电磁波应用的发展推动了人类生产生活方式的变革，每一个新波段的发掘开拓都伴随着新的技术革命。太赫兹（THz）作为宏观电子学到微观光子学的过渡区域，在很多领域具有显著的应用优势，然而目前高功率可调谐的THz源依旧较为匮乏。基于加速器产生的相对论电子束脉冲串有潜力产生高功率、可调谐的THz辐射，因而受到国内外的广泛关注。然而，现有方法所产生的脉冲串通常电荷量和聚束因子较低，限制了最终的THz能量提升。本论文针对此瓶颈开展研究，通过系统的理论分析和模拟计算，提出了基于等离子体尾场调制产生脉冲串的方案。一方面，这种被动式调制方式较为灵活，且不受射频击穿的限制，因而可承载更高电荷量；另一方面，等离子体的特殊尾场结构可在保持电子束束流品质的同时，引入锯齿波状的能量调制，进而可在THz频段获得非常高的聚束因子。两者相结合可大幅度提高THz辐射能量。此外，通过改变等离子体的密度，可实现窄带宽THz频率在较大范围内可调。论文首先提出利用非线性等离子体尾场对单束团进行能量调制，结合磁压缩技术，获得高聚束因子电子束脉冲串的方案。该方案在 1 THz频率处可产生聚束因子高达0.8的高电荷量（约2nC）电子束脉冲串，通过波荡器可产生10 mJ量级的窄带宽THz辐射。在此基础上，论文进一步提出基于双束团的调控方案，可放松对电子束电荷量和横向尺寸的要求，且聚束因子可进一步提升至0.9。此方案在使用较小电荷量的情况下依旧可获得高功率窄带宽THz辐射。论文接着提出了利用中空等离子体通道中的线性尾场，对低流强电子束进行能量调制的方案，并对影响方案的因素展开了深入分析。在此基础上，进一步提出使用分段中空等离子体通道系统的方法，可得到近似理想的锯齿波状能量调制，因而可进一步聚束因子。针对上述中空等离子体通道能量调制方案，论文基于清华大学加速器实验室的汤姆逊散射 X射线平台进行全过程模拟，从束流优化到中空等离子体的产生进行了系统的实验设计。结合实际束流，对可能影响实验的物理参数进行了深入分析，为后续开展验证实验奠定了基础。

The development of electromagnetic wave application has witnessed the change of human production and life style. Terahertz (THz), as a transition region from macro electronics to micro photonics, has significant advantages as applications in many fields. However, high power tunable THz sources are still in high demand. The relativistic electron bunch trains generated by accelerators have the potential to produce high-power and tunable THz radiation, which has attracted extensive attention worldwide. However, the bunch trains generated by the existing methods usually own low charge and low bunching factor, which limits the THz energy of the final radiation. Focusing on this bottleneck, through systematical theoretical analysis and simulation calculation, we propose the scheme of generating pulse train based on plasma wakefield modulation, which owns unique advantages. On one hand, as a passive modulation, it is relatively flexible, and avoids the limitation of radio frequency breakdown of traditional modulation structures, so it can sustain higher charge. On the other hand, the nonlinear wakefields in uniform plasmas and the linear wakefields in hollow channel plasmas help forming a sawtooth-like energy modulation while maintaining the beam quality, so that a very high bunching factor at THz frequency can be obtained. These two advantages combined can greatly increase the THz radiation energy. In addition, by changing the density of the plasma, the generated narrow-bandwidth THz frequency is tunable and can cover a wide spectral range. A novel method based on single beam modulation using the nonlinear wakefields in the uniform plasmas is first proposed. Combined with a chicane, an electron bunch train with high bunching factor can be obtained. This scheme can generate a high charge electron bunch train (~2 nC) with a bunching factor up to 0.8 at 1 THz frequency, so that a 10 mJ level THz radiation can be emitted in the undulator. On this basis, we further propose the scheme of modulating double-beam which loosens the requirements on the beam charge and transverse bunch size, where the bunching factor can be further improved to 0.9. The scheme can still obtain high power narrow bandwidth THz radiation with a reduced beam charge.In order to improve the bunching factor of low-current electron beams, another scheme is proposed to modulate the beam energy distribution by using the linear wake field in the hollow plasma channel. Based on this, a method of using a segmented hollow plasma channel system is further proposed to obtain an ideal sawtooth-like modulation waveform, thereby improving the bunching factor and the subsequent THz radiation energy.In terms of the experimental design, based on Tsinghua Thomson Scattering X-Ray Source (TTX) platform of the Accelerator Laboratory, start-to-end simulations are carried out, from beamline optimization to the generation of hollow channel plasma. Combined with the practical beam distribution, an in-depth analysis of the physical parameters that may affect the experiment is conducted, laying a foundation for the subsequent experiments.