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chi20191126上海光机所徐至展院士 刘建胜研究员557637Particle accelerators can accelerate particles and generate radiation, which have wide applications in biology, medicine, nuclear physics and other fields. While the conventional accelerators usually have a large scale. The acceleration gradient of the super-strong electric field generated by the charge separation in the plasma accelerators can reach 100 GV/m, which is three orders of magnitude higher than the acceleration gradient of the conventional accelerators, greatly reducing the area occupied by the accelerators and making the accelerators tabletop. Plasma accelerators usually include laser-driven plasma accelerators (LWFA) and particle-driven plasma accelerators (PWFA). With the development of the plasma accelerators, GeV-scale high energy electrons can be generated in plasma accelerators in a distance of centimeter scale, and the energy spread of the electrons can be compressed to less than 1%. Moreover, the brightness of the electrons can reach to 1015A/m2/0.1%, which is very close to the typical brightness of electrons from conventional linac accelerators. Besides, great progress has also made in novel radiation sources based on the electrons generated in plasma accelerators. Nowadays, the photon energy of the gamma-ray produced by the novel radiation sources can reach MeV scale and the brightness of the radiation can reach to 1023 photon s-1 mm-2 mrad-2 0.1%BW, which plays an indispensable role in biological medical imaging, material science and fundamental scientific research fields. In this dissertation, we investigated the high-quality electron beams generated in ultra-short laser-driven wakefield accelerators and radiation from the all-optical Compton scattering sources. In the experiments, by optimizing the laser parameters, plasma density and plasma length, we generated high quality electron beams in laser wakefield accelerators and obtained dual-color gamma rays via the self-synchronized all-optical Compton scattering scheme. Furthermore, the experimental results were dicussed by theoretical analysis and simulation study. The detailed works are listed as follows: As a contributor, the experimental platform based on the hundred-terawatt ultra-intense laser-driven cascaded wakefield accelerators was built, which can accelerate high-quality electron beams through the energy chirp control. In the experiments, by designing a structured gas density profile which consisted of a density bump between the dual-stage gas jets, we generated high-brightness high-energy electron beams with peak energies in the range of 200-600 MeV, rms energy spread in the range of 0.4%-1.2%, charge of 10-80 pC, rms divergence of 0.2 mrad and the maximum six-dimensional brightnesss B6D,n at about 6.5×1015A/m2/0.1%. The six-dimensional brightnesss was much higher than the results that previously reported in the world. Based on the experimental platform of hundred-terawatt cascaded laser wakefield accelerators, we built self-synchronized all-optical Compton scattering system. By optimizing the conditions of the laser and plasma density, we have experimentally produced two-color electron beams with peak energies at ~300 MeV and ~210 MeV based on the combination of self-injection with the density-gradient injection in a cascaded laser-driven wakefield accelerator. By performing with the all-optical Compton scattering scheme, the driving laser pulse which was reflected by a plasma mirror, can be directed to collide with the generated electron beams to produce the dual-color gamma-rays peaking at 1.07 MeV and 0.59 MeV. In order to get insights into the experimental results, particle-in-cell simulations have been performed to demonstrate the process of the two-color electron beams’ injection and acceleration. The simulated spectrum of gamma-ray radiation closely matches the experimental one. On the experimental platform based on the hundred terawatts cascaded laser wakefield accelerators, by optimizing the conditions of the laser, plasma density and plasma length, we generated two-color electron beams in the experiments and indicating the hybrid of laser-plasma wakefield acceleration. When the plasma length was increased to be