Cockcroft Institute Capital bid 2018

未来HEP粒子加速器的预期尺寸和成本，如欧洲核子研究中心提议的超过40公里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、更经济的粒子加速方法的需求。目前的微波结构，经过几十年的发展，被电场击穿的加速度梯度限制在100 MV/m左右。击穿极限随频率增加而增加，获得更高梯度的公认途径是在明显更高的频率上开发源和结构。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，需要一种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。使用激光衍生的太赫兹（THz）频率源的直接真空粒子加速具有GV/m加速梯度的潜力，并且可以提供高质量，高度控制的粒子束。太赫兹频率在频率和长度尺度上处于光学和射频之间的中间地带，其频率比当前射频加速中使用的频率高2个数量级。在1太赫兹波长为300微米的情况下，太赫兹驱动的加速度可以采用毫米级的结构孔径，从而提供更小、更紧凑的加速度。虽然直接（光学）激光加速概念也是高梯度加速的候选概念，但光学加速的1微米尺度孔径对粒子物理光度最终所需的高电流高能光束来说是一个障碍。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器相比，直接在真空中进行太赫兹加速需要10mJ脉冲数量级的适度激光器。太赫兹驱动的加速在新型粒子加速领域是一个相对较新的领域，与竞争的光学和等离子体新型加速相比，它在光束质量和控制方面具有优势。在过去的5年里，GV/m场强已经被证明，以及低能光束的加速和控制。然而，到目前为止，还没有证明相对论光束具有高梯度太赫兹加速度。这样的演示是发展这种颠覆性方法的必要下一步，以实现未来紧凑的高能粒子物理加速器。通过这一资本呼吁，我们寻求设备，把太赫兹驱动的加速示范到一个新的国际领先水平。科克罗夫特研究所已经建立了一个介电和太赫兹驱动粒子加速的项目，并开发了太赫兹介电加速结构的领先方法，以及产生太赫兹电磁脉冲的奇异极化状态。我们寻求一种新的激光系统，它将能够以100赫兹或更高的重复率产生高梯度太赫兹场，同时与粒子加速器同步，用于联合太赫兹-相对论电子束实验。该激光器将与STFC达斯伯里测试加速器CLARA相邻并相连。它将用于国际上首次演示太赫兹驱动的相对论束加速，并将成为科克罗夫特研究所新型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的中心部件，在介电激光和介电太赫兹加速领域。

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.