Scheme for attophysics experiments at a X-ray SASE FEL

We propose a concept for production of high power coherent attosecond pulses in X-ray range. An approach is based on generation of eighth harmonic of radiation in a multistage HGHG FEL (high-gain high-harmonic free electron laser) configuration starting from shot noise. Single-spike phenomena occurs when electron bunch is passed through the sequence of four relatively short undulators. The first stage is a conventional "long" wavelength (0.8 nm) SASE FEL which operates in the high-gain linear regime. The 0.1 nm wavelength range is reached by successive multiplication (0.8 nm --> 0.4 nm --> 0.2 nm --> 0.1 nm) in a stage sequence. Our study shows that the statistical properties of the high-harmonic radiation from the SASE FEL, operating in linear regime, can be used for selection of radiation pulses with a single spike in time domain. The duration of the spikes is in the range of 400-600 attoseconds. Selection of single-spike high-harmonic pulses is achieved by using a special trigger in data I acquisition system. The potential of X-ray SASE FEL at TESLA at DESY for generating attosecond pulses is demonstrated. The use of a 10 GW-level attosecond X-ray pulses at X-ray SASE FEL facility will enable us to track process inside atoms for the first time. (C) 2003 Elsevier Science B.V. All rights reserved.