Terahertz driven dielectric linacs

在粒子物理中，未来的线性对撞机，如CLIC或ILC，需要超短、亚皮秒的束团来获得粒子物理科学探索所需的光度。在基于加速器的X射线源中，低于10fs的束流非常受欢迎，为材料科学打开了新的窗口。要超越这些巨大的加速器，将需要更高的梯度结构来缩小未来高能对撞机的尺寸和成本。目前的金属微波结构被电击穿限制在100 mV/m左右。在获得每一个更短的粒子束的过程中，束之间以及与设施基础设施(射频、驱动激光器、设施时钟、诊断系统)的同步对设施优化至关重要，但仍存在未解决的问题。这种超短粒子束的产生和同步都给超短束的测量带来了后续的问题；目前只有两种技术可以满足未来线性对撞机和加速器光源的要求；基于激光的“电光”探测和横向偏转腔。然而，EO探测目前还不能解决少飞秒的情况，而梯度要求使得RF(横向偏转腔)TDC不能在高能粒子物理机上进行亚ps测量。高梯度、高频率(&gt；300 GHz)的TDC将使同样的技术应用于超短、高能对撞机。在这里，我们建议开发一种蓝天方法来解决这些问题，使用激光产生的太赫兹辐射耦合到介质线波导来加速和操纵这些光束。在将GHz-RF技术扩展到皮秒/太赫兹区域时，我们获得了操纵和检测的时间分辨率；我们获得了在亚皮秒时间尺度上操纵所需的时间梯度的数量级；我们通过仅在与要加速的光束匹配的时间窗口(而不是与微秒腔填充时间匹配)上生成加速场和偏转场，获得了能量效率的数量级。斯坦福大学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。所涉及的时间较短，并且没有金属-真空转变，因此可以防止结构中的击穿达到衬里或栅极的介电强度。然而，与大量对光加速方法的研究不同的是，太赫兹方法允许完全捕获“传统的”皮秒束，而不是与激光加速概念的3F周期相关的高频光学拖尾。通过使用太赫兹，电子束可以占据很小范围的相，产生质量高得多的电子束，与对撞机和自由电子激光等加速器应用的要求一致。迈向这一目标的第一步之一是演示基于激光的相对论电子束加速和偏转方案。我们建议在STFC的测试加速器VELA上进行初步的模拟和实验，以进行下一阶段的概念验证演示。我们的方法融合了电光探测和太赫兹产生(Jamison和Graham的专长领域)和粒子物理空腔设计(Burt的专长)方面的概念。通过使用一个集成的团队，可以同时开发结构和源，以提供一种非常适合加速器开发的技术。虽然其他实验都是用亚相对论粒子进行的，但这将是第一次用太赫兹结构加速完全相对论粒子，也将是第一个工作在太赫兹区域的横向偏转空腔。

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.