Terahertz driven dielectric linacs

在粒子物理学中，未来的线性对撞机，如CLIC或ILC，需要超短的，亚皮秒的束流，以获得粒子物理科学探索所需的亮度。在基于加速器的X射线源中，10 fs以下的束流受到高度追捧，为材料科学打开了新的窗口。超越这些巨大的加速器将需要更高的梯度结构，以缩小未来高能对撞机的尺寸和成本。目前的金属微波结构的电击穿限制在100 MV/m左右。在驱动器中，以获得每一个较短的粒子束，束的同步，彼此和设施基础设施（RF，驱动激光器，设施时钟，诊断系统）是至关重要的设施优化，但仍然存在未解决的问题。这种超短粒子束的产生和同步都提出了用于测量超短束团的后续问题;只有两种技术存在接近未来直线对撞机和加速器光源的要求;基于激光的“电光”检测和横向偏转腔。然而，EO检测是目前无法解决的few-fs制度，而梯度的要求，使RF（横向偏转腔）TDC的不可行的高能粒子物理机器上的亚ps测量。高梯度、高频率（>300 GHz）的TDC将允许相同的技术应用于超短、高能对撞机。在这里，我们提出了一种解决这些问题的蓝天方法，使用激光产生的THz辐射耦合到介质内衬波导中，用于加速和操纵这些光束。在将GHz-RF技术扩展到皮秒/THz范围中时，我们获得了用于操纵和检测的时间分辨率;我们获得了亚皮秒时间尺度上操纵所需的时间梯度的数量级;我们在能源效率上获得了数量级的提升，通过仅在与要加速的射束匹配的时间窗口上产生加速场和偏转场（而不是与微秒腔填充时间相匹配）。斯坦福大学进行的类似的高调研究已经证明，使用波长短得多的激光脉冲，梯度超过250 MV/m。所涉及的短时间尺度和金属真空转变的缺乏防止了结构中的击穿，直到衬里或光栅的介电强度。然而，与光学加速方法的广泛研究相比，THz方法允许完全捕获“传统”皮秒聚束，而不是与<3fs周期的激光加速概念相关的高频光学拖尾。通过使用THz，电子聚束可以占据小范围的相位，从而产生与加速器应用（诸如对撞机和自由电子激光器）的要求一致的高得多的质量聚束。实现这一目标的第一步是演示基于激光的相对论电子束加速和偏转方案。我们建议采取初步的模拟和实验的概念验证演示STFC的测试加速器，VELA的下一阶段。我们的方法是将电光检测和太赫兹产生（贾米森和格雷厄姆的专业知识领域）以及粒子物理腔设计（伯特的专业知识）的概念融合在一起。通过使用一个集成的团队，结构和源代码可以协同开发，以提供一种非常适合加速器开发的技术。虽然其他实验已经用亚相对论粒子进行了，但这将是第一次通过太赫兹结构对完全相对论粒子进行加速，并且将是第一个在太赫兹范围内工作的横向偏转腔。

In particle physics, future linear colliders such as CLIC or ILC require ultra-short, sub-picosecond, bunches to obtain the luminosity necessary for the particle physics science exploration. In accelerator based X-Ray sources, sub 10fs bunches are highly sought after, opening new windows on material science. Going beyond these massive accelerators will require higher gradient structures to shrink the size and cost of future high energy colliders. Current metallic microwave structures are limited by electric breakdown to around 100 MV/m.In the drive to obtain every shorter particle bunches, the synchronization of the bunches, both to each other and to facility infrastructure (RF, drive lasers, facility clocks, diagnostic systems) is crucial for the facility optimization, and yet continues to present unsolved problems. Both generation and synchronization of such ultra-short particle beams presents a subsequent problem for the measurement of the ultra-short bunches; only two technologies exist that approach the requirements of future linear colliders and accelerator light sources; laser based 'electro-optic' detection and transverse deflecting cavities. However, EO detection is not currently able to address the few-fs regime, while the gradient requirements make RF (Transverse deflecting cavity) TDC's infeasible for sub-ps measurements on high energy particle physics machines. A high gradient, high frequency (>300 GHz) TDC would allow the same technique to be applied to ultra-short, high energy colliders.Here we propose to develop a blue-skies approach to these problems, using laser generated THz radiation to be coupled to dielectric lined waveguide for acceleration and manipulation of those beams. In extending the GHz-RF techniques into the picosecond/THz regime we gain in time resolution for manipulation and detection; we gain orders of magnitude in the temporal gradient necessary for manipulation on the sub-picosecond time scale; we gain orders of magnitude in energy efficiency, through only generating the accelerating and deflecting fields over a time window matched to the beams to be accelerated (rather than matched to microsecond cavity filling times). Similar high profile research at Stanford has demonstrated gradients in excess of 250 MV/m using laser pulses at much shorter wavelengths. The short timescales involved and the lack of metallic-vacuum transitions prevents the breakdown in the structure up to the dielectric strength of the lining or grating. However in contrast to a wide body of research into optical acceleration methods, the THz approach allows complete trapping of 'conventional' picosecond bunches rather than the high frequency optical smearing associated with the <3fs periods of laser-acceleration concepts. By using THz the electron bunch can occupy a small range of phases producing a far higher quality bunch consistent with requirements from accelerator applications such as colliders and FELs. One of the first steps towards this goal is the demonstration of laser-based schemes for the acceleration and deflection of relativistic electron beams. We propose to take preliminary simulations and experiments to the next stage of proof-of-concept demonstration on STFC's test accelerator, VELA. Our approach is a melding of concepts in electro-optic detection and THz generation (areas of expertise for Jamison and Graham) and particle physics cavity design (expertise of Burt). By using an integrated team the structure and source can be developed in tandem to provide a technology ideally suited to accelerator development. While other experiments have taken place with sub-relativistic particles this would be the first acceleration of fully relativistic particles by a THz structure and would be the first transverse deflecting cavity operating in the THz regime.