D. Giuressi

Super ESCA: First beamline operating at ELETTRA

The Super‐ESCA beamline has been designed for high resolution core level spectroscopy of adsorbates on single crystal surfaces using soft x‐ray synchrotron radiation. It receives the light from an 81 period undulator with 5.6 cm period and 4.5 m length in the storage ring ELETTRA. The tunability of this insertion device, at a storage ring electron energy of 2.0 GeV and the connected modified SX700 monochromator allows the performance of experiments at this beamline in the photon energy range 100–2000 eV. This beamline is now operational and first absorption spectra are presented which show available resolving powers varying from 8000 to 3000 for photon energies between 240 and 850 eV.

The photon analysis, delivery, and reduction system at the FERMI@Elettra free electron laser user facility

The FERMI@Elettra free electron laser (FEL) user facility is currently under construction at the Sincrotrone Trieste laboratory in Trieste (Italy). It will cover the wavelength range from 100 to about 5 nm in the fundamental and 3 or 1 nm using the third harmonic. We report the layout of the photon beam diagnostics section, the radiation transport system to the experimental area, and the photon beam distribution system. Due to the peculiar characteristics of the emitted FEL radiation (high peak power, short pulse length, and statistical variation of the emitted intensity and distribution), the realization of the diagnostics system is particularly challenging. The end users are interested in parameters such as the radiation pulse intensity and spectral distribution, as well as in the possibility to attenuate the intensity. In order to accomplish these tasks, a photon analysis, delivery, and reduction system is now under development and construction and is presented here. This system will work on-line producing pulse-resolved information and will let users keep track of the photon beam parameters during the experiments.

Bunch by bunch beam monitoring in 3rd and 4th generation lightsources by means of single crystal diamond detectors and quantumwell devices

New generation Synchrotron Radiation (SR) sources and Free Electron Lasers (FEL) require novel concepts of beam diagnostics to keep photon beams under surveillance, asking for simultaneous position and intensity monitoring. To deal with high power load and short time pulses provided by these sources, novel materials and methods are needed for the next generation BPMs. Diamond is a promising material for the production of semitransparent in situ X-ray BPMs withstanding the high dose rates of SR rings and high energy FELs. We report on the development of freestanding, single crystal CVD diamond detectors. Performances in both low and radio frequency SR beam monitoring are presented. For the former, sensitivity deviation was found to be approximately 2%; a 0.05% relative precision in the intensity measurements and a 0.1-μm precision in the position encoding have been estimated. For the latter, single-shot characterizations revealed sub-nanosecond rise-times and spatial precisions below 6 μm, which allowed bunch-by-bunch monitoring in multi-bunch operation. Preliminary measurements at the Fermi FEL have been performed with this detector, extracting quantitative intensity and position information for FEL pulses (~ 100 fs, energy 12 ÷ 60 eV), with a long-term spatial precision of about 85 μm; results on FEL radiation damages are also reported. Due to their direct, low-energy band gap, InGaAs quantum well devices too may be used as fast detectors for photons ranging from visible to X-ray. Results are reported which show the capability of a novel InGaAs/InAlAs device to detect intensity and position of 100-fs-wide laser pulses.

Hiresmon: A Fast High Resolution Beam Position Monitor for Medium Hard and Hard X-Rays

The high‐resolution x‐ray beam position monitor (XBPM) is based on the principle of a segmented longitudinal ionization chamber with integrated readout and USB2 link. In contrast to traditional transversal ionization chambers here the incident x‐rays are parallel to the collecting field which allows absolute intensity measurements with a precision better than 0.3 %. Simultaneously the beam position in vertical and horizontal direction can be measured with a frame rate of one kHz. The precision of position encoding depends only on the SNR of the synchrotron radiation and is in the order of micro meters at one kHz frame rate and 108 photon /sec at 9 KeV.

X-Ray Beam Position Monitor Based on a Single Crystal Diamond Performing Bunch by Bunch Detection

Diamond is a promising material for the production of semitransparent in situ photon beam monitors which can withstand the high dose rates occurring in new generation synchrotron radiation storage rings and in free electron lasers. We report on the development of a 500 mu m thick freestanding, single crystal chemical vapor deposited diamond detector with segmented electrodes. Performances in both low and radio frequency beam monitoring are presented as well. By using charge integration techniques at a frame rate of 6.5 kHz in combination with a needle synchrotron radiation beam and mesh scans, the inhomogeneity of the sensor was found to be of the order of 2%; with a measured electronics noise of 2 pA / root Hz a 0.05% relative precision in the intensity measurements (at 1 mu A) and a 0.1 mu m resolution in the position encoding have been estimated. Moreover, the high electron-hole mobility of diamond compared with other active materials enables very fast charge collection characterized by rise-times below 1 ns; this allowed us to utilize single pulse integration to simultaneously detect the intensity and the position of each synchrotron radiation photon bunch generated by a bending magnet

