SLS Detector Group

A synchrotron X-ray diffractometer incorporating a pulsed field magnet for high fields up to 40 T has been developed and a detailed description of this instrument is reported. The pulsed field magnet is composed of two coaxial coils with a gap of 3 mm at the mid-plane for passage of the X-rays. The pixel detector PILATUS 100K is used to store the diffracted X-rays. As a test of this instrument, X-ray diffraction by a powder sample of the antiferromagnet CoO is measured below the Né el temperature. A field-dependent lattice distortion of CoO due to magnetostriction is observed up to 38 T.

PILATUS is a silicon hybrid pixel detector system, operating in single-photoncounting mode, that has been developed at the Paul Scherrer Institut for the needs of macromolecular crystallography at the Swiss Light Source (SLS). A calibrated PILATUS module has been characterized with monochromatic synchrotron radiation. The influence of charge sharing on the count rate and the overall energy resolution of the detector were investigated. The dead-time of the system was determined using the attenuated direct synchrotron beam. A single module detector was also tested in surface diffraction experiments at the SLS, whereby its performance regarding fluorescence suppression and saturation tolerance were evaluated, and have shown to greatly improve the sensitivity, reliability and speed of surface diffraction data acquisition.

The PILATUS 1M detector is a hybrid pixel array detector with over one million pixels that operate in single photon counting mode. The detector, designed for macromolecular crystallography, is the largest pixel array detector currently in use at a synchrotron. It is a modular system consisting of 18 multichip modules covering an area of 21 cm  24 cm. The design of the components as well as the manufacturing of the detector including the bump-bonding was performed at the Paul Scherrer Institute (PSI). The use of a single photon counting detector for protein crystallography requires detailed studies of the charge collection properties of the silicon sensor. The 18 modules are read out in parallel, leading to a full frame readout-time of 6.7 ms. This allows crystallographic data to be acquired in fine-'-slicing mode with continuous rotation of the sample. The detector was tested in several experiments at the protein crystallography beamline X06SA at the Swiss Light Source at PSI. Data were collected both in conventional oscillation mode using the shutter, as well as in a fine-'-slicing mode. After applying all the necessary corrections to data from a thaumatin crystal, the processing of the conventional data led to satisfactory merging Rfactors of the order of 8.5%. This allows, for the first time, determination of a refined electron density map of a macromolecular biological crystal using a silicon pixel detector.

An overview of area detectors in structural biology is presented. Development of these detectors is one of the main reasons for the exponential rise in the number of structure determinations of large biological complexes. The different techniques used for structure determination put different demands on area detectors. The techniques used in structural biology, X-ray and electron diffraction and electron imaging are discussed and the requirements for a good detector are highlighted. Furthermore, an overview is given of the current state of the art of high-resolution area detectors. r

The MYTHEN detector is a one-dimensional microstrip detector with single photon counting readout optimized for time resolved powder diffraction experiments at the Swiss Light Source (SLS). The system has been successfully tested for many different synchrotron radiation applications including phase contrast and tomographic imaging, small angle scattering, diffraction and time resolved pump and probe experiments for X-ray energies down to 5 keV and counting rate up to 3 MHz. The frontend electronics is designed in order to be coupled to 50 mm pitch microstrip sensors but some interest in enhancing the spatial resolution is arising for imaging and powder diffraction experiments.

A new imaging high resolution x-ray crystal spectrometer (XCS) has been developed to measure continuous profiles of ion temperature and rotation velocity in fusion plasmas. Following proof-of-principle tests on the Alcator C-Mod tokamak and the NSTX spherical tokamak, and successful testing of a new silicon, pixilated detector with 1 MHz count rate capability per pixel, an imaging XCS is being designed to measure full profiles of T i and v φ on C-Mod. The imaging XCS design has also been adopted for ITER. Ion-temperature uncertainty and minimum measurable rotation velocity are calculated for the C-Mod spectrometer. The affects of x-ray and nuclear-radiation background on the measurement uncertainties are calculated to predict performance on ITER.

The hybrid pixel technology combines silicon sensors with CMOS-processing chips by a 2D micro bump-bonding interconnection technology developed at Paul Scherrer Institute [C. Broennimann, 41 [4]] are operating in the so-called ''single photon counting mode'': Every X-ray quantum is directly converted into an electrical signal and counted by the detector system. Several prototype detectors in various geometries were produced, tested and established at different synchrotron beamlines worldwide. We explain the technology and present some recent highlights from various fields of applications.

