【作者】 向导；

【导师】 林郁正；

【作者基本信息】 清华大学 ， 核科学与技术， 2008， 博士

【摘要】 利用高亮度电子束作为驱动的大型科研装置如短波长自由电子激光,汤姆逊散射X光源,国际直线对撞机等的成功建造和运行需要强有力的束流测量手段作为保障,以确保在从电子源到作用点的长距离传输中能够维持电子束品质。这类装置对束流性能的要求以低发射度,短束长和小束斑为特征,而现有技术在精确测量其参数方面仍然面临巨大挑战。本论文正是在这样的背景下确定的,论文围绕高亮度电子束测量开展了广泛深入的理论和实验研究。针对低发射度的测量问题,我们在清华大学光阴极微波电子枪实验平台上开展了一系列先进束流测量方法研究。我们利用螺线管扫描法测量了电子束热发射度;设计并加工了多缝系统用于测量空间电荷占优的电子束发射度;在国际上首次利用螺线管对光阴极枪出口的相空间分布进行了计算机断层重建,同时也在国际上首次实验观测到热发射度相空间的无规则随机分布。针对短束长的测量问题,我们设计并搭建了Martin-Puplett干涉仪,并且利用该干涉仪成功实现了对磁压缩器出口超短电子束纵向分布的无阻拦测量。我们首先利用随机行走模型研究了单个电子辐射谱和整个束团辐射谱的关系,为频域下测量电子束纵向分布提供了理论依据;随后利用虚光子衍射模型对实际情况下的衍射辐射场进行了研究,该工作得到了国际同行的高度认可,被国际同行做为基准用于标定新发展的计算模型;最后我们利用搭建的Martin-Puplett干涉仪实现了对超短电子束纵向分布的无阻拦测量,为基于下一代加速器的大科学工程的建设提供了技术储备。针对小束斑的测量问题,我们研究了光学渡越辐射对电子束成像的分辨率问题,提出了利用反卷积获得微米级电子束束斑的方法;国际上首次提出衍射辐射靶扫描法测量极小电子束尺寸的新方法,该方法得到了国际同行的认可;国际上首次研究了光学衍射辐射对电子束成像的点扩散函数和分辨率问题,我们的理论和国际上同期发表的实验结果较好的吻合,有助于进一步将光学衍射辐射用于高能量高密度电子束的无阻拦测量。更多还原

【Abstract】 Advanced beam diagnostics plays a crucial role in the path to the realization of the short wavelength free electron laser, Thomson scattering based X-ray source, International Llinear Collider, etc. The successful construction and operation of the high-brightness beam driven facility requires the beam quality to be maintained during the long transportation from the electron source to the final target. The high quality accelerator is characterized by the low emittance, short bunch length and small beam size, which also challenges the beam diagnostic methods. Our dissertation is devoted to extensively investigating advanced beam diagnostics both theoretically and experimentally for the above mentioned accelerators.We first performed systematical investigations on low emittance measurement with the photocathode RF gun developed at Accelerator Lab of Tsinghua University. The thermal emittance was measured with solenoid scan method under the condition of very low charge for which the space charge induced emittance growth is negligible. A multislit system was designed and fabricated to measure the emittance of the space charge dominated beam at the gun exit. We also for the first time applied the computerized tomography (CT) technique to reconstruct the phase space details of the beam at the photocathode RF gun exit with a solenoid, which may further enable nonlinear emittance compensation that leads to breakthrough in photoinjector performance. Finally, with the CT technique, we observed the stochastic distribution of phase space dominated by thermal emittance. To the best of our knowledge, this is the first time that the thermal emittance was reconstructed from CT technique and visualized with such fruitful details.We then devoted much efforts to developing a cost-effective, simple and non-interceptive technique to measure electron bunch length with sub-ps temporal resolution. We first used the random walk model to find the theoretical basis for bunch length measurement in frequency domain. Then a virtual photon diffraction model was applied to calculate the single electron diffraction radiation spectrum with finite size target effect and near field effect taken into account. Our model and results were recently verified by other researchers with vector electromagnetic theory. We then proceed to develop a home-made Martin-Puplett interferometer with which the diffraction radiation spectrum of a whole bunch was measured and further used to find the bunch form factor. Finally we reconstructed the longitudinal bunch profile with Kramers-Kronig relation. We also proposed a novel method to measure ultrashort bunch length with diffraction radiation deflector. The method has wide applicability, high temporal resolution and great simplicity.Attention was also paid to measurement of micron size beam profile. We calculated the point spread function of optical transition radiation and optical diffraction radiation in beam imaging. A deconvolution method was proposed to restore micron size beam profile from the blurred image. A new method suitable for small beam size determination with diffraction radiation from rectangular slit by scanning the slit in transverse direction is proposed and analyzed. The theories for imaging of high energy beam with optical diffraction radiation were developed and found to be in reasonable agreement with the recently reported experimental results.更多还原