  The FCAL collaboration is preparing large scale prototypes of special
calorimeters to be used in the very forward region at a future linear electron
positron collider for a precise and fast luminosity measurement and
beam-tuning. These calorimeters are designed as sensor-tungsten calorimeters
with very thin sensor planes to keep the Moliere radius small and dedicated FE
electronics to match the timing and dynamic range requirements. A partially
instrumented prototype was investigated in the CERN PS T9 beam in 2014 and at
the DESY-II Synchrotron in 2015. It was operated in a mixed particle beam
(electrons, muons and hadrons) of 5 GeV from PS facilities and with secondary
electrons of 5 GeV energy from DESY-II. The results demonstrated a very good
performance of the full readout chain. The high statistics data were used to
study the response to different particles, perform sensor alignment and measure
the longitudinal shower development in the sandwich. In addition, Geant4 MC
simulations were done, and compared to the data.
