| Paper | Title | Page |
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| TUPB02 | A Simple Method for Controlling the Line Width of SASE X-Ray FELs | 258 |
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We describe a novel single-bunch self-seeding scheme to obtain highly monochromatic X-rays from a baseline XFEL undulator. For a single-bunch self-seeding scheme a long electron beam bypass is required, implying modifications of the baseline undulator configuration. We avoid such requirement exploiting a single crystal in the transmission direction. The method can be realized using a temporal windowing technique, requiring a magnetic delay for the electron bunch only. The proposed setup is extremely simple and composed of as few as two simple elements: the crystal and the short magnetic chicane, which accomplishes three tasks by itself. It creates an offset for crystal installation, removes the electron micro-bunching from the first undulator, and acts as a delay line for temporal windowing. Using a single crystal installed within a short magnetic chicane in the baseline undulator, it is possible to decrease the bandwidth of the radiation well beyond the XFEL design down to 10-5. The installation of the magnetic chicane does not perturb the undulator focusing system and does not interfere with the baseline mode of operation. |
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| WEPA14 | Ultrafast X-Ray Pulse Measurement Method | 386 |
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In this paper we describe a measurement technique capable of resolving femtosecond X-ray pulses from XFEL facilities. Since these ultrashort pulses are themselves the shortest event available, our measurement strategy is to let the X-ray pulse sample itself. Our method relies on the application of a "fresh" bunch technique, which allows for the production of a seeded X-ray pulse with a variable delay between seed and electron bunch. The shot-to-shot averaged energy per pulse is recorded. It turns out that one actually measures the autocorrelation function of the X-ray pulse, which is related in a simple way to the actual pulse width. For implementation of the proposed technique, it is sufficient to substitute a single undulator segment with a short magnetic chicane. The focusing system of the undulator remains untouched, and the installation does not perturb the baseline mode of operation. We present a feasibility study and we make exemplifications with typical parameters of an X-ray FEL. |
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| THPA02 | Control of the Amplification Process in Baseline XFEL Undulators With Mechanical SASE Switchers | 570 |
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The magnetic gap of the baseline XFEL undulators can be varied mechanically for wavelength tuning. In particular, the wavelength range 0.1 nm - 0.4 nm can be covered by operating the European XFEL with the SASE2 undulator. The length of the SASE2 undulator (256.2 m) is sufficient to independently generate three pulses of different radiation wavelengths at saturation. Normally, if a SASE FEL operates in saturation, the quality of the electron beam is too bad for generation of SASE radiation in the subsequent part of undulator which is resonant at a few times longer wavelength. The new method of SASE undulator-switching based on the rapid switching of the FEL amplification process proposed in this paper is an attempt to get around this obstacle. Using mechanical SASE shutters installed within short magnetic chicanes in the baseline undulator, it is possible to rapidly switch the FEL photon beam from one wavelength to another, providing simultaneous multi-color capability. Combining this method with a photon-beam distribution system can provide an efficient way to generate a multi-user facility. |
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| THPA03 | Scheme for Femtosecond-Resolution Pump-Probe Experiments at XFELs With Two-Color Ten GW-Level X-Ray Pulses | 574 |
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This paper describes a scheme for pump-probe experiments that can be performed at LCLS and at the European XFEL and determines what additional hardware development will be required to bring these experiments to fruition. It is proposed to derive both pump and probe pulses from the same electron bunch, but from different parts of the tunable-gap baseline undulator. This eliminates the need for synchronization and cancels jitter problems. The method has the further advantage to make a wide frequency range accessible at high peak-power and high repetition-rate. An important feature of the proposed scheme is that the hardware requirement is minimal. Our technique is based in essence on the "fresh" bunch technique. For its implementation it is sufficient to substitute a single undulator module with short magnetic delay line, i.e. a weak magnetic chicane, which delays the electron bunch with respect to the SASE pulse of half of the bunch length in the linear stage of amplification. This installation does not perturb the baseline mode of operation. We present a feasibility study and we make exemplifications with the parameters of the SASE2 line of the European XFEL. |