Cockcroft Institute Capital bid 2018

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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.