LMU, Garching
University of Oxford, Clarendon Laboratory, Oxford
MPQ, Garching, Munich
LBNL, Berkeley, California
FZD, Dresden
Latest developments in the field of laser-wakefield acceleration (LWFA) have led to relatively stable electron beams in terms of peak energy, charge, pointing and divergence [13]. Electron beams with energies of up to 1 GeV have been produced from only few-centimeters long acceleration distances [4]. Driving undulators with these electron beams holds promise for producing brilliant X-ray sources on the university-laboratory scale. In this talk, we will present an experimental breakthrough on this path: our laser-driven soft-X-ray undulator source [5]. In the second part of the talk, we will discuss the physics behind the unique characteristics of laser-wakefield accelerated electron beams such as the intrinsic ltrashort pulse duration (expected to be about 10 fs) and the low normalized transverse emittances (expected to be < pi mm mrad). The properties of state-of-the-art wakefield accelerators as well as their limits will be discussed. Finally new schemes to overcome those limits and further improve the beam quality will be presented.
[1] Mangles, S. P. D. et al. in Nature 431, 535538 (2004).
[2] Geddes, C. G. R. et al. in Nature 431, 538541 (2004).
[3] Faure, J. et al. in Nature 431, 541544 (2004).
BNL, Upton, Long Island, New York
It was recently suggested[1] to use a laser beam as an undulator for an ultra compact X ray FEL. There are number of challenges in realizing this very attractive approach. This paper will discuss the one related to defining and generating an adequate laser beam. Recent development of a picosecond CO2 laser at Brookhaven ATF allows considering a practical set of laser parameters that would preserve resonant condition over the saturation length of a few mm. Electron beam parameters required for such FEL would be also discussed and will show need for further high brightness beam development. [1] Presentation by Claudio Pellegrini at 48th ICFA Advanced Beam Dynamics Workshop on Future Light Sources. March, 2010
BNL, Upton, Long Island, New York
OFFELO (optics-free FEL oscillator) is a brand new idea for obtaining hard X-ray wavelength radiation using an oscillator without concerning the damage to the mirror. By using an extra electron beam to transport the radiation information, OFFELO also provide pleasant flexibility compared with traditional oscillator scheme. We simulated the lasing process and carry out the saturation condition and explore other properties of this scheme.
USTRAT/SUPA, Glasgow
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
Chicanes placed between undulator modules in a high-gain FEL amplifier have been shown to generate a set of axial modes that may be locked to generate attosecond pulse trains in the x-ray [1]. Using numerical simulations, it is shown in this paper that a similar system of undulator/chicane modules may be used in a low-gain FEL cavity resonator to generate a equally spaced set of frequency modes with a spacing much greater than those of the cavity. As with the high-gain FEL amplifier case, these mode can lock to generate a pulse train.
[1] N.R. Thompson & B.W.J. McNeil, Phys. Rev. Lett. 100, 203901 (2008)
DESY, Hamburg
Longitudinal space charge (LSC) driven microbunching instability in electron beam formation systems of X-ray FELs is a recently discovered effect hampering beam instrumentation and FEL operation. The instability was observed in different facilities in infrared and visible wavelength ranges. In this paper we propose to use such an instability for generation of VUV and X-ray radiation. A typical longitudinal space charge amplifier (LSCA) consists of few amplification cascades (drift space plus chicane) with a short undulator behind the last cascade. A wavelength compression could be an attractive option for LSCA since the process is broadband, and a high compression stability is not required. LSCA can be used as a cheap addition to the existing or planned short-wavelength FELs. In particular, it can produce the second color for a pump-probe experiment. It is also possible to generate attosecond pulses in the VUV and X-ray regimes. Finally, since the amplification mechanism is broadband and robust, LSCA can be an interesting alternative to self-amplified spontaneous emission free electron laser (SASE FEL) in the case of using laser-plasma accelerators as drivers of light sources.
Report DESY 10-048, March 2010