The European XFEL Beam Position Monitor System

The European XFEL is an X-ray free electron laser user facility that is currently being built in Hamburg by an international consortium. The electron BPM system of the XFEL is developed by a collaboration of PSI, DESY, and CEA/Saclay/Irfu. Cavity BPMs will be used in all parts of the E-XFEL where highest resolution and lowest drift is required, e.g. in the undulators and some locations in the beam transfer lines. In the cryostats of the superconducting 17.5GeV main linac, 2/3rds of the BPMs will be buttons, while 1/3rd will be re-entrant cavities that promise higher resolution than buttons at lowbunch charges. The transfer lines will also be equipped with cost-efficient button BPMs. The BPM electronics is based on a modular system concept, with a common FPGA-based digital back-end design for all BPMs and pickup-specific analog RF front-ends. This paper introduces the design concepts and reports on the project status and measurement results of BPM pickup and electronics prototypes

Design and construction of the POLAR detector

The POLAR detector is a space based Gamma Ray Burst (GRB) polarimeter with a wide field of view, which covers almost half the sky. The instrument uses Compton scattering of gamma rays on a plastic scintillator hodoscope to measure the polarization of the incoming photons. The instrument has been successfully launched on board of the Chinese space laboratory Tiangong~2 on September 15, 2016. The construction of the instrument components is described in this article. Details are provided on problems encountered during the construction phase and their solutions. Initial performance of the instrument in orbit is as expected from ground tests and Monte Carlo simulation