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The ePix detector family provides multiple variants of hybrid pixel detectors to support a wide range of applications at free electron laser facilities. We present the results of a systematic study of the influence of radiation induced damage on the performance and lifetime of an ePix100a detector module using a direct attenuated beam of the EuXFEL at 9 keV photon energy and an average power of 10 $\mu$W. An area of 20 x 20 pixels was irradiated with an average photon flux of approx. 7 x $10^{9}$ photons/s to a dose of approximately 760$\pm$65 kGy at the location of the Si/SiO$_2$ interfaces in the sensor. A dose dependent increase in both offset and noise of the ePix100a detector have been observed originating from an increase of the sensor leakage current. Moreover, we observed an effect directly after irradiation resulting in the saturation of individual pixels by their dark current. Changes in gain are evaluated one and half hours post irradiation and suggest damage to occur also on the ASIC level. Based on the obtained results, thresholds for beam parameters are deduced and the detector lifetime is estimated with respect to the requirements to the data quality in order to satisfy the scientific standards defined by the experiments. We conclude the detector can withstand a beam with an energy up to 1 $\mu$J at a photon energy of 9 keV impacting on an area of 1 mm$^2$. The detector can be used without significant degradation of its performance for several years if the incident photon beam intensities do not exceed the detector's dynamic range by at least three orders of magnitude. Our results provide valuable input for the operation of the ePix100a detector at FEL facilities and for the design of future detector technology., Comment: 25 pages, 15 figures, accepted for publication by the Journal of Instrumentation

A method for monitoring the misalignment of the magnetic axis in solenoids is proposed. This method requires only a few measurements of the magnetic field at fixed positions inside the magnet aperture, and thus overcomes the main drawback of sturdy moving mechanics of other Hall sensor-based methods. Conversely to state-of-the-art axis determination, the proposed method can be applied also during magnet operations, when the axis region and almost the whole remaining magnet aperture are not accessible. Moreover, only a few measurements of the magnetic field at fixed positions inside the magnet aperture are required: thus a slow process such as the mapping of the whole aperture of a magnet by means of moving stages is not necessary. The mathematical formulation of the method is explained, and a case study on a model of a multi–layer solenoid is presented. For this case study, the uncertainty is assessed and the optimal placement of the Hall transducers is derived.

A method for monitoring the coils alignment in multi-coil magnets, directly during their operation in particle accelerators, is proposed. Few measures of the magnetic field by Hall transducers and a local field model allows one to monitor the magnetic axis position of each coil. Thus, the particle beam can be kept strongly focused over its operation time by means of feedback. Furthermore, the uncertainty in measuring the magnetic axis was studied with the aim of finding the optimal placing of the transducers, where the minimum uncertainty is achieved. The method was validated on a challenging case study on the European project "ELI Nuclear Physics" (ELI-NP). In particular, simulations results, based on both analytical and finite-element models of the ELI-NP multi-coil solenoid, point to an uncertainty below 100 ?m, for misalignment of the magnetic axes in rotation up to ?/1000 and in translation of 1/1000 times the length of a single coil. This uncertainty is limited by the Hall transducers technology, but has potential for large improvement margins, because the measurement model error is below 100 ?m.

This work presents the first characterization results obtained on a pilot fabrication run of planar sensors, tailored for X-ray imaging applications at FELs, developed in the framework of INFN project PixFEL. Active and slim-edge p-on-n sensors are fabricated on n-type high-resistivity silicon with 450 μm thickness, bonded to a support wafer. Both diodes and pixelated sensors with a pitch of 110 μm are included in the design. Edge structures with different number of guard rings are designed to comply with the large bias voltage required by the application after accumulating an ionizing radiation dose as large as 1GGy. Preliminary results from the electrical characterization of the produced sensors, providing a first assessment of the proposed approach, are discussed. A functional characterization of the sensors with a pulsed infrared laser is also presented, demonstrating the validity of slim-edge configurations.

This work is concerned with the design of a readout chip for application to experiments at the next generation X-ray Free Electron Lasers (FEL). The ASIC, named PixFEL Matrix (PFM2), has been designed in a 65 nm CMOS technology and consists of 32 × 32 pixels. Each cell covers an area of 110 × 110 μm2 and includes a low-noise charge sensitive amplifier (CSA) with dynamic signal compression, a time-variant shaper used to process the preamplifier output signal, a 10-bit successive approximation register (SAR) analog-to-digital converter (ADC) and digital circuitry for channel control and data readout. Two different solutions for the readout channel, based on different versions of the time-variant filter, have been integrated in the chip. Both solutions can be operated in such a way to cope with the high frame rate (exceeding 1 MHz) foreseen for future X-ray FEL machines. The ASIC will be bump bonded to a slim/active edge pixel sensor to form the first demonstrator for the PixFEL X-ray imager. This work has been carried out in the frame of the PixFEL project funded by Istituto Nazionale di Fisica Nucleare (INFN), Italy.

