There is a strong demand for accelerating structures able to achieve higher gradients and more compact dimensions for the next generation of linear accelerators for research, industrial and medical applications.

Notably innovative technologies will permit compact and affordable advanced accelerators as the linear collider and X-ray free-electron lasers (XFELs) with accelerating gradients over twice the value achieved with current technologies. In particular XFELs are able to produce coherent X-ray pulses with peak brightness 10 orders of magnitude greater than preceding approaches, which has revolutionized numerous research fields through imaging of the nanoscopic world at the time and length scale of atom-based systems, that is of femtosecond and Angstrom. There is a strong interest for combining these two fields, to form a proper tool with the goal of producing a very compact XFEL in order to investigate multi-disciplinary topics in chemistry, biology, materials science, medicine and physics.

In the framework of the Ultra-Compact XFEL project under study at the University of California, Los Angeles, a high gradient radio-frequency accelerating structure for the longitudinal phase-space linearization with an integrated voltage of at least 15 MV working on 6th harmonic of the main Linac frequency is required. We here present the electromagnetic design of a cryogenic normal-conducting 8 cm long Ka-band standing-wave linearizer working on $\pi$ mode with a target accelerating gradient beyond 100 MV/m. The studies have been performed analytically and numerically to investigate the beam dynamics and electromagnetic issues.

对于用于研究、工业和医疗应用的下一代直线加速器，对能够实现更高梯度和更紧凑尺寸的加速结构有着强烈的需求。

值得注意的是，创新技术将允许使用紧凑且价格合理的高级加速器，如线性对撞机和 X 射线自由电子激光器 (XFEL)，其加速梯度是当前技术实现的价值的两倍以上。特别是 XFEL 能够产生峰值亮度比以前的方法高 10 个数量级的相干 X 射线脉冲，通过在基于原子的系统的时间和长度尺度上对纳米世界进行成像，这已经彻底改变了许多研究领域，即飞秒和埃。将这两个领域结合起来，形成一个合适的工具，以产生一个非常紧凑的 XFEL 为目标，以研究化学、生物学、材料科学、医学和物理学的多学科主题，这是一种强烈的兴趣。

在加州大学洛杉矶分校正在研究的超紧凑型 XFEL 项目的框架内，一种用于纵向相空间线性化的高梯度射频加速结构，积分电压至少为 15 MV，工作在 6 次谐波上。需要主直线加速器频率。我们在这里展示了低温正常导电 8 厘米长 Ka 波段驻波线性化器的电磁设计$\pi$目标加速梯度超过 100 MV/m 的模式。这些研究已经进行了分析和数值研究，以研究光束动力学和电磁问题。