A new spatially resolving x-ray crystal spectrometer capable of measuring continuous spatial profiles of high resolution spectra / d 6000 of He-like and H-like Ar K lines with good spatial 1 cm and temporal 10 ms resolutions has been installed on the Alcator C-Mod tokamak. Two spherically bent crystals image the spectra onto four two-dimensional Pilatus II pixel detectors. Tomographic inversion enables inference of local line emissivity, ion temperature T i , and toroidal plasma rotation velocity v from the line Doppler widths and shifts. The data analysis techniques, T i and v profiles, analysis of fusion-neutron background, and predictions of performance on other tokamaks, including ITER, will be presented.

A new type of X-ray imaging crystal spectrometer for Doppler measurements of the radial profiles of the ion temperature and plasma rotation velocity in tokamak plasmas is presently being developed in a collaboration between various laboratories. The spectrometer will consist of a spherically bent crystal and a two-dimensional position sensitive detector; and it will record temporally and spatially resolved X-ray line spectra from highly-charged ions. The detector must satisfy challenging requirements with respect to count rate and spatial resolution. The paper presents the results from a recent test of a PILATUS II detector module on Alcator C-Mod, which demonstrate that the PILATUS II detector modules will satisfy these requirements.

A new spatially resolving x-ray crystal spectrometer (XCS) [1] capable of measuring continuous spatial profiles of high resolution spectra (!/d! > 6000) of He-like and H-like Ar K! lines has been installed on the Alcator C-Mod tokamak. [2,3] The spectrometer enables greatly improved measurements of (a) ion-temperature (T i ) and (b) intrinsic-rotation-velocity profiles (v ∀ ) with excellent spatial (~1 cm) and temporal (~10 -20 ms) resolution, as well as (c) study of the atomic physics of highly charged ions. Tomographic inversion enables inference of local line emissivity, T i , and v ∀ from the chord-integrated spectra.

A new spatially resolving x-ray crystal spectrometer capable of measuring continuous spatial profiles of high resolution spectra (/d > 6000) of He-like and H-like Ar K lines with good spatial (~1 cm) and temporal (~10 ms) resolutions has been installed on the Alcator C-Mod tokamak. Two spherically bent crystals image the spectra onto four two-dimensional Pilatus II pixel detectors. Tomographic

A novel type X-ray detector, called PILATUS, has been developed at the Paul Scherrer Institut in Switzerland during the last decade. PILATUS detectors are two-dimensional hybrid pixel array detectors, which operate in single-photon counting mode. PILATUS detectors feature a very wide dynamic range (1:1 000 000), very short readout time (<3.0 ms), no readout noise, and very high counting rate (>2×106counts/s/pixel). In addition, a lower energy threshold can be set in order to suppress fluorescence background from the sample, thus a very good signal-to-noise ratio is achieved. The combination of these features for area detectors is unique and thus the PILATUS detectors are considered to be the next generation X-ray detectors. The basic building block of all the detectors is the PILATUS module having an active area of 83.8×33.5 mm2. The PILATUS 100K is a complete detector system with one module. PILATUS detector systems can have other configurations, including large area systems ...

We have measured scintillation properties of pure CsI crystals used in the shower calorimeter built for a precise determination of the π + →π 0 e + ν e decay rate at the Paul Scherrer Institute (PSI). All 240 individual crystals painted with a special wavelength-shifting solution were examined in a custom-build detection apparatus (RASTA-radioactive source tomography apparatus) that uses a 137 Cs radioactive gamma source, cosmic muons and a light emitting diode as complementary probes of the scintillator light response. We have extracted the total light output, axial light collection nonuniformities and timing responses of the individual CsI crystals. These results predict improved performance of the 3π sr PIBETA calorimeter due to the painted lateral surfaces of 240 CsI crystals. The wavelength-shifting paint treatment did not affect appreciably the total light output and timing resolution of our crystal sample. The predicted energy resolution for positrons and photons in the energy range of 10-100 MeV was nevertheless improved due to the more favorable axial light collection probability variation. We have compared simulated calorimeter ADC spectra due to 70 MeV positrons and photons with a Monte Carlo calculation of an ideal detector light response.