The INFN PixFEL project is developing the fundamental building blocks for a large area X-ray imaging camera to be deployed at next generation free electron laser (FEL) facilities with unprecedented intensity. Improvement in performance beyond the state of art in imaging instrumentation will be explored adopting advanced technologies like active edge sensors, a 65 nm node CMOS process and vertical integration. These are the key ingredients of the PixFEL project to realize a seamless large area focal plane instrument composed by a matrix of multilayer four-side buttable tiles. In order to minimize the dead area and reduce ambiguities in image reconstruction, a fine pitch active edge thick sensor is being optimized to cope with very high intensity photon flux, up to 104 photons per pixel, in the range from 1 to 10 keV. A low noise analog front-end channel with this wide dynamic range and a novel dynamic compression feature, together with a low power 10 bit analog to digital conversion up to 5 MHz, has been realized in a 110 μm pitch with a 65 nm CMOS process. Vertical interconnection of two CMOS tiers will be also explored in the future to build a four-side buttable readout chip with high density memories. In the long run the objective of the PixFEL project is to build a flexible X-ray imaging camera for operation both in burst mode, like at the European X-FEL, or in continuous mode with the high frame rates anticipated for future FEL facilities.

The peak brilliance reached by today's Free-Electron Laser and Synchrotron light sources requires photon detectors matching their output intensity and other characteristics in order to fully realiz ...

iWoRiD 2015, Hamburg, Germany, 28 Jun 2015 - 2 Jul 2015; Journal of Instrumentation 11(02), C02090 (2016). doi:10.1088/1748-0221/11/02/C02090, PERCIVAL ("Pixelated Energy Resolving CMOS Imager, Versatile And Large") is a monolithic active pixel sensor (MAPS) based on CMOS technology. Is being developed by DESY, RAL/STFC, Elettra, DLS, and PAL to address the various requirements of detectors at synchrotron radiation sources and Free Electron Lasers (FELs) in the soft X-ray regime. These requirements include high frame rates and FELs base-rate compatibility, large dynamic range, single-photon counting capability with low probability of false positives, high quantum efficiency (QE), and (multi-)megapixel arrangements with good spatial resolution. Small-scale back-side-illuminated (BSI) prototype systems are undergoing detailed testing with X-rays and optical photons, in preparation of submission of a larger sensor. A first BSI processed prototype was tested in 2014 and a preliminary result—first detection of 350eV photons with some pixel types of PERCIVAL—reported at this meeting a year ago. Subsequent more detailed analysis revealed a very low QE and pointed to contamination as a possible cause. In the past year, BSI-processed chips on two more wafers were tested and their response to soft X-ray evaluated. We report here the improved charge collection efficiency (CCE) of different PERCIVAL pixel types for 400eV soft X-rays together with Airy patterns, response to a flat field, and noise performance for such a newly BSI-processed prototype sensor., Published by Inst. of Physics, London

The PERCIVAL (Pixelated Energy Resolving CMOS Imager, Versatile And Large) soft X-ray 2D imaging detector is based on stitched, wafer-scale sensors possessing a thick epi-layer, which together with back-thinning and back-side illumination yields elevated quantum efficiency in the photon energy range of 125–1000 eV. Main application fields of PERCIVAL are foreseen in photon science with FELs and synchrotron radiation. This requires high dynamic range up to 105 ph @ 250 eV paired with single photon sensitivity with high confidence at moderate frame rates in the range of 10–120 Hz. These figures imply the availability of dynamic gain switching on a pixel-by-pixel basis and a highly parallel, low noise analog and digital readout, which has been realized in the PERCIVAL sensor layout. Different aspects of the detector performance have been assessed using prototype sensors with different pixel and ADC types. This work will report on the recent test results performed on the newest chip prototypes with the improved pixel and ADC architecture. For the target frame rates in the 10–120 Hz range an average noise floor of 14e− has been determined, indicating the ability of detecting single photons with energies above 250 eV. Owing to the successfully implemented adaptive 3-stage multiple-gain switching, the integrated charge level exceeds 4 10^6 e− or 57000 X-ray photons at 250 eV per frame at 120 Hz. For all gains the noise level remains below the Poisson limit also in high-flux conditions. Additionally, a short overview over the updates on an oncoming 2 Mpixel (P2M) detector system (expected at the end of 2016) will be reported.

