Cockcroft Institute Capital bid 2018

未来HEP粒子加速器的预期尺寸和成本，例如CERN提出的大于40 km长的紧凑型线性对撞机或类似规模的国际线性对撞机，刺激了对更高梯度更紧凑和成本有效的粒子加速方法的需求。经过几十年的发展，目前的微波结构被电场击穿限制在100 MV/m左右的加速度梯度。这种击穿极限随着频率的增加而增加，而达到更高梯度的公认途径是通过在显著更高的频率下开发源和结构。在射频（RF）加速方面取得进一步重大进展所面临的挑战表明，需要突破性的颠覆性技术来实现极高的加速梯度，并显著降低成本和规模。直接，在真空中，粒子加速与激光衍生太赫兹（THz）频率源具有潜在的GV/m的加速梯度，并提供高品质，高度受控的粒子束。太赫兹频率在光学和RF之间的频率和长度尺度上占据中间地带，频率比当前RF加速中使用的频率高2个数量级。在1 THz的300微米波长下，太赫兹驱动加速可以通过mm级结构孔径实现，从而提供更小、更紧凑的加速。虽然直接（光学）激光加速概念也是高梯度加速的候选者，但光学加速的1微米尺度孔径是粒子物理学光度最终所需的高电流高能束的障碍。与基于等离子体的新型加速方法所需的多焦耳低重复率激光相比，直接真空太赫兹加速需要10 mJ脉冲量级的适度激光。太赫兹波驱动的粒子加速是一个相对较新的粒子加速领域，它在光束质量和控制方面优于光学和等离子体加速。在过去的5年里，已经证明了GV/m的场强，沿着低能束的加速和控制。然而，到目前为止，还没有相对论光束的高梯度太赫兹加速的演示。这样的演示是为未来紧凑型高能粒子物理加速器开发这种颠覆性方法的必要下一步。通过这次资本呼吁，我们寻求设备，将太赫兹驱动加速的演示提升到一个新的国际领先水平。Cockcroft研究所建立了一个电介质和THz驱动粒子加速的项目，并开发了THz电介质加速结构的领先方法，以及产生THz电磁脉冲的奇异偏振态。我们寻求一种新的激光系统，该系统将能够以100 Hz或更高的重复率产生高梯度THz场，同时与粒子加速器同步，用于THz-相对论电子束组合实验。该激光器将位于STFC达雷斯伯里试验加速器STFC A附近并与之相连。它将用于国际上第一个THz驱动相对论性光束加速的演示，并将成为Cockcroft研究所新颖加速计划的核心部分。我们将建立激光器的能力，作为英国和国际合作在介电激光器和介电太赫兹加速领域的核心。

The expected size and costs of future HEP particle accelerators, such as CERN's proposed greater than 40 km long Compact Linear Collider or the similarly scaled International Linear Collider, stimulates demand for methods for higher-gradient more compact and cost effective particle acceleration. Current microwave structures, with decades of development, are limited to acceleration gradients of around 100 MV/m by electric-field breakdown. This breakdown limit increases with frequency, and an accepted route to higher gradients is through development of sources and structures at significantly higher frequencies. The challenges in delivering further major advances in radio-frequency (RF) acceleration suggests the need for a breakthrough disruptive technology to deliver extremely high accelerating gradients and significant cost and scale reductions. Direct, in-vacuum, particle acceleration with laser derived terahertz (THz) frequency sources has the potential for GV/m acceleration gradients, and for delivering high quality, highly-controlled particle beams. Terahertz frequencies occupy a middle ground in frequency and length scale between optical and RF, with frequencies 2 orders of magnitude higher than used in current RF acceleration. With wavelengths of 300 micron at 1 THz, terahertz driven acceleration is possible with mm-scale structure apertures, offering tractably smaller and more compact acceleration. While direct (optical)-laser acceleration concepts are also candidate for high-gradient acceleration, the 1-micron scale apertures of optical acceleration are an obstacle to the high-current high-energy beams ultimately required for particle-physics luminosity. In comparison to the many-Joule low-repetition rate lasers required for plasma-based novel acceleration approaches, direct in-vacuum THz acceleration require modest lasers of order of 10mJ pulses. THz driven acceleration is a relative new-comer to the field of novel particle acceleration, and offers benefits to beam quality and control over competing optical and plasma novel acceleration. In the last 5 years of GV/m field strengths have been demonstrated, along with and acceleration and control of low-energy beams. Yet, to date there has been no demonstrations of high-gradient THz acceleration with relativistic beams. Such demonstrations are a necessary next step towards developing this disruptive approach to future compact high-energy particle physics accelerators.Through this capital call, we seek equipment to take the demonstration of terahertz driven acceleration to a new and internationally leading level. The Cockcroft Institute has an established a programme in Dielectric and THz driven particle acceleration, and has developed leading approaches to THz dielectric acceleration structures, and in generating exotic polarisation states of THz electro-magnetic pulses. We seek a new laser system that will be capable of generating high-gradient THz fields at repetition rates of 100 Hz or greater while being synchronised to a particle accelerator for combined THz- relativistic electron beam experiments. The laser will be sited adjacent and linked to STFC Daresbury test accelerator CLARA. It will be utilised in international-first demonstrations of THz driven relativistic beam acceleration, and will form a core part of the Cockcroft Institute Novel Acceleration programme. We will establish the capability of the laser as a centre-piece for UK and international collaboration in the area of dielectric laser and dielectric terahertz acceleration.