X波段常温高梯度加速结构可以显著减小部分高能直线对撞机、自由电子激光、小型光源等加速器装置的尺寸，因此具备较大的研究应用价值。但加速梯度的提升受射频击穿问题限制。减小输入功率的脉冲宽度是一种提升加速梯度的有效方法。针对X波段单腔加速结构的短脉冲实验也证实了这一点，其工作脉宽可以在十纳秒量级。然而对于常规X波段多腔高梯度加速结构，其填充时间通常需要百纳秒甚至更高，难以进一步缩短脉宽来提高梯度。 限制常规多腔结构填充时间的主要因素是腔间的功率传输速度，行波与驻波结构均需要较长的功率耦合时间。而平行馈入加速结构的输入功率由腔外传输后并联式地独立馈入各腔，省去了腔间传输时间，因此支持工作在短脉冲高梯度模式。但目前国内外尚未针对平行馈入加速结构开展短脉冲工作的研究。本论文针对短脉冲工作模式下的X波段高梯度平行馈入加速结构进行了理论分析、设计模拟和实验研究。 论文首先分析了结构的等效电路模型和微波网络模型，并得出了当结构相邻馈入口微波相位相差0或pi时，各加速腔等幅同步填充的结论。在满足该相位差的条件下，多腔平行馈入加速结构从微波网络上可等效为一个驻波单腔，并得出整体参数和单腔参数的函数关系。基于理论模型的瞬态分析，确认了各腔在瞬态下等幅填充，并给出了结构最优填充时间，使其可以用于具体平行馈入加速结构的设计优化。 基于理论分析，论文设计了通过褶皱慢波传输的10腔X波段平行馈入加速结构。结构工作在pi模，采用双波导交替平行馈入方案。通过时域瞬态分析，模拟计算了结构在短脉冲下的同步填充过程和对应加速梯度，初步验证了平行馈入加速结构短脉冲高梯度模式的可行性。另外，针对慢波平行馈入加速结构的局限性，论文也设计了基于光滑波导和功分器的小孔径平行馈入加速结构。 论文开展了慢波平行馈入加速结构的研制与实验研究。结合研制的褶皱型脉冲压缩器，开展了结构的高功率测试。作为首个工作在十纳秒量级的X波段多腔短脉冲高梯度结构，结构在47 ns的工作脉宽下达到了120 MV/m的加速梯度，为将来短脉冲高梯度平行馈入加速结构的发展打下了基础。
X-band high gradient normal conducting accelerating structures were being studied for its potential to provide a shorter accelerator design for some linear accelerator projects such as linear collider, free electron laser and other small light sources. Radio frequency (RF) breakdown is one of the main obstacles for the structure to reach the high accelerating gradient. Shortening the pulse length of input power is a possible approach to raise the accelerating gradient limit of normal conducting structures, which has been proved by X-band single-cell structures operating at a short pulse length of tens of nanoseconds. However, conventional X-band multi-cell high-gradient accelerating structures usually require a filling time of hundreds of nanoseconds, and shortening the pulse length seems impractical. The transmission speed through intercavity coupling is the main factor affecting the filling time of a conventional multi-cell structure. Both travelling-wave structures and standing-wave structures have a relatively long time for the power coupling process. For parallel-coupled structures, the input power is transmitted outside the cells, and all cells were fed individually and simultaneously such the time spending on the power transmitting from cell to cell could be avoided. A multi-cell parallel-coupled structure should be able to work at short pulses and achieve a high accelerating gradient. However, such a scheme haven't been considered before. In this thesis, X-band parallel-coupled high-gradient strutures for short input power pulses have been researched, including theoretical analysis, design and experimental demonstration.A equivalent circuit model and a microwave network model are firstly analysed. If two neighboring tap-off ports have a phase advance of 0 or pi, equal power division for all identical cells can be ensured. Such a parallel-coupled structure can be regareded as a standing-wave single-cell structure from the view of the microwave network, and the equivalent RF parameter of the whole structure is derived. By calculating the analytical power-filling process, all cells are fed simultaneously and equally, and a filling time is optimized for designing. Based on the theoretical analysis, an X-band parallel-coupled struture is designed, consisting of two corrugated waveguides, ten cells and their linking components. The structure is operated at pi mode, and the cells are fed by two parallel corrugated waveguides in alternate. By implementing real-time electromagnetic field simulation, the structure's filling process is animated and its accelerating gradient is calcualted with short input pulses. It is feasible to operate X-band parallel-coupled high-gradient strutures for short input power pulses. Besides, to modify the potential limitations caused by the corrugated structure and the iris aperture, a small-iris parallel-coupled structure based on smooth waveguides and power dividers is preliminarily designed.The designed parallel-coupled structure is fabricated and high power tested, and a corrugated microwave pulse compressor is developed to provide sufficient peak power. A gradient of 120 MV/m is achieved with a 47-ns input pulse. The structure is the first X-band multi-cell structure operating at a shorter pulse length of tens of nanoseconds, which lays the foundation for future high-gradient parallel-coupled structures.