The DSSC (DEPFET Sensor with Signal Compression) will be a silicon based, 2d 1 Mpx imaging detector for the European X-ray Free Electron Laser Facility (XFEL.EU) in Hamburg, Germany. The DSSC is foreseen for soft X-radiation from 0.5 keV up to 6 keV . Driven by its scientific requirements, the design goals of the detector system are single photon detection, high dynamic range and a high frame rate of up to 4.5 MHz. Signal compression and amplification will be performed in the silicon sensor pixels yielding a low signal noise. Utilizing an in-pixel active filtering stage and an 8/9-bit ADC, the detector will provide parallel read-out of all pixels. In order to calibrate offset and gain, the procedure currently under investigation relies on determining peak positions in measurements with calibration line sources such as 55Fe. Here the status of studies of the stability and performance of a parameterized fit function designed for this task will be presented.

The PixFEL project aims to develop an advanced X-ray camera for imaging suited for the demanding requirements of next generation free electron laser (FEL) facilities. New technologies can be deployed to boost the performance of imaging detectors as well as future pixel devices for tracking. In the first phase of the PixFEL project, approved by the INFN, the focus will be on the development of the microelectronic building blocks, carried out with a 65 nm CMOS technology, implementing a low noise analog front-end channel with high dynamic range and compression features, a low power ADC and high density memory. At the same time PixFEL will investigate and implement some of the enabling technologies to assembly a seamless large area X-ray camera composed by a matrix of multilayer four-side buttable tiles. A pixel matrix with active edge will be developed to minimize the dead area of the sensor layer. Vertical interconnection of two CMOS tiers will be explored to build a four-side buttable readout chip with small pixel pitch and all the on-board required functionalities. The ambitious target requirements of the new pixel device are: single photon resolution, 1 to 104 photons @ 1 keV to 10 keV input dynamic range, 10-bit analog to digital conversion up to 5 MHz, 1 kevent in-pixel memory and 100 μm pixel pitch. The long term goal of PixFEL will be the development of a versatile X-ray camera to be operated either in burst mode (European XFEL), or in continuous mode to cope with the high frame rates foreseen for the upgrade phase of the LCLS-II at SLAC.

DEPFET Active Pixel Sensors (APS) have been introduced as focal plane detectors for X-ray astronomy already in 1996. Fabricated on high resistivity, fully depleted silicon and back-illuminated they can provide high quantum efficiency and low noise operation even at very high read rates. In 2009 a new type of DEPFET APS, the DSSC (DEPFET Sensor with Signal Compression) was developed, which is dedicated to high-speed X-ray imaging at the European X-ray free electron laser facility (EuXFEL) in Hamburg. In order to resolve the enormous contrasts occurring in Free Electron Laser (FEL) experiments, this new DSSC-DEPFET sensor has the capability of nonlinear amplification, that is, high gain for low intensities in order to obtain single-photon detection capability, and reduced gain for high intensities to achieve high dynamic range for several thousand photons per pixel and frame. We call this property "signal compression". Starting in 2015, we have been fabricating DEPFET sensors in an industrial scale CMOS foundry maintaining the outstanding proven DEPFET properties and adding new capabilities due to the industrial-scale CMOS process. We will highlight these additional features and describe the progress achieved so far. In a first attempt on double-sided polished 725 mm thick 200 mm high resistivity float zone silicon wafers all relevant device related properties have been measured, such as leakage current, depletion voltage, transistor characteristics, noise and energy resolution for X-rays and the nonlinear response. The smaller feature size provided by the new technology allows for an advanced design and significant improvements in device performance. A brief summary of the present status will be given as well as an outlook on next steps and future perspectives.

This report describes the conceptual design of a proposed free electron laser test facility called CLARA that will be a major upgrade to the existing VELA accelerator test facility at Daresbury Laboratory in the UK. CLARA will be able to test a number of new free electron laser schemes that have been proposed but require a proof of principle experiment to confirm that they perform as predicted. The primary focus of CLARA will be on ultra short photon pulse generation which will take free electron lasers into a whole new regime, enabling a new area of photon science to emerge.

The use of C-Band structures for electron acceleration and production of high quality beams has been proposed and adopted in several linac projects all over the world. The two main projects that adopted such type of structures are the Japanese Free Electron Laser (FEL) project in Spring-8 and the SwissFEL project at Paul Scherrer Institute (PSI). Also the energy upgrade of the SPARC photo-injector at LNF-INFN (Italy) from 150 to more than 240 MeV will be done by replacing a low gradient S-Band accelerating structure with two C-band structures. The structures are Traveling Wave (TW) and Constant Impedance (CI), have symmetric axial input couplers and have been optimized to work with a SLED RF input pulse. The paper presents the design criteria of the structures, the realization procedure and the low and high power RF test results on a prototype. The high power tests have been carried out by the Frascati INFN Laboratories in close collaboration with the Japanese Laboratory KEK. Experimental results confirmed the feasibility of the operation of the prototype at 50 MV/m with about 10 6 breakdowns per pulse per meter. Such high gradients have not been reached before in C-Band systems and demonstrated the possibility to use C-band accelerators, if needed, at such high field level. The results of the internal inspection of the structure after the high power test are also presented.

