the laser facility with 100 PW or even higher power are being planned. There are several methods to generate gamma-ray beams based on laser-driven high-quality electrons with energy from tens of MeV (mega-electron-volts) to multi-GeV. The energetic electron beam will be converted into bremsstrahlung radiation to generate gamma-ray beam with broad energy spectrum when it shots into a mm-thick high-Z solid target. The relativistic electrons with energy of hundreds MeV, colliding with a secondary laser pulse, are able to produce a tunable, low-divergence and multi-MeV gamma ray beam by inverse Compton scattering. The betatron oscillations of electrons wiggling transversally in laser wakefield will emit brilliant and collimated gamma-ray radiation with energy up to several MeV along the propagation direction. When the interaction of extremely intense laser and plasma gets into radiation dominant region, the election motion in laser filed can lead to ultraintense burst of gamma-ray radiation with high efficiency. Intense lasers pulse has ability to accelerate proton beams to high energy through different acceleration processes. When the laser pulse intensity exceeds 1022 W/cm2, high-energy proton beams with energy above GeV will be generated based on radiation pressure or bubble mechanisms. These high-energy protons will be used to generate antiprotons, pions or muons. Based on the above points, this paper has mainly done the following aspects of work: Pulse duration of laser-driven ultrafast gamma-ray beam is usually less than picoseconds. The scintillation or high-purity germanium detector are not able to be used to detect the gamma-ray spectrum due to the limited time resolution. Two novel gamma-ray spectrometers have been designed to detect the ultrafast gamma-ray beam: Compton scattering spectrometer and differential filtering detector. These two spectrometers measure scattering electrons and residual intensity information to get the spectrum information by deconvolution. Precise detection of the energy spectrum is significant to the applications of ultrafast gamma-ray beam. A multi-channel ultrafast gamma spectrometer has been proposed based on single photon detection, which will realize high resolution and wide energy spectrum measurement. This spectrometer consists of a scintillator array, a photodetection array, and a signal acquisition system. Each scintillator channel detects one gamma-ray photon and get its energy by adjusting the position and distance of the spectrometer and gamma-ray source. The energy spectrum of gamma-ray beam will be obtained when the integrated signal of multi-photons forms. At present, the spectrometer with 4×4 array prototype has been built up and calibration tests have been performed. Ultrafast gamma-ray generation experiments based on laser-accelerated electrons has been performed based on a femtosecond PW laser system in the State Key Laboratory of High Field Laser Physics. The intense laser pulse interacts with clustering argon gas targets, which produces the relativistic electron beams with the charge beyond 10 nC. Ultrafast multi-MeV high-flux gamma-ray beams have been experimentally produced via bremsstrahlung radiation of laser-accelerated energetic electrons through millimeter-thick copper targets, and its peak intensity exceeds 1023 s-1. The gamma-ray beam spectrum has been measured using a differential filtering detector and has a broad spectrum up to 15 MeV, which is approximately consistent with the Geant4 simulation. The generated high-flux high-energy gamma-ray beams are promising sources for photonuclear reaction, non-destructive inspection and clinical applications. In order to detect neutrons generated by photonuclear reactions, the high-energy electron beam from experimental result was incident on a cm-thick copper target, resulting in the generation of more than 106 neutrons, and the neutrons were nearly uniformly distributed at the 4π solid angle. Antiproton beam generation is investigated based on ultra-intense femtosecond laser pulse by using two-dimensional particle-in-cell and Geant4 simulations. High-flux proton beam with energy of tens of GeV is generated in sequential radiation pressure and bubble regime and then shoots into a high-Z target for producing antiprotons. Both yield and energy of the antiproton beam increase almost linearly with the laser intensity. The generated antiproton beam has a short pulse duration of about 5 ps and its flux reaches "2×" 〖"10" 〗^"20" " " "s" ^"-1" at the laser intensity of "2.14×" 〖"10" 〗^"23" "W" ?〖"cm" 〗^"2" . Compared to conventional method, this new method based on ultra-intense laser pulse is able to provide a compact, tunable and ultrafast antiproton source, which is potentially useful for quark-gluon plasma study, all-optical antihydrogen generation and so on. The generation of pions and muons have also been simulated. The results show that they require lower proton energy and have larger reaction cross sections compared to antiproton generation, which are easier to be produced in experiments. With the increase of laser power, laser-driven particle sources will also be more abundant. |
| 学科主题 | 光学 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/31132]  |
| 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 | 李顺. 强场激光产生伽马射线和反质子[D]. |
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