Theory of electron acceleration and application in tailored plasmas

Broken plasma wake fields in homogeneous plasmas provide a feasible path for high gradient particle acceleration. Especially efficient are the so called bubble regime of laser-plasma wake fields [1] and the blow out regime of particle wake field acceleration. For the laser driven case, the pulse is shorter than the plasma wavelength and fits perfectly into the first half of the plasma period. The laser intensity is thought to be high enough that the created wake field breaks after its first oscillation. In this regime, the wake field - or bubble - takes the form of a distorted spherical cavity from which all electrons are banished. The bubble moves with nearly the speed of light through the plasma and generates quasimonoenergetic electron bunches. All former discussions about tailored plasmas in the context of electron acceleration target the guiding of relativistic laser pulses and their diffraction. At present, plasma channels are used to gain additional control over the plasma wake field. In a recent work Pukhov et al. [4] derived new scaling laws for deep plasma channels in which the density drops to zero on axis. Here the channel is used to adjust the depletion length to the dephasing length and thus to enhance the energy conversion ratio. In this context the key role of the channel is to introduce new degrees of freedom that help adjust measurable quantities as the energy conversion, the bunch energy spread, and the trapping ration. Another phenomenon is that in a vacuum channel the focusing force is removed while a reduction of the plasma density - i.e. in a channel - leads to a decreasing of the bubble length and a simultaneous steepening of its rear and front side. References [1] A. Pukhov, J. Meyer-ter-Vehn, Applied Physics B 74, 355 (2002) [2] O. Jansen, T. Tückmantel, and A. Pukhov, Eur. Phys. J. Special Topics 223, 1017–1030 (2014) [3] J. Thomas, A. Pukhov, and I.Y. Kostyukov, Laser and Particle Beams 32(02), 277-284 (2014) [4] A. Pukhov, O. Jansen, T. Tueckmantel, J. Thomas, and I.Y. Kostyukov, PRL 113, 245003 (2014) [5] S. Hillenbrand, R. Assmann, A.S. Müller, O. Jansen, V. Judin, and A. Pukhov, NIM A 740 (2014)