ABSTRACT
The interaction of intense ultra-short laser pulse with plasma provides the basis for developing new technologies such as ultra-compact wakefield accelerators (Tajima and Dawson 1979), compact light sources (Jaroszynski et al. 2002, 2006) and high power laser amplifiers (Shvets et al 1998). In this lecture we will explore how laser driven plasma waves can be harnessed to accelerate particles and produce useful electromagnetic radiation for various applications. As we have seen in this series of lectures, lasers can be used to drive fission and fusion reactions, the latter of which has potential for energy production. However, lasers are also creating new opportunities for studying new phenomena by realising astrophysical-like conditions in the laboratory (Bingham 2005), creating particles from vacuum and studying nonlinear optics of plasma (Joshi 1990). Plasma has long been recognised as providing acceleration gradients that are three orders of magnitude larger than conventional radio frequency (RF) accelerators that are limited by electrical breakdown of the accelerating cavity structures (Tajima and Dawson 1979). Laser and electron driven wakefield acceleration is creating a revolution in accelerator technology by miniaturising the accelerator module. Researchers have demonstrated gradients exceeding 100 GV/m in plasma using intense laser pulses (Modena et al. 1995, Coverdale et al. 1995, Nakajima et al. 1995). Low density plasma in the range of np = 1017 – 1019 cm−3 can potentially accelerate to GeV energies in a few millimetres. Initially, electron beams were produced with a 100 % Maxwellian energy spread due to plasma wavebreaking (Malka et al. 2002), which limited their usefulness and was seen as a major impediment to controllable acceleration. In 2004 several groups (Mangles et al. 2004, Geddes et al. 2004, Faure et al. 2004) accelerated relatively high charge (20 - 500 pC) monoenergetic electron bunches to more than 100 MeV in several millimetres. These experiments demonstrated gradients in excess of 100 GV/m and effectively put laser-driven wakefield accelerators on the map. A very surprising aspect of these observations was that they did not require a separate injector because electrons were injected into the plasma wake from the background plasma and that the electron beams were produced with a relatively small energy spread, δγ0/γ0 ≈ 1 - 3%, where γ0 = (1−β2)−1/2 is the Lorentz factor and β = v/c
(c and v are the respective velocities of light and the electron bunch in vacuum). Simulations by Martins et al. (2005) show that injection is rapidly shut off by beam loading (Trines et al. 2001), which results in extremely short electron bunches (< 10 fs) with a small energy spread (Pukhov and Meyer-ter Vehn 2002).
