Abstract
Several beam manipulation methods have been studied and experimentally demonstrated to generate x-ray multipulses in free-electron-laser (FEL) facilities, advancing the fields of material science, molecular physics, and photochemistry by enabling x-ray pump/x-ray probe experiments. We have demonstrated a novel method to generate hard x-ray multipulses using a hybrid compression scheme. Compared to other methods, this approach minimizes the time jitter among the FEL subpulses, produces large power FEL subpulses, is suitable for high repetition rate machines, since it does not imply the generation of losses, and it works at short and hard x-ray FEL wavelengths as well. All of these aspects make this approach attractive for the novel FEL facilities aiming to explore the hard x-ray region and to work at high repetition rate.
Highlights
The electron beam is manipulated only at a relatively high beam energy, where the electron beam is already highly relativistic. This makes the beam degradation negligible and the setup time smaller compared to other approaches. This hybrid compression scheme, i.e., where the electron energy chirp is generated by the wakefield induced by the beam itself traveling through the passive structures and only partially by the rf, implies a smaller time jitter among the FEL subpulses compared to other methods, since the effect of the wakefield on the tail is self-synchronized with the head
We showed the tunability of the properties of the FEL subpulses, in terms of separation in time and energy, relative amplitude of the FEL subpulses, and independent control of the length of the single FEL subpulse as well
Compared to other approaches used to obtain two-color FEL pulses, this method is extremely promising to generate large power FEL twocolor subpulses, since it does not imply a massive modification of the machine parameters in the low-energy section of the accelerator, it allows using the entire undulator line, and it does not imply any beam degradation to inhibit the lasing along a portion along the electron bunch duration
Summary
X-ray free-electron-laser (FEL) facilities operating in the so-called two-color mode allow the production of double x-ray subpulses with control of their wavelength and subpulse delay to perform x-ray pump-probe experiments. In this article we show the experimental generation of electron bunch multiple-current spikes and the associated production of multicolor hard x-ray FEL pulses by manipulating the longitudinal electron bunch phase space with an oscillating wakefield [27] induced along a passive structure installed upstream of the first bunch compressor. This method allows using the full undulator line and the majority of the electrons, it works for all the FEL wavelengths. This hybrid compression scheme, i.e., where the electron energy chirp is generated by the wakefield induced by the beam itself traveling through the passive structures and only partially by the rf, implies a smaller time jitter among the FEL subpulses compared to other methods, since the effect of the wakefield on the tail is self-synchronized with the head
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