[en] The maximum, measured energy-contribution of ACC5 at TTF2 is 26.5 + 0.7 MV/m over 7 cavities, each 1.035 m long. For ACC5 gradient measurements, a comparison was made between the beam energy with ACC4 and 5 off and the beam energy with ACC4 detuned and ACC5 cavities 1-7 tuned. The maximum gradient was determined by increasing the amplitude of the RF until the cavity quenched. ACC5 cavities 1-7 were tuned to maximum gradient such that the RF pulse-shape had a flat top. The phase of the RF was, however, 30 + 10 degrees different from the beam phase for 6 of 7 cavities, producing 12.1 + 1.5 % less beam energy than on-crest operation would've produced. The beam energy was determined with a beam image on a screen in the dispersive region of the bypass-dogleg and the strength of the upstream dipole. (orig.)

No abstract available

No abstract available

[en] Full text: A stigmatic grazing-incidence spectrometer for the 2.5-40 nm EUV region has been realized. The optical design consists of a grazing-incidence spherical variable-line-spaced grating with flat-field properties coupled to a spherical focusing mirror that compensates for the astigmatism. The mirror is mounted with its tangential plane coincident with the equatorial plane of the grating in the Kirkpatrick-Baez configuration. The spectrum is acquired by an EUV-enhanced CCD detector, that can be moved along the spectral focal curve to select the spectral region to be acquired. This stigmatic design has also spectral and spatial resolution capability for extended sources. The spectral and spatial resolution of the system have been characterized by using the emission from an hollow-cathode lamp or a laser-produced plasma. The instrument is going to be installed at the DESY synchrotron for the spectral monitoring of the EUV FEL beam in the 20-40 nm region

[en] We present an overview of the vacuum-ultraviolet free electron laser (VUV FEL) user facility at DESY comprising the layout of the experimental hall, radiation transport to the experimental area, as well as photon beam diagnostics. In general, diagnostics of the FEL radiation is particularly challenging due to the laser's unique properties such as extremely high peak powers and short pulse lengths. Yet, pulse-resolved characterization of the photon beam is essential for most user experiments. In order to monitor important parameters like radiation pulse intensity, spectral distribution, etc. new concepts have been developed allowing efficient use of the new source

[en] Photon beam diagnostics for vacuum-ultraviolet free electron lasers (VUV FEL) are critical to monitoring and understanding their performance characteristics. Due to the shot-to-shot fluctuations inherent in FELs based on the self amplified spontaneous emission (SASE) process, it is mandatory to use pulse-resolved diagnostics. We have designed a spectrograph based on a variable-line-spacing (VLS) plane grating and a phosphor/CCD to monitor single shot spectra of the free electron laser at DESY. The basic concept is to allow most of the beam to be reflected towards an experimental station while the first order light is dispersed and focused by the VLS grating onto the CCD. The spectrograph will cover the wavelength range 6.4-60 nm with the CCD accepting a bandwidth of ∼10%. The grazing angle of incidence on the grating is 2 deg., the central line density is 1200 l/mm, and the distance grating-CCD is approximately 2 m. The linear variation of the grating line spacing combined with positioning the detector at the focal curve, allows zeroing the defocus in the full spectrograph wavelength range. The correction of higher order grating aberrations yields a theoretical resolving power greater than 20000 over the full length of the 20 mm CCD when the CCD is positioned tangent to the focal plane. Based on power considerations, a shallow blazed grating is the preferred profile. Efficiency calculations over the spectrograph range show that with a carbon coating the absolute efficiency for zeroth order is higher than 0.85 and the first order efficiency varies between 0.5% and 8%

[en] 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.

[en] A method has been developed and applied to measure the beam waist and spot size of a focused soft x-ray beam at the free-electron laser FLASH of the Deutsches Elektronen-Synchrotron in Hamburg. The method is based on a saturation effect upon atomic photoionization and represents an indestructible tool for the characterization of powerful beams of ionizing electromagnetic radiation. At the microfocus beamline BL2 at FLASH, a full width at half maximum focus diameter of (15±2) μm was determined

[en] We performed time-of-flight (TOF) spectroscopy on a jet of rare gas clusters using light pulses at λ_FEL = 32 nm produced by the FLASH VUV freeelectron-laser (Hamburg, Germany) with a maximum peak power density of about 3 x 10¹³ W/cm² at the sample. Energy deposition on the clusters was found to be strongly dependent on lambda and much more efficient in the VUV than in the IR and visible spectral range. We observed multiple ionization of rare gas atoms coming from clusters; the latter fragment completely upon absorption of a single pulse. We have also measured high quality photoelectron spectra. Small angle soft X-ray scattering (SAXS) from a single light pulse (λ_FEL = 32 nm), was recorded with high signal to noise ratio for very large (N_atoms 3 x 10⁶) Argon clusters

[en] The disintegration mechanisms for xenon clusters in intense femtosecond soft x-ray pulses from the FLASH free electron laser are investigated. The clusters are irradiated at a wavelength of λ = 13.7 nm (hν = 90.5 eV) and power densities of 5 x 10¹⁴ W cm^-2. During the 10 fs pulse the Xe clusters are transformed into a highly excited, multiply charged nanoplasma. Simulating the ion kinetic energies in an electrostatic model suggests that highly charged ions explode off the surface due to Coulomb repulsion while the inner core expands in a hydrodynamic expansion. The current results yield evidence for efficient ionization of the clusters in addition to direct multistep photoemission.