Controlled High-Repetition Plasma Based Electron Accelerators

该基金建议发展基于激光驱动等离子体的加速器，既从基本观点出发，如证明能量缩放和理解注入机制，也从可重复性和产生超紧凑加速器等领域提出等离子体加速器的技术发展。首先，已经在最先进的100太瓦规模激光系统上的开创性工作将得到扩展。对相互作用的完整描述有望阐明导致单能电子束产生的复杂相互作用。激光参数的持续改进有望将该方案中可获得的能量范围扩展到GeV级以上（我们已经非常接近）。我们还将研究低密度等离子体（即不处于高能单能光束所需的气泡匹配状态）中高强度（>0 ^20 Wcm^-2）单束的相互作用，通过对相同的> 100 TW激光器使用更紧密的聚焦（~ f/3，而不是~f/20的单能光束产生）。虽然这限制了可以产生的最大能量，但这种相互作用有望产生极高的激光能量转化为相对论性电子的效率，以及极高的电流密度光束。我们还建议将我们的研究扩展到更先进的方案中，用于将电子脱相并捕获到尾流场加速器中。将研究许多不同的方法，以获得可重复性和低能量扩散（这对许多应用至关重要）。这包括密度调制和光注入机制。由于能够分离注入和加速阶段，大大降低了对驱动激光脉冲的要求，因此可以在较低的等离子体密度下驱动尾流场，从而有可能达到更高的能量。这些实验将继续利用RAL的Astra Gemini激光系统（优化后应提供30秒的双15j激光脉冲），密歇根大学的Hercules激光器（提供超短脉冲的PW功率），以及隆德激光中心，提供最高光束质量的1j30秒激光水平。这项资助的最终主要目标将是在中等脉冲能量下开发一种超短脉冲持续时间（< 10秒，即~几个激光周期）的激光系统。这将使紧凑型加速器的高重复率操作得以开发，同时也为研究紧凑型等离子体加速器提供了一种经济实惠的专用系统。用这种系统产生的窄能量扩散电子束的演示将具有重要的技术意义。

The grant proposes development of laser-driven plasma based accelerators both from the fundamental viewpoint, such as demonstrating energy scaling and understanding injection mechanisms, but also proposes technological development of plasma accelerators in areas such as reproducibility and generating ultracompact accelerators. First the already ground-breaking work on state-of-the-art 100 TW scale laser systems will be extended. A complete characterisation of the interaction promises to elucidate the complex set of interactions that lead to mononenergetic electron beam production in this regime. Continuing improvements in the laser parameters promises to extend the energy range obtainable in this scheme to beyond the GeV level, (to which we are already tantalisingly close). We will also study the interaction of the single beam at high intensity (>10^20 Wcm^-2) in underdense plasma (i.e. not in the bubble matched regime as required for high energy mononenergetic beams), by using tighter focusing (~ f/3 as opposed to ~f/20 for monoenergetic beam production) on the same > 100 TW lasers. Though this limits the maximum energy that can be produced, such interactions promise to produce extremely high efficiency of conversion of laser energy into relativistic electrons, and extremely high current density beams. We also propose to extend our studies to more advanced schemes for dephasing and trapping electrons into a wakefield accelerator. A number of different methods will be investigated for reproducibility and low energy spread (which is of utmost importance for many applications). These include density modulation, and optical injection mechanisms. The ability to separate injection and acceleration phase, dramatically reduces the requirements on the driving laser pulse, hence allowing the wakefield to be driven at lower plasma densities, and thus potentially to much higher energy. These experiments will continue to make use of the Astra Gemini laser system at RAL, (which on optimisation should offer twin 15 J laser pulses at 30 fs), the Hercules laser at the Univesity of Michigan (which offers PW powers in an ultrashort pulse), as well as the Lund Laser Centre, which offers the highest beam quality laser at the 1J 30 fs level. The final major aim of this grant will be development towards producing a laser system of ultrashort pulse duration (< 10 fs i.e. ~ few laser cycles) at moderate pulse energy. This will allow high repetition rate operation of compact accelerators to be developed, whilst also opening the possibility of producing an affordable dedicated system for studying compact plasma accelerators. The demonstration of narrow energy spread beams of electrons produced with such a system would have important technological implications.