larger than the laser pump depletion length, one electron beam was still accelerated to 640.7 MeV with 1.1% FWHM energy spread and the other electron beam lost its energy rapidly up to 230.5 MeV with 50.3% FWHM energy spread. These results were verified using 2D particle-in-cell simulations, and the simulations confirmed that after the laser pump was depleted, the acceleration mode changed from laser-driven wakefield acceleration to beam-driven wakefield acceleration, and thereafter, the beam-driven wakefield acceleration dominated the electron acceleration and enhanced the energy of the second e beam. Moreover, the second e beam could achieve a narrow energy spread because the energy chirp compensation further compressed its energy spread in the beam-driven wakefield acceleration stage. As a contributor, experimental platforms for a compact radiation based on self-amplified spontaneous emission and coherent undulator radiation have been built. The parameters of the transport line were modulated precisely to compress the e-beams’ size, and then the e beams were seeded into the undulator. Radiation signal with wavelength of 20 nm and harmonic signal with wavelength of 400 nm were detected successfully by gratin spectrometer in the experiments. We propose a method to adjust the laser path with off-axis parabolic. In order to ensure the beam quality after laser focusing (without changing the laser focusing characteristics after reflected by off-axis parabolic mirror and without damaging the beam quality), according to the properties of similar triangles and through formula calculation, a method of the laser beam path adjustment to the target position is proposed.2020atalunwen22122715566688laser-driven wakefield accelerators; electron acceleration;energy chirp control; two-color electron beams;all-optical Compton scattering;dual-color gamma-rays; electron beam-driven wakefield accelerationStudy on electron-beam generation from the laser-driven wakefield and the relevant Compton Scattering激光尾场加速电子束及康普顿散射研究粒子加速器产生的高能粒子束及其后续产生的辐射在生物学、医学、核物理学等方面都有着广泛的应用。传统的射频加速器由于材料的限制,其加速梯度只能达到50-100 MV/m,而目前等离子体加速器因等离子体中电荷分离产生的超强的电场的加速梯度可达100 GV/m,比传统加速器的加速梯度高三个量级,大大地缩小了加速器的占地面积,使加速器台式化。根据驱动源的不同,等离子体加速器可以分为激光驱动和粒子束驱动的等离子体加速器。经过了几十年的发展,目前等离子体加速器已经能够在厘米量级范围内产生GeV量级的高能电子束,电子束的能散可压缩至<1%,电子束亮度高达1015A/m2/0.1%量级。而利用等离子加速器产生的电子在新型的高能高亮度射线源方面也取得了重大进步,目前已经可以产生光子能量在MeV量级,亮度高达1023 photon s-1 mm-2 mrad-2 0.1%BW的射线。这在生物医疗成像,材料科学,基础科学研究等方面都起着不可或缺的作用。 本论文针对超强超短激光驱动尾波场加速器中高品质电子束的产生和新型的康普顿散射源进行了实验和理论模拟研究,在实验中通过优化激光参数、等离子体密度以及等离子长度等条件获得了高品质电子束,并利用自同步康普顿散射方案获得了双色γ射线,在理论上对其进行了探讨并利用模拟进行了深入分析。具体的工作和取得的结果如下: 1. 参与搭建了百TW激光驱动级联尾波场电子加速实验研究平台,并在级联激光尾场中通过能量啁啾控制产生高品质电子束。在实验中通过构建含有密度隆起的特殊结构的等离子体密度分布,获得了可调谐的峰值能量在200-600 MeV,能散为0.4%-1.2%,电量为10-80 pC,~0.2mrad rms发散角,电子六维相空间亮度达6.5×1015A/m2/0.1%的高品质电子束。 2. 在百TW激光驱动级联尾波场电子加速实验平台基础上参与搭建了全光自同步康普顿散射源的实验系统。通过优化激光参数与等离子体密度等条件,在级联激光尾波场中产生了峰值能量在~300 MeV,~210 MeV的双束电子束,然后采用全光自同步康普顿散射方案获得了峰值能量在(1.07±0.12) MeV,(0.59±0.08) MeV的双色γ射线辐射。通过模拟发现两团电子束分别是通过自注入和密度梯度注入的方式联合注入空泡并加速。最后对康普顿散射的γ射线能谱特性进行了理论和模拟的分析研究,理论分析和模拟结果与实验都相吻合。 3. 在百TW激光驱动级联尾波场电子加速实验平台上,通过优化激光条件,等离子体密度,调节等离子体长度,观测了激光驱动和电子束驱动的混合型尾波场加速过程,发现电子束能量得到增强并压缩了电子束能散。通过调节等离子体长度在实验中获得了不同能量的双束电子束,并且当等离子体长度大于泵浦损耗长度时,其中一束电子束仍被加速至640.7 MeV,且其FWHM能散被压缩至1.1%,而另一束电子慢慢失去能量至230.5 MeV,FWHM能散约50.3%。模拟验证了这一混合型过程的存在,并表明当激光泵浦损耗后,激光驱动尾场加速渐渐弱化,慢慢地转变成电子束驱动的尾波场加速,并且在后期的加速过程中电子束驱动尾波场占主导。另外模拟还表明混合型的尾波场加速不仅能提高电子的能量,而且还能在电子束驱动尾波场阶段使能量啁啾再次反转,通过啁啾补偿窄化电子束的能散。 4. 参与搭建了基于激光尾场加速的紧凑型自由电子激光辐射实验装置及相干谐波装置,利用四级铁将经历长距离传输的电子压缩到很小的尺寸,然后注入到波荡器中,最后利用光栅光谱仪在实验上成功探测到了20 nm的辐射信号及400 nm的二次谐波信号。 5. 提出了一种含离轴抛面镜的激光光路调节方法。为保证激光聚焦后的光束质量,在光路调节中,利用公式计算,根据相似三角形的性质将激光光路调节至目标位置,不改变离轴抛面镜对激光的聚集特性,不破坏光束质量。激光尾场加速器;电子加速;能量啁啾调制;双束电子束;康普顿散射;双色γ射线;电子束驱动尾波场加速中国科学院上海光学精密机械研究所吴颖光学博士
中文题目: 激光尾场加速电子束及康普顿散射研究
外文题目: Study on electron-beam generation from the laser-driven wakefield and the relevant Compton Scattering
作者: 吴颖
导师姓名: 徐至展院士 刘建胜研究员
学位授予机构: 中国科学院上海光学精密机械研究所
答辩时间: 20191126
中文关键词:
激光尾场加速器;电子加速;能量啁啾调制;双束电子束;康普顿散射;双色γ射线;电子束驱动尾波场加速
英文关键词:
laser-driven wakefield accelerators; electron acceleration;energy chirp control; two-color electron beams;all-optical Compton scattering;dual-color gamma-rays; electron beam-driven wakefield acceleration
中文摘要:
英文摘要:
文献类型:学位论文
学位级别: 博士
正文语种: chi
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