Reduced edge or "edgeless" detector design offers seamless tileability of sensors for a wide range of applications from particle physics to synchrotron and free election laser (FEL) facilities and medical imaging. Combined with through-silicon-via (TSV) technology, this would allow reduced material trackers for particle physics and an increase in the active area for synchrotron and FEL pixel detector systems. In order to quantify the performance of different edgeless fabrication methods, 2 edgeless detectors were characterized at the Diamond Light Source using an 11 μm FWHM 15 keV micro-focused X-ray beam. The devices under test were: a 150 μm thick silicon active edge pixel sensor fabricated at VTT and bump-bonded to a Medipix2 ROIC; and a 300 μm thick silicon strip sensor fabricated at CIS with edge reduction performed by SCIPP and the NRL and wire bonded to an ALiBaVa readout system. Sub-pixel resolution of the 55 μm active edge pixels was achieved. Further scans showed no drop in charge collection recorded between the centre and edge pixels, with a maximum deviation of 5% in charge collection between scanned edge pixels. Scans across the cleaved and standard guard ring edges of the strip detector also show no reduction in charge collection. These results indicate techniques such as the scribe, cleave and passivate (SCP) and active edge processes offer real potential for reduced edge, tiled sensors for imaging detection applications.

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 Electron Lasers. Typical requirements for detector systems at these sources are high frame rates, large dynamic range, single-photon counting capability with low probability of false positives, high quantum efficiency, and (multi)-mega-pixel arrangements. PERCIVAL is a monolithic active pixel sensor, based on CMOS technology. It is designed for the soft X-ray regime and, therefore, it is post-processed in order to achieve high quantum efficiency in its primary energy range (250 eV to 1 keV) . This work will report on the latest experimental results on charge collection efficiency obtained for multiple back-side-illuminated test sensors during two campaigns, at the P04 beam-line at PETRA III, and the CiPo beam-line at Elettra, spanning most of the primary energy range as well as testing the performance for photon-energies below 250 eV . In addition, XPS surface analysis was used to cross-check the obtained results.

The development of Radiation Imaging Detectors dedicated to specific front edge use is a rapidly expanding galaxy taking force from a healthy mixture of growing ambitions within basic science targets and applicative use in many contiguous fields. The growth of the high technology imaging tools market is a relevant motivating element. On the scene of this conference a flow of very accurate and informative presentations has allowed to gather a vivid image on the almost frantic target oriented work, the results shown have often surpassed the most visionary expectations.

This work presents the design of a low-noise front-end implementing a novel active signal compression technique. This feature can be exploited in the design of analog readout channels for application to the next generation free electron laser (FEL) experiments. The readout architecture includes the low-noise charge sensitive amplifier (CSA) with dynamic signal compression, a time variant shaper used to process the signal at the preamplifier output and a 10-bit successive approximation register (SAR) analog-to-digital converter (ADC). The channel will be operated in such a way to cope with the high frame rate (exceeding 1 MHz) foreseen for future XFEL machines. The choice of a 65 nm CMOS technology has been made in order to include all the building blocks in the target pixel pitch of 100 μm. This work has been carried out in the frame of the PixFEL Project funded by the Istituto Nazionale di Fisica Nucleare (INFN), Italy.

A readout chip for diffraction imaging applications at new generation X-ray FELs (Free Electron Lasers) has been designed in a 65~nm CMOS technology. It consists of a $ 32 \times 32 $ matrix, with square pixels and a pixel pitch of $ 110\ \mu m $. Each cell includes a low-noise charge sensitive amplifier (CSA) with dynamic signal compression, covering an input dynamic range from 1 to $ 10^4 $ photons and featuring single photon resolution at small signals at energies from 1 to 10 keV. The CSA output is processed by a time-variant shaper performing gated integration and correlated double sampling. Each pixel includes also a small area, low power 10-bit time-interleaved Successive Approximation Register (SAR) ADC for in-pixel digitization of the amplitude measurement. The channel can be operated at rates up to 4.5~MHz, to be compliant with the rates foreseen for future X-ray FEL machines. The ASIC has been designed in order to be bump bonded to a slim/active edge pixel sensor, in order to build the first demonstrator for the PixFEL (advanced X-ray PIXel cameras at FELs) imager.