Faatz, B.; Baboi, N.; Ayvazyan, V.; Balandin, V.; Decking, W.; Duesterer, S.; Eckoldt, H. -J.; Feldhaus, J.; Golubeva, N.; Honkavaara, K.; Koerfer, M.; Laarmann, T.; Leuschner, A.; Lilje, L.; Limberg, T.; Noelle, D.; Obier, F.; Petrov, A.; Ploenjes, E.; Rehlich, K.; Schlarb, H.; Schmidt, B.; Schmitz, M.; Schreiber, S.; Schulte-Schrepping, H.; Spengler, J.; Staack, M.; Tavella, F.; Tiedtke, K.; Tischer, M.; Treusch, R.; Vogt, M.; Willner, A.; Bahrdt, J.; Follath, R.; Gensch, M.; Holldack, K.; Meseck, A.; Mitzner, R.; Drescher, M.; Miltchev, V.; Roensch-Schulenburg, J.; Rossbach, J.: Flash II: Perspectives and challenges. Nuclear Instruments & Methods in Physics Research A 635 (2011), p. S2-S5
10.1016/j.nima.2010.10.065

Abstract:
FLASH has been a user facility since 2005, delivering radiation in the wavelength range between 7 and 47 nm using the SASE principle. After the present upgrade, the wavelength range is extended to 4.45 nm. With the third harmonic accelerating module in place to linearize the longitudinal phase space, the stability and reproducibility of the machine is substantially improved. The user requests for beam time by far exceeds the time available. In order to increase user beam time and to improve the radiation properties delivered to users, a major extension of the user facility called FLASH II has been proposed by DESY in collaboration with the HZB. FLASH II is a seeded FEL in the parameter range of FLASH. As logical continuation, the seeding with HHG which started with sFLASH will result in direct seeding. Because in the foreseeable future there will probably not be HHG seed lasers available at high repetition rates down to wavelengths of 4 nm, a cascaded HGHG scheme is proposed to produce short wavelengths. After a first design report, the project now enters its technical design phase. During this time, the FLASH beam parameters after the present upgrade 2009/2010 will be characterized and the present design will be re-evaluated and adjusted. In addition, start-to-end simulations will complete the simulations which have been performed so far, including a design of the extraction area.