The MiniSDD-Based 1-Mpixel Camera of the DSSC Project for the European XFEL

Abstract

The first DSSC 1-Mpixel camera became available at the European XFEL (EuXFEL) in the Hamburg area in February 2019. It was successfully tested, installed, and commissioned at the Spectroscopy and Coherent Scattering Instrument. DSSC is a high-speed, large-area, 2-D imaging detector system optimized for photon science applications in the energy range between 0.25 and 6 keV. The camera is based on direct conversion Si sensors and is composed of $1024 \\times 1024$ pixels of hexagonal shape with a side length of $136~\\mu \\text{m}$ . The 256 application-specific integrated circuits (ASICs) provide full parallel readout, comprising analog filtering, digitization, and in-pixel data storage. In order to cope with the demanding X-ray pulse time structure of the EuXFEL, the DSSC provides a peak frame rate of 4.5 MHz. The first Mpixel camera is equipped with miniaturized silicon drift detector (MiniSDD) pixel arrays. The intrinsic response of the pixels and the linear readout limit the dynamic range but allow one to achieve noise values of about 60 electrons r.m.s. at the highest frame rate. The challenge of providing high-dynamic range (~104 photons/pixel/pulse) and single-photon detection simultaneously requires a nonlinear system front end, which will be obtained with the DEPFET active pixel technology foreseen for the advanced version of the camera. This technology will provide lower noise and a nonlinear response at the sensor level. This article describes the architecture of the whole detector system together with the main experimental results achieved up to now.