5th generation light sources based on underdense photocathode plasma wakefield acceleration

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The central importance of high-brightness, monochromatic, extremely short radiation pulses (with fs-duration) generated by a free-electron laser, which gives an in-depth insight into the structure of matter makes the development of free- electron laser (FEL) immensely attractive. Science, information technology, industry and medical benefit from such devices like FEL and moved forward in the past the respective discipline in their work. The above-mentioned radiation sources need high quality electron-beams with energy in the range of few hundred MeV up to tens of GeV, uncorrelated energy spread at the level of 0.1%, low emittance (emittance < 0.1mm - mrad) and high current (kA range). Currently the accelerating gradients in superconducting radiofrequency (SRF) cavities are in order of 100MV/m, meaning that an electron beam would require one meters of such SRF cavities to reach 100 MeV beam energy. Therefore, XFEL facility based on SRF technique becomes extremely bulky and expensive. Towards 5th generation light sources, future accelerators will require novel techniques for more compact designs at moderate costs. Much higher accelerating gradients can be realized by plasmas cavities. The acceleration gradients in thus plasmas cavities can be up to 100GV/m or more. Injecting electrons and trapping them in the plasmas cavities enable the potential to accelerate electrons to high energy in cm scale. This reduces significantly in size and cost, which may leads to a university laboratory scale FEL-facility. Injecting electrons into this plasmas cavity is a significant challenge in the PWFA community. One proposed, promising method is the plasma underdense photocathode (also called the "Trojan Horse") technique for directly injecting electrons in to the blowout due to a moderately intense laser-pulse. This method can potentially produce high quality electron beams with emittances down to nm level. With the "Trojan Horse"-technique generated electrons may be suitable for devices such as university-scale compact FEL and enlarged worldwide the access to XFEL facilities. In order to meet the requirement on electron beams for FEL the quality plasma accelerator based electron beams need to be improved further, i.e mainly in term of energy spread. In addition, a not negligible aspect of a 5th generation light sources is extraction and transport of electron beams generated in plasma accelerator to the aimed application. In particular potential transport optics has to avoid electron beam degradation.