High Intensity Laser Plasma Interactions, Ultrafast X-ray sources and Advanced Ignition Laser Fusion Energy

高强度飞秒激光脉冲在聚焦到相对论强度时（在聚焦激光辐射场中自由电子的振荡速度接近光速时），有望在产生先进的x射线、粒子和放射性同位素源方面取得许多令人兴奋的发展。目前正在研究两种不同的方法，即薄片靶和气体靶，用于产生极电子伏能量的电子、质子和离子，而这两种方法又可用于产生超短的x射线爆发和产生放射性同位素。所有这些过程都需要了解在这种强非线性状态下的高强度激光等离子体相互作用。此外，了解和优化这些过程的产生机制对于快速点燃激光聚变能的应用具有重要意义，其中MeV能量的电子或质子可以作为点火火花点燃压缩燃料颗粒边缘的聚变反应，从而将潜在激光聚变反应堆的超激光能量需求从多兆焦耳降低到亚兆焦耳。这将大大降低未来激光聚变反应堆的成本和工程开发时间。目前的研究计划将继续进行中高能激光等离子体相互作用物理的一些领域的探索研究，包括：1)利用0.1 - 1 PW激光脉冲对电子进行高达GeV能量的尾流场加速，2)激光尾流场加速电子产生的keV x射线betatron辐射及其在等离子体飞秒探测中的应用，3)基于波动器的飞秒x射线和伽马射线源的开发，高z目标的高能轫致共振和从MeV到GeV激光产生的电子束的逆康普顿散射，4) MeV金属箔和气体靶的质子生成以及医用放射性同位素的产生；5)皮秒时间分辨的等离子体相互作用射线成像探测，利用激光产生的电子和质子射流；6)基于二极管泵浦低温冷却Yb:YAG和Yb:CaF2陶瓷晶体的新型高效激光驱动系统的开发，这可能是未来高效率和重复率聚变能驱动的基石。尾流场产生的电子将被优化，以产生多gev、准单色、低发散电子束，应用于电子加速器、同步加速器和轫致辐射产生的x射线到伽马射线。这将使加拿大站在高能电子产生和加速技术的前沿，这些技术最终可用于将TeV粒子加速器从数十公里扩展到数百米，并有可能建立小规模的软x射线自由电子激光器。按需生产多兆电子伏质子和放射性同位素可能导致紧凑的质子癌症治疗源和交钥匙放射性同位素供应系统位于大型医院，而不是国家加速器或反应堆设施。快速点火技术和较新的激波点火技术，以及20%效率的陶瓷基激光系统的发展，可能是在20年而不是过去40年的时间尺度上加速核聚变反应堆发展的关键技术。清洁、普及、环保、无温室气体的核聚变能源是未来人类大规模能源需求的最终解决方案，我们应该积极探索各种方案，使核聚变能源尽快投入使用。

High intensity femtosecond laser pulses when focused to relativistic intensities (I > 1018 W/cm2 where the oscillatory velocity of free electrons in the focused laser radiation field approaches the speed of light) hold the promise of many exciting developments in the generation of advanced x-ray, particle and radioisotope sources. Two distinct approaches, thin foil targets and gas targets, for the generation of MeV energy electrons, protons and ions, are being pursued which in turn can be used for the generation of ultrashort bursts of x-rays and the generation of radioisotopes. All of these processes require an understanding of high intensity laser-plasma interactions in this strongly nonlinear regime. In addition, understanding and optimizing the generation mechanisms of these processes are important for the application to fast ignition laser fusion energy where the MeV energy electrons or protons can be used as an ignition spark to ignite the fusion reactions at the edge of a compressed fuel pellet, reducing the over laser energy requirements from multi-Megajoules to sub Megajoule for a potential laser fusion reactor. This could significantly reduce the cost and engineering development time for future laser fusion reactors. The present research proposal will continue ongoing research on the exploration of a number of areas of intermediate to high energy laser-plasma interaction physics including: 1) Wakefield acceleration of electrons up to GeV energies using 0.1 – 1 PW laser pulses, 2) keV x-ray betatron radiation generation from laser wakefield accelerated electrons and applications in femtosecond probing of plasmas, 3) development of femtosecond x-ray and gamma ray sources based on the use of undulators, high energy Bremssthralung from high-Z targets and inverse Compton scattering from MeV to GeV laser produced electron bunches, 4) MeV Proton generation from foil and gas targets and the production of radioisotopes for medical applications, 5) picosecond time resolved radiographic probing of plasma interaction using laser produced electron and proton jets, 6) Optimization of MeV electron and proton generation and transport studies for fast ignition applications and 7) Development of a new class of high efficiency laser driver systems based on diode pumped cryogenically cooled Yb:YAG and Yb:CaF2 ceramic crystals which could be the building block for future high efficiency and repetition rate fusion energy drivers. The wakefield generation of electrons will be optimized to producing mulit-GeV, quasi-monochromatic, low divergence electron bunches with applications in Betatron, synchrotron and Bremsstrahlung production of x-rays to gamma rays. This will put Canada on the forefront of high energy electron generation and acceleration using techniques which eventually could be used to scale TeV particle accelerators from tens of kilometers to hundreds of metres and potentially build small scale soft x-ray free electron lasers. The generation of multi-MeV protons and radioisotopes on demand could lead to compact proton cancer treatment sources and turnkey radioisotope supply systems located at major hospitals instead of at national accelerator or reactor facilities. The fast ignition technique and newer shock ignition technique together with the development of 20% efficiency ceramic based laser systems could be a critical technology for accelerating the development of fusion reactors on a 20 year time scale rather than the 40 year timescale of the past. Clean, universally available, environmentally safe, green-house-gas-free fusion energy is the ultimate solution for mankind’s large scale energy needs in the future and we should be vigorously exploring all options to bring fusion energy on line as soon as possible.