A novel multi-cell silicon drift detector for Low Energy X-Ray Fluorescence (LEXRF) spectroscopy

The TwinMic spectromicroscope at Elettra is a multipurpose experimental station for full-field and scanning imaging modes and simultaneous acquisition of X-ray fluorescence. The actual LEXRF detection setup consists of eight single-cell Silicon Drift Detectors (SDD) in an annular configuration. Although they provide good performances in terms of both energy resolution and low-energy photon detection efficiency, they cover just about 4% of the whole photoemission solid angle. This is the main limitation of the present detection system, since large part of the emitted photons is lost and consequently a high acquisition time is required. In order to increase the solid angle, a new LEXRF detection system is being developed within a large collaboration of several institutes. The system, composed of 4 trapezoidal multi-cell silicon drift detectors, covers up to 40% of the photoemission hemisphere, so that this geometry provides a 10 times improvement over the present configuration. First measurements in the laboratory and on the TwinMic beamline have been performed in order to characterize a single trapezoidal detector, configured and controlled by means of two multichannel ASICs, which provide preamplification, shaping and peak-stretching, connected to acquisition electronics based on fast ADCs and FPGA and working under vacuum.

Detector Developments at DESY

With the increased brilliance of state-of-the-art synchrotron radiation sources and the advent of free-electron lasers (FELs) enabling revolutionary science with EUV to X-ray photons comes an urgent need for suitable photon imaging detectors. Requirements include high frame rates, very large dynamic range, single-photon sensitivity with low probability of false positives and (multi)-megapixels. At DESY, one ongoing development project - in collaboration with RAL/STFC, Elettra Sincrotrone Trieste, Diamond, and Pohang Accelerator Laboratory - is the CMOS-based soft X-ray imager PERCIVAL. PERCIVAL is a monolithic active-pixel sensor back-thinned to access its primary energy range of 250 eV to 1 keV with target efficiencies above 90%. According to preliminary specifications, the roughly 10 cm × 10 cm, 3.5k × 3.7k monolithic sensor will operate at frame rates up to 120 Hz (commensurate with most FELs) and use multiple gains within 27 µm pixels to measure 1 to ∼100000 (500 eV) simultaneously arriving photons. DESY is also leading the development of the AGIPD, a high-speed detector based on hybrid pixel technology intended for use at the European XFEL. This system is being developed in collaboration with PSI, University of Hamburg, and University of Bonn. The AGIPD allows single-pulse imaging at 4.5 MHz frame rate into a 352-frame buffer, with a dynamic range allowing single-photon detection and detection of more than 10000 photons at 12.4 keV in the same image. Modules of 65k pixels each are configured to make up (multi)megapixel cameras. This review describes the AGIPD and the PERCIVAL concepts and systems, including some recent results and a summary of their current status. It also gives a short overview over other FEL-relevant developments where the Photon Science Detector Group at DESY is involved.

PERCIVAL: The design and characterisation of a CMOS image sensor for direct detection of low-energy X-rays

Free-Electron Lasers and Synchrotrons are rapidly increasing in brilliance. This has led a requirement of large dynamic range and high frame rate sensors that is now being fulfilled by the PERCVIAL CMOS imager for direct X-ray detection developed at Rutherford Appleton Laboratory. Utilising a lateral overflow pixel and back-side illumination, PERCIVAL simultaneously achieves low-noise single-photon detection and high full well up to 107 e-, all while maintaining a frame rate of 120Hz. PERCIVAL is currently in test structure stage, and will be produced in 2 Mpixel and 13 Mpixel “waferscale” variants in 2015.

Development and tests of a new prototype detector for the XAFS beamline at Elettra Synchrotron in Trieste

The XAFS beamline at Elettra Synchrotron in Trieste combines X-ray absorption spectroscopy and X-ray diffraction to provide chemically specific structural information of materials. It operates in the energy range 2.4-27 keV by using a silicon double reflection Bragg monochromator. The fluorescence measurement is performed in place of the absorption spectroscopy when the sample transparency is too low for transmission measurements or the element to study is too diluted in the sample. We report on the development and on the preliminary tests of a new prototype detector based on Silicon Drift Detectors technology and the SIRIO ultra low noise front-end ASIC. The new system will be able to reduce drastically the time needed to perform fluorescence measurements, while keeping a short dead time and maintaining an adequate energy resolution to perform spectroscopy. The custom-made silicon sensor and the electronics are designed specifically for the beamline requirements.

On the Charge Collection Efficiency of the PERCIVAL Detector

The PERCIVAL soft X-ray imager is being developed by DESY, RAL, Elettra, DLS, and PAL to address the challenges at high brilliance Light Sources such as new-generation Synchrotrons and Free Electro ...